The bis-solvato hydride-allenylidene complex [OsH(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with acetic acid to give the hydride-carbyne [OsH(κ2-O2CCH3)(CCHCPh2)(PiPr3)2]BF4 (2), which in 1,2-dichloroethane under reflux is stable and does not evolve into its five-coordinate carbene isomer. In acetonitrile at room temperature, complex 2 is in equilibrium with [OsH{κ1-OC(O)CH3}(CCHCPh2)(CH3CN)(PiPr3)2]BF4 (4; ΔH° = −6.4 ± 0.3 kcal·mol-1, ΔS° = −22.9 ± 1.1 eu). At 353 K, complex 4 is transformed into the carbene [Os{κ1-OC(O)CH3}(CHCHCPh2)(CH3CN)2(PiPr3)2]BF4 (5; 40%), which is obtained in high yield (88%) by reaction of [Os(CHCHCPh2)(CH3CN)3(PiPr3)2][BF4]2 with sodium acetate in 2-propanol. The hydride-carbyne to carbene transformation is analyzed by DFT calculations.

Financial support from the MCYT of Spain (Project CTQ2005-00656) and Diputación General de Aragón (E35) is acknowledged. R.C. thanks CSIC and the European Social Fund for funding through the I3P Program.

5 pages, 5 figures.-- Supporting Information Available: http://pubs.acs.org.

Peer reviewed