Ruthenium(II)-(arene)-N-Heterocyclic Carbene Complexes: Efficient and Selective Catalysts for the N-Alkylation of Aromatic Amines with Alcohols

A series of unsymmetrical 1,3-disubstituted benzimidazolium chlorides were synthesized as N-heterocyclic carbene (NHC) precursors. These compounds were used for synthesis of the new ruthenium(II) complexes of the type [RuCl2(arene)(NHC)], (arene = η 6-p-cymene). The structures of all compounds were characterized by 1 H NMR, 13 C NMR and FT-IR spectroscopy techniques. The catalytic activity of the ruthenium complexes has been evaluated with respect to the mono-N-alkylation reactions of aromatic amines with various alcohol derivatives under solvent-free conditions at 120 o C using the borrowing hydrogen strategy.