Mechanism Insights into the Iridium(III)- and B(C6F5)3-Catalyzed Reduction of CO2 to the Formaldehyde Level with Tertiary Silanes

The catalytic system [Ir(CF3CO2)(K2-NSiMe)2] [1; NSiMe = (4-methylpyridin-2-yloxy)dimethylsilyl]/B(C6F5)3 promotes the selective reduction of CO2 with tertiary silanes to the corresponding bis(silyl)acetal. Stoichiometric and catalytic studies evidenced that species [Ir(CF3COO-B(C6F5)3)(K2-NSiMe)2] (3), [Ir(K2-NSiMe)2][HB(C6F5)3] (4), and [Ir(HCOO-B(C6F5)3)(K2-NSiMe)2] (5) are intermediates of the catalytic process. The structure of 3 has been determined by X-ray diffraction methods. Theoretical calculations show that the rate-limiting step for the 1/B(C6F5)3-catalyzed hydrosilylation of CO2 to bis(silyl)acetal is a boron-promoted Si-H bond cleavage via an iridium silylacetal borane adduct.

Automated summary

The catalytic system enables the selective reduction of CO2 with tertiary silanes to form bis(silyl)acetal. Intermediates of the reaction have been identified and the rate-limiting step involves boron-promoted Si-H bond cleavage.