Formations and electrochemical behavior of mononuclear and binuclear molybdenum dithiolene complexes with nitrosyl ligands: Evidence for the formation of a coordinatively unsaturated species [CpMo(NO)(dithiolene)]

The one-pot reaction of [Cp^∗Mo(NO)(CO)₂] with elemental sulfur and dimethyl acetylenedicarboxylate (C₂Z₂ (Z = COOMe)) gave the [2+2] cycloadduct of the mononuclear molybdenum dithiolene complex [Cp^∗Mo(NO)(S₂C₂Z₂)(C₂Z₂)] (1), and some binuclear complexes:[Cp^∗Mo(NO)(S₂C₂Z₂)]₂ (2), [Cp^∗₂Mo₂(NO)₂S₂(S₂C₂Z₂)] (3) and [Cp^∗Mo(NO)S₂]₂ (4).The reaction of [Cp^∗Mo(NO)(Cl)(μ-Cl)]₂ with OC{S₂C₂(COOMe)₂} in the presence of sodium methoxide also produced complex 2 and the paramagnetic Cp^∗Mo bisdithiolene complex [Cp^∗Mo(S₂C₂Z₂)₂] (5, Z = COOMe).The structures of complexes 1-5 were determined by X-ray crystal structure analysis.The nitrosyl ligands of complexes 1-4 showed a linear coordination to the molybdenum center (the Mo-N-O bond angles = 169-174°), and their N-O bond lengths were 1.17-1.20 Å.In the binuclear complexes 2-4, two nitrosyl ligands were placed at cis-position.Complexes 1 and 2 were characterized by cyclic voltammetry and spectroelectrochemistry (visible and IR). The electrochemical reduction of the dimeric complex 2 formed the monomeric dithiolene complex[Cp^∗Mo(NO)(S₂C₂Z₂)]⁻ (X⁻) whose lifetime was several minutes. When the anion X⁻ was electrochemically oxidized, the coordinatively unsaturated species X was generated, but it was immediately dimerized to afford the original dimeric complex 2. The reduction of the complex 1 included the elimination of the bridged DMAD moiety (C₂Z₂) to give the anion X⁻.     

Asymmetric transfer hydrogenation of ketones catalyzed by nickel complex with new PNO-type ligands

The new polydentate mixed-N,P,O chiral ligands have been synthesized by the condensation of bis（o-formylphenyl）- phenylphosphane and R-phenylglycinol in CHCl₃,and fully characterized by IR,NMR and EIMS spectra.These ligands were employed with a simple Ni complex Ni（PPh_s）₂Cl₂ in situ as catalytic systems for asymmetric transfer hydrogenation of ketones,and the corresponding optical alcohols were obtained with up to 84%ee under mild conditions.     

Synthesis and X-ray crystal structure analysis of the first nickel bisoxazoline pincer complex

The reaction in toluene between 2-iodo-1,3-bis(4′,4′-dimethyl-2′-oxazolinyl)benzene and Ni(COD)₂ gave [2,6-bis(4′,4′-dimethyl-2′-oxazolinyl)phenyl-N,C¹,N′]iodonickle(II) isolated in 69% yield. The structure of this novel nickel bisoxazoline pincer complex was confirmed by a X-ray crystal structure analysis.     

The mechanism of alkene addition to a nickel bis(dithiolene) complex: the role of the reduced metal complex

The binding of an alkene by Ni(tfd)(2) [tfd = S(2)C(2)(CF(3))(2)] is one of the most intriguing ligand-based reactions. In the presence of the anionic, reduced metal complex, the primary product is an interligand adduct, while in the absence of the anion, dihydrodithiins and metal complex decomposition products are preferred. New kinetic (global analysis) and computational (DFT) data explain the crucial role of the anion in suppressing decomposition and catalyzing the formation of the interligand product through a dimetallic complex that appears to catalyze alkene addition across the Ni-S bond, leading to a lower barrier for the interligand adduct.     

3,3′-Functionalized octahydro-BINOL: a facile synthesis and its high enantioselectivity in the alkyne addition to aldehydes

A facile synthesis of an enantiomerically pure 3,3′-bismorpholinylmethyl H₈-BINOL ligand has been developed. This compound in combination with Et₂Zn and Ti(OⁱPr)₄ is found to catalyze the highly enantioselective reaction of phenylacetylene with aromatic aldehydes. The enantioselectivity of this catalytic process for the reactions of ortho-substituted benzaldehydes is significantly higher than that based on H₈-BINOL.     

Oxygen atom transfer from a trans-dioxoruthenium(VI) complex to nitric oxide

In aqueous acidic solutions trans-[Ru(VI)(L)(O)(2)](2+) (L=1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) is rapidly reduced by excess NO to give trans-[Ru(L)(NO)(OH)](2+). When ≤1 mol equiv NO is used, the intermediate Ru(IV) species, trans-[Ru(IV)(L)(O)(OH(2))](2+), can be detected. The reaction of [Ru(VI)(L)(O)(2)](2+) with NO is first order with respect to [Ru(VI)] and [NO], k(2)=(4.13±0.21)×10(1) M(-1) s(-1) at 298.0 K. ΔH(≠) and ΔS(≠) are (12.0±0.3) kcal mol(-1) and -(11±1) cal mol(-1) K(-1), respectively. In CH(3)CN, ΔH(≠) and ΔS(≠) have the same values as in H(2)O; this suggests that the mechanism is the same in both solvents. In CH(3)CN, the reaction of [Ru(VI)(L)(O)(2)](2+) with NO produces a blue-green species with λ(max) at approximately 650 nm, which is characteristic of N(2)O(3). N(2)O(3) is formed by coupling of NO(2) with excess NO; it is relatively stable in CH(3)CN, but undergoes rapid hydrolysis in H(2)O. A mechanism that involves oxygen atom transfer from [Ru(VI)(L)(O)(2)](2+) to NO to produce NO(2) is proposed. The kinetics of the reaction of [Ru(IV)(L)(O)(OH(2))](2+) with NO has also been investigated. In this case, the data are consistent with initial one-electron O(-) transfer from Ru(IV) to NO to produce the nitrito species [Ru(III)(L)(ONO)(OH(2))](2+) (k(2)>10(6) M(-1) s(-1)), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)](2+) and NO(2)(-) (k(2)=54.7 M(-1) s(-1)).     

Comprehensive studies on the DNA-binding and cleavage properties of a nickel complex derived from phthalate and 1,10-phenanthroline

Binding properties of a nickel complex, [Ni(phen)(pha)(H₂O)₃] (phen = 1,10-phenanthroline, pha = o-phthalate) to DNA were comprehensively investigated by electronic absorption spectroscopy, viscosity, electrochemistry, melting temperature and gel electrophoresis measurements. After interaction with DNA, the hypochromism and bathochromism for the characteristic absorption peaks of [Ni(phen)(pha)(H₂O)₃] revealed a typical intercalation, which was proved by viscosity and melting temperature experiments. Electrochemical assays showed that the electrochemical activity of the nickel complex was shielded after inserting into the double-helix structure of DNA. Moreover, the results of agarose gel electrophoresis showed that the complex had moderate cleavage ability to supercoiled DNA in the presence of H₂O₂.     

缓冲剂对镀镍过程作用机理的研究

缓冲剂对镀镍过程作用机理的研究①高灿柱鹿玉理刘汝涛陈方（山东大学环境工程系济南２５０１００）李树本（中国科学院兰州化学物理研究所兰州７３００００）电镀镍是量大面广的镀种，它作为镀铬、贵金属、仿金、枪黑、黑镍的底层，用途非常广泛［１］．在镀镍过程中，...     

The new theory of electron transfer: application to the photosynthetic reaction centre

Based on recent developments in the theory of electron transfer, we prove that a non-polar environment is needed to maintain the high efficiency and chemical integrity of the photosynthetic reaction centre. We also determine the Gibbs energy diagram for the primary act of charge separation in photosynthesis, and propose an equivalent circuit that captures the principal features of the entire acceptor side of the electron transport chain in photosystem II.     

Unexpected Schiff-base complex formation from the oxidation reaction of a nickel(II) complex with the meso-HMPAO ligand by molecular oxygen

The synthesis and characterization of the amine–oxime complex [Ni(meso-HMPAO)–H] · ClO₄ (1) and its oxidized Schiff-base product [Ni(meso-HMPAO)-5H] · ClO₄ (2), where HMPAO is hexamethyl propylene amine oxime, are presented. Complex 2 results from the oxidation of 1 by molecular oxygen in basic aqueous solution. The structural change of the amine complex 1 to the Schiff-base complex 2 was investigated by the means of NMR spectroscopy and X-ray crystallography.     

Energy transfer from C-phycocyanin to phthalocyanine metal complex in reverse micelles

A new mimic system of photosynthetic apparatus was constructed from C-phycocyanin and phthalocyanine zinc. C-PC was solubilized in the reverse micelles of non ionic surfactant Tween-80, cosurfactant pentanol, and solvent cyclohexane, in which the overall concentration of surfactant was 20% (w/v) and the mass ratio of Tween-80 to pentanol was 4:1. When the molar ratio of water to Tween-80 (R_w)≥9.0, the characteristic properties of C-PC were maintained. When it was excited, the energy transfer from C-PC to phthalocyanine zinc took place. The energy transfer efficiency was only related with the concentration of phthalocyanine, but not that of C-PC. Furthermore, the energy transfer was roughly in keeping with Perrin formulation, which indicated that the energy transfer took place approximately through dipole-dipole interaction in rigid system. The radii of the quenching sphere were calculated from the experimental results. For example, when the concentration of phthalocyanine zinc was 2.10 × 10~(-4) mol/     

Electrochemical mass transfer modeling of a complex two phase heat transfer problem: Case of a prototype slagging gasifier

The local and averaged forced-convective heat transfer coefficients were estimated from measured local and averaged mass transfer coefficients in a model slagging-gasifier hearth pool using the Chilton-Colburn analogy. A solution of ferri/ferrocyanide and buffer with addition of CMC (carboxymethylcellulose) was used for the electrochemical mass transfer measurements. This solution had similar properties to those of the slag in the real gasifier. The influence of natural convection due to the differences in temperatures in the hearth was also estimated. Values of heat transfer coefficient similar to those estimated by British Gas for the prototype Westfield gasifier were found using the mass transfer modelling method. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 447–458. The text was submitted by the authors in English.     

Metathetic sulfur transfer mediated by N-(2-aminophenyl)-4-methyl-thiazolin-2-thione derivatives: a route to diversely substituted S-alkylcarbamothioates

A new route to S-alkylcarbamothioates is disclosed. In a first step, N-(2-aminophenyl)-4-methyl-thiazolin-2-thione is transformed into a mono- or disubstituted urea at nitrogen, and then in a second step, alkylated at sulfur. The resulting salts, after treatment with a base, gave S-alkylcarbamothioates in high isolated yields together with 3-methyl[1,3]thiazolo[3,2-a]benzimidazole under very mild conditions.     

Bis(di-t-butylphosphino)methane complexes of rhodium: homogeneous alkyne hydrosilylation by catalyst-dependent alkyne insertion into Rh---Si or Rh---H bonds. Molecular structures of the dimer [(dtbpm)RhCl]2 and of the silyl complex (dtbpm) Rh[Si(OEt)3](PMe3)

The homogeneous, Rh-catalysed hydrosilylation of but-2-yne with triethoxysilane has been studied. All rhodium complexes employed as catalyst precursors contain ^tBu₂PCH₂P^tBu₂ (“dtbpm”) as a chelating ligand. The crystal and molecular structure of the dimer [(dtbpm)RhCl]₂ (10) has been determined by X-ray diffraction. Complex 10 is shown to be a sluggish catalyst in hydrosilylation reactions of hex-1-ene, whereas but-2-yne is hydrosilylated more rapidly. A much more efficient and highly selective catalyst is 10 with added PPh₃, equivalent to the use of monomeric (dtbpm)RhCl(PPh₃). (E)-2-Triethoxysilylbut-2-ene is formed exclusively and with high turnover numbers in this case. For both 10 and its PPh₃ derivative, the 14-electron fragment [(dtbpm)RhCl], formed by dissociation processes, is the most likely active intermediate in a Harrod-Chalk-type catalytic cycle. The PPh₃ dissociation equilibrium has been studied in detail for (dtbpm)RhCl(PPh₃) and its thermodynamic parameters have been determined. With rhodium alkyl complexes as catalyst precursors, a different type of alkyne hydrosilylation catalysis, involving direct alkyne insertion into the Rh---Si bond of an intermediate rhodium silyl complex, (dtbpm)Rh[Si(OEt)₃](PMe₃) (14), has been found. Complex 14 was synthesized independently from (dtbpm)RhMe(PMe₃) and characterized by X-ray diffraction. It is an equally active catalyst itself, yielding (E)-2-triethoxysilylbut-2-ene as the major product (90%) from but-2-yne and HSi(OEt)₃ (turnover number 1000 per 30 min). The insertion step of the alkyne into the Rh---Si bond of 14 and the formation of two stereoisomeric rhodium vinyl complexes were established independently for MeO₂CCCCO₂Me as a more reactive alkyne substrate. A catalytic cycle is proposed for this unprecedented hydrosilylation reaction. The synthesis of the ν³-benzyl complex (dtbpm)Rh(η³-CH₂C₆H₅) (23) is described. This compound allows an alternative, more efficient access to the new silyl complex (dtbpm)Rh[Si(OEt)₃](PMe₃).     

Unexpected transfer of phenyl from a phenylbismuth complex to iridium in [Cp*IrCl2]2

Tetranuclear [PhBi(pyzc)₂]₄·2(H₂O) (1) (where pyzc^??=?2-pyrazinecarboxylic acid) is easily obtained via reaction of BiPh₃ and Hpyzc under reflux. Treatment of 1 with [Cp*IrCl₂]₂ affords phenyliridium complex [Cp*Ir(Ph)(2-(NC₄H₃N)CO₂)] (2). Unexpected transfer of phenyl from 1 to iridium occurs. The structures of 1 and 2 are established by single-crystal X-ray diffraction. Each bismuth in 1 is in the center of distorted pentagonal pyramidal geometry, equatorially coordinating one κ²-N,O and one μ₂-(κ²-N,O),O′ pyzc, axially binding to phenyl. Complex 2 displays a typical piano-stool geometry with the metal center coordinated by Cp*, a terminal phenyl, and a chelating N,O-ligand. The UV–vis spectrum of 2 is described.     

Synthesis and crystal structure of a macrocyclic complex precursor: Bis-(2-amino-1-methyliminobenzene)1,2-ethane nickel(II) dichloride

NiLCIl₂ (L?=?bis-(2-amino-1-methyliminobenzene)1,2-ethane) crystallizes in space group P-1 with a?=?9.042(2), b?=?10.263(10), c?=?11.045(2) Å, α?=?94.76(10), β?=?108.30(10), γ?= 109.86(10)°, Z?=?2, and represents a precursor of a tetradentate azamacrocyclic complex. The structure is stabilized by a system of intramolecular and intermolecular H-bonding involving chloride ions and nitrogen atoms. The coordination geometry about nickel(II) is slightly distorted octahedral.     

Ruthenium-catalyzed cyclization of epoxide with a tethered alkyne: formation of ketene intermediates via oxygen transfer from epoxides to terminal alkynes

Treatment of (o-ethynyl)phenyl epoxides with TpRuPPh(3)(CH(3)CN)(2)PF(6) (10 mol %) in hot toluene (100 degrees C, 3-6 h) gave 2-naphthols or 1-alkylidene-2-indanones very selectively with isolated yields exceeding 72%, depending on the nature of the epoxide substituents. Surprisingly, the reaction intermediate proved to be a ruthenium-pi-ketene species that can be trapped efficiently by alcohol to give an ester compound. This phenomenon indicates a novel oxygen transfer from epoxide to its terminal alkyne catalyzed by a ruthenium complex. A plausible mechanism is proposed on the basis of reaction products and the deuterium-labeling experiment. The 2-naphthol products are thought to derive from 6-endo-dig cyclization of (o-alkenyl)phenyl ketene intermediates, whereas 1-alkylidene-2-indanones are given from the 5-endo-dig cyclization pathway.     

Anodic stripping voltammetry of sulphide at a nickel film: towards the development of a reagentless sensor

The determination of sulphide at an electrochemically generated nickel oxide layer at glassy carbon and screen-printed electrodes in acidic media has been examined and appraised. The NiO layer was found to produce a stripping-like signal to sulphide and gave a linear peak current response from 20 to 90 μM. The response was further enhanced by repetitive cycling allowing accumulation of nickel sulphide at the electrode surface such that lower micromolar levels of sulphide (i.e. 5 μM) can be determined. The response at the NiO layer to sulphide is shown to be reproducible over a period of 24 h, thereby offering the development of a disposable amperometric sensor for sulphide.     

Specific electron transfer mechanism from the photoexcited tetrasulfonated Zn(II)-tetraphenylporphyrin to methylviologen via self-assembled ionic complex

Electron transfer from photoexcited tetrasulfonated Zn(II)-tetraphenylporphyrin (ZnTSTPP) to methyviologen (MV²⁺) was studied. From the investigation of relative fluorescence intensity and emission lifetime against the MV²⁺ concentration, it was concluded that the electron transfer takes place by a static mechanism. Based on the analysis of the quenching behavior, it was concluded that the static reaction did not follow an ordinary Perrin model, but interaction of the donor (photoexcited Zn-TSTPP) and the acceptor (MV²⁺) molecules, ionic interaction in the present case, is responsible. The analysis of the quenching gave the equilibrium constant for the interaction to be K = 6.5 × 10⁴ M⁻¹. A two-dimensional selfassembled macromolecular ionic complex between ZnTSTPP and MV²⁺ is proposed.     

Synthesis and characterization of a nickel metavanadate complex: Ni(pz)(V2O6) (pz = pyrazine)

A nickel metavanadate complex Ni(pz)(V₂O₆) (pz =?pyrazine) (1) was hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy and thermal analysis. The complex was also investigated by single crystal X-ray diffraction analysis. The three-dimensional extended structure in the crystal is constructed by corner sharing {VO₃}_n chains running along the b axis and two types of {Ni(pz)}_n chains oriented in [0?1?1] and [0?1??1] directions, respectively. Ni is coordinated by two N atoms from two pyrazines and four O atoms from three metavanadates in a distorted octahedral geometry. The variable-temperature magnetic susceptibility of 1 was measured. The magnetic coupling parameter indicates an antiferromagnetic interaction within the {Ni(pz)}_n chain.