SIDE-CHAIN OXIDATION OF BENZYLTRIMETHYLSILANES BY IODOSYLBENZENE IN THE PRESENCE OF IRON AND MANGANESE PORPHYRINS

Benzyltrimethylsilanes react with iodosylbenzene in the presence of either iron(III) or manganese(III) tetrakis(pentafluorophenyl)porphyrin (TFPPM, with M = Fe, Mn) to give alpha-hydroxybenzyltrimethylsilanes, which are then rapidly converted into the corresponding benzaldehydes in the reaction medium. In these reactions the active species is the metal-oxo complex, TFPPM(V)=O, formed by iodosylbenzene and TFPPM. A relative reactivity study for a series of ring substituted benzyltrimethylsilanes has shown that when M = Fe, the reaction is quite selective (rho = -1.85), with the m-MeO substituent exhibiting a much higher reactivity than expected. When M = Mn, a lower rho value (-1.15) is observed and no anomalous reactivity is found with the m-MeO group. These result suggest that the side-chain hydroxylation of benzyltrimethylsilane by TFPPMn(V)=O occurs by the well known hydrogen atom transfer mechanism. For the corresponding reactions induced by TFPPFe(V)=O a coupled proton/electron transfer mechanism, which might involve the formation of a charge-transfer complex, seems more likely

Oxidation of N-Methyl-9-t-butylacridane by Iodosylbenzene Catalyzed by Tetrakis(pentafluorophenyl) Porphyrin Iron(III). A Tool to Investigate the Mechanism of the Biomimetic N-Demethylation of Aromatic Tertiary Amines.

The PhIO promoted oxidation of N-methyl-9-t-butylacridane (1) catalyzed by tetrakis(pentafluorophenyl) porphyrin iron(III) leads first to 9-t-butylacridane and then to acridine. It is suggested that 1 can represent a reliable machanistic probe to detect the intervention of radical cations in the oxidation of aromatic amines. (C) 1999 Elsevier Science Ltd. All rights reserved

A kinetic study of the reaction of N,N-dimethylanilines with 2,2-diphenyl-1-picrylhydrazyl radical: A concerted proton-electron transfer?

The reactivity of the 2,2-diphenyl-1-picrylhydrazyl radical (dpph) toward the N-methyl C-H bond of a number of 4-X-substituted-N,N-dimethylanilines (X = OMe, OPh, CH3, H) has been investigated in MeCN, in the absence and in the presence of Mg(ClO4)(2), by product, and kinetic analysis. The reaction was found to lead to the N-demethylation of the N,N-dimethylaniline with a rate quite sensitive to the electron donating power of the substituent (rho(+) = -2.03). With appropriately deuterated N,N-dimethylanilines, the intermolecular and intramolecular deuterium kinetic isotope effects (DKIEs) were measured with the following results. Intramolecular DKIE [(k(H)/k(D))(intra)] was found to always be similar to intermolecular DKIE [(k(H)/k(D))(inter)]. These results suggest a single-step hydrogen transfer mechanism from the N-C-H bond to dpph which might take the form of a concerted proton-electron transfer (CPET). An electron transfer (ET) step from the aniline to dpph leading to an anilinium radical cation, followed by a proton transfer step that produces an alpha-amino carbon radical, appears very unlikely. Accordingly, a rate-determining ET step would require no DKIE or at least different inter and intramolecular isotope effects. On the other hand, an equilibrium-control led ET is not compatible with the small slope value (-0.22 kcal(-1) K-1) of the log k(H)/Delta G plot. Furthermore, the reactivity increases by changing the solvent to the less polar toluene whereas the reverse would be expected for an ET mechanism. In the presence of Mg2+, a strong rate acceleration was observed, but the pattern of the results remained substantially unchanged: inter and intramolecular DKIEs were again very similar as well as the substituent effects. This suggests that the same mechanism (CPET) is operating in the presence and in the absence of Mg2+. The significant rate accelerating effect by Mg2+ is likely due to a favorable interaction of the Mg2+ ion with the partial negatively charged alpha-methyl carbon in the polar transition state for the hydrogen transfer process

Oxidations of Benzyl and Phenethyl Phenyl Sulfides. Implications for the Mechanism of the Microsomal and Biomimetic Oxidations of Sulfides

The study of the oxidation of 4-methoxyphenethyl phenyl sulfide and 3,4-dimethoxyphenethyl phenyl sulfide with potassium 12-tungstocobalt(III)ate [Co(III)W] suggests that in the radical cations of 3,4,5-(MeO)(3)PhCH2SPh (4) and 2,4,6(MeO)(3)PhCH2SPh (5) the positive charge is not localized on the sulfur atom, but in the benzylic aromatic ring. Nevertheless, in the biomimetic and microsomal oxidation of 4 and 5 the products observed are exclusively sulfoxides and sulfones, which appears in contrast with a mechanism involving the formation of an intermediate sulfide radical cation followed by a fast oxygen rebound. A direct oxygen transfer mechanism seems most likely

Formation of quinones in the iron porphyrin catalysed oxidation of benzene and alkylbenzenes by magnesium monoperoxyphthalate.

Biomimetic oxidation of unactivated arenes with magnesium monoperoxyphthalate and a fluorinated iron pophyrin as catalyst lead mainly to p-quinones without involving phenols as reaction intermediates