Synthesis and properties of dicyclopentadienyltantalum(III) carbonyl compounds

Reaction of Cp₂Ta(H)L (L = C₃H₆, C₄H₈, C₅H₁₀ and C₅H₈) with CO under mild conditions gives alkyltantalum carbonyl complexes Cp₂Ta(CO)R (R = C₃H₇, C₄H₉, C₅H₁₁ and C₅H₉, respectively). Depending upon the position of the olefin relative to the hydride ligand in the hydride-olefin complex, Cp₂Ta(CO)H is also formed during the carbonylation reaction. Reduction of Cp₂TaCl₂ by potassium or t-BuMgCl under one atmosphere of CO affords the very stable compound Cp₂Ta(CO)Cl in moderate yields. Reaction of Cp₂Ta(CO)Cl with RLi or RMgX does not give the Cp₂Ta(CO)R complex.     

Synthesis and structural aspects of M-allyl (M = Ir, Rh) complexes

The synthesis, characterization and chemistry of novel η³-allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C₅Me₄H)Ir(PPh₃)Cl₂ (1), (C₅Me₄H)Ir(PPh₃)(η³-1-methylallyl)Br (3a), (C₅Me₄H)Ir(η⁴-1,3,5-hexatriene) (8), and (C₅Me₅)Rh(η³-1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp^∗IrCl(η³-methylallyl)] (5) ionizes in polar solvents to give [Cp^∗Ir(η³-methylallyl)]⁺Cl⁻ (6) and reaches equilibrium (5 ? 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp^∗Ir(η³-methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes.     

Synthesis and properties of dicyclopentadienyltantalum hydride olefin compounds

Reactions of Cp₂TaCl₂ with RMgCl (R = n-C₃H₇, i-C₃H₇, n-C₄H₉, s-C₄H₉, n-C₅H₁₁ and C₅H₉) give tantalum hydride π-olefin complexes Cp₂Ta(H)L (L = C₃H₆, C₄H₈, C₅H₁₀ and C₅H₈). Two isomers of Cp₂Ta(H)C₃H₆ were obtained. The complexes are useful starting materials for the synthesis of other tantalum hydride species, e.g. Cp₂Ta(H)PEt₃ and Cp₂TaH₃.     

Tin(II) Difluoride and Antimony(III) Trifluoride as Fluorine Donors in Reactions with Tantalum Halides in Various Solvents

Reactions of SnF₂and SbF₃with TaF₅and TaCl₅in acetonitrile and dimethyl sulfoxide were studied by ¹⁹F and ¹¹⁹Sn NMR. It was found that SnF₂and SbF₃behave as fluorine donors for tantalum(V). The anionic and cationic tantalum fluorochloride complexes form in acetonitrile, while [TaF₆]^–predominates in dimethyl sulfoxide. Tin(II) occurs in solution in the form of fluorine-containing polymeric cations.     

Preparation and properties of dicyclopentadienylniobium(III) chloride

The preparation of an air-sensitive 16-electron complex, Cp₂NbCl, is described. Its main property is easy transformation to 18-electron mononuclear compounds. Cp₂Nb(=O)Cl and Cp₂Nb(CO)Cl are obtained in oxidation and carbon monoxide gas addition processes, respectively. The physical properties of these complexes are described.     

Synthesis and properties of aryldicyclopentadienyltitanium(III) compounds

The synthesis and properties of the compounds Cp₂TiR, with R = C₆H₅, o-, m-, p-CH₃C₆H₄, 2,6-(CH₃)₂C₆H₃, 2,4,6-(CH₃)₃C₆H₂, C₆F₅, CH₂C₆H₅, are described. Chemical and physical properties indicate that the R groups are σ-bonded to the titanium atom. The complexes are monomeric, with one unpaired electron per titanium atom. They are very air sensitive, and vary markedly in thermal stability; some of the compounds react with molecular nitrogen, to give complexes of the general formula (Cp₂TiR)₂N₂. Compounds CP₂TiR with R = alkyl could not be isolated.     

Anionic cyclopentadienyluranium(III) complexes

The Na/Hg reduction of Cp₃UX (X  Me, n-Bu, BH₄) and Cp₂U(BH₄)₂ in the presence of 18-crown-6 ether has given the anionic uranium(III) complexes [Cp₃UX][Na(18-crown-6)] and [Cp₂U(BH₄)₂][Na(18-crown-6)]; in agreement with cyclic voltammetry experiments, the borohydride anions were found to be reoxidized by TlBH₄ into the corresponding uranium(IV) complexes.     

Electrochemical Studies of Tantalum(V) Chlorides and Bromides in Acetonitrile. Electrochemical Generation of Tantalum(IV) Species

The electrochemical properties of tantalum halides, TaX₅ Et₄NTaCI₆ and Bu₄NTaBr₆ (X = Cl^? and Br^?) were investigated in rigorously dried acetonitrile using cyclic voltammetry and constant potential electrolysis. A special vacuum electrochemical cel1 equipped with a sample loading device and an AI₂O₃ column was used in order to prevent the hydrolysis of tantalum halides with the small amount of water present in “dry” acetonitrile. Two one-electron reduction waves were observed for al1 tantalum(V) species which correspond to consecutive Ta(V) → Ta(IV) and Ta(IV) → Ta(III) reduction. The E_1/2 values for the Ta(V) → Ta(IV) reduction process are criticalIy dependent on the number of CI^? ligands coordinated to the tantalum atom. As the number of Cl^? is increased from 4 to 5 and 6, it becomes more difficult, by 0.4 V, to reduce Ta(V) to Ta(IV). Constant potential electrolysis at –20°C generates Ta(IV) species; thus TaCl₆ ^2-. TaBr₆ ^2-, TaCl₅NCMe^?, TaBr₅NCMe^? and TaCI₄(NCMe)₂, are obtained in acetonitrile solution after electrolysis. It was found that the reduction product of TaCl₅NCMe depends upon the temperature. At a higher temperature (0°C) the initial electron transfer step is fol1owed by a chemical reaction in which some of the product, TaCI₅NCMe^?, reacts with the starting material, TaCI₅NCMe. to produce TaCl₆ ^? and TaCl₄(NCMe)₂. At lower temperatures (–20°C) the rate of the folIowing chemical reaction is much slower and the reduction product is almost exclusively TaCl₅NCMe^?.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XVIII. Darstellung und Eigenschaften von Vanadintetrabenzyl und von Benzyltantalchloriden

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XVIII. On the Preparation and Properties of Tetrabenzyl Vanadium and Benzyl Tantalum Chlorides Pure tetrabenzyl vanadium was isolated and characterized by elementary analyses, EPR and ¹H-NMR spectra, by hydrolysis and thermal decomposition. — Experiments for the preparation of tetra or pentabenzyl compounds of niobium and tantalum failed, but we could prepare C₆H₅CH₂TaCl₄, (C₆H₅CH₂)₂TaCl₃, and (C₆H₅CH₂)₃TaCl₂, the last two in form of bipyridyl complexes.     

Reactions of half-sandwich rhodium(III) and iridium(III) compounds with pyridinethiolate ligands: Mono-, di-, and tri-nuclear complexes

Neutral trinuclear metallomacrocycles, [Cp^*RhCl(μ-4-PyS)]₃ (3) and [Cp^*IrCl(μ-4-PyS)]₃ (4) [Cp^* = pentamethylcyclopentadienyl, 4-PyS = 4-pyridinethiolate], have been synthesized by self-assembly reactions of [Cp^*RhCl₂]₂ (1) and [Cp^*IrCl₂]₂ (2) with lithium 4-pyridinethiolate, respectively. In situ reaction of complex 3 with three equivalent of lithium 4-pyridinethiolate resulted in [Cp^*Rh(μ-4-PyS)(4-PyS)]₃ (5) containing both skeleton and pendent 4-PyS groups. Chelating coordination of 2-pyridinethiolate broke down the triangular skeleton to give mononuclear metalloligands Cp^*Rh(2-PyS)(4-PyS) (6) and Cp^*Ir(2-PyS)(4-PyS) (7) [2-PyS = 2-pyridinethiolate], which could also be synthesized from Cp^*RhCl(2-PyS) (10) and Cp^*IrCl(2-PyS) (11) with lithium 4-pyridinethiolate. The coordination reactions of 6 with complexes 1 and 2 gave dinuclear complexes [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*RhCl₂] (8) and [Cp^*Rh(2-PyS)(μ-4-PyS)][Cp^*IrCl₂] (9), respectively. Molecular structures of 3, 4, 6 and 11 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

REPARATION AND CHARACTERIZATION OF NEW SUPROFEN COMPLEXES OF Fe(III), Co(II) AND Ni(II)

Abstract

The preparation and properties of new complexes containing the biometals Fe(III), Co(II) and Ni(II) coordinated to the anti-inflammatory drug Suprofen are reported. The elemental analyses, together with the magnetic and thermal behavior and electronic, IR and Raman spectra, indicated the following stoichiometries for the latter two complexes: [M(Sup)₂(H₂O)₄]. For the Fe(III) complex, the generation of a dinuclear species may be proposed on the basis of ⁵⁷Fe Mössbauer measurements.     

Oxo- und Thiotantal(V)-Verbindungen: Synthese von TaOX3 und TaSX3 (X = OR,SR)

Oxo- and Thiotantalum(V) Compounds: Synthesis of TaOX₃ and TaSX₃ (X = OR, SR) TaO(OR)₃ [R = ^tC₄H₉, Mes* ( 2 )], TaO(SR)₃ [R = ^tC₄H₉, p-Tolyl], TaS(OR)₃ [R = ^tC₄H₉, Mes* ( 6 )] and TaS(SR)₃ [R = ^tC₄H₉, p-Tolyl] have been prepared by reaction of TaOCl₃ and TaSCl₃ with LiOR or LiSR. The reaction of TaCl₅ with an excess of LiOMes* yields the chlorotantalum(V)compounds TaCl₃(OMes*)₂ and TaCl₂(OMes*)₃ ( 10 ). The synthesis of TaCl₂(ⁿC₄H₉)(OMes*)₂ ( 11 ), Ta(Sp-Tolyl)₅ and TaCl₂(OEt)₃ · C₅H₅N are also described. 2, 6, 10 and 11 decompose in benzolic solution or by heating under vacuum splitting off 2,4,6-tri-tert-butyl-phenol, n-butane respectively, and forming cyclometallated tantalum(V) complexes with the bidentate ligand OC₆H₂^tBu₂CMe₂CH₂. TaCl₂(OEt)₃ was investigated by X-ray diffraction analysis; the crystal structure has been found to be a binuclear tantalum complex with two bridging ethoxo ligands.     

Binuclear dinitrogen complexe of aryl- and benzyldicyclopentadienyltitanium(III) compounds

The preparation of the deep-blue diamagnetic dinitrogen complexes (Cp₂TiR)₂N₂ with R=C₆H₅, o-, m-, p-CH₃C₆H₄, C₆F₅, CH₂C₆H₅ is described. Their chemical and physcial properties confirm the formulation in which the R groups are σ-bonded to the Cp₂Ti moiety, and the two nitrogen atoms are equivalent. The heats of formation of the complexes from Cp₂TiR and N₂ in toluene have been determined from spectrophotometric data; for R=C₆H₅, o-, m-, p-CH₃C₆H₄, C₆F₅, CH₂C₆H₅, the values are ?18, ?9, ?17, ?20, ?17 and ?14 kcal·mol^?1, respectively. The solid complexes vary markedly in thermal stability, and are extremely air sensitive. The complexed nitrogen can be completely reduced with sodium naphthalene; after hydrolysis of the products, NH₃ and N₂H₄ are obtained. In the thermolysis of the solids, some of the nitrogen is reduced.     

Catenated polysulfur ligands: the pentasulfides of di-η5-cyclopentadienyl-zirconium(IV) and -hafnium(IV)

The thiols Cp₂M(SH)₂, where M = Ti and Zr, react to form the complexes Cp₂MS₅ when treated with mono- and di-sulfur transfer reagents. Treatment of Cp₂MCl₂ with Li₂S₂ and sulfur gave Cp₂MS₅, M = Ti, Zr and Hf, in better yield. The new Zr and Hf complexes have a six-membered MS₅ ring in a chair conformation similar to the previously observed for M = Ti. Variable temperature NMR studies show that the barriers to MS₅ ring inversion decrease in the order Ti > Hf > Zr.     

Mono and dinuclear hydrotris(3,5-dimethylpyrazolyl)borato tantalum complexes

In an effort to obtain suitable starting materials, the synthesis and crystal structure of hydrotris(3,5-dimethylpyrazolyl)borato (Tp^Me2) tantalum(III) complexes are reported. Reaction of KTp^Me2 with [TaCl₂(tht)]₂(μ-Cl)₂(μ-tht) (1) (tht=tetrahydrothiophene) gives the X-ray characterized unsymmetrical (Tp^Me2Ta)(TaCl₃)(μ-Cl₂)(μ-tht) (2) in fair yield. This doubly bonded TaTa complex [2.6791(5) Å, diamagnetic, 18e per Ta] is a rare example of an unsymmetrical Ta₂X₆L₃ complex. The X-ray structure of Tp^Me2TaCl₂(PhCCMe) (3) is also reported. It has the (4e)-alkyne in the symmetry plane of the molecule. The trans effects of tht and phenylpropyne are discussed. 1 is inert towards the reaction with a second equivalent of KTp^Me2.     

Elimination of bis(trimethylsilyl)stannylene from tris(trimethylsilyl)stannylated zirconocene and hafnocene chlorides

Reactions of (Me₃Si)₃SnK with Cp₂MCl₂ (M = Zr, Hf) give the respective stannylated metallocene chlorides. These complexes display a tendency to eliminate bis(trimethylsilyl)-stannylene under Cp₂M(Cl)SiMe₃ formation.     

Studies on ruthenium(III), rhodium(III) and iridium(III) complexes of indazoles

Summary New complexes of the general formula M(L)₃Cl₃ and M(5-AInz)₂Cl₃ · n H₂O (where M = Ru^III, Rh^III and Ir^III; L = indazole and 5-nitroindazole; n=1–2) have been synthesized and characterised by elemental analysis, molar conductance, magnetic susceptibility and i.r. and electronic spectral measurements. All the complexes are covalent and apparently have an octahedral geometry. The ligands are monocoordinated through the pyrrole nitrogen. From the far i.r. spectra amer configuration has been assigned to the indazole and 5-nitroindazole complexes.     

Reactions of 2-pyridinethiolate cobalt(III) complexes with pyridinethiolate or benzenethiolate ligands

Four half-sandwich cobalt complexes, Cp^∗Co(2-PyS)₂ (2), Cp^∗Co(2-PyS)₂ · HI (3), Cp^∗Co(2-PyS) (4-PyS) (4), (Cp^∗Co)₂(μ-PhS)₂(μ-2-PyS)I (5) [Cp^∗ = pentamethylcyclopentadienyl, 2-PyS = 2-pyridinethiolate, 4-PyS = 4-pyridinethiolate, PhS = benzenethiolate] were successfully synthesized by the reactions of 2-pyridinethione, lithium 4-pyridinethiolate and lithium benzenethiolate with Cp^∗Co(2-PyS)I (1), respectively. Complexes 2 and 3 have the structures with two 2-pyridinethiolates ligands coordinated to the cobalt atom. Two different pyridinethiolates ligands can be identified in complex 4. The molecular structure of 5 consists of two Cp^∗-Co fragments, which are triply bridged by three sulfur atoms from different ligands. The molecular structures of 3 and 5 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Structure,thermal stability and decomposition of bis-allyl-zinc compounds

The structure, thermal stability and decomposition of solutions of diallylzinc (I), bis(2-methylallyl)zinc (II), bis(3-methylallyl)zinc (III) and bis(3,3-dimethylallyl)zinc (IV) in deuterated solvents, have been investigated by¹H NMR and by kinetic measurements at temperatures between ?125 and +180°C. At room temperature I, II, III and IV are dynamic systems and are best described as being rapidly equilibrating mixtures of all isomeric σ-allyl forms; the NMR spectra are averages weighted according to the relative concentrations of the respective forms. I displays a¹H NMR spectrum of a static σ-allyl system only below ?125°C and II only below ?115°C. At temperatures above 100°C the thermal decomposition of I–IV results in coupling of the allyl groups, decomposition via radicals being the major process. The coupled products exhibit CIDNP, in which the multiplet polarisations confirm a decomposition via randomly diffusing allyl radicals. In the allyl radicals CH₂CR¹CR²R³ an alternating spin density was proved experimentally. The thermal stability decreases in the order I > II > III > IV.     

Triphenylamine‐Appended Half‐Sandwich Iridium(III) Complexes and Their Biological Applications

Organometallic half‐sandwich Ir^III complexes of the type [(η⁵‐Cp^x)Ir(N^N)Cl]PF₆ (Cp^x: Cp* or its phenyl Cp^xph or biphenyl Cp^xbiph derivatives; N^N: triphenylamine (TPA)‐substituted bipyridyl ligand groups) were synthesized and characterized. The complexes showed excellent bovine serum albumin (BSA) and DNA binding properties and were able to oxidize NADH to NAD⁺ (NAD=nicotinamide adenine dinucleotide) efficiently. The complexes induced apoptosis effectively and led to the emergence of reactive oxygen species (ROS) in cells. All complexes showed potent cytotoxicity with IC₅₀ values ranging from 1.5 to 7.1 μm toward A549 human lung cancer cells after 24 hours of drug exposure, which is up to 14 times more potent than cisplatin under the same conditions.