14446-92-5

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• 14035-33-7 1-(3,5-di-tert-butyl-4-hydroxyphenyl)ethanone 

Relevant academic research and scientific papers

Hydrogen Atom Abstraction by High-Valent Fe(OH) versus Mn(OH) Porphyrinoid Complexes: Mechanistic Insights from Experimental and Computational Studies

High-valent metal-hydroxide species have been implicated as key intermediates in hydroxylation chemistry catalyzed by heme monooxygenases such as the cytochrome P450s. However, in some classes of P450s, a bifurcation from the typical oxygen rebound pathway is observed, wherein the FeIV(OH)(porphyrin) species carries out a net hydrogen atom transfer reaction to form alkene metabolites. In this work, we examine the hydrogen atom transfer (HAT) reactivity of FeIV(OH)(ttppc) (1), ttppc = 5,10,15-tris(2,4,6-triphenyl)-phenyl corrole, toward substituted phenol derivatives. The iron hydroxide complex 1 reacts with a series of para-substituted 2,6-di-tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, Et, H, Ac), with second-order rate constants k2 = 3.6(1)-1.21(3) × 104 M-1 s-1 and yielding linear Hammett and Marcus plot correlations. It is concluded that the rate-determining step for O-H cleavage occurs through a concerted HAT mechanism, based on mechanistic analyses that include a KIE = 2.9(1) and DFT calculations. Comparison of the HAT reactivity of 1 to the analogous Mn complex, MnIV(OH)(ttppc), where only the central metal ion is different, indicates a faster HAT reaction and a steeper Hammett slope for 1. The O-H bond dissociation energy (BDE) of the MIII(HO-H) complexes were estimated from a kinetic analysis to be 85 and 89 kcal mol-1 for Mn and Fe, respectively. These estimated BDEs are closely reproduced by DFT calculations and are discussed in the context of how they influence the overall H atom transfer reactivity.

A cobalt(ii) iminoiodane complex and its scandium adduct: Mechanistic promiscuity in hydrogen atom abstraction reactions

In addition to oxometal [Mn+O] and imidometal [Mn+NR] units, transient metal-iodosylarene [M(n-2)+-OIPh] and metal-iminoiodane [M(n-2)+-N(R)IPh] adducts are often invoked as a possible second oxidant responsible for the oxo and imido group transfer reactivity. Although a few metal-iodosylarene adducts have been recently isolated and/or spectroscopically characterized, metal-iminoiodane adducts have remained elusive. Herein, we provide UV-Vis, EPR, NMR, XAS and DFT evidence supporting the formation of a metal-iminoiodane complex 2 and its scandium adduct 2-Sc. 2 and 2-Sc are reactive toward substrates in the hydrogen-atom and nitrene transfer reactions, which confirm their potential as active oxidants in metal-catalyzed oxidative transformations. Oxidation of para-substituted 2,6-di-tert-butylphenols by 2 and 2-Sc can occur by both coupled and uncoupled proton and electron transfer mechanisms; the exact mechanism depends on the nature of the para substituent.

Hydrogen atom transfer reactions of imido manganese(V) corroie: One reaction with two mechanistic pathways

Hydrogen atom transfer (HAT) reactions of (tpfc)MnNTs have been investigated (tpfc = 5,10,-15-tris(pentafluorophenyl)corrole and Ts = p-toluenesulfonate). 9,10-Dihydroanthracene and 1,4-dihydrobenzene reduce (tpfc)MnNTs via HAT with second-order rate constants 0.16 ± 0.03 and 0.17 ± 0.01 M-1 s-1, respectively, at 22°C. The products are the respective arenes, TsNH2 and (tpfc)MnIII. Conversion of (tpfc)MnNTs to (tpfc)Mn by reaction with dihydroanthracene exhibits isosbestic behavior, and formation of 9,9′,10,10′- tetrahydrobianthracene is not observed, suggesting that the intermediate anthracene radical rebounds in a second fast step without accumulation of a MnIV intermediate. The imido complex (tpfc)-MnVNTs abstracts a hydrogen atom from phenols as well. For example, 2,6-di-tert-butyl phenol is oxidized to the corresponding phenoxyl radical with a second-order rate constant of 0.32 ± 0.02 M-1 s-1 at 22°C. The other products from imido manganese(V) are TsNH2 and the trivalent manganese corrole. Unlike reaction with dihydroarenes, when phenols are used isosbestic behavior is not observed, and formation of (tpfc)-Mn IV(NHTs) is confirmed by EPR spectroscopy. A Hammett plot for various p-substituted 2,6-di-tert-butyl phenols yields a V-shaped dependence on σ, with electron-donating substituents exhibiting the expected negative ρ while electron-withdrawing substituents fall above the linear fit (i.e., positive ρ). Similarly, a bond dissociation enthalpy (BDE) correlation places electron-withdrawing substituents above the well-defined negative slope found for the electron-donating substituents. Thus two mechanisms are established for HAT reactions in this system, namely, concerted proton - electron transfer and proton-gated electron transfer in which proton transfer is followed by electron transfer.