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

Abstract

Oxidation of cyclohexene and styrene with sodium periodate and tetra-nbutylammonium periodate (TBAP) catalyzed by MnT(3-MePy)P(OAc), MnT(4-SO 3 )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-SO 3 )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-SO 3 )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 oxidation of olefins in dichloromethane gave the corresponding epoxide as the exclusive products. The product distributions observed in the protic and aprotic solvents were used to provide indirect evidence on the relative contribution and reactivity of high valent manganese oxo and periodato Mn(III) porphyrin species to the oxidation reactions.

Graphene Oxide Supported Oxovanadium (IV) Complex for Catalytic Peroxidative Epoxidation of Styrene: An Eye‐Catching Impact of Solvent

“…As we focused mainly on commercially remunerative products, we executed the experiment to analyze the effect of diverse solvents on the epoxidation of styrene which has significant effect on the product distribution. [37] The study of effect of different solvents on the epoxidation of styrene was aimed to reduce the other byproduct formation and to increase the major key yield. A very little conversion was observed with solvents like toluene, DMF and acetonitrile ( Figure 6).…”

Manganese porphyrins/mesoporous amberlyst 15 nanocomposites: Robust biomimetic catalysts for aqueous oxidation of olefins

“…Also, Mohajer et al found spectroscopic evidence for the formation of high valent oxo manganese porphyrin species in the presence of hydrogen bond donor additives under homogeneous conditions. [ 44 ] Furthermore, the product distribution upon the oxidation of olefins with periodate [ 41 ] and iodosylarenes [ 45 ] was shown to provide evidence on the nature of active oxidant species; the observation of allylic products in the oxidation of olefins such as cyclohexene also the formation of benzaldehyde in the oxidation of styrenes are in accord with the formation of the high valent Mn‐O species as the active oxidant. As was explained above (Section 3.5), no allylic products were observed in the oxidation of cycloocetene and indene.…”

“…It is noteworthy that the formation of allylic products necessitates the presence of high valent oxo manganese(V) porphyrin species. [ 41,42 ] Also, the abstraction of methyl from styrene and formation of benzaldehyde required a similar mechanism. [ 43 ]…”

Periodate-Mediated Aerobic Oxidation of Sulfides over a Bifunctional Porphyrin-polyoxometalate Catalyst: Photosensitized Singlet Oxygen Oxidation of Iodate to Periodate

“…The oxidation of organic compounds with periodate on tungsten polyoxometalate (POM) is the first report on the activation of periodate by d 0 transition metals. It is noteworthy that the presence of a cocatalyst (imidazoles or pyridines) was most often necessary to achieve an acceptable conversion value in the oxidation of organic substrates catalyzed by metalloporphyrins and metal Schiff base complexes. − Also, in the case of the d n transition-metal complexes, the formation of high-valent metal oxo species with higher oxidizing ability than the corresponding six-coordinate periodato intermediates ,,− led to the overoxidation of organic substrates such as sulfides and a decrease in the selectivity of the reaction toward sulfoxides. As shown in various studies, ,,, the formation of high-valent metal oxo species is significantly facilitated in water and organic solvents containing water or hydrogen-bond donors such as alcohols.…”