Mechanistic Insights on the Reduction of CO₂ to Silylformates Catalyzed by Ir‐NSiN Species

Abstract

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.

Mechanistic Insights on the Functionalization of CO2 with Amines and Hydrosilanes Catalyzed by a Zwitterionic Iridium Carboxylate‐Functionalized Bis‐NHC Catalyst

“…The higher activity found for HSiMe 2 Ph in comparison with HSiEt 3 and HSiMePh 2 , which has been attributed to a balance of steric and electronic factors, agrees with the behavior reported for Ir‐NSiN and Ir‐NSi catalysts. However, draws attention the results obtained when using HSiMe(OSiMe 3 ) 2 .…”

“…The next step involves the activation of a hydrosilane molecule by means of a ligand assisted Si–H bond cleavage . This process is possible because of the high oxophilicity of silicon atoms in conjunction with the presence of an available oxygen atom in the uncoordinated carboxylate group at the bis‐NHC ligand linker.…”

Reactivity of Ir–NSiN Complexes: Ir‐Catalyzed Dehydrogenative Silylation of Carboxylic Acids

“…The formation of the silyl ether CF 3 CH 2 OSiMe(OSiMe 3 ) 2 during the hydrosilylation of CO 2 with HSiMe(OSiMe 3 ) 2 using complex [Ir(H)(CF 3 CO 2 )(NSiN)(coe)] ( 8 ) as a catalyst precursor has been recently reported (Scheme ) . This evidence prompted us to study the potential of Ir–NSiN species as catalysts for the reduction of carboxylic acids using HSiMe(OSiMe 3 ) 2 as reducing agent.…”

“…The chloride ligand (Ir−Cl, 2.5229(10) Å) is coordinated trans to the Si atom. Structural parameters describing the metal coordination sphere are close to those reported in related Rh and Ir–(NSiN) metal complexes …”

“…Rh and Ir complexes with tridentate monoanionic NSiN ligands (NSiN= fac ‐bis‐(pyridine‐2‐yloxy)methylsilyl) have been found to be effective catalysts for CO 2 hydrosilylation, dehydrogenative silylation of arenes and of acetophenone derivatives, and for processes involving CO 2 insertion into N−Si and P−Si bonds. Noticeably, in this context, the formation of the silyl ether CF 3 CH 2 OSiMe(OSiMe 3 ) 2 by the reduction of the trifluoroacetate ligand during the Ir(CF 3 CO 2 )(NSiN)‐catalyzed hydrosilylation of CO 2 with HSiMe(OSiMe 3 ) 2 has been observed. These outcomes stimulated us to study the potential of Ir–NSiN species as catalyst precursors for the reduction of carboxylic acids with HSiMe(OSiMe 3 ) 2 .…”