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.