(Bis(imino)aryl)rhodium(III) Halide and Methyl Compounds

The synthesis and X-ray crystal structure of a number of aryl−rhodium dihalide and aryl−rhodium methyl halide complexes [RhX2(NCN)] and [RhX(CH3)(NCN)] with bis(imino)aryl
type tridentate NCN ligands are reported. These are interesting examples of compounds on
the reaction coordinate of C−halogen, halogen−halogen, and C−C bond-forming and bond-breaking reactions. Due to the strong C(sp2)−C(sp3) bond, only very few transition-metal
compounds having an aryl as well as a methyl group bonded to the same metal atom are
known and, usually, reductive elimination occurs. It has been shown that the imine moieties
of the isophthalaldimine ligand in the rhodium(III) dihalide compounds [RhX2(NCN)]
coordinate quite strongly, since the addition of an excess of pyridine or PPh3 resulted in
their coordination to rhodium, not in substitution of the imine moieties. Transmetalation of
the rhodium(III) isophthalaldimine dihalide compounds [RhX2(NCN)] with Me2Zn provides
novel rhodium(III) methyl halide isophthalaldimine compounds [RhX(CH3)(NCN)]. These
diorganorhodium compounds are stable and do not give rise to reductive C−C coupling, which
must be partially ascribed to the relatively high electron density on the rhodium(III) center,
due to the strongly electron donating imine moieties.