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

Abstract

Six ruthenium(II) complexes with the general molecular formula [RuCl2(NHC)(η6‐p‐cymene)] (NHC = N‐heterocyclic carbene) were synthesized by the transmetalation method from [RuCl2(η6‐p‐cymene)]2 and silver(I)‐NHC complexes. All complexes were fully characterized by analytical and spectral methods (FT‐IR, elemental analysis and 1H and 13C 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.