Reactivity patterns of carbyne hydride complexes of tungsten

Tungsten carbyne chlorides of the type W(CMes)(CO)(CI)L2L' (L = P(OMe)(3), L' = CO (2a); L = PMe3, L' = CO (2b); L = P((OPr)-Pr-i)(3), L' = pyridine ( py) (2c); L=PPh3, L' = CO (2d); 2L = Ph2PCH2CH2PPh2, L' = CO (2e)), W(CMes) (CO)(Cl)L-3 (L = P(OMe)(3) (3a); L = PMe3 (3b); 3L = Ph2PCH2CH2)(2)PPh (3d) ), and W(CMes)(Cl)L-4 (L = P(OMe)(3) (4a)) have been prepared by starting f rom W(CMes)(CO)(2)(Cl)(py)(2) (1). Treatment of the chloride complexes with NaBH4 in THF furnished the borohydride adducts W(eta(2)-H2BH2)(CMes)(CO)L- 2 (L = P(OMe)(3) (5a); L = PMe3 (5b); L = P((OPr)-Pr-i)(3) (5c); L =PPh3 (5 d)) and W(eta(2)-H2BH2)(CMes)L-2 (L = P(OMe)(3) (6a)), which served as prec ursors for new tungsten carbyne hydrides. The compounds W(CMes)(CO)(H)L-3 ( L = P(OMe)(3) (7a); L = PMe3 (7b); 3L = (Ph2PCH2CH2)(2)PPh (7d)) and TN(CMe s)(H)L-4 (L = P(OMe)(3) (8a)) were obtained from the reaction of the berate complexes 5a,b,d and 6a with quinuclidine in THF at -20 degrees C in the p resence of excess phosphorus donor ligands. The hydrides can be kept and ch aracterized at low temperatures but decompose when warmed to room temperatu re. The reactivity of this novel class of compounds has been investigated f or 7a, which reacts even at low temperatures with phenol, carbon dioxide, a nd unsaturated organic compounds. In the presence of excess phosphorus dono r 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 Sa. Density functional calculations support the notion that this transformation is initiated by ligand dissociation and tha t formyl species are not likely to occur as reaction intermediates. Reactio n 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 c arbene ligand in the d(4) complex 17 pivots in place to establish an eta(2) -type coordination with an agostic interaction.