A mechanism for the addition of ethylene to nickel bis‐dithiolene

Density functional theory calculations predict a new lower energy route for the formation of the desired interligand addition product from the reaction between ethylene and nickel bis(dithiolene). The new route involves the initial binding of ethylene along the nickel–sulfur bond. The barrier heights for adding ethylene along this bond for the neutral and anionic nickel complexes are compared to each other as well as to a previously published previous mechanism. Selected structural parameters of the studied species have been analyzed to highlight the structural change on specific reactions. It was found that the ethylene/nickel bis‐dithiolene reaction occurs preferably via the nickel–sulfur bond of the neutral species, forming a complex which then rearranges to a desired interligand adduct via a low barrier. © 2012 Wiley Periodicals, Inc.     

Thermal studies on addition compounds of bis(ethylxathato)nickel(II)

Ni(xanthate)₂, a diamagnetic square planar complex forms 1:1 six-coordinated high-spin paramagnetic adducts with dinitrogen donors in different organic solvents. The thermal studies of these compounds show the loss of trapped solvent(ether) followed by the loss of the addendum leaving behind the parent xanthate complex. In the compounds with 1:3 ratio of Ni(xanthate): dinitrogen donors, the xan^? acts as an anion. The different steps of thermal decomposition in the compounds, Ni(phen)₃xan₂ and Ni(bipy)₃xan₂, can be explained on the basis of the conformational rigidity of the ligands. For the parent compound Ni(xan)₂, its 1:1 and 1:3 adducts as well as the thermal decomposition products (residues) have been analysed by chemical and physical methods. New intermediate complexes with the composition, Ni(phen)₂xan₂, Ni(bipy)S₂ and Ni(bipy)S have been obtained from the decomposition process, leading finally to NiO. The kinetic parameters were calculated using five different methods to check the applicability of these standard methods towards the elucidation of the decomposition mechanism.     

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.     

Computational study of iron bis(dithiolene) complexes: redox non-innocent ligands and antiferromagnetic coupling

The molecular and electronic structure of monomeric ([Fe(S2C2H2)2](z), [Fe(S2C2(C6H4-p-OCH3)2)2](z)) and dimeric ([{Fe(S2C2H2)2}2](z)) iron bis(dithiolene) complexes, and of their phosphine adducts ([(PH3)Fe(S2C2H2)2](z), [(P(C6H5)3)Fe(S2C2H2)2](z), [(PH3)Fe(S2C2(C6H4-p-OCH3)2)2](z)), carrying various charges (z = 0, 1-, 2-), have been investigated by density functional theory (DFT). Net total spin polarization values S of zero, two, and four have been considered for all neutral model compounds and their dianions, whereas all monoanions have been examined with net total spin polarization values S of one, three, and five. The DFT calculations utilized the pure functional BP86, as well as the hybrid functionals B3LYP and B3LYP*. For the monomers, the calculations reveal the presence of redox non-innocent dithiolene ligands and antiferromagnetic coupling between the ligands and the metal center. For the dimers, complexes with antiferromagnetically coupled iron centers have been found to represent structures of low energy, if not lowest energy structures. The spin-coupling constant of [{Fe(S2C2H2)2}2](2-) is calculated as J = -230 cm(-1). On the basis of the computational results, a model for reversible, electrochemically controlled binding and release of phosphine ligands to iron bis(dithiolene) complexes is proposed. Only BP86 and B3LYP* results, but not those of B3LYP calculations, are in qualitative agreement with experimental findings. BP86 calculations provide the best quantitative match in comparison with the experiment.     

Synthesis,structure and physical properties of nickel bis(dithiolene) complexes with different cations

A series of new complexes of multi-sulfur 1,2-dithiolene ligands, [Ru(bipy)₃][Ni(L)₂]₂ (bipy?=?2,2′-bipyridine; L?=?pddt (6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate), dddt (5,6-dihydro-1,4-dithiin-2,3-dithiolate)), have been synthesized and characterized. One typical complex, [Ru(bipy)₃][Ni(pddt)₂]₂·2H₂O (1), crystallized in an acentric space group of P2₁2₁2₁, with the cell dimensions of a?=?8.634(1), b?=?14.560(1), c?=?49.889(5)?Å, α?=?β?=?γ?=?90°, and Z?=?4. It consists of alternating columns of cations and anions along the a direction. The structure was refined by full matrix least squares methods to R ₁?=?0.0340, wR ₂?=?0.0670. Magnetic studies on [Ph₂Cr][Ni(dddt)₂] are also reported.     

A simple nickel bis(dithiolene) complex as an excellent n-type molecular semiconductor for field-effect transistors

A simple nickel bis(dithiolene) complex has been developed as an excellent n-type molecular semiconductor for FETs, with an electron mobility of 0.11 cm(2) V(-1) s(-1) and an on/off ratio of 2 × 10(6) despite its small π-conjugated system. Good FET stability in ambient conditions has also been observed.     

Syntheses, structures, and physical properties of nickel bis(dithiolene) complexes containing tetrathiafulvalene (TTF) units

To contribute to the development of single-component molecular metals, several nickel complexes with cyclohexeno-condensed or ethylenedioxy-substituted TTF (tetrathiafulvalene) dithiolate ligands, (R(4)N)(n)[Ni(chdt)(2)] [R = Me, n = 2 (1); R = (n)Bu, n = 1 (2); n = 0 (3)] and (R(4)N)(n)[Ni(eodt)(2)] [R = Me, n = 2 (4); R = (n)Bu, n = 1 (5); n = 0 (6)], were prepared. X-ray structures were determined on the monoanionic species 2 and 5. The tetra-n-butylammonium complex of the monoanionic [Ni(chdt)(2)] (2) with a 1:1 composition revealed that its magnetic susceptibility gave a good agreement with the Bonner-Fisher model (J/k(B) = -28 K), which was derived from the one-dimensional chains of anions with a regular interval. On the other hand, the magnetic susceptibility of the tetra-n-butylammonium complex of the monoanionic [Ni(eodt)(2)] (5) showed the Curie-Weiss behavior (C = 0.376 K.emu.mol(-1) and Theta = -4.6 K). Both of the monoanionic species 2 and 5 indicate that they belong to the S = 1/2 magnetic system and have relatively large and anisotropic g-values, suggesting the contribution of the nickel 3d orbital. Electrical resistivity measurements were performed on the compressed pellets of the neutral species 3 and 6. Fairly large conductivities were obtained (sigma(rt) = 1-10 S.cm(-1)). In addition, despite the measurements on the compressed pellets of powder samples, the neutral species 6 showed metallic behavior down to ca. 120 K and retained high conductivity even at 0.6 K [sigma(0.6 K)/sigma(rt) approximately 1/30], suggesting the crystal to be essentially metallic down to very low temperature. The electrical behavior and Pauli paramagnetism of 6 indicate the system to be a new single-component metal.     

Generation of bis(dithiolene)dioxomolybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media

Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum(iv) (Mo(IV)OL(x)) complexes is studied as a model of oxidative-half reaction of arsenite oxidase molybdenum enzymes. The reactions are revealed to involve proton-coupled electron transfer. Electrochemical oxidation of Mo(IV)OL(x) yields the corresponding bis(dithiolene)dioxomolybdenum(vi) complexes in basic solution, where the conversion of Mo(IV)OL(dmed) supported by a smaller electron donating dithiolene ligand (1,2-dicarbomethoxyethylene-1,2-dithiolate, L(dmed)) to Mo(VI)O(2)L(dmed) is faster than that of Mo(IV)OL(bdt) with a larger electron donating dithiolene ligand (1,2-benzenedithiolate, L(bdt)) under the same conditions. Titration experiments for the electrochemical oxidation reveal that the reaction involves two-electron oxidation and two equivalents of OH(-) consumption per Mo(IV)OL(x). In the conversion process of Mo(IV)OL(x) to Mo(VI)O(2)L(x), the five-coordinate bis(dithiolene)monooxomolybdenum(v) complex (Mo(V)OL(x)) being a one-electron oxidized species of Mo(IV)OL(x) is suggested to react with OH(-). Mo(V)OL(x) reacts with OH(-) in CH(3)CN or C(2)H(5)CN in a 2?:?2 ratio to give one equivalent Mo(IV)OL(x) and one equivalent Mo(VI)O(2)L(x), which is confirmed by the UV-vis and IR spectroscopies. The low temperature stopped-flow analysis allows investigations of the mechanism for the reaction of Mo(V)OL(x) with OH(-). The kinetic study for the reaction of Mo(V)OL(dmed) with OH(-) suggests that Mo(V)OL(dmed) reacts with OH(-) to give a six-coordinate oxo-hydroxo-molybdenum(v) species, Mo(V)O(OH), and, then, the resulting species undergoes successive deprotonation by another OH(-) and oxidation by a remaining Mo(V)OL(dmed) to yield the final products Mo(IV)OL(dmed) and Mo(VI)O(2)L(dmed) complexes in a 1?:?1 ratio. In this case, the Mo(V)O(2) species are involved as an intermediate in the reaction. On the other hand, in the reaction of Mo(V)OL(bdt) with OH(-), coordination of OH(-) to the Mo(V) centre to give a six-coordinate Mo(V)O(OH)L(bdt) species becomes the rate limiting step and other intermediates are not suggested. On the basis of these results, the ligand effects of the dithiolene ligands on the reactivity of the bis(dithiolene)molybdenum complexes are discussed.     

Synthesis,structures and magnetic properties of nickel bis (dithiolene) complexes with [Fe(qsal)2]+

Two new compounds containing the possible Fe(III) spin-crossover cation, [Fe(qsal)₂]⁺ (qsalH = N-(8-quinolyl)salicylaldimine), and nickel bis(dithiolene) anions have been synthesized. Both are 1 : 1 salts [Fe(qsal)₂][Ni(dddt)₂] · CH₃CN · CH₃OH (1) and [Fe(qsal)₂][Ni(pddt)₂] (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate; pddt = 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate). They have been characterized by X-ray crystal structure determination, elemental analysis, UV-Vis spectra and magnetic susceptibility measurements. The UV–Vis spectra are dominated by [Ni(L)₂]^? (1, L = dddt; 2, L = pddt). Magnetic studies show antiferromagnetic interaction in 1 from intermolecular S···S contacts and π–π stacking interactions, while the antiferromagnetic interaction in 2 is very weak.     

Thermal decompostion studies on nickel(II) bis(oxalato)nickelate(II) pentahydrate

The paper describes the synthesis and thermal decomposition of nickel(II)bis(oxalato)nickelate(II)pentahydrate, Ni[Ni(C₂O₄)2].5H₂O. The complex was characterized by elemental analysis, infrared, electronic, e.s.r., magnetic moment measurement and X-ray powder diffraction studies. The thermal decompostion of the complex led to NiO in air at about 338° and in nitrogen at about 720°. The activation energies (E ^*) for the dehydration and decompostion reactions in air and nitrogen were evaluated. Tentative reaction mechanisms have been suggested for the termal decompostion of the complex in air and nitrogen.

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Zusammenfassung Es wird die Synthese und thermische Zersetzung von Nickel(II) -bis(oxalato)- nickelat(II) - pentahydrat beschrieben: Ni[Ni(C₂O₄)2].5H₂O. Dieser Komplex wurde mittels Elementaranalyse, IR-Spektroskopie, ESR-Spektroskopie, der Messung des magnetischen Momentes sowie mittels Pulverdiffraktionsuntersuchungen charakterisiert. Im Ergebnis der thermischen Zersetzung entsteht NiO, in Luft bei etwa 338°, in Stickstoffatmosphäre bei ca. 720°. Die Aktivierungsenergien (E^*) der Dehydratations- und Zersetzungsreaktionen in Luft und in Stickstoff wurden ermittelt. Für die thermische Zersetzung des Komplexes in Luft bzw. in Stickstoff wurde ein Reaktionsmechanismus entwickelt.

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The authors thank the RSIC, CDRI, Lucknow for microanalysis, RSIC, NEHU, Shillong for i.r. spectra, RSIC, IIT, Madras for far i.r. spectra, RSIC, Nagpur University for thermal analysis, Dr. S. K. Datta for Forensic Science Laboratory, Guwahati, Assam for DSC and Dr. K. L. Deori of Dibrugarh University for X-ray powder diffraction photographs.     

Effects of nano nickel powders addition on flash pyrolysis of poly(ethylene glycol)

Pure PEG and the mixture of PEG and nano nickel powders (PEG/n-Ni) were pyrolyzed at 500 °C for 5 min in N₂ atmosphere. GC/MS and FTIR were employed to detect the volatile products. Some important regularity in the mass spectra of the PEG pyrolysis products was discovered, and 11 series of PEG pyrolysis products were identified. The experimental results show that the nano Ni powders evidently change the relative contents of each products series. The statistical results of the ratio of C-O cleavage to C-C cleavage, as well as the ratio of hydrogenation to dehydrogenation, indicate that nano Ni powders have remarkable effects on the bonds cleavage and free radicals annihilation. The process of hydrogenolysis and hydrogenation were propounded to explain the effects of nano Ni addition on PEG flash pyrolysis.     

Phosphine-substituted dithiolene complexes as ligands: communication between ruthenium(II) centers through a dimolybdenum bis(dithiolene) core

The reaction of Mo2(SCH2CH2S)2Cp2 (1; Cp=eta-C5H5) with an excess of an alkyne in refluxing dichloromethane affords the bis(dithiolene) complexes Mo2(micro-SCR1=CR2S)2Cp2 (2a, R1=R2=CO2Me; 2b, R1=R2=Ph; 2c, R1=H, R2=CO2Me) whereas with 1 equiv of alkyne at room temperature the mixed dithiolene-dithiolate species Mo2(micro-SCR1=CR2S)(micro-SCH2CH2S)Cp2 (3a, R1=R2=CO2Me; 3b, R1=R2=Ph) are formed. The remaining dithiolate ligand in 3 can then be converted into a different dithiolene by reaction with a second alkyne. Applying this methodology, we have used bis(diphenylphosphino)acetylene to prepare the first examples of complexes containing phosphine-substituted dithiolene ligands: Mo2{micro-SC(CO2Me)=C(CO2Me)S}{micro-SC(PPh2)=C(PPh2)S}Cp2 (2g) and Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2 (2h). Tri- and tetrametallic complexes can then be assembled by coordination of these diphosphines to CpRuCl units by reaction with CpRu(PPh3)2Cl. Electrochemical studies of the Ru(II)/Ru(III) couple in Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2(RuClCp)2 (4b) reveals that the two separate ruthenium centers are oxidized electrochemically at different potentials, demonstrating communication between them through the dimolybdenum bis(dithiolene) core. Density functional theory calculations were carried out to explore the electronic structures of these species and to predict and assign their electronic spectra.     

Structural studies of bis(histidinato)nickel(II): Combined experimental and computational studies

A distorted octahedral nickel(II) complex, [Ni(2-amino-3-(1H-imidazol-4-yl)propanoic acid)₂] (1), has been synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction. Geometry optimization in the gas phase and pyridine together with Hirshfeld surface and reduced density gradient analyses reveal that this complex shows different distortions from octahedral in the gas, liquid, and solid phases. The reason seems to be because of the presence of two intramolecular NH⋯O weak interactions in the gas phase and two sets of rather strong intermolecular NH⋯O and CH⋯O interactions in the solid phase. Time-dependent density functional theory (TD-DFT) calculations suggest that these different distortions result in different electronic absorption spectra.     

Reversible, electrochemically controlled binding of phosphine to iron and cobalt bis(dithiolene) complexes

The homoleptic bis(dithiolene) complexes [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl) undergo two successive reductions to form anions that display [M(S(2)C(2)R(2))(2)](2)(2-) <--> 2[M(S(2)C(2)R(2))(2)](1-) solution equilibria. The neutral dimers react with Ph3P to form square pyramidal [M(Ph(3)P)(S(2)C(2)R(2))(2)](0). Voltammetric measurements upon [M(Ph(3)P)(S(2)C(2)R(2))(2)](0) in CH(2)Cl(2) reveal only irreversible features at negative potentials, consistent with Ph(3)P dissociation upon reduction. Dissociation and reassociation of Ph(3)P from and to [Fe(Ph(3)P)(S(2)C(2)R(2))(2)](0) is demonstrated by spectroelectrochemical measurements. These collective observations form the basis for a cycle of reversible, electrochemically controlled binding of Ph(3)P to [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl). All members of the cycle ([M(S(2)C(2)R(2))(2)](2)(0), [M(S(2)C(2)R(2))(2)](2)(1-), [MM(S(2)C(2)R(2))(2)](2)(2-), [M(S(2)C(2)R(2))(2)](1-), [M(Ph(3)P)(S(2)C(2)R(2))(2)]) for M = Fe, Co have been characterized by crystallography. Square planar [Fe(S(2)C(2)R(2))(2)](1-) is the first such iron dithiolene species to be structurally identified and reveals Fe-S bond distances of 2.172(1) and 2.179(1) Angstrom, which are appreciably shorter than those in corresponding square planar dianions.