288394-52-5Relevant academic research and scientific papers
Mechanistic study of iron(III) tetrakis(pentafluorophenyl)porphyrin triflate (F20TPP)Fe(OTf) catalyzed cyclooctene epoxidation by hydrogen peroxide
Stephenson, Ned A.,Bell, Alexis T.
, p. 2278 - 2285 (2007)
We have recently proposed a mechanism for the epoxidation of cyclooctene by H2O2 catalyzed by iron(III) [tetrakis-(pentafluorophenyl) ]porphyrin chloride, (F20TPP)FeCl, in solvent containing methanol [Stephenson, N. A.; Bell, A.T. Inorg. Chem. 2006, 45, 2758-2766]. In that study, we found that catalysis did not occur unless (F20TPP)FeCl first dissociated, a process facilitated by the solvation of the Cl- anion by methanol and the coordination of methanol to the (F20TPP)Fe + cation. Methanol as well as other alcohols was also found to facilitate the heterolytic cleavage of the O-O bond of H2O 2 coordinated to the (F20TPP)Fe+ cation via a generalized acid mechanism. In the present study, we have shown that catalytic activity of the (F20TPP)Fe+ cation can be achieved in aprotic solvent by displacing the tightly bound chloride anion with a weakly bound triflate anion. By working in an aprotic solvent, acetonitrile, it was possible to determine the rate of heterolytic O-O bond cleavage in coordinated H2O2 unaffected by the interaction of the peroxide with methanol. A mechanism is proposed for this system and is shown to be valid over a range of reaction conditions. The mechanisms for cyclooctene epoxidation and H2O2 decomposition for the aprotic and protic solvent systems are similar with the only difference being the mechanism of proton-transfer prior to heterolytic cleavage of the oxygen-oxygen bond of coordinated hydrogen peroxide. Comparison of the rate parameters indicates that the utilization of hydrogen peroxide for cyclooctene epoxidation is higher in a protic solvent than in an aprotic solvent and results in a smaller extent of porphyrin degradation due to free radical attack. It was also shown that water can coordinate to the iron porphyrin cation in aprotic systems resulting in catalyst deactivation; this effect was not observed when methanol was present, since methanol was found to displace all of the coordinated water.
Hydroxylation of aliphatic hydrocarbons with m-chloroperbenzoic acid catalyzed by electron-deficient iron(III) porphyrin complexes
Lim, Mi Hee,Lee, Yoon Jung,Goh, Yeong Mee,Nam, Wonwoo,Kim, Cheal
, p. 707 - 713 (2007/10/03)
The catalytic hydroxylation of aliphatic hydrocarbons by m- chloroperbenzoic acid (MCPBA) has been studied in the presence of electron- deficient iron(III) porphyrin complexes. High yields of alcohol products were obtained with small amounts of ketone formation under mild reaction conditions. The stereospecificity and regioselectivity of the iron porphyrin complexes have been investigated in hydroxylation reactions as well. The hydroxylation of alkanes has been performed in the presence of isotopically 18O-labeled water, H218O, in order to understand the effects of the electronic nature of iron porphyrin complexes, the concentration of H218O, the C-H bond strength of alkanes, and the reaction temperature on the 18O- incorporation from the labeled water into alcohols. We found that the amounts of 18O incorporated into the alcohol products varied in the reactions; these results were interpreted with that the reaction of oxygen atom transfer from a high-valent iron oxoporphyrin complex to alkanes competes with that of oxygen atom exchange between the intermediate and labeled water that leads to 18O-incorporation from H218O into the alcohol products. Deuterium kinetic isotope effects (KIEs) in the alkane hydroxylations by the iron porphyrin complexes and MCPBA have been studied with a mixture of cyclohexane and cyclohexane-d12. The KIE values obtained in the reactions were found to depend significantly on the nature to the iron porphyrin complexes. The temperature dependence of k(H)/k(D) was also studied from -40 to 25 °C and the parameters of Arrhenius equation (i.e., the pre-exponential factor ratio, A(H)/A(D), and the isotopic difference of C-H and C-D bond activation energies, E(a)(D)-E(a)(H)) were determined.
