Tandem Frustrated Lewis Pair/Tris(pentafluorophenyl)borane-Catalyzed Deoxygenative Hydrosilylation of Carbon Dioxide

The frustrated Lewis pair system consisting of 2 equiv of 2,2,6,6-tetramethylpiperidine (TMP) and tris(pentafluorophenyl)borane [B(C6F5)3] activates carbon dioxide to form a boratocarbamate−TMPH ion pair. In the presence of triethylsilane, this species is converted to a silyl carbamate and the known ion pair [TMPH]+[HB(C6F5)3]−, which recently was shown to react with CO2 via transfer of the hydride from the hydridoborate to form the formatoborate [TMPH]+[HC(O)OB(C6F5)3]−. In the presence of extra B(C6F5)3 (0.1−1.0 equiv) and excess triethylsilane, the formatoborate is rapidly hydrosilated to form a formatosilane and regenerate [TMPH]+[HB(C6F5)3]−. The formatosilane in turn is rapidly hydrosilated by the B(C6F5)3/Et3SiH system to CH4, with (Et3Si)2O as the byproduct. At low [Et3SiH], intermediate CO2 reduction products are observed; addition of more CO2/Et3SiH results in resumed hydrosilylation, indicating that this is a robust, living tandem catalytic system for the deoxygenative reduction of CO2 to CH4.