Terminal Carbido Complexes of Osmium: Synthesis, Structure, and Reactivity Comparison to the Ruthenium Analogues

The first terminal carbide complex of osmium, Os(⋮C)(PCy 3 ) 2 Cl 2 ( 4 ), was synthesized via S-atom abstraction from Os(CS)(PCy 3 ) 2 Cl 2 ( 4-S ) by Ta(OSi- t -Bu 3 ) 3 ( 7 ). Compound 4 reacts with HO 3 SCF 3 (HOTf) to form the first cationic osmium methylidyne complex [Os(⋮CH)(PCy 3 ) 2 Cl 2 ][OTf] ( 18 ). The analogous ruthenium complex [Ru(⋮CH)(H 2 IMes)(PCy 3 )Cl 2 ][OTf] is not observed upon protonation of Ru(⋮C)(H 2 IMes)(PCy 3 )Cl 2 ( 2 ) with HOTf. Substitution of the chloride ligands in 4 is surprisingly difficult compared to the case of 4-S, but Os(⋮C)(PCy 3 ) 2 I 2 can be obtained. Compound 4 also reacts with a variety of electrophiles to afford cationic five-coordinate and neutral six-coordinate carbyne complexes. In general, 4 reacts more readily with electrophiles than does 1, and cationic carbyne complexes formed from 4 are more resistant to degradation than are their Ru counterparts.