New rhenium(III) complexes with fluorinated β-diketones

Five new rhenium(III) complexes of the general formula ReCl₂(R_FCOCHCOR_F)(PPh₃)(OPPh₃), where R_F = CF₃ (I), C₂F₅ (II), C₃F₇ (III), C₄F₉ (IV), and CF₃CFOC₃F₇ (V), were synthesized. The known rhenium(V) complex ReOCl₂(OC₂H₅)(PPh₃)₂, which can readily be obtained from metallic rhenium, was used as a precursor. Two polymorphous modifications of compound I were found and studied by X-ray diffraction analysis. The thermal properties of the synthesized complexes were characterized by the DTA-TG method.     

Synthesis,structure, and luminescence of rhenium(I) complexes with substituted bipyridines

Two new rhenium(I) complexes chelated by a substituted 2,2′-bipyridine with general formula Re(CO)₃LCl, where L?=?6?-(2″-methoxyphenyl)-2,2′-bipyridine (L₁ ) and 6?-(4″-diphenylaminophenyl)-2,2′-bipyridine (L₂ ), are synthesized and characterized by IR, NMR, and elemental analysis. Structure of 1 was determined by single-crystal X-ray crystallography, revealing that rhenium is six-coordinate octahedral. The electrochemical, photophysical, and thermal properties of the two rhenium(I) complexes were investigated. Electroluminescent devices were fabricated by doping 1 in polymer blend host of poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole using simple solution spin-coating technique. The device exhibits a maximum current efficiency of 2.97?cd?A^?1 and peak brightness in excess of 2390?cd?m^?2.     

Reactions of pyridine-2-ethyl/methyl cyclopentadienes with metal carbonyls

Abstract

Thermal treatment of pyridine-2-ethyl cyclopentadiene (1) with Fe(CO)₅ and Ru₃(CO)₁₂ gave novel intramolecular C–H activated dinuclear products (3 and 5). In the case of Fe(CO)₅, the reaction also afforded the normal bis(cyclopentadienyl) diiron complex (4). However, similar reaction of pyridine-2-methyl cyclopentadiene (2) with Fe(CO)₅ and Ru₃(CO)₁₂ only afforded the normal bis(cyclopentadienyl) dinuclear metal complexes (7 and 8). For Ru₃(CO)₁₂, the reaction also yielded a pendant η¹-pyridyl-coordinated product (9). In addition, the reactions of 1 and 2 with Re₂(CO)₁₀ formed the corresponding pyridylethyl/pyridylmethyl cyclopentadienyl rhenium tricarbonyl complexes 10 and 11, which further underwent pyridine to rhenium cyclization via photoirradiation to provide the rhenium dicarbonyl complexes 12 and 13. The molecular structures of 3, 5, 6, 7, 8, 9, and 12 were determined by X-ray diffraction.     

Solvothermal synthesis,characterization and properties of [ReCl<Subscript>5</Subscript>(py)]<Superscript>−</Superscript> complex with T (Néel) of 5.5 K

The synthesis and properties of a rhenium(IV) complex with pyridine as a ligand are presented. The complex, with the formula (2-methyl-pyH)[ReCl₅(py)] 4,4′-bipyridyl 1 has been characterized by elemental analysis, IR spectroscopy, SQUID and X-ray measurements. The single crystal X-ray structure of 1 shows that the rhenium center is of distorted octahedral environment, consisting of five chloride atoms and one pyridine ligand. The solid-state magnetic measurements show antiferromagnetic interactions with T (Néel) of 5.5 K.     

Synthesis,structure, and 77Se NMR study of the (PPh4)2[Re6Se6Br8] complex

The octahedral cluster anion [Re₆Se₆Br₈]^2– was prepared by high-temperature synthesis from elementary substances in the presence of KBr. This cluster anion was isolated and structurally characterized by single-crystal X-ray diffraction analysis as the (PPh₄)₂[Re₆Se₆Br₈] complex (1). Refluxing of polymeric rhenium selenide bromide Re₆Se₆Br₆ in DMF in the presence of Bu₄NBr led to the cleavage of the Re—Br—Re bridges to form the complex (Bu₄N)₂[Re₆Se₆Br₈]. Comparative analysis of the interatomic distances in the octahedral rhenium(iii) selenide bromide clusters was carried out.     

Catalytic Hydrodehydration of Cyclohexanone,Hydrogenation of 2-Cyclohexen-1-one,and Dehydrogenation of Cyclohexene over a Mo Chloride Cluster with an Octahedral Metal Framework

A silica gel-supported molybdenum halide cluster, (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O (1), developed selective catalytic activity for the condensation of cyclohexanone to cyclohexylbenzene and cyclohex-1-enylbenzene, when it was allowed to react in a stream of helium at 300°C. Halide clusters of Nb, Ta, and W of the same metal framework supported on SiO₂ also catalyzed the condensation at 400°C. However, at 400°C, 1 catalyzed disproportionation, and selectivity increased with increasing temperature, yielding cyclohexene and its dehydrogenation products, 1,3-cyclohexadiene and benzene, and 2-cyclohexen-1-one and its dehydrogenation product, phenol. When the same reaction was performed in a stream of hydrogen above 400°C, hydrodehydration proceeded almost exclusively, producing cyclohexene and its dehydrogenation products. 2-Cyclohexen-1-one was hydrogenated to cyclohexanone under the same reaction conditions utilizing hydrogen molecules, whereas cyclohexene was dehydrogenated via 1,3-cyclohexadiene to benzene. The active site developed on 1 was assumed to be a molybdenum atom, which becomes isoelectronic with the platinum metals by accepting two or more electrons from the ligands.     

A novel rhenium-aqua structure: the synthesis and structural characterization of (PPh4)4[ReN(H2O)(CN)3-μ-CN-ReN(CN)4]?·?5H2O

A novel cyano bridged rhenium nitrido complex, [ReN(H₂O)(CN)₄-μ-CN-ReN(CN)₄]⁴⁻ (I) was isolated during a kinetic study of the reaction of ReN(H₂O)(CN)₄]²⁻ with pyridine-2,3-dicarboxylic acid. Yellow crystals of (I), suitable for X-ray structure determination were isolated and the structural data showed an unsymmetrical binuclear rhenium complex with a cyano ligand acting as a bridge between two metal atoms, Re(1) and Re(2). The nitrogen of the bridged cyano ligand coordinates trans to the nitrido ligand of Re(1). The rhenium-nitrido bond distances are 1.657(4) and 1.656(5) ? for Re(1)–N(9) and Re(2)–N(10) respectively. Re(1) and Re(2) are displaced from the planes formed by the four carbon atoms of the cyano ligands towards the nitrido ligands by 0.348(2) and 0.3403(2) ?, respectively.     

The Synthesis,Crystal, Molecular and Electronic Structure of [ReCl2(NO)(py)3]

In line with our investigations of rhenium nitrosyl complexes, we have studied the reaction of [ReCl₃(NO)(OPPh₃)(PPh₃)] with pyridine. The [ReCl₂(NO)(py)₃] complex obtained in this reaction has been characterised by IR, electronic spectra and magnetochemical measurements; ligand field parameters and the electronic structure have been determined. The crystal and molecular structure of [ReCl₂(NO)(py)₃] has been solved by the heavy atom method. Crystals of [ReCl₂(NO)(py)₃] contain distorted octahedral molecules with the pyridine ligands in the mer-arrangement. The nitrosyl group is coordinated linearly to the rhenium atom as NO⁺.     

Novel and Efficient Synthesis of 4-Indazolyl-1,3,4-trisubstituted Pyrazole Derivatives

In the present study, 1-(4,5-dihydro-3,6-dimethyl-4-(1,3-diphenyl-1H-pyrazol-4-yl)-3aH-indazol-5-yl)methanone derivatives (9–12) and isoxazoleyl (13–16) have been synthesized by the condensation of 1,3-diphenyl-1H-pyrazole-4-carbaldehyde (1–4) with acetyl acetone via Knoevenagel/Michael/aldol reactions in a sequential manner to yield intermediate cyclohexanone (5–8). The intermediates (5–8) treated with NH₂NH₂ · H₂O/NH₂OH · HCl afforded 4-indazolyl-1,3,4-trisubstituted pyrazole and isoxazoleyl derivatives. All of these compounds are reported for the first time, and the structures of these compounds were confirmed by means of infrared, ¹H NMR, ¹³C NMR, and mass spectroscopy.     

The Economic Synthesis of Pyridinium Fluorochromate(VI), C5H5NH[CrO3F] (PFC), and Solvent‐Free Oxidation of Organic Substrates with PFC

Abstract

A 1:1:1 stoichiometric reaction among CrO₃, aqueous HF and pyridine affords orange crystalline pyridinium fluorochromate(VI), C₅H₅NH[CrO₃F] (PFC), in 99.2% isolated yield. The reagent under solvent‐free conditions readily converts benzylic, secondary, and allylic alcohols to the corresponding carbonyls and selectively oxidizes secondary alcohols in the presence of primary alcohols, polycyclic hydrocarbons to cyclic ketones, benzoin to benzil, PPh₃ to O?PPh₃, methylphenyl sulfide to sulfoxide, cyclohexanone oxime to cyclohexanone, an allylic Δ⁵‐steroid to the corresponding α,β‐unsaturated ketone and deprotects dioxolanes and dithiolanes to aldehydes; the economic synthesis of PFC, its ease of reaction without solvent, versatility, and high isolated yields of the products are the significant features of the protocol.     

Epitaxial growth of rhenium on intrinsic and foreign substrates

Epitaxial growth of rhenium electrodeposited from a CsCl-Cs₂ReCl₆ chloride melt onto single crystal substrates (planar and bent) of rhenium with (10 $ \overline 1 Epitaxial growth of rhenium electrodeposited from a CsCl-Cs₂ReCl₆ chloride melt onto single crystal substrates (planar and bent) of rhenium with (100), (110), and (0001) orientations and tungsten with (110), (100), (112), and (111) orientations is studied. Optimum conditions of epitaxial growth on a rhenium single crystal with (0001) and (110) orientations are found. The basic possibility is shown of the rhenium heteroepitaxial growth on the (111)-and (100)-tungsten single crystal substrates under specified conditions of electrodeposition from a melt. The rhenium epitaxial growth depends both on the electrolysis conditions and on the substrate orientation. The surface morphology of the rhenium deposits is studied. The microhardness of single crystal and polycrystalline rhenium layers with (0001) orientation is measured. Original Russian Text ? N.O. Esina, L.M. Minchenko, A.A. Pankratov, 2008, published in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 738–744.     

Excellent Synthesis of Adipic Acid

Abstract

A simple, straightforward, and environmentally benign protocol for the synthesis of adipic acid from oxidation of cyclohexanone with Oxone® in the presence of 0.5 mol% RuCl₃ · nH₂O is reported. The reaction completes within a very short time even at room temperature. The generality of the method is shown successfully for synthesis of other C-5 to C-8 dicarboxylic acids.     

Photoelectron Spectroscopy (XPS) and Thermogravimetry (TG) of Pure and Supported Rhenium Oxides. 2. Rhenium Oxides on Titanium Dioxide

Ammonium perrhenate supported on titanium dioxide has been investigated in order to elucidate the interaction between the carrier and the dispersed species. The samples, containing up to 14% by weight of rhenium, have been prepared by impregnation with an ammonium perrhenate solution. The study, performed using X-ray photoelectron spectroscopy and thermogravimetric techniques, demonstrates that a different situation is present depending on the starting rhenium content and gas environment. At low rhenium content (0–2.5%), rhenium is mainly atomically dispersed as per-rhenate-like surface compound; on heating in H₂ up to 500°C, the surface compound is reduced to metal which is still in a dispersed form. In the range 2.5–10% in addition to the perrhenate-like surface compound, small crystallites of NH₄ReO₄ are initially present on the surface. During the heat treatment in hydrogen these crystallites are reduced to ReO₂. The incorporation of Re(IV) in the TiO₂ structure preserves it from further reduction. At higher rhenium content large crystallites of ammonium perrhenate are present on the titanium dioxide surface. They show the reduction behaviour expected for this compound. The data also indicate that when metallic rhenium is heated in air, the heptoxide formed reacts with the free surface of the support and is not lost by volatilization.     

Graphite Oven Flame Analysis: Application to Phosphorus Analysis

Abstract

A graphite furnace has been coupled to a flame photometer as a means of analyzing for phosphorus. An analysis is accomplished by adding a phosphorus sample to the furnace, drying it, vaporizing it into a stream of nitrogen, mixing the stream of nitrogen with air, and drawing part of the nitrogen/air/sample into a fuel-rich hydrogen-air flame. The resulting POH emission is simultaneously recorded and integrated. This system has a detection limit of 0.001 mg/liter phosphorus for a 100 microliter sample of H₃PO₄. Response is linear over four orders of magnitude. Calcium and ferric ions depress phosphorus emission, however, the interference is less severe than previous systems for determining phosphorus by flame photometry. The relative standard deviation on repeat measurements of the same sample is better than 3%.     

Optimizing the preparation of an alumina-supported rhenium catalyst for olefin metathesis

The processes involved in the formation of the alumina-supported rhenium catalyst for olefin metathesis, from the impregnation of the support (thermally activated alumina) with ammonium perrhenate to thermal activation, are studied. The monolayer coverage of the Al₂O₃ surface is observed at a rhenium content of 10 wt % (on Re₂O₇ basis), and the surplus rhenium is sublimed as heptoxide from the support upon thermal activation. In the metathesis of both linear α-olefins and methylenecyclobutanes, the optimum supported rhenium content of the catalyst is 10 wt % on Re₂O₇ basis.     

Asymmetric cross-aldol reaction of isatin and ketones catalyzed by crude earthworm extract as efficient biocatalyst

ABSTRACT

The asymmetric cross-aldol reaction of simple ketones (acetone, cyclohexanone) with isatin derivatives in the presence of crude extract from earthworms as green and effective biocatalyst proceeds easily in MeCN/H₂O (1:1) as solvent to afford 3-hydroxy-2-oxindoles derivatives. Ten compounds were synthesized in high yields (62–88%) and moderate ee (29–42%). Structure of the synthesized compounds has been characterized on the basis of NMR spectra and CHN analysis. The ee of the obtained compounds was determined by chiral phase HPLC analysis.     

Kinetic Studies of Picolinic Acid Catalyzed Chromic Acid Oxidation of Cyclohexanone

The chromic acid oxidation of cyclohexanone catalyzed by picolinic acid in water undergoes a change from first-to zero-order dependence in both cyclohexanone and acidity. The mechanism proposed indicates the formation of an intermediate C₁ by picolinic acid and chromic acid. Then C₁ would react with enol form of cyclohexanone to give another intermediate C₂. C₂ finally cleaves into products.     

CO Hydrogenation over Re-Co Bimetallic Catalysts Supported over SiO2, Al2O3 and NaY Zeolite

The promotion of rhenium on the reduction of Co²⁺ ions in cobalt based samples prepared by various methods, such as, sol/gel technique, incipient wetness impregnationof Al₂O₃ and NaY, has been investigated in the CO hydrogenation. Among the samples the reducibility of the sol/gel, Re-Co/Al₂O₃ and Re-Co/NaY(IM) were the highest compared to Re-Co/NaY (IE) [8]. In addition to facilitating reduction of Co²⁺ ions, the rhenium increased the rate of reaction and the formation ofC₅₊ hydrocarbons at 10 bar pressures. The samples pretreated in various manner, revealed an about five fold increase in activity and an increase in the chain length in the NaYsupported sample while the activity and selectivity changed in various way in the sol/gel prepared samples. Simultaneously, rhenium increased the amount of olefins of low carbon numbers.In the mechanism the rhenium provides an action preventing fast deactivation of cobalt.     

The Molecular and Electronic Structure of [ReOX3(AsPh3)(OAsPh3)] Complexes (X = Cl,Br)

New rhenium oxo-complexes [ReOX₃(OAsPh₃)(AsPh₃)] (X = Cl and Br) have been synthesised and characterised by X-ray diffraction, IR, electronic and magnetochemical measurements. They were obtained in high yield in reactions between [ReOX₃(AsPh₃)₂] and acetonitrile in air.     

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.