Well-defined Nickel Research Articles

Facile synthesis of nickel nanowires with controllable morphology

Nickel nanowires of controllable morphology were synthesized by a facile wet chemical reduction method using hydrazine hydrate as the reducing agent. Synthesis parameters such as reaction temperature, concentration of nickel ions, and pH of reaction medium were observed to have significant effects on the morphology of nickel nanowires formed. Only randomly aggregated nanoparticles were obtained at the reaction temperature of 30°C. However, visibly defined nickel nanowires of longitudinally aligned nanoparticles, and fully transformed, well-defined long and slender nanowires were obtained at reaction temperatures of 60°C and 120°C, respectively. Higher reaction temperature led to the formation of nickel nanowires of decreasing mean diameters, whereas increasing initial concentration of nickel ions resulted in the formation of nickel nanowires of larger mean diameters. Besides, well-defined nickel nanowires were formed at the reaction medium pH of 4–5. Henceforth, the morphology of nickel nanowires could be modulated readily via precise control of the synthesis parameters such as reaction temperature and initial concentration of nickel ions. Nickel nanowires of tailored morphology could potentially be useful for the fabrication of nanowire-based electronic or electrochemical devices.

Exploring the Reactivity of Nickel Pincer Complexes in the Decomposition of Formic Acid to CO2/H2 and the Hydrogenation of NaHCO3 to HCOONa

AbstractThe nickel‐catalyzed decomposition of formic acid to yield molecular hydrogen and the nickel‐catalyzed hydrogenation of bicarbonate as a carbon dioxide mimic have been examined. Well‐defined nickel complexes modified by a PCP‐pincer ligand, especially nickel hydride and nickel formate complexes, revealed catalytic activity with turnover numbers of up to 626 (decomposition) and 3000 (hydrogenation). Thus, a formal hydrogen storage and release cycle performed by a well‐defined nickel catalyst was accomplished.

ChemInform Abstract: Controlling First‐Row Catalysts: Amination of Aryl and Heteroaryl Chlorides and Bromides with Primary Aliphatic Amines Catalyzed by a BINAP‐Ligated Single‐Component Ni(0) Complex.

First-row metal complexes often undergo undesirable one-electron redox processes during two-electron steps of catalytic cycles. We report the amination of aryl chlorides and bromides with primary aliphatic amines catalyzed by a well-defined, single-component nickel precursor (BINAP)Ni(η(2)-NC-Ph) (BINAP = 2,2'-bis(biphenylphosphino)-1,1'-binaphthalene) that minimizes the formation of Ni(I) species and (BINAP)2Ni. The scope of the reaction encompasses electronically varied aryl chlorides and nitrogen-containing heteroaryl chlorides, including pyridine, quinoline, and isoquinoline derivatives. Mechanistic studies support the catalytic cycle involving a Ni(0)/Ni(II) couple for this nickel-catalyzed amination and are inconsistent with a Ni(I) halide intermediate. Monitoring the reaction mixture by (31)P NMR spectroscopy identified (BINAP)Ni(η(2)-NC-Ph) as the resting state of the catalyst in the amination of both aryl chlorides and bromides. Kinetic studies showed that the amination of aryl chlorides and bromides is first order in both catalyst and aryl halide and zero order in base and amine. The reaction of a representative aryl chloride is inverse first order in PhCN, but the reaction of a representative aryl bromide is zero order in PhCN. This difference in the order of the reaction in PhCN indicates that the aryl chloride reacts with (BINAP)Ni(0), formed by dissociation PhCN from (BINAP)Ni(η(2)-NC-Ph), but the aryl bromide directly reacts with (BINAP)Ni(η(2)-NC-Ph). The overall kinetic behavior is consistent with turnover-limiting oxidative addition of the aryl halide to Ni(0). Several pathways for catalyst decomposition were identified, such as the formation of the catalytically inactive bis(amine)-ligated arylnickel(II) chloride, (BINAP)2Ni(0), and the Ni(I) species [(BINAP)Ni(μ-Cl)]2. By using a well-defined nickel complex as catalyst, the formation of (BINAP)2Ni(0) is avoided and the formation of the Ni(I) species [(BINAP)Ni(μ-Cl)]2 is minimized.

Controlling first-row catalysts: amination of aryl and heteroaryl chlorides and bromides with primary aliphatic amines catalyzed by a BINAP-ligated single-component Ni(0) complex.

First-row metal complexes often undergo undesirable one-electron redox processes during two-electron steps of catalytic cycles. We report the amination of aryl chlorides and bromides with primary aliphatic amines catalyzed by a well-defined, single-component nickel precursor (BINAP)Ni(η2-NC-Ph) (BINAP = 2,2′-bis(biphenylphosphino)-1,1′-binaphthalene) that minimizes the formation of Ni(I) species and (BINAP)2Ni. The scope of the reaction encompasses electronically varied aryl chlorides and nitrogen-containing heteroaryl chlorides, including pyridine, quinoline, and isoquinoline derivatives. Mechanistic studies support the catalytic cycle involving a Ni(0)/Ni(II) couple for this nickel-catalyzed amination and are inconsistent with a Ni(I) halide intermediate. Monitoring the reaction mixture by 31P NMR spectroscopy identified (BINAP)Ni(η2-NC-Ph) as the resting state of the catalyst in the amination of both aryl chlorides and bromides. Kinetic studies showed that the amination of aryl chlorides and bromides is first order in both catalyst and aryl halide and zero order in base and amine. The reaction of a representative aryl chloride is inverse first order in PhCN, but the reaction of a representative aryl bromide is zero order in PhCN. This difference in the order of the reaction in PhCN indicates that the aryl chloride reacts with (BINAP)Ni(0), formed by dissociation PhCN from (BINAP)Ni(η2-NC-Ph), but the aryl bromide directly reacts with (BINAP)Ni(η2-NC-Ph). The overall kinetic behavior is consistent with turnover-limiting oxidative addition of the aryl halide to Ni(0). Several pathways for catalyst decomposition were identified, such as the formation of the catalytically inactive bis(amine)-ligated arylnickel(II) chloride, (BINAP)2Ni(0), and the Ni(I) species [(BINAP)Ni(μ-Cl)]2. By using a well-defined nickel complex as catalyst, the formation of (BINAP)2Ni(0) is avoided and the formation of the Ni(I) species [(BINAP)Ni(μ-Cl)]2 is minimized.

Dehydrogenative coupling of aromatic thiols with Et3SiH catalysed by N-heterocyclic carbene nickel complexes

A series of new tetramethylcyclopentadienyl-functionalised N-heterocyclic carbene ligands with different wingtip substituents have been prepared and characterised. These ligands have been successfully coordinated to nickel affording complexes of the general type (Cp*-NHC(R))NiX (X = Cl, I). These well-defined nickel complexes selectively catalysed the coupling of aromatic thiols with Et3SiH to give the corresponding silylthioethers (RSSiEt3). The nickel complexes bearing ethyl, iso-butyl, and n-butyl wingtips displayed comparable catalytic efficiency, while the nickel complex bearing a methyl substituent on the wingtip was the worst performing catalyst.

ChemInform Abstract: Organometallic Aspects of Fluoroalkylation Reactions with Copper and Nickel

AbstractReview: 158 refs.

Organometallic Aspects of Fluoroalkylation Reactions with Copper and Nickel

The development of perfluoroalkylation methods has become increasingly important in synthetic chemistry. However, many of the metal-mediated transformations that occur readily with alkyl substrates can proceed slowly, with limited scope, or not proceed at all with fluoroalkyl derivatives. To develop more sophisticated transformations with fluoroalkyl groups using base metals, a better understanding of their fundamental fluoro-organometallic chemistry is needed. This account describes our recent investigations into the organometallic chemistry of well-defined nickel– and copper–fluoroalkyl complexes, as well as our efforts towards trifluoromethoxylations and trifluoromethylthiolations using those metals. Synthetic routes to the new complexes are discussed, as are their structural and electrochemical properties and chemical reactivities. 1 Introduction 2 Bottling a Copper(I)–Trifluoromethyl Source 3 The Redox Chemistry of Copper– and Nickel–Fluoroalkyl Complexes 4 Nickel- and Copper-Mediated Trifluoromethylthiolations 5 The Organometallic Chemistry of Nickel–Perfluoroalkyl Complexes 6 Outlook

ChemInform Abstract: Hydrosilylation of Aldehydes and Ketones Catalyzed by an N‐Heterocyclic Carbene‐Nickel Hydride Complex under Mild Conditions.

Half-sandwich N-heterocyclic carbene (NHC)-nickel complexes of the general formula [Ni(NHC)ClCp†] (Cp†=Cp, Cp*) efficiently catalyze the hydrosilylation of aldehydes and ketones at room temperature in the presence of a catalytic amount of sodium triethylborohydride and thus join the fairly exclusive club of well-defined nickel(II) catalyst precursors for the hydrosilylation of carbonyl functionalities. Of notable interest is the isolation of an intermediate nickel hydride complex that proved to be the real catalyst precursor.

Nickel-catalyzed C(sp2)–C(sp2) Cross Coupling Reactions of Sulfur-Functionalities and Grignard Reagents

In the present study, the nickel-catalyzed carbon carbon bond formation of a range of sulfur containing substrates with Grignard reagents via desulfurization has been explored. After investigation of different reaction parameters with a well-defined nickel complex an excellent and easy-accessible pre-catalyst was found. The obtained system was capable to convert a broad scope of substrates under mild reaction conditions.

Nickel-Mediated Oxidative Fluorination for PET with Aqueous [18F] Fluoride

A one-step oxidative fluorination for carbon-fluorine bond formation from well-defined nickel complexes with oxidant and aqueous fluoride is presented, which enables a straightforward and practical (18)F late-stage fluorination of complex small molecules with potential for PET imaging.

Magnetic recyclable Ag catalysts with a hierarchical nanostructure

This study reports the fabrication of a novel hierarchically structurednanocatalyst system possessing a well-defined nickel silicate (NS) protectedFe3O4 core and a layer of uniform Ag nanoparticles on the NS shell by using a multi-step approach.The multifunctional microparticles show high performance in the reduction of 4-nitrophenoland the rate of the catalytic reaction can be controlled by changing the concentration ofnanocatalysts. In particular, there was no visible decrease in the catalytic activity of thereused catalysts even after being recycled five times. Thus the hierarchically structuredFe3O4@NS particles are very suitable as a catalyst support for catalyst separation and redispersion.

A novel method to produce Pd nanoparticle ink for ink-jet printing technology

A novel method for the preparation of ink-jet printing ink with palladium (Pd) nanoparticles reduced by styrene (St) oligomers is presented in this study. The noble metal nanoparticles reduced and stabilized by styrene oligomer showed their well dispersion in the organic solvent without surfactant and reductant in the mixture. These Pd nanoparticles can be used as activator for electroless metal deposition. The deposition rate of St/Pd nanoparticles system was higher than that of conventional Sn/Pd colloids. It is an indication that the catalytic activity of St/Pd is better than Sn/Pd colloids. The ink based on St/Pd colloids was successfully ink-jet printed onto a flexible substrate. The formed metallic palladium patterns were subjected to electroless nickel plating, yielding well-defined nickel lines at low temperature. The properties of Pd nanoparticle ink and kinetics of electroless nickel deposition (EN) were characterized by transmission electron microscopy (TEM), quartz crystal microbalance (QCM), four-point probe, mixed potential theory (MPT) and scanning electron microscopy (SEM), respectively.

DFT Analysis of g and 13C Hyperfine Coupling Tensors for Model NiI(CO)nLm (n = 1−4, L = H2O, OH−) Complexes Epitomizing Surface Nickel(I) Carbonyls

Relativistic calculations within the spin-orbit mean-field (SOMF) approximation, the zero-order regular approximation (ZORA), and the scalar relativistic method based on the Pauli Hamiltonian were performed for the prediction and interpretation of the electronic g tensor and (13)C hyperfine tensor for a set of model polycarbonyl nickel(I) complexes with aqua or hydroxy coligands. They exhibit extensive similarities with heterogeneous [Ni(I)(CO)(n)]-surface complexes produced upon adsorption of carbon monoxide on Ni(I) ions grafted on silica or inside the zeolite channels. Benchmark calculations showing the influence of the exchange-correlation functional on the g tensor were carried out for well-defined nickel(I) complexes of known structure. On this basis, the SOMF-B3LYP scheme was chosen for calculations of the g tensor, and the obtained results were in satisfactory agreement with literature EPR data found for the [Ni(I)(CO)(n)]/SiO(2) system. The calculated g and A((13)C) tensors allowed polycarbonyl complexes of various stereochemistries to be distinguished. The nature of the Deltag(ii) shifts was assessed in terms of the molecular orbital contributions due to the magnetic-field-induced couplings and their structure sensitivity. The noncoincidence of g and (13)C hyperfine principal axes and their orientation with respect to the molecular framework was also examined. The ability of DFT calculations to follow consistently variations of the EPR parameters induced by stereochemical changes around the Ni(I) center provides an invaluable reference for the interpretation of experimental results.

Structural and magnetic properties of nano nickel–zinc ferrite synthesized by reverse micelle technique

Nanocrystalline nickel–zinc ferrites (Ni 0.58Zn 0.42Fe 2O 4) at different pH values (less than 9.6, 9.6, 10.96, and 11.40) for the alkali-precipitating reaction were synthesized by reverse micelle technique. X-ray diffraction reveals a well-defined nickel–zinc ferrite crystal phase at pH=9.6. Increase in pH value obstructs pure-phase formation and results in partial formation of α-Fe 2O 3. The magnetic behaviour of the samples was studied by superconducting quantum interference device. All the samples show superparamagnetic behaviour at room temperature (300 K) and negligible hysteresis at low temperature (5 K). The low value of saturation magnetization is explained on the basis of spin canting. The high-field irreversibility and shifting of the hysteresis loop detected in single-phase sample has been assigned to a spin-disordered phase, which has a spin-freezing temperature of approximately 42 K and other two samples have an antiferromagnetic phase (α-Fe 2O 3) coupled to the ferromagnetic phase.

Catalytic methane decomposition on nickel-based model anodes of SOFCs fabricated on various oxide ion conductors

The catalytic methane decomposition on well-defined nickel (Ni) based model anodes of SOFCs fabricated on various oxide ion conductors was investigated. Stripe-shaped Ni films deposited on substrates of various oxide ionic conductors as model anodes of SOFCs, and the substrates were annealed in slightly humidified methane of 1.2%H 2O–CH 4 at 1073 K. During annealing, carbon deposition did not clearly proceed on Ni films. When dry methane was supplied during the cooling process after annealing, catalytic methane decomposition was proceeded on Ni films. The morphology and the amount of carbon deposition on Ni films were different due to the substrate materials. The Ni film on the doped lanthanum gallate showed the lowest carbon deposition rate in comparison with the Ni films on the stabilized zirconias and the gadolia doped ceria.

Hydrogen-transfer reduction of carbonyl compounds catalysed by nickel nanoparticles

We report for the first time the hydrogen-transfer reduction of carbonyl compounds catalysed by well-defined nickel(0) nanoparticles. The nickel nanoparticles could be reutilised several times in a very simple reaction medium composed of the nickel nanoparticles, isopropanol and the substrate, without any added base.

Characterisation by test reactions of nickel-copper-molybdenum catalysts prepared by reduction of well-defined complex precursors

A series of well-defined nickel, copper and nickel-copper molybdenum complex compounds isomorphous of the ammonium triammine tetranickel pentamolybdate were prepared. The characterisation of the catalysts obtained by reduction in hydrogen of these precursors is difficult but the use of the chemisorptive decomposition of nitrous oxide together with the reactions of benzene hydrogenation and propanol decomposition make possible an estimation of the surface atomic copper-nickel ratio. Although the precursors are very homogeneous, an enrichment in copper of the surface metallic phase obtained after reduction is observed.

Quantitative aspects of nickel dermatitis. Sensitization and eliciting threshold concentrations

Nickel is the most common cause of contact allergy among females. A recent Danish population study found 11.1% of the females and 2.2% of the males nickel-sensitized. Primary nickel sensitization is caused by well-defined nickel exposures. Trace amounts of nickel present in the general environment don't induce nickel sensitization. Based on a wide range of studies, an arbitrary non-sensitizing nickel concentration of 0.5 μg/cm 2/week has been suggested for consumer items made of nickel alloys. Eliciting of nickel dermatitis is unlikely for concentrations <0.1-1 μg/cm 2 during occluded exposure and 15 μg/cm 2 when non-occluded. The effect of repeated exposures to normal skin is unexplored. Highly sensitized individuals might react to 0.5 ppm nickel (0.0075 μg/cm 2) when exposed on inflamed skin under occlusion. It is concluded that most cases of nickel allergy/nickel dermatitis are preventable without interfering with the quality of life or imposing economic costs to society.