(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.