Iridium NHC Based Catalysts for Transfer Hydrogenation Processes Using Glycerol as Solvent and Hydrogen Donor

A series of iridium and ruthenium N-heterocyclic carbene based catalysts of general formula [IrI(2)(AcO)(bis-NHC)] or [Ru(eta(6)-arene)(NHC)CO(3)] have been tested in the reduction of several organic carbonyl compounds using glycerol as solvent and hydrogen donor, by the transfer hydrogenation methodology. The Ir(III) complexes with a chelating bis-NHC ligand and sulfonate groups were the most efficient, due to their solubility in the reaction media and to the strong electron-donor properties of the bis-carbene ligands. The same two catalysts were moderately active in the reduction of olefins and alkynes and, more remarkably, show excellent chemoselectivity in the reduction of the alkenic double bond of alpha,beta-unsaturated ketones, a valuable process for which glycerol had never been used before.