14333-24-5Relevant academic research and scientific papers
Fragmentation pathways of [Re2(μ-OR)3(CO)6]- (R = H, Me) and ligand exchange reactions with oxygen donor ligands, investigated by electrospray mass spectrometry
Jiang, Chenghua,Andy Hor,Van Kai, Yaw,Henderson, William,McCaffrey, Louise J.
, p. 3197 - 3203 (2000)
The rhenium hydroxy and methoxy carbonyl complexes [Re2(u-OR)3(CO)6] (R = H or Me) have been studied by negative-ion electrospray mass spectrometry (ESMS). The complexes undergo facile exchange reactions with protic compounds, including alcohols and phenols. With dimethyl malonate, ester hydrolysis occurs giving carboxylatecontaining complexes, and with H2O2 or Bu'OOH, oxidation to ReO4- occurs. The feasibility and extent of these reactions can conveniently, rapidly, and unambiguously be determined by electrospray mass spectrometry, and is dependent on the acidity and steric bulk of the protic compound. The results also suggest that the complexes can be used as versatile starting materials for the synthesis of a wide range of analogous [Re2(μ-OR)3(CO)6]- complexes by simple reaction with an excess of the appropriate alcohol. By varying the applied cone voltage the fragmentation pathways have been investigated; the hydroxy complex undergoes dehydration followed by CO loss, whereas for the methoxy complex -hydride elimination (and CO loss) is observed, with confirmation provided by deuterium labelling studies. Under ESMS conditions, the neutral complexes [Re2(μ-OR)2(μ-dppf)(CO)6] [R = H or Me; dppf= 1,1'-bis(diphenylphosphino)ferrocene] undergo substantial solvolysis and hydrolysis to give mainly mononuclear species; simple parent ions (e.g. [M + H]+) are not formed in appreciable abundance, probably due to the lack of an efficient ionisation pathway. The Royal Society of Chemistry 2000.
Facile electroreduction of perrhenate in weakly acidic citrate and oxalate media
Vajo,Aikens,Ashley,Poeltl,Bailey,Clark,Bunce
, p. 3328 - 3333 (1981)
In weakly acidic solution, oxalate and citrate markedly increase the ease of reduction of ReO4- through reversible formation of 1:1 complexes. The citrate complex (ReO4·H2Cit)2- is sufficiently stable that it yields a diffusion limited current, whereas the oxalate complex (ReO4·H2Ox)- is formed only as a transient intermediate and it yields a kinetic limited current. Below pH 3 the mechanism of formation of the citrate complex corresponds to ReO4- + H3Cit ? (ReO4·H2Cit)2- + H+ while above pH 3 it corresponds to ReO4- + H2Cit- ? (ReO4·H2Cit)2-. The enhanced ease of reduction of the citrate and oxalate complexes is ascribed to expansion of the Re coordination sphere from 4 to, e.g., 6 through formation of chelated structures by a concerted process in which the incoming ligand transfers protons to coordinated oxo groups. The hydroxyl group of citric acid is necessary for formation of an easily reduced Re(VII) complex, and Dreiding models indicate that citrate is bidentate and occupies one face of the coordination octahedron, with the hydroxyl group H bonded to a coordinated oxo group.
Mechanistic Studies on the cis-(1+) and (3-) Oxidations of the ReIV2 Complex (4-)
Atkinson, J. William,Hong, Mao-Chun,House, Donald A.,Kyritsis, Panayotis,Li, Yu-Jin,et al.
, p. 3317 - 3322 (1995)
Rate constants (25 deg C) have been determined for the oxidation of the Re(IV)2 complex di-μ-oxobis, (4-), I = 1.00 M (ClO4(1-) or Cl(1-)).Whereas the complex is itself stable in air at pH 7 over many days, at lower pH there is a slow decay of the 446 nm peak (ε = 6840 M-1cm-1 per Re(IV)2) to give in air the colourless perrhenate(VII) (1-) product, peak at 225 nm (ε = 3400 M-1cm-1).The kinetics indicate a protonation step, equilibrium constant K = 2.4 M-1, followed by the decay proces k = 4.3E-5 s-1.With the one-equivalent oxidants cis-(1+) (1.0 V) and (3-) (0.80 V) , stoichiometries of 6 mol of oxidant per Re(IV4)2 are obtained indicating conversion through to Re(VII).Two kinetic stages have been monitored with the oxidant in large excess.For the raction with V(V) as oxidant the first stage is dependent on and as well as , giving the rate constant k1 = 3.31E4 M-2s-1.Since in the corresponding reaction with Mo(V) as oxidant the reaction is independent of (kMo = 2.27E4 M-1s-1), it is concluded that the V(V) reactant introduces the -dependent term.The second stage of the V(V) reaction gives the rate law dependence k2obs = k2+k0, but with the less strong Mo oxidant k2obs = k0 wchich is ca. 0.20 s-1.The spectrum of the Re(IV)Re(V) intermediate, peak at 529 nm (ε = 3800 M-1cm-1), was obtained by stopped-flow rapid-scan spectrophotometry.Reactions of less than full stoichiometric amounts of V(V) with Re(IV)2, followed by QAE-Sephadex chromatography at 0 deg C gave orange-pink (peak at ca. 495 nm) and maroon (ca. 550 nm) intermediates, which undergo spontaneous decay.
Syntheses of metal carbonyls. 23: Crystal structure and reactivity of heptamethylindenyl carbonyl metal complexes
Herrmann, Wolfgang A.,Geisberger, Martin R.,Kühn, Fritz E.,Artus, Georg R. J.,Herdtweck, Eberhardt
, p. 1229 - 1236 (1997)
Reaction of heptamethylindene (C9(CH3)7, 1) with Re2(CO)10 yields [η5-C9(CH3)7]Re(CO)3 (2), which reacts with NO+BF4- to form the cationic complex [{η5-C9(CH3)7}Re(CO) 2NO]+BF4- (3). Irradiation of 2 with UV light in the presence of triethyl phosphite leads to formation of [η5-C9)(CH3)7]Re(CO) 2[P(OC2H5)3] (4). Alkylation of (CH3)3SnCl with Ind*Li gives [η1-C9(CH3)7]Sn(CH 3)3 (5). All compounds were characterized by spectroscopic methods. The molecular structures of 3 and 5 were determined by single crystal X-ray diffraction (3: P21/n (14), a = 1497.7(4) pm, b = 879.0(2) pm, c = 1609.0(4) pm and β = 110.99(2)°, R1 = 0.038, wR2 = 0.080; 5: P21/n (14), a = 726.1(1) pm, b = 2930.7(3) pm, c = 930.0(1) pm and β = 112.834(5)°, R1 = 0.044, Rw = 0.048). Complexes 2-4 exhibit a piano stool configuration with a η5-coordinated permethylindenyl ligand (Ind*). Compound 5 displays a η1-coordination of the Ind* ligand. Temperature enhancement causes a hapticity change, as observed by NMR spectroscopy.
Essays ueber Metallorganische Chemie V. Stand und Aussichten der Rhenium-Chemie in der Katalyse
Herrmann, Wolfgang A.
, p. 1 - 18 (1990)
The most recent review article on catalytic epoxidation reactions gives a rather discouraging statement of the heavier group VII transition metal compounds as oxidation catalysts : The catalytic activity of technetium seems to be comparable to that of rhenium ..., and both seem to be low .The present account briefly describes the status of rhenium chemistry in catalysis, showing that there are many more perspectives than were first believed.It is shown that high-valent organorhenium oxides function as very effective catalysts in both olefin metathesis (heterogeneous catalysis) and in olefin oxidation (homogeneous catalysis).In this context it becomes evident that rhenium chemistry in general has been much less investigated and understood than that of the neighbouring elements tungsten and osmium.Furthermore, work concerning technetium compounds is necessary in order to gain better insight in catalytic and other properties of the corresponding rhenium compounds.Beyond the known, relationship between technetium and rhenium with regard to their inorganic and coordination compounds, the first similarities in the chemistry of their organic compounds are being uncovered, at the same time marked differences cannot be neglected.
Synthesis, structure elucidation, and redox properties of 99Tc complexes of lacunary Wells-Dawson polyoxometalates: Insights into molecular 99Tc-metal oxide interactions
McGregor, Donna,Burton-Pye, Benjamin P.,Howell, Robertha C.,Mbomekalle, Israel M.,Lukens, Wayne W.,Bian, Fang,Mausolf, Edward,Poineau, Frederic,Czerwinski, Kenneth R.,Francesconi, Lynn C.
, p. 1670 - 1681 (2011)
The isotope 99Tc (βmax, 293.7; half-life, 2.1 × 105 years) is an abundant product of uranium-235 fission in nuclear reactors and is present throughout the radioactive waste stored in underground tanks at the Hanford and Savannah River sites. Understanding and controlling the extensive redox chemistry of 99Tc is important in identifying tunable strategies to separate 99Tc from spent fuel and from waste tanks and, once separated, to identify and develop an appropriately stable waste form for 99Tc. Polyoxometalates (POMs), nanometer-sized models for metal oxide solid-state materials, are used in this study to provide a molecular level understanding of the speciation and redox chemistry of incorporated 99Tc. In this study, 99Tc complexes of the (α2-P2W17O61)10- and (α1-P2W17O61) 10- isomers were prepared. Ethylene glycol was used as a "transfer ligand" to minimize the formation of TcO2? xH2O. The solution structures, formulations, and purity of Tc VO(α1/α2-P2W 17O61)7- were determined by multinuclear NMR. X-ray absorption spectroscopy of the complexes is in agreement with the formulation and structures determined from 31P and 183W NMR. Preliminary electrochemistry results are consistent with the EXAFS results, showing a facile reduction of the TcVO(α1-P 2W17O61)7- species compared to the TcVO(α2-P2W17O 61)7- analog. The α1 defect is unique in that a basic oxygen atom is positioned toward the α1 site, and the TcVO center appears to form a dative metal-metal bond with a framework W site. These attributes may lead to the assistance of protonation events that facilitate reduction. Electrochemistry comparison shows that the ReV analogs are about 200 mV more difficult to reduce in accordance with periodic trends.
The photooxidation of hexabromorhenate(IV) in ethanol
Estill, Christina N.,Cohen, Jessica L.,Hoggard, Patrick E.
, p. 688 - 689 (2008)
Irradiation (λ a secondary photochemical reaction. Copyright Taylor & Francis Group, LLC.
Oxorhenium phosphinophenolato complexes with model peptide fragments: Synthesis, characterization, and stability considerations
Nock,Maina,Tisato,Raptopoulou,Terzis,Chiotellis
, p. 5197 - 5202 (2000)
The synthesis and characterization of a series of mixed-ligand oxorhenium(V) complexes containing the o-diphenylphosphinophenolato ligand (HL) and model peptide fragments acting as the tridentate coligand are reported. Thus, by reacting equimolar amounts of tiopronin, Gly-Gly, Gly-L-Phe, or glutathione (GSH) peptides on the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing MeCN/MeOH or aqueous MeCN/MeOH mixtures, the following complexes were obtained: ReO{[SC(CH3)CONCH2COO][L]}[(n-C4H9)4N], 1, ReO{[H2NCH2CONCH2-COO][L]}, 2, ReO{[H2NCH2CONCH(CH2C6H5)COO][L]}, 3, and ReO{[SCH2CH(NHCOCH2CH2CHNH2-COOH)CONCH2COO][L]}Na, 4. The compounds are closed-shell 18-electron oxorhenium species adopting a distorted octahedral geometry, as demonstrated by classical spectroscopical methods including multinuclear NMR. X-ray diffraction analyses for 1 and 2 are also reported. By comparative stability studies of complexes 1-3 against excess GSH it was shown that complex 3 containing the bulky C6H5CH2 substituent adjacent to the coordinated carboxylate group of Phe is the most stable complex.
Ligand exchange reactions of Re2(u-OR)3(CO)6r (R = H, Me) with sulfur, selenium, phosphorus and nitrogen donor ligands, investigated by electrospray mass spectrometry
Jiang, Chenghua,Andy Hor,Van Kai, Yaw,Henderson, William,McCaffreyc, Louise J.
, p. 3204 - 3211 (2000)
Negative-ion electrospray mass spectrometry has been used to investigate the reactions of the dinuclear rhenium aggregates [Re2(u-OH)3(CO)6]- 1 and [Re2(u-OMe)3(CO)6]- 2 with a range of thiols, benzeneselenol, and some other sulfur-, phosphorus- and nitrogen-based ligands. Typically up to three of the hydroxo ligands are replaced by simple thiolates, giving the series of species [Re2(OH)2(SR)(CO)6]-, [Re2(OH)(SR)2(CO)6]-, and [Re2(SR)3(CO)J-. Similarly, reaction of 1 with H2S gives the species [Re2(u-SH)3(CO)6]-, which undergoes an analogous fragmentation process to [Re2(u-OH)3(CO)6r, at high cone voltages, by loss of H2S and formation of [Re2(S)(SH)(CO)6]-. With ligands which are good chelating agents (such as dithiocarbamates R2NCS2-, and thiosalicylic acid, HSC6H4CO2H) initial substitution of one or two OH groups readily occurs, but on standing the dimer is cleaved giving [Re(S2CNR2)2-(CO)3]- and [Re(SC6H4CO2)(CO)3]-. The different reactivities of the dithiol reagents benzene-1,2- and benzene-1,4-dimethanethiol towards 1 are also described. Complex 1 also reacts with aniline, and with primary (but not secondary) amides RC(O)NH2, giving monosubstituted species [Re2(OH)2(NHPh)(CO)6]- and [Re2(OH)2{NHC(O)R}-(CO)6]- respectively. The reactions with adenine and thymine, and with the inorganic anions thiocyanate and thiosulfate, are also described. The Royal Society of Chemistry 2000.
Base Hydrolysis of Methyltrioxorhenium. The Mechanism Revised and Extended: A Novel Application of Electrospray Mass Spectrometry
Espenson, James H.,Tan, Haisong,Mollah, Sahana,Houk,Eager, Matthew D.
, p. 4621 - 4624 (1998)
The full kinetic pH profile for the base-promoted decomposition of MTO to CH4 and ReO4- was examined with the inclusion of new data at pH 7-10. Spectroscopic and kinetic data gave evidence for mono- and dihydroxo complexes: MTO(OH-) and MTO(OH-)2. Parallel unimolecular eliminations of methane from these species account for the rate-pH profile; the respective rate constants are MTO(OH-), k = 4.56 × 10-5 s-1 and MTO(OH-)2, k = 2.29 × 10-4 s-1 at 25 °C. Some kinetic data were acquired with electrospray mass spectrometry to monitor the buildup in the concentration of perrhenate ions. Reliable signals for each of the isotopomers of ReO4- were obtained by this method with initial MTO concentrations of 160 μM.
