Ru‐Catalyzed Transfer Hydrogenation of Nitriles, Aromatics, Olefins, Alkynes and Esters

Abstract

Abstract This paper reports the preparation of new ruthenium(II) complexes supported by a pyrazole‐phosphine ligand and their application to transfer hydrogenation of various substrates. These Ru complexes were found to be efficient catalysts for the reduction of nitriles and olefins. Heterocyclic compounds undergo transfer hydrogenation with good to moderate yields, affording examples of unusual hydrogenation of all‐carbon‐rings. Internal alkynes with bulky substituents show selective reduction to olefins with the unusual E– selectivity. Esters with strong electron‐withdrawing groups can be reduced to the corresponding alcohols, if ethanol is used as the solvent. Possible mechanisms of hydrogenation and olefin isomerization are suggested on the basis of kinetic studies and labelling experiments.