Synthesis, spectral characterization, and catalytic efficiency of aroylhydrazone-based Cu(ii) complexes

Abstract

A series of copper(II) complexes [Cu(DKMB)Cl] (1), [Cu(DKMB)NO₃] (2), [Cu(APMBH)Cl₂] (3) and [Cu(APMB)NO₃(H₂O)] (4) (where DKMBH = di-2-pyridyl ketone-4-methoxybenzhydrazone and APMBH = 2-acetylpyrazine-4-methoxybenzhydrazone) were prepared. The structural aspects of aroylhydrazones and metal complexes were examined using a combination of spectroscopic techniques, such as FT-IR, UV-Visible, mass, and ¹H NMR analysis, and further followed by analytical methods, such as CHN elemental analyses, thermal analyses, and molar conductivity studies. The molecular and crystal structures of aroylhydrazone, APMB and copper complex 4 were resolved using single-crystal X-ray diffraction (XRD) studies. The occurrence of the amido form of the aroylhydrazone in the solid state was confirmed by IR spectroscopy and single-crystal XRD studies. The crystal structure of the aroylhydrazone is stabilized through various non-covalent interactions including hydrogen bonding, C–H⋯π and π⋯π interactions. The IR spectral studies further substantiated the tridentate nature of the aroylhydrazone ligands. Additionally, the copper(II) complexes demonstrated their potential as a promising catalyst for oxidation of cinnamyl alcohol using tert-butyl hydroperoxide (TBHP) as an oxidant. The copper(II) complex 1 exhibited better catalytic activity than the other complexes for cinnamyl alcohol conversion. A maximum cinnamyl alcohol conversion of 79% with 74% cinnamaldehyde selectivity was observed using copper(II) complex 1 in acetonitrile as solvent at 70 °C for 4 h using TBHP (70% water) as an oxidant.