Phosphine-free ruthenium complexes supported by a pincer ligand bearing 1,2-dihydropyrimidine for Oppenauer-type oxidation of secondary alcohols

Treatment of the (diethylaminomethyl-picolyl)pyrazolium ( A3 ) with NaOH in dichloromethane affords the pincer ligand ( L ) bearing a 1,2-dihydropyrimidine unit. Reaction of [RuCl2(DMSO)(4)] and the ligand (L) affords the complex [RuCl2(L)(DMSO)] (Ru1). Removal of the chlorides from Ru1 with either NaBF4 or KPF6 in CH3CN produces the complexes [Ru(L)(CH3CN)(3)](BF4)(2) (Ru-2) and [Ru(L)(CH3CN)(3)](PF6)(2) (Ru3), respectively. Ru2 has been characterized with X-ray crystallography. All of the new ruthenium complexes (Ru1-Ru3) are catalytically active in the Oppenauer-type oxidation of secondary alcohols. Among them, the complex Ru1 is the most active. Steric effects were observed from the outcome of substituted acetophenones. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This article describes the synthesis of (picolyl)pyrazolium-based ligands and their reactions with [RuCl2(DMSO)(4)] to form new ruthenium complexes. The study shows that these ruthenium complexes exhibit catalytic activity in the Oppenauer-type oxidation of secondary alcohols.