70197-13-6Relevant articles and documents
Metathesis Reactions of Tris(adamantylimido)methylrhenium and Aldehydes and Imines
Wang, Wei-Dong,Espenson, James H.
, p. 5170 - 5175 (1999)
The tris(imido)methylrhenium compound CH3Re(NAd)3 (Ad = 1-adamantyl) was prepared and characterized. It reacts with aromatic aldehydes ArCHO forming the imines ArCH= NAd. The reaction occurs in three stages, during which CH3Re(NAd)2O and CH3Re(NAd)O2 could be detected. In the third and slowest stage CH3ReO3 (MTO) was formed, eventually in quantitative yield. The second-order rate constant for PhCHO in C6D6 at 298 K is 1.4 × 10-4 L mol-1 s-1. Electron-donating substituents at the para-position of ArCHO cause a significant diminution in rate. Treated by the Hammett equation, the reaction constant is p = +0.90. The reactions between CH3Re(NAd)3 and linear aliphatic aldehydes occur much faster than do reactions of nonlinear aliphatic or aromatic aldehydes, indicating an important steric effect. Ketones do not react. The imidorhenium complex evidently undergoes a metathesis reaction with the aldehyde. Analogously, CH3Re(NAd)3 reacts with imines. Imine-imine metathesis is catalyzed by MTO homogeneously and by MTO supported on Nb2O5.
Kinetics and mechanism of rhenium-catalyzed oxygen atom transfer from pyridine N-oxides to phosphines
Wang, Ying,Espenson, James H.
, p. 2266 - 2274 (2002)
The oxygen atom transfer (OAT) reaction cited does not occur on its own in > 10 h. Oxorhenium(V) compounds having the formula MeReO(dithiolate)PZ3 catalyze the reaction; the catalyst most studied was MeReO(mtp)PPh3, 1, where mtpH2 = 2-(mercaptomethyl)thiophenol. The mechanism was studied by multiple techniques. Kinetics (initial-rate and full-time-course methods) established this rate law: v = kc[-1][PyO]2[PPh3]-1. Here and elsewhere PyO symbolizes the general case XC5H4NO and PicO that with X = 4-Me. For 4-picoline, kc = (1.50 ± 0.05) × 104 L mol-1 s-1 in benzene at 25.0 °C; the inverse phosphine dependence signals the need for the removal of phosphine from the coordination sphere of rhenium prior to the rate-controlling step (RCS). The actual entry of PPh3 into the cycle occurs in a fast step later in the catalytic cycle, after the RCS; its relative rate constants (k4) were evaluated with pairwise combinations of phosphines. Substituent effects were studied in three ways: for (YC6H4)3P, a Hammett correlation of kc against 3σ gives the reaction constant ρcP = +1.03, consistent with phosphine predissociation; for PyO ρcN = -3.84. It is so highly negative because PyO enters in three steps, each of which is improved by a better Lewis base or nucleophile, and again for (YC6H4)3P as regards the k4 step, ρ4 = -0.70, reflecting its role as a nucleophile in attacking a postulated dioxorhenium(VII) intermediate. The RCS is represented by the breaking of the covalent N-O bond within another intermediate inferred from the kinetics, [MeReO(mtp)-(OPy)2], to yield the dioxorhenium(VII) species [MeRe(O)2(mtp)(OPy)]. A close analogue, [MeRe(O)2(mtp)Pic], was identified by 1H NMR spectroscopy at 240 K in toluene-d8. The role of the second PyO in the rate law and reaction scheme is attributed to its providing nucleophilic assistance to the RCS. Addition of an exogenous nucleophile (tetrabutylammonium bromide, Py, or Pic) caused an accelerating effect. When Pic was used, the rate law took on the new form v = kNA[1][PicO][Pic][PPh3]-1; kNA = 2.6 x 102 L mol-1 s-1 at 25.0 °C in benzene. The ratio kc/kNA is 58, consistent with the Lewis basicities and nucleophilicities of PicO and Pic.
Organometallic catalysis in aqueous solution. Oxygen transfer to bromide
Espenson,Pestovsky,Huston,Staudt
, p. 2869 - 2877 (1994)
The reaction between hydrogen peroxide and bromide ions in aqueous acidic solutions, ordinarily very slow, is strongly catalyzed by CH3ReO3, a water-soluble organometallic oxide. The complex catalytic kinetics showed that the rate-controlling process consists of two steps: (1) reversible formation of the independently-known 1:1 and 2:1 adducts of hydrogen peroxide and methylrhenium trioxide (the formulas, including the water that had been shown to be coordinated, are CH3Re(O)2(η2-O2)(H2O) and CH3Re(O)(η2-O2)2(H2O)) and (2) their reactions with bromide ions that yield HOBr. The rate constants for these steps were evaluated by several steady-state kinetic techniques. The HOBr intermediate reacts with Br to yield Br2. When hydrogen peroxide was in excess, the reaction yielded oxygen instead of bromine. This can be accounted for by the reaction of HOBr with H2O2. The 2:1 peroxide-rhenium adduct, formed only at the higher concentrations of hydrogen peroxide, also reacts with bromide ions, but more slowly. Kinetic modeling by numerical techniques was used to provide verification of the reaction scheme. The various steps of peroxide activation consist of nucleophilic attack of bromide ions on peroxide ions that have become electrophilically activated by binding to the rhenium compound. The rhenium catalyst bears some resemblance to the enzyme vanadium bromoperoxidase.
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Hatzopoulos, Ioannis,Brauer, Hans-Dieter,Geisberger, Martin R.,Herrmann, Wolfgang A.
, p. 201 - 209 (1996)
The photolysis of CH3ReO(O2)2 ? H2O in methylene chloride yields, like the thermolysis, molecular oxygen in the triplet spin state. The quantum yield QPh of photolysis shows a remarkable dependence on the wavelength, increasing from 0.12 at 365 nm to 1.0 at 248 nm. One single excited state is responsible for this behaviour. The wavelength-dependent quantum yield profile corresponds in a first approximation to the ratio between the LMCT-band and the total absorption spectrum. The analysis of the latter spectrum was made on a mathematical basis using symmetrical Gauss curves. This is the first time that a fluorescence and phosphorescence emission of an alkyl transition-metal complex of d0-configuration has been detected, thus allowing for the determination of both the S1-and the T1-energy levels. The quantum yield of the fluorescence (QF) is below 10-3; that of the phosphorescence is below 0.04.
Kinetics and mechanisms of reactions of methyldioxorhenium(V) in aqueous solutions: Dimer formation and oxygen-atom abstraction reactions
Espenson, James H.,Yiu, Douglas Tak Yeung
, p. 4113 - 4118 (2000)
The stable compound CH3ReO3 (MTO), upon treatment with aqueous hypophosphorous acid, forms a colorless metastable species designated MDO, CH3ReO2(H2O)(n) (n = 2). After standing, MDO is first converted to a yellow dimer (λ(max) = 348 nm; ε = 1.3 x 104 L mol-1 cm-1). That reaction follows second-order kinetics with k = 1.4 L mol-1 s-1 in 0.1 M aq trifluoromethane sulfonic acid at 298 K. Kinetics studies as functions of temperature gave ΔS((+)) = -4 ± 15 J K-1 mol-1 and ΔH((+)) = 71.0 ± 4.6 kJ mol-1. A much more negative value of ΔS((+)) would be expected for simple dimerization, suggesting the release of one or more molecules of water in forming the transition state. If solutions of the dimer are left for a longer period, an intense blue color results, followed by precipitation of a compound that does, even after a long time, retain the Re-CH3 bond in that aq. hydrogen peroxide generates the independently known CH3Re(O)(O2)2(H2O). The blue compound may be analogous to the intensely colored purple cation [(Cp*Re)3(μ2-O)3(μ3-O)3ReO3]+. If a pyridine N-oxide is added to the solution of the dimer, it is rapidly but not instantaneously lost at the same time that a catalytic cycle, separately monitored by NMR, converts the bulk of the PyO to Py according to this stoichiometric equation in which MDO is the active intermediate: C5H5NO + H3PO2 → C5H5N + H3PO3. A thorough kinetic study and the analysis by mathematical and numerical simulations show that the key step is the conversion of the dimer D into a related species D* (presumably one of the two μ-oxo bonds has been broken); the rate constant is 5.6 x 10-3 s-1. D* then reacts with PyO just as rapidly as MDO does. This scheme is able to account for the kinetics and other results.
Mechanism of MTO-catalyzed deoxydehydration of diols to alkenes using sacrificial alcohols
Liu, Shuo,Senocak, Aysegul,Smeltz, Jessica L.,Yang, Linan,Wegenhart, Benjamin,Yi, Jing,Kenttaemaa, Hilkka I.,Ison, Elon A.,Abu-Omar, Mahdi M.
, p. 3210 - 3219 (2013/07/19)
Catalytic deoxydehydration (DODH) of vicinal diols is carried out employing methyltrioxorhenium (MTO) as the catalyst and a sacrificial alcohol as the reducing agent. The reaction kinetics feature an induction period when MTO is added last and show zero-order in [diol] and half-order dependence on [catalyst]. The rate-determining step involves reaction with alcohol, as evidenced by a KIE of 1.4 and a large negative entropy of activation (ΔS? = -154 ± 33 J mol-1 K -1). The active form of the catalyst is methyldioxorhenium(V) (MDO), which is formed by reduction of MTO by alcohol or via a novel C-C bond cleavage of an MTO-diolate complex. The majority of the MDO-diolate complex is present in dinuclear form, giving rise to the [Re]1/2 dependence. The MDO-diolate complex undergoes further reduction by alcohol in the rate-determining step to give rise to a putative rhenium(III) diolate. The latter is the active species in DODH extruding stereoselectively trans-stilbene from (R,R)-(+)-hydrobenzoin to regenerate MDO and complete the catalytic cycle.
Insights into a nontoxic and high-yielding synthesis of methyltrioxorhenium (MTO)
Mitterpleininger, Josef K. M.,Szesni, Normen,Sturm, Stefanie,Fischer, Richard W.,Kuehn, Fritz E.
, p. 3929 - 3934 (2009/02/07)
The versatile catalyst methyltrioxorhenium(VII) (MTO) is now available in high yields by utilizing easily accessible nontoxic starting materials. The new synthetic pathway allows an inexpensive, large-scale production of MTO, paving the way for industrial applications. A variety of starting materials is compared with respect to their applicability, availability and ease of handling. The reaction times and the by-products formed are compared under different reaction conditions. It was seen that silver perrhenate in combination with methylzinc acetate, which was derived from trimethylaluminum and zinc acetate, are the best starting materials for a high-yielding large-scale synthesis of MTO. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
