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

Treatment of the bulky metallocene hydride CpZr(H)OMes (Cp = pentamethylcyclopentadienyl, Mes = mesityl) with Piers' borane [HB(CF)] and carbon monoxide (CO) gave the formylhydridoborate complex [Zr]-O═CH-BH(CF) ([Zr] = CpZr-OMes). From the dynamic NMR behavior, its endergonic equilibration with the [Zr]-O-CH-B(CF) 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 (CO) 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 H to give CpZr(OH)OMes and HC-B(CF), which then slowly reacted further with H to eventually give [Zr]-O(H)-B(H)(CF) and methane (CH). Most complexes were characterized by X-ray diffraction.