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

The complexes [Co(N<boolean AND>O)(2)] (1) and [Cu(N<boolean AND>O)(2)] (2) (N<boolean AND>O = eta(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 trans-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<boolean AND>O)(2)]-Y (3) and [Cu(N<boolean AND>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<boolean AND>O)(2)]-Al2O3 (5); [Cu(N<boolean AND>O)(2)]-Al2O3 (6); [Co(N<boolean AND>O)(2)]-AMPS (7) and [Cu(N<boolean AND>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<boolean AND>O)(2)]-Y (4) with a 1:2 molar ratio reaction of cyclohexene and H2O2. (c) 2008 Elsevier Ltd. All rights reserved.