2687-45-8Relevant articles and documents
Biomimetic oxidation reactions of a naked manganese(V)-Oxo porphyrin complex
Lanucara, Francesco,Crestoni, Maria Elisa
experimental part, p. 12092 - 12100 (2011/11/28)
The intrinsic reactivity of a manganese(V)-oxo porphyrin complex, a typically fleeting intermediate in catalytic oxidation reactions in solution, has been elucidated in a study focused on its gas-phase ion-chemistry. The naked high-valent MnV-oxo porphyrin intermediate 1 ([(tpfpp)Mn VO]+; tpfpp=meso-tetrakis(pentafluorophenyl)porphinato dianion), has been obtained by controlled treatment of [(tpfpp)Mn III]Cl (2-Cl) with iodosylbenzene in methanol, delivered in the gas phase by electrospray ionization and assayed by FT-ICR mass spectrometry. A direct kinetic study of the reaction with selected substrates, each containing a heteroatom X (X=S, N, P) including amines, sulfides, and phosphites, was thus performed. Ionic products arising from electron transfer (ET), hydride transfer (HT), oxygen-atom transfer (OAT), and formal addition (Add) may be observed, with a predominance of two-electron processes, whereas the product of hydrogen-atom transfer (HAT), [(tpfpp)MnIVOH]+, is never detected. A thermochemical threshold for the formation of the product radical cation allows an evaluation of the electron-transfer ability of a Mn V-oxo complex, yielding a lower limit of 7.85 eV for the ionization energy of gaseous [(tpfpp)MnIVO]. Linear free-energy analyses of the reactions of para-substituted N,N-dimethylanilines and thioanisoles indicate that a considerable amount of positive charge is developed on the heteroatom in the oxidation transition state. Substrates endowed with different heteroatoms, but similar ionization energy display a comparable reaction efficiency, consistent with a mechanism initiated by ET. For the first time, the kinetic acidity of putative hydroxo intermediates playing a role in catalytic oxidations, [(tpfpp)FeIVOH]+ and [(tpfpp)Mn IVOH]+, has been investigated with selected reference bases, revealing a comparatively higher basicity for the ferryl, [(tpfpp)Fe IVO], with respect to the manganyl, [(tpfpp)MnIVO], unit. Finally, the neat association reaction of 2 has been studied with various ligands showing that harder ligands are more strongly bound.
Synthesis and oxygen-atom transfer reactions of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes
Baumstark,Chen,Rodriguez
, p. 1399 - 1402 (2007/10/03)
A series of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes 2a-d were synthesized in good yield from the corresponding 3-hydroxy-1,2-dioxolanes by reaction with concentrated hydrogen peroxide in acetonitrile with p-toluenesulfonic acid as catalyst. The 3-hydroperoxy-1,2-dioxolanes were effective oxygen-atom transfer reagents for the oxidation of thioanisole, triethylamine and 2,3-dimethyl-2-butene to the sulfoxide, N-oxide and epoxide, respectively. The reactions occurred under mild conditions and were found to be of the second order overall. The second order rate constants (k2) were determined for oxidation of thioanisole by 2a-d in deuteriochloroform. For 2a, k2 values for N-oxidation and epoxidation were also measured. The 3-hydroperoxy-1,2-dioxolanes were found to be less reactive than the structurally similar cyclic α-azohydroperoxides but much more reactive than simple hydroperoxides. The mechanism of oxygen-atom transfer is postulated to occur via nucleophilic attack of the substrate on the terminal oxygen of the hydroperoxide. Intramolecular hydrogen bonding of the hydroperoxy proton to a dioxolane oxygen appears to account for the reaction order in aprotic media.
