Schiff base ligand derived from (±)trans-1,2-cyclohexane¬diamine and its Cu(II), Co(II), Zn(II) and Mn(II) complexes: Synthesis, characterization, styrene oxidation and a hydrolysis study of the imine bond in the Cu(II) Schiff base complex

Abstract

A Schiff base ligand (H2L) derived from 2′-hydroxypropiophenone and (±)trans-1,2-cyclohexanediamine was synthesized. The reactions of MCl2·xH2O (M = Cu(II), Co(II), Zn(II) and Mn(II)) with the di-Schiff base ligand (H2L) were studied. When stirred with 1 equivalent of CuCl2.2H2O in a solution of ethanol and chloroform, this ligand undergoes partial hydrolysis of the imino bond and the resultant tridentate ligand (HL′) immediately forms the complex[CuL′Cl]·3/2CHCl3 (1) with an N2O coordination sphere. Under the same condition, the reaction of H2L with MCl2·xH2O (M = Co(II) (3), Zn(II) (4) and Mn(II) (5)) gave the complexes [ML]·1/2CHCl3·3/2H2O (3–5) with an N2O2 coordination sphere and no hydrolytic cleavage occurred. In addition, the reaction of H2L with CuCl2·2H2O in THF gave the complex CuL (2) with an N2O2 coordination sphere. The ligand and the complexes were characterized by FTIR, UV–Vis, 1H-NMR spectroscopy and elemental analysis. The homo­geneous catalytic activities of complexes 1, 3 and 5 were evaluated for the oxidation of styrene using tert-butyl hydroperoxide (TBHP) as oxidant. Finally, the copper(II) complex 1 was encapsulated in the nanopores of zeolite Y by the flexible ligand method (CuL′–Y) and its encapsulation was demonstrated in different studies. The catalytic performance of heterogeneous catalyst in the styrene oxidation with TBHP was investigated. The catalytic tests showed that the homogeneous and heterogeneous catalysts were active in the oxidation of styrene.