70197-13-6Relevant academic research and scientific papers
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.
Ligand displacement and oxidation reactions of methyl(oxo)rhenium(V) complexes
Shan, Xiaopeng,Ellern, Arkady,Guzei, Ilia A.,Espenson, James H.
, p. 3854 - 3862 (2004)
Compounds that contain the anion [MeReO(edt)(SPh)]- (3 -) were synthesized with the countercations 2-picolinium (PicH +3-) and 2,6-lutidinium (LutH+3-), where edt is 1,2-ethanedithiolate. Both PicH+3- and MeReO(edt)-(tetramethylthiourea) (4) were crystallographically characterized. The rhenium atom in each of these compounds exists in a five-coordinate distorted square pyramid. In the solid state, PicH+3- contains an anion with a short (dSH = 232 pm) and nearly linear hydrogen-bonded (N-H...S) interaction to the cation, Ligand substitution reactions were studied in chloroform. Displacement of PhSH by PPh3 follows second-order kinetics, d[MeReO(edt)(PPh3)]/dt = k[PicH+3 -][PPh3], whereas with pyridines an unusual form was found, d[MeReO(edt)(Py)]/dt = k[PyH+3-][Py]2, in which the conversion of PicH+3- to PyH +3- has been incorporated. Further, added Py accelerates the formation of [MeReO(edt)(PPh3)], v = k·[PicH +3-]·[PPh3]·[Py]. Compound 4, on the other hand, reacts with both PPh3 and pyridines, L, at a rate given by d[MeReO(edt)(L)]/dt = k·[4]·[L]. When PicH +3- reacts with pyridine N-oxides, a three-stage reaction was observed, consistent with ligand replacement of SPh- by PyO, N-O bond cleavage of the PyO assisted by another PyO, and eventual decomposition of MeRe(O)(edt)(OPy) to MeReO3. Each of first two steps showed a large substituent effect; Hammett analysis gave ρ1 = -5.3 and ρ2 = -4.3.
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.
Alkylrhenium oxides from perrhenates: A new, economical access to organometallic oxide catalysts
Herrmann,Kratzer,Fischer
, p. 2652 - 2654 (1997)
Methyltrioxorhenium in an Erlenmeyer flask: An in situ activation with chloroalkylsilanes converts readily available perrhenates into organorhenium(VII) oxides (as depicted below), which are valuable and diverse homogenous catalysts. Reaction intermediates are trimethylsilyl perrhenate, dirhenium heptoxide, and chlorotrioxorhenium. The application of methyltrioxorhenium CH3ReO3 (1) in industrial processes might become feasible, particularly since the catalyst can be recycled.
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.
A cheap, efficient, and environmentally benign synthesis of the versatile catalyst methyltrioxorhenium (MTO)
Herrmann, Wolfgang A.,Rost, Alexandra M. J.,Mitterpleininger, Josef K. M.,Szesni, Normen,Sturm, Stefanie,Fischer, Richard W.,Kuehn, Fritz E.
, p. 7301 - 7303 (2007)
Avoiding toxic starting materials such as (CH3)4Sn, a cheap, environmentally benign high-yield synthesis has been developed for the multitalented catalyst methyltrioxorhenium(VII) (MTO; see picture: black C, white H, blue Re, red O). This novel approach is applicable on a large scale and for several derivatives of MTO, such as ethyltrioxorhenium(VII). (Figure Presented)
Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands
Shah, Xiaopeng,Ellern, Arkady,Guzei, Ilia A.,Espenson, James H.
, p. 2362 - 2367 (2003)
Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO3 under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr3), 3, and MeReO(ONO)(PPh3), 4. These compounds were characterized spectroscopically and crystallographically. Compounds 1 and 2 have a five-coordinate distorted square pyramidal geometry about rhenium, whereas 3 and 4 are six-coordinate compounds with distorted octahedral structures. The kinetics of oxidation of 2 and 3 in chloroform with pyridine N-oxides follow different patterns. The oxidation of 2 shows first-order dependences on the concentrations of 2 and the ring-substituted pyridine N-oxide. The Hammett analysis of the rate constants gives a remarkably large and negative reaction constant, p = -4.6. The rate of oxidation of 3 does not depend on the concentration or the identity of the pyridine N-oxide, but it is directly proportional to the concentration of water, both an accidental and then a deliberate cosolvent. The mechanistic differences have been interpreted as reflecting the different steric demands of five- and six-coordinate rhenium compounds.
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.
Water-catalyzed activation of H2O2 by methyltrioxorhenium: A combined computational-experimental study
Hwang, Taeho,Goldsmith, Bryan R.,Peters, Baron,Scott, Susannah L.
supporting information, p. 13904 - 13917 (2014/01/06)
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.
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.
