Liquid-phase catalytic oxidation of organic substrates by a recyclable polymer-supported copper(II) complex

Abstract

Chloromethylated polystyrene beads crosslinked with 6.5 % divinylbenzene were functionalized with 2-(2 0 -pyridyl) benzimidazole (PBIMH) and on subsequent treatment with Cu(OAc) 2 in methanol gave a polymersupported diacetatobis(2-pyridylbenzimidazole)copper(II) complex [PS-(PBIM) 2 Cu(II)], which was characterized by physicochemical techniques. The supported complex showed excellent catalytic activity toward the oxidation of industrially important organic compounds such as phenol, benzyl alcohol, cyclohexanol, styrene, and ethylbenzene. An effective catalytic protocol was developed by varying reaction parameters such as the catalyst and substrate concentrations, reaction time, temperature, and substrateto-oxidant ratio to obtain maximum selectivity with high yields of products. Possible reaction mechanisms were worked out. The catalyst could be recycled five times without any metal leaching or much loss in activity. This catalyst is truly heterogeneous and allows for easy work up, as well as recyclability and excellent product yields under mild conditions.

Synthesis, Structural Characterization and Catalytic Oxidation Property of Schiff Base Copper(ii) Complexes

“…Elemental analyses of the complexes are in accordance with the molecular structures proposed by the X-ray analysis. FT-IR spectra of both complexes are of similar type, except the existence of intense absorption at 2091 cm -1 of the thiocyanate ligand of complex (2). The complexes show typical C=N absorptions at about 1620 cm -1 , and typical Ar-O absorptions at about 1185 cm -1 .…”

“…There are two independent molecules in the asymmetric unit of complex (2). In each of the complexes, the coordination sphere has a tetrahedrally distorted square planar geometry.…”

“…In each of the complexes, the coordination sphere has a tetrahedrally distorted square planar geometry. The four coordinate atoms come from the phenolate O and imino N atoms of L 1 for (1), and the phenolate O, imino N and amino N atoms of L 2 , and thiocyanate N atom for (2). The distortion of the square planar geometry can be observed from the bond values.…”

“…[1][2][3][4] Copper(II) complexes have been proved to possess excellent catalytic activity towards a number of organic reactions. [5][6][7][8] In particular, copper complexes derived from Schiff bases are amongst the most versatile catalysts known for oxygenation reactions.…”

“…The mixtures were stirred for 30 min at room temperature to give yellow solution. The solvent was evaporated to give yellow precipitate or gummy product, which was dried by P 2 The mixture was refluxed for 2 h and then cooled to room temperature, and filtered. The filtrate was kept at ambient temperature.…”