Synthesis and characterization of Co(II) and Cu(II) supported complexes of 2-pyrazinecarboxylic acid for cyclohexene oxidation

Abstract

The complexes [Co(N^O) 2] ( 1) and [Cu(N^O) 2] ( 2) {N^O = η 2-(N,O) coordinated 2-pyrazinecarboxylic acid} have been synthesized and characterized by elemental (including metal) analyses, FT-IR spectroscopy and powder X-ray diffraction. The molecular structure of complex 2 was determined by single X-ray crystallography. In the molecule, the Cu atom occupies the center of a square planar geometry, which consists of two trans-O atoms and two t rans-N atoms of two 2-pyrazinecarboxylic acid ligands. The complexes 1 and 2 were well encapsulated into zeolite–Y super-cage to yield the corresponding zeolite–Y encapsulated metal complexes, abbreviated herein as [Co(N^O) 2]–Y ( 3) and [Cu(N^O) 2]–Y ( 4). Similarly, the metal complexes 1 and 2 were immobilized on alumina and organically modified silica surfaces to lead to the formation of immobilized metal complexes [Co(N^O) 2]–Al 2O 3 ( 5); [Cu(N^O) 2]–Al 2O 3 ( 6); [Co(N^O) 2]–AMPS ( 7) and [Cu(N^O) 2]–AMPS ( 8) (AMPS = aminopropyl silica). Elemental (including metal) analyses, FT-IR spectroscopy, powder X-ray diffraction and thermal analysis have been used to characterize these materials. The catalytic activity of all the catalysts 1– 8 towards the oxidation of cyclohexene into different chemically and pharmaceutically important products were evaluated under homogeneous and heterogeneous conditions. In order to obtain a maximum conversion of cyclohexene, the reaction parameters, like reaction temperature and time, were optimized. Under the optimized conditions, a maximum of 90.47% cyclohexene conversion was achieved with [Cu(N^O) 2]–Y ( 4) with a 1:2 molar ratio reaction of cyclohexene and H 2O 2.