inorganic and organometallic chemistry · inorganic, organometallic and intermetallic compounds of...

7

Inorganic and Organometallic Chemistry

Introduction

The activity of the group comprises the synthesis, characterization and reactivity studies of

inorganic, organometallic and intermetallic compounds of actinides and lanthanides and ion

molecule reactions with the same elements, in order to understand the influence of the

electronic configuration and of the size of these elements in the chemical behaviour of their

compounds. Due to the type of chemistry we are dealing with, we extended our work to the

chemistry of rhenium, with the aim of developing compounds that could be used as

intermediates in reactions directed to organic synthesis and that can be models for compounds

with 99m

Tc to be used as radiopharmaceuticals. These activities are supported by X-ray

diffraction analysis for structural studies and thermochemical studies for determination of

metal-ligand bond disruption enthalpies. The gas-phase reactions of metallic, intermetallic and

oxide ions involving lanthanides and actinides with organic substrates are studied by means of

Fourier transform ion cyclotron resonance spectroscopy.

The work done during 1996 in the domain of organometallic compounds allowed to

accomplish the study of the reactivity of the system UCl2(HBpz3)2 towards several organic

substrates. The analogous UCl2(Bpz4)2 system is now under investigation. The introduction of

more sterically hindered polypyrazolylborate ligands, such as [HB(3-tBupz)3] and [HB(3-

Mespz)3] allowed the synthesis of new systems of U (IV) and Ln(II) and their reactivity is

being studied.

The synthesis of alkoxides of lanthanides that could be active in some catalytic

transformations was also studied. We were trying to get alkoxides of low nuclearity using

alcohols with additional ether or amine functions. The compounds were tested in the

carboxylation reaction of methanol but probably due to the highly aggregated structures

obtained, the compounds did not show to be active in this particular transformation. The only

compound which showed to be active in this reaction was the ytterbium:nickel (1:1) alloy.

78% of conversion of methanol to dimethylcarbonate was achieved by reacting the alloy with

methanol under CO2.

The reactivity of oxo-complexes of rhenium towards several neutral substrates was studied as

well as the properties of rhenium (V) diolates. Attempts to prepare 99m

Tc analogues have been

done.

The work in the gas-phase included studies of the reactivity of lanthanide and actinide metal

and oxide ions with hydrocarbons, alcohols and phenols. Comparative studies with alkaline-

earth ions were made due to the similarity of these elements with lanthanides in low oxidation

states. The studies undertaken provided further examples confirming the relevance of the

accessibility of reactive electronic configurations to the reactivity of lanthanide and actinide

ions with organic molecules. Formation of f-d intermetallic ions was achieved and these

species may be available for future studies of the influence of the d element in the reactivity

with organic molecules. Reactivity of several lanthanide oxide cluster ions with small

oxygenated molecules was also studied. Collaborative work has extended the gas-phase

research to studies of transition metal ions.

Inorganic and Organometallic Chemistry ________________________________________________________

8

Research Team

Researchers – 12 * (10 PhD)

Research Students – 4

BSc Last Year Students – 4

Technicians – 2

* 2 Post-doctoral

Publications:

Journals – 7

Special Publ. – 1

Conf. Commun.: 10

Internal Reports: 1

Theses:

PhD – 1

MSc – 1

Lic. – 4

________________________________________________________ Inorganic and Organometallic Chemistry

9

f - Element Chemistry

Hydrocarbyl Derivatives of [UCl2{HB(pz)3}2]: Synthesis, Characterization

and Reactivity Studies Towards Protic Substrates and Ketones

M. Paula C. Campelloa, Maria José Calhorda

c, Ângela Domingos

a, Adelino Galvão

b,

João

Paulo Leala, A.Pires de Matos

a and Isabel Santos

a

aDepartamento de Química, ITN, 2686 Sacavém Codex, Portugal

bDepartamento de Engenharia Química, Instituto Superior Técnico, 1096 Lisboa Codex, Portugal

cI. T. Q. B., R. da Quinta Grande 6, Apt. 127, 2780 Oeiras, Portugal and Faculdade de Ciências,

Edifício C4, Campo Grande, 1700 Lisboa

Abstract

The reaction of [UCl2{HB(pz)3}2] (1) with lithium alkyls LiR (R=Me, CH2SiMe3, C6H4-o-

CH2NMe2) in the 1:1 or 1:2 molar ratio affords the compounds [UClR{HB(pz)3}2] (pz=

C3H3N2, R=Me (2), CH2SiMe3 (3), C6H4-o-CH2NMe2 (4)) and [UR2{HB(pz)3}2] (R=Me (5),

CH2SiMe3 (6)), respectively in 60-80% yield. Complex 2 can also be obtained (60%, yield) by

redistribution at room temperature between the complexes 1 and 5. Compounds 2, 3 and 4

react with pzH providing [UCl(pz){HB(pz)3}2] (7) in almost quantitative yield and 5 and 6

react also with pzH leading to [U(pz)2{HB(pz)3}2] (8). The alkoxide [U(OC6H4-o-

OMe)2{HB(pz)3}2] (9) was synthesized by reacting 5 or 6 with guaiacol. By reacting the

clorohydrocarbyls 2, 3 or 4 with excess of acetone the aldolate

[UCl(OCMe2CH2(C=O)Me){HB(pz)3}2] (11) was obtained, due to the activation of -CH

bond of acetone; however, for 3 the reaction is not clean and a mixture of (11) and

[UCl(OCMe2CH2SiMe3){HB(pz)3}2] (12) is always obtained. Stoichiometric amounts of

acetone insert into the metal-carbon bonds of 2 and 5 yielding [UCl(OtBu){HB(pz)3}2] and

[U(OtBu)2{HB(pz)3}2], respectively, while the insertion product

[U(OCMe2CH2SiMe3)2{HB(pz)3}2] (10) can only be obtained when 6 reacts with excess of

this substrate. (9) crystallizes from toluene/hexane in the triclinic space group P1 with unit

cell dimensions a=12.295 (2) Å, b=12.640(2) Å, c=13.994(2) Å, =76.10(1)º, =72.50(1)º,

=80.71(1)º, V=2004(2) Å3and Z=2. Recrystallization of a mixture containig

[UCl(OtBu){HB(pz)3}2] and 11 led to a decomposition product which has been characterized

by X-ray structural analysis as [UCl(Hpz)(OtBu){(-O)B(-pz)(pz)2}]2 (13): monoclinic

P21/n, a=13.701(3) Å, b=11.337(2) Å, c=14.857(4) Å, =104.65(2)º, V=2233(1) Å3 and Z=2.

Extended Hückel molecular orbital calculations provided some information on the bonding

capabilities of the [U{HB(pz)3}2] fragment compared to [U(C5Me5)2] and on the vulnerability

of the poly(pyrazolyl)borate ligands to nucleophilic attack.

Journal of Organometallic Chemistry (in press).


10

Synthesis of lanthanide complexes coordinated by an asymmetric

cyclopentadienyl ligand

A.A. Trifonova, P. Van de Weghe

a, J. Collin

a, A. Domingos

b, I. Santos

b

a Laboratoire de Synthése Asymétrique, URA, ICMO, Université Paris-sud, 91405 Orsay, France

b Departamento de Química, Instituto Tecnológico e Nuclear, 2686 Sacavém Codex, Portugal

Abstract

The synthesis and characterization of bis- and monocyclopentadienyl lanthanide iodides

(S)-Cp’2 LnI (Ln = Sm, 3; Ln = La, 4) and (S)-Cp’LnI2 (THF)n’ (Ln = Sm, n = 3, 5; Ln = La,

n = 2, 6) coordinated by an asymmetric cyclopentadienyl ligand (Cp’ =

C5H4CH2CH(CH3)OCH2Ph) have been carried out. Variable-temperature NMR study

compounds 3 and 4 reveals a fluxional process in solution. The X-ray crystal structure

analysis of 3 shows a bent metallocene structure with intramolecular coordination to the

oxygen atoms of the side chains of both cyclopentadienyl ligands. For monocyclopentadienyl

complexes, intramolecular coordination is observed only for the lanthanum complex 6. All

compounds exhibit activity for the catalysis of Diels-Alder reactions.

Journal of Organometallic Chemistry (in press).

Current Work

Reduction of Copper-Lanthanide oxides catalysts derived from LnCu2

intermetallics and their catalytic behaviour in mesityl oxide hydrogenation

D. Ballivet-Tkatchenkoa J. Branco

b and A. Pires de Matos

b

a Institut de Recherches sur la Catalyse, Avenue Albert Einstein 2, 69626 Villeurbanne Cedex, France

b Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

The reduction under hydrogen of the oxidized intermetallics described by the formulas

CeO2.2CuO and Ln2CuO4.3CuO (Ln = La, Pr, Nd) was followed by thermo-

gravimetric/differential thermal analysis (TG/DTA) and by temperature programmed

reduction (TPR). These techniques confirm two mass losses over 473 - 1173 K corresponding

the first to the reduction of the CuO phase and the second to the reduction of the ternary

phases as shown by X-ray powder diffraction (XRD). Energy dispersive X-ray analysis (EDX)

on several particles gave a Cu:Ln ratio close to that of the oxidized intermetallic compounds.

A two step treatment - oxidation followed by reduction - allows us to obtain catalysts which

are supported copper on lanthanide oxides. It was found that the reduction step does not alter

the copper composition on the surface resultant from the previous oxidation. These systems

proved to be active in the hydrogenation of mesityl oxide, being the only product the saturated

ketone.

To be submitted to J. Phys. Chem.


11

Catalytic behaviour of LnCu2 intermetallics and derived supported

Copper-Lanthanide oxide catalysts in propionitrile hydrogenation

D. Ballivet-Tkatchenko,a J. Branco,

b and A. Pires de Matos

b

a Institut de Recherches sur la Catalyse, Avenue Albert Einstein 2, 69626 Villeurbanne Cedex,

France b Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

The intermetallic compounds LnCu2 (Ln=La, Ce, Pr, Nd) and the derived copper-lanthanide

oxide catalysts CeO2.2Cu and Ln2O3.4Cu (Ln = La, Pr, Nd), show high selectivity for the

hydrogenation of propionitrile into the primary amine. The intermetallic compounds are

essentially good catalytic precursors and the derived copper-lanthanide oxide catalysts show

higher activity than the parent compounds. They show also higher selectivity for the primary

amine than copper catalysts obtained from impregnation of different supports with metallic

copper.

To be submitted to J.Catal.

Uranium (IV) complexes with polypyrazolylborate ligands

Ângela Domingosa, Noémia Marques

a, Manuela Silva

a, and Swiatoslaw Trofimenko

b

a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

b E. I. Du Pont de Nemours & Company, Inc., Experimental Station, Wilmington, Delaware 19880-0302

During the last years we have been studying the reactivity of the U-C bond of -hydrocarbyl

uranium (IV) complexes of general formula UCl2RTpMe2 (TpMe2 = HB(3,5-Me2pz)3. Since it

was found that the reactivity patterns were dependent of the size of the R group, it will be of

interest to determine which effect in the reactivity could be achieved by changing the steric

and/or electronic requirements of the ancillary ligands. We have decided to use the ligand

TpMs

(TpMs

=[HB(3-Mespz)3] ), one of the so-called 2nd

generation Trofimenko’s ligands. The

reaction of UCl4 with Tl[HB(3-Mespz)3] when performed in CH2Cl2 or THF yielded the

complex UCl3[(HB(3-Mespz)2(5-Mespz)] (1) (HB(3-Mespz)2(5-Mespz)=TpMs

*) due to

isomerization of the TpMs

ligand. 1 undergoes metathetical reactions with K[N(SiMe3)2] and

LiC6H4CH2NMe2 to yield the corresponding UCl2XTpMs

* compounds. The crystal and

molecular structures of 1 and 2 were determined by means of X-ray diffraction analysis.

Uranium compounds with Poly(pyrazolyl)borate ligands: attempts to

prepare Uranium cations

Alexandra Rolo de Oliveira, A.Pires de Matos and Isabel Santos

Departamento de Química, ITN, 2686 Sacavém CODEX, Portugal

We have been trying to prepare uranium cations by reacting the compounds

[UCl2{HB(pz)3}2], [UClR{B(pz)4}2] and [UR2{B(pz)4}2] (R=CH3, CH2SiMe3) with AgBPh4

or NHEt3BPh4. Some compounds were obtained, but their full characterization needs crystals

suitable for X-ray crystallographic analysis.


12

Chemistry of Uranium compounds containing the fragment "U{B(pz)4}2"

M. Paula Campello, Ângela Domingos, A.Pires de Matos and Isabel Santos

Departamento de Química, ITN, 2686 Sacavém CODEX, Portugal

Reactions of [UCl2{B(pz)4}2] (1) with LiMe, LiCH2Ph, LiCH2CMe3, LiC6H4-o-CH2NMe2

and LiCH2C6H4-o-NMe2 have been studied in different stoichiometries. Generally, we

observed reduction of the metal, but in the case of LiMe the complex [UClMe{B(pz)4}2] was

isolated and characterized. We also studied the possibility of preparing compounds with U-S

bonds. The complex [U(SiPr)2{B(pz)4}2] has been isolated and characterized, including by X-

ray crystallographic analysis.

Synthesis of Sm (II) and Yb(II) complexes

Irene Lopes, Ângela Domingos, and Noémia Marques Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

We have been studying the capability of the bulkier poly(pyrazol-1-yl)borates, [HB(3-

Mespz)3]- and [HB(3-

tBupz)3]-, to stabilize compounds of lanthanides in low coordination

numbers. Amide and thiolate derivatives of the compounds YbI[HB(3-Mespz)3](thf)2 and

YbI[HB(3-tBupz)3](thf) were obtained, but reactivity studies are still scarce. In some cases the

complexes formed were not stable and disproportionate yielding Yb[HB(3-tBupz)3]2. Due to

accidental presence of HCl in the course of one reaction, crystals of [Yb{(HB(3-Mespz)2(5-

Mespz)}(-Cl)]2 were obtained. The isomerization of the ligand [HB(3-Mespz)3], that must be

related with lability of the M-N bonds induced by the electron withdrawing effect of the

mesityl substituents of the pyrazolyl rings, seems to be a way to decrease steric overcrowding

around the metal centre.

We studied also the ability of the complexes LnTpMe2

(Ln=Sm, Eu; TpMe2

=HB(3,5-Me2pz)3)

to reduce organic substrates. The quinones can be reduced in two one-electron steps.

SmTpMe2

Me2 and EuTpMe2

react with 1,4-benzoquinone in the molar ratio 1:1 to yield the

Ln(III) compounds, LnTpMe2

(OC6H4O). When the reaction is carried in the molar ratio 2:1, the

quinone can be reduced by two samarium centres yielding the complex (SmTpMe2

)2(-

OC6H4O). Due to its lower reducing power, the Eu compound can not reduce the second one-

electron step of the quinone and only EuTpMe2

(OC6H4O) is formed, remaining the excess of

EuTpMe2

unreacted.

SmTpMe2

reduces also benzophenone to yield the ketyl SmTpMe2

(OCPh2) and E2R2 reagents to

yield Sm TpMe2

(ER) compounds.

The compound SmTpMe2

can not reduce protic substrates, but using iodine as a catalyst,

several Sm(III) complexes of the type SmTpMe2

X (X=OPh, pz) could be obtained.


13

Synthesis and characterization of alkoxides and aryloxides of lanthanides

Joaquim Branco, José Manuel Carretas , Adelaide Carvalho, Ângela Domingos, Maria Teresa

Duarte, Joaquim Marçalo, Noémia Marques, António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Alkoxides are known for almost all the elements, but the structural chemistry of these

compounds is dominated by the formation of polymeric structures. Due to the large ionic radii

of the lanthanides, the formation of multinuclear species is still more general for lanthanide

alkoxides, leading to compounds with low solubility and reactivity.

In order to get lanthanide alkoxides of low nuclearity we have been using bulky phenoxo

ligands ([OC6H2Me3-2,4,6]-, [OC6H3Bu

t-2,6]

-, [OC6H2Bu

t-2,6-Me-4]

- and [OC6H2Bu

t3-2,4,6]

-)

or phenoxo ligands bearing an additional ether or amine function ([OC6H4-OCH3-2]-,

[OC6H2-(CH2NMe2)2-2,6-Me-4)]-.and [OC6H2-(CH2NMe2)-2-Me3-3,5,6]-). We have been

using several synthetic routes. Conventional routes such as : a) the alcoholysis of a lanthanide

tris[bis(trimethylsilyl)amido] compound, Ln(N(SiMe3)2)3 ,(Ln=La, Eu, Yb), with HOC6H4-

OCH3-2, HOC6H2-(CH2NMe2)2-2,6-Me-4) and HOC6H2-(CH2NMe2)-2-Me3-3,5,6] in hexane

or toluene solutions at 0 ºC, b) the reaction between LnCl3 (Ln=La, Eu, Yb) and the

potassium salt of the phenoxo ligands [OC6H2Me3-2,4,6]-, [OC6H3Bu

t-2,6]

-, [OC6H2Bu

t-2,6-

Me-4]- and [OC6H2Bu

t3-2,4,6]

- in THF at room temperature and the ammoniacal route c) the

reaction of Yb or Eu metal in liquid ammonia at -78 ºC with 3 equiv. of HOC6H4-OCH3-2.

Full characterization of most of the compounds was not achieved due to the lack of crystals

suitable for X-ray diffraction studies. However, recrystallization from thf/hexane mixtures of

the products obtained by reacting YbCl3 with KOC6H4-OCH3-2 or by reacting ytterbium

metal in liquid ammonia with HOC6H4-OCH3-2 provided crystals for X-ray diffraction

analysis. The compound was formulated as the polymeric [Yb6(3-OH)4(OC6H4-2-OCH3)2(-

OC6H4--OCH3)10(OC6H4--OCH3)2].

We have also been exploring the capability of metallic ytterbium and europium to be

activated by ammonia gas. When ammonia gas is bubbled through a suspension of metal

pieces (Yb, Eu), in a solution of the phenol (C6H2Me3-2,4,6-OH, C6H3But-2,6-OH and

C6H2But3-2,4,6-OH) in THF, the evolution of H2 on the surface of the metal and the

dissolution of the metal is observed. After several hours of stirring, all the metal pieces have

been consumed and a solution is obtained. After the work-up the products were characterized

by several techniques. Unfortunately, this characterization is not completed because we didn't

get crystals to make X-ray crystallographic studies. The reactions of ytterbium and europium metals with several alcohols (methanol, ethanol and

isopropanol) were also studied by this method. Surprinsingly, the metallic europium reacted

directly with the alcohols without amonia gas. Work is in progress in order to get crystals to

complete the characterization of the trivalent ytterbium alkoxides and of the divalent

europium alkoxides.

Some of the compounds formed in these reactions were tested as catalysts in the reaction of

the carboxylation of the methanol to obtain dimethylcarbonate, an industrially important

product.

The ytterbium, europium and rhenium alkoxides {"M(OC6H4-OCH3-2)3", M=Yb, Eu;

"M(OC6H2-N(CH3)2-2-CH3-4,6)", M=La, Yb; ReOBPz4(OCH3)2} and the intermetallic

compounds {YbNi, YbCu} obtained by ammoniacal synthetic route were tested in batch

conditions (50 0C/50 bar), but they did not show activity for this reaction. However, ytterbium

: nickel (1:1) alloys obtained by MVS showed to be active, with 78% of conversion of

methanol to dimethyl carbonate.


14

Rhenium Chemistry

Synthesis, Characterization and Study of the Redox Properties of

Rhenium(V) Diolates. Attempts to Prepare some 99m

Tc Analogues

Dina Nunesa, Ângela Domingos

a, António Paulo

a, Luciana Patrício

a, Isabel Santos

a,

M. Fernanda N. N. Carvalhob, and Armando J. L. Pombeiro

b

a Departamento de Química e Radioisótopos, ITN, 2686 Sacavém Codex, Portugal

b CQE, Complexo 1, Instituto Superior Técnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal

Abstract

Rhenium(V) diolate complexes of the type [ReO(diolate){3-B(pz)4}] (diolate =

OCH(CH3)CH2O2-

(3), OCH(CH3)CH(CH3)O2-

(4), OC(CH3)2C(CH3)2O2-

(5) OCH2CH2CH2O2-

(6), OC6H10O2-

(7) and OCH2CH2CH2CH2O2-

(8),) have been obtained by reacting [ReO{3-

B(pz)4}(OMe)2] (1) with the corresponding diols, in CH2Cl2, or by one step preparation using

[ReOCl3(PPh3)2], K[B(pz)4] and the respective diols. These compounds have been

characterized by elemental analyses, IR, 1H NMR spectroscopy and, in some cases, by mass

spectrometry. The redox properties of these and related complexes were studied by cyclic

voltammetry and by controlled potential electrolysis. 1 crystallizes from methanol in the

monoclinic space group P21/c with cell parameters a=10.539(2) Å, b=13.556(2) Å, c=12.153

(2) Å, =92.04(2)º, V=1735.2(5) Å3, Z=4. The possibility of preparing some diolate

99mTc

analogues was also evaluated and will be described.

Submitted to Inorganic Chemistry.

Current Work

Trans-Dioxo Rhenium Complexes

António Paulo, Ângela Domingos and Isabel Santos* Departamentos de Química e Radioisótopos, ITN, 2686 Sacavém Codex, Portugal

We have been studying the reactivity of the complex [ReO(-O){B(pz)4}]2 (1) towards neutral

substrates. In this type of reactions we observed the formation of trans-dioxo complexes. The

structural characterization of trans-[ReO2{2-B(pz)4}(pyridine)2] has been made and the the

affinity of the rhenium for neutral phosphorous donor ligands is beeing studied.


15

Synthesis, Characterization and Reactivity Studies of Rhenium Complexes

with Cores [Re≡N]2+

and [Re=O2]+

K. Rajender Reddy and Isabel Santos Departamento de Química, ITN,2686 Sacavém Codex, Portugal

We have been investigating the reactivity of poly(pyrazolyl)borates of the type K[H2B(pz*)2]

(pz* = pyrazolyl, 3,5-dimetilpyrazolyl) and K[B(pz)4] with rhenium compounds with the

core [Re=O].1-3

It was found that the reactions depend on the number of hydrogens

coordinated to the boron, on the substituints in the pyrazole ring and on the nature of the

solvent. To evaluate whether these reactions depend on the electronic properties of the metal,

we extend our studies to rhenium compounds with the cores [Re≡N]2+

and cis-[Re=O2]+.

We studied reactions of K[B(pz)4] with cis-[ReO2(PPh3)2I] and cis-[ReO2(py)4]+ in

different solvents. The compounds obtained are under characterization, and we are trying to

get single crystals for X-ray crystallographic analysis.

1- António Paulo, Ângela Domingos, A.Pires de Matos, Isabel Santos, M. Fernanda Carvalho,

A. Pombeiro, Inorg. Chem. 1994, 33, 4729.

2- António Paulo, Ângela Domingos, Joaquim Marçalo, A.Pires de Matos and Isabel Santos,

Inorg. Chem. 1995, 34, 2113.

3- António Paulo, Ângela Domingos and Isabel Santos, Inorg. Chem. 1996, 35, 1798.


16

Gas Phase Chemistry

Gas Phase Actinide Ion Chemistry: Activation of Alkanes and Alkenes by

Thorium Cations

Joaquim Marçalo, João Paulo Leal, and António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

The activation of methane and of several small alkanes and alkenes by thorium cations, as

studied by FT-ICR/MS, is described. Thermalized Th+ ions dehydrogenate methane with a

rather low efficiency (k/kL = 0.02) to form ThCH2+. Th

+ ions react exothermically with the

studied alkanes (ethane, propane, n-butane, isobutane and cyclopropane) and alkenes (ethene,

propene and 1-butene): single and/or double dehydrogenation is observed for all the substrates

studied and, in the case of cyclopropane, propene and 1-butene, loss of hydrocarbons is also

observed. C–C coupling processes occur in secondary reactions of the products formed, in the

case of cyclopropane and the alkenes. This study indicates that Th+ ions are more reactive than

U+ ions. A tentative preview of 5f metal ion reactivity is also presented, based on comparisons

of the data reported herein with available data on lanthanide and uranium ions.

Int. J. Mass Spectrom. Ion Processes 157/158 (1996) 265.


17

Studies on gas-phase chemistry of actinides - The role of f electrons in their

chemistry

António Pires de Matos and Joaquim Marçalo Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

Recent work in our laboratories using FT-ICR mass spectrometry allowed us to compare the

gas phase reactivity of thorium ions with the data already described for uranium and the

lanthanide series ions. Based on these reactivity studies, some aspects of the role of f electrons

in the observed chemistry are addressed.

The reactivity studies of actinide ions have been practically limited to U+ and Th

+. Published

work for U+ is scarce and recent work allowed us to compare the reactivity of thorium ions

with the data already described for uranium and the lanthanide series ions. The efficiencies

and product distributions of the reactions of Th+ and U

+ ions with hydrocarbons clearly

demonstrate that Th+ is more reactive than U

+. U

+ exhibits a more rich chemistry than its

congener of the 4f series Nd+; with our work we were able to show that Th

+ is also more

reactive than its lanthanide congener Ce+.

For the actinide ions, the trends along the series are somewhat different from the lanthanide

ions. At the beginning of the series, from Ac+ to Np

+, there are several low-lying

configurations with at least two non f electrons available to the ions. In the case of Th+, the

ground state is already 6d27s. From the greater spatial extension of the 5f orbitals in the first

half of the actinide series compared to the 4f orbitals, we can as well expect a non-negligible

participation of the 5f electrons in the bonding, facilitating in this way the reactivity.

Based on these simple electronic structure arguments and also on the experimental results

already obtained for Th+ and U

+, we can anticipate that the actinide series ions Ac

+, Pa

+, Np

+

and Cm+ could bring about the activation of hydrocarbons, while for Pu

+, Am

+ and the

remainder of the actinide series ions from Bk+ to the end reduced reactivity should be

observed. Further experimental work on actinide ions is needed to get a better insight on a

possible 5f electron contribution to reactivity. Unfortunately protactinium and the

transuranium elements are extremely toxic and a dedicated instrument for gas phase chemistry

is needed. We have no knowledge of the existence of such facility. We think that the gas

phase chemistry of actinides is a subject that is worthwhile to explore and the results of the

research could complement the contribution given by condensed phase chemists to understand

the role of 5f electrons in actinide chemistry.

Extended Abstracts, CO1, Vol. I., Eds. F. David and J.C.Krupa, I.P.N., Orsay.

Communication to: 4th International Conference on Nuclear and Radiochemistry, St. Malo,

France, 8-13 September 1996.


18

Activation of Phenol by Lanthanide Monocations in the Gas Phase

M. Pissavini, S. Géribaldi, J. Marçalo,* M. Decouzon, M. Azzaro

Groupe FT-ICR, Laboratoire de Chimie Physique Organique, Université de Nice-Sophia

Antipolis, Parc Valrose, 06108 Nice Cedex 2, France

*Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

It is now well established that the knowledge of the phenomena of activation of organic

molecules by “naked” metal ions in the gas phase is indispensable to the understanding of

processes occurring in the condensed phase, in particular in what respects catalysis [1].

Although, and contrarily to the metals of the first two transition series, lanthanide ions have

been relatively neglected, these last years have witnessed a considerable development of

studies of the reactivity of these metals in the gas phase. Rare earth metals are being

increasingly used either in organic synthesis and in the fabrication of high-tech materials [2].

Recent work has shown that the gas phase reactivity of lanthanide, scandium and yttrium

cations toward arenes, and in particular benzene, is directly related to the ground-state electron

configuration of the cation: the metal ions presenting a d1s

1 ground state or a sufficiently weak

promotion energy to reach such a state, activate the C-H bonds of the arenes, while the others

only form adducts [3]. In our Laboratories we have shown that the reactivity of these cations

with oxygenated compounds is related to their oxophilicity, and that C-O and O-H bonds were

always activated according to different processes [4].

In this work, we have studied competitive activation reactions of C-H, C-O and O-H bonds of

phenol by three rare earth cations showing different ground-state electronic configurations

(gs) and different promotion energies (PE): Sc+ (gs: 4s

13d

1, PE = 0 eV), Y

+ (gs: 5s

2, PE = 0.15

eV) and Lu+

(gs: 6s2, PE = 1.63 eV).

Apparently, the general reactivity is similar for the three metal ions, and there is simultaneous

activation of the O-H bond and of the aromatic C-H bonds. However, the mechanisms that can

explain the activation reactions effectively depend on the metal ion.

Acknowledgement: We thank Bruker-France for support.

1- Martinho Simões, J.A.; Beauchamp, J.L. Chem. Rev. 1990, 90, 629; Eller, K.; Schwarz, H.

Chem. Rev. 1991, 91, 1121; Eller, K. Coord. Chem. Rev. 1993, 126, 93.

2- Takaki, K.; Fujiwara, Y. Appl. Organomet. Chem. 1990, 4, 297; Schumann, H.; Meese-

Marktscheffel, J.A.; Esser, L. Chem. Rev. 1995, 95, 865; Hubert-Pfalzgraf, L.G. New J. Chem.

1995, 19, 727.

3- Yin, W.W.; Marshall, A.G.; Marçalo, J.; Pires de Matos, A. J. Am. Chem. Soc. 1994, 116,

8666.

4- Breton, S.; PhD Thesis, Université de Nice-Sophia Antipolis, 1995; Azzaro, M.; Breton, S.;

Decouzon, M.; Geribaldi, S. Int. J. Mass Spectrom. Ion Processes 1993, 128, 1; Geribaldi, S.;

Breton, S.; Decouzon, M.; Azzaro, M. New J. Chem. 1995, 19, 887.

Communication to: 9ème

Journée de la Chimie / Provence-Alpes-Côte d’Azur, Nice, France,

March 22, 1996.


19

Current Work

Reactivity of alkaline earth metal and oxide ions with

pentamethylcyclopentadiene in the gas phase

Joaquim Marçaloa, António Pires de Matos

a and William J. Evans

b


b Department of Chemistry, University of California, Irvine

The gas-phase reactivity of the alkaline earth metal (Ca+, Sr

+ and Ba

+) and oxide (CaO

+, SrO

+

and BaO+) ions with pentamethylcyclopentadiene was studied by FTICR/MS, for comparative

purposes with previous results obtained with lanthanide (Ln = La - Lu) and group 3 (Sc and

Y) metal and metal oxide ions. The alkaline earth metal ions were produced by laser

desorption/ionization of metal hydroxide pellets and the oxide ions by reaction of the metal

ions with N2O introduced through pulsed valves. The organic reagent was admitted to the

instrument through a leak valve, and pulsed-in argon was used for collisional cooling of the

reagent ions. The reactivity of the metal cations was similar to the one observed before for

Sm+, Eu

+, Tm

+ and Yb

+, namely the formation of the fulvenide ion (C5Me4CH2)M

+ as main

primary product and of the metallocene ion (C5Me5)2M+ as main secondary product. These

similarities in the reactivity can be explained by the similar behaviour of the s1 ground states

of the group 2 metal ions and the fns

1 ground states (with large promotion energies to f

n-1d

1s

1

states) of the referred lanthanide ions. In the case of the metal oxide ions MO+, the reactivity

with pentamethylcyclopentadiene, being mainly determined by the strength of the M+ – O

bonds, again showed similarities with EuO+ and YbO

+ (the lanthanide ions with the weakest

M+ – O bonds, similar to the ones present in the alkaline earth oxide ions), with formation of

MOH+ as main primary product and M(C5Me5)

+ as secondary product.

Gas phase reactivity of rare earth ions with alcohols, phenols and other

oxygenated molecules

José Manuel Carretasa, Joaquim Marçalo

a, António Pires de Matos

a, Serge Geribaldi

b, Marc

Pissavinib, Michele Decouzon

b, Maurice Azzaro

b


b Laboratoire de Chimie Physique Organique, Université de Nice-Sophia Antipolis

The gas phase reactions of the rare earth ions Sc+, Y

+ and Ln

+ (Ln = La - Lu) with isopropanol

and phenol were studied by FT-ICR/MS. The metallic ions were produced by laser ionisation

of the corresponding metals and were thermalised by collisions with argon; the reagents were

introduced through leak valves to pressures of (1-5) 10-7

Torr. All the ions except Yb+

reacted exothermically with isopropanol and phenol, with formation of MO+ and MOH

+ ions

as primary products, as well as of MOC6H4+ in the case of phenol, a product resulting from

the simultaneous activation of O-H and aromatic C-H bonds. The primary product ions

participate in subsequent reactions that lead to M(OR)x(HOR)y+ species, where x = 1-2 and y

= 0-3. The detailed study of the mechanisms of the primary reactions, of the reaction

sequences, of the corresponding kinetics and of the energies involved in the various steps,

showed important differences in the relative reactivity of the metallic ions.


20

Gas phase synthesis of lanthanide and actinide - transition metal

intermetallic ions

Maria da Conceição Vieira, Joaquim Marçalo and António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

FT-ICR/MS was used to study the formation of intermetallic ions involving metals of the f

and d blocks. In particular, the series of ions LnFe+ (Ln = La - Lu), as well as ThFe

+ and UFe

+,

were synthesized by gas phase reaction of the metal ions, produced by laser ionization of pure

metal pieces, with the volatile carbonyl complex Fe(CO)5, followed by excitation and

collision with argon of the MFe(CO)2+ product ions formed. Advantage was taken from the

potentialities of the FT-ICR/MS technique for performing kinetic studies, which showed that

significant differences in reaction efficiencies existed along the lanthanide series.

Gas phase reactivity of lanthanide oxide cluster ions with small oxygenated

molecules

Joaquim Marçaloa, António Pires de Matos

a, Hans H. Cornehl

b, Christoph Heinemann

b and

Helmut Schwarzb


b Institut für Organische Chemie, Technische Universität Berlin

The reactivity of several lanthanide (Ln = La, Pr, Eu, Tb, Ho, Tm, Lu) oxide cluster cations

LnxOy+ with O2, N2O and H2O in the gas phase was studied by FT-ICR/MS. The cluster ions

were produced by direct laser desorption/ionization of surface oxidized metal pieces or of

metal oxide pellets, and the reagents were admitted to the mass spectrometer through a leak

valve; argon, introduced through pulsed valves, was used for collisional cooling of the reagent

ions. Oxydation reactions with O2 and N2O were observed for some cluster ions, while the

reactivity with water corresponded only to adduct formation. Several effects of the formal

metal valency in the cluster ions as well as of the cluster size on the reactivity and in the

kinetics could be observed.

Characterization and reactivity of transition metal oxide cluster anions in

the gas phase

Maria da Conceição Oliveira*, Maria Alzira Almoster Ferreira

* Joaquim Marçalo

+, Maria da

Conceição Vieira+

* Departamento de Química, FCUL

+ Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Laser desorption/ionization was used in conjunction with FT-ICR/MS to produce and

characterize first-row transition metal oxide anions of the type MxOy-, with M = Mn, Fe, Co,

Ni and Cu. Metal oxide pellets were used as targets and argon, introduced through pulsed

valves, was used for collisional cooling of the reagent ions. Methanol was used to probe the

reactivity of these barely studied anionic species, uncovering important effects of the nature of

the metal and of cluster size in the reaction products formed and in the corresponding kinetic

efficiencies.


21

Thermochemistry

Alkaline metal alkoxides

João Paulo Leala, P. Nunes

b, M. E. Minas da Piedade

b

aDepartamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal

Abstract

In spite of the wide use of alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) in synthetic

chemistry, thermochemical data for this family of compounds are scarce. The knowledge of

their enthalpies of formation, lattice energies, etc. is of key importance to predict new data and

to discuss the energetics of several reactions involving alkaline metal alkoxides. One example

is the study of the formation and reactivity of the now commonly used super-bases (mixed

aggregates of alkillithium compounds and alkaline metal alkoxides).

In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;

R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The

corresponding lattice energies, LUº, were also derived, and used to calculate thermochemical

radii, r-, for the alkoxi anions, from the Kapustinskii equation. The estimation of new data for

MOR compounds is discussed using the results obtained in the present work and those

previously published for LiOR and NaOR compounds.

Communication to: Reunião final do Network “Selective Processes and Catalysis Involving

Small Molecules”, ITQB, Oeiras, Portugal, April 1996.

Bond dissociation enthalpies in U-L. What’s the real value?

João Paulo Leala, Noémia Marques

a, J. Takats

b

a Instituto Tecnológico e Nuclear, Dep. Química, Est. Nac. nº 10, P-2686 Sacavém Codex, Portugal

b Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2

Abstract

Uranium-ligand bond dissociation enthalpies had been widely studied in last years (see a

compilation of existing values in ref. 1). Despite of the considerable quantity of data already

known doubts about their absolute value persist. This is mainly due to the fact that

experimentally differences between two bonds are measured, and than one of them is assumed

(or estimated) and considered as an anchor being all the others related to that one.

On the present work the energetic of the U-O, U-I and U-Cl bonds in compounds of the type

UI2L{HB(dmpz)3} (L=O-tBu, I; dmpz=3,5-dimethylpirazole) and UCl3{HB(dmpz)3} have

been studied by means of oxidative reactions of UI2{HB(dmpz)3}.2thf with appropriate

reagents and using reaction solution calorimetry. The results allow a critical review of

literature data and suggest that a universal scale for uranium-ligand bond dissociation

enthalpies can be achieved.

1) J. P. Leal, J. A. Martinho Simões, J. Chem. Soc. Dalton Trans.1994, 2687.

Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.


22

Potassium and Cesium alkoxides energetics

João Paulo Leal,a P. Nunes,

b M. E. Minas da Piedade

b


bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal

Abstract

Alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) had been extensively used in

synthetic chemistry. Despite that thermochemical data for this family of compounds are

scarce. The knowledge of their energetics is crucial to predict new data and to discuss the

energetics of several reactions involving alkaline metal alkoxides [eg.: super-bases (mixed

aggregates of alkillithium compounds and alkaline metal alkoxides)].

In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;

R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The

corresponding lattice energies were also derived, and used to calculate thermochemical radii,

r-, for the alkoxi anions assuming a ionic lattice structure. This values allow the estimation of

new data for other MOR compounds not yet studied. Critical review of previously published

data for LiOR and NaOR compounds is also made1.

1

(a) J. P. Leal, A. Pires de Matos, J. A. Martinho Simões, J. Organometal. Chem. 1991, 403,

1; (b) J. P. Leal, J. A. Martinho Simões, J. Organometal. Chem. 1993, 460, 131.

Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.


23

Surface Studies

Photon stimulated ion desorption of C2H4 adsorbed on graphite

J.M. Coquel1, T. Almeida Gasche

1,2, J. Wilkes

1,3, C. M. Friedrich

4, C.L.A. Lamont

3, M.A.

MacDonald5, R.E. Palmer

1, A.M.C. Moutinho

6

1 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of

Birmingham, Edgbaston, Birmingham B 15 2 TT, U K 2 Instituto Tecnológico e Nuclear, Dep. de Química, Estrada Nacional 10, 2685 Sacavém, Portugal

3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK

4 Cavendish Laboratory, Univ. of Cambdrige, Cambdrige CB3 OHE, UK

5 CLRC, Daresbury Laboratory, Warrington WA4 4AD, UK

6 GIDS/ CeFITeC, Dep. de Física, FCT, Univ. Nova de Lisboa; 2825 Monte da Caparica, Portugal

Abstract Photon stimulated desorption from C2H4 on highly oriented pyrolitic graphite using VUV synchroton radiation in the energy range 13-40 eV was studied. In contrast with gas phase measurements, only H

+ ions are detected. This is due to the image potential barrier to

desorption from the surface and unequal distribution of kinetic energy amongst the molecular photofragments. The yield of desorbed H

+ ions shows a threshold at 20.5 eV and a resonance

at 24 eV. This behaviour is different from the gas phase and is attributed to selective quenching of excited molecular electronic states on the surface and to chemical reactions between specific molecular dissociated fragments and the substrate.

Communication to: ECOSS 16 (16

th European Conf. on Surface Science), Sept. 1996, Genova,

Italy and also in Física 96, (10 th

Nacional Conf. of Physics), Sept. 1996, Faro, Portugal.

Sample holder for using in surface studies (77-1300 K)

Carlos M.M. Leitão1, Teresa Almeida Gasche

2, Roger Bennet

3, O. M. N. Teodoro

1, G.

Bonfait2, A.M.C. Moutinho

1

1 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de

Lisboa; 2825 Monte da Caparica, Portugal 2 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal

3 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of

Birmingham, Edgbaston, Birmingham B 15 2 TT, U K

Abstract

The construction of this sample holder have as aim to conceive a system where quick cycles

of cooling and heating would be possible, in the temperature range 77-1300 K. The sample

holder is mounted in a horizontal position. A molybdenum support will be used to mount the

sample. The heating will be done by electronic bombardment. The cooling system is a "cold

finger" type.

The sample holder is going to be used in a surface system in each several surface techniques

are available, e.g. XPS- X-Ray Photoelectron Spectroscopy; AES- Auger Electron

Spectroscopy, ESD- Electron Stimulated Desorption, TDS- thermal Desorption Spectroscopy.

The sample holder will allow not only to work at low temperatures but also to do annealing to

crystals.

Communication to: FÍSICA 96 -10 th

Nacional Conference of Physics, Faro, Portugal,

13-17 September 1996.


24

Carbon-dioxide adsorbed on graphite: a photon stimulated desorption study

J. M. Coquel1, L. Siller

1, R. E. Palmer

1, R. Carrapa

2, A.M.C. Moutinho

2, J. Wilkes

3, C.L.A.

Lamont3, T. Almeida Gasche

4

1 Nanoscale Physics Research Laboratory, School of Physics and Space Research, University of

Birmingham, Edgbaston, Birmingham B 15 2 TT, U K; 2 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de

Lisboa; 2825 Monte da Caparica, Portugal; 3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK;

4 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal

Abstract

Carbon-dioxide physisorbed on graphite at 50 K was studied by photon stimulated desorption

(PSD) graphite using VUV synchrotron radiation in the energy range 13-40 eV 1. Previous

studies showed that the physisorption of CO2 on graphite was not possible for temperatures

below 104 K 2,4. The results obtained in our studies are in contradiction with these

conclusions.

The sample was heated to 900 K. The measurements were done for different dosages of CO2,

in the range of 0.18 to 3.0 L. H+, CO

+ and O2

+ were the ions detected. In the mass

spectrometer, neither negative ions or neutral species were observed. The yield of desorbed

O2+ ions shows a threshold at 15 eV and a resonance at 25 eV. The yield of desorbed CO

+ ions

shows a small resonance at 15 eV and a threshold at 25 eV.

[1] Bennet, R.A.; Sharp, R.J. ; Guest, R.J.; Barnard, J.C.; Palmer, R.E.; MacDonald, M.A.;

Chemical Physics Letters, 98 (1992) 241.

[2] Terlain, A., Laeher, Y., Surface Science, 125 (1983) 304.

[3] Morishige, K., Molecular Physiscs, 78 (1993) 1203.

Communication to: FÍSICA 96 -10 th

Nacional Conference of Physics, Faro, Portugal,

13-17 September 1996.


25

Special Publications

Handling of air sensitive compounds

João Paulo Leal Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

Is quite usual in chemistry to handle compounds that react with the water and the oxygen

presents in atmosphere. Several techniques had been developed to allow the work in

environments with a composition distinct from that of the earth atmosphere, the so called

“inert atmospheres”. A general overview of such techniques is presented with special

relevance to vacuum and inert gas systems, “Schlenk” type systems and gloveboxes.

Química, 1996, 59, 56.

The strenght of a chemical bond

João Paulo Leal Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal

Abstract

The strength of a chemical bond is introduced, although in a qualitative way, very early in the

curricula of most chemistry courses. But sometimes it is not fully understanded. Some

considerations about this subject are made and the definition of bond dissociation enthalpy

(D) and bond enthalpy term (E) are introduced.

Submitted to J. Chem. Ed.


26

inorganic and organometallic chemistry · inorganic, organometallic and intermetallic compounds of...

Documents