Abstract:
Interaction of Copper(II) exchanged zeolite-Y with N,N'-
ethylenebis(pyridoxyliminato) (H2pydx-en, I) and
propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) in refluxing methanol leads to the formation of corresponding complexes, abbreviated here in as [Cu(pydx-en)]-Y (1) and [C,u(pydx-l,3-pn)]-Y (2) in the super cages of the zeoiite-Y. Neat complexes, [Cu(pydx-en)] (3) and [Cu(pydx-l,3-pn)] (4) have also been prepared with these ligands. Spectroscopic studies (IR, electronic and EPR), elemental analyses, thermal study, magnetic susceptibility, scanning electron micrographs (SEM) and X-ray diffraction patterns have been used to characterise these complexes. The crystal and molecular structure of 4.CH3OH, has been determined, confirming the ONNO binding mode of the ligands. The encapsulated complexes catalyse the oxidation, by H202 and tert-butylhydroperoxide, of styrene, cyclohexene and thioanisole efficiently. Under the optimised reaction conditions, the oxidation of styrene catalysed by 1 and 2 gave 23.6 % and 28.0 % conversion, respectively using H202 as oxidant where styreneoxide, benzaldehyde, benzoic acid, and phenylacetaldehyde being the major products. Oxidation of cyclohexene catalysed by these complexes gave cyclohexenepoxide, 2-cyclohexene-1-ol, cyclohexane-1,2-diol and 2-cyclohexene-1-one as major products. A maximum of 90.1% conversion of cyclohexene with 1 and 79.3% with 2 was obtained under optimized conditions. Similarly, a maximum of 68.4% conversion of methyl phenyl sulfide with 1 and 81.0 % with 2 was observed where the selectivity of major product methyl phenyl sulfoxide was found to be ca. 60 %. Tests for recycle ability and heterogeneity of the reactions have also been carried out and results suggest their recyclability. A possible reaction mechanism has been proposed by titrating methanolic solution of 3 and 4 with H202 and identifying the possible intermediate.
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