Manganese porphyrin, reaction

Green-yellow salts of the tetrahedral [MX4] (X = Cl, Br, I) ions can be obtained from ethanolic solutions and are well characterized. Furthermore, a whole series of adducts [MnX2L2] (X = Cl, Br, I) are known where L is an N-, P- or A -donor ligand, and both octahedral and tetrahedral stereochemistries are found. Of interest because of the possible role of manganese porphyrins in photosynthesis is [Mn (phthalocyanine)] which is square planar. The reaction of aqueous edta with MnC03 yields... 

Scheme 4 Electron- and proton-transfer reactions of manganese porphyrins in aqueous media.

The first reports on iron-catalyzed aziridinations date back to 1984, when Mansuy et al. reported that iron and manganese porphyrin catalysts were able to transfer a nitrene moiety on to alkenes [90]. They used iminoiodinanes PhIN=R (R = tosyl) as the nitrene source. However, yields remained low (up to 55% for styrene aziridination). It was suggested that the active intermediate formed during the reaction was an Fev=NTs complex and that this complex would transfer the NTs moiety to the alkene [91-93]. However, the catalytic performance was hampered by the rapid iron-catalyzed decomposition of PhI=NTs into iodobenzene and sulfonamide. Other reports on aziridination reactions with iron porphyrins or corroles and nitrene sources such as bromamine-T or chloramine-T have been published [94], An asymmetric variant was presented by Marchon and coworkers [95]. Biomimetic systems such as those mentioned above will be dealt with elsewhere. 

A significant result was obtained in the study of manganese porphyrin behavior in aqueous solutions [70], Manganese porphyrins (Mn3+P) in aqueous alkaline solutions are easily oxidized to corresponded Mn4+P, which, in their turn, are able to catalyze H202 synthesis in accordance with the following reaction ... 

The results from the publications mentioned are of interest because they can help in the creation of effective catalytic systems containing porphyrins, which combine functions typical of multienzyme systems. The task in hand is the possible synthesis of bifunctional catalysts based on metalloporphyrin systems, when with the help of manganese porphyrins, for example, or SOD mimic, hydrogen peroxide is accumulated in the system. Afterwards, the accumulated hydrogen peroxide is used in oxidation reactions of various substrates with iron porphyrin components of the catalyst. 

Tabushi and Koga reported the use of manganese porphyrins to catalyze the 02-oxidation of cyclohexene to cyclohexanol and cyclohexene-ol in the presence of borohydride these workers suggest that an equilibrium such as depicted in Reaction 32 is involved in non free-radical pathways (112). 

In a reaction modeled on the use of cytodirtxne P-450 to catalyze oxidations with iodosylbenzene, iron or manganese porphyrins have been used to catalyze aziridinations with iodinanes (Scheme 22). In this early report cis- or rranr-stilbene each gave the rrans-aziridine, but stereoselectivity has since been achieved for the sulfonylaziridines (Section 3.5.2.6). 

Apart from the commonly used NaOCl, urea—H2O2 has been used/ With this reaction, simple alkenes can be epoxi-dized with high enantioselectivity. The mechanism of this reaction has been examined.Radical intermediates have been suggested for this reaction, polymer-bound Mn -salen complex, in conjunction with NaOCl, has been used for asymmetric epoxidation. Chromium-salen complexes and ruthenium-salen complexes have been used for epoxidation. Manganese porphyrin complexes have also been used. Cobalt complexes give similar results. A related epoxidation reaction used an iron complex with molecular oxygen and isopropanal. Nonracemic epoxides can be prepared from racemic epoxides with salen-cobalt(II) catalysts following a modified procedure for kinetic resolution. 

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