Zerovalent Nickel Research Articles

Joshua S. Figueroa

Joshua S. Figueroa

Ni(0)-Catalyzed Dimerization of o-Keto Carboxylic Acid Pseudochlorides

A new protocol of the synthesis of 3,3′-diaryl-3,3′-diphthalides by dehalogenation of o-keto carboxylic acid pseudochlorides is implemented. The feature of the new protocol is that the reaction is carried out in the presence of a zero-valent nickel complex catalyst generated in situ by mixing zinc powder, nickel(II) chloride, triphenylphosphine, and 2,2′-bipyridine. Along with the target dimerization products of pseudochlorides, minor products were isolated, whose structure allowed to propose possible schemes of side reactions.

Carbon-Capped Zerovalent Nickel and Cobalt Nanoparticles as Multitask Hybrid Electrocatalysts

To attend to the worldwide need for clean energy technologies, multifunctional hybrid catalysts based on zerovalent metal nanoparticles protected by N-doped carbon matrices were developed. A cost-effective and scalable sol–gel process is used, in which metal ions coordinated to melamine-formaldehyde resins are the precursors. The carbon-capped zerovalent Ni/Co nanoparticles have metal content ranging from 43 to 63 wt % and N-doped carbon with the N/C ratio between 3% and 20%. It was found that the as-prepared or postmodified hybrid materials can catalyze the three most important electrochemical processes for hydrogen and fuel cell technology (oxygen evolution reaction, hydrogen evolution reaction, and oxygen reduction reaction; OER, HER, and ORR). For these three reactions, the carbon-capped zerovalent Ni/Co nanoparticles have comparable, or better, activity and stability in comparison to state-of-the-art noble metal catalysts as IrO2, Ir/C, Ru/C, and Pt/C. The most active catalysts presented η10 at 400 a...

CO2 hydrogenation to formate over nano-scale zero-valent nickel catalyst under atmospheric pressure

To reduce the energy consumption in the current CO2 hydrogenation with gaseous H2, a novel method of CO2 hydrogenation with potassium borohydride (KBH4) at moderate temperature and ambient pressure under the catalysis of nano-scale zero-valent nickel (nZVN) was developed. Under the optimal experimental conditions where the nZVN dosage was 0.2 g, KBH4 concentration was 0.28 mol·L−1, solution pH was 9.5, reaction temperature was 65 °C and residence time was 24 s, the average highest CO2 absorption efficiency of 45.88% with formate selectivity of 40.81% was achieved based on the ion chromatograph (IC) analyses of the reaction products. Especially, the physicochemical properties of the fresh and spent catalysts, such as morphological structure, physical structure properties, phase and crystallization and chemical compositions, were characterized systematically by using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS). In combination with the relevant references, the heterogenetic catalytic transfer hydrogenation reaction mechanism of CO2 with KBH4 over nZVN was proposed.

Zerovalent Nickel Compounds Supported by 1,2-Bis(diphenylphosphino)benzene: Synthesis, Structures, and Catalytic Properties.

Zerovalent nickel compounds which feature 1,2-bis(diphenylphosphino)benzene (dppbz) were obtained via the reactivity of dppbz towards Ni(PMe3)4, which affords sequentially (dppbz)Ni(PMe3)2 and Ni(dppbz)2. Furthermore, the carbonyl derivatives (dppbz)Ni(PMe3)(CO) and (dppbz)Ni(CO)2 may be obtained via the reaction of CO with (dppbz)Ni(PMe3)2. Other methods for the synthesis of these carbonyl compounds include (i) the formation of (dppbz)Ni(CO)2 by the reaction of Ni(PPh3)2(CO)2 with dppbz and (ii) the formation of (dppbz)Ni(PMe3)(CO) by the reaction of (dppbz)Ni(CO)2 with PMe3. Comparison of the ν(CO) IR spectroscopic data for (dppbz)Ni(CO)2 with other (diphosphine)Ni(CO)2 compounds provides a means to evaluate the electronic nature of dppbz. Specifically, comparison with (dppe)Ni(CO)2 indicates that the o-phenylene linker creates a slightly less electron donating ligand than does an ethylene linker. The steric impact of the dppbz ligand in relation to other diphosphine ligands has also been evaluated in terms of its buried volume (%Vbur) and steric maps. The nickel center of (dppbz)Ni(PMe3)2 may be protonated by formic acid at room temperature to afford [(dppbz)Ni(PMe3)2H]+, but at elevated temperatures, effects catalytic release of H2 from formic acid. Analogous studies with Ni(dppbz)2 and Ni(PMe3)4 indicate that the ability to protonate the nickel centers in these compounds increases in the sequence Ni(dppbz)2 < (dppbz)Ni(PMe3)2 < Ni(PMe3)4; correspondingly, the pKa values of the protonated derivatives increase in the sequence [Ni(dppbz)2H]+ < [(dppbz)Ni(PMe3)2H]+ < [Ni(PMe3)4H]+. (dppbz)Ni(PMe3)2 and Ni(PMe3)4 also serve as catalysts for the formation of alkoxysilanes by (i) hydrosilylation of PhCHO by PhSiH3 and Ph2SiH2 and (ii) dehydrocoupling of PhCH2OH with PhSiH3 and Ph2SiH2.

Influence of a diimine ligand and an activator on the processes taking place in Brookhart-type nickel catalytic systems

Brookhart-type catalytic systems based on zero-valent nickel complexes Ni(COD)2 and Ni(COD)L [where COD is cyclooctadiene and L is bis-2,6-diisopropylphenyl-diazabutadiene (DPP-DAB) or N,N′-bis-2,6- diisopropylphenyl-bis-iminoacenaphthene (DPP-BIAN)] activated with Lewis acids such as methylaluminoxane (MAO) and boron trifluoride etherate BF3·OEt2 were investigated via electron spin resonance (ESR) spectrometry, revealing that presence of diimine ligand results in Lewis acids, formally oxidating Ni(0) to Ni(I). An oxidation mechanism is proposed.

Electrooxidation of nickel-ammonia complexes and simultaneous electrodeposition recovery of nickel from practical nickel-electroplating rinse wastewater

In this experiment, a combined electrooxidation-electrodeposition (EO-ED) system using RuO2/Ti anode and stainless steel cathode was employed to treat nickel-ammonia complexes wastewater, which simultaneously achieved the decomplexation of nickel-ammonia complexes and recovery of nickel metal. Effects of current density, pH value and reaction temperature on electrochemical performance were analyzed. When the current density was 32mA/cm2, pH was 9.0 and the temperature was 60°C, the nickel recovery percentage was 99% and the ammonia removal efficiency was 70%. Combined with the SEM-EDX, XRD and XPS analysis for the cathode surface, it was confirmed that the generation of deposition on the cathode surface was zero-valent nickel. Firstly, Nickel-ammonia complexes were destroyed by electrooxidation process, generating Ni2+ ions and free NH3. Then, Ni2+ ions were reduced onto the cathode and free NH3 were further oxidized. Stability of the system for nickel-ammonia complexes treatment was examined by repeated experiments for fifteen successive cycles. The electrochemical system exhibited a satisfactory stability for nickel recovery and ammonia removal, achieving nickel recovery percentage of 85–95% and ammonia removal efficiency of 65–70%, respectively.

Termination reaction of living poly(3-hexylthiophene) using thiophene Grignard reagents: Substituent effect on the functionalization

Two 2-chloromagnesiothiophenes having the methoxy group at the 3- and 4-position were applied for the termination reaction of living poly(3-hexylthiophene) (P3HT). The number-averaged molecular weights of obtained P3HT approximately agreed with the theoretical value, and the high regioregularity of polymers were confirmed. The comparison of the 1H NMR spectra of P3HT with those of model compounds in addition to the analysis of the MALDI-TOF mass spectra suggested the incorporation of the methoxythiophene unit. The termination reaction using 2-chloromagnesio-3-methoxythiophene (GT1) and 2-chloromagnesio-4-methoxythiophene (GT2) resulted in P3HT with the non-uniform terminal structure and that having the terminating unit at both chain ends, respectively. These facts can be ascribed to the efficiency of the elementary process (transmetallation, reductive elimination, reverse chain walking, and oxidative addition) in the catalytic cycle. On the other hand, 2-chloromagnesio-3-oxazolylthiophene (GT3) exhibited the poor transmetallation activity due to the pronounced steric hindrance. It was found that the addition of LiCl for accelerating the transmetallation step and the coexistence of styrene for trapping the zero-valent nickel complex give P3HT bearing the oxazolylthiophene unit at the propagating end.

Ring-Walking of Zerovalent Nickel on Aryl Halides.

While ring-walking is a critical step in transition metal catalyzed cross-coupling reactions, the associated metastable intermediates are often difficult to isolate and characterize. In this work, theoretical structures and energetics for ring-walking and oxidative addition of zerovalent nickel with 1-bromo-2-methylbenzene, 2-bromopyridine, 2-bromo-3-methyl-thiophene, and 2-bromopyrrole were computed at the B3LYP-D3/TZ2P-LANL2TZ(f)-LANL08d level. The mechanisms vary qualitatively with substrate ring size and type-the catalyst weaves along the edges of the benzene and pyridine rings, cuts through the interior of the thiophene ring, and arcs along the bond opposite the nitrogen atom in the pyrrole ring. Analogous computations on the ring-walking and oxidative addition of zerovalent palladium with 1-bromo-2-methylbenzene reveal an energetic profile similar to that of Ni but with much weaker overall binding to the arene. In all cases, dispersion corrections are found to be very important for computing accurate metal-substrate binding energies.

Electrosynthesis of ammonia in hydrogen-producing sorption-active electrochemical matrix

A fundamentally new low-temperature method of synthesizing ammonia has been suggested, which is carried out directly in a hydrogen-producing matrix with a material made of cellulose fabric with porous layers of ethanol–cyclam PVC derivatives with activated carbon with aquacomplexes of sodium hydroxide grafted onto its fibers. Complexes of zero-valent nickel and iron within the cyclam structure are formed in the matrix. Hydrogen is formed on the cathode in the course of electrolysis of water from sodium hydroxide aqua complexes on particles of activated carbon as microelectrodes. Hydrogen forms bonds with complexes of zero-valent nickel. Nitrogen from adsorbed air is bound in complexes of zero-valent iron and interacts with active atomic hydrogen. Water is transported to carbon particles through the fabric onto which the layer is grafted. The process is carried out at the room temperature. It has been found that the forming hydrogen is almost completely used. As opposed to the existing methods of synthesis of ammonia, the suggested process is carried out at room temperature and normal pressure.

Facile green deposition of nanostructured porous NiO thin film by spray coating

One-step green deposition of nanostructured porous nickel oxide thin film by spray coating is introduced. Low-temperature reduction of nickel ions by glucose followed by an oxidation step at 300°C produces a nanostructured porous thin film of nickel oxide. The results shows that glucose, as a green reducer, could reduce the nickel ions to crystalline nano zero-valent nickel (nZVNi) at 250°C and nanostructured nickel oxide (nNiO) at 300°C forming a nanostructured porous thin film. The porous structure is formed by partial burning the glucose byproducts just after reducing the nickel ions to nZVNi and NiO at deposition temperature of 300°C.

Nickel-catalyzed release of H2 from formic acid and a new method for the synthesis of zerovalent Ni(PMe3)4.

Ni(PMe3)4 serves as a catalyst for the release of H2 and CO2 from formic acid. The capacity of Ni(PMe3)4 to achieve this transformation is linked to the ability of the PMe3 ligand to induce decarboxylation, as illustrated by the observation that both Ni(py)4(O2CH)2 and Ni(O2CH)2·2H2O react with PMe3 to afford Ni(PMe3)4; the latter transformation also provides a convenient method for the synthesis of a zerovalent nickel compound.

Formation of a tetranickel octacarbonyl cluster from the CO2 reaction of a zero-valent nickel monocarbonyl species

The CO2 reaction of a nickel(0) complex involves multiple reaction pathways including tetranickel cluster formation via reductive disproportionation of CO2.

Tuning Nickel with Lewis Acidic Group 13 Metalloligands for Catalytic Olefin Hydrogenation.

A series of bimetallic complexes pairing zero-valent nickel with group 13 M(III) ions is reported. Stronger Ni→M(III) dative bonds that render Ni more electron-deficient are seen for larger ions (In > Ga > Al). The larger Ga and In ions stabilize rare, nonclassical Ni-H2 adducts that catalyze olefin hydrogenation. In contrast, neither the Ni-Al complex nor a single nickel center enables H2 binding or olefin hydrogenation. By comparison of the structures, redox properties, and catalytic activities of the Ni-M series, the electronic and steric effects of the supporting metal ion are elucidated.

Sonocatalytic degradation of phenol catalyzed by nano-sized zero valent Cu and Ni

In this study, a successful degradation of phenol was achieved using nanosized zero-valent copper (NZVC) or nanosized zero-valent nickel (NZVN) in combination with H2O2 and 20 kHz ultrasound irradiation. The effect of H2O2 concentration, initial pH, catalyst amount, and ultrasonic irradiation time on the degradation efficiency was investigated, and the reaction kinetics was discussed. The results showed that the degradation extent increases with increasing catalyst amount and irradiation time, but decreases with increasing initial pH value. These results also revealed that the degradation of phenol is intensified in the presence of NZVC or NZVN and H2O2, which can be attributed to the enhanced production of ⋅OH radicals in the system. Thus, an appropriate selection of operating conditions will lead to an economical and highly efficient technology with eventual large-scale commercial applications for the degradation of organic pollutants in aqueous effluents.

Nickel promoted functionalization of CO2 to anhydrides and ketoacids.

The reductive functionalization of carbon dioxide into high value organics was accomplished via the coupling with carbon monoxide and ethylene/propylene at a zerovalent nickel species bearing the 2-((di-t-butylphosphino)methyl)pyridine ligand (PN). An initial oxidative coupling between carbon dioxide, olefin, and (PN)Ni(1,5-cyclooctadiene) afforded five-membered nickelacycle lactone species, which were produced with regioselective 1,2-coupling in the case of propylene. The propylene derived nickelacycle lactone was isolated and characterized by X-ray diffraction. Addition of carbon monoxide, or a combination of carbon monoxide and diethyl zinc to the nickelacycle lactone complexes afforded cyclic anhydrides and 1,4-ketoacids, respectively, in moderate to high yields. The primary organometallic product of the transformation was zerovalent (PN)Ni(CO)2.

Preparation and chemical properties of π-conjugated poly(1,10-phenanthroline-3,8-diyl)s with crown ether subunits

π-Conjugated polymers consisting of 1,10-phenanthroline units and crown ether subunits (Poly-1, Poly-2, and Poly-3) were prepared by dehalogenation polycondensation of the corresponding dibromo monomers using a zero-valent nickel complex as a condensing agent. They were characterized by elemental analysis, 1H NMR and UV–Vis spectroscopies, and cyclic voltammetry (CV). They were partly soluble in CHCl3, and the number average molecular weight of the soluble part of Poly-2, which had 15-crown-5 subunits, was estimated to be 5300. The polymers exhibited UV–Vis peaks at approximately λmax=360nm, which was reasonable. Complexation with [Ru(bpy)2]2+ and alkaline metal ions made the polymer soluble in organic solvents. The complexation of [Ru(bpy)2]2+ to the 1,10-phenanthroline unit proceeded quantitatively, and the [Ru(bpy)2]2+ complexes exhibited CV curves characteristic of [Ru(N-N)3]2+ complexes.

In situ synthesis of scorpion-like complexes isolated from the system containing zerovalent nickel

Two novel complexes [NiL1 (NCS)2CH3CN] (1), [NiL1(NCS)2DMF] (2) (L1-N,N-bis(1-(3,5-dimethylpyrazolylmethyl)amine)) have been isolated in one pot synthesis from the system containing zerovalent nickel powder, 1-hydroxymethyl-3,5-dimethylpyrazole (L), MoO3, and NH4SCN. Ligand L1, a product of condensation of L, was formed in situ during redox processes. The created nickel ion coordinates through nitrogen atoms belonging to one tridentate (L1), two isothiocyanate NCS− and a respective solvent: acetonitrile or dimethylformamide forming NiN5N′ (1) and NiN5O (2) chromophores of pseudooctahedral geometry. Both complexes were characterized by X-ray diffraction, IR, UV–Vis spectra and thermal investigations. The structures of (1) and (2) were confirmed by spectroscopic methods, thermal analysis and DFT studies. The effect of coordinated solvent molecule was manifested through subtle changes of structural, spectroscopic and thermal data.

Preparation of new polysulfones with –O–(CH2)3–SO3H side chains

New polymer electrolytes consisting of diphenyl sulfone units with –O–(CH2)3SO3M (M=H or Na) side chains have been prepared. Dehalogenative polycondensation using a zero-valent nickel complex, [Ni(0)Lm], gave a homopolymer, Polymer-1(Na), from Cl–Ph(R)–SO2–Ph(R)–Cl (monomer-1; Ph(R)=1,3-phenylene unit having the –O–(CH2)3SO3Na side group at the 4-position). Protonolysis of Polymer-1(Na) gave Polymer-1(H) with a weight average molecular weight of 25,000. Polymer-2(H) was synthesized by Suzuki-Miyaura cross coupling of Br–Ph(R)–SO2–Ph(R)–Br (monomer-2) and C6H4(B(OH)2)2-p using [Pd(PPh3)4] and ensuing protonolysis. Crosslinking of Polymer-2(H) with 1,4-benzenedimethanol gave a water-protected film. The cross-linked film of Polymer-2(H) showed proton conductivity of 0.26Scm−1 at 80°C and 90% humidity.

Preparation and Chemical Properties of π-Conjugated Polymers Containing Indigo Unit in the Main Chain.

π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of N-hexyl-6,6′-dibromoindigo with a zerovalent nickel complex gave a homopolymer, P(HexI), in 77% yield. Copolymer of N-hexyl-indigo and pyridine, P(HexI-Py), was also prepared in 50% yield. P(HexI) showed good solubility in organic solvents, whereas P(HexI-Py) was only soluble in acids such as HCOOH. The weight-average molecular weights (Mw) of P(HexI) and P(HexI-Py) were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6′-dibromoindigo with N-BOC (BOC = t-butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer, P(BOCI-Flu), as a deep red solid in 98% yield. P(BOCI-Flu) was soluble in N-methyl-2-pyrroridone and showed an Mw of 29,000 in GPC analysis. Treatment of P(BOCI-Flu) with CF3COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer, P(I-Flu), in a quantitative yield. Diffuse reflectance spectra of powdery P(BOCI-Flu) and P(I-Flu) showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit.