Novel supramolecular network in tri- and mono-nuclear oxovanadium(V)-salicyl-hydroximate: Synthesis, structure and catalytic oxidation of hydrocarbons using H2O2 as terminal oxidant

Two oxovanadium(V) salicylhydroximate complexes, [VO(SHA)(H2O)] · 1.58H2O (1) and [V3O3(CSHA)3(H2O)3] · 3CH3COCH3 (2) have been synthesized by reaction of VO43− with N-salicyl hydroxamic acid (SHAH3) and N-(5-chlorosalicyl) hydroxamic acid (CSHAH3), respectively, in methanol medium. Compound 1 on reaction with pyridine 2,6-dicarboxylic acid (PyDCH2) yields mononuclear complex [VO(SHAH2)(PyDC)] (3). Treatment of compound 3 with hydrogen peroxide at low pH (2-3) and low temperature (0–5 °C) yields a stable oxoperoxovanadium(V) complex H[VO(O2)(PyDC)(H2O)] · 2.5H2O (4). All four complexes (1–4) have been characterized by spectroscopic (IR, UV–Vis, 51V NMR) and single crystal X-ray analyses. Intermolecular hydrogen bonds link complex 1 into hexanuclear clusters consisting of six {VNO5} octahedra surrounded by twelve {VNO5} octahedra to form an annular ring. While the molecular packing in 2 generates a two-dimensional framework hydrogen bonds involving the solvent acetone molecules, the mononuclear complexes 3 and 4 exhibit three-dimensional supramolecular architecture. The compounds 1 and 2 behave as good catalysts for oxygenation of benzylic, aromatic, carbocyclic and aliphatic hydrocarbons to their corresponding hydroxylated and oxygenated products using H2O2 as terminal oxidant; the process affords very good yield and turnover number. The catalysis work shows that cyclohexane is a very easily oxidizable substrate giving the highest turnover number (TON) while n-hexane and n-heptane show limited yield, longer time involvement and lesser TON than other hydrocarbons.

Two oxovanadium(V)salicylhydroximate complexes, [VO(SHA)(H2O)] · 1.58H2O (1) and [V3O3(CSHA)3(H2O)3] · 3CH3COCH3 (2) and a mono nuclear oxovanadium(V) complex [VO(SHAH2)(PyDC)] (3) with salicylhydroxamic acid (SHAH3) and 2,6-pyridine dicarboxylic acid (PyDCH2), a mono nuclear oxoperoxo vanadium(V)complex H[VO(O2)(PyDC)(H2O] · 2.5H2O (4) with PyDC2−, have been synthesized and structurally characterized. All the complexes exhibit supramolecular networks. Compound 1 and 2 behave as a good catalyst for functionalization of hydrocarbons.Figure optionsDownload as PowerPoint slide