Interaction and Activation of Carbon–Heteroatom π Bonds with a Zr/Co Heterobimetallic Complex

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).