Abstract
Single-electron transfer from the ZrIVCo–I 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 (4) via coupling of two ketyl radicals. Thermolysis of 4 led to cleavage of the C═O bond to generate a Zr/Co μ-oxo species featuring an unusual terminal Co═CPh2 carbene linkage (3). In this work monomeric ketyl radical complexes have been synthesized, and the reactivity of these compounds has been explored. The electronic preference for the formation of a ketyl radical complex or a coordination complex has been investigated computationally. Furthermore, thione substrates were allowed to react with 1, generating new complexes that bind the thione to the Co rather than undergoing single-electron transfer (12, 14). The preference of thiones to coordinate to Co can be overridden if the Co is ligated by CO, in which case a thioketyl radical complex forms (13) analogous to 4. The reaction between 1 and imines resulted in N–H bond activation, affording a μ-methyleneamido Co–H complex (16) that can undergo cyclometalation and loss of H2 (15).
