A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb₄(μ₂-O)₂(μ₂-OC₂H₅)₄Cl₄(OC₂H₅)₄(HOC₂H₅)₄, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) ų, M_r=1090.19,R₁=0.0327 and wR₂=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb₂(μ₂-OC₂H₅)₄Cl₂(OC₂H₅)₂(HOC₂H₅)₂ units that are joined by two axial oxo ligands. The Nb-Nb distance of 2.7458(3) Å is consistent with a single metal-metal bond.     

Oxidation of [Ir(η-C5Me5)(C8H4S8)] and crystal structures of [IrI(η-C5Me5)(C8H4S8)](I3) and [IrI(η-C5Me5)(C8H4S8)](I3)1/2(I7)1/2

[Ir(η⁵-C₅Me₅)(C₈H₄S₈)] (1) [ = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithionate(2−)] was reacted with iodine in dichloromethane to afford one-electron- and two-electron-oxidized species [IrI(η⁵-C₅Me₅)(C₈H₄S₈)] (2), [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₃) (3) and [IrI(η⁵-C₅Me₅)(C₈H₄S₈)](I₅) (4). The oxidized species exhibit electrical conductivities of (1.1-5.0) × 10⁻⁶ S cm⁻¹ measured for compacted pellets at room temperature. The X-ray crystal structures of the two-electron-oxidized complexes 3 and 4 revealed the Ir-I bonds for both of them and the presence of for 3 and ions for 4 as the counter anions. They have many S-S and S-I non-bonding contacts to form two-dimensional molecular interaction sheets in the solid state.     

Ethanol catalyzed synthesis of titanocene aryl carboxylate complexes and crystal structure of (η-C5H5)2Ti(2-OH-5-S-O2CC6H3)2

A method for the synthesis of titanocene (IV) aryl carboxylate complexes is presented in this paper. It is based on the fact that alcohol can catalyze the reaction between Cp₂TiCl₂ and aryl carboxylate ligands in the presence of sodium hydroxide (NaOH). The effects of the catalyst on the reaction system were studied and the possible reaction mechanism was proposed. This method was used to prepare a series of titanocene (IV) aryl carboxylate complexes and a macrocyclic titanocene (5,5′-dithiodisalicylato titanocene), whose structure was determined by X-ray diffraction analysis.     

Oxidation of [Ir(η-C5Me5)(C3S5)] [C3S5 = 4,5-disulfanyl-1,3-dithiole-2-thionate(2−)] and X-ray crystal structure of [IrBr(η-C5Me5)(μ-C2S4)IrBr(η-C5Me5)]

[Ir(η⁵-C₅Me₅)(C₃S₅)] [C₃S₅²⁻ = 4,5-disulfanyl-1,3-dithiole-2-thionate(2−)] was prepared by a reaction of [NMe₄]₂[C₃S₅] with [Ir(η⁵- C₅Me₅)Cl₂]₂ in ethanol. It was reacted with bromine to afford a paramagnetic species [IrBr(η⁵-C₅Me₅)(C₃S₅)] with the Ir-Br bond and in the one-electron-oxidized state, and a diamagnetic dinuclear species [IrBr(η⁵-C₅Me₅)(μ-C₂S₄)IrBr(η⁵-C₅Me₅)]. ESR spectra for the one-electron-oxidized species in solution are discussed. The X-ray crystal structural analysis for the latter complex revealed the geometry consisting of dinuclear IrBr(η⁵-C₅Me₅) moieties bridged by the C₂S₄²⁻ ligand.     

Synthesis, characterization and crystal structure of the bimetallic cyano-bridged [(η-C5H5)(PPh3)2Ru(μ-CN)Ru(PPh3)2(η-C5H5)][PF6]

The bimetallic cyano-bridged [(η⁵-C₅H₅)(PPh₃)₂Ru(μ-CN)Ru(PPh₃)₂(η⁵-C₅H₅)][PF₆] (1) was prepared by reaction of [(η⁵-C₅H₅)(PPh₃)₂RuCl] with N,N′-bis(cyanomethyl)ethylenediamine. The single crystal structure determined by X-ray diffraction showed crystallization on the triclinic P1 space group with a perfect alignment of the cyanide bridges. This accentric crystallization was explored having in view the NLO properties at the macroscopic level, determined by the Kurtz Powder technique. Besides the very low efficiency values for the second harmonic generation, the value obtained for the bimetallic complex 1 showed to be higher than one of the parent complex [(η⁵-C₅H₅)(PPh₃)₂RuCN] (2).     

Actinide complexes with the Kläui tripodal oxygen ligand - crystal structure of [{η-C5H5(CH2C(CH3)3)}Co{P(O)(OC2H5)2}3]2U

Reaction between [(C₅H₅)Co{P(O)(OEt)₂}₃]₂UCl₂ and neopentyl lithium affords the novel complex, [{η⁴-C₅H₅(CH₂C(CH₃)₃)}Co{P(O)(OEt)₂}₃]₂U, in which the uranium metal center has been dehalogenated and the neopentyl nucleophiles have attacked the cyclopentadienyl groups on the Kläui ([(C₅H₅)Co{P(O)(OEt)₂}₃]⁻) ligands. The uranium atom in the title compound possesses octahedral geometry defined by the oxygen atoms from two sets of tripodal oxygen ligands, while the cyclopentadienyl ligands are bound η⁴ to the cobalt atoms. The formation of this complex suggests that the Kläui ligand may not be a suitable ligand framework for supporting organometallic complexes of oxophilic early actinides.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.     

First crystallographic determination of dichloro-bridged dinuclear rhodium Cp* complex with neutral Me2CO molecules. [Rh2(Cp*)2(μ-Cl)2(Me2CO)2](BF4)2 (Cp* = η-C5Me5)

The single crystals of dichloro-bridged dinuclear Rh-Cp* complex with neutral Me₂CO molecules, [Rh₂(Cp*)₂(μ-Cl)₂(Me₂CO)₂](BF₄)₂ (Cp* = η⁵-C₅Me₅), was isolated and the structure was in first determined crystallographically.     

Macropolyhedral boron-containing cluster chemistry: two-electron variations in intercluster bonding intimacy. Contrasting structures of 19-vertex [(η-C5Me5)HIrB18H19(PHPh2)] and [(η-C5Me5)IrB18H18(PH2Ph)]

Fused double-cluster [(η⁵-C₅Me₅)IrB₁₈H₁₈(PH₂Ph)] (8), from syn-[(η⁵-C₅Me₅)IrB₁₈H₂₀] (1) and PH₂Ph, retains the three-atoms-in-common cluster fusion intimacy of 1, in contrast to [(η⁵-C₅Me₅)HIrB₁₈H₁₉(PHPh₂)] (6), from PHPh₂ with 1, which exhibits an opening to a two atoms-in-common cluster fusion intimacy. Compound 8 forms via spontaneous dihydrogen loss from its precursor [(η⁵-C₅Me₅)HIrB₁₈H₁₉(PH₂Ph)] (7), which has two-atoms-in-common cluster-fusion intimacy and is structurally analogous to 6.     

The effect of prostaglandins A2,E1,E2,15 methyl E2, 16, 16 dimethyl E2 and F2α on erythropoiesis

Prostaglandins A₂, E₁, E₂, methylated E₂s and F₂α affected erythropoiesis and/or erythropoietin (Ep) production. This action is indicated in the exhypoxic, polycythemic mouse where radioiron incorporations into RBC increased after administration of these compounds. The kidney and liver have been indicated through previous studies, to actively participate in Ep production. By the removal of one of these active sites in a murine system treated with prostaglandins it is shown that a response is reflected in Ep levels. Interference of the action of prostaglandins (PG) is altered by the removal of one of these target sites of Ep production. The erythropoietic responses elicited by PGA₂, E₁, and perhaps the methylated PGE₂s act through the liver whereas PGE₂ may operate through a renal pathway for its response. PGF_2α reveals no effect on erythropoietic activity and is no different than that observed for vehicle-treated controls. The prostaglandins tested appear to act primarily through the kidney or liver but the possibility exists that some yet undetermined organ site may also be involved.     

Molecular structure of tetranuclear [{Mo2O(S2CNEt2)(η-O2CCF3)(μ-N-o-tol)2}2(μ-O)(μ-O2CCF3)2] formed upon addition of trifluoroacetic acid to syn-[MoO(μ-N-o-tol)(S2CNEt2)]2

Addition of trifluoroacetic acid to syn-[MoO(μ-N-o-tol)(S₂CNEt₂)]₂ in chloroform affords tetranuclear [{Mo₂O(S₂CNEt₂)(η¹-O₂CCF₃)(μ-N-o-tol)₂}₂(μ-O)(μ-O₂CCF₃)₂] which has been crystallographically characterised. It consists of four molybdenum(V) centres linked via bridging imido, trifluoroacetate and oxo ligands and results from replacement of a dithiocarbamate by two trifluoroacetate ligands.     

Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U⁴⁺ cyclooctatetraenyl complex, [(C₅Me₅)(C₈H₈)U]₂(μ-C₈H₈), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me₂bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η⁵-C₅Me₅)(η⁸-C₈H₈)U(Me₂bipy-κ²N,N′) and (η⁵-C₅Me₅)(η⁸-C₈H₈)U(bipy-κ²N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U⁴⁺ complexes of bipyridyl radical anions. Hence, only one of the (C₈H₈)²⁻ ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C₈H₈)²⁻, Me₂bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.     

The reaction of [η:C5H4-(CH2)n-C6H5]2MCl2 complexes (n=1-5; M=Zr, Hf) with EtLi

The reaction of metallocene complexes of the type [η⁵:C₅H₄-(CH₂)_n-C₆H₅]₂MCl₂ (n=1-5; M=Zr, Hf) with EtLi gives the mono nuclear ethyl derivatives [η⁵:C₅H₄-(CH₂)_n-C₆H₅]₂M(Et)Cl and the metallacycles [η⁵:C₅H₄-(CH₂)_n-C₆H₅][η⁵:C₅H₄-(CH₂)_n-η¹:C₆H₄]MEt. A large excess of EtLi affords the dinuclear species [η⁵:C₅H₄-(CH₂)_n-η⁶:C₆H₅]₂M₂Cl₂ (n=2-5). All types of complexes can be activated with methylalumoxane (MAO) and then be used for catalytic polymerization of ethylene.     

Reactions of the pentamethylcyclopentadienyl trisulfido tungsten with M′Cl2 (M′ = Zn, Cd, Hg): Isolation and structural characterization of [PPh4][(η-C5Me5)WS3(ZnCl2)] and [{(η-C5Me5)WS3}2Hg]

Reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] with equimolar M′Cl₂ (M′ = Zn, Cd) in MeCN or 0.5 equiv. of HgCl₂ in DMF afforded two binuclear clusters [PPh₄][(η⁵-C₅Me₅)WS₃(M′Cl₂)] (1: M′ = Zn; 2: M′ = Cd) and one trinuclear cluster [{(η⁵-C₅Me₅)WS₃}₂Hg] (3). Compounds 1-3 were characterized by elemental analysis, IR, UV-Vis, ¹H NMR and X-ray crystallography. Compound 1 may be viewed as a 1:1 composite of [PPh₄][(η⁵-C₅Me₅)WS₃] and ZnCl₂, in which one [(η⁵-C₅Me₅)WS₃]⁻ anion binds a ZnCl₂ moiety via two μ-S atoms. In the structure of 3, two [(η⁵-C₅Me₅)WS₃]⁻ anions coordinate the central Hg atom via two μ-S atoms, forming an unique bent linear structure. In addition, internal redox reactions of [PPh₄][(η⁵-C₅Me₅)WS₃] under the presence of M′Cl₂ (M′ = Zn, Cd, Hg) in high concentrations were discussed.     

Synthesis and structural characterization of the molecular loop [cis-Mo2(N,N-di-p-anisylformamidinate)2]2(O2C-CHCCH-CO2)2

A new molecular loop composed of two quadruply bonded Mo₂(DAniF)₂ units (DAniF=N,N^′-di-p-anisylformamidinate) linked by two chiral allene-1,3-dicarboxylate anions has been prepared from the reaction of [cis-Mo₂(DAniF)₂(MeCN)₄](BF₄)₂ with the bis(tetraethylammonium) salt of allene-1,3-dicarboxylic acid. This compound, [cis-Mo₂(DAniF)₂]₂(O₂C-CHCCH-CO₂)₂ (1), has been characterized by X-ray crystallography and by ¹H NMR and UV-Vis spectroscopy. The molecule possesses a center of inversion and hence is meso. There is only weak electronic coupling between the two Mo₂ ⁴⁺ units as revealed by electrochemical measurements.     

Influence of CH3 group of μ-N-C-S ligand on the properties of [Fe2(C4H5N2S)2(NO)4] complex

Bi-nuclear neutral sulfur-nitrosyl iron complex [Fe₂(SR)₂(NO)₄] (I) has been obtained by replacement of thiosulfate ligands in dianion [Fe₂(S₂O₃)₂(NO)₄]²⁻ by 1-methyl-imidazole-2-yl. From X-ray analysis data, the complex has centrosymmetrical dimeric structure, with the iron atoms being linked via μ-N-C-S bridge. From Mossbauer spectroscopy, isomeric shift δ_Fe is 0.180(1) mm/s and quadrupole splitting ΔE_Q is 0.928(2) mm/s at T = 290 K. By comparative studying the mass-spectra in the gaseous phase of solid samples decomposition and kinetics of NO release in 1% aqueous solutions of dimethylsulfoxide, using of the ligand with CH₃ substituent in position 1 of imidazole-2-thiol was shown to yield a more stable donor of nitrogen monoxide than earlier obtained analog with imidazole-2-thiol, [Fe₂(C₃H₃N₂S)₂(NO)₄].     

Novel Rh-Mn mixed-metal carbonyl cluster containing μ3 and μ-bridging carbyne ligands, [(μ3-CC6H5)(μ-CC6H5)Rh2Mn2Cp2(μ-CO)3(CO)3]: structure, electrochemistry and catalytic properties

The cationic carbyne complex [Cp(CO)₂MnCC₆H₅]BBr₄ (1) reacts with PPN[Rh(CO)₄] (2) to give the title cluster [(μ₃-CC₆H₅)(μ-CC₆H₅) Rh₂Mn₂Cp₂(μ-CO)₃(CO)₃] (3) whose structure has been determined by X-ray diffraction. The electrochemical properties of 3 have been investigated using cyclic voltammetric method. At 60 °C and 2.0 MPa of initial total CO/H₂ (1:1) pressure, the catalytic activity of 3 towards hydroformylation of styrene has also been checked.     

Thallium(III) complexes of the metalloligands [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-Se)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with the diarylthallium(III) bromides Ar₂TlBr [Ar = Ph and p-ClC₆H₄] in methanol gave good yields of the thallium(III) adducts [Pt₂(μ-S)₂(PPh₃)₄TlAr₂]⁺, isolated as their salts. The corresponding selenide complex [Pt₂(μ-Se)₂(PPh₃)₄TlPh₂]BPh₄ was similarly synthesised from [Pt₂(μ-Se)₂(PPh₃)₄], Ph₂TlBr and NaBPh₄. The reaction of [Pt₂(μ-S)₂(PPh₃)₄] with PhTlBr₂ gave [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]⁺, while reaction with TlBr₃ gave the dibromothallium(III) adduct [Pt₂(μ-S)₂(PPh₃)₄TlBr₂]⁺[TlBr₄]⁻. The latter complex is a rare example of a thallium(III) dihalide complex stabilised solely by sulfur donor ligands. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄TlPh₂]BPh₄, [Pt₂(μ-S)₂(PPh₃)₄TlBrPh]BPh₄ and [Pt₂(μ-S)₂(PPh₃)₄TlBr₂][TlBr₄] reveal a greater interaction between the thallium(III) centre and the two sulfide ligands on stepwise replacement of Ph by Br, as indicated by shorter Tl-S and Pt?Tl distances, and an increasing S-Tl-S bond angle. Investigations of the ESI MS fragmentation behaviour of the thallium(III) complexes are reported.     

The arylation of [Pt2(μ-S)2(PPh3)4]

Routes to the synthesis of the mixed sulfide-phenylthiolate complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ have been explored; reaction of [Pt₂(μ-S)₂(PPh₃)₄] with excess Ph₂IBr proceeds readily to selectively produce this complex, which was structurally characterised as its PF₆⁻ salt. Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with other potent arylating reagents (1-chloro-2,4-dinitrobenzene and 1,5-difluoro-2,4-dinitrobenzene) also produce the corresponding nitroaryl-thiolate complexes [Pt₂(μ-S){μ-SC₆H₂(NO₂)₂X}(PPh₃)₄]⁺ (X = H, F). The complex [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ reacts with Me₂SO₄ to produce the mixed alkyl/aryl bis-thiolate complex [Pt₂(μ-SMe)(μ-SPh)(PPh₃)₄]²⁺, but corresponding reactions with the nitroaryl-thiolate complexes are plagued by elimination of the nitroaryl group and formation of [Pt₂(μ-SMe)₂(PPh₃)₄]²⁺. [Pt₂(μ-S)(μ-SPh)(PPh₃)₄]⁺ also reacts with Ph₃PAuCl to give [Pt₂(μ-SAuPPh₃)(μ-SPh)(PPh₃)₄]²⁺.     

Synthesis of some pentanuclear platinum clusters [Pt5(CO)6(L)4]. The X-ray structure of [Pt5(μ-CO)5(CO)(PCy3)4]

[Pt₅(μ-CO)₅(CO)L₄] (L = PPh₃1, PPh₂Bz 2, AsPh₃3, PEt₃4, PCy₃5) have been synthesized by reacting [Pt₃(μ-CO)₃(PR₃)₃] with H₂O₂ (1 and 2), by reduction of cis-[PtCl₂(CO)(PEt₃)] with Zn dust (4), and by the Zn reduction of [Pt₃(μ-CO)₃(PCy₃)₃] in the presence of [PtCl₂(CH₃CN)₂] (5). Complex 5 has not been observed previously and has been characterized by X-ray crystallography. Oxidation of the phosphine ligands with H₂O₂ is a new way to synthesize 1 and 2. The first complete NMR characterization of these complexes has also been achieved, and showed that these pentanuclear cluster complexes exhibit similar stereochemistries in solution and in the solid state. The observed ¹J_Pt-Pt values do not have any correlation with the corresponding bond lengths, again pointing out the irregular behaviour of such parameter in Pt complexes.