Mechanistic Insights on the Reduction of CO to Silylformates Catalyzed by Ir-NSiN Species.

The hydrosilylation of CO with different silanes such as HSiEt , HSiMe Ph, HSiMePh , HSiMe(OSiMe ) , and HSi(OSiMe ) in the presence of catalytic ammounts of the iridium(III) complex [Ir(H)(CF CO )(NSiN*)(coe)] (1; NSiN*=fac-bis-(4-methylpyridine-2-yloxy); coe=cis-cyclooctene) has been comparatively studied. The activity of the hydrosilylation catalytic system based on 1 depends on the nature of the reducing agent, where HSiMe(OSiMe ) has proven to be the most active. The aforementioned reactions were found to be highly selective toward the formation of the corresponding silylformate. It has been found that using 1 as catalyst precursor above 328 K decreases the activity through a thermally competitive mechanistic pathway. Indeed, the reduction of the ancillary trifluoroacetate ligand to give the corresponding silylether CF CH OSiR has been observed. Moreover, mechanistic studies for the 1-catalyzed CO -hydrosilylation reaction based on experimental and theoretical studies suggest that 1 prefers an inner-sphere mechanism for the CO reduction, whereas the closely related [Ir(H)(CF SO )(NSiN)(coe)] catalyst, bearing a triflate instead of trifluoroacetate ligand, follows an outer-sphere mechanism.