Stoichiometric and Catalytic Reduction of Carbon Dioxide by a Sterically Encumbered Amidinato Magnesium Hydride

A sterically encumbered dinuclear amidinato magnesium hydride 3 with bridging hydrido ligands was synthesized from the metalation of the corresponding amidine 1 with dibutylmagnesium and subsequent treatment with phenylsilane. This complex reacts stoichiometrically with 1 atm of carbon dioxide at room temperature in tetrahydrofuran (THF) to the corresponding bis(thf) adduct of the dinuclear formate complex 4‐2thf with bridging formate anions. This complex is stable in THF at 60°C for more than 16 hours but decomposes into the amidine 1 upon removal of ligated thf ligands . Complex 3 efficiently catalyzes the reduction of carbon dioxide with 9‐BBN, yielding bis(boryl)acetal (R2BO)2CH2, and with silanes H4‐nSiPhn (n = 1, 2, and 3). The bis(silyl)acetal is quantitatively accessible for Ph3SiH (n = 3) whereas during the reduction of CO2 with hydrogen‐richer silanes (n = 1, 2) siloxanes form and methane evolves.