Solvent effects on catalytic activity of manganese porphyrins with cationic, anionic and uncharged meso substituents: Indirect evidence on the nature of active oxidant species

Solvent effects on the oxidation of olefins with periodate in water, acetonitrile, methanol and dichloromethane catalyzed by the manganese(III) complexes of meso ‐tetra(aryl)porphyrins (aryl = phenyl, 3‐methylpyridyl, 4‐sulfonatophenyl) have been studied to provide indirect evidence on the nature of active oxidants. Oxidation of cyclohexene and styrene with sodium periodate and tetra ‐n‐butylammonium periodate (TBAP) catalyzed by MnT(3‐MePy)P(OAc), MnT(4‐SO3)PP(OAc) and MnTPP(OAc) has been studied in water, methanol, acetonitrile and dichloromethane as solvents. The results show significant dependence of the product distribution on the type of solvent and the electronic nature of the aryl substituents introduced at the porphyrin periphery. While the oxidation of cyclohexene and styrene in the presence of MnT(3 ‐MePy)P(OAc) and MnTPP(OAc) in water (also in methanol) gave the corresponding epoxides as nearly the sole product, performing the reactions in the presence of MnT(4‐SO3)PP(OAc) yielded the products of allylic oxidation, cyclohexene ‐2‐ol and cyclohexene‐2‐one and acetophenone as the major products. In the case of styrene, performing the reaction in the presence of MnT(4‐SO3)PP(OAc), MnT(3 ‐MePy)P(OAc) and MnTPP(OAc) in acetonitrile gave a mixture of styrene oxide and acetophenone as the products. Under the same conditions, the oxidation of cyclohexene afforded cyclohexene oxide as approximately the exclusive product. Furthermore, the oxi...

Source: Applied Organometallic Chemistry - November 7, 2018 Category: Chemistry Authors: Zahra Esfandiari bayat, Hajar Rahiminezhad, Saeed Zakavi Tags: FULL PAPER Source Type: research