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

Three tetranuclear Ni(II) compounds having the molecular formula [Ni₄L₂(RCOO)₂(MeOH)₂]·<i>X</i>H₂O (<b>1</b>: R = Me and <i>X</i> = 7; <b>2</b>: R = Ph and <i>X</i> = 6 and <b>3</b>: R = 4-NO₂-Ph and <i>X</i> = 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.