phosphido-borane stabilised tetrylenes presentation final final
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Phosphido-Borane
Stabilised Tetrylenes
By Alexander Craig
Stabilisation of Group 14 (II) Oxidation States
Heavier Group 14 elements favour (II) oxidation state versus (IV) oxidation state, E = Pb > Sn > (Ge), eg PbI2
Heteroatom (NR2, PR2) ligands: Thermodynamic stabilisation
Efficient pπ-pπ orbital overlap in planar configuration
P: Higher energetic barrier to planarization (planar only seen once in tetrylene systems)
Bulky hydrocarbon ligands: Kinetic stabilisationSnP P
PhPh
Armes2 Armes2
(1) P. P. Power et al., Inorg. Chim. Acta., 2007, 360, 1278-1286.
Phosphine-Borane Stabilised Carbanion Tetrylenes Sn(II) centre with two carbanion ligands Agostic-type interactions between B-H…E contacts, (E =
Sn, Pb) Delocalisation of electron density from B-H σ-orbitals
into vacant pπ-orbital on E
EPMe2RMe2Si
SiMe2RMe2P
H2B
BH2
H
H
(1) K. Izod et al., Organometallics, 2009, 28, 2211-2217.(2) K. Izod et al., Organometallics, 2009, 28, 5661-5668.
E
SiMe2
Me2Si
Me3Si
Me3Si
Me2P
PMe2
BH3
BH3
Project Aims
Synthesis and characterisation of [R2P(BH3)]- ligands Investigate [R2P(BH3)]- ligands in the stabilisation of low
valent Sn(II) centres Isolation and characterisation of novel bis-phosphido-
borane stannylenes, [R2P(BH3)]2Sn
R2PLi2SnCl2
THF, -78 oC SnP P
H2B BH2
H H
R RR R
2 LiClBH3
-105-95-85-75-65-55-45-35-25-15-5f1 (ppm)
Synthesis of Phosphido-Borane Precursor LigandPCl3
2 MesMgBrEt2O, -78 oC
Mes2PClLiAlH4 Mes2PH
Et2O, 0 oC
Mes2PHBH3.SMe2THF, RT Mes2PH
BH3
Mes2PHBH3 n-BuLi
THF, RT Mes2PLiBH3
31P NMR spectra in CDCl3 or THF-d8/toluene-d8
Mes2P [Li(THF)2]BH3BH3
Mes2PLiBH3 BH3.SMe2
THF, RT
Crystal Structure Analysis
η2-B…Li = 2.426(3) Å
η2-B2…Li = 2.455(4) Å
η1-B2…Li = 2.505(4) Å
R3PB H
H H Li R2PB2
B1
H HH
HHH Li
Attempted Synthesis of [Mes2P(BH3)]2Sn
Rapid decomposition: P-Sn bond
weaker vs C-Sn No pπ-pπ
overlap Reductive
phosphorus centre
Mes2PLiBH3
2SnCl2
THF, -78 oC Decomposition Products
-95-90-85-80-75-70-65-60-55-50-45-40-35-30-25-20-15-10-5f1 (ppm)
Mes2P [Li(THF)2]BH3BH3
Mes2PHBH3
Mes2PH
31P NMR spectrum in THF
Attempted Synthesis of [Dipp2P(BH3)]2Sn
Dipp: Increased kinetic stabilisation
Rapid decomposition
-100-95-90-85-80-75-70-65-60-55-50-45-40-35-30-25-20-15f1 (ppm)
Dipp2PLi2SnCl2
THF, -78 oC Decomposition ProductsBH3
Dipp2P [Li(THF)2]BH3BH3
Dipp2PHBH3
Dipp2PH
31P NMR spectrum in THF
Synthesis of [Ph2P(BH3)]Li in situ
-60-55-50-45-40-35-30-25-20-15-10-505101520f1 (ppm)
Ph2PHBH3.SMe2THF, RT Ph2PH
BH3
Ph2PH n-BuLiTHF, RT Ph2PLi
BH3BH3
Ph2PH
31P NMR spectra in CDCl3 or THF-d8/toluene-d8
Attempted Synthesis of [Ph2P(BH3)]2Sn
-55-45-35-25-15-505101520253035404550f1 (ppm)
[{Ph2P(BH3)}3Sn]Li(THF)
JSnP = 1630 Hz
Ph2PLiBH32
SnCl2THF, -78 oC [{Ph2(BH3)}3Sn]Li(THF) X
The stannate, [{Ph2P(BH3)}3Sn]Li(THF), was isolated by crystallisation from toluene
X
31P NMR spectrum in THF
Crystal Structure of [{Ph2P(BH3)}3Sn]Li(THF)
η2-B1…Li = 2.470(13) Å
η1-B2…Li = 2.798(14) Å
η2-B3…Li = 2.477(14) Å
Attempted Synthesis of [Ph2P(BH3)]2Sn
-29-27-25-23-21-19-17-15-13-11-9-8-7-6-5f1 (ppm)
31P NMR spectrum in THF-d8/toluene-d8
Ph2PLiBH32
SnCl2THF, -78 oC [{Ph2(BH3)}3Sn]Li(THF)
[{Ph2P(BH3)}3Sn]Li(THF)
JSnP = 1630 Hz
-16.5-15.5-14.5-13.5-12.5-11.5-10.5-9.5-8.5-7.5-6.5f1 (ppm)
Direct Synthesis of [{Ph2P(BH3)}3Sn]Li(THF)
Ph2PLi3SnCl2
THF, -78 oC [{Ph2P(BH3)}3Sn]Li(THF)BH3
JSnP = 1630 Hz
-85-80-75-70-65-60-55-50-45-40-35f1 (ppm)
JSnP = 1630 Hz
31P NMR spectrum in THF-d8/toluene-d8119Sn NMR spectrum in THF-d8/toluene-d8
Summary Isolated & characterised novel
dimesitylphosphido-borane & bis-(borane) lithium salts Agostic-type interactions between BH3 and lithium
Rapid decomposition of bis-phosphido-borane stabilised stannylenes, [R2P(BH3)]2Sn, where R = Mes, Dipp
Isolated & characterised the novel tris-phosphido-borane stannate, [{Ph2P(BH3)}3Sn]Li(THF) No agostic-type interactions between BH3 and Sn(II)
Acknowledgements
I would like to thank: Dr Keith Izod Peter Evans Claire Jones Dr Paul Waddell Richard Wardle
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