The role of N-heterocyclic carbene substituents on ruthenium(II) complexes in the catalytic transfer hydrogenation of acetophenone

The novel ruthenium(II) complexes [RuCl2 (NHC)(p-cymene)], 3a e, containing 1-alkyl-3-benzylimidazol2-ylidene ligands were prepared. All synthesized compounds were characterized by NMR spectroscopy and elemental analyses. Ru(II)-NHC complexes were tested as catalysts for the transfer hydrogenation of acetophenone, showing modest to high activity in this reaction. The results revealed that efficiencies depend on the substituents of the benzene ring of the benzyl on the N atom of the NHC ring.