Hydride-Alkenylcarbyne to Alkenylcarbene Transformation in Bisphosphine-Osmium Complexes

The elongated dihydrogen complex (1) reacts with 1,1-diphenyl-2-propyn-1-ol and 2-methyl-3-butyn-2-ol to give the hydride-hydroxyvinylidene-π-alkynol derivatives [OsH{CCHC(OH)R2}{η 2-HC⋮CC(OH)R2}(P i Pr3)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)S2(P i Pr3)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 i Pr3)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)(P i Pr3)2 (10), which reacts with AgBF4 and acetonitrile to give [OsHCl(⋮CCHCPh2)(CH3CN)(P i Pr3)2]BF4 (11). In this solvent complex 11 is converted to [OsCl(CHCHCPh2)(CH3CN)2(P i Pr3)2]BF4 (12). Complex 5 reacts with CO to give [Os(CHCHCPh2)(CO)(CH3CN)2(P i Pr3)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 η 2-carbene species 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.