Peroxidative Oxidation of Cyclohexane Using 3d Metal Complexes with Hydrazone-Derived Ligands as Catalysts: Exploring (Un)Conventional Conditions

Two tetranuclear and two mononuclear Cu(II) complexes with arylhydrazones of malononitrile derived ligands (compounds 1–2 3–4, respectively), one trinuclear Co(II/III) complex an arylhydrazone acetoacetanilide (5) Zn(II) 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione (6) were screened as potential catalysts in the peroxidative oxidation cyclohexane by aqueous H2O2 acetonitrile. The best results attained presence pyrazine-2-carboxylic acid (PCA) 1 (26% yield, TON = 52.0) 2 (24%, 48.0) after 4 h at 40 °C. In 5 6, no oxygenated products detected studied conditions. employment non-conventional conditions like supercritical carbon dioxide (scCO2) reaction medium or microwave (MW) irradiation was assessed for 2. After 6 acetonitrile–scCO2, 50 °C HNO3 promoter, only 17% yield achieved using catalyst, 21% Total yields oxygenates up to 14 (with 1) 13% (2) TOFs 56.0 52.0 h−1, respectively, obtained working under MW 70 much shorter time 0.5 h.