Highly efficient homogeneous and heterogenized ruthenium catalysts for transfer hydrogenation of carbonyl compounds

Abstract

[Ru(acac)₂(CH₃CN)₂] was synthesized from [Ru(acac)₃] by refluxing it with zinc powder in ethanol–acetonitrile mixture. The prepared catalyst was characterized by FT-IR, ¹H and ¹³C NMR techniques. The silica supported catalyst (‘SiO₂’–NH₂–Ru^II) was prepared by stirring [Ru(acac)₂(CH₃CN)₂] with ‘SiO₂’–NH₂ in a 1 : 1 mixture of CH₂Cl₂–toluene for 3 days at room temperature. It was characterized by FT-IR, SEM, solid state NMR, ICP and BET surface area methods. The transfer hydrogenation reaction of carbonyl compounds was carried out separately using [Ru(acac)₂(CH₃CN)₂] and ‘SiO₂’–NH₂–Ru^II as catalysts. The reaction conditions were optimized with different solvents, bases, catalyst amounts and temperatures using acetophenone as a model system. The scope of the reaction was extended to various substituted aryl ketones including heteroaryl ketones.