162331-68-2Relevant articles and documents
Photolysis of CH3Re(O2)2O induced by ligand-to-metal charge transfer and by peroxide intraligand excitation
Kunkely, Horst,Vogler, Arnd
, p. 467 - 470 (2005)
The electronic spectrum of the diperoxo complex MeReVII(O 2)2O shows a peroxide IL (intraligand) absorption at λmax ～ 260 nm in addition to the well-known peroxide to Re(VII) LMCT band at λmax = 358 nm. Upon IL excitation, the diperoxo group undergoes a dismutation. Accordingly, MeRe(O2) 2O photolyzes to MeReVIIO3 and O2. LMCT excitation at λirr = 405 nm is assumed to generate the radical pair MeReVI(O2)O+/O2- in the primary photochemical step. Back electron transfer and reaction with water leads finally to the monoperoxo complex MeReVII(O2)O2 and H2O2.
Water-catalyzed activation of H2O2 by methyltrioxorhenium: A combined computational-experimental study
Hwang, Taeho,Goldsmith, Bryan R.,Peters, Baron,Scott, Susannah L.
, p. 13904 - 13917 (2013)
The formation of peroxorhenium complexes by activation of H 2O2 is key in selective oxidation reactions catalyzed by CH3ReO3 (methyltrioxorhenium, MTO). Previous reports on the thermodynamics and kinetics of these reactions are inconsistent with each other and sometimes internally inconsistent. New experiments and calculations using density functional theory with the ωB97X-D and augmented def2-TZVP basis sets were conducted to better understand these reactions and to provide a strong experimental foundation for benchmarking computational studies involving MTO and its derivatives. Including solvation contributions to the free energies as well as tunneling corrections, we compute negative reaction enthalpies for each reaction and correctly predict the hydration state of all complexes in aqueous CH3CN. New rate constants for each of the forward and reverse reactions were both measured and computed as a function of temperature, providing a complete set of consistent activation parameters. New, independent measurements of equilibrium constants do not indicate strong cooperativity in peroxide ligand binding, as was previously reported. The free energy barriers for formation of both CH3ReO2(η2-O 2) (A) and CH3ReO(η2-O2) 2(H2O) (B) are predominantly entropic, and the former is much smaller than a previously reported value. Computed rate constants for a direct ligand-exchange mechanism, and for a mechanism in which a water molecule facilitates ligand-exchange via proton transfer in the transition state, differ by at least 7 orders of magnitude. The latter, water-assisted mechanism is predicted to be much faster and is consequently in much closer agreement with the experimentally measured kinetics. Experiments confirm the predicted catalytic role of water: the kinetics of both steps are strongly dependent on the water concentration, and water appears directly in the rate law.
Behaviour of dimeric methylrhenium(VI) oxides in the presence of hydrogen peroxide and its consequences for oxidation catalysis
Rost, Alexandra M. J.,Scherbaum, Andrea,Herrmann, Wolfgang A.,Kuehn, Fritz E.
, p. 1599 - 1605 (2007/10/03)
Avoiding the use of toxic methyltin precursors to synthesize methyltrioxorhenium (MTO) and its mono- and bis-peroxo derivatives, applicable as oxidation catalysts, dimethyl zinc might be considered a promising alternative alkylating agent. However, the methylrhenium(vi) dimers, formed as reduction products alongside MTO during the reaction of dimethyl zinc with Re2O7, are not as straightforwardly transformed into the epoxidation catalysts as MTO itself in the presence of excess H 2O2. In the case of red (μ-oxo) bis[trimethyloxorhenium(vi)], the main reaction product with H2O 2 is the catalytically inactive trimethyldioxorhenium(vii). In the case of bis[dimethyl(μ-oxo)oxorhenium(vi)], slow conversion to the monomeric mono- and bis-peroxo congenes of MTO occurs. Furthermore, part of the Re(vi) starting complex is transformed into inactive perrhenate. While bis[dimethyl(μ-oxo)oxorhenium(vi)] might be applied (also in a mixture with MTO) as an oxidation catalyst precursor, (μ-oxo)bis[trimethyloxorhenium(vi)] can be applied as a useful precursor for the synthesis of trimethyldioxorhenium(vii), which was previously only accessible by less convenient synthetic pathways. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.
Thermal and Photochemical Reactions of Methylrhenium Diperoxide: Formation of Methyl Hydroperoxide in Acetonitrile
Wang, Wei-Dong,Espenson, James H.
, p. 5069 - 5075 (2008/10/09)
Compared to the system in aqueous solution, the equilibration reactions in acetonitrile between MTO and the methylrhenium peroxides CH3ReO2(η2-O2) (A) and CH3ReO(η2-O2)2(H2O) (B) are slower but more favored thermodynamically. In CH3CN, small concentrations of water facilitate the formation of A (especially) and B. These species decompose to methyl hydroperoxide and perrhenic acid in CD3CN, rather than to methanol and perrhenic acid as in aqueous solution. The proposed mechanism involves the intramolecular migration of the methyl group to a peroxo oxygen, followed by hydrolysis, and it is facilitated by photolysis. The potential use of B as photocatalyst does not seem promising, however.
Deactivation of methylrhenium trioxide - Peroxide catalysts by diverse and competing pathways
Abu-Omar,Hansen,Espenson
, p. 4966 - 4974 (2007/10/03)
The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH3ReO2(η2-O2), A, and CH3Re(O)(η2-O2)2(H2O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV-vis). In aqueous solution, the equilibrium constants for their formation are K1 = 16.1 ± 0.2 L mol-1 and K2 = 132 ± 2 L mol-1 at pH 0, μ = 2.0 M, and 25 °C. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H2O2] and [H3O+]. The complex peroxide and pH dependences could be explained by one of two possible pathways: attack of either hydroxide on A or HO2- on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are k(A) = (6.2 ± 0.3) x 109 and k(MTO) = (4.1 ± 0.2) x 108 L mol-1 s-1 at μ = 0.01 M and 25 °C. The plot of log k(ψ) versus pH for the decomposition reaction is linear with a unit slope in the pH range 1.77-6.50. The diperoxide B decomposes much more slowly to yield O2 and CH3ReO3. This is a minor pathway, however, amounting to -4 s-1 at pH 3.21, μ = 0.10 M, and 25 °C. Without peroxide, CH3ReO3 is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH4 and ReO4-. As a consequence, the decomposition rate rises sharply with [H2O2), peaking at the concentration at which [A] is a maximum, and then falling to a much smaller value. Variable-temperature 1H NMR experiments revealed the presence of a labile coordinated water in B, but supported the anhydride form for A. The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH3ReO2(η2-O2), A, and CH3Re(O)(η2-2)2(H2O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV-vis). In aqueous solution, the values of the equilibrium constants for their formation are given. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H2O2] and [H3O+]. The complex peroxide and pH dependences could be explained by one of two possible pathways: attack of either hydroxide on A or HO2- on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are given. The plot of log k versus pH for the decomposition reaction is linear with the unit slope in the pH range 1.77-6.50. The diperoxide B decomposes much more slowly to yield O2 and CH3ReO3. This is a minor pathway, however, amounting to 3ReO3 is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH4 and ReO4-. As a consequence, the decomposition rate rises sharply with [H2O2], peaking at the concentration at which [A] is a maximum and then falling to a much smaller value. Variable-temperature 1H NMR experiments revealed the presence of a labile coordinated water in B, but supported the anhydride form for A.
