- Metathesis Reactions of Tris(adamantylimido)methylrhenium and Aldehydes and Imines
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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.
- Wang, Wei-Dong,Espenson, James H.
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- Ligand displacement and oxidation reactions of methyl(oxo)rhenium(V) complexes
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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.
- Shan, Xiaopeng,Ellern, Arkady,Guzei, Ilia A.,Espenson, James H.
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- Kinetics and mechanism of rhenium-catalyzed oxygen atom transfer from pyridine N-oxides to phosphines
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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.
- Wang, Ying,Espenson, James H.
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- Alkylrhenium oxides from perrhenates: A new, economical access to organometallic oxide catalysts
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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.
- Herrmann,Kratzer,Fischer
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- Organometallic catalysis in aqueous solution. Oxygen transfer to bromide
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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.
- Espenson,Pestovsky,Huston,Staudt
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- A cheap, efficient, and environmentally benign synthesis of the versatile catalyst methyltrioxorhenium (MTO)
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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)
- Herrmann, Wolfgang A.,Rost, Alexandra M. J.,Mitterpleininger, Josef K. M.,Szesni, Normen,Sturm, Stefanie,Fischer, Richard W.,Kuehn, Fritz E.
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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.
- Hatzopoulos, Ioannis,Brauer, Hans-Dieter,Geisberger, Martin R.,Herrmann, Wolfgang A.
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- Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands
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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.
- Shah, Xiaopeng,Ellern, Arkady,Guzei, Ilia A.,Espenson, James H.
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- Kinetics and mechanisms of reactions of methyldioxorhenium(V) in aqueous solutions: Dimer formation and oxygen-atom abstraction reactions
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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.
- Espenson, James H.,Yiu, Douglas Tak Yeung
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- Water-catalyzed activation of H2O2 by methyltrioxorhenium: A combined computational-experimental study
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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.
- Hwang, Taeho,Goldsmith, Bryan R.,Peters, Baron,Scott, Susannah L.
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supporting information
p. 13904 - 13917
(2014/01/06)
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- Mechanism of MTO-catalyzed deoxydehydration of diols to alkenes using sacrificial alcohols
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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.
- Liu, Shuo,Senocak, Aysegul,Smeltz, Jessica L.,Yang, Linan,Wegenhart, Benjamin,Yi, Jing,Kenttaemaa, Hilkka I.,Ison, Elon A.,Abu-Omar, Mahdi M.
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p. 3210 - 3219
(2013/07/19)
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- Sulfite-driven, oxorhenium-catalyzed deoxydehydration of glycols
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Methyltrioxorhenium and perrhennate salts catalyze the deoxydehydration (DODH) of glycols by sulfite, producing olefins regiospecifically. The scope and efficiency of these reactions with respect to the polyol substrate, reducing agent, catalyst, solvents, and various additives are investigated. In general, MeReO3 is a more active catalyst for sulfite-driven DODH, but the Z+ReO4- derivatives (Z = Na, Bu4N) are more selective. Epoxides are also deoxygenated by Na2SO 3/MeReO3, but not by Bu4NReO4. The perrhenate catalysts also promote glycol DODH with other reductants, e.g., PR3, secondary alcohols, and ArSMe. The DODH reactions of 1,2-cyclohexanediol and (+)-diethyl tartrate occur with high syn-stereoselectivity. The polyol meso-erythritol is largely converted to 1,3-butadiene with minor amounts of 2-butene-1,4-diol and 2,5-dihydrofuran, indicating faster terminal glycol DODH. Stoichiometric reaction studies demonstrate the viability of a catalytic pathway involving (a) glycol condensation with MeReO3 to form MeReVIIO 2(glycolate); (b) O-transfer reduction of the ReVII- glycolate by sulfite or PR3 to produce [MeRevO(glycolate)] 2; and (c) thermal fragmentation of the reduced Re-glycolates to produce olefin (and regeneration of MeReO3).
- Ahmad, Irshad,Chapman, Garry,Nicholas, Kenneth M.
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p. 2810 - 2818
(2011/07/31)
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- Insights into a nontoxic and high-yielding synthesis of methyltrioxorhenium (MTO)
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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.
- Mitterpleininger, Josef K. M.,Szesni, Normen,Sturm, Stefanie,Fischer, Richard W.,Kuehn, Fritz E.
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p. 3929 - 3934
(2009/02/07)
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- Behaviour of dimeric methylrhenium(VI) oxides in the presence of hydrogen peroxide and its consequences for oxidation catalysis
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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.
- Rost, Alexandra M. J.,Scherbaum, Andrea,Herrmann, Wolfgang A.,Kuehn, Fritz E.
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p. 1599 - 1605
(2007/10/03)
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- METHOD FOR EFFICIENTLY PRODUCING METHYLTRIOXORHENIUM(VII) (MTO) AND ORGANORHENIUM(VII) OXIDES
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The invention relates to a novel method for producing organorhenium(VII) oxides
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(2008/06/13)
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- Photolysis of CH3Re(O2)2O induced by ligand-to-metal charge transfer and by peroxide intraligand excitation
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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.
- Kunkely, Horst,Vogler, Arnd
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p. 467 - 470
(2008/10/09)
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- METHOD FOR THE SYNTHESIS OF METHYL-TRI-OXO-RHENIUM
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A method for the synthesis of methyltrioxorhenium is described, wherein 0.5-1.5 moles of dirhenium heptaoxide are reacted with 1-3 moles of tetramethyl tin in the presence of 1-3 moles of chlorotrimethyl silane. The synthesis is carried out in the dark for approximately 24 hours in a polar aprotic organic solvent, preferably in acetonitrile.
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- Electronic structure of ReO3Me by variable photon energy photoelectron spectroscopy, absorption spectroscopy and density functional calculations
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Valence photoelectron (PE) spectra have been measured for ReO3Me using a synchrotron source for photon energies ranging between 20 and 110 eV. Derived branching ratios (BR) and relative partial photoionization cross sections (RPPICS) are interpreted in the context of a bonding model calculated using density functional theory (DFT). Agreement between calculated and observed ionization energies (IE) is excellent. The 5d character of the orbitals correlates with the 5p → 5d resonances of the associated RPPICS; these resonances commence around 47 eV. Bands with 5d character also show a RPPICS maximum at 35 eV. The RPPICS associated with the totally symmetric 4a1 orbital, which has s-like character, shows an additional shape resonance with an onset of 43 eV. The PE spectrum of the inner valence and core region measured with photon energies of 108 and 210 eV shows ionization associated with C 2s, O 2s, and Re 4f and 5p electrons. Absorption spectra measured in the region of the Ols edge showed structure assignable to excitation to the low lying empty d orbitals of this d0 molecule. The separation of the absorption bands corresponded with the calculated orbital splitting and their intensity with the calculated O 2p character. Broad bands associated with Re 4d absorption were assigned to 2D5/2 and 2D3/2 hole states. Structure was observed associated with the C1s edge but instrumental factors prevented firm assignment. At the Re 5p edge, structure was observed on the 2P3/2 absorption band resulting from excitation to the empty d levels. The intensity ratios differed from that of the O 1s edge structure but were in good agreement with the calculated 5d character of these orbitals. An absorption was observed at 45 eV, which, in the light of the resonance in the 4a1 RPPICS, is assigned to a 4a1 → ne, na2 transition. The electronic structure established for ReO3Me differs substantially from that of TiCl3Me and accounts for the difference in chemical behavior found for the two complexes.
- De Simone, Monica,Coreno, Marcello,Green, Jennifer C.,McGrady, Sean,Pritchard, Helen
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p. 1908 - 1918
(2008/10/08)
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- Kinetics and mechanism of oxygen atom abstraction from a dioxo-rhenium(VII) complex
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The kinetics of reaction between triarylphosphanes and two newly prepared dioxorhenium(VII) compounds has been evaluated. The compounds are MeReVII(O)2( O,S ) in which O,S represents an alkoxo, thiolato chelating ligand. With MeReO3, ligands derived from 1-mercaptoethanol and 1-mercapto-2-propanol form MeRe(O)2(met), 2, and MeRe(O)2(m2p), 3. These compounds persist in chloroform solution for several hours at room temperature and for 2-3 weeks at -22°C, particularly when water is carefully excluded. They were obtained as red oils with clean 1H NMR spectra, but attempts to obtain pure, crystalline products were not successful because one decomposition pathway shows a kinetic order >1. The fastest reaction occurs between P(p-MeOC6H4)3 and 2; k298 = 215(7) L mol-1 s-1 in chloroform at 25(1)°C. The other rate constants follow a Hammett correlation against 3σ, with ρ = -0.69(7). This study relates to oxygen atom transfer reactions catalyzed by MeReO(mtp)PPh3, 1, in which MeRe(O)2(mtp), 4, is a postulated intermediate that does not build up to a measurable concentration during the catalytic cycle. Compound 2 does not react with MeSTol, but MeS(O)Tol was formed when tert-butyl hydroperoxide was added. This suggests that equilibrium lies to the left in this reaction, 2 + MeSTol + L = MeReO(met)L + MeS(O)Tol, and is drawn to the right by a reaction between MeReO(met)L and the hydroperoxide. Triphenyl arsane does not react with 2, but thermodynamic versus kinetic barriers were not resolved.
- Dixon, JaNeille,Espenson, James H.
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p. 4727 - 4731
(2008/10/08)
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- Preparation, properties, and reactions of five-coordinate Re(VII) dioxo and diimido complexes
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The reactions of aliphatic and aromatic 1,2-diamines, diols, and dithiols with CH3ReO3 (1), {CH3Re(NAr)2O}2 (2, Ar = 2,6-diisopropylphenyl), and {CH3Re(NAr)2S}2 (3) have been studied. Two of the reaction products, [CH3Re(O)2{l,2-(NH)2C6H4} ]2{μ-l,2-(NH2)2C6H4} (4a′) and CH3Re(NAr)2(SCH2CH2S) (5c), have been structurally characterized. The former is a binuclear species in which each rhenium is six-coordinate with a pseudo-octahedral structure. The bridging phenylenediamine ligand can be replaced by pyridine and its derivatives. Unlike the known catecholato complex CH3ReVII(O)2(1,2-O2C6H 4)(Py), the Rev-benzoquinonediimine resonance form contributes noticeably to the overall structure of 4a′. The five-coordinate diimido complex 5c does not interact with coordinating ligands such as pyridines. The initial reactions of 2 with catechol and ethylene glycol lead to CH3Re(NAr)2(l,2-O2C6H4) (5b′) and CH3Re(NAr)2(OCH2CH2O) (5b), respectively. Further hydrolysis of 5b affords CH3Re(NAr)-(O)(OCH2CH2O) (6b). Compound 3, a sulfur analogue of 2, condenses only with dithiols. The high reactivity of 2 is likely due to the presence of a four-coordinate monomeric form in solution and the formation of H2O with strong O - H bonds as a byproduct.
- Wang, Wei-Dong,Ellern, Arkady,Guzei, Ilia A.,Espenson, James H.
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p. 5576 - 5582
(2008/10/08)
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- Direct synthesis of organorhenium oxides from compounds containing rhenium
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The present invention relates to a process for the preparation of organorhenium oxides from rhenium-containing compounds, where the rhenium-containing compound is reacted with a silylating agent and organylating reagent, and the rhenium-containing compound originates in particular from the residue from a spent organorhenium oxide catalyst or rhenium oxide catalyst.
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- Hydrolysis, hydrosulfidolysis, and aminolysis of imido(methyl)rhenium complexes
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The tris(imido)methylrhenium complex CH3Re(NAd)3 (1a, Ad = 1-adamantyl) reacts with H2O to give CH3Re(NAd)2O (2a) and AdNH2. The resulting di(imido)oxo species can further react with another molecule of H2O to generate CH3Re(NAd)O2 (3a). The kinetics of these reactions have been studied by means of 1H NMR and UV-vis spectroscopies. The second-order rate constant for the reaction of 1a with H2O at 298 K in C6H6 is 3.3 L mol-1 s-1, which is much larger than the value 1 x 10-4 L mol-1 s-1 obtained for the reaction between CH3Re(NAr)3 (1b, Ar = 2,6-diisopropylphenyl) and H2O in CH3CN at 313 K. Both 1a and 1b react with H2S to produce the rhenium(VII) sulfide, {CH3Re(NR)2}2(μ-S)2 (4a, R = Ad; 4b, R = Ar), with second-order rate constants of 17 and 1.6 x 10-4 L mol-1 s-1 in C6H6 and CH3CN, respectively. Complex 4b has been structurally characterized. The crystal data are as follows: space group C2/c, a = 30.4831 (19) A, b = 10.9766 (7) A, c = 18.1645 (11) A, β = 108.268(1)°, V = 5771.5 (6) β3, Z = 4. The reaction between CH3Re(NAr)2O (2b) and H2S also yields the dinuclear compound 4b. Unlike 1b, 1a reacts with aniline derivatives to give mixed imido rhenium complexes.
- Wang, Wei-Dong,Guzei, Ilia A.,Espenson, James H.
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p. 4107 - 4112
(2008/10/08)
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- Synthesis and reactivity of nitrido-rhenium and -osmium complexes with an oxygen tripod ligand
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Interaction of [ReNCl3(PPh3)2] or [ReOCl2(PPh3)3] with NaLOEt (LOEt = [Co(η5-C5H5){PO(OEt)2} 3]) afforded [ReLOEtN(PPh3)Cl] 1 and [ReLOEtOCl2] 2, respectively. Reaction of I with AgBF4 gave the nitridorhenium(vi) complex [ReLOEtN(PPh3)Cl]BF4 1·BF4, which has a μeff of 1.8 μB. Treatment of I with MeOSO2CF3, PhCH2Br or [Ph3C]BF4 afforded the respective organoimido species [ReLOEt(NMe)(PPh3)Cl][CF3SO3] 3, [ReLOEt(NCH2Ph)-(PPh3)Cl]Br 4, and [ReLOEt(NCPh3)(PPh3)Cl] 5. Reaction of 1 with [Au(PPh3)(CF3SO3)], [Ru(Et2dtc)(PPh3)2-(CO)(CF3SO 3)], or [ReMeO3] yielded the bimetallic nitrido complexes [Au(PPh3){NReLOEt(PPh3)Cl}j[CF 3SO3] 6, [Ru(Et2dtc)(PPh3)(H2O)(CO){NReL OEt(PPh3)Cl}][CF3SO3] 7 or [ReMeO3{NReLOEt(PPh3)Cl}] 8, respectively. Treatment of [NBu4n][OsNCl4] with NaLOEt gave [OsLOEtNCl2]J 9. The average Os-O, Os-Cl and Os-N distances in 9 are 2.066, 2.289 and 2.58(1) A, respectively. Reaction of 9 with PPh3 afforded the osmium(iv) phosphoran iminate species [OsLOEt(NPPh3)Cl2] 10, which has aμeff of 2.0 μB. The average Os-O, Os-Cl and Os-N distances in 10 are 2.099, 2.342, 1.893(5) A, respectively, the Os-N-P angle being 137.5(3)°. The formal potentials of the LOEt-Re and -Os complexes have been determined by cyclic voltammetry. On the basis of the ReVI-ReV formal potential, the π-donor strength was found to decrease in the order N3- > [NAu(PPh3)]2- > NMe2-. The Royal Society of Chemistry 2000.
- Leung, Wa-Hung,Chan, Eddie Y. Y.,Lai, Tracy C. Y.,Wong, Wing-Tak
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- Kinetics and mechanism of oxygen atom abstraction from sulfenatocobalt(III) complexes by hydrated methyldioxorhenium(V)
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Cationic sulfenatocobalt(III) complexes, with the remaining ligands amines, are deoxygenated upon reaction with hydrated methyldioxorhenium(V). The reactions of (Am)5Co-S(O)R2+ yield the thiolato complexes (Am)5Co-SR2+ and methyltrioxorhenium(VII), MTO. A kinetic study of these reactions was carried out, using the known reaction between MTO and hypophosphorous acid to prepare the Re(V) reagent in solution. The second-order rate constants between (Am)5Co-S(O)R2+ and MeReO2(aq), after correction for protonation, fall in the range 47-455 L mol-1 s-1 in aqueous solution at 25.0 °C and 1.0 M ionic strength. In the analysis of the pH effects, allowance was made for the formation of the protonated species (Am)5Co-S(OH)R3+ at high [H3O+]. The values of pKa are in the range 0.49-0.96, as determined from fitting the rate-pH profiles.
- Lahti, David W.,Espenson, James H.
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p. 5230 - 5234
(2008/10/08)
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- Chiralrhenium catalysts and processes for preparing the same
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A novel catalyst comprising the formula: wherein L is selected from the group consisting of (a) (R1)(AL) wherein R1 is an alkyl side chain containing at least one carbon-rhenium covalent bond, and AL is a molecule having C2 to C50, and has at least one hetero atom selected from the group consisting of N, O, S, and P wherein there is at least one hetero-rhenium dative bond, and has at least one chiral center. and (b) RAL is a straight or branched chain alkyl or arylalkyl group containing C2 to C50 and containing at least one heteroatom selected from the group consisting of N, O, S, and P, with the proviso that said alkyl group contains at least one carbon-rhenium covalent bond and at least one hetero-rhenium dative bond, and has at least one chiral center: and n is an integer which is 2, 3, 4, or 5 and which has utility in areas such as epoxidation of olefins.
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- Deactivation of methylrhenium trioxide - Peroxide catalysts by diverse and competing pathways
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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.
- Abu-Omar,Hansen,Espenson
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p. 4966 - 4974
(2007/10/03)
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- Multiple bonds between main-group elements and transition metals. 137.1 Polymeric methyltrioxorhenium: An organometallic nanoscale double-layer structure of corner-sharing ReO5(CH3) octahedra with intercalated water molecules
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A two-dimensional structural model of polymeric methyltrioxorhenium (MTO) has been established by means of diffraction techniques and a variety of analytical methods. The unusual compound, constituting the first example of a polymeric organometallic oxide, has a layer structure of methyl-deficient, corner-sharing ReO5(CH3) octahedra. It adopts the three-dimensional extended ReO3 motif in two dimensions as a {ReO2}∞ network. Adjacent layers of corner-sharing ReO5(CH3) octahedra (A) are capable of forming staggered double layers (AA′). In the crystalline areas of poly-MTO , such double layers are separated by intercalated water molecules (monolayer) (B) with an ...AA′BAA′... layer sequence. For the partially amorphous areas of poly-MTO , we propose a turbostratic and 00l-defect stacking model for the poly-MTO and water layers. Interactions between the adjacent layers in this polymeric MTO are very weak, resulting in graphite-like macroscopic properties such as flaky appearance, softness, and lubricity. High electric conductivity results from understoichiometry with respect to the CH3/Re ratio (9.2/10) and partial reduction by extra hydrogen equivalents. For the purpose of comparison, the solid-state structure of monomeric MTO as established by a combination of X-ray and powder neutron diffraction techniques is also reported.
- Herrmann, Wolfgang A.,Scherer, Wolfgang,Fischer, Richard W.,Blümel, Janet,Kleine, Matthias,Mertin, Wilhelm,Gruehn, Reginald,Mink, Janos,Boysen, Hans,Wilson, Chick C.,Ibberson, Richard M.,Bachmann, Luis,Mattner, Mike
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p. 3231 - 3243
(2007/10/02)
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- Multiple Bonds between Transition Metals and Main-Group Elements. 142. Lewis-Base Adducts of Organorhenium(VII) Oxides: Structures and Dynamic Behavior in Solution
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Organorhenium(VII) oxides such as methyltrioxorhenium(VII) (1) and its longer-chain alkyl derivatives form 1:1 and 1:2 adducts with nitrogen-donor Lewis bases. These compounds adopt well-defined structures in the solid state. In solution, they undergo exc
- Herrmann, Wolfgang A.,Kuehn, Fritz E.,Rauch, Monika U.,Correia, Joao D. G.,Artus, Georg
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p. 2914 - 2920
(2008/10/08)
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- Alkylrhenium oxides as homogeneous epoxidation catalysts: activity, selectivity, stability, deactivation
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Methyltrioxorhenium (VII) (MTO, 1a) and several congeners 1b and 2a-d of formula R-ReO3 and R-ReO3·L, respectively, qualify as olefin epoxidation catalysts of high activity and selectivity. Related alkylrhenium (VI) complexes form efficient catalyst precursors as well, since they get oxidized by H2O2 to the same active species CH3ReO(O2)2·H2O (3). The present paper presents a comparison of this novel class of catalysts with the performance of known, commonly used catalysts. Catalyst stability has been recorded and deactivation reactions are described. The synthesis and crystal structure (X-ray diffraction) of the (pale pink-coloured) monomeric amino-functionalized complex O3Re-CH2CH2CH2N (C2H5)2 (4A) and its (violet) polymeric form (4B) are reported. Only the latter is an active epoxidation catalyst with H2O2. An improved laboratory method of the standard catalyst MTO 1a is described.
- Herrmann, Wolfgang A.,Fischer, Richard W.,Rauch, Monika U.,Scherer, Wolfgang
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p. 243 - 266
(2008/10/08)
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- Multiple Bonds between Main Group Elements and Transition Metals, CXXIX. - Chlorotrioxorhenium. Novel Syntheses, Reactions and Derivatives
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Chlorotrioxorhenium (1a) and homologs of formula X-ReO3 (1b-e) are generated from Re2O7 and either ZnX2, (n-C4H9)3SnX, X, or X in clean reactions.Compounds 1a-f form with stable six-coordinate adducts XReO3*L (2a-f, 3a, 4a, 5a: L = N,N'-ligand) upon addition of the free ligand L, e.g. 2,2'-bipyridine. 1a is readily alkylated by means of SnR4 or ZnR2 to form organorhenium(VII) oxides in good yields.These synthetic routes have the advantage to proceed under very mild conditions.The adducts of 2,2'-bipyridine with halorhenium(VII) oxides show characteristic thermogravimetric (TG) behavior that reflects the volatility of the uncoordinated complexes X-ReO3. - Key Words: Rhenium compounds / Thermogravimetry / Organometallic Oxides
- Herrmann, Wolfgang A.,Kuehn, Fritz E.,Romao, Carlos C.,Kleine, Matthias,Mink, Janos
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- Equilibria and kinetics of the reactions between hydrogen peroxide and methyltrioxorhenium in aqueous perchloric acid solutions
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In aqueous solutions the colorless compounds CH3ReO3 (=MTO) and H2O2 form 1:1 and 1:2 adducts. The latter is yellow, with ε360 = 1.1 × 103 L mol-1 cm-1. Peroxide binding to MTO shows cooperativity, as shown by the inversion of the usual order of binding constants. The stepwise equilibrium constants are K1 = 7.7 L mol-1 and K2 = 145 L mol-1 at 25°C. The buildup of product, which occurs on the stopped-flow time scale at 9-680 mM H2O2, is fit by biexponential kinetics. The equilibria and rates are independent of [H3O+] in the range 10-1-10-3 M. The peroxide complexes decompose more rapidly at lower [H3O+], particularly at pH > 3. Possible structures for 1:1 and 1:2 MOT-H2O2 adducts are presented and discussed.
- Yamazaki, Shigekazu,Espenson, James H.,Huston, Patrick
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p. 4683 - 4687
(2008/10/08)
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- Mehrfachbindungen zwischen Hauptgruppenelementen und Uebergangsmetallen LXIV. Methyl(trioxo)rhenium: Basenaddukte und Basenreaktionen. Kristallstruktur von -perrhenat
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In contrast to trioxo(η5-pentamethylcyclopentadienyl)rhenium(VII), (η5-C5Me5)-ReO3, te organometallic oxide methyl(tripoxo)rhenium(VII), CH3ReO3 (1), reacts with bases, e.g., sodium hydroxide and organic amines, with expansion of the
- Herrmann, Wolfgang A.,Kuchler Jose G.,Weichselbaumer, Georg,Herdtweck, Eberhardt,Kiprof, Paul
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p. 351 - 370
(2007/10/02)
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