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^IIICo⁰ heterobimetallic complex (THF)­Zr­(MesNP^<i>i</i>Pr₂)₃Co–N₂ (<b>1</b>) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph₂CO)­Zr­(MesNP^<i>i</i>Pr₂)₃Co–N₂]₂ (<b>2</b>) via coupling of two ketyl radicals. In this work, thermolysis of <b>2</b> 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-MesNP^<i>i</i>Pr₂)­Zr­(μ-O)­(MesNP^<i>i</i>Pr₂)₂CoCPh₂ (<b>3</b>). This complex was characterized structurally and spectroscopically, and its electronic structure is discussed in the context of density functional theory calculations. Complex <b>3</b> was also shown to be active toward carbene group transfer (cyclopropanation), and silane addition to <b>3</b> leads to PhSiH₂O–Zr­(MesNP^<i>i</i>Pr₂)₃Co–N₂ (<b>5</b>) via a proposed Co–alkyl bond homolysis route