1,721,011 research outputs found
The solution State of Nickel(II) and Nickel (I) in the Presence of Diphosphines in Acetonitrile. A Combined Electroanalytical and Spectrophotometric Approach.
No full textThe equilibria involving nickel(II), nickel(I) and nickel(0) in the presence of bidentate phosphine ligands in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry. The obtained results show that when both cone angles and PP distance make the diphosphine well-suited to act as a chelating ligand, only bis-chelate complexes of the type NiL2 are formed by nickel in all the three achieved oxidation states. Longer methylene chains interposed between the phosphorus atoms make the diphosphine less suited to act in a bidentate fashion, thus allowing lower-order complexes, e.g. NiLS2 (S = solvent), to be obtained for nickel in the +2 and +1 oxidation states. Evidence for the poor stability of the [NiILS2]+ complexes and for a higher-order complex of the type NiL3 for nickel(II) have also been obtained. The dependence of the reduction potentials on the nature of the diphosphine employed is discussed. © 1984
Electrochemical Reduction of Triphenyltin Chloride in Aprotic Medium
No full textThe electrode mechanism for the reduction of theSnPh3Cl organometallic species in aprotic solvent is define
An Electroanalytical Investigation on the Electrocatalysed Coupling of Allyl Halides Promoted by the Nickel -Triphenylphosphine System.
No full textThe electrochemical reduction of allyl halides is strongly catalysed when it is carried out by cathodically generating and continuously recycling the nickel(0) complex promoter |Ni(PPh3)4|(PPh3= triphenylphosphine). This species undergoes oxidative addition by allyl halides leading to π-bonded organometallic nickel(I) derivatives, the metal-carbon bond of which is cleaved by means of an electrochemical reduction providing 1,5-hexadiene as the coupling product and renewing the nickel(0) promoter, thus allowing an electrocatalytic cycle to be completed. Voltammetric, coulometric and gas-chromatographic data are presented and analysed. To account for the catalytic action of the nickel(0) complex, a mechanistic scheme is proposed which is consistent with the kinetic data obtained by studying the chemical reaction coupled with charge transfers by means of the voltammetric technique. © 1984 Elsevier Sequoia S.A
An Electroanalytical Investigation on the Olefin Isomerization Reaction Promoted by Electrogenerated Cationic Nickel Hydride.
No full textThe isomerization of allylbenzene has been carried out by the cationic nickel hydrides [NHiL4]+ (L = 1 2dppe; PPh3; P(OEt)3) directly prepared in situ by electrogenerating the corresponding Ni(0) complexes in the presence of hydrogen ions. Such a procedure allows one also to take advantage of the catalytic activity of the poorly stable hydrides obtained when L = PPh3 or P(OEt)3. In these cases, a small but finite steady-state concentration of the promoter can be maintained in the solution by the occurrence of an electrocatalytic process cyclically renewing this species, thus making possible its interaction with olefin molecules in spite of its instability. The results obtained point out that high stability for the cationic nickel hydrides is accompanied by quite a low promoting activity, while hydrides which decay quickly also exhibit high reactivity. The information collected concerning the reaction pathway through which the catalyzed isomerization reactions occur, has then been exploited for devising an electrocatalytic process in which the coupling of allyl bromide and the isomerization of the diolefin product can occur simultaneously. © 1987
An Electroanalytical investigation on the reduction of high-spin octahedral complexes of nickel(II) with schiff-base ligands.
No full textThe electrochemical reduction of a series of high-spin octahedral complexes of nickel(II) with a variety of Schiff base ligands of the type RNCHPy (Py=pyridyl; R=CH3; C6H5; o-, m- or p-CH3-C6H4; o-, m- or p-ClC6H4; o-, m- or p-CH3O-C6H4) has been investigated in acetonitrile. All these complexes undergo a fairly reversible two-electron reduction process in which the parent hexacoordinate nickel(O) species is initially formed. This primary electrode product decomposes quickly in the homogeneous phase leading to the release of free ligands and to the formation of a tetracoordinate nickel(O) complex which is in turn of fairly low stability. The kinetic constant of the chemical decay following the charge transfer step has been determined for all the complexes investigated by the cyclic voltammetric approach. The dependence of the obtained kinetic constant values on the nature of the ligands present in the coordination shell is discussed together with the effect of these ligands on peak potential values. Also the circumstance under which all the nickel(II) complexes investigated are not reduced in steps to nickel(O) but undergo a direct two-electron uptake is considered by taking into account their high- spin configuration. © 1991
Simple Relationship for Calculating Backward to Forward Peak-current Ratios in Cyclic Voltammetry
No full textCombined use of electroanalytical methods to derive calibration plots for species difficult to standardize.
No full textA simple method is described for the derivation of calibration graphs for electroactive active analytes which are difficult to standardize from a calibration for an easily standardized reference species dissolved in the same medium. The method is based on evaluation of the ratios between the current-signals recorded for the analyte and for the reference solution by rotating-disk-electrode voltammetry and by an electroanalytical technique based on stationary electrodes which provides purely diffusion-controlled responses (e.g., chronoamperometry or normal-pulse voltammetry). This approach can be applied to all electroactive species which undergo diffusion-controlled processes, regardless of the degree of reversibility involved. Reliability tests, done with electroactive organic species dissolved in dimethyl sulphoxide, show that both accuracy and precision are within ±5%. The method is applied to the determination of hydrogen and oxygen solubilities in dimethyl sulphoxide and acetonitrile, respectively, as an example of quantitative evaluations of species which are difficult to standardize. © 1986
Determination of residual aromatic amine hydrochlorides in process samples of di-isocyanate used in the manufacture of polyurethane. A comparison of electroanalytical methods
No full textAromatic diamine hydrochlorides have been determined in the presence of different amounts of hydrochloric acid by acid-base titration followed potentiometrically, by linear sweep voltammetry, by differential pulse voltammetry and also by direct DPV measurement. Tests on simulated and production samples have shown that the best results are obtained by using DPV at a mercury electrode, because of its good resolution, which makes it possible to achieve good accuracy (error < - 1 %) and good precision (rsd 1.5%) at 0.1M levels. Moreover, it has the advantage that neither preliminary treatment of the sample nor a trial titration is required. © 1988
An Electroanalytical Investigation on the Nickel-Triphenylphosphine in the Presence of Acrylonitrile.
No full textCyclic voltammetry, potential-dependent chronoamperometry and controlled potential electrolysis have been used to investigate the redox reactions which the nickel-triphenylphosphine system undergoes in acetonitrile solution in the presence of the activated olefin acrylonitrile. For the reduction of Ni(II) electrochemically generated in this medium, a mechanism is proposed which is consistent with the data. This species undergoes an irreversible two-electron reduction giving the corresponding Ni(0) complex which reacts quickly with the olefin. In this last homogeneous redox reaction an unusual and not previously reported olefin-Ni(I) derivative is obtained. The geometric configuration of such an organometallic compound has been then inferred on the basis of near-infrared and ESR spectra. © 1983 Elsevier Sequoia S.A
- …
