Novel quasi-scorpionate ligand structures based on a bis-N-heterocyclic carbene chelate core: synthesis, complexation and catalysis

A series of novel quasi-scorpionate CNC donor ligands, MeC(2-C5H4N){CH2(imidazole-R)} (R = methyl, n-butyl, n-propenyl), in which a chelating bis(NHC) core is supplemented by a hemi-labile pyridyl donor, were prepared. The coordination chemistry of these ligands was investigated with silver, palladium, rhodium and iridium. The single crystal X-ray structures of [Rh(NC2Me)(COD)]Cl 8a and [Ir(NC2Pr)(COD)]Br 9b were determined. The catalytic potential of the rhodium and iridium complexes was assessed in the transfer hydrogenation of ketones; the iridium complexes, which show superior performance, form very effective and stable catalysts. Copyright (C) 2011 John Wiley & Sons, Ltd.