CO-Reduction Chemistry: Reaction of a CO-Derived Formylhydridoborate with Carbon Monoxide, with Carbon Dioxide, and with Dihydrogen

Treatment of the bulky metallocene hydride Cp*2Zr­(H)­OMes (Cp* = pentamethyl­cyclopentadienyl, Mes = mesityl) with Piers’ borane [HB­(C6F5)2] and carbon monoxide (CO) gave the formylhydridoborate complex [Zr]–OCH–BH­(C6F5)2 ([Zr] = Cp*2Zr–OMes). From the dynamic NMR behavior, its endergonic equilibration with the [Zr]–O–CH2–B­(C6F5)2 isomer was deduced, which showed typical reactions of an oxygen/boron frustrated Lewis pair. It was trapped with CO to give an O–[Zr] bonded borata-β-lactone. Trapping with carbon dioxide (CO2) gave the respective O–[Zr] bonded cyclic boratacarbonate product. These reaction pathways were analyzed by density functional theory calculation. The formylhydridoborate complex was further reduced by dihydrogen via two steps; it reacted rapidly with H2 to give Cp*2Zr­(OH)­OMes and H3C–B­(C6F5)2, which then slowly reacted further with H2 to eventually give [Zr]–O­(H)–B­(H)­(C6F5)2 and methane (CH4). Most complexes were characterized by X-ray diffraction.