Low-valent Rhenium Research Articles

{MI(CO)X(CNArDArF2)4} (DArF = 3,5-(CF3)2C6H3; M = Re and Tc; X = Br and Cl) Complexes: Convenient Platforms for the Synthesis of Low-Valent Rhenium and Technetium Compounds

[Re(CO)Br(CNArDArF2)4] and [Tc(CO)Cl(CNArDArF2)4] (ArDArF = 2,6-(3,5-(CF3)2C6H3)2-4-F-C6H2) were prepared by reactions of [Re(CO)5Br] or (NBu4)[Tc2(CO)6(μ-Cl)3] with the sterically encumbered isocyanide CNArDArF2. These two compounds proved to be excellent starting materials for the synthesis of unprecedented low-valent rhenium and technetium complexes. The reduction of [Re(CO)Br(CNArDArF2)4] with Na/Hg produces an equimolar mixture of [Re(CO)(CNArDArF2)4] and Na[Re(CO)(CNArDArF2)4] containing the transition metal in the formal oxidation states “0” and “–1”, respectively. The reduction of [Tc(CO)Cl(CNArDArF2)4] with Na/Hg produces Na[Tc(CO)(CNArDArF2)4], which was characterized by 19F and 99Tc NMR spectroscopy. The reactivity of Na[Re(CO)(CNArDArF2)4] resembles that of [Re(CO)5]−, proved by reactions with a number of electrophiles such as MeI, HCl, or F6C5C(O)Cl.

A Water-Soluble Rhenium(I) Catalyst for the Regio- and Stereoselective C(sp2)-H Alkenylation of N-Pyridyl-/N-Pyrimidylindole and the N-H Alkenylation of N-Pyrimidylaniline Derivatives with Ynamides.

A water-soluble and low-valent rhenium(I) catalyst for the C2 alkenylation of N-pyridyl/N-pyrimidylindole derivatives with ynamides under mild conditions using water as the solvent has been described. The reaction of N-pyridyl/N-pyrimidyl indole with the ynamide afforded the C2-Z-selective alkenylation derivative as the sole product, and the reactions of N-pyrimidylanilines delivered the corresponding N-alkenylated product rather than the expected C-H alkenylation products in high yields under the same conditions.

Homogeneous molecular catalysis of the electrochemical reduction of N2O to N2: redox vs. chemical catalysis.

Homogeneous electrochemical catalysis of N2O reduction to N2 is investigated with a series of organic catalysts and rhenium and manganese bipyridyl carbonyl complexes. An activation-driving force correlation is revealed with the organic species characteristic of a redox catalysis involving an outer-sphere electron transfer from the radical anions or dianions of the reduced catalyst to N2O. Taking into account the previously estimated reorganization energy required to form the N2O radical anions leads to an estimation of the N2O/N2O˙− standard potential in acetonitrile electrolyte. The direct reduction of N2O at a glassy carbon electrode follows the same quadratic activation driving force relationship. Our analysis reveals that the catalytic effect of the mediators is due to a smaller reorganization energy of the homogeneous electron transfer than that of the heterogeneous one. The physical effect of “spreading” electrons in the electrolyte is shown to be unfavorable for the homogeneous reduction. Importantly, we show that the reduction of N2O by low valent rhenium and manganese bipyridyl carbonyl complexes is of a chemical nature, with an initial one-electron reduction process associated with a chemical reaction more efficient than the simple outer-sphere electron transfer process. This points to an inner-sphere mechanism possibly involving partial charge transfer from the low valent metal to the binding N2O and emphasizes the differences between chemical and redox catalytic processes.

σ or π? Bonding interactions in a series of rhenium metallotetrylenes.

Salt metathesis reactions between a low-valent rhenium(i) complex, Na[Re(η5-Cp)(BDI)] (BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and a series of amidinate-supported tetrylenes of the form ECl[PhC(NtBu)2] (E = Si, Ge, Sn) led to rhenium metallotetrylenes Re(E[PhC(NtBu)2])(η5-Cp)(BDI) (E = Si (1a), Ge (2), Sn (4)) with varying extents of Re-E multiple bonding. Whereas the rhenium-stannylene 4 adopts a σ-metallotetrylene arrangement featuring a Re-E single bond, the rhenium-silylene (1a) and -germylene (2) both engage in π-interactions to form short Re-E multiple bonds. Temperature was found to play a crucial role in reactions between Na[Re(η5-Cp)(BDI)] and SiCl[PhC(NtBu)2], as manipulation of reaction conditions led to isolation of an unusual rhenium-silane, (BDI)Re(μ-η5:η1-C5H4)(SiH[PhC(NtBu)2]) (1b) and a dinitrogen bridged rhenium-silylene, (η5-Cp)(BDI)Re(μ-N2)Si[PhC(NtBu)2] (1c), in addition to 1a. Finally, the reaction of Na[Re(η5-Cp)(BDI)] with GeCl2·dioxane led to a rare μ2-tetrelido complex, μ2-Ge[Re(η5-Cp)(BDI)]2 (3). Bonding interactions within these complexes are discussed through the lens of various spectroscopic, structural, and computational investigations.

Study of the process of rhenium extraction from lead slime

This article studies the oxidative firing process of lead sludge of copper production for the purpose of extracting rhenium. As an oxidizer, calcium hypochlorite is used, which is simultaneously an oxidizer of low-valent rhenium compounds and a binding reagent of rhenium oxides to calcium perrenate. Optimal conditions for the firing process are found: the firing temperature is 500-600°C, the firing duration is 30-60 minutes, and the oxidizer consumption is 20-40 % of the sludge mass. As a result of thermal studies and experimental work, it was established that the rhenium oxidation process begins at 180-260 °C after the decomposition of calcium hypochlorite and completely ends at 500-600 °C with the formation of calcium perrenate. During water leaching of the stub under the following conditions: T: W=1: 3, temperature of 70 °C, duration of 60 minutes, a solution containing 546 mg/l of rhenium was obtained. The degree of rhenium recovery in the solution was 93-94 %.

The nature of active sites in Pt–ReOX/TiO2 catalysts for selective hydrogenation of carboxylic acids to alcohols

The highly dispersed Pt–ReOX (x ≤ 1) sites ca. 0.5 nm in size were formed via a successive and strong interaction of the Re precursor with titania and then of the Pt complex with deposited low-valent rhenium oxide clusters. The size, charge and chemical composition were characterized by means of HRTEM/STEM with EDX mapping, XPS, and FTIRS. These sites with Re/Pt = 2 were shown to be highly active and selective in the hydrogenation of carboxylic acid to alcohol under very mild conditions (T = 130 °C, P = 50 bar). The reaction rate constant for the hydrogenation of hexanoic acid increased linearly with the Pt content. As for the homogeneous pincer-type Ru-organic complexes, the active Pt–ReOX sites can dissociate heterolytically the molecular hydrogen with the formation of hydroxyl groups and Pt hydride for hydrogenation of the carboxylic group. Indeed, TOF of 20 h−1 and selectivity of 98%–99% are approaching the values typical of homogeneous catalysts. The first order kinetics described well the experimental data obtained in a wide range of reaction conditions.

Performance of Density Functionals for Activation Energies of Re-Catalyzed Organic Reactions

By employing high-level coupled cluster CCSD(T)-F12 calculations as reference, we herein systematically assessed the performance of 16 popular density functional theory (DFT) approximations for typical rhenium-catalyzed reactions. The reactions under study cover those catalyzed by low-valent rhenium(I)/(III) carbonyl complexes as well as high-valent organorhenium(VII) bisperoxo complex. Without DFT dispersion correction, the four best-performing functionals for the barrier heights are B2GP-PLYP, TPSSh, B3LYP, and PBE0 with the mean unsigned deviations (MUDs) under 1.6 kcal/mol. Among these four functionals, B2GP-PLYP generates more accurate barrier heights, while B3LYP and TPSSh behave more reliably in the barrier trend description for these Re-catalyzed reactions. In general, herein the hybrid functionals are better choices than pure GGA or pure meta-GGA functionals. DFT empirical dispersion corrections were found to have beneficial effects on MUDs only for four tested functionals of BMK, CAM-B3LYP, LC-ωPBE, and ωB97X. Often associated with very large errors up to about 15 kcal/mol in barrier height for many tested functionals, the reaction catalyzed by high-valent rhenium(VII) bisperoxo is apparently different from the ones catalyzed by low-valent rhenium(I)/(III) carbonyl complexes. For reactions catalyzed by Re(I)/(III) carbonyl complexes, ωB97XD with dispersion correction performs excellently (MUD = 0.63 kcal/mol) and hence is highly recommended for these Re(I)/Re(III)-mediated reactions.

Role of Low-Valent Rhenium Species in Catalytic Hydrosilylation Reactions with Oxorhenium Catalysts

The catalytic competency of a Re(III) complex has been demonstrated. In the presence of silane, oxorhenium(V) catalysts are deoxygenated to produce species that are significantly more active than t...

Rhenium-Catalyzed Didehydroxylation of Vicinal Diols to Alkenes Using a Simple Alcohol as a Reducing Agent

A new method for the catalytic didehydroxylation of vicinal diols is described. Employing a readily available low-valent rhenium carbonyl complex and a simple alcohol as a reducing agent, both terminal and internal vicinal diols are deoxygenated to olefins in good yield. The optional addition of acid (TsOH, H(2)SO(4)) provides access to lower reaction temperatures. This new system enables the transformation of a four-carbon sugar polyol into an oxygen-reduced compound, providing promising evidence for its practical application to produce unsaturated compounds from biomass-derived materials.

Luminescent Low-Valent Rhenium Complexes with 1,2-Bis(dialkylphosphino)ethane Ligands. Synthesis and X-ray Crystallographic, Electrochemical, and Spectroscopic Characterization

A series of low-valent rhenium phosphine complexes with the general formula [Re(dmpe)(3-x)(depe)(x)](2+/+) (x = 0-3), where dmpe is 1,2-bis(dimethylphosphino)ethane and depe is 1,2-bis(diethylphosphino)ethane, were synthesized and characterized. The reaction of [Re(benzil)(PPh(3))Cl(3)] with the appropriate phosphine yielded the homoleptic tris complexes [Re(dmpe)(3)](+) and [Re(depe)(3)](2+), while the mixed-ligand complexes [Re(dmpe)(2)(depe)](+) and [Re(dmpe)(depe)(2)](2+) were prepared from [Re(dmpe)(2)Cl(2)](+) and [Re(depe)(2)Cl(2)](+), respectively. The oxidation state of the final product strongly depends on the donating properties of the ligand. Each complex, however, exhibits a diffusion-controlled, reversible one-electron transfer between Re(I) and Re(II) with formal reduction potentials, E degrees ', ranging from -0.09 to -0.28 V versus a ferrocene external standard. Subsequent oxidation to Re(III) was found to be chemically irreversible. UV-vis and luminescence spectroelectrochemical techniques were used to study the spectral properties of the Re(I) and Re(II) forms. The Re(II) complexes are red in color and exhibit absorption features from 350 to 600 nm; the lowest-energy transition was assigned as a sigma(P) to dpi(Re) ligand-to-metal charge-transfer (LMCT) transition. Excitation into the lowest-energy absorption band revealed rare examples of luminescent (Phi approximately 0.07) LMCT excited states from d(5) transition-metal complexes in a room temperature solution. Structural characterization of salts of both oxidation states of [Re(dmpe)(2)(depe)](2+/+) was also performed.

Systematic Coordination of Water-Soluble Monoand Bidentate Phosphine Ligands to the Organometallic Precursor fac-[Rebr3(Co)3]2-

As part of our ongoing studies to develop new radiopharmaceuticals (and catalysts) based on water-soluble phosphines for diagnostic and thera- peutic purposes, we are investigating the basic coordination behavior of mono- (PTA) and bidentate (HMPE, HMPB) ligand systems towards the low valent rhenium centerfnc-[ReBr3(CO)3]2−(1) in water and organic solvents at room temperature.

Synthesis, characterization and crystal structure of hexakis-(thiourea-S) rhenium(III) trichloride tetrahydrate: A potential precursor to low-valent rhenium complexes

A new rhenium(III) complex, [Re(SC(NH 2) 2) 6] 3+, has been prepared by reduction of perrhenate with tin chloride in strongly acidic solution in the presence of thiurea. The complex has been characterized in solution and the solid state by elemental and thermal analyses, electronic and IR spectroscopy, conductimetric measurements, EPR spectra and cyclic voltammetry. Stability in aqueous solution was tested spectrophotometrically. The molecular structure of the complex in the [Re(tu-S) 6]Cl 3·4H 2O salt was determined by X-ray diffraction. The compound is isomorphous to [Tc(tu-S) 6]Cl 3·4H 2O. The rhenium ion, sited at an inversion center, is quasi-octahedrally coordinated by six thiourea sulfur atoms [ d(ReS) vary from 2.412(2) to 2.429(2) Å]. Average thiourea bond distances are similar to those observed for the Tc analog [d( S C) = 1.746(8) and d( C N) = 1.32(1) A ̊ ] .

Coordination Chemistry of Low-Valent Rhenium Polypyridyl Complexes: Synthesis, Reactivity, and Electrochemistry.

The complex Re(III)(benzil)(PPh(3))Cl(3) (2) is used to synthesize a variety of Re(III) and Re(II) polypyridyl complexes of the type cis-[Re(III)(L(2))(2)Cl(2)](+), [Re(II)(L(2))(3)](2+), Re(III)(L(3))Cl(3), [Re(III)(L(3))(2)Cl](2+), and [Re(III)(L(4))Cl(2)](+), where L(2) = bpy (3and 6), tbpy (4 and 7), phen (5 and 8); L(3) = terpy (9and 10); L(4) = TMPA (11). The complex cis-[Re(III)(bpy)(2)Cl(2)](+) (3) is a useful synthon in the formation of complexes of the type [Re(bpy)(2)L(x)()](n)()(+) that are six- or seven-coordinate Re(III) complexes (13, 16, and 18) or octahedral Re(II) or Re(I) complexes (12 and 17). The [Re(III)(terpy)(2)Cl](2+) (10) complex can be reduced to form the Re(I) complex, [Re(I)(terpy)(2)](+) (21) and then electrochemically reoxidized to form new complexes of the type [Re(III)(terpy)(2)L](n)()(+). Similar behavior is observed for the [Re(II)(bpy)(3)](2+) (6) complex where [Re(III)(bpy)(3)((t)BuNC)](3+) (20) and [Re(I)(bpy)(3)](+) (19) may be formed. The electrochemistry of these complexes is discussed in relation to their reactivity and the observed pi-acidity of the polypyridyl ligands. In addition, X-ray crystal structures for cis-[Re(III)(bpy)(2)Cl(2)]PF(6) (3) and [Re(I)(bpy)(3)]PF(6) (19) are reported. cis-[Re(III)(bpy)(2)Cl(2)]PF(6) (3, ReC(20)H(16)N(4)Cl(2)F(6)P) crystallizes in the monoclinic space group C2/c with Z = 4 and lattice parameters a = 15.043(5) Å, b = 13.261(4) Å, c = 12.440(4) Å, and beta = 108.86(2) degrees at -100 degrees C. [Re(I)(bpy)(3)]PF(6) (19, ReC(30)H(24)N(6)F(6)P) crystallizes in the rhombohedral space group R&thremacr;c(h) (No. 167) with Z = 12 and lattice parameters a = 13.793(3) Å and c = 51.44(3) Å at -100 degrees C.

Reactions of the low-valent rhenium oxo anions NaRe(O)(RC.tplbond.CR)2 with alkyl and aryl halides; evidence for both S 2 and radical mechanisms

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactions of the low-valent rhenium oxo anions NaRe(O)(RC.tplbond.CR)2 with alkyl and aryl halides; evidence for both S 2 and radical mechanismsRebecca R. Conry and James M. MayerCite this: Organometallics 1991, 10, 9, 3160–3166Publication Date (Print):September 1, 1991Publication History Published online1 May 2002Published inissue 1 September 1991https://doi.org/10.1021/om00055a034RIGHTS & PERMISSIONSArticle Views144Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Thiophene hydrodesulphurization activity of alumina-, silica- and carbon-supported sulphided Re 2O 7 catalysts

Re 2O 7 catalysts supported on various carriers (Al 2O 3, SiO 2 and activated carbon), with various rhenium loadings (between 0.01 and 2.5 at. nm −2), and after different heat treatments, at 380, 575 or 825 K, were subjected to a thiophene hydrodesulphurization test at 675 K. The catalysts were very active, viz. 2–20 times more active than molybdenum catalysts with a similar surface coverage. The activity of rhenium sulphides depended slightly on the support used and increased in the order SiO 2<Al 2O 3<carbon. The HDS activity of molybdenum catalysts, however, was much more affected by support choice. Calcination at 575 or 825 K of oxidic catalyst precursors containing NH 4ReO 4 crystallites led to increased HDS activity, due to increased rhenium dispersion caused by the decomposition of these crystallites. The influence of rhenium content on the HDS activity per mol rhenium was relatively small. Three different regions of rhenium loading could be discriminated. At the lowest loadings (<0.1 at. nm −2) HDS activity was attributed to Al 2O 3 and SiO 2 carrier sites, promoted by low-valent rhenium species. At medium loadings, the activity was fully determined by well-dispersed sulphided rhenium species, and at high loadings, the HDS activity decreased due to the presence of ReS 2 crystallites. The capacity for the formation of well-dispersed sulphided rhenium species is much larger on Al 2O 3 and SiO 2 supports (ca. 1.5 at. nm −2) than on carbon (ca. 0.1 at nm −2). The differences between rhenium and molybdenum catalysts are explained in terms of polarization of metal sulphides due to an inductive effect of the supports.

Low-valent oxo compounds. 5. Low-valent rhenium oxo alkoxide complexes. Synthesis, characterization, structure, and ligand exchange and carbon monoxide insertion reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLow-valent oxo compounds. 5. Low-valent rhenium oxo alkoxide complexes. Synthesis, characterization, structure, and ligand exchange and carbon monoxide insertion reactionsTorsten K. G. Erikson, Jeffrey C. Bryan, and James M. MayerCite this: Organometallics 1988, 7, 9, 1930–1938Publication Date (Print):September 1, 1988Publication History Published online1 May 2002Published inissue 1 September 1988https://doi.org/10.1021/om00099a006RIGHTS & PERMISSIONSArticle Views240Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

X-ray spectral investigation by synchrotron radiation of supported Re/SiO2 and (Re+Pt)/SiO2 catalysts prepared via triethoxyrhenium

Using synchrotron radiation LIII absorption spectra of rhenium in Re/SiO2 and (Re+Pt)/SiO2 catalysts prepared via triethoxyrhenium have been studied. The conclusion has been drawn that reduced catalysts contain lowvalent rhenium ions and their composition is more uniform than that of the previously examined catalysts Re/Al2O3 and (Re+Pt)/Al2O3 prepared by a conventional impregnation technique.