Rhenium(I) Tellurolate,Telluroether and Bidentate-Telluroether Complexes: Crystal Structures of Re(CO)3Br(PhTe(CH2)3TePh), PhTeRe(CO)5 Re2(μ-SePh)2(CO)8 and [(PhTeMe)Re(CO)5][BF4]

The monomeric rhenium(I) complex with bidentate telluroether ligand Re(CO)₃Br(PhTe(CH₂)₃TePh) (1) was accessible via reaction of the PhTe(CH₂)₃TePh with Re(CO)₅Br. This chelate complex crystallized in triclinic space group $ {\rm P}\bar 1 $ with a = 9.390(5) Å, b = 10.961(3) Å, c = 11.849(4) Å a = 63.30(3)°, β = 87.49(4)° γ = 69.31(4)°, V = 1009.5(7) ų Z = 2, R = 0.033, and R_w = 0.034. Reaction of Re(CO)₅Cl with NaTePh yielded the Re(I) specics PhTeRe(CO)₅ (2). This complex crystallized in triclinic space group $ {\rm P}\bar 1 $ with a = 7.085(1) Å, b = 9.203(1) Å, c = 11.341(1) Å, α = 107.24(1)°, β = 100.56(1)°, γ = 96.47(1)°, V = 683.2(2) ų, Z = 2, R = 0.027, R_w = 0.022. Reaction of PhTeRe(CO)₅ and (PhSe)₂ in THF at 65 °C yielded a product that was confirmed crystallographically to be the known species Re₂(μ-SePh)₂(CO)₈ (3), in which two phenylselenolate ligands bridge the two Re(I). Compound 3 crystallized in monoclinic space group P2₁/n with a = 7.210(2) Å, b = 18.862(6) Å, c = 9.083(3) Å, β = 107.48(3)° V = 1178.2(7) ų, Z = 2, R = 0.046, and R_w = 0.051. Methylation of PhTeRe(CO)₅ with [Me₃O][BF₄] afforded Re(I) product [(PhTeMe)Re(CO)₅][BF₄] (4). This monodentate telluroether species crystallized in monoclinic space group P2₁/n with a = 8.405(1) Å, b = 13.438(3) Å, c = 15.560(2) Å, β = 92.59(1)° V = 1755.5(5) ų, Z = 4, R = 0.035, and R_w = 0.035.     

Ligand-promoted solvent-dependent ionization and conformational equilibria of Re(CO)3Br[CH2(S-tim)2] (tim = 1-methylthioimidazolyl). Crystal structures of Re(CO)3Br[CH2(S-tim)2] and {Re(CO)3(CH3CN)[CH2(S-tim)2]}(PF6)

The compounds Re(CO)3Br[CH2(S-tim)2] (1) and {Re(CO)3(CH3CN)[CH2(S-tim)2]}(PF6) (2), where tim is 1-methylthioimidazolyl, were prepared in high yields and characterized both in the solid state and in solution. The solid-state structures show that the ligand acts in a chelating binding mode where the eight-member chelate ring adopts twist-boat conformations in both compounds. A comparison of both solid-state IR data for CO stretching frequencies and the solution-phase voltammetric measurements for the Re(1+/2+) couples between 1, 2, and related N,N-chelates of the rhenium tricarbonyl moiety indicate that the CH2(S-tim)2 ligand is a stronger donor than even the ubiquitous dipyridyl ligands. A combination of NMR spectroscopic studies and voltammetric studies revealed that compound 1 undergoes spontaneous ionization to form {Re(CO)3(CH3CN)[CH2(S-tim)2]+}(Br-) in acetonitrile. Ionization does not occur in solvents such as CH2Cl2 or acetone that are less polar and Lewis basic (less coordinating). The equilibrium constant at 293 K for the ionization of 1 in CH3CN is 4.3 x 10(-3). The eight-member chelate rings in each 1 and 2 were found to be conformationally flexible in all solvents, and boat-chair conformers could be identified. Variable-temperature NMR spectroscopic studies were used to elucidate the various kinetic and thermodynamic parameters associated with the energetically accessible twist-boat to twist-boat and twist-boat to boat-chair interconversions.     

Reduction of CO2 on a tricarbonyl rhenium(I) complex: modeling a catalytic cycle

Tricarbonyl rhenium(I) complexes, such as Re(bpy)(CO)(3)Cl where bpy = 2,2'-bipyridyl, have demonstrated superior activity in catalyzing CO(2) reduction in the presence of sacrificial electron donors. We have utilized density functional theory (DFT) to investigate a potential pathway for formate production via a rhenium-hydride insertion mechanism in the presence of triethylamine (TEA). On the basis of prior studies, we re-examined the role of TEA and studied a catalytic cycle for CO(2) reduction in which TEA functions as both the hydrogen atom and the electron donor for reducing CO(2) into formate. The catalytic cycle is found to be exothermic with inclusion of solvation and may be viewed as a two-electron reduction of CO(2) because the net result is a transfer of hydride from TEA to CO(2). In addition, we have identified structures of key intermediates in the CO(2)-reduction process and found that the insertion step has a very modest barrier in acetonitrile. These findings provide a molecular-level understanding to formate production via CO(2) reduction mediated by transition-metal complexes. A theoretical investigation is underway to elucidate the formation of carbon monoxide, another common product in Re-catalyzed CO(2) reduction.     

Molecular and Crystal Structures of CpSmX2(THF)3 (X = Br,I)

The reaction of Cp₂Sm(THF) with 1,2-dibromoethane or 1,2-diiodoethane leads to an equimolar mixture of Cp₃Sm(THF) and CpSmX₂(THF)₃ (X = Br, I). CpSmBr₂(THF)₃ crystallizes in the monoclinic system (P2₁, Z = 2, a = 804.6(1), b = 1507.6(2), c = 913.8(1) pm, β = 107.36(1)°, R₁ = 0.0327, wR₂ = 0.0578), while CpSmI₂(THF)₃ is orthorhombic (Pna2₁, Z = 4, a = 1950.6(3), b = 1377.1(2), c = 831.93(9) pm, R₁ = 0.0438, wR₂ = 0.0412). The ligand arrangement around the formally eight coordinate Sm atom is a distorted octahedron with the centroid of the Cp-ring and one THF-molecule in the apical positions, whilst the halides are transoid in the equatorial plane.     

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The novel complexes CpRe(CCHPh)(CO)₂ and Cp₂Re₂(μ-CCHPh)(CO)₄ containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)₂Re[CC(Ph)C(Ph)CH₂]Re(CO)₂Cp were obtained in the reaction of CpRe(CO)₃ with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η¹-bonded to one Re atom and η²-bonded to the other.     

Preparation and characterization of rhenium (I) tricarbonyl dithiocarbamate compounds; Re(CO)3(S2CNMe2)(L)

The title compounds were prepared in good yield by treatment of Re(CO)₅Cl or [Re(CO)₃(H₂O)₃]Br with sodium dimethyldithiocarbamate hydrate (NaS₂CNMe₂·H₂O) and a neutral ligand yielding eight Re(CO)₃(S₂CNMe₂)(L) derivatives: L = NH₃1, pyridine (py) 2, imidazole (im) 3, pyrazole (pz) 4, triphenylphospine (PPh₃) 5, 1,3,5-triaza-7-phosphaadamantane (PTA) 6, t-butyl isocyanide (t-BuNC) 7, and cyclohexyl isocyanide (CyNC) 8. The resulting new complexes were characterized by ¹H and ¹³C NMR and infrared spectroscopy. Each was also structurally elucidated by X-ray crystallography. General structural features in all eight compounds were similar. The orientation of the three single-faced ligands, py, im and pz, demonstrates an interaction with the filled π orbital of the dithiocarbamate. Compounds were tested for stability under conditions that mimic physiological conditions; 1-4 quickly decomposed, 7 and 8 decomposed over 24 h while 5 and 6 were stable.     

Formation of a rhenium(III) carbonyl complex by electrophilic attack on rhenium isocyanides. Synthesis and molecular structure of {Re[N(CH2CH2S) 3][CNC(CH3) 3]} and {Re[N(CH2CH2) 3](CO)}

Treatment of the trigonal-bipyramidal complex {Re[N(CH₂CH₂S)₃](CNCH₂COOEt)} (1a) with LiOH in THF leads to ester hydrolysis and yields the complex {Re[N(CH₂CH₂S)₃](CNCH₂COOH)} (2). Attempts to hydrolyze the ester in 1a in the two-phase system toluene/concentrated hydrochloric acid proceeded under electrophilic attack at the isocyanide nitrogen atom and formation of the carbonyl complex {Re[N(CH₂CH₂S)₃](CO)} (3). Complex 3 was also obtained by treatment of {Re[N(CH₂CH₂S)₃][CNC(CH₃)₃]} (1b) with toluene/hydrochloric acid. The molecular structures of 1b and 3 were established by X-ray structure analysis.     

Investigation of mixed oxidation state cyanide-bridged Re(V)oxo (acac(2)en/pn) and Re(I)(bipy)(CO)3 complexes

A series of cyanide-bridged complexes that combine a low-valent photoacceptor rhenium(I) metal center with an electroactive midvalent rhenium(V) complex were prepared. The synthesis involved the preparation of novel asymmetric rhenium(V) oxo compounds, cis-Re(V)O(CN)(acac(2)en) (1) and cis-Re(V)O(CN)(acac(2)pn) (2), formed by reacting trans-[Re(V)O(OH(2))(acac(2)en)]Cl or trans-Re(V)O(acac(2)pn)Cl with [NBu(4)][CN]. The μ-bridged cyanide mixed-oxidation Re(V)-Re(I) complexes were prepared by incubating the asymmetric complexes, 1 or 2, with fac-[Re(I)(bipy)(CO)(3)][OTf] to yield cis-[Re(V)O(acac(2)en)(μ-CN-1κC:2κN)-fac-Re(I)(bipy)(CO)(3)][PF(6)] (3) and [cis-Re(V)O(acac(2)pn)(μ-CN-1κC:2κN)-fac-Re(I)(bipy)(CO)(3)][PF(6)] (4), respectively.     

Synthesis, characterization, photoluminescence and electroluminescence properties of new 1,3,4-oxadiazole-containing rhenium（I） complex Re（CO）3（Bphen）（PTOP）

A new 1,3,4-oxadiazole-contanining rhenium(I) complex,with the formula [Re(CO)_3(Bphen)(PTOP)],(Bphen=bathophe- nardine,PTOP=4-(5-p-tolyl-1,3,4-oxadiazd-2-yl)pyridine),is synthesized and characterized by elemental analysis,IR,~1H NMR, UV-vis and luminescence spectroscopy.The double-layer electroluminescence devices based on the Re(I) complex have been fabricated by spin-coating technique.The turn-on voltage,maximum efficiency,and brightness for green emission obtained from the devices are 9V,2.1cd/A and 165cd/m~2,respectively.     

Reaction of alkenes with trans-MeOIr(CO)(PPh3)2. Crystal and molecular structure of the pentacoordinate alkoxy-alkene iridium(I) complex,MeOIr(CO)(PPh3)2(TCNE)

The reaction of trans-MeOIr(CO)(PPh₃)₂ with TCNE (tetracyanoethylene) gives rise to the stable adduct MeOIr(CO)(PPh₃)₂(TCNE), the structure of which has been determined via a single-crystal X-ray diffraction study. This complex crystallizes in the centrosymmetric orthorhombic space group Pbca (D¹⁵_2h; No. 61) with a 17.806(4), b 20.769(4), c 20.589(6) Å, V 7614(3) ų and Z = 8. Diffraction data (Mo-K_α, 2θ = 5–45°) were collected on a Syntex P2₁ automated four-circle diffractometer and the structure was solved and refined to R_F 6.2% for 3502 data with |F₀| > 3σ(|F₀|) (R_F 4.3% for those 2775 data with |F₀| > 6 σ(|F₀|)). The central iridium atom has a distorted trigonal bipyramidal coordination geometry in which the methoxy group (Ir-OMe 2.057(8) Å) and carbonyl ligand (Ir-CO 1.897(14) Å) occupy axial sites with ∠MeOIrCO 174.7(4)°. The two triphenylphosphine ligands occupy equatorial sites (IrP(1) 2.399(3), IrP(2) 2.390(3) Å, ∠P(1)IrP(2) 110.32(11)° and the TCNE ligand is linked in an η² “face-on” fashion with the olefinic bond parallel to the equatorial coordination plane (IrC(4) 2.176(10), IrC(7) 2.160(12) Å) and lengthened substantially from its value in the free olefin (C(4)C(7) 1.539(17) Å).     

Reactivity of 17 e- complex [Re(II)Br4(CO)2]2- with bridging aromatic ligands. Characterization and CO-releasing properties

Carbon monoxide releasing molecules (CO-RMs) are a newly emerging class of compounds of pharmacological interest. Among the transition metal-based CO-RMs, 17-electron complexes of general formula cis-trans-[Re(II)(CO)(2)Br(2)L(2)] are promising candidates but their poor hydrophilicity hampers future applications. In an effort to increase water solubility of d(5) dicarbonyl rhenium CO-RMs, the reaction of the cis-[Re(II)(CO)(2)Br(4)](2-) anion with bridging aromatic ligands of the pyridine and diazine type was investigated. Mononuclear and binuclear complexes are presented and it is shown that the nature of the bridging ligand critically dictates the formation of either species. Most complexes retained their fundamental CO-releasing properties. The synthesis of the molecules together with structural, spectroscopic and theoretical details are discussed.     

Dichroic, dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes of rhenium of the type [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et)

A series of unusual dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et) with dichroic properties have been synthesised by reaction of pentacarbonylhalogenorhenium(I) [(CO)5ReX] (X = Cl, Br, I) with the corresponding nitrosoaniline derivatives R2NC6H4NO (R = Me, Et). The deeply coloured solutions in CH2Cl2 show broad UV/Vis absorptions from 595 to 620 nm depending on the halogen bridges and N substituents. Single crystals of all six compounds exhibit a pronounced linear dichroism. The molecular structures have been determined by single-crystal X-ray analyses. All the compounds contain two face-shared octahedra, with two halogens and one NO ligand as bridges. The NO ligand coordinates in a nonsymmetrical eta2-like fashion with N or O coordination to each Re centre. Therefore, the C-nitroso group and the planar NC2 moiety of NR2 both lie almost exactly within the symmetry plane of the dinuclear complexes. These complexes belong to the novel and simple class of neutral dinuclear C-nitroso complexes that include the rare, non-assisted mu2-(eta2-NO) ligand function and have only single halogen atoms in bridging positions.     

Electronic structures and spectroscopic properties of rhenium (I) tricarbonyl photosensitizer: [Re(4,4'-(COOEt)2-2,2'-bpy)(CO)3py]PF6

The ground state and lowest triplet-state structures of [Re(4,4'-(COOEt)(2)-2,2'-bpy)(CO)(3)py]PF(6) photosensitizer (bpy=bipyridine, py=pyridine) have been studied with density functional theory (DFT). Time-dependent density functional theory (TD-DFT) was carried out to predict the photophysical properties of the photosensitizer. The effects of the solvents were evaluated using the conductor-like polarizable continuum (CPCM) method in dichloromethane, chloroform, acetonitrile, acetone, ethanol and dimethylsulfoxide. The electronic transition energies computed with BLYP, MPWPW91, B3LYP and MPW1PW91 functionals are compared with the experimental spectra. Based on the calculated excited energies, the experimental absorption maximum is assigned as metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) mixed transition, and the luminescence originates from the lowest triplet state that is ascribed as the mixed transition of MLCT/LLCT.     

Photochemistry and photophysics of a Pd(II) metalloporphyrin: Re(I) tricarbonyl bipyridine molecular dyad and its activity toward the photoreduction of CO2 to CO

The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2'-bipyridine-4'-carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO)(3)(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C(6)H(4) group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λ(ex) = 520 nm) of [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] is employed as a photocatalyst for the reduction of CO(2) to CO in DMF/NEt(3) solution with λ(ex) > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)(3)(Pic)Bpy][PF(6)] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO)(3)(Pic)Bpy][PF(6)], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be ΔG(ox)* = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] was monitored using time-resolved infrared (TRIR) spectroscopy in the ν(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH(2)Cl(2) with and without NEt(3). Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm(-1)) and to the charge-separated state (2008, 1908 cm(-1)); these bands decay and the parent recovers with lifetimes of 20-50 ps. Spectra recorded on longer time scales (ns, μs, and seconds) show the growth and decay of further species with ν(CO) bands indicative of electron transfer to Re(Bpy).     

Synthesis and structural characterization of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH3CO2)Mn(CO)2[P(C6H5)3]2: An organometallic complex containing a chelating acetate ligand

The accidental but intriguing synthesis of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH₃CO₂)Mn(CO)₂[P(C₆H₅)₃]₂, has been accomplished by the reaction of NaMn(CO)₅ with (CH₃)₃SiCl followed by the addition of triphenylphosphine and acetic acid. A three-dimensional single-crystal X-ray diffraction analysis has shown an octahedral-like molecule containing a symmetrically oxygen-chelating acetate group, the first such group to be reported in a metal carbonyl complex. The two triphenylphosphine ligands occupy mutually trans positions with the two carbonyl ligands possessing the remaining cis sites in the octahedral complex. The compound crystallizes with four molecules in a monoclinic unit cell of space group symmetry $\text{P}\text{2}{}_1\text{c}$ and of dimensions a = 17.744(2) Å, b = 9.692(1) Å, c = 20.004(2) Å, and β = 106.195(4)°. The relatively long MnO(acetate) bond lengths [2.066(6) and 2.069(7) Å] and the relatively short MnCO bond lengths [1.701(12) and 1.760(13) Å] and the relatively short MnP(C₆H₅)₃ bond lengths [2.260(3) and 2.275(3) Å], compared to the corresponding MnCO and MnP(C₆H₅)₃ bond lengths in other manganese carbonyl triphenylphosphine complexes, are rationalized on the basis that the acetate ligand in this molecule functions primarily as a σ-donor.     

The oligoselenide metallacycle complex Cp*Re(NBut) (Se4) as an organometallic ligand. Preparation of the M(CO)5 (M=Cr,Mo, W) adducts [Cp*Re(NBut)(Se4){M(CO)5}2]

Transition Metal Chemistry -     

Crystal and molecular structure of complex compound (C5H5)2Re(H)Cu(μ-I)2CuRe(H)(C5H5)2: A first direct proof of the formation of the Cu(I)Cu(I) bond

The structure of the bimetallic dimer complex [(η⁵-C₅H₅)₂Re(H)CuI]₂ has been investigated. The crystals are monoclinic: a = 16.070(4) Å, b = 7.788(2)Å, c = 17.439(5) Å; b = 96.62(2)°; the space group I2/a; z = 4. The bond between rhenium and copper atoms (2.60 Å) is of the donor-acceptor type; dimerization occurs by the way of formation of the double bridge CuI₂Cu and the direct inter-metal bond CuCu(2.55 Å). The hydride hydrogen atom is the terminal one. The cyclopentadienyl rings form a bent sandwich with the angle between the ring centres and rhenium atom being equal to 158°. It is suggested that the CuCu inter-metal bonding takes place on account of the transition of the non-bonding d-electrons of copper atoms to a high-spin state.