115259-01-3Relevant articles and documents
Synthesis, characterization, and reactivities of manganese(V)-oxo porphyrin complexes
Woon, Ju Song,Mi, Sook Seo,George, Serena DeBeer,Ohta, Takehiro,Song, Rita,Kang, Min-Jung,Tosha, Takehiko,Kitagawa, Teizo,Solomon, Edward I.,Nam, Wonwoo
, p. 1268 - 1277 (2007)
The reactions of manganese(III) porphyrin complexes with terminal oxidants, such as m-chloroperbenzoic acid, iodosylarenes, and H2O2, produced high-valent manganese(V)-oxo porphyrins in the presence of base in organic solvents at room temperature. The manganese(V)-oxo porphyrins have been characterized with various spectroscopic techniques, including UV-vis, EPR, 1H and 19F NMR, resonance Raman, and X-ray absorption spectroscopy. The combined spectroscopic results indicate that the manganese(V)-oxo porphyrins are diamagnetic low-spin (S = O) species with a longer, weaker Mn-O bond than in previously reported Mn(V)-oxo complexes of non-porphyrin ligands. This is indicative of double-bond character between the manganese(V) ion and the oxygen atom and may be attributed to the presence of a trans axial ligand. The [(Porp)MnV=O]+ species are stable in the presence of base at room temperature. The stability of the intermediates is dependent on base concentration. In the absence of base, (Porp)-Mn IV=O is generated instead of the [(Porp)MnV=O]+ species. The stability of the [(Porp)MnV=O]+ species also depends on the electronic nature of the porphyrin ligands: [(Porp)Mn V=O]+ complexes bearing electron-deficient porphyrin ligands are more stable than those bearing electron-rich porphyrins. Reactivity studies of manganese(V)-oxo porphyrins revealed that the intermediates are capable of oxygenating PPh3 and thioanisoles, but not olefins and alkanes at room temperature. These results indicate that the oxidizing power of [(Porp)MnV=O]+ is low in the presence of base. However, when the [(Porp)MnV=O]+ complexes were associated with iodosylbenzene in the presence of olefins and alkanes, high yields of oxygenated products were obtained in the catalytic olefin epoxidation and alkane hydroxylation reactions. Mechanistic aspects, such as oxygen exchange between [(Porp)MnV=16O]+ and H2 18O, are also discussed.
Unprecedented Reactivities of Highly Reactive Manganese(III)-Iodosylarene Porphyrins in Oxidation Reactions
Zhang, Lina,Lee, Yong-Min,Guo, Mian,Fukuzumi, Shunichi,Nam, Wonwoo
, p. 19879 - 19884 (2020)
We report that Mn(III)-iodosylarene porphyrins, [MnIII(Porp)(sArIO)]+, are capable of activating the C-H bonds of hydrocarbons, including unactivated alkanes such as cyclohexane, with unprecedented reactivities, such as a low kinetic isotope effect, a saturation behavior of reaction rates, and no electronic effect of porphyrin ligands on the reactivities of [MnIII(Porp)(sArIO)]+. In oxygen atom transfer (OAT) reactions, the sulfoxidation of para-X-substituted thioanisoles by [MnIII(Porp)(sArIO)]+ affords a very unusual behavior in the Hammett plot with the saturation behavior of reaction rates and no electronic effect of porphyrin ligands on reactivities. The reactivities and mechanisms of [MnIII(Porp)(sArIO)]+ are then compared with those of the corresponding MnIV(Porp)(O) complex. The present study reports the first example of highly reactive Mn(III)-iodosylarene porphyrins with unprecedented reactivities in C-H bond activation and OAT reactions.
Enthalpy-Entropy Compensation Effect in Oxidation Reactions by Manganese(IV)-Oxo Porphyrins and Nonheme Iron(IV)-Oxo Models
Guo, Mian,Zhang, Jisheng,Zhang, Lina,Lee, Yong-Min,Fukuzumi, Shunichi,Nam, Wonwoo
supporting information, p. 18559 - 18570 (2021/11/22)
"Enthalpy-Entropy Compensation Effect"(EECE) is ubiquitous in chemical reactions; however, such an EECE has been rarely explored in biomimetic oxidation reactions. In this study, six manganese(IV)-oxo complexes bearing electron-rich and -deficient porphyrins are synthesized and investigated in various oxidation reactions, such as hydrogen atom transfer (HAT), oxygen atom transfer (OAT), and electron-transfer (ET) reactions. First, all of the six Mn(IV)-oxo porphyrins are highly reactive in the HAT, OAT, and ET reactions. Interestingly, we have observed a reversed reactivity in the HAT and OAT reactions by the electron-rich and -deficient Mn(IV)-oxo porphyrins, depending on reaction temperatures, but not in the ET reactions; the electron-rich Mn(IV)-oxo porphyrins are more reactive than the electron-deficient Mn(IV)-oxo porphyrins at high temperature (e.g., 0 °C), whereas at low temperature (e.g., -60 °C), the electron-deficient Mn(IV)-oxo porphyrins are more reactive than the electron-rich Mn(IV)-oxo porphyrins. Such a reversed reactivity between the electron-rich and -deficient Mn(IV)-oxo porphyrins depending on reaction temperatures is rationalized with EECE; that is, the lower is the activation enthalpy, the more negative is the activation entropy, and vice versa. Interestingly, a unified linear correlation between the activation enthalpies and the activation entropies is observed in the HAT and OAT reactions of the Mn(IV)-oxo porphyrins. Moreover, from the previously reported HAT reactions of nonheme Fe(IV)-oxo complexes, a linear correlation between the activation enthalpies and the activation entropies is also observed. To the best of our knowledge, we report the first detailed mechanistic study of EECE in the oxidation reactions by synthetic high-valent metal-oxo complexes.
Highly Reactive Manganese(IV)-Oxo Porphyrins Showing Temperature-Dependent Reversed Electronic Effect in C-H Bond Activation Reactions
Guo, Mian,Seo, Mi Sook,Lee, Yong-Min,Fukuzumi, Shunichi,Nam, Wonwoo
supporting information, p. 12187 - 12191 (2019/08/20)
We report that Mn(IV)-oxo porphyrin complexes, MnIV(O)(TMP) (1) and MnIV(O)(TDCPP) (2), are capable of activating the C-H bonds of hydrocarbons, including unactivated alkanes such as cyclohexane, via an oxygen non-rebound mechanism. Interestingly, 1 with an electron-rich porphyrin is more reactive than 2 with an electron-deficient porphyrin at a high temperature (e.g., 0 °C). However, at a low temperature (e.g., -40 °C), the reactivity of 1 and 2 is reversed, showing that 2 is more reactive than 1. To the best of our knowledge, the present study reports the first example of highly reactive Mn(IV)-oxo porphyrins and their temperature-dependent reactivity in C-H bond activation reactions.
Mechanism of manganese porphyrin-catalyzed oxidation of alkenes. Role of manganese(IV)-oxo species
Arasasingham, Ramesh D.,He, Gong-Xin,Bruice, Thomas C.
, p. 7985 - 7991 (2007/10/02)
The mechanism for the bimolecular reaction of meso-tetrakis(2,6-dichlorophenyl)porphinato-oxo-manganese-(IV), [(C18TPP)MnIV(O)], with alkenes has been investigated by kinetics and product identification. Kinetic studies were carried out with 11 alkenes (trear-4-methoxystilbene, cis-4-methoxystilbene, 1,4-diphenyl-1,3-butadiene, 4-methoxystyrene, 1,1-diphenylethylene, 4-methylstyrene, 2,3-dimethyl-2-butene, trans-stilbene, cis-stilbene, styrene, 4-acetoxystyrene) in methylene chloride solution (30 °C) in air. The reactivities of the alkenes show that the trans alkenes are slightly more reactive than their cis isomers and that electron releasing substituents slightly favor the reaction. The second-order rate constant values (k2) correlate well with the potentials for the le- oxidation (E1/2) of the alkenes. The slope of the linear plot of log k2 vs E1/2for the series of alkenes (slope = -0.89 V-1) indicate that a mechanism of epoxidation involving rate-determining formation of an alkene derived π-cation-radical is unlikely. For the reaction with substituted styrenes, the linear free-energy relationship of log k2 vs σ (p+ = -0.99) supports a transition state with very little charge separation. Product yields determined for the reactions with cis-stilbene, transstilbene, 2,3-dimethyl-2-butene, cis-4-methoxystilbene, and trans-4-methoxystilbene are in accord with a mechanism involving the formation of a (porph)MnIIIOCC? radical intermediate. Thus, the products of cis-stilbene oxidation under aerobic conditions are cis-stilbene oxide (7%), frans-stilbene oxide (5%), and benzaldehyde (3%). Comparison with the reactions carried out under conditions favoring the transiently stable manganese(V)-oxo species showed more efficient epoxidation with a greater degree of stereospecificity. In a search for radical intermediates the cis olefinic substrate (Z)-1,2-bis(trans-2,trans-3-diphenylcyclopropyl)ethene was used as a radical trap. While no epoxide products were found, a polar oxygen-containing product resulting from the opening of one trans-2,trans-3-diphenylcyclopropyl ring by a cyclopropylcarbinyl to homoallylcarbinyl radical rearrangement (CPCRR) was detected supporting the formation of a neutral carbon radical species.
