Triazole based oxidovanadium(V) complex supported on chloromethylated polymer and its catalytic activity for the synthesis of dihydropyrimidinones (DHPMs)

Abstract

Oxidovanadium(V) complex [VVO(OEt)(µ-Hhptb)]2 (1) of 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl] benzoic acid (H3hptb) has been prepared by the reaction of VVO(OEt)3 with ligand in EtOH. Complex 1 has been immobilized on chloromethylated polystyrene (PS–Cl) to obtain PS–[VVO(OEt)(hptb)(EtOH)] (2). The homogeneous complex 1 was characterised by elemental analysis, spectroscopic techniques (FT-IR, UV-Vis, 1H and 13C NMR) and thermogravimetric analysis, while the heterogeneous complex was additionally studied by field emission-scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy. These complexes have been utilized in catalysing one-pot three-component (benzaldehyde or its derivatives, urea and ethyl acetoacetate) Biginelli reaction producing multifunctionalized 3,4-dihydropyrimidin-2-(1H)-ones (DHPMs) under solvent-free conditions. It was observed that H2O2 helps in improving the yield of the products. Various parameters, such as the amount of catalyst and oxidant, time, temperature, and solvent effects, were optimized for the maximum yield of DHPMs. The heterogeneous complex is found to show excellent catalytic activity giving more than 90% conversion of DHPMs under the optimized reaction conditions. A suitable reaction pathway for this reaction has been proposed with the help of DFT computation.