Ruthenium(II)-(p-cymene)-N-Heterocyclic Carbene Complexes for the N-Alkylation of Amine Using the Green Hydrogen Borrowing Methodology

Six ruthenium(II) complexes with the general molecular formula [RuCl2(NHC)((6)-p-cymene)] (NHC = N-heterocyclic carbene) were synthesized by the transmetalation method from [RuCl2((6)-p-cymene)](2) and silver(I)-NHC complexes. All complexes were fully characterized by analytical and spectral methods (FT-IR, elemental analysis and H-1 and C-13 NMR). The solid-state structure of one of the ruthenium complexes [dichloro-{1-[2-(2-ethoxyphenoxy)ethyl]-3-(3,5-dimethylbenzyl)benzimidazol-2-ylidene}(p-cymene) ruthenium(II)] has been established by single-crystal X-ray diffraction study, which revealed that the ruthenium atom adopt a classical piano-stool coordination geometry. Under the optimised conditions, these ruthenium complexes were found to be efficient catalysts for N-alkylation of aniline with arylmethyl alcohols using the hydrogen borrowing strategy, which is a cost-effective and environmentally attractive reaction for the preparation of N-alkylated amines.