Re(VII) complex of N-fused tetraphenylporphyrin

By treatment of N-fused tetraphenylporphyrin rhenium(I) tricarbonyl complex with trimethylamine N-oxide, oxidation of the metal center proceeded to afford N-fused tetraphenylporphyrin rhenium(VII) trioxo complex, which was quite stable against air, light and heat.     

Recovery of rhenium(VII) with triisooctylamine from sulfuric acid solutions

Extraction recovery of rhenium(VII) with triisooctylamine from model sulfuric acid solutions was studied. The effect of the composition of the organic and aqueous phases on the recovery of rhenium(VII) was analyzed, and the composition of rhenium(VII) complexes in the organic phase was determined. The possibility of effective re-extraction of rhenium(VII) from triisooctylamine with ammonia solutions was demonstrated.     

Rhenium(VII) catalysis of Prins cyclization reactions

The rhenium(VII) complex O3ReOSiPh3 is a particularly effective catalyst for Prins cyclizations using aromatic and alpha,beta-unsaturated aldehydes. The reaction conditions are mild, and the highly substituted 4-hydroxytetrahydropyran products are formed stereoselectively. Rhenium(VII) complexes appear to spontaneously form esters with alcohols and to directly activate electron-rich alcohols for solvolysis. Re2O7 and perrhenic acid are equally effective in catalyzing these cyclizations.     

Extraction of rhenium(VII) with aliphatic alcohols from acid solutions

Extraction of rhenium(VII) with C₇–C₁₀ aliphatic alcohols from HCl and H₂SO₄ solutions was examined. The rhenium(VII) distribution coefficients were examined in relation to the acidity and temperature. The composition of the extracted complexes and the thermodynamic parameters of extraction were determined. The extraction method of recovery and preconcentration of rhenium(VII) from H₂SO₄ solutions with secondary octyl alcohol was tested in the counterflow mode.     

Spectrophotometric determination of rhenium with dithio-oxamide in strongly alkaline medium

The interaction between rhenium(VII) and dithio-oxamide in strongly alkaline medium in presence of tin(II) chloride as reluctant has been studied. A purple complex is obtained, with lambda(max) 526 nm and (max) = 4.0 x 10(3) l.mole(-1).cm(-1). The reaction has been applied to the determination of rhenium in tungsten-rhenium alloy after its anodic electrochemical dissolution in alkaline medium. A 1000-fold excess of molybdenum or tungsten does not interfere. A modification of the proposed method can be used as a spot-test for rapid control of rhenium content in industrial solutions.     

Photometrische Rheniumbestimmung in industriellen Proben. Eine schnelle und einfache Methode mit hoher Selektivität

Summary Malachite green reacts with rhenium(VII) to produce a green 1:1-compound which has a maximum of absorption at =630 nm. The system in benzene obeys Lambert-Beer's law from 0.4 to 40 ppm Re(VII). The composition of the extracted complex was determined by Job's method. The influence of interfering ions on the method was examined. Benzene was substituted by different organic solvents. The method was used for rhenium determination in a new hydrodesulfurization catalyst [1].

     

Application of Silica Chemically Modified by Sulfur-Containing Groups to the Separation and Determination of Platinum and Rhenium in Catalysts Based on Aluminum Oxide

Adsorbents based on silica chemically modified by sulfur-containing groups (dithiocarbamate, thiodiazolethiol, mercaptophenyl, and aminobenzothiazole) quantitatively extract (recovery ≥99%) platinum( IV) from solutions ranging from 4 M HCl to pH 6. Under the conditions of the adsorption separation of platinum(IV), rhenium(VII) is not extracted and remains in the solution. The subsequent quantitative (98–99%) adsorption of rhenium(VII) is achieved in the presence of a 1000-fold excess of tin(II) chloride. Adsorption on the surface of adsorbents leads to the formation of platinum(II) complexes with sulfur-containing groups, luminescent at 77 K on irradiation with UV light. The luminescence spectra of surface platinum( II) complexes are located in the region of 550–700 nm. In the adsorption of rhenium(III) in the presence of tin(II) chloride, intensely colored brown complexes of rhenium formed on the surface of adsorbents. Electron paramagnetic resonance showed that, in the surface complexes, rhenium is in the oxidation state 2+. Silicas chemically modified by sulfur-containing groups were used in the development of procedures for the sequential isolation and determination of platinum and rhenium in solutions after the decomposition of aluminum–platinum–rhenium catalysts.     

Separation studies of molybdenum(VI) and rhenium(VII) using TPPO as an extractant

A simple, rapid and reproducible method for the extractive separation of molybdenum(VI) and rhenium(VII) is proposed using triphenylphosphine oxide (TPPO) dissolved in toluene as an extractant. The extractions are carried out from the hydrochloric and hydrobromic acid medium. The extraction of molybdenum is quantitative from 2.54-3.10 M hydrochloric acid and from 3.76-3.98 M hydrobromic acid, and that of rhenium is from 6.78-7.91 M hydrochloric acid. The probable nature of the extractable species is established using log distribution ratio-log concentration plots. The method permits mutual separation of molybdenum(VI) and rhenium(VII) and is applicable for the analysis of alloys and pharmaceutical sample. The detection limits for molybdenum(VI) and rhenium(VII) are 0.8 ppm and 4 ppm respectively.     

A simple approach to room temperature phosphorescent allenylidene complexes

A warm (blue) glow: A stable bis-cyclometalated iridium(III) allenylidene complex is prepared from a bis-cyclometalated iridium(III) complex. This strategy gives the first allenylidene complex that is phosphorescent at room temperature.     

Analytical separation of rhenium by extraction with n-benzylaniline in chloroform from sulphuric acid media

Analytical separation of rhenium(VII) is achieved by solvent extraction with N-benzylaniline in chloroform from sulphuric acid media. Few cations interfere: common anions such as phosphate, tartrate, citrate, oxalate, fluoride, EDTA and ascorbic acid do not interfere. A simple method is described for the separation of micro amounts of rhenium from macro amounts of molybdenum, tungsten, niobium and tantalum. The method also separates rhenium from V, Cr, Se, Te, Os, Ru, Rh, Pd and Pt. The molar absorptivity of rhenium thiocyanate complex in butyl acetate and diisopropyl ether is 40280 ± 280 at 430 nm.     

Extraction of rhenium(VII) and molybdenum(VI) with hexabutyltriamide of phosphoric acid from acid media

Extraction of rhenium(VII) and molybdenum(VI) from sulfuric, hydrochloric, and nitric acid solutions with hexabutyltriamide of phosphoric acid was studied. The influence exerted on the extraction of Re(VII) and Mo(VI) by the nature and concentration of an acid in the aqueous phase, temperature, time of contact between phases, and concentration of the extracting agent in the organic phase was analyzed. Isotherms of extraction of rhenium(VII) and molybdenum(VI) with solutions of hexabutyltriamide phosphoric acid in kerosene were obtained, the composition of the complexes being extracted was determined, the enthalpies and entropies were evaluated, and the concentration constants of extraction of the metals were found.     

The X-ray photoelectron spectra of inorganic molecules: VI. Compounds containing rhenium-oxygen and rhenium-halogen bonds: rhenium 4f,chlorine 2p and oxygen 1s binding energies and their co

Rhenium 4f, chlorine 2p and oxygen 1s binding energies have been recorded for a series of coordination complexes of rhenium(V) and rhenium(VII) containing rhenium-oxygen bonds. Related studies on the rhenium(III) acetates Re₂(OAc)₄X₂(X = Cl, Br) and on several adducts of the rhenium chlorides (Re 4f and Cl 2p binding energies only) are also reported. Chemical shift data are related where possible to the molecular structures of the complexes. Correlations between rhenium 4f binding energies and oxidation state are of diagnostic value only in distinguishing the high oxidation state species (rhenium(V) and (VII)). Differences in rhenium 4f_{$\text{7}\text{2}$} and oxygen 1s binding energies [δ(O1s, Re 4f_{$\text{7}\text{2}$})] may be useful in probing the nature of the rhenium-oxygen bonds.     

Total synthesis of 27-hydroxy-bullatacin and its C-15 epimer, and studies on their inhibitory effect on bovine heart mitochondrial complex I functions

The total synthesis of 27-hydroxybullatacin and its C-15 epimer has been achieved using rhenium(VII) oxides-mediated and Co(modp)₂-catalyzed oxidative cyclization (OC), diastereoselective alkynylation, Brown's enantioselective allylboration, and Grubbs' cross metathesis as the key reactions. The inhibitory effect of these compounds on the complex I function, as determined by using bovine submitochondrial particles, was in low nanomolar range.     

Zur Koordinationschemie des Rhenium(VII). IV. t-Butylperrhenat

On the coordination chemistry of rhenium(VII). IV. t-Butylperrhenate t-Butylperrhenate is obtained in good yield form Re₂O₇ and di-t-butylether (data of an improved instruction for the preparation of the either) or from Re₂O₇ and t-butanol. The colourless crystals are decomposed already at ?40°C. The position of Re? O valence vibrational bands in the IR spectra of t-butylperrhenate and trimethylsilylperrhenate indicate a high formal bonding number at rhenium(VII) in these compounds. They do not add dimethylformamide as a mere ligand, but interact with it to form DMF complexes of Re₂O₇.     

Multiple bonds between main group elements and transition metals, 155. (Hexamethylphosphoramide) methyl(oxo) bis(η-peroxo)rhenium(VII), the first example of an anhydrous rhenium peroxo complex: crystal structure and catalytic properties

Methyl(oxo)bis(η²-peroxo)rhenium(VII)1, the active species of the system CH₃ReO₃/H₂O₂ in the catalytic oxidation of different organic and organometallic compounds, is stabilized by a water molecule attached to the rhenium center. This water molecule can be removed and substituted by hexamethylphosphoramide (HMPA) to yield (hexamethylphosphoramide)methyl(oxo)bis(η²-peroxo rhenium(VII) (3). The synthesis, crystal structure (X-ray difraction study), and catalytic properties of which compound are reported. Crystal data are as follows: monoclinic, space group P2₁/n, A = 900.76(7) pm, B = 1229.80(11) pm, C = 1318.57(11) pm, β = 90.251(7)°, R_w = 0.034 for 1878 reflections. The catalytic properties of compound 3 in the oxidation of olefins with H₂O₂ are similar to those of 1.     

Untersuchungen zum polarographischen Verhalten des Rheniums in perchlorsauren L?sungen

Zusammenfassung Das polarographische Verhalten des Rheniums(VII) wurde in konzentrierteren PerchlorsäureLösungen untersucht. Zur Bestimmung kleiner Rhenium(VII)-Konzentrationen ist eine 10 M Perchlorsäure geeignet. Die Bestimmung kann mit der Gleichstrom-, Wechselstrom- und differentiellen Pulse-Polarographie durchgeführt werden. Mit der Gleichstrompolarographie lassen sich noch 2·10^–8 M Re(VII) erfassen. Die Eichkurven sind im Bereich von 5·10^–8 bis 6·10^–5M linear. Die Temperatur- und Tropfzeitabhängigkeit der polarographischen Ströme macht ihren katalytisch/kinetischen Ursprung wahrscheinlich.

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Investigations on the polarographic behaviour of rhenium in perchloric acid solutions

Summary The polarographic behaviour of rhenium(VII) was investigated in perchloric acid solutions of higher concentrations. For the polarographic determination of small concentrations of rhenium(VII) a 10 M perchloric acid is properly suited. The determination can be performed by DC-, AC- and DP-polarography. With DC-polarography 2×10^–8 M Re(VII) can be detected. The calibration curves are linear in the range from 5×10^–8 to 6×10^–5M Re(VII). From investigations of the temperature- and droptime dependence the catalytic/kinetic origin of the polarographic currents is made probable.

     

Radiochemical separation of rhenium(VII) from tungsten(VI)

The absorption of rhenium(VII) and tungsten(VI) ions on Al₂O₃ from HCl, HClO₄, HNO₃, H₂SO₄, H₃PO₄, NaOH, NH₄OH, NaCl, NaF, and Na-tartarate solutions by batch equilibration, as well as by passage through a chromatographic column, has been studied. The results show that rhenium(VII) can be effectively separated from tungsten(VI) using any of the acid or salt solutions investigated. The experimental data allowed to develop a simple procedure for the radiochemical separation of rhenium isotopes from an irradiated WO₃ sample.     

Kinetic and mechanistic studies of sulfur transfer from imidomethylrhenium sulfides

The bis(2,6-diisopropylphenylimido)methylrhenium(VII) sulfide dimer, [CH(3)Re(NAr)(2)](2)(mu-S)(2) (1), reacts with a 1:1 amount of a phosphine or an alkyl isocyanide to yield a dimeric rhenium(VI) species, [CH(3)Re(NAr)(2)](2)(mu-S) (2), which has been structurally characterized. The two rhenium atoms in 2 are within bonding distance, 280 pm, more than 90 pm shorter than in 1. With excess L, 1 reacts to give a monomeric rhenium(V) complex, CH(3)Re(NAr)(2)L(2) (3A, L = PZ(3), Z = alkyl, aryl; 3B, L = isocyanide). The rate of formation of 3A is first-order with respect to [1] and second-order with respect to monodentate phosphine concentrations. With bidentate phosphines, however, the order with respect to the phosphine drops to unity. The addition of another (nonoxidizable) coordinating ligand, such as pyridine or one of its derivatives, accelerates the formation of 3A. In the presence of a pyridine ligand the reaction is first-order with respect to phosphine concentration, both monodentate and bidentate. The reactions between phosphines and 2 are slower than those with 1, which excludes [CH(3)Re(NAr)(2)](2)(mu-S) from being the intermediate in the reactions of 1. To account for that, we have proposed an intervening species that partitions between transformation to 3 with excess L and to 2 otherwise.     

Photoelectron spectroscopy (XPS) and thermogravimetry (TG) of pure and supported rhenium oxides 1. Pure rhenium compounds

To investigate the interaction of rhenium with several supports, a preliminary study on pure rhenium compounds has been carried out in order to achieve a better understanding of their surface chemical properties. To this end X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) methods have been applied. The results show that metallic rhenium, ReO₂ and ReO₃ are covered with Re(VII). By heating in H₂, NH₄ReO₄ and rhenium oxides are reduced to metallic rhenium in different temperature ranges. In the case of Re₂O₇ a spillover effect has been found when platinum is present. For ReO₃ and ReO₂ a morphological model has been described on the basis of combined XPS, TG and surface area measurements. The binding energy values of the different rhenium oxidation states have been assessed and their variation with the oxidation number briefly discussed.     

Kinetics and mechanisms of catalytic oxygen atom transfer with oxorhenium(V) oxazoline complexes

The rhenium(V) monooxo complexes (hoz)2Re(O)Cl (1) and [(hoz)2Re(O)(OH2)][OTf] (2) have been synthesized and fully characterized (hoz = 2-(2'-hydroxyphenyl)-2-oxazoline). A single-crystal X-ray structure of 2 has been solved: space group = P1, a = 13.61(2) A, b = 14.76(2) A, c = 11.871(14) A, alpha = 93.69(4) degrees, beta = 99.43(4) degrees, gamma = 108.44(4) degrees, Z = 4; the structure was refined to final residuals R = 0.0455 and Rw = 0.1055. 1 and 2 catalyze oxygen atom transfer from aryl sulfoxides to alkyl sulfides and oxygen-scrambling between sulfoxides to yield sulfone and sulfide. Superior catalytic activity has been observed for 2 due to the availability of a coordination site on the rhenium. The active form of the catalyst is a dioxo rhenium(VII) intermediate, [Re(O)2(hoz)2]+ (3). In the presence of sulfide, 3 is rapidly reduced to [Re(O)(hoz)2]+ with sulfoxide as the sole organic product. The transition state is very sensitive to electronic influences. A Hammett correlation plot with para-substituted thioanisole derivatives gave a reaction constant rho of -4.6 +/- 0.4, in agreement with an electrophilic oxygen transfer from rhenium. The catalytic reaction features inhibition by sulfides at high concentrations. The equilibrium constants for sulfide binding to complex 2 (cause of inhibition), K2 (L x mol(-1)), were determined for a few sulfides: Me2S (22 +/- 3), Et2S (14 +/- 2), and tBu2S (8 +/- 2). Thermodynamic data, obtained from equilibrium measurements in solution, show that the S=O bond in alkyl sulfoxides is stronger than in aryl sulfoxides. The Re=O bond strength in 3 was estimated to be about 20 kcal x mol(-1). The high activity and oxygen electrophilicity of complex 3 are discussed and related to analogous molybdenum systems.