Aluminum-Hydride-Catalyzed Hydroboration of Carbon Dioxide.

This study describes the first use of a bis(phosphoranyl)methanido aluminum hydride, [ClC(PPhNMes)AlH] (, Mes = MeCH), for the catalytic hydroboration of CO. Complex was synthesized by the reaction of a lithium carbenoid [Li(Cl)C(PPhNMes)] with 2 equiv of AlH·NEtMe in toluene at -78 °C. (10 mol %) was able to catalyze the reduction of CO with HBpin in CD at 110 °C for 2 days to afford a mixture of methoxyborane [MeOBpin] (; yield: 78%, TOF: 0.16 h) and bis(boryl)oxide [pinBOBpin] (). When more potent [BH·SMe] was used instead of HBpin, the catalytic reaction was extremely pure, resulting in the formation of trimethyl borate [B(OMe)] () [catalytic loading: 1 mol % (10 mol %); reaction time: 60 min (5 min); yield: 97.6% (>99%); TOF: 292.8 h (356.4 h)] and BO (). Mechanistic studies show that the Al-H bond in complex activated CO to form [ClC(PPhNMes)Al(H){OC(O)H}] (), which was subsequently reacted with BH·SMe to form and , along with the regeneration of complex . Complex also shows good catalytic activity toward the hydroboration of carbonyl, nitrile, and alkyne derivatives.