Dinuclear Di(N-heterocyclic carbene) iridium(III) complexes as catalysts in transfer hydrogenation

Two novel di(N-heterocyclic carbene) complexes of formula (μ-PyrIm-CH2-ImPyr)[IrCp∗Cl]2(PF6)2 (1) and μ-MeIm-CH2(p-C6H2)CH2-ImMe[IrCp∗ Cl]2 (2) (Im = imidazol-2-ylidene) have been synthesised by transmetallation of the dicarbene ligand from the corresponding dicarbene silver complex, using [IrCp∗(μ-Cl)Cl]2 as an iridium precursor. The structure of complex 2 has been determined by X-ray diffraction and is characterized by a double ortho-metallation of the p-xylylene bridge between the carbene units. Both complexes show good activity in the transfer hydrogenation of ketones to alcohols in 2-propanol. Dinuclear iridium(III) complexes bearing a bridging di(NHC) ligand have been synthesised and tested as catalysts in transfer hydrogenation reactions.