298705-05-2Relevant articles and documents
Reactivity patterns of carbyne hydride complexes of tungsten
Bannwart, Ewald,Jacobsen, Heiko,Furno, Franck,Berke, Heinz
, p. 3605 - 3619 (2008/10/08)
Tungsten carbyne chlorides of the type W(CMes)(CO)(Cl)L2L′ (L = P(OMe)3, L′ = CO (2a); L = PMe3, L′ = CO (2b); L = P(OiPr)3, L′ = pyridine (py) (2c); L =PPh3, L′ = CO (2d); 2L = Ph2PCH2CH2PPh2, L′ = CO (2e)), W(CMes)(CO)(Cl)L3 (L = P(OMe)3 (3a); L = PMe3 (3b); 3L = Ph2PCH2CH2)2PPh (3d)), and W(CMes)(Cl)L4 (L = P(OMe)3 (4a)) have been prepared by starting from W(CMes)(CO)2(Cl)(py)2 (1). Treatment of the chloride complexes with NaBH4 in THF furnished the borohydride adducts W(η2-H2BH2)(CMes)(CO)L2 (L = P(OMe)3 (5a); L = PMe3 (5b); L = P(OiPr)3 (6c); L =PPh3 (5d)) and W(η2-H2BH2)(CMes)L3 (L = P(OMe)3 (6a)), which served as precursors for new tungsten carbyne hydrides. The compounds W(CMes)(CO)(H)L3 (L = P(OMe)3 (7a); L = PMe3 (7b); 3L = (Ph2PCH2CH2)2PPh (7d)) and W(CMes)(H)L4 (L = P(OMe)3 (8a)) were obtained from the reaction of the borate complexes 5a,b,d and 6a with quinuclidine in THF at -20°C in the presence of excess phosphorus donor ligands. The hydrides can be kept and characterized at low temperatures but decompose when warmed to room temperature. The reactivity of this novel class of compounds has been investigated for 7a, which reacts even at low temperatures with phenol, carbon dioxide, and unsaturated organic compounds. In the presence of excess phosphorus donor ligands or CO, 7a rearranges into the carbene complexes W(CHMes)(CO)(L)(L′)(P(OMe)3)2 (L = L′ = P(OMe)3 (15a); L = L′ = PMe3 (15b); L = P(OMe)3, L′ = CO (16)) via intramolecular hydride migration. A similar reaction could not be observed for 7d or 8a. Density functional calculations support the notion that this transformation is initiated by ligand dissociation and that formyl species are not likely to occur as reaction intermediates. Reaction of 3a with HCl provides access to another carbene complex, W(CHMes)(Cl)2(CO)(P(OMe)3)2 (17). It was concluded from NMR spectroscopy that the carbene ligand in the d4 complex 17 pivots in place to establish an η2-type coordination with an agostic interaction.
