Synthesis and characterization of uranium(III) compounds supported by the hydrotris(3,5-dimethyl-pyrazolyl)borate ligand: Crystal structures of [U(Tp)2(X)] complexes (X = OC6H2-2,4,6-Me3, dmpz, Cl)

Reaction of [U(Tp^Me2)₂(NR₂)] (R = Ph, SiMe₃) with protic substrates such as 2,4,6-trimethylphenol (HOC₆H₂-2,4,6-Me₃), 3,5-dimethylpyrazole (Hdmpz), 2-mercaptopyridine (HSC₅H₄N) and phenylacetylene (HCCPh) afforded the corresponding [U(Tp^Me2)₂(OAr)] (Ar = C₆H₂-2,4,6-Me₃) (1), [U(Tp^Me2)₂(dmpz)] (2), [U(Tp^Me2)₂(η²-SC₅H₄N)] (3), and [U(Tp^Me2)₂(CCPh)] (4) compounds. Reaction of [U(Tp^Me2)₂(NR₂)] with Me₃SnCl or Me₃SiBr gave [U(Tp^Me2)₂Cl] (5) and [U(Tp^Me2)₂Br] (6), respectively, in high yield. The amido precursors failed to react with cyclopentadiene, but metathesis of [U(Tp^Me2)₂I] with NaCp yielded [U(κ³-Tp^Me2)(κ²-Tp^Me2)(η⁵-Cp)] (7). Thermolysis of 7 resulted in oxidation of the metal centre and redistribution of the ligands, giving [UCp₃(dmpz)] (8), pyrazabole (9) and [U(Tp^Me2)(dmpz)₃] (10). The complexes have been fully characterized by spectroscopic methods and the structures of 1, 2, and 5 were confirmed by X-ray crystallographic studies. In the solid state the complexes exhibit distorted pentagonal bipyramidal geometries.     

A one-pot method to prepare the carbene complex [TpRhCl2(CHNiPr2)] from [TpRh(CO)2], CHCl3, and NHiPr2

The complex [Tp^Me₂,ClRh(CO)₂] reacts with chloroform to give quantitatively the rhodium(III) complex [Tp^Me₂,ClRhCl(CHCl₂)(CO)] resulting from the oxidative addition of a C-Cl bond. Further reaction with diisopropylamine gives the aminocarbene complex [Tp^Me₂,ClRhCl₂(CHNiPr₂)], whose X-ray crystal structure has been solved. Addition of an excess of diisopropylamine to [Tp^Me₂,ClRh(CO)₂] in chloroform provides directly [Tp^Me₂,ClRhCl₂(CHNiPr₂)].     

Titanium and zirconium complexes containing sterically hindered hydrotris(pyrazolyl)borate ligands: synthesis, structural characterization, and ethylene polymerization studies

The synthesis, characterization and ethylene polymerization behavior of a set of Tp^′MCl₃ complexes (4, M=Ti, Tp^′=HB(3-neopentyl-pyrazolyl)₃⁻(Tp^Np); 5, M=Ti, Tp^′=HB(3-tert-butyl-pyrazolyl)₃⁻(Tp^tBu); 6, M = Ti, Tp^′=HB(3-phenyl-pyrazolyl)₃⁻(Tp^Ph); 7, M=Zr, Tp^′=HB(3-phenyl-pyrazolyl)₃⁻(Tp^Ph); 8, M=Zr, Tp^′ = HB(3-tert-butyl-pyrazolyl)₃⁻(Tp^tBu)) is described. Treatment of these tris(pyrazolyl)borate Group IV compounds with methylalumoxane (MAO) generates active catalysts for ethylene polymerization. For the polymerization reactions performed in toluene at 60 °C and 3 atm of ethylene pressure, the activities varied between 1.3 and 5.1 × 10³ g of PE/mol[M] · h. The highest activity is reached using more sterically open catalyst precursor 4. The viscosity-average molecular weights () of the PE’s produced with these catalyst precursors varying from 3.57 to 20.23 × 10⁵ g mol⁻¹ with melting temperatures in the range of 127-134 °C. Further polymerization studies employing 7 varying Al/Zr molar ratio and temperature of polymerization showed that the activity as well as the polymer properties are dependent on these parameters. In that case, higher activity was attained at 60 °C. The viscosity-average molecular weights of the polyethylene’s decreases with increasing Al/Zr molar ratio.     

Synthesis, structural characterization, and properties of heavier alkaline earth complexes containing bis(pyrazolyl)borate or bis(3,5-diisopropylpyrazolyl)borate ligands

Treatment of a solid mixture of KBH₄ with six equivalents of 3,5-diisopropylpyrazole (iPr₂pzH) at 180 °C afforded KTp^iPr2(iPr₂PzH)₃ in 53% yield. KBp^iPr2 was synthesized in 56% yield by treatment of a 1:2 M ratio of KBH₄ and iPr₂PzH in refluxing dimethylacetamide. Treatment of MI₂ (M = Ca, Sr, Ba) with two equivalents of KBp or KBp^iPr2 in tetrahydrofuran afforded MBp₂(THF)₂ (M = Ca, 64%, M = Sr, 81%), BaBp₂(THF)₄ (32%), and M(Bp^iPr2)₂(THF)₂ (M = Ca, 63%; M = Sr, 61%, M = Ba, 48%) as colorless crystalline solids upon workup. These complexes were characterized by spectral and analytical techniques and by X-ray crystal structure determinations of all complexes except KBp^iPr2. KTp^iPr2(iPr₂PzH)₃ contains one κ³-N,N,N-Tp^iPr2 ligand and three κ¹-iPr₂pzH ligands, with overall distorted octahedral geometry about the K ion. The iPr₂PzH nitrogen-hydrogen bonds are engaged in intramolecular hydrogen bonding to the 2-nitrogen atoms of the Tp^iPr2 ligand. The solid state structures of MBp₂(THF)₂, BaBp₂(THF)₄, and M(Bp^iPr2)₂(THF)₂ contain κ³-N,N,H Bp and Bp^iPr2 ligands, which form through metal-nitrogen bond formation to the 2-nitrogen atoms of the pyrazolyl fragments and metal-hydrogen bond formation to one boron-bound hydrogen atom per Bp ligand. SrBp₂(THF)₂has the shortest metal-hydrogen interactions among the series. A combination of preparative sublimations, solid state decomposition temperatures, and thermogravimetric analysis demonstrated that MBp₂(THF)₂, BaBp₂(THF)₄, and M(Bp^iPr2)₂(THF)₂ undergo solid state decomposition at moderate temperatures.     

Rhodium(III) NCN pincer complexes catalyzed transfer hydrogenation of ketones

Air-stable monomeric rhodium(III) NCN pincer complexes were synthesized via direct C-H bond activation of 1,3-bis(2-pyridyloxy)benzene, 3,5-bis(2-pyridyloxy)toluene and 3,5-bis(2-pyridyloxy)anisole with RhCl₃·3H₂O in ethanol under reflux. The synthesized complexes were characterized by elemental analysis and ¹H NMR. One of the complexes was structurally characterized by X-ray analysis. An investigation into the catalytic activity of the complex 1a as catalyst for transfer hydrogenation of ketones to alcohols at 82 °C in the presence of iPrOH/KOH was undertaken with the conversions up to 99%.     

Norfloxacin La(III)-based complex: synthesis,characterization, and DNA-binding studies

A La(III) complex, [La^IIICl₂(NOR)₂]Cl (2), containing norfloxacin (NOR) (1), a synthetic fluoroquinolone antibacterial agent, has been synthesized and characterized by elemental analysis, IR, UV–vis spectra and ¹H NMR spectroscopy, and molar conductance measurements. The interaction between 2 and CT-DNA was investigated by steady-state absorption and fluorescence techniques in different pH media, and showed that 2 could bind to CT-DNA presumably via non-intercalative mode and the La(III) complex showed moderate ability to bind CT-DNA compared to other La(III) complexes. The binding site number n, and apparent binding constant K_A, corresponding thermodynamic parameters ΔG^#, ΔH^#, ΔS^# at different temperatures were calculated. The binding constant (K_A) values are 0.23 ± 0.05, 0.56 ± 0.05, and 0.18 ± 0.08 × 10⁵ L mol^?1 for pH 4, 7, and 11, respectively. It was also found that the fluorescence quenching mechanism of CT-DNA by La(III) complex was a static quenching process.     

Synthesis, spectroscopic characterization, X-ray structure and DFT calculations of rhenium(III) complex with bis(3,5-dimethylpyrazol-1-yl)methane

[ReCl₃(MeCN)(PPh₃)₂] reacts with bis(3,5-dimethypyrazol-1-yl)methane (bdmpzm) in acetone to give [ReCl₃(bdmpzm)(PPh₃)]. The compound has been studied by IR, UV–Vis spectroscopy and X-ray crystallography. The molecular orbital diagram of [ReCl₃(bdmpzm)(PPh₃)] has been calculated with the density functional theory (DFT) method.     

Thermal and spectroscopic studies of terbium(III) and dysprosium(III) complexes with piperidin-4-ones

Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L¹)-(L¹⁰) of general formula [Ln(L)(NO₃)₂(H₂O)₂]NO₃ have been synthesized. These complexes have been characterized by analytical, spectral and thermal studies. Molar conductance data show that these complexes are 1:1 electrolytes. The presence of two coordinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones, in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (β), covalency factor (b^1/2) and Sinha’s parameter (δ) evaluated from electronic spectral data of dysprosium(III) complexes indicate a little covalency in metal-ligand bonding.     

三价铑催化硝酮与炔的碳氢活化偶联合成二氢吲哚

三价铑在氧化还原中性条件下催化硝酮与炔发生偶联,经过氮芳环的碳氢键活化和氧转移可以高化学选择性、中等到良好非对映选择性的得到三取代二氢吲哚。     

Mechanistic aspects of uncatalyzed and ruthenium(III) catalyzed oxidation of dl-ornithine by copper(III) periodate complex in aqueous alkaline medium: A comparative kinetic study

The oxidation of dl-ornithine monohydrochloride (OMH) by diperiodatocuprate(III) (DPC) has been investigated both in the absence and presence of ruthenium(III) catalyst in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm⁻³ spectrophotometrically. The stiochiometry was same in both the cases, i.e., [OMH]/[DPC] = 1:4. In both the catalyzed and uncatalyzed reactions, the order of the reaction with respect to [DPC] was unity while the order with respect to [OMH] was < 1 over the concentration range studied. The rate increased with an increase in [OH⁻] and decreased with an increase in [IO₄⁻] in both cases. The order with respect to [Ru(III)] was unity. The reaction rates revealed that Ru(III) catalyzed reaction was about eight-fold faster than the uncatalyzed reaction. The oxidation products were identified by spectral analysis. Suitable mechanisms were proposed. The reaction constants involved in the different steps of the reaction mechanisms were calculated for both cases. The catalytic constant (K_C) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of the mechanism and also the thermodynamic quantities were determined. Kinetic experiments suggest that [Cu(H₂IO₆)(H₂O)₂] is the reactive copper(III) species and [Ru(H₂O)₅OH]²⁺ is the reactive Ru(III) species.     

Insulin-like model complexes: Synthesis,spectra characterization and crystal structure of two novel oxovanadium complexes with poly(pyrazolyl)borate ligands VO(HB(pz)3)(H2B(pz)2) and VO(B(pz)4)2

Two new oxovanadium (IV) complexes VO(HB(pz)₃)(H₂B(pz)₂) (1) and VO(B(pz)₄)₂ (2) have been obtained by the reaction of oxovanadium sulfate with the corresponding ligands KHB(pz)₃, KH₂B(pz)₂ and KB(pz)₄, respectively. The two complexes were characterized by elemental analyses, IR, UV–Vis and X-ray diffraction. Complex 1 crystallizes in the orthorhombic space group, Pca2₁. Complex 2 crystallizes in the orthorhombic space group, Pna2₁. In both complexes, five nitrogen atoms and one oxygen atom coordinate to the vanadium atom, forming a distorted octahedral geometry (VON₅). In addition, related spectra characterization, hydrogen-binding properties, structural configuration and quantum chemistry calculations are also discussed.     

Antimony(III) complexes with pyridine-derived thiosemicarbazones: Structural studies and investigation on the antitrypanosomal activity

The antimony(III) complexes [Sb(2Fo4Ph)Cl₂] (1), [Sb(2Ac4Ph)Cl₂] (2) and [Sb(2Bz4Ph)Cl₂] (3) were prepared with N(4)-phenyl-2-formyl- (H2Fo4Ph), 2-acetyl- (H2Ac4Ph) and 2-benzoylpyridine (H2Bz4Ph) thiosemicarbazones. The antimony(III) complexes presented antitrypanosomal activity against the epimastigote and trypomastigote forms of Trypanosoma cruzi. Complexes (1) and (2) exhibited higher activity than the reference drugs benznidazole and nifurtimox.     

Copper(I) complexes with fluorinated hydrotris(pyrazolyl)borate: Influence of electronic effects on their structure,physicochemical properties,and reactivity

Copper(I) coordination complexes of the anionic fluorinated ligand, hydrotris(3-trifluoromethyl-5-methyl-1-pyrazolyl)borate (L0f⁻), i.e. the copper(I) carbonyl complex, [Cu^I(L0f)(CO)] (1), the copper(I) triphenylphosphine complex, [Cu^I(L0f)(PPh₃)] (2), the copper(I) acetonitrile complex, [Cu^I(L0f)(NCMe)] (3), and the corresponding copper(I) triphenylphosphine complex with hydrotris(3,5-diisopropyl-1-pyrazolyl)-borate anion (L1⁻), i.e. [Cu^I(L1)(PPh₃)] (4), were synthesized in order to investigate the influence of the electron-withdrawing groups on the pyrazolyl rings. The structures of complexes 1, 2, and 4 were determined by X-ray crystallography. While X-ray crystallography did not show definitive trends in terms of copper(I) atom geometry, the clear influence of the electronic structure of the pyrazolyl rings is observed by spectroscopic techniques, namely, IR and multinuclear NMR spectroscopy. Finally, the relative stability of the copper(I) complexes is discussed.     

Hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide: selective synthesis of (Z)-1-alkenyl sulfides and selenides

A simple, stereoselective and efficient method for the hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide has been developed. In the presence of CuI, rongalite, and Cs₂CO₃, a variety of disulfides underwent the reaction of terminal alkynes stereoselectively to afford the corresponding (Z)-1-alkenyl sulfides in moderate to excellent yields. It is noteworthy that hydroselenations of 1,2-diphenyldiselane with alkynes are also conducted smoothly to afford (Z)-1-alkenyl selenides in good yields under the standard conditions.     

Synthesis of an anthracene-based bis(pyrazolyl)methane ligand and the structural characterization of its dinuclear tricarbonylrhenium(I) complex

The new anthracene-based, bitopic bis(pyrazolyl)methane ligand 1,8-bis(4-[bis(1-pyrazolyl)methyl]phenyl)anthracene (1,8-[4-CH(pz)₂C₆H₄]₂C₁₄H₈) has been prepared by the cobalt-catalyzed reaction between thionyldipyrazole and 1,8-bis(4-formylphenyl)anthracene. The reaction between 1,8-[4-CH(pz)₂C₆H₄]₂C₁₄H₈ and Re(CO)₅Br yielded the dirhenium complex {μ-1,8-[4-CH(pz)₂C₆H₄]₂C₁₄H₈}[Re(CO)₃Br]₂. The solid state structure of this complex displays extensive noncovalent interactions, particularly CH-π and π-π interactions.     

Oxidative Addition to Gold(I) by Photoredox Catalysis: Straightforward Access to Diverse (C,N)‐Cyclometalated Gold(III) Complexes

Herein, we report the oxidative addition of aryldiazonium salts to ligand‐supported gold(I) complexes under visible light photoredox conditions. This method provides experimental evidence for the involvement of such a process in dual gold/photoredox‐catalyzed reactions and delivers well‐defined (C,N)‐cyclometalated gold(III) species. The remarkably mild reaction conditions and the ability to widely vary the ancillary ligand make this method a potentially powerful synthetic tool to access diverse gold(III) complexes for systematic studies into their properties and reactivity. Initial studies show that these species can undergo chloride abstraction to afford Lewis acidic dicationic gold(III) species.     

Asymmetric epoxidation of chromenes catalyzed by chiral pyrrolidine SalenMn(III) complexes with an anchored functional group

Chiral pyrrolidine SalenMn(III) complexes with an anchored functional group at the N_aza‐substituent in the pyrrolidine backbone were synthesized, and used as catalysts for asymmetric epoxidation of substituted chromenes. The complex 1 with an anchored imidazole as acceptor could effectively catalyze epoxidation of substituted chromenes in the absence of expensive additive 4‐phenyl pyridine N‐oxide (PPNO) by the coordination of the anchored organic base to the central manganese ion. Complexes 2 and 3 with a quaternary ammonium salt unit at the N_aza‐substituent in the pyrrolidine backbone displayed higher activities than Jacobsen catalyst and the analogous complex 4 without anchored functional group in the aforementioned reaction. Copyright © 2008 John Wiley & Sons, Ltd.     

Modelling the use of lanthanides(III) as probes at calcium(II) binding sites in biological systems: Preparation and characterization of neodymium(III) and calcium(II) malonamato(-1) complexes

A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H₂malm) with Ca^II and Nd^III sources under similar conditions yielded the compounds [Ca(Hmalm)₂]_n (1), [Nd(Hmalm)₂(H₂O)₂]_n(NO₃)_n (2) and [Nd(Hmalm)₂(H₂O)₂]_nCl_n·2nH₂O (3·2nH₂O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three Ca^II ions in 1 and two Nd^III ions in 2 and 3·2nH₂O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH₂O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH₂O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH₂O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed.