Isolation of an Oxomanganese(V) Porphyrin Intermediate in the Reaction of a Manganese(III) Porphyrin Complex and H2O2 in Aqueous Solution

Synthesis, Characterization, and Reactivities of Manganese(V)−Oxo Porphyrin Complexes

“…[6][7][8][9] The intermediate persisted for several hours (t 1/2 ~40 min) at 35 °C. The formation of 1a was also observed when Mn(TDCPP)Cl was treated with other oxidants such as iodosylarenes (i.e., PhIO and F 5 PhIO) and H 2 O 2 under the identical conditions.…”

“…3,4 Synthetic manganese(III) porphyrins have also been extensively studied as CYP 450 models in oxygen atom transfer reactions.5 Although manganese porphyrins have shown promise as versatile catalysts in oxidation reactions over the past two decades, only recently have the key manganese(V)-oxo porphyrin intermediates been isolated, spectroscopically characterized, and studied in oxidation reactions.6 -9 Groves and co-workers reported the generation and characterization of the first manganese(V)-oxo porphyrin complexes in aqueous solution and the reactivities of these complexes in olefin epoxidation and in the oxidation of bromide and nitrite ions.6 Subsequently, Nam and co-workers demonstrated that a manganese(V)-oxo porphyrin can be generated with a biologically relevant oxidant, H 2 O 2 , in aqueous solution and that the formation of the intermediate depends markedly on the pH of reaction solutions. 7 Very recently, Newcomb and co-workers reported the generation of manganese(V)-oxo complexes via laser flash photolysis methods in organic solvents and the kinetic studies of the intermediates in olefin epoxidation and alkane hydroxylation. 8 Naruta and co-workers synthesized a dinuclear Mn V =O porphyrin complex in the presence of base in organic solvents that showed an O 2 -evolution via O-O bond formation between the manganese(V)-oxo moieties.9 In addition to the manganese(V)-oxo porphyrins, manganese(V)-oxo complexes bearing non-porphyrinic macrocycles, such as corrole and corrolazine, have been isolated and characterized.10 -15 Interestingly, the manganese(V)-oxo complexes of non-porphyrin ligands are very stable at room temperature and are poor oxidants in oxygen atom transfer reactions.…”

Mechanistic studies on versatile metal-assisted hydrogen peroxide activation processes for biomedical and environmental incentives

“…Such properties are acquired through cleavage of coordinated H2O2, resulting in electron withdrawal from the central metal ion and formation of Mn V =O species. Existence of such a reactive form was confirmed by spectroscopic [145] and electrochemical [146] methods. In further studies, the efficient transfer of its oxo ligand to the substrate, such as bromide [147] or alkenes [148] was shown.…”

Ionic Manganese Porphyrins with S-containing Counter Anions: Mimicking Cytochrome P450 Activity for Alkene Epoxidation

“…Moreover, the improved conversion of styrene in the ionic system 3 in comparison with that in the neutral system 4 was attributed to the strong electron-withdrawing nature of quaternary ammonium cations in the porphyrin ring, suppressing the oxidative degradation of 3 [7][8][9][10].…”

“…Great efforts have been made to the chemical modification of metalloporphyrin microenvironment for the improvement of the catalytic efficiency as oxidation catalysts. Significant advances have been achieved by the introduction of bulky and/or electronwithdrawing substituents into the porphyrino ring to restrict the formation of unreactive l-oxo Mn IV -porphyrin dimmer and hence improve the activity/selectivity/stability of metalloporphyrins [4][5][6][7][8]. In addition, the supportedmetalloporphyrins such as mesoporous molecular sieve (MCM-41) [9], Merrifield's peptide resin [10], highly crossing-linked polymer [11] are robust catalysts toward oxidative degradation/self aggregation for alkene epoxidations due to efficient porphyrin site-isolation.…”