N-heterocyclic carbene based ruthenium complexes for selective β-C(sp3)-H functionalization of N-fused saturated cyclic amines

Abstract

Herein, a series of new ruthenium(II) complexes with the general molecular formula [RuCl2(arene)(NHC)], (arene = η6-p-cymene, NHC = N-heterocyclic carbene) were synthesized from in situ prepared silver(I)-NHCs by the transmetallation method. These complexes were fully characterized by analytical and spectral methods. Ruthenium(II) complexes were tested as promising catalyst for selective β-C(sp3)-H functionalization of N-methylpiperidine with various aldehydes through hydrogen transfers in presence of external acidic additive. These eco-friendly cross-dehydrogenative couplings enable the production of C(3)-alkylated N-methylpiperidine derivatives without enamines with only carbon dioxide and water as benign by-product.