Hydride-alkenylcarbyne to alkenylcarbene transformation in bisphosphine-osmium complexes

Abstract

The elongated dihydrogen complex [Os{C6H4C(O)CH 3}(η2-H2)(H2O)(P iPr3)2]BF4 (1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-π-r-alkynol derivatives [OsH{=C=CHC(OH)R 2}{η2-HC≡CC(OH)R2}(P iPr3)2]BF4 (R = Ph (2), Me (3)), where the π-alkynols act as four-electron donor ligands. Treatment of 2 and 3 with HBF4 and coordinating solvents leads to the dicationic hydride-alkenylcarbyne compounds [OsH(≡CCH=CR2)S 2(PiPr3)2][BF4] 2 (R = Ph, S = H2O (4), CH3CN (5); R = Me, S = CH3CN (6)), which in acetonitrile evolve into the alkenylcarbene complexes [Os(=CHCH=CR2)(CH3CN)3(P iPr3)2][BF4]2 (R = Ph (7), Me (8)) by means of a concerted 1,2-hydrogen shift from the osmium to the carbyne carbon atom. Treatment of 2-propanol solutions of 5 with NaCl affords OsHCl2(≡CCH=CPh2)(PiPr3) 2 (10), which reacts with AgBF4 and acetonitrile to give [OsHCl-(≡CCH=CPh2)(Ch3CN)(PiPr 3)2]BF4 (11). In this solvent complex 11 is converted to [OsCl(=CHCH= CPh2)(CH3CN)2(P iPr3)2]BF4 (12). Complex 5 reacts with CO to give [Os(=CHCH=CPh2)(CO)(CH3CN) 2-(PiPr3)2][BF4] 2 (15). DFT calculations and kinetic studies for the hydride-alkenylcarbyne to alkenylcarbene transformation show that the difference of energy between the starting compounds and the transition states, which can be described as η2-carbene species (Os=C(R)H), increases with the basicity of the metallic center. The X-ray structures of 4 and 7 and the rotational barriers for the carbene ligands of 7, 8, and 12 are also reported. © 2005 American Chemical Society.