Hydrogen Migration and HCl Elimination Promoted by Metal-Centered Nucleophilic Attack on Osmium Hydrido−Carbynes

The carbynes [OsHCl 2 (CCH 2 R)L 2 ] (R = Ph, CH 3; L = P i Pr 3 ) react with CO to give, after 1,2-hydride migration from osmium to C α of the carbyne ligand, the osmium carbene complexes [OsCl 2 (CO)( CHCH 2 R)L 2 ]. For R = Ph, reactions with excess CO lead to HCl elimination to form [OsCl(CO) 2 (( E )-CH CHPh)L 2 ], which reacts with liberated HCl at C α to yield [OsCl 2 (CO) 2 L 2 ] and CH 2 CHPh. Abstraction of chloride from either the carbynes or carbenes with NaBAr‘ 4 (Ar‘ = 3,5-C 6 H 3 (CF 3 ) 2 ) yields the corresponding coordinatively unsaturated carbyne and carbene complexes [OsHCl(CCH 2 R)L 2 ][BAr‘ 4 ] and [OsCl(CO)( CHCH 2 R)L 2 ][BAr‘ 4 ], respectively. The carbynes [OsHCl(CCH 2 Ph)L 2 ] + react with reagent L‘ (L‘ = CO, HCCR‘) to initially give the carbenes [OsCl(L‘)( CHCH 2 Ph)L 2 ] + after 1,2-hydride migration to C α of the carbyne ligand. These carbenes react further, eliminating HCl and undergoing selective protonation to yield either [OsCl(CO) 3 L 2 ] + and CH 2 CHPh (with L‘ = CO) or the σ-vinyl carbyne complexes [OsCl(CCH 2 R‘)(( E )-CH CHPh)L 2 ] + (with L‘ = HCCR‘).