Synthesis and Structures of Arene Ruthenium (II)–NHC Complexes: Efficient Catalytic α-alkylation of ketones via Hydrogen Auto Transfer Reaction

Abstract

A panel of six new arene Ru (II)-NHC complexes 2a-f, (NHC = 1,3-diethyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1a, 1,3-dicyclohexylmethyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1b and 1,3-dibenzyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1c) were synthesized from the transmetallation reaction of Ag-NHC with [(η6-arene)RuCl2]2 and characterized. The ruthenium (II)-NHC complexes 2a-f were developed as effective catalysts for α-alkylation of ketones and synthesis of bioactive quinoline using primary/amino alcohols as coupling partners respectively. The reactions were performed with 0.5 mol% catalyst load in 8 h under aerobic condition and the maximum yield was up to 96%. Besides, the different alkyl wingtips on NHC and arene moieties were studied to differentiate the catalytic robustness of the complexes in the transformations.