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

Single electron transfer from the ZrIIICo0 heterobimetallic complex (THF)­Zr­(MesNPiPr2)3Co–N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)­Zr­(MesNPiPr2)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, (η2-MesNPiPr2)­Zr­(μ-O)­(MesNPiPr2)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(MesNPiPr2)3Co–N2 (5) via a proposed Co–alkyl bond homolysis route.