Stoichiometric C═O Bond Oxidative Addition of Benzophenone by a Discrete Radical Intermediate To Form a Cobalt(I) Carbene

Abstract

Single electron transfer from the Zr(III)Co(0) heterobimetallic complex (THF)Zr(MesNP(i)Pr2)3Co-N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)Zr(MesNP(i)Pr2)3Co-N2]2 (2) via coupling of two ketyl radicals. In this work, thermolysis of 2 in an attempt to favor a monomeric ketyl radical species unexpectedly led to cleavage of the C-O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co═CPh2 carbene linkage, (η(2)-MesNP(i)Pr2)Zr(μ-O)(MesNP(i)Pr2)2Co═CPh2 (3). This complex was characterized structurally and spectroscopically, and its electronic structure is discussed in the context of density functional theory calculations. Complex 3 was also shown to be active toward carbene group transfer (cyclopropanation), and silane addition to 3 leads to PhSiH2O-Zr(MesNP(i)Pr2)3Co-N2 (5) via a proposed Co-alkyl bond homolysis route.