Highly efficient Cu(ii)-pyrazoledicarboxylate heterogeneous catalysts for a base-free aerobic oxidation of benzylic alcohol to benzaldehyde with hydrogen peroxide as the oxidant

Abstract

A new Cu(II) pyrazoledicarboxylate coordination polymer [Cu(Hpdc)(ImH)]_n (1) (H₃pdc = 3,4-pyrazoledicarboxylic acid; ImH = imidazole) has been hydrothermally synthesized and characterized by elemental analysis, FT-IR, X-ray diffraction, and thermogravimetric analysis. In 1, the tetradentate Hpdc²⁻ anion coordinated to three Cu(II) ions in a μ₃-κO: κN, O′: κN′ mode, forming a two-dimensional (2D) (4,4) network; the other ImH ligand acted as a terminal ligand. Cu(II)-MOF 1 displayed high activity and selectivity in the base-free aerobic oxidation of benzyl alcohol to benzaldehyde combined with the green oxidant H₂O₂. The catalytic system of 1 could be reused for several cycles without any obvious decay of the catalytic efficiency.