Heterobimetallic Reductive Cross-Coupling of Benzonitrile with Carbon Dioxide, Pyridine, and Benzophenone

Described herein are heterobimetallic radical cross-coupling reactions between the benzonitrile adduct of the molybdenum(III)
complex Mo(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2) and titanium(III)
complexes with carbon dioxide, pyridine, and benzophenone. The
titanium(III) system employed was either Ti(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2) or Ti(N[t-Bu]Ph)3. Crystal structure studies are described
for the Mo/PhCN/CO2/Ti coupled system and for an analogue of
the Mo/PhCN/Ph2CO/Ti coupled system in which PhCN is replaced
with 2,6-Me2C6H3CN. In the case of the couplings involving pyridine
and benzophenone, C−C bond formation takes place with
dearomatization, with the new C−C bond being formed between
the nitrile carbon of PhCN and the para carbon of pyridine or one
of the benzophenone phenyl groups. Of the radical metal complex/substrate adducts invoked in this work, that between titanium(III)
and CO2 is the only one not directly observable. In all cases, the
selective cross-coupling reactions are interpreted as arising by
heterodimerization of titanium(III) substrate complexes (substrate
= CO2, py, or Ph2CO) with the persistent molybdenum−PhCN
radical adduct. All of the heterobimetallic coupling products are
diamagnetic, and the metal ions Ti and Mo in them both are
assigned to the formal 4+ oxidation state.