Biomimetic Oxidation of Hydrocarbons with Air over Metalloporphyrins

The oxidation of C-H, C-C and C=C of hydrocarbons, from the syntheses of many fine chemicals to the manufacture of various commodities in large scale, plays great important role in transformation of basic materials to useful synthetic building in organic chemistry and in conversion of hydrocarbon to oxygen-containing industrial production especially the hydroxylation, epoxidation, degradation of hydrocarbon derivatives[1-6]. Conventional oxidation methodologies often suffer low chemoand/or regio-selectivity with low conversion and low turnover number (TON) in an unfriendly way from both economical and environmental aspects which the catalyst is very expensive and generates amounts of hazardous waste. Oxidation reactions catalyzed by both non-metal[7-8] and metal[9-14] catalysts have been receiving increasing attention, particularly for the highly selective aerobic oxidations catalyzed by metal complexes[15-17]. In nature, aerobic oxidation processes are carried out in a highly selective manner by monoor dioxygenases under mild conditions[18-19]. A well-known type of monooxygenase is cytochrome P-450(CP-450)[2023], which features an iron porphyrin core, and can catalyze a wide variety of oxidation reactions including epoxidation, hydroxylation, dealkylation, degradation, dehydrogenation, and oxidation of amines, sulfides, alcohols and aldehydes, even for unreactive substrates such as unactivated hydrocarbons. This stimulates numerous efforts in developing biomimetic oxidation systems[24-26]. Metalloporphyrins, with a core structure closely resembling that of the iron porphyrin core of CP-450, have been extensively studied as catalysts to oxidate a series kind of reactions mimic the natural style[24,27]. In 1979, Groves and co-workers[28] reported the first oxidation system with synthetic metalloporphyrin as a catalyst. They developed the oxidation system of terminal oxidant iodosylbenzene(PhIO) and ironporphyrin catalyst [FeIII(por)Cl], which can effect both epoxidation of styrene and cyclohexene, and hydroxylation of cyclohexane and adamantane. Subsequently, many reports focusing on metalloporphyrin-catalyzed oxidation systems have appeared in the literature, as described in previous reviews[29-34]. As documented in the literature, the hydroxylation of alkanes and epoxidation of alkenes catalyzed by iron, manganese and ruthenium porphyrins with the traditional terminal oxidants PhIO, NaOCl and 2,6-dichloropyridine-N-oxide, including enantioselective oxidations are the most extensively studied systems.