Efficient biomimetic aerobic oxidation of phenylethane catalyzed by P(4VP-co-St)/SiO2-supported metalloporphyrins

In this work, three kinds of metalloporphyrins (CoPs, FePs, and MnPs) were immobilized on the grafting particles P(4VP-co-St)/SiO2 through the axial coordination reaction, respectively, and the supported biomimetic catalysts MP-P(4VP-co-St)/SiO2 (M = Co, Fe and Mn) were prepared. The catalytic performances of various supported biomimetic catalysts for the oxidation of phenylethane in the absence of any reductant and solvent were investigated and compared detailedly. The experimental results show that the supported catalystsMP-P(4VP-co-St)/SiO2 can effectively activate dioxygen, and obviously catalyze the oxidation of phenylethane to hypnone. When MPs are immobilized on the supports P(4VP-co-St)/SiO2, the catalytic activity of MP-P(4VP-co-St)/SiO2 is improved greatly. Also the catalytic activities of MP-P(4VP-co-St)/SiO2 differ among the different metals, according to the following series: Co(II) > Fe(III) > Mn(III). Under the reaction conditions of 393 K and the ordinary pressure of oxygen, the catalyst CoP-P(4VP-co-St)/SiO2 gave wonderful results with 24 mol% yield and 95% selectivity to the main product hypnone, and the another product, alpha-phenylethanol was few. All these results indicate that the grafting particles P(4VP-co-St)/SiO2 can not only protect metalloporphyrin from oxidation, but also promote it to activate O-2. Additionally, some rules were specially found in the studies: (1) CoPs as a biomimetic catalyst had an optimum used amount, and excess addition would make the catalyst activity worse; (2) the immobilization density of CoPs on P(4VP-co-St)/SiO2 surface still had the high-point; (3) the catalyst activity trended to steady during nine cycle. (c) 2009 Elsevier B.V. All rights reserved.