Metalloporphyrin oxygen donors

The observation that cytochrome P 450 can be driven by hydroperoxides and related oxygen donors suggests that metalloporphyrins can be made to function as oxygen-transfer catalysts in simple model systems. 

C. L. Hill, R. B. Brown Jr., Sustained epoxidation of olefins by oxygen donors catalyzed by transition metal-substituted polyoxometalates, oxidatively resistant inorganic analogs of metalloporphyrins, J. Am. Chem. Soc. 108 (1986) 536. 

The kinetics of product evolution in a typical reaction of adamantane hydroxylation showed an initial induction period followed by a fast, apparently zero-order phase with the maximum rate and highest efficiencies (Fig. 2). Deviation from linear behavior took place only after 90% oxygen donor and 80% of the substrate had been consumed. When Ru (TPFPP)(0)2, prepared by reaction of Ru"(TPFPP)(CO) with 3-chloroperbenzoic acid was used as the catalyst, no induction time was detected and zero-order kinetics were observed as well. The well defined and characteristic UV-vls spectra of metalloporphyrins provide an invaluable tool for the mechanistic studies. Thus, monitoring the state of the metalloporphyrin catalysts during the course of both model reactions by UV-vis spectroscopy revealed that the initial form of the catalyst remained the predominant one throughout the oxidation, i.e. in the Ru°(TPFPP)(CO) catalyzed reaction c.a. 80% of the porphyrin catalyst existed as Ru"(TPFPP)(CO) and in Ru (TPFPP)(0)2 catalyzed reaction more than 90% of... 

A number of high-valent metalloporphyrin complexes have been reported. Again high-valency is taken relative to normal species. Many of these species are stabilized by the presence of oxygen donors in the form of oxo or alkoxo ligands. One such set is a series of binuclear p-oxo complexes where the metals (Ru, Os, Mn) have the formal oxidation state +4. All complexes of this class are six-coordinate and include [Ru(0EP)(0H)]20 " [Ru(TPP)(0C6H4CH3)]20 ), [Ru(OEP)C1]20 ),... 

Metalloporphyrins can also be used as catalysts for oxygenations using other single oxygen donors like NaOCl, amine oxides, Na SO ... 

Metalloporphyrin catalyzed olefin epoxidations using single oxygen donors... 

The main features of olefin epoxidation with metalloporphyrin catalysts and single oxygen donors are as follows ... 

This is similar to the oxenoid species proposed earlier as the active intermediate of enzymatic oxidations. It has been made accessible for mechanistic studies via the reaction of metalloporphyrins (Fe,Mn) with single oxygen donors, such as iodosylbenzene, hypochlorite, etc. This concept helped design efficient and selective epoxidation systems. Selective epoxidizing catalysts utilizing dioxygen are based on ruthenium porphyrins. 

In conclusion, POMs and metalloporphyrins have been shown to be excellent catalysts for the in vitro biomimetic oxidative transformation of organic compounds, namely their sp and sp carbon centers, when hydrogen peroxide is used as the oxygen donor and acetonitrile as solvent. 

The observation that iron porphyrins can catalyze, under mild conditions, epoxidations of alkenes when iodosylbenzene is used as the oxidant has been followed up by a number of studies on metallopor-phyrins as models for cytochrome P-4S0 enzymes. Cytochrome P-4S0 enzymes catalyze epoxidation of alkenes by molecular oxygen in the presence of a hydrogen donor, NAOPH cofactor. This has led to the study of a number of systems based on a metalloporphyrin/02/reducing agent, to bring about epoxidation of alkenes. 

B. Meunier, Potassium monopersulfate-Just another primary oxidant or a highly versatile oxygen atom donor in metalloporphyrin-mediated oxygenation and oxidation reactions. New J. Chem. 16 (1992) 203. 

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