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(NC₂^Me)(COD)]Cl 8a and Ir(NC₂^Pr)(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 © 2011 John Wiley & Sons, Ltd.