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 ZrIIICo0 heterobimetallic complex (THF)Zr(MesNPiPr2) 3Co-N2 (1) to benzophenone was previously shown to result in the isobenzopinacol product [(Ph2CO)Zr(MesNPiPr 2)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=CPh 2 carbene linkage, (η2-MesNPiPr 2)Zr(μ-O)(MesNPiPr2)2Co=CPh 2 (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-N 2 (5) via a proposed Co-alkyl bond homolysis route. © 2013 American Chemical Society.