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

Abstract

Six ruthenium(II) complexes with the general molecular formula [RuCl 2 (NHC)(η 6 ‐ p ‐cymene)] (NHC = N‐heterocyclic carbene) were synthesized by the transmetalation method from [RuCl 2 (η 6 ‐ p ‐cymene)] 2 and silver(I)‐NHC complexes. All complexes were fully characterized by analytical and spectral methods (FT‐IR, elemental analysis and 1 H and 13 C 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.