Polyoxometalate-supported transition metal complexes for the oxidative cross-coupling of amines and alcohols

Abstract

Three new hybrid polyoxometalates (POMs) based on transition metals, namely, copper metal with γ-[Mo₈O₂₆]⁴⁻ polyoxometalates [Cu(DMF)₄(Mo₈O₂₆)·2C₃H₈NO]·1.8 DMF (1), cobalt metal with hexamolybdate [Co(DMSO)₆][Mo₆O₁₉] (2), and nickel metal with hexamolybdate [Ni(DMSO)₆][Mo₆O₁₉] (3), were developed. These materials were characterised by applying both analytical and spectroscopic techniques (IR, TGA, and CHNO elemental analysis), and structural elucidation was performed using single-crystal X-ray diffraction studies. Among these hybrid POMs, octamolybdate with copper was used for the catalytic production of benzimidazoles. The incorporation of [Cu(DMF)₄] between two octamolybdates results in the transformation of POMs into a useful catalyst, which effectively catalyses the oxidative cross-coupling of anilines, benzyl alcohol, and sodium azide to produce benzimidazole. This catalytic reaction occurs in the presence of tert-butyl hydroperoxide (TBHP) at a moderate temperature. Benzimidazole and its derivatives are highly preferred owing to their wide-ranging biological activities and clinical applications. These compounds are exceptionally effective in terms of their selectivity ratio and inhibitory activity. The catalytic reaction presented herein is a one-pot procedure that includes a series of reactions, such as C–H functionalization, condensation, ortho selective amination, and cyclization.