royal society of chemistry coordination and organometallic
TRANSCRIPT
Royal Society of Chemistry
Coordination and Organometallic
Chemistry Discussion Group Meeting
St. Anne’s College, Oxford
3rd–4th September 2015
The organisers acknowledge the generous support of
the following sponsors:
Practical Information
Venue
The lecture programme will take place in Mary Ogilvie Lecture Theatre at St Anne’s.
Lunch around St. Annes’s
About 5 minutes walk away …
Taylors Oxford – Sandwich shop – 1 Woodstock Road
Maison Blanc – French baker, patisserie cafe – 3 Woodstock Road
The Royal Oak – Classic British pub – 42-44 Woodstock Road
Will’s Deli – A restaurant offering a range of salads, hot dishes and cheeses – 15
Woodstock Road
About 10 minutes walk away …
The Eagle and Child – Traditional british pub, best known for being a watering hole for
CS Lewis and JRR Tolkien – 49 St. Giles
St Giles cafe – Cafe with simple British menu – 52 St Giles
The Jericho Cafe –Neighourhood cafe with locally sourced blackboard menu – 112
Walton Street
The Victoria – Traditional tavern with real ales plus simple pub food – 90 Walton Street
Taxis
From Oxford city centre to St. Anne’s or from Oxford train station to St. Anne’s, the
cost is approximately £5.
ABC Taxis: 01865 770077 / 01865 775577
Botley Taxis: 01865 423264 / 07866 423264
001 Taxis: 01865 240000
PROGRAMME RSC Coordination and Organometallic Chemistry
Discussion Group Meeting
St. Anne’s College, Oxford; 3rd–4th September 2015
Thursday 3rd of September
10.30–12.00 pm Registration and setting up of posters
Arrival at St. Anne’s and registration with tea and coffee
Lunch (not provided): 12.00–12.50 pm
Session 1: 12.50–3.00 pm
12.50–1.00 pm: Introductory remarks (Jose M. Goicoechea/Simon Aldridge/Andrew
Weller)
1.00–1.45 pm: PL1: Neil Champness, University of Nottingham
“From frameworks to spheres and surfaces – Exploiting the
coordination bond”
1.45–2.20 pm: IL1: Mark Crimmin, Imperial College London
“Transforming carbon–fluorine bonds into carbon–aluminium bonds”
2.20–2.40 pm: George Kostakis, University of Sussex
“Custom-designed heteronuclear 3d/Dy(III) coordination clusters as
catalysts in a domino reaction”
2.40–3.00 pm: Peter Portius, University of Sheffield
“Nitrogen-rich coordination compounds of p-block elements
Coffee break: 3.00–3.30 pm
Session 2: 3.30–5.30 pm
3.30–4.15 pm: PL2: Joshua Figueroa, University of California San Diego
“Structural dynamics and substrate activation in highly congested π-
Acidic ligand fields”
4.15–4.50 pm: IL2: Simon Pope, University of Cardiff
“Fluorophore functionalised metal complexes”
4.50–5.10 pm: Rhiann Andrew, University of Warwick
“Synthesis, reactivity and dynamic behaviour of NHC-based Rhodium
macrocycles”
5.10–5.30 pm: George Britovsek, Imperial College London
“Towards robust alkane oxidation catalysts using non-heme iron(II)
complexes”
5.30–6.00 pm: Meeting of RSC CODG members
Poster session: 5.30–7.00 pm
Pre-dinner drinks and dinner 7.00 pm onwards
Friday 4th of September
Session 3: 9.00–10.40 am
9.00–9.20 am: Tom Hooper, University of Oxford
“Phosphine-borane dehydrocoupling using a {Cp*Rh(PR3)}2+ fragment:
Stoichiometric reactivity and catalysis”
9.20–9.40 am: Rebecca Musgrave, University of Bristol
“Reversible formation of magnetic polynickelocenes”
9.40–10.00 am: Sergey Zlatogorsky, University of Central Lancashire
“Towards metal carbenes as hydrogenase models”
10.00–10.20 am: Nicola Bell, University of Edinburgh
“Taking uranyl Pacman chemistry to the next level”
10.20–10.40 am: Nathan Patmore, University of Huddersfield
“Mechanistic studies of charge transfer in hydrogen bonded ‘dimers of
dimers’”
Coffee break: 10.40–11.10 am
Session 4: 11.10–12.40 pm
11.10–11.20 am: Katie Dryden-Holt, RSC. Presentation on opportunities for younger
members
11.20–11.25 am: Presentation of Sir Edward Frankland Fellowship to Scott Dalgarno
(Richard Walker; RSC)
11.25–12.00 am: IL3: Scott Dalgarno, Heriot-Watt University
“Calixarene-supported clusters”
12.00–12.20 pm: Lee Collins, University of Bath
“eNHChanting new reactivity with Cu and Zn”
12.20–12.40 pm: Phil Dyer, Durham University
“Exploring phosphine-alkene ligand chemistry”
Lunch (not provided): 12.40–1.40 pm
Session 5: 1.40–4.00 pm
1.40–2.00 pm: Introduction by Philip Mountford
Presentation of the RSC Award for Service to Peter Tasker
Introduction of Jason Love for the Dalton Transactions Lecture
2.00–2.45 pm: Dalton Lecture: Jason Love, University of Edinburgh
“An adventure in ligand design: From Pacman to dynamic assemblies
via uranyl”
2.45–3.20 pm: IL4: Kylie Vincent, University of Oxford
“Proton transfer from a metal hydride: Insight from Infrared
spectroscopy applied to nickel-iron hydrogenases under
electrocatalytic turnover”
3.20–3.40 pm: Matthew Blake, University of Oxford
“Group 2- and group 12-metal complexes”
3.40–4.00 pm: Closing remarks
Abstracts for Plenary Lectures
FROM FRAMEWORKS TO SPHERES AND SURFACES –
EXPLOITING THE COORDINATION BOND
N.R. Champness
School of Chemistry, University of Nottingham, University Park, Nottingham, UK.
Non-covalent directional intermolecular interactions provide a pre-determined
recognition pathway which has been widely exploited in supramolecular chemistry to
form functional nanostructures. Our results using coordination bonding interactions to
enable the directed assembly of extended nanostructures will be presented. The lecture
will focus on the development of coordination polymers and metal-organic frameworks
(MOFs) but with an emphasis on the construction of spherical coordination
architectures and their subsequent organisation into larger arrays, notably on surfaces.
The lecture will span three themes: the use of MOFs to host photoactive species
modifying the properties of the incorporated species1,2 (Fig. i); the development of
nanoscale spheres using coordination interactions3 (Fig. ii); and, lastly, the organisation
of magnetic molecules on surfaces4,5 (Fig. iii). In summary the lecture will draw a direct
connection between supramolecular and coordination chemistry and nanostructure
fabrication.
References.
[1] Blake, A.J.; Champness, N.R.; Easun, T.L.; Allan, D.R.; Nowell, H.; George, M.W.;
Jia, J.; Sun, X-Z. Nat. Chem., 2010, 2, 688.
[2] Easun, T.L.; Jia, J.; Reade, T.J.; Sun, X-Z.; Davies, E.S.; Blake, A.J.; George,
M.W.; Champness, N.R. Chem. Sci., 2014, 5, 539.
[3] Argent, S.P.; Greenaway, A.; Gimenez-Lopez, M.C.; Lewis, W.; Nowell, H.;
Khlobystov, A.N.; Blake, A.J.; Champness, N.R.; Schröder, M. J. Am. Chem. Soc.,
2012, 134, 55.
[4] Slater, A.G.; Perdigao, L.M.A.; Beton, P.H.; Champness, N.R. Acc. Chem. Res.,
2014, 47, 3417.
[5] Saywell, A.; Magnano, G.; Satterley, C.J.; Perdigão, L.M.A.; Britton, A.J.; Taleb,
N.; Giménez-López, M.C.; Champness, N.R.; O’Shea, J.N.; Beton, P.H. Nat.
Commun., 2010, 1, 75.
STRUCTURAL DYNAMICS AND SUBSTRATE ACTIVATION IN
HIGHLY CONGESTED -ACIDIC LIGAND FIELDS
Joshua S. Figueroa
Department of Chemistry and Biochemistry
University of California, San Diego
9500 Gilman Drive, MC 0358
La Jolla, CA 92093 (USA)
Recent results concerning the construction and reactivity of low-coordinate transition-
metal complexes featuring sterically encumbering m-terphenyl isocyanide ligands are
presented. Given the isolobal relationship between organoisocyanides and carbon
monoxide, these complexes serve as mimics of the unsaturated binary metal carbonyls.
The latter have traditionally been studied in either the gas phase or by matrix-isolation
techniques and, consequently, their condensed-phase reactivity patterns are significantly
underexplored. Specifically addressed will be synthetic studies that have delivered
homoleptic isocyanide complexes that model binary carbonyls of the mid-to-late
transition metals. In addition, coordinatively unsaturated heteroleptic isocyanide
complexes are presented that mimic the structural and spectroscopic properties of
reactive intermediates in catalytic processes mediated by transition-metal carbonyls. As
expected for mimics such reactive carbonyl complexes, the newly prepared isocyanide
complexes display rich reactivity patterns. Novel aspects of small-molecule
coordination chemistry and activation, especially as a function of structural and ligand
dynamics, by these isocyanide complexes are discussed.
AN ADVENTURE IN LIGAND DESIGN: FROM PACMAN TO
DYNAMIC ASSEMBLIES VIA URANYL
Jason B. Love
EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh EH9 3FJ, UK
Sustainability in the chemical sciences, especially in making best use of our critical
energy and material resources, is a recurring and global challenge. In this contribution,
the use of ligand design, its application to molecular coordination chemistry, catalysis,
and supramolecular chemistry, and the insight gained from these themes regarding
chemical sustainability will be described. This will include (i) the use of Pacman
complexes as platforms for redox catalysis, in particular oxygen reduction and C-H
bond oxygenation,1 (ii) the development of the f-element chemistry of these ligands to
facilitate the reduction and oxo-functionalisation of the uranyl dication,2 and (iii) the
spontaneous assembly of supramolecular ion pairs to form catalysts for oxidation and
reduction reactions under biphasic conditions.3
References
1 A. M. J. Devoille and J. B. Love, "Double-pillared cobalt Pacman complexes:
synthesis, structures and oxygen reduction catalysis." Dalton Trans., 2012, 41, 65-72; J.
R. Pankhurst, T. Cadenbach, D. Betz, C. Finn and J. B. Love, Dalton Trans., "Towards
dipyrrins: oxidation and metalation of acyclic and macrocyclic Schiff-base
dipyrromethanes," Dalton Trans., 2015, 44, 2066-2070.
2 P. L. Arnold, D. Patel, C. Wilson and J. B. Love, "Reduction and selective oxo
group silylation of the uranyl dication." Nature, 2008, 451, 315-317; P. L. Arnold, R.
M. Lord, A-F. Pécharman, G. M. Jones, E. Hollis, G. S. Nichol, L. Maron, J. Fang, T.
Davin, J. B. Love, "Control of oxo-group functionalization and reduction of the uranyl
ion," Inorg. Chem., 2015, 54, 3702-3710
3 M. Cokoja, I. I. E. Markovits, M. H. Anthofer, S. Poplata, A. Pöthig, D. S.
Morris, P. A. Tasker, W. A. Herrmann, F. E. Kühn and J. B. Love, "Catalytic
epoxidation by perrhenate through the formation of organic-phase supramolecular ion
pairs," Chem. Commun., 2015, 51, 3399-3402; A. M. Wilson, P. J. Bailey, P. A. Tasker,
J. R. Turkington, R. A. Grant, J. B. Love, "Solvent extraction: the coordination
chemistry behind extractive metallurgy." Chem. Soc. Rev., 2014, 43, 123-134
Abstracts for Invited Lectures
TRANSFORMING CARBON–FLUORINE BONDS INTO
CARBON–ALUMINIUM BONDS
Olga Ekkert, Adi Nako, Shuhui Yow and Mark R. Crimmin
Department of Chemistry, Imperial College, South Kensington, London, SW7 2AZ, UK
We report the activation of carbon–fluorine bonds using the aluminium dihydride 1. In
the presence of a transition metal catalyst, 1 is an effective stoichiometric reagent for
two competitive reactions that break strong C–F bonds in fluoroarenes. These include
the the transformation of a C–F bond to a C–Al bond (Figure – C–F Alumination) and
conversion of a C–F bond to a C–H bond (Figure – Hydrodefluorination).1 The former
reaction can be conceptualised in terms of a net elimination of H2 from and net addition
of the C–F bond to the group 13 element.
Through investigating the coordination chemistry,2-3 we show that the generation of an
Al(I) fragment from the dehydrogenation of 1 is possible. Control reactions in which an
Al(I) analogue of 1 is reacted with fluoroarenes and fluoroalkanes give the products of
C–F bond cleavage by oxidative addition. Our findings raise the possibility of catalytic
control in the redox chemistry of main group reagents.
[1] (a) Yow S.; Gates, S. J.; White, A. J. P.; Crimmin, M. R. Angew. Chem., Int. Ed.
2012, 51, 12559. (b) Ekkert, O.; Strudley, S. D. A.; Rozenfeld, A.; White, A. J. P.;
Crimmin, M. R. Organometallics 2014, 33, 7027.
[2] Abdalla, J. A. B.; Riddlestone, I. M.; Turner, J.; Kaufman, P. A.; Tirfoin, R.;
Phillips, N.; Aldridge, S. Chem. Eur. J., 2014, 20, 17624.
[3] (a) Ekkert, O.; Toms, H.; White, A. J. P.; Crimmin, M. R. Chem. Sci. 2015, DOI:
10.1039/C5SC01309G. (b) Nako, A. E.; Tan, Q. W.; White, A. J. P.; Crimmin, M. R.
Organometallics, 2014, 33, 2685.
FLUOROPHORE FUNCTIONALISED METAL COMPLEXES
Simon J. A. Pope
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff
Luminescent metal ion coordination complexes, including organometallic variants, have
shown great utility in their application, from optoelectronic devices to biological
studies. In a biological context, application can vary from cellular imaging agents, to the
development of multimodal imaging agents, to visualising complexes of therapeutic
interest and studying metal-ligand interactions with DNA and/or proteins.
The focus of this presentation will be the development of fluorescent ligands that
can facilitate the optical bioimaging application of the corresponding complexes.
Discussion will include the design and
synthesis of ligands based upon functionalised
anthraquinone and 1,8-naphthalimide species.
Both anthraquinone and 1,8-naphthalimide
species can possess advantageous fluorescent
properties that are tuneable via the differing
substitution patterns of the aromatic cores.
The ligand design and coordination chemistry
with gold(I) [1] and rhenium(I) [2] will be a
primary focus of the presentation.
Our studies encompass the structural, spectroscopic and photophysical
characterisation of all ligands and complexes. These species were also investigated as
potential bioimaging agents, using confocal fluorescence microscopy, with studies
including cancer cell lines, human osteoarthritic cells and the protistan fish parasite
Spironucleus vortens. The results show that both anthraquinone and 1,8-naphthalimide
based complexes can facilitate cell imaging studies. More specifically, the nature of the
1,8-naphthalimide structure serves to influence the cytotoxicity, uptake and intracellular
localization of these imaging agents. In the case of the gold(I) complexes, the
cytotoxicity was significantly enhanced versus the corresponding free ligands.
References
[1] Langdon-Jones, E.E.; Lloyd, D.; Hayes, A.J.; Wainwright, S.D.; Mottram, H.J.;
Coles, S.J.; Horton, P.N.; Pope, S.J.A. Inorg. Chem. 2015, 54, 6606; Langdon-Jones,
E.E.; Pope, S.J.A. Chem. Commun. 2014, 50, 10343; Balasingham, R.G.; Williams,
C.F.; Mottram, H.J.; Coogan, M.P.; Pope, S.J.A. Organometallics 2012, 31, 5835.
[2] Langdon-Jones, E.E.; Symonds, N.O.; Yates, S.E.; Hayes, A.J.; Lloyd, D.; Williams,
R.; Coles, S.J.; Horton, P.N.; Pope, S.J.A. Inorg. Chem. 2014, 53, 3788,
CALIXARENE-SUPPORTED CLUSTERS
Scott J. Dalgarno
Rm 2.04 William Perkin Building, Institute of Chemical Sciences, Heriot-Watt
University, Riccarton, Edinburgh, EH14 4AS
Methylene-bridged calix[n]arenes display markedly different coordination chemistry to
their thia-, sulfonyl- and sulfinyl-bridged analogues, and have recently emerged as
excellent ligand supports for the synthesis of polynuclear transition, lanthanide metal
and 3d-4f clusters. The presentation will cover the formation of a series of cluster motifs
including MnIII2MnII
2(Calix[4])2 SMMs,1 structurally related MnIII2MnIILnIII(Calix[4])2
and MnIII2LnIII
2(Calix[4])2 species (Figure 1),2 MnIII4LnIII
4(Calix[4])4 SMMs and
magnetic refrigerants,3 tri-capped trigonal prismatic enneanuclear CuII9(Calix[4])3 and
octahedral LnIII6(Calix[4])2 clusters. Metal ion binding rules arising from experiments
with calix[4 and 8]arenes will be discussed as they allow one to control metal ion
incorporation depending on the building block employed. New developments in related
bis-calix[4]arene cluster chemistry will also be presented as these a) display structural
characteristics of calix[4]arene and b) allow one to employ cluster formation in directed
assembly.8,9
Figure 1. Series of structurally related calix[4]arene-supported Mn , Mn / Ln and Ln
clusters formed under various conditions.
References
[1] Karotsis, G.; Teat, S. J.; Wernsdorfer, W.; Piligkos, S.; Dalgarno, S. J.; Brechin, E.
K. Angew. Chem. Int. Ed. 2009, 48, 8285.
[2] Palacios, M. A.; McLellan, R.; Taylor, S. M.; Beavers, C. M.; Teat, S. J.;
Wernsdorfer, W.; Piligkos, S.; Dalgarno, S. J.; Brechin, E. K. Chem. Eur. J. 2015, 21,
11212.
[3] Karotsis, G.; Evangelisti, M.; Dalgarno, S. J.; Brechin, E. K. Angew. Chem. Int. Ed.
2009, 48, 9928.
[4] McLellan, R.; Palacios, M. A.; Beavers, C. M.; Teat, S. J.; Piligkos, S.; Brechin, E.
K.; Dalgarno, S. J. Chem. Eur. J. 2015, 21, 2804.
[5] Coletta, M.; McLellan, R.; Murphy, P.; Leube, B. T.; Sanz, S.; Clowes, R.; Gagnon,
K. J.; Teat, S. J.; Cooper, A. I.; Paterson, M. J.; Brechin, E. K.; Dalgarno, S. J.
submitted.
PROTON TRANSFER FROM A METAL HYDRIDE: INSIGHT
FROM INFRARED SPECTROSCOPY APPLIED TO NICKEL-
IRON HYDROGENASES UNDER ELECTROCATALYTIC
TURNOVER
R. Hidalgo, P.A. Ash and K.A. Vincent
University of Oxford, Department of Chemistry, Inorganic Chemistry Laboratory, South
Parks Road, Oxford, OX1 3QR, UK
Rapid oxidation of H2 is catalysed at a NiFe catalytic site in the family of nickel-iron
hydrogenase enzymes. The reaction is controlled readily using electrochemistry, where
the electrode provides a sink for fast uptake of the electrons released during H2
oxidation by a film of immobilised hydrogenase. We have made use of a new approach
to infrared (IR) spectroscopy coupled with electrochemistry to study a NiFe
hydrogenase under catalytic turnover and gain insight into the catalytic cycle for H2
activation.[1] The native CO and CN– ligands on Fe at the active site of the enzyme
provide sensitive spectroscopic probes for identifying redox and coordination changes at
the active site.
It is established that H2 reacts with the NiFe hydrogenase active site at the NiII FeII
level. A NiIII(H–)FeII intermediate is known, but the steps required to remove the
hydrido ligand to restore the starting NiII FeII state have remained obscure. A NiI FeII
state, resulting from initial transfer of a proton from the active site to a nearby base, has
been proposed in computational studies,[2,3] but has not previously been observed
experimentally under conditions relevant to catalysis. Here we provide evidence from
IR spectroelectrochemical studies on hydrogenase I from E. coli, under turnover and
non-turnover conditions, that the NiIII(H–)FeII level does indeed give rise to a detectable
NiI FeII intermediate rather than requiring concerted removal of a proton and
electron.[1,4]
The mechanistic insight gained from these studies of the hydrogenase active site during
fast catalytic turnover should help to inspire development of functional biomimetic
catalysts for H2 activation at non-noble metal sites.
References.
[1] Hidalgo, R.; Ash, P.A.; Healy, A.J.; Vincent, K.A. Angew. Chemie Int. Ed. 2015,
127, 7216.
[2] Pardo, A.; De Lacey, A. L.; Fernández, V. M.; Fan, H.-J.; Fan, Y.; Hall, M. B. J.
Biol. Inorg. Chem. 2006, 11, 286.
[3] Lill, S. O. N.; Siegbahn, P. E. M. Biochemistry 2009, 48, 1056.
[4] Murphy, B.J.; Hidalgo, R.; Roessler, M.M.; Evans, R.M.; Ash, P.A.; Myers, W.K.;
Vincent, K.A.; Armstrong, F.A. J. Am. Chem. Soc. 2015, 137, 8484.
Abstracts for Oral Presentations
CUSTOM-DESIGNED HETERONUCLEAR 3D/DY(III)
COORDINATION CLUSTERS AS CATALYSTS IN A DOMINO
REACTION
Kieran Griffiths, Christopher W. D. Gallop, Alaa Abdul-Sada, Alfredo Vargas, Oscar
Navarro and George E. Kostakis
School of Life Sciences, University of Sussex, Brighton BN1 9QJ, United Kingdom [email protected]
The synthesis of polynuclear Coordination Clusters (CCs) containing 3d and
Dy(III) metal ions is currently extremely popular and a research objective for several
groups due to their aesthetically pleasant structures and potential applications.1
The present work is directed on synthesizing tetranuclear 3d/Dy(III) CCs,
possessing a defect dicubane topology, with Schiff base ligands and their functional
uses, for the first time in catalysis. Thus, three isoskeletal tetranuclear CCs with general
formula [MII
2DyIII
2L4(EtOH)6](ClO4)2·2(EtOH), (M = Co, 1; M= Ni, 2) and
[NiII
2DyIII
2L4Cl2(CH3CN)2]·2(CH3CN) (3), have been synthesized and characterized.
These air-stable compounds, and in particular 3, display efficient homogeneous catalytic
behavior towards the room temperature synthesis of trans-4,5-diaminocyclopent-2-
enones from 2-furaldehyde (Scheme 1) and primary or secondary amines under a non-
inert atmosphere.2
Scheme 1 The proposed domino reaction catalyzed by compounds 1 – 3.
This work signifies a unique contribution to 3d/4f coordination chemistry and
opens new research directions by producing a new generation for 3d/Dy(III) molecules
that can act in tandem in catalysis.
References.
(1) Sessoli, R.; Powell, A. K. Coord. Chem. Rev. 2009, 253, 2328–2341.
(2) Griffiths, K.; Gallop, C. W. D.; Abdul-Sada, A.; Vargas, A.; Navarro, O.;
Kostakis, G. E. Chem. Eur. J. 2015, 21, 6358–6361.
NITROGEN-RICH COORDINATION COMPOUNDS OF P-BLOCK
ELEMENTS
R. M. Campbell, B. Peerless, B. F. Crozier and P. Portius
Department of Chemistry, The University of Sheffield, Brook Hill, S3 7HF, UK [email protected]
N-rich compounds are a fascinating and promising replacement for conventional propel-lants, explosives & pyrotechnics. They generate mainly N2 upon decomposition - ideal for smokeless, CO2-free and “green” energetic materials.1 However, low barriers towards decomposition pose major challenges in their preparation, isolation, and
characterisation. Our research aims at stabilising and controlling the reactivity of N-rich coordination compounds. Specifically, the presentation will focus on E(Y)n, n = 2-6, Y = N-rich ligand; E = p-block coord. centre in low or high ox. states. Applying synthetic approaches novel to energetic chemistry, involving combinations of hypercoordination, bulky counter ions, and ligand exchanges, the preparation and isolation of several new classes of N-rich tetrazolato and azido complexes has been achieved as candidates for efficient & controllable energy storage.5 These include neutral Lewis base adducts and homoleptic complexes (a),2-4, 6,7 covalent, binary E(N3)n azides which were generated in bulk for the first time (b),4 the first homoleptic tetrazolato p-block element complexes
E(CHN4)62 and E(CHN4)3
(E = Si, Ge, Sn, Fig. 1) (c). The new complexes have a unique chemistry – reactions with nitriles and phosphines afford unusual poly(tetrazolato) and poly(phosphiniminato) complexes. Syntheses, reactivity, structures, and thermal and spectroscopic properties of the new species, including application of time-resolved infrared spectroscopy to study photoreactivity, will be described.
[1] Steinhauser, G.; Klapoetke, T. M. Angew. Chem. Int. Ed. 2008, 2. [2] Portius, P.; Fowler, P. W.; et al. Inorg. Chem. 2008, 12004. [4] Portius, P.; Filippou, A. C.; et al. Angew. Chem. Int. Ed. 2010, 8013. [5] Davis, M.; Portius, P. Coord. Chem. Rev. 2013, 1011. [6] Peerless, B.; Keane, T.; et al. Chem. Commun. 2015, 7435. [7] Campbell, R. M.; Davis, M. F.; Fazakerley, M.; Portius, P. paper in preparation 2015.
Fig. First examples of tetrazol-based N-rich coord. networks and complexes with p-block centres.
SYNTHESIS, REACTIVITY AND DYNAMIC BEHAVIOUR OF
NHC-BASED RHODIUM MACROCYCLES
Rhiann E. Andrew,a Dominic W. Ferdani,
a C. André Ohlin
b and Adrian B. Chaplin
a,*
a Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
b School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
Pincer ligand architectures featuring N-heterocyclic carbene (NHC) donors are
increasingly prominent in organometallic chemistry, combining the strong σ-donor
characteristics of NHCs with the favourable thermal stability and reaction control
possible with a mer-tridentate geometry.1 With a view to exploiting their unique steric
profile, we have recently become engaged in the investigation of macrocyclic variants
of these NHC pincers.2 In this report we present the synthesis, fluxional behaviour and
reactivity of rhodium complexes containing macrocyclic pincer ligands.3 A general
synthetic procedure involving ring-closing olefin metathesis enabled access to rhodium
systems incorporating both lutidine (1a, n = 1) and pyridine (1b, n = 0) central donor
groups. For comparison, a bidentate xylene bridged macrocyclic system (1c) was also
prepared.
In the presence of CO, 1a exhibits coordination-induced atropisomerisation akin to that
reported for its acyclic analogues.4 Through computational modelling and simulation-
aided analysis of variable temperature 1H NMR spectra, we deduced that
interconversion occurs through a symmetric intermediate similar to 1c. The absence of
bridging methylene groups makes for a more rigid architecture (1b) that cannot
coordinate excess CO or dissociate pyridine, but more readily undergoes oxidative
addition – in comparison to 1a – to provide isolable rhodium(III) complexes.
References
1. Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109, 3677– 3707.
2. Andrew, R. E.; Chaplin, A. B. Dalton Trans. 2014, 43, 1413– 1423.
3. a) Andrew, R. E.; Chaplin, A. B. Inorg. Chem. 2015, 54, 312– 322; b) Andrew, R.
E.; Ferdani, D. W.; Ohlin, C. A.; Chaplin, A. B. Organometallics 2015, 34, 913–917.
4. Miecznikowski, J. R.; Grundemann, S.; Albrecht, M; Megret, C; Clot, E.; Faller, J.
W.; Eisenstein, O.; Crabtree, R. H. Dalton Trans. 2003, 5, 831 – 838.
TOWARDS ROBUST ALKANE OXIDATION CATALYSTS USING NON-HEME IRON(II) COMPLEXES
Michaela Grau and George Britovsek
Department of Chemistry, Imperial College London, Exhibition Road, London, SW72AY
The selective oxidation of organic molecules under energy efficient, cheap, non toxic
and environmentally friendly conditions is an important target for the chemical industry
and organic synthesis on laboratory scale. In nature there are metalloenzymes such as
cytochrome P450 or methane monooxygenase, which feature iron complexes at the
active site and perform excellent regio- and stereoselective oxidation catalysis.[1]
Inspired by the reactivity and selectivity of metalloenzymes, a large variety of non-
heme iron(II) complexes featuring linear, tripodal or cyclic tetradentate N-donor ligands
have been developed.[2]
A key finding has been that catalysts with tetradentate ligands
tend to give the most active catalysts. However, rapid degradation of most catalysts
under the operating conditions presents a major problem.[3]
N
N
N
N N
N
N N
N N
N
N N
N N
X
L3 X = H
L4 X = Cl
L1 L2
To establish whether catalyst stability is affected by an increase in ligand denticity,
we present here our results on mononuclear non-heme iron(II) complexes containing
linear pentadentate ligands (L1-4). The reactivity of these complexes as catalysts for the
oxidation of cyclohexane with hydrogen peroxide has been investigated. Analysis of
the different complexes revealed an interesting and unusual change in the coordination
geometry from octahedral to pentagonal bipyramidal. Furthermore, in solution it was
found that the pentagonal bipyramidal complex changes its coordination geometry with
temperature resulting in a novel temperature-dependent coordination equilibrium.[4]
References [1] B. Meunier, S. P. de Visser, S. Shaik, Chem. Rev. 2004, 104, 3947-3980.
[2] M. Grau, G. J. P. Britovsek, Top. Organomet. Chem. 2015, 50, 145-172.
[3] a) J. England, C. R. Davis, M. Banaru, A. J. P. White, G. J. P. Britovsek, Adv.
Synth. Catal. 2008, 350, 883-897; b) J. England, R. Gondhia, L. Bigorra-Lopez,
A. R. Petersen, A. J. P. White, G. J. P. Britovsek, Dalton Trans. 2009, 5319-
5334; c) M. Grau, A. Kyriacou, F. Cabedo Martinez, I. de Wispelaere, A. J. P.
White, G. J. P. Britovsek, Dalton Trans. 2014, 43, 17108-17119.
[4] M. Grau, J. England, R. Torres Martin de Rosales, H. S. Rzepa, A. J. P. White,
G. J. P. Britovsek, Inorg. Chem. 2013, 52, 11867-11874.
PHOSPHINE-BORANE DEHYDROCOUPLING USING A
{Cp*Rh(PR3)}2+
FRAGMENT: STOICHIOMETRIC REACTIVITY
AND CATALYSIS
Thomas N. Hooper and Andrew S. Weller*
University of Oxford, Department of Chemistry, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA
Phosphinoborane polymers are valence isoelectronic with polyolefins and have been
shown to have applications in lithography and as preceramic polymers for
semiconductors.1 Manners et al. reported the homogeneous catalytic synthesis of
polyphosphinoboranes using Rh(I) and Rh(III) precatalysts, but the nature of the active
species and the mechanism was not determined.1 We present a new system based on a
{Cp*Rh(PR3)}2+
fragment which allows for analysis of intermediates and mechanism
through stoichiometric reactivity and catalytic production of dehydrocoupled products.
H3B·PH2Ph was catalytically dehydrocoupled in toluene solution using
[Cp*RhMe(PMe3)(CH2Cl2)][BArF
4] (100 °C, 1 mol%) to produce well-defined
polymeric material. Under similar conditions at 5 mol%, the secondary phosphine-
borane H3B·PHPh2 was dehydrocoupled to form a linear dimer and temporal
interrogation allowed the organometallic species to be identified.
Stoichiometric reaction of secondary phosphine-boranes with
[Cp*RhMe(PMe3)(CH2Cl2)][BArF
4] formed products dependent on the phosphine-
borane substituents (see figure 1).Reaction intermediates were studied to probe the
mechanism by which dehydrocoupling could occur.
Figure 1. Reaction of [Cp*RhMe(PMe3)(CH2Cl2)][BArF
4] with H3B·PHR2.
References
[1] Clark, T.J.; Lee, K.; Manners, I. Chem. Eur. J., 2006, 12, 8634.
REVERSIBLE FORMATION OF MAGNETIC
POLYNICKELOCENES
R. A. Musgrave, A. D. Russell, G. R. Whittell and Ian Manners
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
The field of [n]metallocenophane chemistry has been expanding rapidly since the
1960s; in particular, the propensity of these strained molecules to undergo ring-opening
polymerization (ROP). Recently this reaction has been extended to
[n]nickelocenophanes, yielding polynickelocenes, a class of magnetic S = 1
metallopolymers.1 Interestingly, this ROP reaction shows reversibility at ambient
temperatures (Figure 1), and thermodynamic propensity for this unusual reactivity is
explored.2 The synthesis and characterization of a number of other novel
[n]nickelocenophane monomers and their respective magnetic polymers will also be
presented.
Figure 1. Reversible formation of poly(nickelocenylpropylene).
[1] Baljak, S.; Russell, A. D.; Binding, S. C.; Haddow, M. F.; O’Hare, D.; Manners, I. J. Am. Chem. Soc. 2014, 136, 5864-5867.
[2] Musgrave, R. A.; Russell, A. D.; Whittell, G. R.; Manners, I. Unpublished Results
TOWARDS METAL CARBENES AS HYDROGENASE MODELS
D. Britton, A. Boak, S. McDougall, Z. Moinuddin, N. Bramah, A. Panchal, and
S. Zlatogorsky
School of Physical Sciences and Computing, UCLan, Preston, UK [email protected]
Structural and functional models of hydrogenases are important for understanding redox
reactions involving hydrogen in nature, modelling enzymatic behaviour, and are the key
to new materials for hydrogen storage.
N-Heterocyclic carbenes (NHCs) are known to support iron in a range of oxidation
states. Electronic properties of NHCs (σ-donors capable of backbonding) are similar to
those of CN- and CO found in native hydrogenases and, unlike carbenes, already tried in
their modelling.1 The basicity of a free carbene coupled with its lability when
coordinated to Fe2,3
makes Fe-NHCs ideal unexplored candidates for hydrogenase-like
behaviour (e.g. heterolytic H2 cleavage across the Fe-NHC bond). The validity of this
idea is strongly supported by the finding that Fe acts as an electrophile to activate H2 in
an Fe-NHC system.4 However, due to their lability, Fe-NHC complexes lack stability.
2,3
We propose to introduce sulphur-based “Fe-anchoring” function(s) into an NHC ligand.
Metallation of the latter, given the well-known stability of sulphur-bridged Fe clusters,
will give stable Fe-S-NHC complexes.
We suggest that sulphur-containing functional groups will include thioketone(s),
thiolate(s), thiocarboxylate(s), thiazole(s), etc. (Scheme 1)
N
E
E'
N
N
N
E'
E
D DS
N
E
E'
N
N
N
E'
E
DD
S
S
x x yy
SPACER = o-/m-xylylidene, hexamethylenebenzene, oligomethylene
D = donor group, e.g.
E, E' = C, N (imidazole/triazole)
SR, R = H, Alk/Ar
SPACERSPACER
Scheme 1
N
S
N
S
SPACERx x
The preparation of imidazolium, triazolium and (benzo)thiazolium pro-ligands shown
above, as well as initial attempts at their metallation, will be reported.
[1] Tard, C.; Pickett, C. J. Chem. Rev. 2009, 109, 2245.
[2] Zlatogorsky, S.; Muryn, C. A.; Tuna, F.; Evans, D. J.; Ingleson, M. J.
Organometallics 2011, 30, 4974.
[3] Zlatogorsky, S.; Ingleson, M. J. Dalton Trans. 2012, 41, 2685.
[4] Runyon, J. W.; Steinhof, O.; Rasika Dias, H. V.; Calabrese, J. C.; Marchall, W. J.;
Arduengo III, A. J. Aust. J. Chem., 2011, 64, 1165.
TAKING URANYL PACMAN CHEMISTRY TO THE NEXT
LEVEL
Nicola L. Bell1, Jason Love
1 and Polly L. Arnold
1
1 EastChem, University of Edinburgh, The Kings Buildings, Edinburgh
The strong and covalent O=U=O multiple bonds in the linear uranyl dication [UO2]2+
are relatively inert with most reactivity of the U(VI) metal occurring around the
equatorial plane.1 However, we have previously shown that encapsulation of [UO2]
2+
within the orthophenylene-linked polypyrrolic Schiff base ‘Pacman’ macrocycle can result in facile reduction of the U(VI) to U(V) and allow silylation and metalation
reactivity.2 Due to steric constraints two linear uranyl moieties cannot be accommodated
within a single orthophenylene-linked ‘Pacman’ ligand; instead a doubly reduced ‘butterfly’ compound with a ‘cis-uranyl’ motif is accessed (Scheme 1).3
Scheme 1: Synthesis of bis-uranyl ‘Pacman’ complexes
Working with our extended anthracenylene-linked macrocycle we have recently
developed a synthetic route to both mono- and bis-uranyl complexes the latter of which
contains two U(VI) linear trans-dioxo uranyl cations in contrast to the reduced
U(V)/U(V) ‘butterfly’ species observed with the orthophenylene-linked macrocycle.4
Herein, we will discuss their synthesis, properties and reactivity.
References. [1] Denning, R. G.; Green, J. C.; Hutchings, T. E.; Dallera, C.; Tagliaferri, A.; Giarda, K.; Brookes,
N. B.; Braicovich, L. J. Chem. Phys. 2002, 117, 8008; Vallet, V.; Wahlgren, U.; Grenthe, I. J.
Phys. Chem. A 2012, 116, 12373-12380.
[2] Arnold, P. L.; Blake, A. J.; Wilson, C.; Love, J. B. Inorg. Chem. 2004, 43, 8206-8208; Arnold,
P. L.; Patel, D.; Wilson, C.; Love, J. B. Nature 2008, 451, 315-U313; Arnold, P. L.;
Pecharman, A. F.; Hollis, E.; Yahia, A.; Maron, L.; Parsons, S.; Love, J. B. Nat. Chem. 2010, 2,
1056-1061; Arnold, P. L.; Hollis, E.; Nichol, G. S.; Love, J. B.; Griveau, J.-C.; Caciuffo, R.;
Magnani, N.; Maron, L.; Castro, L.; Yahia, A.; Odoh, S. O.; Schreckenbach, G. J. Am. Chem.
Soc. 2013, 135, 3841-3854.
[3] Arnold, P. L.; Jones, G. M.; Odoh, S. O.; Schreckenbach, G.; Magnani, N.; Love, J. B. Nat Chem
2012, 4, 221-227.
[4] Arnold, P. L.; Jones, G. M.; Pan, Q.-J.; Schreckenbach, G.; Love, J. B. Dalton Trans. 2012, 41,
6595-6597.
MECHANISTIC STUDIES OF CHARGE TRANSFER IN
HYDROGEN BONDED ‘DIMERS OF DIMERS’
L. A. Wilkinson, Kevin B. Vincent, Anthony J. H. M Meijer and N. J. Patmore
Department of Chemical Sciences, University of Huddersfield, Huddersfield HD1 3DH
Small molecule models are vital tools in improving our understanding of electron
transfer processes that occur in nature and chemistry. Mixed-valence (MV) compounds
consist of an electron donor and acceptor bridged by a conjugated spacer. As well as
covalently linked systems, it is also conceivable that hydrogen bond bridges could be
used to link redox centers in MV systems. However, examples remain rare, with little
detail about possible mechanisms by which the MV state is stabilised.1
In this talk we discuss charge transfer in hydrogen bonded ‘dimers of dimers’ of form
[Mo2(TiPB)3(HDON)]2 (TiPB = 2,4,6-triisopropylbenzoate; H2DON = 2,7-
dihydroxynaph-thyridine) and [Mo2(TiPB)3(HDOP)]2 (H2DOP = 3,6-
dihydroxypyridazine). The cyclic voltammograms of these compounds show two one-
electron processes indicating stabilization of the MV state.2 The magnitude of
stabilization is affected by addition of electron donating and withdrawing groups to the
ancillary and bridging ligands, providing insight into possible mechanisms. We have
recently probed the timescale and mechanism of charge transfer in these compounds by
cyclic voltammetry, UV/vis/NIR and EPR spectroscopy, and theoretical studies.
Stabilisation of the MV state in these compounds is proposed to be related to the proton
coordinate of the bridging ligand, and is termed proton-coupled mixed valency (Figure
1). These are the best models to date for studying this process, and a possible
mechanism will be discussed.
Figure 1. Proton-coupled mixed valency in [Mo2(TiPB)3(HDOP)]2
+.
[1] a) Goeltz, J. C.; Kubiak, C. P. J. Am. Chem. Soc., 2010, 132, 17390. b) Sun, H.:
Steeb, J.; Kaifer, A. E. J. Am. Chem. Soc., 2006, 128, 2820. c) Tadokoro, M.; Inoue,
T.; Tamaki, S.; Fujii, K.; Isogai, K.; Nakazawa, H.; Takeda, S.; Isobe, K.; Koga, N.;
Ichimura, N.; Nakasuji, K. Angew. Chem. Int. Ed., 2007, 46, 5938.
[2] a) Wilkinson, L. A.; McNeill, L.; Meijer, A. J. H. M.; Patmore, N. J. J. Am. Chem.
Soc., 2013, 135, 1723. b) Wilkinson, L. A.; McNeill, L.; Scattergood, P. A.;
Patmore, N. J. Inorg. Chem. 2013, 52, 9683.
eNHChanting NEW REACTIVITY WITH Cu AND Zn
Lee R. Collins, Mary F. Mahon, Ian M. Riddlestone and Michael K. Whittlesey
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK
N-heterocyclic carbenes (NHCs) are increasingly employed as ligands in
organometallic chemistry. Their easily tuneable electronic and steric demands make
them ideal for varying the reactivity of metal centres.
A diverse range of NHC structures are now available, with enhanced
nucleophilic or electrophilic character through altering their HOMO-LUMO energies.1
Di-amido carbenes (DACs) exhibit enhanced electrophilicity at the C2 position due to
electron withdrawing carbonyls α to the carbene’s nitrogen substituents.2
We have previously reported on the remarkable electrophilicity of DACs, and
the facile intramolecular migratory insertion reactions of [(6-MesDAC)MR2] (M = Zn,
Cd; R = Et, Me) complexes.3 We now report that this migratory insertion chemistry
also occurs for catalytically relevant copper hydride complexes, and even for di-amino
carbene complexes. The difference in susceptibility to migratory insertion is used to
explain the stark difference in activity of di-amino and di-amido carbene complexes for
catalytic reductions.
References
[1] Melaimi, M.; Soleilhavoup, M.; Bertrand, G. Angew. Chem. Int. Ed. 2010, 49, 8810–8849
[2] Verlinden, K.; Buhl, H.; Frank, W.; Ganter, C. Eur. J. Inorg. Chem 2015, 14, 2416-
2425
[3] Collins, L. R.; Hierlmeier, G.; Mahon, M. F.; Riddlestone, I. M.; Whittlesey, M. K.
Chem. Eur. J. 2015, 21, 3215–3218
EXPLORING PHOSPHINE-ALKENE LIGAND CHEMISTRY
L. W. Tuxworth,1 L. Estévez,
2 J-M. Sotiropoulos,
2 K. Miqueu,
2 and P. W. Dyer
1
1
Centre for Sustainable Chemical Processes, Department of Chemistry, Durham
University, South Road, Durham, DH1 3LE, UK. 2
Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux, Université de Pau et des Pays de l’Adour, Hélioparc, 64053 Pau, France.
Phosphine-alkene (P^=) ligands have received much recent attention, finding use in a
range of metal-mediated reactions, e.g. 1,4-additions and imine hydrogenations [1,2].
P^= systems provide electronic asymmetry that results from the combination of a
weakly π-acidic phosphine and a strongly π-accepting alkene within the same scaffold.
When bound in a bidentate fashion, this unusual electronic character can accelerate
reductive elimination reactions, something often the rate-limiting step in many Pd-
mediated cross-couplings [3].
P
Pd
L1
P
Pd
P(L1)
X
Cl
Me
L1 P
Pd
P(L1)
Me
P(L1)
PPd
P
–[L1Me]Cl
Assisted TS
1
Me
X : Cl
L1
P
Pd
P(L1)
Me
Me
X : Me
direct reductive elimination
pseudo-reductive elimination
#
P
Pd
P(L1)
Me
Me
#
Cl
–C2H6
N
Ph2P
L1 :
5-coordinate intermediate
P^= L1 promotes reductive elimination of ethane from [PdMe2(TMEDA)] forming
pseudo-homoleptic [Pd0(κ2
-P,C-L1)2] (1) [4]. Reaction of L1 with
[PdCl(Me)(TMEDA)] also leads to the formation of complex 1, but via an unusual
ligand-assisted methyl abstraction pathway, which has been probed by computation and
by variable temperature NMR studies.
References.
[1] Maire, P.; Deblon, S.; Breher, F.; Geier, J.; Bohler, C.; Ruegger, H.; Schonberg, H.;
Grützmacher, H. Chem. Eur. J., 2004, 10, 4198.
[2] Shintani, R.; Duan, W.L.; Nagano, T.; Okada, A.; Hayashi, T. Angew. Chem. Int.
Ed., 2005, 44, 4611.
[3] Zhang, H.; Luo, X.C.; Wongkhan, K.; Duan, H.; Li, Q.; Zhu, L.Z.; Wang, J.;
Batsanov, A.S.; Howard, J.A.K.; Marder, T.B.; Lei, A.W. Chem. Eur. J., 2009, 15,
3823.
[4] Estévez, L.; Tuxworth, L.W.; Sotiropoulos, J.-M.; Dyer, P.W.; Miqueu, K. Dalton
Trans, 2014, 43, 11165.
GROUP 2– AND GROUP 12–METAL COMPLEXES
M. P. Blakea, N. Kaltsoyannis
b and P. Mountford
a
aDepartment of Chemistry, University of Oxford, OX1 3TA, UK
bDepartment of Chemistry, University College London, WC1H 0AJ, UK
The structure, bonding and reactivity of molecular compounds containing unusual
metal–metal bonds continues to be a topic of considerable interest.[1]
Reports of the first
Zn–Zn[2]
and Mg–Mg single bonds,[3]
and the emergence of a growing body of
lanthanide– and actinide–transition metal bonds highlight the activity in this area.[4]
Despite this, there remains relatively little experimental or theoretical information
regarding bonds between the Group 2 elements and the transition metals. We recently
showed that reductive cleavage of Fp2 (Fp = CpFe(CO)2) with Ca/Hg or Yb/Hg
amalgams gave the Ca–Fe and Yb–Fe compounds 1 and 2, with 1 possessing the first
bond between calcium and a transition metal.[5]
Analogous Mg–Fe (e.g. 3) and related
compounds were also readily formed, with or without supporting ligand sets,[6]
and this
led us to the first insertion reactions of Group 2–transition metal bonds. Recent related
studies in our laboratory gave the first compound with a bond between two different
Group 12 metals, namely 4 which contains a formal ZnI–Hg
0–ZnI linkage.
[7] In this
presentation we report further on some of these recently communicated results, along
with additional new work from our laboratories in this area.
[1] Liddle, S. T. (Ed.), Molecular Metal-Metal Bonds: Compounds, Synthesis,
Properties, Wiley-VCH: Weinheim, Germany, 2015. [2] Resa, I.; Carmona, E.;
Gutierrez-Puebla, E.; Monge, A. Science 2004, 305, 1136. [3] Green, S. P.; Jones, C.;
Stasch, A. Science 2007, 318, 1754. [4] Liddle, S. T.; Mills, D. P. Dalton Trans. 2009,
5592; Roesky, P. W. Dalton Trans. 2009, 1887; Bauer, J.; Braunschweig, H.; Dewhurst,
R. D. Chem. Rev. 2012, 112, 4329; Oelkers, B.; Butovskii, M. V.; Kempe, R. Chem.
Eur. J. 2012, 18, 13566. [5] Blake, M. P.; Kaltsoyannis, N.; Mountford, P. J. Am. Chem.
Soc. 2011, 113, 15358. [6] Blake, M. P.; Kaltsoyannis, N.; Mountford, P. Chem.
Commun. 2013, 49, 3315. [7] Blake, M. P.; Kaltsoyannis, N.; Mountford, P. Chem.
Commun. 2015, 51, 5743.
Abstracts for Poster Presentations
SILVER N-HETEROCYCLIC CARBENES DERIVED FROM
NATURAL PRODUCTS AS ANTICANCER AGENTS
Dr. Charlotte E. Willans,1 Prof. Roger M. Phillips2 and H. Abdelgawad1
1School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK, 2School of Applied Sciences, University of Huddersfield, HD1 3DH, UK.
The discovery of the platinum-containing compound cisplatin as a chemotherapeutic compound opened a new area of research in organometallic chemistry for the treatment of cancer.1 Some of this research is focused on silver with silver-N-heterocyclic carbene (NHC) complexes showing significant promise as chemotherapeutic agents.2-4 This work describes the synthesis of novel silver-NHC complexes derived from xanthine precursors such as theophylline, theobromine and caffeine which are found naturally in cocoa beans. These complexes were assessed for their cytotoxicity against eight cancerous cell lines and results were compared to those obtained for cisplatin. Hydrophobicity studies and structure activity relationships indicate that both stability and ligand sterics play a part in their activity as anticancer agents.5
[1] Rosenber.B; Vancamp, L.; Krigas, T. Nature 1965, 205, 698. [2] Monteiro, D. C. F.; Phillips, R. M.; Crossley, B. D.; Fielden, J.; Willans, C. E. Dalton Trans. 2012, 41, 3720. [3] Medvetz, D. A.; Hindi, K. M.; Panzner, M. J.; Ditto, A. J.; Yun, Y. H.; Youngs, W. J. Metal-based Drugs 2008, 2008. [4] Mohamed, H. A.; Willans, C. E. RSC Specialist Periodical Reports in Organometallic Chemistry 2014, 39, 26. [5] Mohamed, H. A.; Lake, B. R. M.; Laing, T.; Phillips, R. M.; Willans, C. E. Dalton Trans. 2015, 44, 7563.
E.g.1. R1 = Me, R2 = Benzyl
E.g.2. R1 = Me, R2 = nBu
A STUDY OF NEW {Rh(XANTPHOS)}+ COMPLEXES
FOR THE DEHYDROPOLYMERISATION OF AMINE-BORANES
G. M. Adams and A. S. Weller*
Department of Chemistry, University of Oxford, UK
Polyaminoboranes, [H2BNRH]n, are an underdeveloped class of materials that are
isoelectronic with technologically and societally ubiquitous polyolefins. They are
formed by the controlled dehydropolymerisation of a parent amine-borane, and the
fundamental understanding of this mechanism has only recently started to be
investigated.[1]
Herein, we report the synthesis of new dehydropolymerisation catalysts
based upon a previously reported {Rh(Xantphos)}+ fragment,
[2] one example being the
straightforwardly prepared mer-[Rh(κ3-POP-Xantphos)(η2
-PhCCPh)][BArF
4] complex
(1).[3]
This system produces polymer of low PDI at 0.2 mol% catalyst loading, and by
tuning the reaction conditions the molecular weight of the resulting polymeric material
can be controlled. Modifying the Xantphos ligand backbone is also explored with regard
to the mechanism of dehydropolymerisation.
Scheme 1: Dehydropolymerisation of an amine-borane by complex 1
References
[1] Staubitz, A.; Sloan, M. E.; Robertson, A. P. M.; Friedrich, A.; Schneider, S.; Gates,
P. J.; Gunne, J; Manners, I. J. Am. Chem. Soc. 2010, 132, 13332
[2] Johnson, H. C.; Leitao, E. M.; Whittell, G. R.; Manners, I.; Lloyd-Jones, G. C.;
Weller, A. S. J. Am. Chem. Soc. 2014, 136, 9078
[3] Ren, P.; Pike, S. D.; Pernik. I; Weller, A. S.; Willis, M. C. Organometallics 2015,
34, 711
UPGRADING ETHANOL; MECHANISTIC INSIGHTS
H. Aitchison, R. L. Wingad, and D. F. Wass
School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS [email protected]
The search for renewable and sustainable sources of energy is a matter of exceptional importance and demands substantial attention and research effort. Numerous studies have shown the damaging and detrimental effects increased carbon dioxide can have on the Earth’s fragile climate; a direct consequence of utilising fossil-based fuels. All alternative fuels presently being used have both distinct advantages and inadequacies, such as the current plant-based fuel bioethanol.
Research within the Wass group has focused on the synthesis of n-butanol and iso-butanol from ethanol and ethanol/methanol blends respectively. Both butanol isomers have energy densities much more similar to that of gasoline (>86%), and their more alkane-like features assist in reducing the disadvantages bioethanol presents as a sustainable biofuel. The proposed feedstock is waste plant-matter, hence combustion of biobutanol results in a complete carbon cycle and does not adversely affect the environment.
Specifically novel transition metal catalysed routes are currently under investigation. The reaction is postulated to proceed via a well-known process known as the Guerbet reaction. We have developed ruthenium based catalysts that achieve unprecedented selectivity in the catalytic upgrading of ethanol and ethanol/methanol blends. The catalytic capability of these systems has been studied, and several important and intriguing observations highlight the need to investigate the specifics of the mechanism.
Subtle changes in the ligand sets allow for n-butanol, iso-butanol (catalysts 1
and 2) and sec-butanol (catalyst 3) formation. Unambiguously defining the origins of the selectivity of these ruthenium systems will enable selectivity tuning. This is a mechanistic feature that will undoubtedly provide information necessary for scale-up, as well as future design of new catalysts for the transformation of alcoholic substrates. [1] Dowson, G. R. M.; Haddow, M. F.; Lee J.; Wingad R. L.; Wass D. F., Angew.
Chemie – Int. Ed., 2013, 52, 9005-9008.
DEVELOPMENT OF FLUORINE-18 RADIOLABELLED THIA-
FATTY ACID TRACERS AND A COORDINATION CHEMISTRY
DELIVERY MECHANISM FOR IMAGING CARDIAC
METABOLISM BY POSITRON EMISSION TOMOGRAPHY (PET)
Zainab Al-Alia,b
, Juozas Domarkasa,b
, Benjamin Burkea,b
, Torsten Ruestb, Faisal Nuhu
d,
Robert Atkinsond, Chris Cawthorne
bc, Anne-Marie Seymour
bc and Stephen J.
Archibaldab
aDepartment of Chemistry, bPositron Emission Tomography Research Centre, cSchool of Biological, Biomedical and Environmental Sciences, University of Hull, Cottingham
Road, Hull, HU6 7RX, UK.
Clinical need. Cardiac diseases are the leading cause of death worldwide, thus, an early
detection and better understanding of different pathologies is needed. Positron emission
tomography1 is the most sensitive noninvasive medical imaging technique capable of
detecting metabolic changes during or preceding the establishment of a pathology.
Biochemical rational. Cardiac retention of thia-fatty acids (TFAs) is expected to reflect
the extent of fatty acid metabolism.2 Long chain TFAs are actively taken up by
myocites, but show poor blood solubility and fast liver-based elimination due to their
high lipophilicity.2 There is no active transport of short TFAs which may result in more
favorable pharmacokinetics. Project aims. Develop a novel TFA delivery mechanism
to the cardiac cells, based on their coordination to mitochondria targeted transition
metal complexes, allowing us to take advantage of the pharmacokinetics of various
short fatty acids and enable their use as tracers of cardiac metabolism.3 Results. 16-
[18
F]-fluoro-4-thia-palmitic acid (18
F-FTP) which should be actively transported into
cells and 10-[18
F]-fluoro-4-thia-capric acid (18
F-FTC2) which should enter only by
passive diffusion, were successfully radiolabelled from in house made precursors. 18
F-
FTP cardiac uptake was confirmed by PET imaging. Non mitochondria targeted zinc-
cross bridged cyclam complex was prepared as a model for coordination. Future work.
Free 18
F-FTC2 cardiac uptake will be investigated by PET and compared with that of 18
F-FTP. FTC2 will be coordinated with prepared Zn-cross bridged cyclam complex and
its in vitro and in vivo behavior will be studied by LC/MS and PET.
References.
[1] S. Vallabhajosula, Molecular Imaging: Radiopharmaceuticals for PET and SPECT,
2009, 299.
[2] A. P. Belanger, M. K. Pandey and T. R. DeGrado, Nucl. Med. Biol., 2011, 38, 435.
[3] A. Khan et al. J. Am. Chem. Soc. 2009, 131, 3416–3417
SUPPORTED INDENYL METALLOCENES FOR ETHYLENE
POLYMERISATION
P. Angpanitcharoen, G. Hay, J.-C. Buffet and D. O’Hare
Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA.
With a global production volume of 150 million metric tonnes per annum, mostly by
heterogeneous Ziegler-Natta catalysts, polyolefins have become an essential material for
the modern world.[1]
The use of metallocenes in polyolefins production has enabled an
unprecedented ability to fine-tune polymer microstructure by ligand design.[2]
Supported
metallocene catalysts capture the best of both worlds by, to an extent, retaining high
polymerisation activity and control of metallocenes while providing templates for
polymer growth.[3]
A new substituted indenyl family have recently shown very high
activity towards solution-phase polymerisation of ethylene.[4,5]
Here, we will present our study on the effects of ligand modification. (Me2SB(
3-
EtI*))ZrCl2, its unbridged analogues and alkyl analogues have been synthesised,
characterised and tested for ethylene polymerisation activity.
Synthesis of dimethylsilylbis(3-ethyl-2,4,5,6,7-tetramethylindenyl)zirconium
dichloride, (Me2SB(
3-EtI*))ZrCl2.
References:
[1] Gahleitner, M.; Resconi, L.; Doshev, P. MRS Bull. 2013, 38, 229.
[2] Welborn, H. C.; Ewen, J. A. US5324800 1991.
[3] Severn, J. R.; Chadwick, J. C.; Duchateau, R.; Friederichs, N. Chem. Rev. 2005,
105, 4073.
[4] Ransom, P.; Ashley, A. E.; Brown, N. D.; Thompson, A. L.; O’Hare, D. Organometallics 2011, 30, 800.
[5] Arnold, T. A. Q.; Buffet, J.-C.; Turner, Z. R.; O’Hare, D. J. Organomet. Chem. 2015. http://dx.doi.org/10.1016/j.jorganchem.2015.01.019
PALLADIUM-STIBINE COMPLEXES: UNPRECEDENTED TRIPLY BRIDGING COORDINATION OF
TRIMETHYLANTIMONY
S. Benjamina, T. Kraemer
b, W. Levason
c, S. Macgregor
b and G. Reid
c.
aNottingham Trent University, NG11 8NS
bHeriot-Watt University, EH14 4AS
cUniversity of Southampton, SO17 1BJ
Palladium phosphine complexes are widely used as catalysts in organic cross coupling reactions, and the electronic and steric characteristics of the phosphine ligands can be
varied in order to tune catalyst activity and selectivity.1 Palladium complexes with
stibines, SbR3, the heavier congeners of phosphines, have been much less explored. Stibine ligands exhibit a number of unusual coordination behaviours which are distinct from their lighter analogues, such as redox activity and formation of acceptor
interactions with anions and other electron donors both intra- and intermolecularly.2,3
The first (and still rare) example of a bridging organopnictine was a µ 2-SbiPr3 bridged
Rh2 dimer, and though the phosphine analogue could not be prepared directly, ligand metathesis with this stibine complex allowed a bridging phosphine to be isolated for the
first time.4
Investigation of the coordination chemistry of stibine
ligands with Pd(II) has led to the isolation of a number
of dimeric or cluster complexes, featuring short Pd-Pd Pd Sb
distances and several unusual ligand behaviours. The
Lewis acidity of coordinated halostibines is
demonstrated by the formation of intermolecular
secondary interactions between stibine and halide
ligands. A [Pd(0)]4 tetrahedron incorporating µ3-SbMe3
ligands has been prepared. The triply-bridging behaviour
of a monodentate organopnictine is unprecedented, and
the electronic structure and bonding in this complex has
been examined using ADF calculations.
[1] Gillespie, J. A.; Zuidema, E.; van Leeuwen, P. W. N. M.; Kamer, P. C.
J. In Phosphorus(III) Ligands in Homogeneous Catalysis: Design and Synthesis; John
Wiley & Sons, Ltd. 2012, ch. 1, 1-26.
[2] Benjamin, S. L.; Reid, G. Coord. Chem. Rev. 2015, 297–298, 168-180.
[3] Wade, C. R.; Ke, I.; Gabbaï, F. P. Angew. Chem. Int. Ed. 2012, 51, 478-481.
[4] Werner, H. Angew. Chem. Int. Ed. 2004, 43, 938-954.
DISCERNING THE MECHANISM(S) OF IRON-CATALYZED
CROSS-COUPLING REACTIONS.
L. Brown, J. R. Birkett, J. B. Sweeney and N. J. Patmore
Department of Chemical Sciences, University of Huddersfield, HD1 3DH [email protected]
Formation of new carbon-carbon bonds via metal-catalyzed cross-coupling reactions are
amongst the most indispensable tools in the repertoire of synthetic chemists. Precious
metals are routinely used and chief amongst these is palladium, unrivaled in the
versatility of its application. The inherent cost of the metal leads to costly syntheses
driving prices of commodities and pharmaceuticals. While the use of catalysis is
essential in the drive towards greener chemistry the catalysts themselves should be both
environmentally and biologically benign. As a result the use of the more abundant first
row transition metals has been investigated. Iron in particular has proven a promising
candidate.1 Being less well explored however, there remain many questions regarding
the exact functioning mechanism(s) in already established catalytic schemes.2–4
This work explores the mechanism(s) operating in iron-catalyzed Kumada type
couplings; the reaction between halogenated hydrocarbons and Grignard reagents using
simple iron salt catalysts.5 A number of catalytically relevant species, including novel
hetero-bimetallic species are isolated by stoichiometric reaction of Fe(acac)3 with aryl
Grignards. These complexes have been characterized by a variety of methods including 1H NMR and IR spectroscopy, X-ray crystallography and magnetic susceptibility
measurements. Furthermore, the isolation of Fe(acac)2 as a side product and the
revelation that each of these species has equal catalytic competence in selected cross-
coupling reactions suggests the presence of competing catalytic pathways.
(1) Tamura, M.; Kochi, J. J. Am. Chem. Soc. 1971, 93, 1487–1489.
(2) Smith, R. S.; Kochi, J. J. Org. Chem. 1976, 41, 502–509.
(3) Fürstner, A.; Martin, R.; Krause, H.; Seidel, G.; Goddard, R.; Lehmann, C. W. J. Am. Chem. Soc. 2008, 130, 8773–8787.
(4) Hatakeyama, T.; Yoshimoto, Y.; Gabriel, T.; Nakamura, M. Org. Lett. 2008, 10, 5431–5344.
(5) Tamao, K.; Sumitani, K.; Kumada, M.; Kiso, Y. J. Am. Chem. Soc. 1972, 94, 9268–9269.
POLYETHYLENE SYNTHESIS USING PERMETHYLINDENYL
METALLOCENE COMPLEXES
J.-C. Buffet, Z. R. Turner and D. O'Hare
Chemistry Research Laboratory, 12 Mansfield Road, OX1 3TA, Oxford, UK
Polyethylene (PE) is the most widely used polyolefin with an annual production of
above 75 million tons per year and a global demand poised for growth. In contrast to
heterogeneous Ziegler-Natta systems, homogeneous metallocene-based catalysts
produce polyethylene with a narrow molecular weight distribution due to their single-
site nature; polymer properties can also be fine-tuned through careful ligand design.[1]
By immobilising metallocene catalysts onto support materials, the processability
problem is solved and the advantages of metallocene catalysts are preserved to a great
extent.[2]
We recently reported the synthesis of permethylindenyl complexes and their use in
the solution polymerisation of ethylene,[3] and the development of solid catalysts using
layered double hydroxides as a support.[4]
Here, we present the synthesis of unsymmetrical permethylindenyl complexes,
Figure 1a, and their use in the polymerisation of ethylene in both solution and slurry,
Figure 1b.
a) b)
Figure 1. a) Solid-state molecular structure of a permethylindenyl zirconocene Me
2SB(tBu2Flu,I*)ZrCl2 and b) SEM images of PE synthesised in the slurry process.
References. [1]Hlatky, G. G. Chem. Rev. 2000, 100, 1347. [2]Severn, J. R.; Chadwick, J. C.;
Duchateau, R.; Friederichs, N. Chem. Rev. 2005, 105, 4073. [3]Arnold, T.A.Q.; Buffet,
J.-C.; Turner, Z. R.; O’Hare, D. J. Organomet. Chem., 2015, DOI:
10.1016/j.jorganchem.2015.01.019. [5]Buffet, J.-C.; Wanna, N.; Arnold, T. A. Q.;
Gibson, E. K.; Wells, P. P.; Wang, Q.; Tantirungrotechai, J.; O'Hare, D. Chem Mater.
2015, 27, 1495.
DEVELOPING THE COORDINATION CHEMISTRY OF LEAD(II)
– NEW DIPHOSPHINE COMPLEXES AND REAGENTS FOR
SUPERCRITICAL FLUID ELECTRODEPOSITION
W. Levason, G. Reid and J. Burt
Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
Owing to the unique properties of supercritical fluids, the technique of supercritical
fluid electrodeposition (SCFED) has the potential to produce technologically important
materials on the nanoscale with atomic layer control. SCFED has already been
successfully used to deposit a range of reactive materials, including Ge films and 3 nm
diameter Cu nanowires.1
The development of this approach to enable deposition of other p-block materials is of
particular interest, and recently work has focussed on identifying, synthesising and
characterising suitable tin(II) and lead(II) precursors. Here we present voltammetric and
deposition studies of several Sn(II) and Pb(II) reagents in CH2Cl2, together with the
growth of 13 nm tin nanowires from supercritical CH2F2.
While numerous phosphine complexes of most heavy p-block elements (e.g. Bi(III),
Sn(II) and Sn(IV)) are known,2 surprisingly the only well characterised examples with
Pb(II) are two recently reported adducts with lead thiolates.3 In order to further explore
the coordination chemistry of lead(II) complexes with neutral diphosphine ligands we
have synthesised and characterised (by X-ray crystallography, IR spectroscopy,
microanalysis and NMR spectroscopy where possible) several diphosphine complexes
of Pb(NO3)2 and Pb(SiF6).2H2O, finding evidence for anion coordination in all cases.
Despite its size and ability to achieve large coordination numbers (up to 12) only one
diphosphine ligand is observed to coordinate to Pb(II).4
[1] Bartlett, P.N.; Cook, D.C.; George, M.W.; Hector, A.L.; Ke, J.; Levason, W.; Reid,
G.; Smith, D.C.; Zhang, W. Phys. Chem. Chem. Phys. 2014, 16, 9202. The SCFED
Project (www.scfed.net) is a multidisciplinary collaboration of British universities
investigating the fundamental and applied aspects of supercritical fluids.
[2] Burt, J.; Levason, W.; Reid, G. Coord. Chem. Rev. 2014, 260, 65.
[3] Rossini, A.J.; Macgregor, A.W.; Smith, A.S.; Schatte, G.; Schurko, R.W.; Briand,
G.G. Dalton Trans. 2013, 9533.
[4] Burt, J.; Grantham, W.; Levason, W.; Reid, G. Dalton Trans. 2015, 11533.
(E)-SELECTIVE ALKENE ISOMERISATION CATALYSED BY A
HETEROBIMETALLIC Mg---Zr TRIHYDRIDE
M. J. Butler and M. R. Crimmin
Department of Chemistry, Imperial College, South Kensington, London, SW7 2AZ, UK
We recently reported the hydride-bridged heterobimetallic complex Al•Zr (Figure -
M•Zr), thought to play a role in the activation of a group 4 pre-catalyst in two separate
C–X (X = F, O) inert bond cleavages.1 Here we describe the preparation of Mg•Zr and
Zn•Zr: well-defined heterobimetallic hydrides of M(II) and Zr(IV). The Mg•Zr complex is a selective, single-site catalyst for the isomerisation of terminal alkenes,
controlling the stereoselectivity of the reaction.
We show that terminal alkenes are isomerised to internal alkenes across one position
with a strong bias for (E)-stereochemistry in the products.2
Absence of a M(II) fragment
– i.e. use of [Cp2ZrH(-H)]2 – results in loss of activity, selectivity, and competitive
substrate hydrogenation. The labile Al•Zr is also vulnerable to these pitfalls. In-situ pre-
catalyst activation is possible through mixing of the main group hydride and [Cp2ZrCl2].
Finally, we have probed the mechanism with a simple stoichiometric reaction of
(Dipp
BDI)Mg-alkyl complexes, which give Mg•Zr when reacted with [Cp2ZrH(-H)]2.
References
[1] a) Yow, S.; Gates, S. J.; White, A. P.; Crimmin, M. R. Angew. Chem. Int. Ed. 2012,
51, 12559-12563 b) Yow, S.; Nako, A. E.; Neveu, L.; White, A. J. P.; Crimmin, M. R.
Organometallics 2013, 32, 5260-5262.
[2] Examples of other group 4 systems: a) Averbuj, C.; Eisen, M. J. Am. Chem. Soc.
1999, 121, 8755-8759 b) Petrisor, C. E.; Frutos, L. M.; Castaño, O.; Mosquera, M. E.
G.; Royo, E. ; Cuenca, T. Dalton Trans. 2008, 2670-2673
SYNTHETIC APPLICATIONS OF BORYLZINC COMPOUNDS:
BORYL TRANSFER CHEMISTRY AND CATALYTIC
BORYLATION
Jesus Campos, Simon Aldridge*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, OX1 3TA,
Oxford
Since the groundbreaking isolation of the first boryllithium species by Yamashita and
Nozaki,[1]
the chemistry of boryl nucleophiles has rapidly expanded. Interestingly, the
reactivity of the boryl anion is highly dependent on its metallic counterion, as
exemplified by the dissimilar reactivity between a diaminosubstituted boryllithium and
its magnesium analogue when added to benzaldehyde.[2]
Considering the rich chemistry
of alkyl zinc reagents in synthetic applications and the growing interest in zinc as an
inexpensive and environmentally benign metal in catalysis, we decided to explore the
still undeveloped chemistry of borylzinc compounds (A in Figure 1).
Figure 1. Synthetic applications of borylzinc compounds.
Transmetalation reactions using borylzinc species allowed us to synthesize a number of
Transition Metal and Main Group metal boryl complexes with considerably higher
yields and increased selectivity when compared to the commonly used boryllithium
analogues. More interestingly, the direct use of borylzinc precursors for cross-coupling
processes resulted in the borylation of a plethora of organic halides and pseudohalides,
including unactivated alkyl halides, in high yields, with high functional group tolerance
and under mild conditions.
[1] Segawa, Y.; Yamashita, M.; Nozaki, K. Science 2006, 314, 113.
[2] Yamashita, M.; Suzuki, Y.; Segawa, Y.; Nozaki, K. J. Am. Chem. Soc. 2007, 129,
9570.
SOFT DONOR COMPLEXES WITH TRI- AND TETRA-VALENT NIOBIUM AND TANTALUM
Yao-Pang Chang; William Levason; Gill Reid.
School of Chemistry, University of Southampton, Southampton, SO17 1BJ, UK
The chemistry of early transition metal halide complexes with soft, neutral donor
ligands such as phosphines, thio- or selenoethers is often different from that with hard
O- or N-donor ligands.1 Very recently, we have reported a series of group V metal
halide complexes with chalcogenoethers in their highest oxidation state (+5), and
showed their utility in the chemical vapour deposition of NbS2 and NbSe2 thin films.2
However, complexes of the lower oxidation states, such as Nb(III), Ta(III), Nb(IV) or
Ta(IV) with soft donor ligands are unusual and their chemistry is not well developed.
Mononuclear Nb(III) or Ta(III) halides (NbCl3 or TaCl3) do not exist, instead, dinuclear
complexes of the form [M2Cl6(L)3] (M = Nb, Ta; L = Me2S, THT) are known to form
from Na/Hg or Mg/Et2O reduction of MCl5 in the presence of the S ligand.3 Complexes
obtained via these starting materials often form edge-sharing dimers and contain a
M=M double bond.4 Nb(IV) halides, in contrast, are made by aluminium reduction of
MCl5 over a temperature gradient.5,6
Here we report a series of Nb(III) and Ta(III) dimer complexes obtained by reaction of
[M2Cl6(Me2S)3] with soft, neutral dithioether or diselenoether ligands. In addition,
NbCl4 has been prepared and directly reacted with neutral ligands. The chemistry
associated with these complexes is described, together with their spectroscopic and
structural characterisation.
References:
[1] S. L. Benjamin, W. Levason and G. Reid, Chem. Soc. Rev., 2013, 42, 1460-
1499.
[2] S. L. Benjamin, Y. P. Chang, C. Gurnani, A. L. Hector, M. Huggon, W. Levason
and G. Reid, Dalton Trans., 2014, 43, 16640-16648.
[3] T. Waters, A. G. Wedd, M. Ziolek and I. Nowak, in Comprehensive
Coordination Chemistry II, eds. J. A. McCleverty and T. J. Meyer, Elsevier B.V.,
Toronto, Editon edn., 2003, vol. 4.
[4] E. Babaian-Kibala, F. A. Cotton and P. A. Kibala, Inorg. Chem., 1990, 29, 4002-
4005.
[5] McCarley, R. E.; Torp, B. A., Inorg. Chem. 1963, 2, 540
[6] Fowles, G. W. A.; Tidmarsh, D. J.; Walton, R. A., Inorg. Chem. 1969, 8, 631.
AN ELECTROCHEMICAL FLOW-REACTOR FOR THE
SYNTHESIS OF ORGANOMETALLIC COMPLEXES
Dr C. E. Willans, Dr B. N. Nguyen and M. R. Chapman
Institute of Process Research and Development (iPRD), School of Chemistry, University
of Leeds, LS2 9JT, UK
Developed by Arduengo over two decades ago, the notion of employing N-heterocyclic
carbenes (NHCs) as ancillary ligands for transition metal-based catalysts has been
refined such that they now present all required attributes for broad application –
typically offering high return over their phosphine rivals (e.g. enhanced thermal stability
and greater tunability).[1] Despite these advances, a number of drawbacks currently
exist with traditional methods of metal-NHC preparation, notably when considering
such complexes for industrial use. The pre-requisite for strongly basic/strictly inert
conditions within current syntheses largely limits the scope of suitable substrate for
metal-NHC complexation.[2] Complementary routes include transmetallation of a
carbenic moiety from a basic metal oxide (e.g. Ag2O),[3] leading to the accumulation of
metal salt byproducts.
In light of these challenges, the design, construction and optimisation of an innovative
electrochemical flow-reactor has been developed which circumvents such issues. The
electrochemical approach, which has been published in Chemical Communications, [4,
5] provides a clean and atom economical route to metal-NHCs as a result of: (i) no
external reagents are required, (ii) a simple evaporative work-up and (iii) only H2 gas
byproduct.
[1] Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361-
363.
[2] Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100,
39-91.
[3] Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251 (5+6), 642-670.
[4] Lake, B. R. M.; Bullough, E. K.; Williams, T. J.; Whitwood, A. C.; Little, M.
A.; Willans, C. E. Chem. Commun. 2012, 48 (40), 4887-4889.
[5] Chapman, M. R.; Shafi, Y. M.; Kapur, N.; Nguyen, B. N.; Willans, C. E. Chem.
Commun. 2015, 51 (7), 1282-1284.
SYNTHESIS AND REACTIVITY OF TITANIUM BORYLIMIDO
COMPOUNDS
Benjamin A. Clough, Andrey V. Protchenko, Simon Aldridge and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, U.K.
The chemistry of metal–nitrogen multiple bonds has been of interest to researchers for
more than thirty years.1 In particular, the synthesis and small molecule reactivity of
Group 4 imido and hydrazido complexes, (L)M=NR and (L)M=NNR2, have been
extensively studied within this research group and by others,2
and more recently, the
first titanium alkoxyimido complexes, (L)Ti=NOR, were reported.3
In contrast, only five examples of the related borylimides, (L)M=NBR2, have been
reported across all of the transition metals to date,4 and we here present the first
systematic pursuit of borylimido complexes, namely of titanium, using the borylamine
H2NB{N(Ar')CH}2 (Ar' = 2,6-C6H3iPr2).
To this end, we report two novel routes into titanium borylimido chemistry, and the
subsequent installation of a varied range of supporting ligand sets (see Figure 1), which
have allowed us to begin the first reactivity studies of this functional group.
Figure 1: Examples of new titanium borylimido complexes.
References.
[1] For example: Acc. Chem. Res., 2005, 38, 955; Acc. Chem. Res., 2005, 38, 839; J.
Am. Chem. Soc., 2001, 123, 2923.
[2] For example: Organometallics, 2011, 30, 1182; J. Am. Chem. Soc., 2004, 126, 1794;
Organometallics, 2009, 28, 4747.
[3] Chem. Commun., 2011, 47, 4926; Inorg. Chem. 2011, 50, 12155; Organometallics,
2013, 32, 7520.
[4] Polyhedron, 1993, 12, 1061; Z. Anorg. Allg. Chem., 2003, 629, 744; Angew. Chem.
Int. Ed. Engl., 2002, 41, 3709-3712; J. Am. Chem. Soc., 2014, 136, 8197.
BIMETALLIC GROUP 4 COMPLEXES AS OLEFIN
POLYMERISATION CATALYSTS
R. A. Collins,a A. F. Russell,
a A. Berthoud,
b R. T. W. Scott
b and P. Mountford*
,a
a Chemistry Research Laboratory, Department of Chemistry, University of Oxford,
Mansfield Road, Oxford, OX1 3TA, UK. [email protected]
b LANXESS Elastomers B.V., Global R&D, P.O. Box 1130, 6160 BC Geleen, The Netherlands
LANXESS Elastomers have introduced (as Keltan ACETM) a new class of к1
-amidinate
complexes of the type (η-C5R5)M{NC(Ar)NR'2}X2 (X = Me or Cl; M = Ti, Zr or Hf),
which are extremely active pre-catalysts for the commercial homo- and co-
polymerization of olefins.[1,2]
Bimetallic catalysts can have beneficial cooperative effects in olefin polymerisation,
which arise from the complementary interaction of the polymeric chain between the
adjacent metal centres. This often results in an increased molecular weight, chain
branching and incorporation of alternate monomeric species. [3]
Here we report new bimetallic catalysts with different bridging moieties and compare
their catalytic activity and the resultant polymer properties to that of their mononuclear
analogues.
Figure 1. Solid state structures of representative mononuclear and bimetallic cyclopentadienyl-amidinate
complexes
[1] Ijpeij, E. G.; Coussens, B.; Zuideveld, M. A.; van Doremaele, G. H. J.; Mountford,
P.; Lutz, M.; Spek, A. L. Chem. Commun. 2010, 46, 3339.
[2] Ijpeij, E. G.; Windmuller, P. J. H.; Arts, H. J.; Van, d. B. F.; Van, D. G. H. J.;
Zuideveld, M. A. WO2005090418A1 2005.
[3] Delferro, M.; Marks, T. J. Chem. Rev. 2011, 111, 2450.
ON THE ROAD TO TETRAZOLATE BASED NITROGEN RICH
MATERIALS
Peter Portius and Ben Crozier
Dainton Building, Brook Hill, Sheffield, S3 7HF
My research is focussed on the synthesis of homoleptic tetrazolato- main group
complexes of the type [E(N4CH)6]2-
(where E= Si, Ge and Sn). Such complexes are
unknown for p-block elements, while only certain transition metal examples exist, such
as [ML6](BF4)2 where M = Mn, Co, Cu, Zn and L = 1-methyltetrazole, 1-ethyltetrazole
and 1-propyltetrazole. 1 The appeal of the tetrazolate ligand is its high nitrogen content
which imparts this class of compounds with a high nitrogen content and a high energy
density. This characteristic originates within the strength of the dinitrogen triple bond.
Compounds that contains the weaker N-N and N=N bonds strain against an enthalpic
drive to exist as dinitrogen. Therefore, thermally activated decomposition of these
compounds is accompanied by a large release of heat and the formation of mostly N2
gas. It is for this reason that nitrogen-rich energetics are seen as a more environmentally
friendly alternative to conventional energetic materials. 2
The novel homoleptic anionic polytetrazolate complexes [Si(N4CH)6]2-
and
[Ge(N4CH)6]2-
were prepared recently in our laboratory. 3 The next step was an
extension of the reaction scheme to the related heavier analog [Sn(N4CH)6]2-
.
Employing ligand exchange reactions, the reaction was found to stop at the stage of
(PPN)2[Sn(N4CH)3Cl3]. For this reason, alternative tetrazoles transfer reagents were
investigated, amongst which trimethylsilyltetrazole, TMS-N4CH, 4
was found to be
highly promising. TMS-N4CH is readily accessible. It is synthetically highly versatile as
it relies on the formation of TMS-F in the exchange reaction with the relative strength
of the Si-F bond providing the driving force. In a one-pot synthesis SnF4, TMS-N4CH
and PPN(N4CH) are combined and react to produce the fully exchanged
(PPN)2[Sn(N4CH)6]. TMS-N4CH also holds promise for generating low-valent
tetrazolates. Combination with SnF2 in dry pyridine has yielded a co-ordination polymer
with a repeating unit of {Sn(N4CH)2(py)}. 5
This is the first example of a tetrazolate-
bridge main group co-ordination polymer. From each 2D planar sheet pyridine rings
extend out of the plane and pi-pi stack with pyridine bound to an opposing sheet,
producing a bilayer in the extended structure. This is a highly interesting structure as it
suggests a 3D metal organic framework (MOF) utilising a tin-tetrazolate core could be
synthesised. Such a system could preferentially adsorb CO2.6 In addition with a suitably
nitrogen rich organic linker, it would be a rare example of an energetic MOF. 7
[1] J. Kusz, H. Spiering, and P. Gütlich, J. Appl. Crystallogr., 2004, 37, 589.
[2] G. Steinhauser and T. M. Klapötke, Angew. Chem. Int. Ed., 2008, 47, 3330.
[3] P. Portius, B. F. Crozier, In preparation, 2015.
[4] L. Birkofer et al., Chem. Ber., 1963, 96, 2750.
[5] P. Portius, B. F. Crozier, In preparation, 2015.
[6] R. Banerjee et al., Cryst. Growth Des., 2011, 11, 5176.
[7] M Shreeve et al., Angew. Chem. Int. Ed., 2014, 53, 2540.
STOICHIOMETRIC AND CATALYTIC C-F BOND ACTIVATION
BY TRANS-DIHYDRIDE RUTHENIUM NHC COMPLEXES
Mateusz K. Cybulski, Mary F. Mahon, Ian M. Riddlestone and Michael K. Whittlesey
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
In light of our previous work on catalytic hydrodefluorination (HDF) of fluorinated
aromatics using ruthenium N-heterocyclic (NHC) dihydride precursors and a well
understood mechanism involving nucleophilic attack by metal-bound hydride ligands
investigated with DFT calculations [1], we now present our recent findings on
stoichiometric and catalytic C-F activation by Ru NHC complexes containing
increasingly more nucleophilic hydride ligands. The mixed phosphine-carbene species,
Ru(IEt2Me2)2(PPh3)2H2 (1), proved to be a viable precursor for HDF, converting C6F6 to
a mixture of tri, di and monofluorobenzenes over several days at 90°C with 10 mol%
catalyst and Et3SiH as the reductant [2]. The employment of the tetracarbene species,
Ru(IMe4)4H2 (2), allowed for milder reaction conditions, affording selective formation
of 1,2,4,5-tetrafluorobenzene within minutes at room temperature.
References.
[1] Reade, S. P.; Mahon, M. F.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 1847;
Panetier, J. A.; Macgregor, S. A.; Whittlesey, M. K. Angew. Chem. Int. Ed. 2011, 50,
2783; Macgregor, S. A.; McKay D.; Panetier, J. A.; Whittlesey, M. K. Dalton Trans.
2013, 42, 7386
[2] Cybulski, M. K.; Riddlestone, I. M.; Mahon, M. F.; Woodman, T. J.; Whittlesey, M.
K. Dalton Trans. 2015, DOI: 10.1039/c5dt01996f
ALKALINE EARTH ORGANOHYDROBORATE COMPLEXES FOR THE RING-OPENING POLYMERISATION OF RAC-
LACTIDE
Nichabhat Diteepeng, Junjuda Unruangsri, Insun Yu and Philip Mountford*
Chemistry Research Laboratory, Department of Chemistry, University of Oxford
Mansfield Road Oxford OX1 3TA UK. [email protected]
Polymers from renewable resources such as polylactide (PLA) have gained great
attraction from both commercial and academic perspectives because of their
environmental advantages and various applications ranging from drug delivery to
packaging materials. The preparation of well-characterised metal complexes employed
as ring-opening polymerisation (ROP) catalysts has been a focus in both industrial and
academic research.1
The hydride transfer and reducing potential of metal organohydroborate complexes
allows them to be candidates for rac-LA ROP initiators. To date, no alkaline earth
organohydroborate complexes have been established as ROP initiators.2 Here we report
mechanistic investigations and polymerisation studies of the ROP of rac-LA using
alkaline earth organohydroborate complexes (HBEt3) supported by 3-methyl,5-tert-
butyl tris(pyrazolyl)hydroborate ligands (TptBu,Me
) (1-2, Figure 1)3 and the synthesis and
characterisation of a new calcium alkoxide complex derived from the hydride transfer
between TpCaHBEt3(THF) and benzophenone (3, Figure 1).
Figure 1: New alkaline earth initiators (1 – 3) for the ROP of rac-LA.
References
[1] Recent reviews: Wheaton, C. A.; Hayes, P. G.; Ireland, B. J. Dalton Trans. 2009, 25, 4832, Platel, R. H.; Hodgson, L. M.; Williams, C. K. Polym. Rev. 2008, 48,
11, Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. Rev. 2004, 104,
6147, O'Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B. J.Chem. Soc., Dalton Trans.
2001, 2215.
[2] See for example: Harvey, M. J.; Hanusa, T. P.; Pink, M. Chem. Commun. 2000, 6,
489, Pillai Sarish, S.; Jana, A.; Roesky, H. W.; Schulz, T.; John, M.; Stalke, D.
Inorg. Chem. 2010, 49, 3816, Krieck, S.; Görls, H.; Westerhausen, M. Inorg.
Chem. Commun. 2010, 13, 1466.
[3] Unruangsri, J.; Mountford, P. unpublished results.
EXPLOITING THE POLYAMINE TRANSPORT SYSTEM TO
DELIVER THERANOSTIC RHENIUM(I) COMPLEXES
P. M. Cullis, M. P. Lowe, H. L. Parker and V. L. Emms.
Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH
Polyamines are crucial to cell viability and play a key role in proliferation. Cancer cells
frequently exhibit an upregulated polyamine transport system; as such polyamine-drug
conjugates have been designed to selectively target cancer cells.1 Polyamines have been
shown to enter the cell via endocytosis, and be sequestered into acidic vesicles.2
Targeted Re(I) complexes have been developed for use as luminescent probes for
biological imaging.3 We have extended this approach to use the Re(I) tricarbonyl core
as a scaffold upon which to build a theranostic complex, incorporating cancer cell
specific delivery and controlled release of cytotoxic agents.
Bioconjugation of polyamines to the Re(I) tricarbonyl core is achieved using
diazotransfer4 and Cu(I) catalyzed azide-alkyne cycloaddition
5 to generate
pyridyltriazole (pyta) chelating ligands. Luminescent Re(I) tricarbonyl pyta complexes
have long emission lifetimes and a large Stokes shift, which makes them suitable for use
as biological probes. However, these complexes show weak emission when excited at
405 nm, a wavelength commonly used in confocal microscopy. The electronic structure
of the ligand has been modified to shift the absorption wavelength to generate more
emissive biological probes.
References. [1] Leblond, P.; Boulet, E.; Bal-Mahieu, C.; Pillon, A., Kruczynski, A.; Guilbaud, N.; Bailly, C.; Sarrazin,
T.; Lartigau, E.; Lansiaux A. and Meignan, S. Invest. New Drugs, 2014, 32, 883.
[2] Belting, M.; Mani, K.; Jönsson, M.; Cheng, F.; Sandgren, S.; Jonsson, S.; Ding, K. ; Delcros J.-G. and
Fransson, L.-A. J. Biol. Chem., 2003, 278, 47181.
[3] Coogan M. P. and Fernández-Moreira, V. Chem. Commun., 2014, 50, 384.
[4] Ethan D. Goddard-Borger, E. D. and Stick, R. V. Org. Lett., 2007, 9, 3797.
[5] Rostovtsev, V. V.; Green, L. G.; Fokin, V. V. and Sharpless, K. B. Angew. Chem. 2002, 114, 2708.
GROUP IV PERMETHYLPENTALENE COMPLEXES AS
ETHYLENE POLYMERISATION CATALYSTS
D. A. Fraser, F. Mark Chadwick, J.-C. Buffet and D. O'Hare*
Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford.
OX1 3TA [email protected]
Polyethylene accounts for nearly 65% of total annual polyolefin output, with global production over 70 million tonnes per year.[1,2] Although heterogeneous Ziegler-Natta systems define the industry standard, large molecular weight distributions and uneven monomer incorporation restricts application of the resultant polymer. Homogeneous catalysts meanwhile often give far more desireable polymer properties. Following the synthesis of the permethylpentalenyl dianion (Li2[Pn*], Pn* = C8Me6)
[3] a series of new titanium and zirconium complexes were synthesised and their activity for the polymerisation of ethylene in solution were tested.[4] They were considered “Very active” on the Gibson scale[5]
Here, we present a more detailed study of the solution phase polymerisation of ethylene including mechanistic studies. Variable temperature NMR studies were carried out to probe the early stages of activation following addition of AlMe3. References.
[1] Severn, J. R.; Chadwick, J. C.; Duchateau, R.; Friederichs, N., Chem. Rev., 2005, 105, 4073 [2] Piringer, O. G.; Baner, A. L. Plastic Packaging: Interactions with Food and Phatmaceuticals;
2nd Ed.; Wiley, 2008 [3] a) A. E. Ashley, A. R. Cowley, D. O’Hare, Chem. Comm., 2007, 1512 b) A. E, Ashley, a. R.
Cowley, D. O’Hare, Eur. J. Org. Chem., 2007, 26, 2239 [4] F. M. Chadwick; R. T. Cooper; A. E. Ashely; J.-C. Buffet; D. M. O’Hare, Organometallics,
2014, 33(14), 3775 – 3785 [5] G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem. Int. Ed. Engl., 1999, 38(4), 428-447
Fig. 1: Representation and solid state molecular structure of Pn*ZrClCp. Ellipsoids at 50%
HYDROPHOSPHINATION USING AN AIR-STABLE IRON PRE-
CATALYST
K. J. Gallagher and R. L. Webster*
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK [email protected]
The synthesis of phosphines using a 100% atom-economic transformation is an attractive process, not least because phosphorus compounds in the +3 oxidation state are important ligands for transition metal catalysis. They also make excellent organocatalysts and reagents in organic synthesis.
Hydrophosphination reactions are most commonly catalysed by Group 10 (Ni, Pd, Pt), Group 3 (Y) and lanthanide (La, Sm, Yb) metal salts.1 More recently, iron salts have also been used, a particularly appealing approach due to the vast abundance and low toxicity of the metal.2
Although the use of iron salts is operationally simple, catalyst design is needed to further advance iron catalysed hydrophosphination. By introducing an easily accessible salen ligand we have significantly improved functional group tolerance, lowered catalyst loading and have shown that the reaction can proceed efficiently under milder reaction conditions than those reported using iron chloride salts.2,3 These simple phosphine products have also been shown to be active for iron-catalysed Negishi coupling.
This is the first time a designed iron catalyst has been used for hydrophosphination, these results, along with comprehensive mechanistic studies, will be presented.
[1] L. Rosenberg, ACS Catal. 2013, 3, 2845-2855. [2] L. Routaboul, F. Toulgoat, J. Gatignol, J.-F. Lohier, B. Norah, O. Delacroix, C. Alayrac, M. Taillefer and A.-C. Gaumont, Chem. Eur. J. 2013, 19, 8760-8764. [3] K. J. Gallagher, R. L. Webster, Chem. Commun. 2014, 50, 12109-12111
TANTALUM HYDRAZIDE COMPLEXES WITH A TRIDENTATE
TRIANIONIC LIGAND
Karen Y. Gamero-Vega, Richard A. Collins and Philip Mountford*
Department of Chemistry, University of Oxford, OX1 3TA, UK
The chemistry of metal-nitrogen multiple bond has been an ongoing area of extensive
interest. The study of imido and hydrazido complexes of Group 4 and 6 metals is well
established and many applications have been reported.[1]
The synthesis, properties and
applications of the tridentate trianionic pincer have been explored with high valent
metals over the past decade.[2]
The aim of this project is to synthesise the first Group 5 hydrazido complex with a
tridentate trianionic ligand and explore any reactivity exhibited with small molecules.
Three different synthetic routes to this compound, using 2,2’-bis(trimethylsilylamino)diphenylamine
[3,4] as a ligand backbone, are reported and the
chemistry of the synthetic intermediates explored.
[1] Gade, L. H.; Mountford, P. Coordination Chemistry Reviews 2001, 216-217, 65-
97. Pickett, C. J. J. Biol. Inorg. Chem., 1996, 1, 601. Hazari, N.; Mountford, P.
Acc. Chem. Res. 2005, 38, 839. Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem.,
Int. Ed., 1999, 38, 3389.
[2] O’Reilly, M. E.; Veige, A. S. Chem. Soc. Rev. 2014, 43, 6325.
[3] Ren, P.; Vechorkin, O.; von Allmen, K.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc.
2011, 133, 7084–7095.
[4] Schrock, R. R.; Lee, J.; Liang, L.; Davis, W. M. Inorg. Chim. Acta. 1998, 270,
353-362.
SYNTHESIS OF IRIDIUM COMPLEXES CONTAINING N-
HETEROCYCLIC CARBENE-BASED PINCER LIGANDS
Lucero González-Sebastin and Adrian B. Chaplin*
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
N-heterocyclic carbenes (NHCs) are of growing interest in organometallic chemistry
and catalysis as alternatives to widely used phosphine ligands.1 In addition to their
strong donor properties, inclusion into rigid mer-tridentate ‘pincer’ ligand architectures
is of great interest for chemically challenging applications requiring high thermal
stability, such as alkane dehydrogenation.2 Our research has focused on developing a
new series of NHC-based pincer ligands containing imidazolinylidene donor groups
(see below). These CCC-pincer ligands were prepared from 1,3-diaminobenzene
through standard multistep synthetic routes.3 The coordination chemistry of these
ligands with various iridium precursors is currently being pursued and will be
discussed. Ongoing and future research aims to evaluate iridium derivatives in
hydrocarbon activation reactions.
[Ir]
R =
[Ir]N
N
N
N
R
R
2(Cl)
N
N
N
N
R
R
References 1. Pugh, D.; Danopoulos, A. A., Coord. Chem. Rev. 2007, 251, 610-641.
2. Chianese, A. R.; Drance, M. J.; Jensen, K. H.; McCollom, S. P.; Yusufova, N.;
Shaner, S. E.; Shopov, D. Y.; Tendler, J. A., Organometallics 2014, 33, 457-464.
3. Rubio, R. J.; Andavan, G. T. S.; Bauer, E. B.; Hollis, T. K.; Cho, J.; Tham, F. S.;
Donnadieu, B., J. Organomet. Chem. 2005, 690, 5353-5364.
ALKALINE EARTH-TRANSITION METAL COMPLEXES
Ross Green, Alicia Walker, Matthew P. Blake and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road,
Oxford OX1 3TA, UK.
Molecular compounds containing metal-metal bonds have long been of interest in
inorganic chemistry.1 Although there are numerous examples of compounds with bonds
between transition metal (TM) elements, there exist relatively few between transition
metals and the alkaline earth (Ae) elements.2
Our group has recently reported several compounds containing Ae–TM bonds. The
reaction of the β-diketiminate magnesium species Mg(NacNac)I(THF) with KFp (Fp =
CpFe(CO)2) afforded Mg(NacNac)Fp(THF) (Mg–Fe = 2.6326(4) Å).3 This was shown
to react with TolNCNTol to afford Mg(NacNac){(NTol)2CFp}, the first net insertion of
an unsaturated substrate into an alkaline earth-transition metal bond.
We have recently developed amidinate species of the type Mg{RC(NR')2}M'(THF)
(M' = CpFe(CO)2, CpRu(CO)2 or Co(CO)3(PCy3), R = Mes, R' = iPr, Dipp or Mes),
which feature fewer carbon atoms in the ligand backbone and yield a more sterically
open system which may have the potential for increased reactivity with respect to the
analogous system. In addition, the guanidinate species [Mg{Me2NC(NDipp)2}Fp]2 has
been synthesised which features two Mg–Fe bonds (Mg–Fe = 2.5279(4) Å). These are
the shortest known Mg–Fe bonds to date.
Figure 1. Mg–TM bonded complexes featuring β-diketiminate, amidinate and
guanidinate ligands.
[1] (a) F. A. Cotton, C. A. Murillo and R. A. Walton, Multiple Bonds Between Metal Atoms; 3rd
ed.;
Springer: New York, 2005. (b) S. T. Liddle (ed.), Molecular Metal-Metal Bonds; Wiley:
Weinheim, Germany, 2015. (c) L. H. Gade, Angew. Chem. Int. Ed., 2000, 39, 2658.
[2] For example: (a) H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem. Int. Ed., 2009, 48,
4239. (b) H. Felkin, P. J. Knowles, B. Meunier, A. Mitschler, L. Ricard and R. Weiss, J. Chem.
Soc. Chem. Commun., 1974, 44. (c) K. Jonas, G. Koepe and C. Krüger, Angew. Chem. Int. Ed.,
1986, 25, 923. (d) H. Deng and S. G. Shore, J. Am. Chem. Soc., 1991, 113, 8538.
[3] M. P. Blake, N. Kaltsoyannis, P. Mountford, Chem. Commun., 2013, 49, 3315.
MECHANISTIC STUDY OF OF ANHYDRIDE FORMATION
FROM RHODIUM(III) ACETYL COMPLEXES AND
CARBOXYLATES
D. Griffin and A. Haynes
Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK,
Product formation in rhodium-catalysed methanol carbonylation is conventionally
proposed to proceed via reductive elimination of acetyl iodide from
[Rh(COMe)(CO)2I3]- and subsequent hydrolysis to form acetic acid.
1 Evidence has
recently been reported for an alternative mechanism involving replacement of an I-
ligand by acetate, formed in situ, and subsequent reductive elimination of acetic
anhydride which is then hydrolysed.2
The reactions of chelate complexes [Rh(COMe)(L-L)I2] (1a-d) with carboxylates have
been studied to elucidate the mechanism of anhydride formation. Rapid substitution of I-
by acetate occurs to give 2a-d, followed by relatively slow reductive elimination of
acetic anhydride. Intermediates 2a-c were observed in situ by IR and NMR
spectroscopy and 2d has been isolated and characterised by X-ray crystallography.
References
[1] Haynes, A. Adv. Catal. 2010, 53, 1–45 and references therein.
[2] (a) Lassauque, N.; Davin, T.; Nguyen, D. H.; Adcock, R. J.; Coppel, Y.; Le
Berre, C.; Serp, P.; Maron, L.; Kalck, P. Inorg. Chem. 2012, 51, 4–6.
(b) Nguyen, D. H.; Lassauque, N.; Vendier, L.; Mallet-Ladeira, S.; Le Berre, C.;
Serp, P.; Kalck, P. Eur. J. Inorg. Chem. 2014, 326–336.
FUNCTIONALISATION OF METAL-ORGANIC FRAMEWORK
UiO-66-NH2 VIA POST-SYNTHETIC MODIFICATION
A. D. Burrows, H. Amer Hamzah
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
[email protected], [email protected]
Metal-organic frameworks (MOFs) are a relatively new class of porous materials which
find applications in gas storage, catalysis, drug delivery and sensors. MOFs can be post-
synthetically modified to introduce complex functionalities in the pores thus altering
their physical and chemical properties. In this context, post-synthetic modification
(PSM) is defined as a process in which a pre-formed MOF is transformed into a new
MOF via crystal-to-crystal transformation.1 PSM is of interest as it can allow for the
formation of functionalised MOFs which cannot be formed via direct synthesis.
We report herein the functionalisation of an amine-containing MOF [Zr6O4(OH)4(BDC-
NH2)6] (BDC-NH2 = 2-amino-1,4-benzenedicarboxylate), UiO-66-NH2 via PSM. An α-
amino phosphonate moiety has been partially incorporated into the pores of UiO-66 via
a one pot, three component reaction (Scheme 1). Tandem PSM was achieved by further
reaction of the unreacted amino groups with acetic anhydride. Crystallinity and porosity
were maintained during the transformations. The physical and chemical properties (e.g.
thermal stability, BET surface area and CO2/N2 selectivity) of the modified MOF have
been compared to the pristine UiO-66-NH2.
Scheme 1. PSM of UiO-66-NH2 via Kabachnik-Fields reaction.
Reference
[1] Wang, Z.; Tanabe, K. K.; Cohen, S. M. Inorg. Chem. 2009, 48, 296-306.
NOVEL SINGLE SOURCE PRECURSORS FOR THE DEPOSITION
OF TiSe2 FILMS Samantha L. Hawken,
a Andrew L. Hector,
a Marek Jura,
b William Levason,
a Gillian
Reida and Gavin Stenning
b
aSchool of Chemistry, University of Southampton, Southampton SO17 1BJ, United
Kingdom
Email: [email protected]
bSTFC, ISIS, Harwell Innovation Campus, Didcot, Oxfordshire OX11 0QX, United
Kingdom
Properties including superconductivity, exhibiting charge density waves and a tuneable
band gap make transition metal dichalcogenide materials exciting prospects for many
applications.1 The pseudo octahedral complexes [TiCl4{
nBuSe(CH2)nSe
nBu}] (n= 2,3)
have been synthesized by the reaction of TiCl4 with nBuSe(CH2)nSe
nBu (1:1) and
characterised by IR, multinuclear 1H,
13C{
1H} and
77Se{
1H} NMR spectroscopy and
microanalysis. Low pressure chemical vapour deposition (LPCVD) using the complexes
show that they function effectively as single source precursors (SSP) for the deposition
of crystalline TiSe2 thin films on SiO2 substrates. The hexagonal 1T-TiSe2 films,
characterised by X-ray diffraction patterns, show a high degree of stability in air when
prepared from these precursors. The analysis revealed that both precursors showed
equal promise as LPCVD SSP, hence only the C2 linked complex was used in further
experiments. The dependence on temperature and precursor quantity of the orientation,
film thickness and roughness is shown through a number of deposition experiments.
1 M. Chhowalla, H. S. Shin, G. Eda, L.-J. Li, K. P. Loh and H. Zhang, Nat. Chem., 2013, 5,
263–75.
ONE-STEP, MODULAR ROUTE TO OPTICALLY ACTIVE
DIPHOS LIGANDS
E. Louise Hazeland and Paul G. Pringle
School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K. [email protected]
Efficient asymmetric hydrogenation using metal-phosphine catalysts is one of the
success stories of modern chemistry with multiple industrial applications.1 The field is
over 40 years old but challenges still remain. For example, there are potentially
commercially valuable substrates for which highly enantioselective catalysts have not
yet been discovered. One-step automated routes to chiral monophos ligands have been a
major development since 2000 and led to the application by DSM of high-throughput
ligand development.2 Chiral diphos ligands have advantages over monophos ligands for
several catalytic processes, but their synthesis is often multi-step and laborious.
Previously, single atom-backbone chiral diphos ligands3,4
with C2- or C1-symmetry
have been shown to be very effective for asymmetric hydrogenation. We have exploited
our discovery of the one-step reaction (Scheme 1) to synthesise a range of chiral diphos
ligands.5
Specifically, this presentation will focus on the exploitation of this route to synthesise
a range of novel C1-symmetric, C1-backbone, diphos ligands such as those shown in
Scheme 2, their application in asymmetric hydrogenation and their potential for the
application of high-throughput catalyst discovery methods.
[1] de Vries, J. G.; Elsevier C. J., The Handbook of Homogeneous Hydrogenation,
2008, Wiley-VCH. [2] Lefort, L.; Boogers, J. F.; deVries, A. M.; deVries, J., Top. Catal. 2006, 40, 185-191. [3] Hoge, G.; Wu, H.-P.; Kissel, W. S.; Pflum, D. A.; Greene,
D. J.; Bao, J., J. Am. Chem. Soc. 2004, 126, 5966-5967. [4] Gridnev, I. D.; Imamoto, T.;
Hoge, G.; Kouchi, M.; Takahashi, H., J. Am. Chem. Soc. 2008, 130, 2560-2572. [5]
Hazeland, E. L.; Chapman, A. M.; Pringle, P. G.; Sparkes, H. A., Chem. Commun.
2015, 51, 10206-10209.
= optically active
phosphacycle
Scheme 1: General one-step route where X = C, N; R = Ph, tBu,
iPr, Cy and R’ = Me, Ph.
Scheme 2: One-step route to diphos ligands
-COMPLEXES OF COPPER(I) WITH MAIN GROUP HYDRIDES
(M = Mg, Zn)
A. Hicken and M. R. Crimmin
Department of Chemistry, Imperial College, South Kensington, London, SW7 2AZ, UK
We have recently documented the synthesis of a series of σ–complexes of copper in
which M–H (M = Al, Zn) and E–H (E = B) σ–bonds coordinate to a copper(I)
fragment.1,2
Here we report a series of fluorinated copper(I) complexes (1-3), prepared
by the reaction of copper mesityl with nac-nac and ac-nac proligands. We show that the
hexafluorinated complex 22toluene crystallises as an inverse-sandwich.3 In solution,
displacement of the arene from 1-3 with molecular magnesium and zinc hydrides has
allowed the generation of six new σ–complexes of copper(I), including the first
examples that incorporate a Mg–H bond.
References
(1) Nako, A. E.; White, A. J. P.; Crimmin, M. R. Dalton Trans. 2015, 44, 12530.
(2) Nako, A. E.; Tan, Q. W.; White, A. J. P.; Crimmin, M. R. Organometallics 2014,
33, 2685.
(3) Badiei, Y. M.; Dinescu, A.; Dai, X.; Palomino, R. M.; Heinemann, F. W.; Cundari,
T. R.; Warren, T. H. Angew. Chem., Int. Ed. 2008, 120, 10109.
A TETHERED NHC-CARBORANE LIGAND: SELECTIVE C-H
ACTIVATION AND VERSITILE COORDINATION
Dr. C. E. Willans and J. Holmes
School of Chemistry, University of Leeds, LS2 9JT [email protected]
The development of new catalysts and catalytic processes is essential for a
sustainable and green future. Ligand design is central to these developments as they
control the activity and reactivity of a metal centre. Whilst modifying current ligands
may induce incremental changes in the outcome of a reaction, brand new ligand
architectures can lead to more diverse pathways and processes. The fusion of two very
different ligand families namely N-Heterocyclic carbenes (NHCs)[1]
and carboranes[2]
,
gives rise to a brand new ligand architecture; dicarba-dodecaboranes bearing
imidazolium tethers. This ligand system exhibits unprecedented C-H activation with
divergent reactivity towards cyclometalation leading to versatile coordination to a RhI
centre.
Figure 1. Synthesis of a tethered NHC-carborane ligand and its subsequent coordination to Rh
I
[1] Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. Nature 2014, 510, 485.
[2] Grimes, R. N. Coord. Chem. Rev 2000, 200, 773.
CCH N N tBu CCHBr N NtBu + CCHN NtBu +N N tBu H-
Br-xs.
NucleophilicSubstitution Deboronation
CC
NNtBu
HRh ClC C
NNtBu
RhC
CHNN
tBuRh NCMe
RhAg2OMeCN
Ag2O DCM[Rh(COD)Cl]2i) NaH, THFii) [Rh(COD)Cl]2, MeCN
SYNTHESIS AND CATALYTIC ACTIVITY OF OXO-
FUNCTIONALISED TRIAZOLYLIDENE RUTHENIUM(II)
COMPLEXES
C. Johnson and M. Albrecht
Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012
Bern, Switzerland
In recent years, mesoionic 1,2,3-triazolylidenes have emerged as a highly versatile
subclass of N-heterocyclic carbene (NHC) ligands.1 This NHC scaffold can be
effectively tailored to specific functions as a consequence of the flexibility of the [3 + 2]
cycloaddition of alkynes with azides. This feature, coupled with the ligands’ stong σ-
donor abilities have led to their diverse application in catalytic transformations.2
Here we present the synthesis of a range of oxo-functionalised triazolylidene
ruthenium(II) complexes. The implications of this C,O-bidentate motif is discussed in
terms of catalytic activity.
N N
NMes
ORuCl
References:
[1] Mathew, P.; Neels, A.; Albrecht, M. J. Am. Chem. Soc. 2008, 130, 13534.
[2] Donnelly, K. F.; Petronilho, A.; Albrecht, M. Chem. Commun. 2013, 49, 1145.
DEVELOPMENT OF CHELATORS FOR 89
Zr IN
POSITRON EMISSION TOMOGRAPHY IMAGING
Boon-Uma Jowanaridhi a,b
, Johanna Seemannb, Benjamin P. Burke
a,b and Stephen J.
Archibald a,b
* aDepartment of Chemistry,
bPositron Emission Tomography Research Centre
University of Hull, Cottingham Road, Hull, HU6 7RX, UK.
Positron emission tomography (PET) is used for the non-invasive study of dynamic
processes.1 Immuno-PET is a relatively young discipline used to improve visualisation
by combining the high sensitivity of PET with the specificity of monoclonal antibodies.
It allows images to be collected after the highly specific accumulation of radioactive
compound in the target organ and the clearance of unbound tracer from the blood pool,
which increases target-to-background activity ratio.2 Zirconium-89 is an ideal immuno-
PET radionuclide as it decays with a half-life of 78.41 h via positron emission and
therefore allows tracking of the relatively slow accumulating antibodies over several
days.3 DFO is the most common ligand used as
89Zr-chelate. However, it has been
reported that 89
Zr-DFO-mAb conjugates show significant uptake of radioactivity in
bone of mice which indicates release of the radiometal.4
Recently, the development of a more suitable chelate for 89
Zr has been gaining
attention. The rigid structure of macrocycles, such as cyclen or cyclam can be utilised as
stabilising platform offering preorientation for attached donating groups. In a first
instance, cyclen-based ligands were synthesised and functionalised with various types
of pendant arms containing hydroxamate, phosphonic acid, phosphinic acid, picolinic
acid, kojic acid and acrylamide as donating moieties. Radiolabelling with 89
Zr was
evaluated using variations in temperature, pH, type and concentration of buffer, as well
as concentration of ligands. 6,6',6'',6'''-((1,4,7,10-Tetraazacyclododecane-1,4,7,10-
tetrayl)tetrakis(methylene))-tetrapicolinic acid could be labelled to 39.8 % RCY using a
temperature of 90 oC and 0.2 M NaOAc at pH 4 with a ligand concentration of 20 µM.
In an additional experiment the ligand was labelled with another PET radioisotope, 68
Ga, to 91.2 % RCY in 3 min and the stability tested against apotransferrin with only 4
% of tracer decomposed over 2 h.
References. 1. Van Der Veldt, A.; Smit, E.; Lammertsma, A. A., Positron emission tomography as a method for
measuring drug delivery to tumors in vivo: the example of [11C]docetaxel. Frontiers in
Oncology 2013, 3.
2. Deri, M. A.; Ponnala, S.; Zeglis, B. M.; Pohl, G.; Dannenberg, J. J.; Lewis, J. S.; Francesconi, L.
C., Alternative Chelator for 89Zr Radiopharmaceuticals: Radiolabeling and Evaluation of 3,4,3-
(LI-1,2-HOPO). Journal of Medicinal Chemistry 2014, 57 (11), 4849-4860.
3. van de Watering, F. C. J.; Rijpkema, M.; Perk, L.; Brinkmann, U.; Oyen, W. J. G.; Boerman, O.
C., Zirconium-89 Labeled Antibodies: A New Tool for Molecular Imaging in Cancer Patients.
BioMed Research International 2014, 2014, 13.
4. Holland, J. P.; Divilov, V.; Bander, N. H.; Smith-Jones, P. M.; Larson, S. M.; Lewis, J. S., 89Zr-
DFO-J591 for ImmunoPET of Prostate-Specific Membrane Antigen Expression In Vivo. Journal
of Nuclear Medicine 2010, 51 (8), 1293-1300.
REACTIVITY OF THE 2-PHOSPHAETHYNOLATE ANION
AND PHOSPHINECARBOXAMIDE
Jose M. Goicoechea and Andrew R. Jupp
Department of Chemistry, University of Oxford,
Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA, U.K
We recently reported the synthesis of the 2-phosphaethynolate anion, PCO–, by an
unprecedented activation of the group 15 Zintl cluster, P73–
.[1]
This phosphorus-
containing analogue of the ubiquitous cyanate anion has been the subject of a number of
recent articles by our group and those of Grützmacher[2]
and Cummins.[3]
We have
systematically explored the cycloaddition chemistry[1,4]
and ligand properties of this
remarkable anion compared to its isoelectronic counterparts.[5]
Furthermore, by analogy with Wöhler’s paradigm-shifting synthesis of urea in 1828, the
reaction of PCO– with ammonium salts yields the unprecedented
phosphinecarboxamide.[6]
This inorganic analogue of urea is a rare example of an air-
stable primary phosphine, and its ligand properties have been explored.[7]
We have also
explored its Brønsted acidity to afford a series of novel phosphides, secondary and
tertiary phosphines, and phosphine oxides.[8]
References
[1] Jupp, A. R.; Goicoechea, J. M. Angew. Chem., Int. Ed. 2013. 52, 10064.
[2] Puschmann, F. F.; Stein, D.; Heift, D.; Hendriksen, C.; Gal, Z. A.; Grützmacher, H.-
F.; Grützmacher, H. Angew. Chem. Int. Ed. 2011, 50, 8420.
[3] Krummenacher, I.; Cummins, C. C. Polyhedron, 2012, 32, 10.
[4] Heift, D.; Benkő, Z.; Grützmacher, H.; Jupp, A. R.; Goicoechea, J. M. Chem. Sci.
2015, 6, 4017.
[5] Jupp, A. R.; Geeson, M. B.; McGrady, J. E.; Goicoechea, J. M. manuscript
submitted.
[6] Jupp, A. R.; Goicoechea, J. M. J. Am. Chem. Soc. 2013, 135, 19131.
[7] Jupp, A. R.; Trott, G.; Payen de la Garanderie, É.; Holl, J. D. G.; Carmichael, D.;
Goicoechea, J. M. Chem. Eur. J. 2015, 21, 8015.
[8] Geeson, M. B.; Jupp, A. R.; McGrady, J. E.; Goicoechea, J. M. Chem. Commun.
2014, 50, 12281.
TITANIUM ‘DOUBLE-SANDWICH’ COMPLEXES FOR THE REDUCTIVE ACTIVATION OF CO2
A. F. R. Kilpatrick, J. C. Green and F. G. N. Cloke
Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK [email protected]
Metalmetal bonds have been the subject of intense research, given that many
bimetallic compounds exhibit unusual electronic properties and novel reactivity. The
pentalene ligand, Pn = C8H6, displays a variety of coordination modes in its
organometallic complexes and can bind two metal centres with η5- hapticity in so-called
'double-sandwich' complexes.
We have recently reported the synthesis of a di-titanium bis(pentalene) complex,
Ti2(Pn†)2, Pn
† = 1,4-{Si
iPr3}2C8H4, which features a rare example of a TiTi double
bond.[1]
Ti2(Pn†)2 reductively splits CO2 under very mild conditions into O
2- and CO
complexes,[2]
and shows exceptional reactivity with heteroallenes CS2 and COS.[3,4]
Synthetic, structural and computational studies into the CO2 reaction mechanism are
presented, in addition to recent results exploring the reductive activation of other
unsaturated compounds by titanium double-sandwiches.
[1] Kilpatrick, A. F. R.; Green, J. C.; Cloke, F. G. N.; Tsoureas, N. Chem. Commun. 2013, 9434–9436.
[2] Kilpatrick, A. F. R.; Cloke, F. G. N. Chem. Commun. 2014, 50, 2769–2771.
[3] Kilpatrick, A. F. R.; Green, J. C.; Cloke, F. G. N. Organometallics 2015, DOI:
10.1021/acs.organomet.5b00315.
[4] Kilpatrick, A. F. R.; Green, J. C.; Cloke, F. G. N. Organometallics 2015, DOI:
10.1021/acs.organomet.5b00363.
A NEW SMALL MOLECULE GELATOR AND 3D FRAMEWORK
LIGATOR OF LEAD(II)
Jane V. Knichal, William J. Gee, Andrew D. Burrows, Paul R. Raithby and Chick C.
Wilson
Univeristy of Bath Bath BA2 7AY
Supramolecular gels formed by low molecular weight gelators are a class of material in
which interest is rapidly expanding to provide a diverse range of applications to
commerce, industry and medicine1. Our continued work on uncommonly substituted
benzene dicarboxylate ligands in metal frameworks2 has lead us to one of the first lead
based metallogels to be reported. The solvothermal reaction of a new diacid allene,
(H2abd) with hydrated lead(II) acetate has yielded a metallogel with a critical gelation
point of 1% w/v in DMF. SEM studies confirm a worm-like morphology composed of
nanoscale fibres. Under non-solvothermal conditions, combining H2abd and hydrated
lead(II) acetate resulted in formation of single crystals, which were identified as a 3D
coordination polymer by X-ray diffraction. Structural features observed within this
framework provide the basis for assigning the molecular structure to the fibrils present
within the corresponding metallogel. This is a useful addition to the literature focusing
on understanding metal-based gel materials and their applications3.
References.
[1] A. Y.-Y. Tam and V. W.-W. Yam, Chem. Soc. Rev., 2013, 42, 1540
[2] (a) J. V. Knichal, W. J. Gee, A. D. Burrows, P. R. Raithby and C. C. Wilson, Cryst. Growth & Des., 2015, 15, 465-474 (b) J. V. Knichal, W. J. Gee, A. D. Burrows, P. R.
Raithby, S. J. Teat and C. C. Wilson, Chem. Commun., 2014, 50, 14436
[3] (a) A. Mallick, E.-M. Schön, T. Panda, K. Sreenivas, D. D. Díaz and R. Banerjee,
Journal of Materials Chemistry, 2012, 22, 14951 (b) S. Sengupta and R. Mondal, J. Mater. Chem. A, 2014, 2, 16373-16377
COORDINATION-DRIVEN FORMATION OF INCLUSION
COMPLEXES OF RESORCIN[4]ARENE CAVITANDS
Richard C. Knighton and Adrian B. Chaplin*
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
Since the inception of supramolecular chemistry, resorcin[4]arene cavitands have been
synonymous with host-guest chemistry.1 Guests have ranged from polar substrates such
as charged2 and hydrogen-bonded species
3 to apolar substrates which are included in the
cavity due to solvophobic effects.4 While non-covalent interactions are important in the
formation of host-guest complexes, they can be augmented through ligation of the guest
to a metal centre - thereby increasing the strength of association.5
In this work we describe the use of tetrasubstituted asymmetric resorcin[4]arene
cavitands as bidentate ligands for metal complexes to obtain 'metal-strapped' capsules
(Figure 1).
Figure 1: Small-molecule binding by an asymmetric resorcin[4]arene cavitand
References
1. (a) Koblenz, T. S.; Wassenaar, J.; Reek, J. N. H. Chem. Soc. Rev. 2008, 37, 247-262;
(b) Pochorovski, I.; Ebert, M.-O.; Gisselbrecht, J.-P.; Boudon, C.; Schweizer, W. B.;
Diederich, F. J. Am. Chem. Soc. 2012, 134, 14702-14705; (c) Pochorovski, I.;
Diederich, F. Acc. Chem. Res. 2014, 47, 2096-2105.
2. Carnegie, R. S.; Gibb, C. L. D.; Gibb, B. C. Angew. Chem. Int. Ed. 2014, 126,
11682-11684.
3. Cacciarini, M.; Azov, V. A.; Seiler, P.; Kunzer, H.; Diederich, F. Chem. Commun.
2005, 5269-5271.
4. Sullivan, M. R.; Gibb, B. C. Org. Biomol. Chem 2015, 13, 1869-1877.
5. (a) Iwamoto, H.; Nishi, S.; Haino, T. Chem. Commun. 2011, 47, 12670-12672; (b)
Wieser-Jeunesse, C.; Matt, D.; De Cian, A. Angew. Chem. Int. Ed. 1998, 37, 2861-
2864.
CHELATING BIS(DIAZABORYL) LIGANDS FOR PREPARATION
OF CYCLIC BISBORYL COMPLEXES
Eugene L. Kolychev, Rémi Tirfoin, Simon Aldridge*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, OX1 3TA,
Oxford
Recent reports by Yamashita and Nozaki et al. on the isolation[1]
and reactivity[2]
of the
first stable boryllithium reagent have opened new possibilities for the application of
diazaboryl fragments as strong -donor anionic ligands. Preliminary studies conducted
in our laboratory showed that diazaboryl complexes of Main Group elements[3]
are
encouraging candidates as transition metal free bond activation reagents. Further
investigation is currently focused on the preparation of bifunctional boryl ligands, with
the aims (i) of increasing the stability of complexes by the chelate effect, and (ii) of
facilitating re-reduction to lower oxidation states due to the presence of constrained ring
systems with appropriately narrow bite angles.
Synthetically, key precursors for such chelate systems are bis(diazaboryl) dibromides
which can be prepared by high yielding routes starting from commercially available
starting materials. In subsequent steps, a range of approaches including metathesis using
alkali metal boryl complexes and oxidative insertion of low valent metal centres into B-
H bonds of the analogous boryl hydrides have been examined to establish reliable
synthetic routes to chelating boryl complexes.
Figure 1. Cyclic bis(diazaboryl) complexes.
[1] Segawa, Y.; Yamashita, M.; Nozaki, K. Science 2006, 314, 113.
[2] Segawa, Y.; Suzuki, Y.; Yamashita, M.; Nozaki, K. J Am Chem Soc, 2008, 130,
16069.
[3] e.g. Protchenko, A.V. ; Dange, D.; Schwarz, A.D.; Blake, M.P.; Jones, C.;
Mountford, P.; Aldridge, S. J Am Chem Soc. 2014, 136, 10902.
UNEXPECTED DIMER FORMATION DURING
{Rh(PiPR2(CH2)3P
iPR2)}
+ CATALYSED DEHYDROCOUPLING OF
H3B·NH3
A. Kumar and A. S. Weller
Department of Chemistry, University of Oxford, Oxford, U.K
Transition metal catalysed dehydrocoupling of H3B·NH3 is of significant interest
because of its potential use in chemical hydrogen storage and the synthesis of new
polymers, ceramics and piezoelectric materials. Recently, the Weller group has reported
the use of {Rh(PPh2(CH2)3PPh2)}+ fragment in 1,2-C6H4F2 for the fast dehydrocoupling
of H3B·NMe2H.1 Although complete mechanistic details are yet to be resolved,
formation of a dimeric species [{Rh(Ph2P(CH2)3PPh2)}2(H)2(H2BNMe2)]+ was observed
during the dehydrocoupling process through ESI-MS (as [M-H]+). However, no further
role of the dimeric species in the catalysis was explored.
We here report the use of a {Rh(PiPr2(CH2)3P
iPr2)}
+ fragment for the dehydrocoupling
of H3B·NH3 in Et2O. Interestingly, we observe the formation of
[Et2O·H2B·NH3][BArF
4] and [{Rh(PiPr2(CH2)3P
iPr2)}2(H)(BH2NH2)][BAr
F4]
intermediates during the dehydrocoupling process (Scheme 1). Formation of the dimeric
species is consistent with the previous report by the Weller group as mentioned earlier.1
[{Rh(PiPr2(CH2)3P
iPr2)}2(H)(BH2NH2)][BAr
F4] has also been independently
synthesized and to the best of our knowledge represents the first example of bridging
amino-borane bound to two metal centres. The role of the dimeric species in the
catalytic dehydrocoupling is currently being studied.
Scheme 1: Reaction of {Rh(PiPr2(CH2)3P
iPr2)}
+ fragment with H3B·NH3, [BAr
F4]
-
anion not shown.
References:
1. Dallanegra, R.; Robertson, A. P. M.; Chaplin, A. B.; Manners I.; Weller, A. S.
Chem. Commun. 2011, 47, 3763.
GEOMETRY CONSTRAINED MAIN-GROUP COMPLEXES FOR
SMALL MOLECULES ACTIVATION
J. M. Goicoechea and S. K. Lo
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12
Mansfield Road, Oxford, OX1 3TA, U.K.
Precious transition metals are well known for undergoing reversible redox processes in
the activation of small molecules and subsequent catalytic synthesis of many
compounds. However these metals are rare and expensive, therefore creating a lot of
interest in abundant main-group alternatives. In line with this, recent studies have
highlighted a number of main-group systems that are able to activate challenging small
molecules.1
The Arduengo group has previously shown that by distorting a P(III)
compound into a planar “T-shaped” geometry it provides an orbital arrangement akin to
transition metal, which allow for the cleavage of polarised E–H bonds and preliminary
evidence of catalytic activity.2 Radosevich and his group has successfully developed
catalytic hydrogenations using the Arduengo’s compound.3
Our group is interested in tuning the steric and electronic properties of a variety of novel
geometry constrained ligands of group 15 elements. Our under study includes redox
active ligands as well as saturated and unsaturated ligands (see figure 1). Our
investigation expands to arsenic analogous of described ligands. The +3 oxidation state
of arsenic is lowered in energy which should enhance the reactivity of the reductive
elimination step. We are currently investigating the reactivity of these compounds
towards small molecules.
N
N
H
N
H
Dipp DippP
N
O OAs
N
O OPn
MeO OMe
tBu
tBu
tBu
tBu
Figure 1
Pn = P, As
References:
[1] (a) Power, P.P. Nature 2010, 463, 171 (b) Stephan, D.W.; Erker, G. Angew. Chem.
Int. Ed. 2010, 49, 46
[2] Cully, S. A.; Arduengo, A. J. Am. Chem. Soc. 1984, 106, 1164
[3] (a) Dunn, N. L. ; Radosevich, A. T. J. Am. Chem. Soc. 2012, 13, 11330 (b)
McCarthy, S. M. ; Lin, Y.-C. ; Devarajan, D. ; Chang, J. W. ; Yennaway, H. P. ; Rioux,
R. M. ; Ess, D. H. ; Radosevich, A. T. J. Am. Chem. Soc. 2014, 136, 4640
B-H ACTIVATION REACTIONS OF TITANIUM COMPOUNDS
Simona Mellino
a, Eric Clotb and Philip Mountforda
aChemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1
3TA, U.K., bInstitut Charles Gerhardt, Université Montpellier 2 and CNRS, cc 1501,
Place Eugène Bataillon, 34095 Montpellier cedex 5, France. [email protected]
Reactions of Group 4 (L)M=NR imido complexes have been extensively reported in the literature [1]. More recently the corresponding Group 4 hydrazide (L)M=NNR2 chemistry has been developed [2]. The reaction of both imido and hydrazido compounds with small molecules is an area of ongoing interest and many reaction products have been reported. Recently the activation of Si-H bonds of RSiH3 (R= Ph or Bu) has been demonstrated by the hydrazide compound Cp*Ti{MeC(NiPr)2}(NNMe2) which was found to undergo reversible 1,2-addition across Ti=N bond to yield titanium hydride species [3]. Following this line of research we decided to explore the reactivity of Cp*Ti{MeC(NiPr)2}(NNR2) compounds, where R2 = Me2, Ph2, CPh2, with boranes. For for the alkylidene hydrazide (R2 = CPh2) reaction with both pinacolborane (HBPin) and 9-BBN gives B-H addition across the N=C double bond, yielding compounds 1 and 2. The reactivity of the analogues hydrazido compounds (R2 = Me2) is different, resulting in either the product of 1,2-addition across the Ti=N bond with HBPin (3) or the borylimido compound (4) with one equivalent of 9-BBN dimer. [1] R. R. Schrock, Acc. Chem. Res., 2005, 38, 955; N. Hazari and P. Mountford, Acc. Chem.
Res., 2005, 38, 839.[2] P. J. Tiong, A. Nova, L. R. Groom, A. D. Schwarz, J. D. Selby, A. D Schofield, E. Clot and P. Mountford, Organometallics, 2011, 30, 1182. A. D. Schofield, A. Nova, J. D. Selby, A. D. Schwarz, E. Clot and P. Mountford, Chem. Eur J., 2011, 17, 265-285. [3] P. J. Tiong, A. Nova, E. Clot and P. Mountford, Chem. Commun., 2011, 47, 3147-3149. P. J. Tiong, A. Nova, A. D. Schwarz, J. D. Selby, E. Clot and P. Mountford, Dalton Trans., 2012, 41, 2277-2288.
ADVANCES IN TRANSITION METAL FRUSTRATED LEWIS
PAIR (FLP) CHEMISTRY
Owen J. Metters, Stephanie R. Flynn, Duncan F. Wass, Ian Manners
School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK, BS8 1TS
Recent work in the Wass group has focussed on the development of novel
intramolecular frustrated Lewis pair (FLP) systems containing transition metal (Zr(IV),
Ti(III)) fragments. These systems have been shown to be highly reactive towards small
molecules (e.g. CO2, H2, ethers), and also competent catalysts for the dehydrocoupling
of amine-boranes.1 Modifications to these current systems have led us to synthesise a
range of intermolecular FLPs containing the analogous transition metal fragments (A).
These intermolecular systems (A) demonstrate reactivity towards small molecules
similar to that of their intramolecular counterparts, however the absence of the tether
provides easy access to a wider range of Lewis bases, allowing us to explore the effect
of varying phosphine sterics and electronics on FLP reactivity.
Zirconium (IV) cations of the type [(CpR)2ZrOMes][B(C6F5)4] are also found to
be competent catalysts in the catalytic hydrogenation of imines. The mechanism is
found to be FLP-mediated with the formation of a Zr+/N FLP between catalyst and
substrate. Such reactions require low pressures of H2 (1 bar), ambient temperatures (25
ºC) and short reaction times (90 mins).
1 (a) Chapman, A. M.; Haddow, M. F.; Wass D. F., J. Am. Chem. Soc., 2011, 133,
18463, (b) Chapman A. M.; Haddow, M. F.; Wass D. F., J. Am. Chem. Soc., 2011, 133,
8826 (c) Chapman A. M.; D. F; Dalton Trans., 2012, 41, 9067
QUANTITATIVE UNDERSTANDING OF MULTIMETALLIC CLUSTER GROWTH
Stefan Mitzinger,1 Lies Broekaert,
1,2 Werner Massa,
1 Florian Weigend,
2
Stefanie Dehnen1
1Department of Chemistry and Scientific Centre for Material Science, Philipps
University of Marburg, Hans-Meerwein-Straße, D-35043 Marburg, Germany.
2Institute of Nanotechnology, Karlsruhe Institute of Technology,
Hermann-von- Helmholtz Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
The chemistry of homoatomic and binary intermetalloid Zintl anions has been
investigated for several decades.1 In most cases, the structural features of Zintl anions
can be explained with Wade-Mingos rules or the Zintl-Klemm concept.2 By extraction
of quaternary metallic phases containing K/Ge/As/MV (MV = V, Nb, Ta) with
ethylenediamine (en), a new class of multimetallic Zintl anions was synthesized under
encapsulation of electron-poor transition metals.3
In case of the extraction of a K/Ge/As/Ta phase five new compounds were fully
characterized within one reaction allowing the elucidation of the stepwise formation of
multimetallic clusters, based on the crystal structures and complementary quantum
chemical studies of the involved clusters (Ge2As2)2–
, (Ge7As2)2–
, [Ta@Ge6As4]3–
,
[Ta@Ge8As4]3–
, and [Ta@Ge8As6]3–
. The results can even be generalized for an entire
family of multimetallic clusters. Furthermore first Zintl anions of the Ge/P and Si/P
system will be presented.
References:
[1] S. Scharfe, F. Kraus, S. Stegmaier, A. Schier, T. F. Fässler, Angew. Chem. Int. Ed.
2011, 50, 3630–3670. [2] W. Klemm, in Festkörperprobleme 3 (Ed.: F. Sauter),
Springer, Heidelberg, 1964, pp. 233–251.; K. Wade, Advances in Inorganic Chemistry
and Radiochemistry 1976, 18, 1–66. [3] S. Mitzinger, L. Broeckaert, W. Massa, F.
Weigend, S. Dehnen, Chem. Commun. 2015, 51, 3866–3869.
NEW DEVELOPMENTS IN THE COORDINATION CHEMISTRY
OF GROUP 13 METAL FLUORIDE
Rajiv Bhallaa, William Levason
b, Graeme McRobbie
c, Francesco M. Monzittu
b, Gill
Reidb.
a Centre for advanced imaging, University of Queensland, Brisbane, Queensland 4072,
AUS b School of Chemistry, University of Southampton, Southampton SO17, 1BJ, UK c GE Healthcare, The Grove Centre, White Lion Road, Amersham HP7 9LL, UK
Although the hydrates of the Group 13 metal fluorides, MF3·3H2O (M = Ga, Al, In),
have very poor solubility in organic solvents or water, several new complexes have been
studied in recent years.1,2
Hydrothermal synthesis, or in a few examples refluxing in
polar solvents (such as alcohols)3, have been exploited to overcome the poor solubility
of these fluorides. However, the forcing conditions of these methods can lead to
decomposition of the ligand. For these reasons, there is a need to find a pathway into
this chemistry which goes through milder reaction conditions.
Moreover, the Group 13 metal fluorides complexes have attracted much attention for
their possible application as PET imaging agents4,5
in the last few years. 18
F is the most
commonly used PET-imaging isotope due to its high abundance, its low-energy positron
emission, and its short half-life of 109.8 min. Usually, 18
F is attached to targeted
peptides by binding it to a carbon atom, this process however is challenging and often
involves multistep syntheses, so M18
F-complexes have arisen as attractive, possible,
future alternatives.
In this study, we report a new entry
into the chemistry of the hydrates
Group 13 metal fluorides, which
enables reactions with different
ligands, such as pyridine oxide
(Figure 1) or N,N,N’,N’,N’’-pentamethyldiethylenetriamine
(pmdta) at room temperature, further
investigating their coordination
chemistry.
[1]. Bhalla R., Darby C., Levason W., Luthra S. K., McRobbie G., Reid G., Sanderson G., Zhang W.,
Chem. Sci. 2013, 5, 381.
[2]. Bhalla R., Levason W., Luthra S. K., McRobbie G., Monzittu F. M., Palmer J., Reid G.,
Sanderson G., Zhang W., Dalton Trans. 2015, 44, 9569.
[3]. Penkert F. N., Weyhermüller T., Wieghardt K., Chem. Commun. 1998, 5, 557.
[4]. Laverman P., McBride W. J., Sharkey R. M., Eek A., Joosten L., Oyen W. J. G., Goldenberg D.
M., Boerman O. C., J. Nucl. Med. 2010, 51, 454.
[5]. Bhalla R., Levason W., Luthra S. K., McRobbie G., Sanderson G., Reid G., Chem. Eur. J. 2015,
21, 4688.
Figure 1. Structure of the H-bonded dimer of
[GaF3(OH2)2(PyNO)] showing the H-bonding contacts
(blue) and the two geometric isomers of Ga(III).
MACROCYCLIC TRANSITION METAL COMPLEXES FOR
ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE
James R. Pankhurst, Thomas Cadenbach and Jason B. Love*
EaStCHEM School of Chemistry, University of Edinburgh, UK
[email protected], *[email protected]
In March 2015, the concentration of carbon dioxide in the Earth’s atmosphere exceeded
400 ppm,1 having increased steadily from 280 ppm since the Industrial Revolution due
to anthropogenic activity.2 The electrochemical reduction of CO2 to useful products is a
viable method to be deployed in carbon-capture and utilisation (CCU) strategies,
however the single-electron reduction of CO2, that occurs at -1.90 V vs NHE, is
kinetically disfavoured.3 There is therefore a requirement to design homogeneous
systems that can function as electrocatalysts, to lower the kinetic barriers and required
overpotential for CO2 reduction.
We recently reported a pair of new polypyrrolic Schiff-base macrocycles that act as
binucleating ligands for the late transition metals.4,5
These complexes fold into
structures that offer a reactive cleft between the two metal centres. Their
electrochemically reversible redox features, both in the reductive and oxidative
directions from the +2 oxidation state, make their application in catalysis viable. Cyclic
voltammetry has indicated that some of these complexes react with CO2 at moderate
overpotentials of around -1.2 V vs. NHE, using H2O as a proton source.
[1]
P. Tans and R. Keeling, http://www.esrl.noaa.gov/gmd/ccgg/trends/ 30/05/2015
[2] A. Neftel, E. Moor, H. Oeschger and B. Stauffer, Nature, 1985, 315, 45
[3] E.E. Benson, C.P. Kubiak, A.J. Sathrum and J.M. Smieja, Chem. Soc. Rev., 2009, 38, 89
[4] J.R. Pankhurst, T. Cadenbach, D. Betz, C. Finn and J.B. Love, Dalton Trans., 2015, 44,
2066
[5] T. Cadenbach, J.R. Pankhurst, T.A. Hofmann, M. Curcio, P.L. Arnold and J.B. Love,
Organometallics, 2015
COORDINATION CHEMISTRY OF BIDENTATE
CALIX[4]ARENE-BASED NHC LIGANDS
Ruth Patchett and Adrian B. Chaplin*
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
Calix[4]arenes are attractive complexing agents and enzyme mimics due to their
characteristic “basket-like” shape. These macromolecules have been observed to
encapsulate guests and can provide flexible trans-disposed ligand systems.1 In
particular, functionalisation of the upper rim with donor groups enables the possibility
to alter the reactivity of bound transition metals, through their close proximity to the
calix[4]arene cavity.
As part of our work investigating the coordination chemistry of calix[4]arene-based
coordination complexes, we describe and contrast the coordination chemistry of a N-
Heterocyclic Carbene (NHC) functionalised calix[4]arene ligand with a simple mono-
dentate NHC analogue.
References
[1] (a) Wieser-Jeunesse, C.; Matt, D.; De Cian, A. Angew. Chem. Int. Ed. 1998, 37,
2861–2864; (b) Dinarès, I.; Garcia de Miguel, C.; Mesquida, N.; Alcalde, E. J. Org.
Chem., 2009, 74, 482–485; (c) Fang, X. ; Scott, B.L.; Watkin, J.G.; Carter, C.A.G.;
Kubas, G.J. Inorg. Chim. Acta, 2001, 317, 276–281.
NOVEL MAIN GROUP POLYAZIDES: HOMOLEPTIC LOW
VALENT GROUP 14 POLYAZIDES AND BASE STABILISED
GROUP 13 AND 15 POLYAZIDES
P.Portius and B. Peerless
University of Sheffield, Dainton Building, Brook Hill, S3 7HF
Abstract text: Main Group binary azides represent an interesting class of nitrogen rich
compounds owing to their potential as energetic materials, however, due to their
expressed shock and thermal sensitivities binary azides are an experimental challenge to
prepare and characterize. This has led to a number of methods to stabilize these
sensitive compounds including using Lewis bases [1]
or using bulky cations in the
preparation of anionic hypercoordinate azido complexes [2]
. These methods have been
used to prepare low valent germanium and tin azides of the form L’Ge(N3) [3]
,
L”Ge(N3)2 [4]
and L’Sn(N3) [3]
(L’ = N-(n-propyl)-2-(n-propylamino)-troponiminate, L” = N-heterocylcic carbene), however, no Si(II) azido complex or homoleptic polyazido
low valent complex has been prepared previously. Treating GeCl2(1,4-dioxane) or
SnCl2 with PPh4N3 and NaN3 we have shown it is possible to prepare and fully
characterise the new species (PPh4)Ge(N3)3 and (PPh4)Sn(N3)3, representing the first
low valent Main Group homoleptic polyazido complexes [5]
. Attempts to reduce base
stabilised Si(IV) polyazides to Si(II) using a Mg dimer has led to the isolation of a
previously known Si(I) complex and a novel base stabilised magnesium azido
compound. Group 13 and 15 binary azides are scarcer in the literature than Group 14,
Al(N3)3 has only been observed in argon matrices [6]
and P(N3)5 is currently unknown.
Using an N-heterocylic carbene (NHC) we have been able to isolate and structurally
characterise the first Lewis base adducts of Al(N3)3 and P(N3)5 in the form
(NHC)Al(N3)3 and (NHC)P(N3)5.
References.
[1] Filippou, A. C.; Portius, P.; Neumann, D. U.; Wehrstedt, K.-D. Angew. Chem. 2000,
112, 4524; Angew. Chem., Int. Ed. 2000, 39, 4333.
[2] Filippou, A. C.; Portius, P.; Schnakenburg, G. J. Am. Chem. Soc. 2002, 124, 12396
[3] Ayers, A. E.; Marynick,D. S.; Dias, R. H.V. Inorg. Chem. 2000, 39, 4147
[4] Lyhs, B.; Blaser, D.; Wolper, C.; Schulz, S.; Haack, R.; Jansen, G. Inorg. Chem.
2013, 52, 7236−7241
[5] Peerless, B.; Keane, T.; Meijer, A. J. H. M.; Portius, P. Chem. Comm. 2015, 51,
7435
[6] Linnen, C. J.; Macks, D. E.; Coombe, R. D. J. of Phys. Chem. B, 1997, 101, 1602.
NEW CATALYSTS FOR THE UPGRADING OF ETHANOL TO
ADVANCED BIOFUELS
K. J. Pellow and D. F. Wass
School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK, BS8 1TS
www.wassresearchgroup.com
The need to find alternatives to fossil fuels is crucial both from an environmental perspective, as well as to ensure energy security and sustainability.1 Higher alcohols, termed advanced biofuels, such as butanol are ideal “drop in” gasoline alternatives, outperforming bioethanol both in terms of energy content and ease of use.2
Figure 1. NHC ruthenium complexes employed as catalysts for the upgrading of ethanol to
butanol.
The Wass group have previously employed ruthenium catalysts for the upgrading of ethanol to butanol by way of the Guerbet reaction.3,4 We have extended the known library of catalysts able to carry out this transformation and have developed a series of N-heterocyclic carbene (NHC) ruthenium complexes (figure 1) that successfully catalyse ethanol to the advanced fuels n-butanol and iso-butanol with up to 93 % selectivity. [1] Ragauskas, A. J.; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert, C. A.; Frederick, W. J.; Hallett, J. P.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.; Murphy, R.; Templer, R.; Tschaplinski, T. Science 2006, 311, 484. [2] Peralta-Yahya, P. P.; Zhang, F.; del Cardayre, S. B.; Keasling, J. D. Nature 2012, 488, 320. [3] Guerbet, M. C. R. Hebd. Seances Acad. Sci. 1909, 149, 129. [4] Dowson, G. R. M.; Haddow, M. F.; Lee, J.; Wingad, R. L.; Wass, D. F. Angew.
Chem. Int. Ed. 2013, 52, 9005.
COORDINATION CHEMISTRY OF S-BLOCK CATIONS WITH
SOFT DONOR MACROCYCLES
M. J. D. Champion, M. Everett, A. Jolleys, W. Levason, D. Pugh, J. Purkis and G. Reid
Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ
The s-block elements form hard metal cations which have a high affinity for O-donor
ligands, especially water. Consequently the vast majority of their reported coordination
chemistry is with hard O-donor ligands. Coordination complexes with neutral soft donor
ligands are rare, which may in part be due to the lack of suitable precursors. Most s-
block salts have limited solubility in organic media and solvents which solubilise the s-
block cations usually contain competitive O-donor groups (e.g. thf, MeOH, dmso).
We recently discovered that NaBArF has a high affinity for aza macrocycles, resulting
in the isolation of several unusual coordination compounds of Na+, including the
sandwich complex [Na(Me3tacn)2][BArF] (left; Me3tacn = 1,4,7-trimethyl-1,4,7-
triazacyclononane).1
Recently we extended the aza macrocycle chemistry to other Group 1 cations, isolating
compounds such as a sandwich complex of K+.2 We have also reacted even softer
neutral donor ligands such as [24]aneS8 (1,4,7,10,13,16,19,22-octathiacyclotetracosane)
to Na+, forming [Na([24]aneS8)][BAr
F] with homoleptic thioether coordination at Na
+
(right).3 Our methodology is also applicable to Group 2, allowing the isolation of
complexes which contain bonds between soft thio- and selenoether moieties and hard
Group 2 dications.
This chemistry is possible because the BArF salts are highly soluble, allowing reactions
to take place in non-competitive solvents, thus revealing a rich new area of the
coordination chemistry of s-block cations with soft donor ligands.
[1] Everett, M., Jolleys, A., Levason, W., Pugh, D., Reid, G., Chem. Commun., 2014, 50, 5843.
[2] Dyke, J. M. et al., Dalton. Trans., 2015, 44, DOI: 10.1039/c5dt01865j.
[3] Champion, M. J. D. et al., Inorg. Chem., 2015, 54, 2497.
[4] The SCFED project (www.scfed.net) is a multidisciplinary collaboration of British
universities investigating the fundamental and applied aspects of supercritical fluids.
NaBArF
[24]aneS8 2(Me
3tacn)
CATALYSIS IN SERVICE OF MAIN GROUP CHEMISTRY:
SYNTHESIS OF P-BLOCK MATERIALS
D. A. Resendiz–Lara, T. Jurca, J. Turner, A. Schäfer, G. R. Whittell, Ian Manners.
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
Catalytic dehydrocoupling chemistry is a versatile approach for the formation of p block
element-element bonds, and is becoming a promising methodology for the formation of
inorganic polymers under mild conditions with high-yielding reactions compared to
analogous routes (e. g. condensation reactions, reductive coupling, etc.).1
Recently, iron-based complexes have been reported to catalyse the polymerisation of
phosphine-boranes,2 and the molecular weight of the resulting polymeric material was
found to vary as a function of the catalyst loading. The synthesis and characterization of
two novel phosphine-borane monomers and their respective polymers will be
presented.3
Scheme 1. Dehydrocoupling of arylphosphine-boranes by [Fe] catalyst.
[1] a) Leitao, E. M.; Jurca T.; Manners, I. Nature Chem., 2013, 5, 817-829. b) Clark,
T. J. Lee, K. Manners, I. Chem. Eur. J., 2006, 12, 8634-8648.
[2] Schäfer A.; Jurca, T.; Turner, J.; Vance, J. R.; Lee, K.; Du, V. A.; Haddow, M. F.;
Whitell, G. R.; Manners, I. Angew. Chem. Int. Ed., 2015, 54, 4836-4841.
[3] Jurca, T.; Turner, J.; Resendiz-Lara, D. A.; Manners, I. Unpublished Results
SYNTHESIS AND REACTIVITY OF ALKALINE EARTH
GALLYL COMPLEXES
J. Adan Reyes-Sanchez, Matthew P. Blake and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, UK.
Discrete molecular entities containing metal–metal bonds have enabled a better
understanding of chemical bonding and the reactivity in intermetallic and more complex
species. Their practical applications are of interest in the development of new materials1
and the solution to current energy problems,2 amongst others.
Mountford et al. recently reported the synthesis of complexes containing magnesium–transition metal
3 and lanthanide–gallium and boron
4 bonds. Here, we report the salt
metahesis reactions of the gallium(I) N-heterocyclic carbene (NHC) analogue
[(Dipp
DAB)GaK(Et2O)]2 (DAB = {N(Dipp)C(H)}2, Dipp = 2,6-diisopropylphenyl) with
Group 2 iodide complexes to form compounds containing alkaline earth–gallium bonds.
Group 2 metals in these species are supported by Dipp
NacNac or CzOxMe
ligands (Fig.
1). These compounds have been reacted with small molecules such as carbodiimides,
isocyanates, thioisocyanates and epoxides.
Figure 1. Alkaline earth–gallium complexes.
References
[1] Goll, D.; Kronmller, H. Naturwissenschaften 2000, 87, 423-438.
[2] David, E., J. Mat. Proc. Techn. 2005, 162-163, 169-177.
[3] Blake, M. P.; Kaltsoyannis, N.; Mountford, P. J. Am. Chem. Soc. 2011, 133 (39),
15358-15361.
[4] Saleh, L. M. A.; Birjkumar, K. H.; Protchenko, A. V.; Schwarz, A. D.; Aldridge,
S.; Jones, C.; Kaltsoyannis, N.; Mountford, P. J. Am. Chem. Soc. 2011, 133 (11),
3836-3839.
SMALL MOLECULE COORDINATION AND ACTIVATION BY
[Ru(IPr)2(CO)H]+ (IPr = 1,3-BIS(2,6-
DIISOPROPYLPHENYL)IMIDAZOL-2-YLIDENE)
Ian M. Riddlestone,a David McKay,
b Stuart A. Macgregor,
b Mary F. Mahon,
a and
Michael K. Whittleseya
aDepartment of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY
bSchool of Engineering and Physical Sciences, Heriott-Watt University, Edinburgh,
EH14 4AS
Very low coordinate transition metal fragments represent long standing synthetic targets
due to their potential for both novel and high reactivity with organic substrates. The
synthesis and characterization of four-coordinate Ru(II)L4 species represents a
challenging target due to the high coordinative unsaturation and corresponding high
Lewis acidity. Although rare, cationic species of the type [Ru(L)2(CO)R]+ (L =
PtBu2Me, R = Ph (1) or H (2)
[1,2]; L = IMes, R = H (3)
[3]) can be accessed via halide
abstraction reactions from the appropriate chloride containing precursors. All feature a
saw-horse geometry at ruthenium and 1 and 2 are stabilized by double agostic
interactions from the supporting phosphine ligand.[1,2]
By contrast, 3 was reported free
of agostic bonding, based on a combination of computational studies and trapping
experiments.[3]
Employment of the sterically demanding IPr
ligand allowed isolation and structural
characterization of the agostically stabilised
16-electron cation [Ru(IPr)2(CO)H]+ (4). 4
readily coordinates (H2, CO and
H3B.NMe2H), but undergoes hydride
abstraction with HBcat and Et2Zn,
eliminating H2 and ethane, forming rare
Ru-boryl and bimetallic Ru-Zn species
respectively.
References
[1] Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G., Angew. Chem. Int. Ed.
Engl. 1997, 36, 2004.
[2] Huang, D.; Bollinger, J. C.; Streib, W. E.; Folting, K.; Young, J. V.; Eisenstein, O.;
Caulton, K. G., Organometallics 2000, 19, 2281
[3] Lee, J. P.; Ke, Z.; Ramírez, M. A.; Gunnoe, T. B.; Cundari, T. R.; Boyle, P. D.;
Petersen, J. L., Organometallics 2009, 28, 1758
N N
iPr
iPriPr
Ru
H CO
CH2H
N N
iPriPr
BArF4
ACYCLIC TWO-COORDINATE CATIONIC GERMYLENES – METAL ELEMENT BOND FORMATION
Arnab Rit, Simon Aldridge*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, OX1 3TA,
Oxford
The chemistry of thermally stable divalent neutral germanium compounds has attracted
much recent attention.[1]
In contrast to neutral compounds, :GeX2, cationic species of
the type [:Ge(L)X]+
are relatively rare.[2]
Given recent interest in comparisons of
fundamental properties between carbon and its heavier congeners, understanding the
structure and reactivity of cationic germylenes might open up many interesting areas as
has been seen for the corresponding carbenium ions. In addition, the presence of a
cationic charge may lead to the isolation of unsaturated monomeric species (e.g.
containing Ge=E multiple bonds) by discouraging the sorts of oligomerization processes
seen for neutral analogues.
Herein we present the synthesis of rare acyclic two-coordinate cationic germylenes by
chloride abstraction from NHC-stabilized chlorogermylenes. Steric and electronic
tuning of the substituents at germanium allows control of aggregation. Thus, smaller
NHCs result in dimerization to give novel dicationic digermenes [X(L)Ge=GeX(L)]2+
.
Bulkier substituents yield monocationic germylenes which react cleanly with azido or
diazo compounds under N2 release to give monomeric imido or alkylidene complexes.
[1] (a) Kühl, O. Coord. Chem. Rev. 2004, 248, 411; (b) Z. Rappoport, The Chemistry of
Organic Germanium, Tin and Lead compounds; Wiley: Chichester, 2002; Vol. 2, p.
284.
[2] (a) Dias, H. V. R.; Wang, Z. J. Am. Chem. Soc. 1997, 119, 4650; (b) Stender, M.;
Phillips, A. D.; Power, P. P. Inorg. Chem. 2001, 40, 5314.
SMALL MOLECULE ACTIVATION AT A GEOMETRY-
CONSTRAINED PHOSPHORUS CENTRE
T. P. Robinson, D. M. De Rosa, S. Aldridge and J. M. Goicoechea
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Rd, Oxford, UK.
The activation of small molecules and subsequent catalytic transformations has long
been considered the domain of precious transition metals, for which low crustal
abundance, high cost and toxicity are discouraging factors. Consequently there has been
much interest in the development of main-group species that are able to “mimic” this behavior, with a number of systems shown to activate highly challenging small
molecules including dihydrogen and ammonia.[1]
Recent studies have demonstrated the
application of geometry constraining chelating ligands to synthesise P(III) compounds
that facilitate the oxidative addition of polarised E-H bonds (E = O and N).[2-6]
We have
developed this chemistry by investigating the reactivity of a N,N-bis-(2-
phenoxide)amide supported phosphorus system (1) (Scheme 1). The geometry
constrained product is extremely reactive towards a range of small molecule substrates,
resulting in oxidative additions over the phosphorus centre. The rapid and quantitative
reactions with both H2O and NH3 are of particular importance on account of the
difficulties associated with analogous transition-metal mediated activations.
Scheme 1
References:
[1] Power, P. P. Nature 2010, 463, 171–177.
[2] Arduengo III, A. J.; Stewart, C. A.; Davidson, F.; Dixon, D. A.; Becker, J. Y.;
Culley, S. A.; Mizen, M. B. J. Am. Chem. Soc. 1987, 109, 627–647.
[3] McCarthy, S. M.; Lin, Y. –C.; Devarajan, D.; Chang, J. W.; Yennawar, H. P.;
Rioux, R. M.; Ess, D. H.; Radosevich, T. J. Am. Chem. Soc. 2014, 136, 4640–4650.
[4] Dunn, N. L., Ha, M.; Radosevich, A. T. J. Am. Chem. Soc. 2012, 134, 11330–11333.
[5] Zhao, W.; McCarthy, S. M.; Lai, T. Y.; Yennawar, H. P.; Radosevich, A. T. J. Am. Chem. Soc. 2014, 136, 17634−17644.
[6] Cui, J.; Li, Y.; Ganguly, R.; Inthirarajah, A.; Hirao, H.; Kinjo, R. J. Am. Chem. Soc. 2014, 136, 16764−16767.
TETHERED CYCLOPENTADIENYL-STANNYLENE LIGANDS
FOR C-H ACTIVATION
M. Roselló-Merino and S. M. Mansell*
Institute of Chemical Sciences, School of Engineering and Physical Sciences,
Heriot-Watt University, Edinburgh, EH14 4AS, UK.
[email protected], [email protected]
Tethered ligands are interesting candidates for designing the next generation of
homogeneous catalyst as they combine two different ligand classes into one flexible
chelating ligand.[1]
N-heterocyclic stannylenes (NHSns) are an interesting alternative to
the ubiquitous N-heterocyclic carbene (NHC) ligands which have been recently
described,[2]
but have yet to be explored as ligands in catalysis. We are interested in
combining these concepts by synthesising tethered cyclopentadienyl-stannylene ligands
which are expected to open up new modes of reactivity including: 1. Hemilability of the
stannylene moiety, facilitating bond activation at the TM centre, 2. Bridging binding
modes (typically observed in NHSns) promoting unusual bimetallic bond activation, 3.
Transfer of ligands between Sn and the TM, 4. Increased complex stability and
improved product selectivity facilitated by the presence of a tether.
We have synthesised new indenyl- and fluorenyl-tethered diamines in order to target
new functionalised NHSn ligands. The formation of transition metal complexes via two
routes has then been explored using reactions of the ligand precursor with
Sn{N(SiMe3)2}2] followed by addition of the transition metal precursor, or introduction
of the transition metal first before reaction with a tin source.
[1] a) a) Butenschön, H. Chem. Rev. 2000, 100, 1527; b) Siemeling, U. Chem. Rev.
2000, 100, 1495.
[2] a) Mansell, S. M.; Russell, C. A.; Wass, D. F. Inorg. Chem. 2008, 47, 11367; b)
Mansell, S. M.; Herber, R. H.; Nowik, I.; Ross, D. H.; Russell, C. A.; Wass, D. F. Inorg.
Chem. 2011, 50, 2252.
NON-INNOCENT ACTIVITIES OF N-HETEROCYCLIC
CARBENES AT COPPER
C. E. Willans and W. Rungtanapirom
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9 JT, UK
N-heterocyclic carbenes (NHCs) have been used as ligands to support copper in a broad
range of catalytic reactions.[1]
However, reactivities in which the NHC ligands become
involved have also been observed, especially reductive elimination of the NHC.[2]
We
have previously observed the reductive elimination of 1-allyl-3-pyridylimidazol-2-
ylidene from copper to form bis-imidazolium salts, which is thought to proceed via
copper(III).[2c]
Furthermore, we discovered that 1-allyl-2-bromo-3-pyridylimidazolium
cuprate salts undergo a cyclisation reaction (Figure 1), similar to those previously
reported with Rh[3]
and Ni.[4]
Further investigation is needed to understand the
mechanism of these cyclisation reactions, with a view to both preventing catalyst
deactivation and using them to our advantage in the synthesis of heterocycles. Further
studies in this work include investigating the deactivation of copper catalysts bearing 1-
alkenyl-3-picolylimidazole-2-ylidene through reductive elimination of the NHC with an
aryl group (Figure 2).
Figure 1. Cyclisation of an allyl-substituted bromoimidazolium salt at copper.
Figure 2. Deactivation of a copper catalyst via reductive elimination of the NHC and aryl group.
[1] J. E. Egbert, C. S. J. Cazin, S. P. Nolan, Catal. Sci. Technol. 2013, 3, 912-926.
[2] aE. L. Kolychev, V. V. Shuntikov, V. N. Khrustalev, A. A. Bush, M. S. Nechaev, Dalton. Trans.
2011, 40, 3074; bB.-L. Lin, P. Kang, T. D. P. Stack, Organometallics 2010, 29, 3683-3685;
cB.
R. M. Lake, A. Ariafard, C. E. Willans, Chem. Eur. 2014, 20, 12729-12733.
[3] K. I. Tan, R. G. Bergman, J. A. Ellman, J. Am. Chem. Soc. 2001, 123, 2685-2686.
[4] A. T. Normand, S. K. Yen, H. V. Huynh, T. S. A. Hor, K. J. Cavell, Organometallics 2008, 27,
3153-3160.
CORRELATIONS OF THE STRUCTURAL PROPERTIES OF A
COMPLETE R2PX SERIES (X = HYDROGEN OR HALOGEN)
Timothy A. Shuttleworth, Jonathan P. Hopewell, Claire L. McMullin, Paul G. Pringle
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
The importance of phosphorus(III) ligands in coordination chemistry and homogeneous
catalysis is undeniable. The quest for rational ligand design has engendered numerous
spectroscopic, crystallographic and theoretical studies aimed at quantifying the
stereoelectronic properties of P donors. However, the separation of steric and electronic
effects is a recurrent problem, precluding the presentation of unambiguous empirical
evidence to support even simple concepts. A study of a series of PX3 molecules (X = H
or Hal) would be the most accurate, as variation in the steric properties is minimised.
Unfortunately, the high reactivity of these molecules, even when coordinated to a metal,
makes full characterisation and analysis problematic. However, R2PX molecules offer
greater stability, whilst alteration of only one atom means stereoelectronic deviation is
again minimised. Complete R2PX series are known for R = Me, tBu, Ph and η1
-C5Me5,
although many of these molecules are air sensitive or fluids at room temperature.
CgPX molecules (where R2P = CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-
tetramethyladamant-6-yl cage depicted below; X = H,1 F,
2 Cl,
1 Br
1) have been reported
as air stable, crystalline solids. Building on this, recently we reported the synthesis and,
for the first time, the crystal structures of a complete series of R2PX molecules (R2P =
CgP), along with their corresponding selenium adducts (Scheme 1).3 In this study, we
were able to compare a range of spectroscopic and crystallographic data, allowing
analysis of the stereoelectronic properties of the P donor series.
Scheme 1. Synthesis of CgPX and CgP(Se)X, where X = H, F, Cl, Br and I.
[1] Downing, J. H.; Floure, J.; Heslop, K.; Haddow, M. F.; Hopewell, J.; Lusi, M.;
Phetmung, H.; Orpen, A. G.; Pringle, P. G.; Pugh, R. I.; Zambrano-Williams, D.
Organometallics 2008, 27, 3216–3224.
[2] Fey, N.; Garland, M.; Hopewell, J. P.; McMullin, C. L.; Mastroianni, S.; Orpen, A.
G.; Pringle, P. G. Angew. Chem. Int. Ed. 2012, 124, 122–126.
[3] Hopewell, J. P.; McMullin, C. L.; Pringle, P. G.; Shuttleworth, T. A.; Woodall, C.
H. Eur. J. Inorg. Chem. 2014, 1843–1849.
REDOX PROMOTED CYCLOMETALATION REACTIONS OF PLATINUM(0) COMPLEXES
Thibault Troadec and Adrian B. Chaplin*
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
Due to the diverse potential applications in organic synthesis and petroleum research,
transition-metal-mediated C-H bond activation reactions are of significant contemporary
interest in organometallic chemistry and catalysis. Cyclometalation reactions based on
intramolecular C-H bond oxidative addition are useful model reactions for the more
coveted intermolecular variants, whilst also being of interest in their own right as
pathways in catalytic organic transformations. Building upon previous work by Goel
and Conejero, involving bis-phosphine and bis-(N-Heterocyclic carbene) platinum(II)
complexes (Figure 1),1,2
we present a novel redox-based method for promoting
intramolecular C-H reactions in platinum(0) systems.
Figure 1: Intramolecular cyclometalation reactions in platinum(II) complexes
References
1. Clark, H. C.; Goel, A. B.; Goel, R. G.; Goel, S.; Ogini, W. O. Inorg. Chim. Acta
1978, 31, L441–L442; Clark, H. C.; Goel, A. B.; Goel, R. G.; Goel, S. Inorg. Chem.
1980, 19, 3220–3225; Goel, R. G.; Ogini, W. O.; Srivastava, R. C. Organometallics,
1982, 1, 819-824.
2. Rivada-Wheelaghan, O.; Donnadieu, B.; Maya, C.; Conejero, S. Chem. Eur. J.
2010, 16, 10323 – 10326; Rivada-Wheelaghan, O.; Ortuno, M. A.; Diez, J.; Lledos,
A.; Conejero, S. Angew. Chem. Int. Ed. 2012, 51, 3936 –3939; Rosello-Merino, M.;
Lopez-Serrano, J.; Conejero, S. J. Am. Chem. Soc. 2013, 135, 10910-10913; Rivada-
Wheelaghan, O.; Rosello-Merino, M.; Ortuno, M. A.; Vidossich, P.; Gutierrez-
Puebla, E.; Lledos, A.; Conejero, S. Inorg. Chem. 2014, 53, 4257–4268. Rivada-
Wheelaghan, O.; Rosello-Merino, M.; Diez, J.; Maya, C.; Lopez-Serrano, J.;
Conejero, S. Organometallics 2014, 33, 5944-5947.
DEHYDROCOUPLING OF DIMETHYLAMINE-BORANE BY
CYCLOPENTADIENYL BASED IRON PRECATALYSTS
J. R. Turner, T. Jurca and Ian Manners
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
Utilising transition metals to catalyse the dehydrocoupling of main group substrates has
been an expanding field since the 1980s, with the dehydrocoupling of amine-boranes
being a more recent area of interest. This has been extended towards iron, where in
2014, two complexes, CpFe(CO)2I and [CpFe(CO)2]2, were shown to dehydrocouple
dimethylamine-borane.1 Interestingly, these two systems proceed via vastly different
mechanisms, the former via a homogeneous process and the latter heterogeneous.
However, irradiation with UV/vis light has hindered mechanistic investigations, and the
search for an Fe catalyst that does not require photoactivation has been ongoing (Figure
1). The synthesis and characterisation of a number of Cp based Fe complexes and their
room temperature reactivity towards dimethylamine-borane will also be presented.2
Figure 1. Room temperature dehydrocoupling of dimethylamine-borane
[1]Vance, J. R.; Schäfer, A.; Robertson, A. P. M.; Lee, K.; Turner, J.; Whittell, G. R.;
Manners, I., J. Am. Chem. Soc. 2014, 136 (8), 3048-3064.
[2] Turner, J. R.: Titel, J.; Manners, I. Unpublished Results.
Requires hν
GROUP 1 AND 2 CYCLIC (ALKYL)(AMINO)CARBENE
COMPLEXES
Z. R. Turner and J.-C. Buffet
Chemistry Research Laboratory, 12 Mansfield Road, OX1 3TA, Oxford, UK
Cyclic (alkyl)(amino)carbenes (CAACs) are a more recently developed and less
explored class of the ubiquitous N-heterocyclic carbenes (NHC).[1]
They have unique
stereoelectronic properties, being both stronger σ-donors and π-acceptors with respect to
classical NHCs, and demonstrating redox activity.[2]
The alkaline earth metals (Ae; magnesium – barium) are earth abundant and benign
in nature, making them attractive targets for homogeneous catalysis.[3]
There remain
relatively few examples of electropositive metal NHC complexes,[4]
and we recently
described the first examples of CAACs bound to both group 1 and 2 metal ions (Figure
1).[5]
We report here the use of these complexes as efficient catalysts for polar monomer
polymerisation and examples of reactivity unique to these systems.
Figure 1. Solid state molecular structures of potassium and barium CAAC complexes.
[1] Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. Nature 2014, 510, 485-496.
[2] Soleilhavoup, M.; Bertrand, G. Acc. Chem. Res. 2015, 48, 256-266. [3] Harder, S.;
Editor Alkaline-Earth Metal Compounds: Oddities and Applications. [In: Top.
Organomet. Chem., 2013; 45]; Springer GmbH, 2013. [4] a) Bellemin-Laponnaz, S.;
Dagorne, S. Chem. Rev. 2014, 114, 8747-8774; b) Arnold, P. L.; Casely, I. J. Chem.
Rev. 2009, 109, 3599-3611. [5] Turner, Z. R.; Buffet, J.-C. Dalton Trans. 2015, 44,
12985-12989.
PROTON COUPLED MIXED VALENCY IN HYDROGEN BONDED
DIMERS
K.B. Vincent, L.A. Wilkinson, L. Brown and N.J. Patmore
University of Huddersfield, Department of Chemical Sciences, Queensgate,
Huddersfield, HD1 3DH, UK
The study of organometallic mixed valence systems has achieved much attention over
recent decades with potential applications in photochromic systemsI and as components
in future molecular electronics technology.II Such systems are of the archetypal donor-
bridge-acceptor (D-B-A) architecture bearing redox active metal units linked through
covalently bonded bridging units, often organic in nature. To this extent there have been
many reports of systems comprising two multiply bonded di-metallic moieties linked
through covalent bridges where the redox chemistry of the metal fragments is exploited
to give rise to D-B-A systems.III
In contrast to this we present here a ‘new’ class of systems where metal-bridge-metal systems are prepared by exploiting hydrogen
bonding functionality of the ligand to form dimeric species, Figure 1a.IV
Electrochemical and spectroelectrochemical analyses of these hydrogen bonded dimers
show that in weakly / non- coordinating solvents the thermodynamic stability of the
cation is observed giving rise to voltammograms showing two consecutive reversible
one-electron oxidations. The requirement for the hydrogen bond is then observed by the
addition of DMSO which serves to break the dimeric bond as evidenced by the
breakdown two a single redox process, Figure 1b. Further evidence to support the
requirement for the hydrogen bond is observed in UV-vis NIR spectroelectrochemistry
of the mixed valence state where no IVCT band is observed, as would be expected in
classic mixed valence systems.
Figure 1: a) Metal dimers prepared by hydrogen bonding ligands. c) CV of bimetallic species showing
the dimeric species (green) and monomer (red).
I Sakamoto, R. et al. Chem. Eur. J. 2008, 14, 6978.
II Low, P. J. Dalton Trans. 2005 2821.
III Casas, J. M; Cayton, R. H; Chisolm, M. H. Inorg. Chem., 1991, 30, 360.
IV Patmore, N. J. et al, J. Am. Chem. Soc., 2013, 135, 1723. Wilkinson, L. A; McNeill, L;
Scattergood, P; Patmore, N. J. Inorg. Chem., 2013, 52, 9683
SYNTHESIS AND REACTIVITY OF DITOPIC CARBANIONIC N-
HETEROCYCLIC CARBENE COMPLEXES
Lajoy S. Tucker, Jose M. Goicoechea and Jordan B. Waters
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, OX1 3TA
Since the discovery of the first isolable N-heterocyclic carbene (NHC) 24 years ago,1
these compounds have gone from chemical curiosities to ubiquitous ligands in modern
organometallic chemistry. NHCs can bond to metals through the “conventional” (C2) or “abnormal” (C4) positions.2 Recently, Robinson reported the synthesis of the first N-
heterocyclic “dicarbene” (NHDC), by deprotonation of an NHC resulting in a species
capable of binding through the C2 and C4 positions simultaneously.3 Accordingly, we
have recently reviewed the known chemistry of ditopic carbanionic NHCs.4
We have been investigating the reactivity of the lithium salt of the deprotonated IPr
carbene towards E[N(SiMe3)2]2 complexes (E = Ge, Sn, Pb). Such reactions in an
equimolar ratio result in the formation of novel germylene, stannylene or plumbylene
species. We have also synthesised the analogous potassium salt (KIPr) and studied the
reactivity towards E[N(SiMe3)2]2 (E = Ge, Sn, Pb and Zn).5 The products are all C4
bonded adducts E[:CCH{[N(2,6-iPr2C6H3)]2C:}][N(SiMe3)2]2]
− which in the case for E
= Ge and Pb, will slowly rearrange to afford the bis-carbene adduct along with the
homoleptic metal tris-amide.
We have also synthesised the neutral
organomercury species Hg(aIPr:)2 by
the reaction of two equivalents of
KIPr with HgCl2 (see figure). This
complex consists of two abnormally
bonded NHCs; the carbenic carbons
can then be protonated resulting in
the formation of the dicationic salt
[Hg(aIPr)]2+
[BAr4F]2.
6
References
1. Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc., 1991, 113, 361.
2. Aldeco-Perez, E.; Rosenthal, A. J.; Donnadieu, B.; Parameswaran, P.; Frenking, G.
Bertrand, G. Science, 2009, 326, 556.
3. Wang, Y.; Xie, Y.; Abraham, M. Y.; Wei, P.; Schaefer, H. F.; Schleyer, P. v. R.;
Robinson, G. H. J. Am. Chem. Soc., 2010, 132, 14370.
4. Waters, J. B.; Goicoechea, J. M. Coord. Chem. Rev., 2014, 293-294, 80.
5. Waters, J. B.; Goicoechea, J. M. Dalton Trans., 2014, 43, 14239. 6. Waters, J. B.; Goicoechea, J. M. manuscript in preparation.
Hg1 C1
C2
C3
C28
C29
C30
SWAPPING THE ROLE OF DONOR/ACCEPTOR AND BRIDGE IN
A DYCLIC DIMER OF DIMERS
L. A. Wilkinson1, and N. J. Patmore
2
1University of Sheffield, Western Bank, Sheffield, S10 2TN 2University of Huddersfield, Queensgate, Huddersfield, HD13DH
The fundamental study of electron transfer is paramount for understanding many
complicated processes in nature and for applications in molecular electronics1 and
mixed valence systems have been extensively employed to study this process.2 In many
systems, the donor/acceptor units are metal-based and the bridge is an organic linker
(such as the Creutz-Taube ion)3, however there are also multiple reports of the
inverse.4,5
To our knowledge, there has never been a report of a single molecule wherein
electron transfer could occur between metal centres via an organic bridge or between
organic redox sites via a metal-based bridge. Our laboratory has developed a cyclic
dimer of dimers of the form [Mo2(TiPB)2]2(μ-ADC)2 (where TiPB = 2,4,6-
triisopropylbenzoic acid and H2ADC = anthracene-1,8-dicarboxylic acid). DFT
calculations show that the HOMO is based on the Mo2 units whereas the LUMO is
based on the ADC fragments. This allows the possibility of forming two mixed valence
states: a metal based radical cation and a ligand based radical anion. This concept is
investigated by cyclic voltammetry and EPR spectroscopy.
References.
[1] Ward, M. D. Chem. Soc. Rev. 1995, 24, 121–134.
[2] Winter, R. F. Organometallics 2014.
[3] Creutz, C.; Taube, H. J. Am. Chem. Soc. 1969, 91, 3988–3989.
[4] Jones, S. C.; Coropceanu, V.; Barlow, S.; Kinnibrugh, T.; Timofeeva, T.; Bredas,
J.; Marder, S. R. J. Am. Chem. Soc. 2004, 126, 11782–11783.
[5] Lu, C. C.; Bill, E.; Weyhermüller, T.; Bothe, E.; Wieghardt, K. J. Am. Chem. Soc. 2008, 130, 3181–3197.
Figure 1: Cyclic dimer of dimers and the possible redox processes. Ancillary ligands omitted for clarity.
WELL DEFINED TUNGSTEN CATALYSTS FOR SELECTIVE
ETHYLENE OLIGOMERISATION
C. M. R. Wright, J.-C. Buffet, D. O’Hare
Chemistry Research laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA.
[email protected] Feedstocks of ethane which can be cracked on a huge scale to produce ethylene have
increased due to shale gas exploration.1 Processes that upgrade such low molecular
weight α-olefins to higher homologues are therefore of increasing value. Olefin
oligomerisation is one such method employed by industry, although selectivity for such
transformations is still an issue.2,3
Ill-defined tungsten systems formed from WCl6,
aniline and triethylamine have shown promise in this area, displaying good selectivity in
ethylene oligomerisation when a Lewis acid cocatalyst is employed.4 Here we report a
well-defined tungsten imido complex which is active for ethylene dimerisation in the
presence of methylaluminoxane. The cocatalyst ratio has a marked effect on the
stability, activity and selectivity of the complex.
Left: Scheme showing the dimerisation of ethylene to 1-butene utilising a well-defined tungsten imido complex
with MAO as a cocatalyst. Right: Graph showing conversion of ethylene to 1-butene with varying cocatalyst
ratios.
Utilising the technique of surface organometallic chemistry (SOMC),5 tungsten imido
complexes have been grafted onto solid supports. The activity and selectivity for the
dimerisation can be maintained and in some cases enhanced compared to the
homogeneous reaction.
[1] Chem. World 2015, 12, 18–19.
[2] Grasset, F.; Magna, L. EP2388069 (A1), 2011.
[3] Mol, J. J. Mol. Catal. A Chem 2004, 213, 39–45.
[4] Hanton, M. J.; Daubney, L.; Lebl, T.; Polas, S.; Smith, D. M.; Willemse, A. Dalt. Trans. 2010, 39, 7025–7037.
[5] Copéret, C. New J. Chem. 2004, 28, 1–10.
USING IN SITU X-RAY DIFFRACTION TO OBSERVE SOLVENT
EXCHANGE DURING MOF SYNTHESIS
Y. Wu,a M. I. Breeze,
b G. J. Clarkson,
b F. Millange, D. O’Hare,a and R. I. Walton*
b
a Department of Chemistry University of Oxford, Oxford, OX1 3TA, U.K.
b Department of Chemistry, University of Warwick, Coventry, CV4 7AL, U.K.
c Département de Chimie, Université de Versailles-St-Quentin-en-Yvelines, France
In most cases of metal-organic framework (MOF) synthesis using solvothermal
methods, it is unclear whether the framework is initially formed with coordinated
solvent that is then exchanged with another ligand to reach the final product, or if the
final product is formed from the start as the sole species. Using time-resolved
monochromatic high energy X-ray diffraction with a custom IR furnace cell (‘ODISC’, the Oxford-Diamond In-Situ Cell, Fig. 1, left),
1 we have been able to understand this
behaviour at an unprecedented level of detail.
Figure 1. ODISC furnace (left); Observation of in situ guest exchange (right)
We present an in situ study of the solvothermal crystallisation of a new ytterbium MOF
from a water/DMF mixture under solvothermal conditions. Analysis of high resolution
powder patterns using Rietveld refinement reveals an evolution of lattice parameters
and electron density during the crystallisation process. Quenching studies confirm that
this is due to a gradual topochemical replacement of coordinated solvent molecules: the
water initially coordinated to Yb3+
is replaced by DMF as the reaction progresses (Fig.
1, right).
(1) Moorhouse, S. J.; Vranješ, N.; Jupe, A.; Drakopoulos, M.; O’Hare, D. Rev. Sci.
Instrum. 2012, 83 (8), 084101.
SYNTHESIS AND REACTIVITY OF ZIRCONIUM AND HAFNIUM
BORYLIMIDO COMPOUNDS
Bowen Xie, Benjamin A. Clough, Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, U.K.
Complexes containing transition metal-nitrogen multiple bonds have been applied in a range of important organic and inorganic transformations.1 The synthesis and small molecule reactivity of Group 4 imido and hydrazido complexes, (L)M=NR and (L)M=NNR2, have been extensively studied within this research group and by others.2
Of relevance to this contribution, imidozirconocene complexes Cp2Zr=NR(THF) have shown a wild range of reactivity with different small molecules.3 Only five examples of the related borylimides, (L)M=NBR2, have been reported across all of the transition metals to date,4 and we here report the synthesis the first zirconium and halnium borylimido complex analogue by using the borylamine H2NB(NAr'CH)2 (Ar' = 2,6-C6H3
iPr2) (see Figure 1). Furthermore, the zirconium complex was found to give some unusual E-H (E = H, C) activation reactions, which we also report here.
Figure 1: Examples of new zirconium and hafnium borylimido complexes.
References. [1] For example: Acc. Chem. Res., 2005, 38, 955; Acc. Chem. Res., 2005, 38, 839; J.
Am. Chem. Soc., 2001, 123, 2923; John Wily and Sons, 1988 [2] For example: Organometallics, 2011, 30, 1182; J. Am. Chem. Soc., 2004, 126, 1794; Organometallics, 2009, 28, 4747. [3] Chem Rec, 2002, 2, 431 [4] Polyhedron, 1993, 12, 1061; Z. Anorg. Allg. Chem., 2003, 629, 744; Angew. Chem.
Int. Ed. Engl., 2002, 41, 3709-3712; J. Am. Chem. Soc., 2014, 136, 8197.
TRIS(PYRAZOLYL)METHANIDE MAGNESIUM COMPLEXES AS
CATALYSTS FOR THE RING-OPENING POLYMERISATION OF
ε-CL AND rac-LA
Xinning Yin, Insun Yu, Junjuda Unruangsri, and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA
Among many face-capping, six-electron N-donor ligands reported in the literature,
tris(pyrazolyl)hydroborate is one of the most widely used. The isoelectronic
tris(pyrazolyl)methane (Tpm) was later introduced as a supporting ligand because C-N
bonds are stronger than B-N bonds, therefore providing robustness in catalyst
activities.1,2
Herein, we report the synthesis and transformation of a series of
tris(pyrazolyl)methanide (Tpmd) magnesium complexes, Scheme 1. (Tpm
d)MgBH4 and
(Tpmd)MgOBn were efficient catalysts for the ring-opening polymerisation (ROP) of ε-
CL and rac-LA. In addition, borate ester derivatives were applied as chain transfer
agents and some ROP results were shown in Figure 1.
Scheme 1. Synthesis of a series of tris(pyrazolyl)methanide magnesium compounds.
0
5000
10000
15000
20000
25000
30000
0 20 40 60 80 100
Mn
(GP
C)/
gm
ol-1
% Conversion
Mn (GPC) 8PhCHOMn (GPC) B(OBn)3Mn (GPC) none线性 (Calcd for 1 chain)线性 (Calcd for 4 chains)
References [1]. Cushion, M.; Meyer, J.; Heath, A. and Mountford, P. Organometallics, 2010, 29, 1174.
[2]. Bigmore, H.; Meyer, J.; Krummenacher, I. and Mountford, P. Chem. Eur. J., 2008, 14, 5918.
Figure 1. Mn (GPC) vs % conversion
plot of ε-CL ROP using TpmdMgBH4,
TpmdMgOBn and various additives in
THF.
OLEFIN POLYMERISATION WITH CARBON-BASED TITANIUM
COMPLEXES
George J.P. Britovsek1, Serge Bettonville
2, Maria Gragert
1, Craig T. Young
1*
1Department of Chemistry, Imperial College London, U.K.
2INEOS Technologies, Brussels, Belgium
Long chain branching (LCB) in polyethylene (PE) results in behaviour considerably
different to that of purely linear polymer. In particular, LCB levels influence (a) swell
during blow moulding, (b) bubble stability, orientation, melt fracture, and extensional
viscosity in film blowing, (c) melt strength in geomembrane resins, (d) sag during large
diameter pipe extrusion and (e) various mechanical properties in finished articles.[1]
Certain Group 4 single-site catalysts (SSCs) are capable of producing long chain
branching, but the mechanism of formation is debatable.[2-4]
The majority of these SSCs
are metallocene based and/or contain Group 15-16 donor atoms.[3-5]
In comparison,
Group 4 SSCs with η1-bound carbon donor ligands have thus far received only little
attention.
Our aim was to synthesise Group 4 metal SSCs with aromatic carbon donor ligands,
which are η1-bound to the metal centre. We present herein the synthesis of new titanium
complexes with biphenyl (A), diphenylpyridine (B) and terphenyl (C, D) ligands. The
dimethylamido complexes could easily be prepared as opposed to the corresponding
metal halide complexes, which suffered significant decomposition. Preliminary ethylene
polymerisation experiments have shown that these complexes are active polymerisation
catalysts. The syntheses of ligands and metal complexes will be discussed.
[1] McDaniel, M. P.; Rohlfing, D. C.; Benham, E. A. Polym. React. Eng. 2003, 11, 101.
[2] Yang, Q.; Jensen, M. D.; McDaniel, M. P. Macromolecules 2010, 43, 8836.
[3] Reinking, M. K.; Orf, G.; Mcfaddin, D. J. Polym. Sci. A Polym. Chem. 1998, 36,
2889.
[4] Budzelaar, P. H. M. WIREs Comput. Mol. Sci. 2012, 2, 221.
[5] Piel, C.; Stadler, F. J.; Kaschta, J.; Rulhoff, S.; Münstedt, H.; Kaminsky, W.
Macromol. Chem. Phys. 2006, 207, 26.
UNIQUE GROUP 1 CATIONS STABILISED BY HOMOLEPTIC PHOSPHINE COORDINATION
Marina Carravetta, Maria Concistre, William Levason, Gillian Reid and Wenjian Zhang
School of Chemistry, University of Southampton, Southampton UK SO17 1BJ.
Phosphine ligands are ubiquitous in transition metal chemistry, owing to their capacity
to tune the electronic and steric properties, and hence the reactivity, of the complexes.
This has led to wide utilisation of phosphine co-ligands in many transition metal
catalysts and reagents. Phosphine complexes containing p-block acceptors have also
been developed substantially in recent years. However, examples of soft phosphine
coordination towards the hard s-block elements, particularly the Group 1 cations, have
remained extremely elusive. To-date there has been only one reported example of
neutral phosphine coordination to an alkali metal cation, although this is in an
organometallic silylamide dimer [Li{N(Ar)CC(R)Si(R)2NAr}(-Me2PCH2CH2PMe2)]2.
In this poster we report the first series of homoleptic phosphine complexes with group 1
cations, in the form of distorted octahedral Li+ and Na
+ cations containing tris-
diphosphine coordination. These complexes can be achieved by using
Li[Al{OC(CF3)3}4] and Na[BArF] ([BAr
F] = [B{3,5-(CF3)2-C6H3}4]
), which bear
large weakly-coordinating anion and ‘naked’ electrophilic Group 1 cations, together with strong -donor diphosphines, Me2P(CH2)2PMe2 and o-C6H4(PMe2)2.
1. G. Wilkinson, R. D. Gillard, J. A. McCleverty (Eds.), Comprehensive
Coordination Chemistry, Pergamon Press, Oxford, 1987; J. A. McCleverty, T. J.
Meyer (Eds.), Comprehensive Coordination Chemistry II, Elsevier, Oxford, 2004;
2. J. Burt, W. Levason, G. Reid, Coord. Chem. Rev., 2014, 260, 65.
3. R, J. Bowen, M. A. Fernandes, P. B. Hitchcock, M. F. Lappert, M. Lay, J. Chem. Soc., Dalton Trans., 2002, 3253.
4. M. Carravetta, M. Concistre, W. Levason, G. Reid, W. Zhang, Chem. Commun., 2015, 51, 9555.
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