Coordination clusters with a [Ni4O4] core as catalysts for α-alkylation of ketones with benzyl alcohols

Abstract

Three tetranuclear Ni(II) compounds having the molecular formula [Ni₄L₂(RCOO)₂(MeOH)₂]·XH₂O (1: R = Me and X = 7; 2: R = Ph and X = 6 and 3: R = 4-NO₂–Ph and X = 6) have been synthesized through the reaction of a polydentate pro-ligand H₃L with nickel chloride hexahydrate in the presence of a base in methanol under refluxing conditions. All the compounds were characterized by the standard spectroscopic and analytical methods such as elemental analysis, FT-IR spectroscopy and powder X-ray diffraction. The solid-state molecular structures of compounds 1–3 were determined by single-crystal X-ray crystallography. All three compounds feature a Ni₄O₄ cubane core. Each Ni(II) ion is coordinated to six donor atoms, forming a distorted octahedral geometry. All the compounds show catalytic efficiency in the α-alkylation of ketones with benzyl alcohols using the borrowing hydrogen methodology. For the first time, polynuclear coordination cluster compounds have been utilized for α-alkylation of ketones with benzyl alcohols. A plausible mechanism is also proposed based on mechanistic investigation and earlier reports.