Efficient and versatile transfer hydrogenation catalysts: Iridium (III) and ruthenium (II) complexes with 4-acetylbenzyl-N-heterocyclic carbenes

New 4-acetylbenzyl-N-heterocyclic carbene ligands (1-4) have been used to synthesize iridium complexes 6-9 and ruthenium complex 10. All complexes were characterized by FT-IR, H-1 and C-13 NMR spectroscopy, elemental analysis, and in the case of 6, by X-ray diffraction studies. The catalytic performance of these iridium and ruthenium complexes for transfer hydrogenation of ketones and imines and N-alkylation of amines with primary alcohols were tested in a range of substrates, and showed high catalytic activity with 1 mol% catalytic loading. The neutral complex 8 with two acetyl groups also showed good catalytic efficiency under lower catalyst loading (0.01 mol%), with the maximum TON of 8000, while on the other hand, the cationic complex 9 with PF6- as counteranion showed good to excellent catalytic activity toward the N-alkylation of amines in a wide scope of substrates. We also found out that the Ir complex 6' was formed through the intramolecular C-H activition of 6 under the transfer hydrogenation conditions. (C) 2014 Elsevier B.V. All rights reserved.