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

Abstract

The first terminal carbide complex of osmium, Os(⋮C)(PCy3)2Cl2 (4), was synthesized via S-atom abstraction from Os(CS)(PCy3)2Cl2 (4-S) by Ta(OSi-t-Bu3)3 (7). Compound 4 reacts with HO3SCF3 (HOTf) to form the first cationic osmium methylidyne complex [Os(⋮CH)(PCy3)2Cl2][OTf] (18). The analogous ruthenium complex [Ru(⋮CH)(H2IMes)(PCy3)Cl2][OTf] is not observed upon protonation of Ru(⋮C)(H2IMes)(PCy3)Cl2 (2) with HOTf. Substitution of the chloride ligands in 4 is surprisingly difficult compared to the case of 4-S, but Os(⋮C)(PCy3)2I2 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.