Windmill-type mixed-metal clusters containing Schiff-base ligands as an efficient catalyst for cyclohexene oxidation

Abstract

Two new mixed-metal clusters {CuM₂(H₂O)₂[Cu(C₁₄H₁₆N₂O₃)Cl]₆}·H₂O (M = Mn 1, Zn 2) based on Schiff-base ligands were designed and synthesized by the reaction of 1,2-cyclohexanediamine-N,N′-bis-(3-carboxylsalicylide), copper chloride and zinc chloride or manganese chloride under solvothermal conditions. They were characterized by various techniques including single-crystal X-ray diffraction, powder X-ray diffraction (XPRD), elemental analysis, TG analysis, IR and UV-visible spectroscopy. Compounds 1 and 2 are isostructural, and display an interesting windmill-type structure built from a trinuclear mixed-metal center [CuM₂(CO₂)₆(H₂O)₂] (M = Mn 1, Zn 2) linked with six [CuLCl] (L = C₁₄H₁₆N₂O₃) units. The oxidation of cyclohexene catalysed by 1 and 2 as heterogeneous catalysts was investigated and showed high activity. In addition, a magnetic study indicates that antiferromagnetic interactions exist in compound 1.