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.