Substituent And Solvent Effects On The Catalytic Activity Of Manganese(Ⅲ) Corroles

Manganese corroles have been implicated as superb catalysts in numerous chemicalreactions such as oxidation, cyclopropanation, decomposition of peroxynitrite andhydroxylation. Among these catalytic reactions, manganese corroles catalyzed oxidation oforganic substrates, such as alkanes, alkenes and alcohols, have flourished prominently inrecent years. Many terminal oxidants, such as ozone, iodosylbenzene (PhIO), tert-butylhydroperoxide (t-BuOOH) and m-chloroperbenzoic acid (m-CPBA) have been employed asoxygen source in the catalytic systems of manganese corroles to explore their reactivity. Itwas found that substrate, substituent, nature of solvent, oxidant and the axial ligand have longbeen known to play crucial roles in the oxdiation reactions. Although a lot of reports havefocused on manganese corrole catalyzed oxidation reactions, the factors controlling theirreactivity are still ambiguous. we here report the systematic investigations of the role ofsolvent on the catalytic oxidation of styrene by Mn(III) corroles bearing different electronicfeatures using PhIO as oxidant. The plausible mechanism for the oxidation reaction is alsosuggested. The main content of this paper is as follows:Four Mn(III) corroles that differ in their electronic environments based on meso-substitution by pentafluorophenyl and phenyl groups were synthesized and characterized byspectroscopic techniques (UV-visible, mass spectrometry and nuclear magnetic resonance).The four Mn(III) corroles are: Manganese (III)5,10,15-tris (pentafluorophenyl) corrole (F15C-Mn(III)); Manganese (III)5,15-bis(pentafluorophenyl),10-(phenyl) corrole (F10C-Mn(III));Manganese(III)5,15-bis(phenyl),10-(pentafluorophenyl) corrole (F5C-Mn(III)); Manganese(III)5,10,15-tris(phenyl) corrole (F0C-Mn(III)). Utilization of these Mn(III) corroles forstyrene oxidation using iodosylbenzene (PhIO) as oxygen source in toluene, dichloromethane(DCM), DMF, DMAc, THF and DMSO revealed a remarkable effect of solvent on thecatalytic activity.Furthermore, the transformation of Mn(III) corroles into their corresponding Mn(V)-oxocorroles, and subsequent treatment with styrene also indicated that more electron-deficientMn(V)-oxo corroles exhibit higher reactivity in toluene and DCM, while less electron-deficient Mn(V)-oxo corroles exhibit higher reactivity in DMF and DMAc. A significantdifference in the observed rates of reaction suggest that the catalytic oxidation of styrene bymanganese corroles may proceed through different pathways, and is strongly solvent-dependent.