Mechanism Insights into the Iridium(III)- and B(C 6 F 5 ) 3 -Catalyzed Reduction of CO 2 to the Formaldehyde Level with Tertiary Silanes.

The catalytic system [Ir(CF 3 CO 2 )(κ 2 -NSi Me ) 2 ] [ 1 ; NSi Me = (4-methylpyridin-2-yloxy)dimethylsilyl]/B(C 6 F 5 ) 3 promotes the selective reduction of CO 2 with tertiary silanes to the corresponding bis(silyl)acetal. Stoichiometric and catalytic studies evidenced that species [Ir(CF 3 COO-B(C 6 F 5 ) 3 )(κ 2 -NSi Me ) 2 ] ( 3 ), [Ir(κ 2 -NSi Me ) 2 ][HB(C 6 F 5 ) 3 ] ( 4 ), and [Ir(HCOO-B(C 6 F 5 ) 3 )(κ 2 -NSi Me ) 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(C 6 F 5 ) 3 -catalyzed hydrosilylation of CO 2 to bis(silyl)acetal is a boron-promoted Si-H bond cleavage via an iridium silylacetal borane adduct.