Cationic Nickel Research Articles

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin.

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP4+, where H2TMPyP4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP4+ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP4+-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex.

Nickel–PNN catalysed sustainable synthesis of polysubstituted quinolines under microwave irradiation

This manuscript describes the synthesis of triazolyl-pyridine-based pincer cationic and neutral nickel complexes and their application in microwave-assisted synthesis of quinolines.

Halogen-Dependent Diversity and Weak Interactions in the Heterometallic Ni/Cd Complex Solids: Structural and Theoretical Investigation.

Three novel heterometallic Ni/Cd coordination compounds [Ni(en)3][CdCl4]∙3dmso (1), [Ni(en)2(dmf)2][CdBr4] (2), and [Ni(en)3]2[CdI4](I)2 (3) have been synthesized through the self-assembly process in a one-pot reaction of cadmium oxide, nickel salt (or nickel powder), NH4X (X = Cl, Br, I), and ethylenediamine in non-aqueous solvents dmso (for 1) or dmf (for 2 and 3). Formation of the one- (1) or three-dimensional (2 and 3) hydrogen-bonded frameworks has been observed depending on the nature of the [CdX4]2- counter-anion, as well as on the nature of the solvent. The electronic structures of [Ni(en)3]2+ and [Ni(en)2(dmf)2]2+ cations were studied at the DFT and CASSCF levels, including the ab initio ligand field theory (AILFT) calculations. The non-covalent intermolecular contacts between the cationic nickel and anionic cadmium blocks in the solid state were investigated by the QTAIM analysis. The mechanism of ligand substitution at the nickel center in [Ni(en)2(dmf)2]2+ was theoretically investigated at the ωB97X-D4/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP level. The results demonstrate that thermodynamic factors are structure-determining ones due to low energy barriers of the rotation of dmf ligands in [Ni(en)2(dmf)2]2+ (below 3 kcal mol-1) and the reversible transformation of [Ni(en)2(dmf)2]2+ into [Ni(en)3]2+ (below 20 kcal mol-1).

Direct synthesis of polyethylene thermoplastic elastomers with high molecular weight and excellent elastic recovery via a hybrid steric bulky strategy

Recently, α-diimine nickel-catalyzed ethylene chain walking polymerization has enabled the direct preparation of polyethylene thermoplastic elastomers using ethylene as a single feedstock. In this study, a series of hybrid bulky butyl-based α-diimine nickel complexes constructed with o-aryl and -diarylmethyl anilines were synthesized and employed for the ethylene polymerization. All the nickel complexes showed high activities (level of 106 g mol-1h−1) and high molecular weight (Mn up to 1230.9 kg/mol) polyethylene with high branching density (82–118/1000C) were yielded in ethylene polymerization. The polyethylene obtained by Ni1-3 showed distinguished elastic properties (SR = 72–91 %) and the sample obtained by Ni1 at 50 °C exhibited optimal elastic recovery values (91 %), which is also the best reported so far in polyethylene elastomers. Compared to the corresponding nickel complexes with symmetrical ligand substituents, the complexes with unsymmetrical substituents (hybrid) in this study facilitate the synthesis of significantly higher branched polyethylene with much better elastic recovery. The hybrid cationic nickel catalysts are also capable of catalyzing the copolymerization of ethylene with methyl 10-undecenoate.

Neutral and cationic nickel(II) complexes with substituted salicylaldehydes: Characterization, antibacterial activity, and interaction with biomacromolecules

Four neutral and six cationic nickel(II) complexes of the substituted salicylaldehydes (X–diCl–saloH), namely 3,5–dichloro–salicylaldehyde (3,5–diCl–saloH) and 5–fluoro–salicylaldehyde (5–F–saloH), were synthesized in the absence or presence of the N,N′–donors 1,10–phenanthroline (phen), 2,9–dimethyl–1,10–phenanthroline (neoc), or 2,2′–bipyridylamine (bipyam) as co–ligands and were characterized by various techniques. The obtained complexes bear the general formulas [Ni(X–salo)2(H2O)2], [Ni(3,5–diCl–salo)2(neoc/phen)] and [Ni(X–salo)(N,N′–donor)2](PF6). The crystal structures of three complexes were determined by single–crystal X–ray crystallography revealing a bidentate coordination of the salicylaldehydes. The interaction of the compounds with calf–thymus DNA was studied by diverse techniques which revealed an intercalative interaction for the neutral complexes [Ni(X–salo)2(H2O)2] and [Ni(3,5–diCl–salo)2(neoc/phen)]and the co–existence of electrostatic interactions for the cationic complexes [Ni(X–salo)(N,N′–donor)2](PF6). The compounds bind tightly and reversibly to serum albumins. The antibacterial activity of the compounds was investigated against Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633, Escherichia coli NCTC 29,212 and Xanthomonas campestris ATCC 1395 and the complexes bearing neoc as co–ligand proved the most potent.

Design of bi-functional Ni-zeolites for ethylene oligomerization: Controlling Ni speciation and zeolite properties by one-pot and post-synthetic Ni incorporation

The design of diverse Ni-zeolites has been performed attempting to control different physico-chemical properties of the zeolite supports as well as the Ni speciation to study their influence on the industrially relevant ethylene oligomerization reaction. In this sense, Ni-containing medium-pore MFI and large-pore BEA zeolites have been synthesized with different particle sizes, Si/Al molar ratios and following different Ni-incorporation strategies (one-pot versus post-synthesis). Characterization techniques reveal the preferential presence of cationic Ni2+ and NiO nanoclusters inside the zeolitic pores when Ni has been incorporated by post-synthesis impregnation or one-pot approaches, respectively. The presence of Ni2+ species, rather than other factors, mainly governs olefin oligomerization under near-ambient pressures, guiding preferentially towards C4-C6 olefins as main products. Crystal size, acidity and/or Ni incorporation methodology, on the other hand, play key roles under high-pressure reaction conditions, resulting in the formation of heavier olefins, especially in zeolites containing less cationic nickel, larger proportion of NiO clusters and higher Brønsted acid site density.

Steric and electronic effects in cationic pyridine carboxamidate nickel mediated ethylene polymerization and copolymerization with methyl 10-undecenoate

Improvement of catalysts performance by structural modification is a well recognised and more reliable way in catalysis. Amide derived catalysts were already used in olefin polymerization but possessed many limitation regarding to their poor thermal stability and mostly generating low molecular weight oligomers. Steric and electronic factors have played a characteristic role to control the catalyst stability, activity, molecular weight and branch densities of the polymers. So in continuity of our interest to improve the performance of olefin polymerization catalysts, we contributed here by synthesized cationic nickel catalysts (Ni1–Ni3) by simple amidation of picolinoyl chloride with sterically bulky and electronically varied anilines. Effect of steric and electronic factors also has been explored. Compared with previously reported sterically open pyridine carboxamidate nickel catalysts, these bulky nickel catalysts have two orders of magnitude higher activity of up to 3.73× 106 g (mol Ni)−1 h−1 towards ethylene polymerization and thermal stability up to 80 °C, producing higher molecular weight semi-crystalline polyethylene with tunable branching densities (17–67 branches/1000C) and melting points (65–121 °C). Moreover, these cationic nickel catalysts also promote the copolymerization of ethylene and methyl 10-undecenoate (MU) to afford polar functionalized polyethylenes with maximum incorporation of MU up to 1.53 mol%.

NiII-Catalyzed Enantioselective Anti-Markovnikov Hydrophosphination of Unactivated Alkynes

A mechanism-inspired, reaction mode-controlled enantio- and regioselective anti-Markovnikov hydrophosphination of unactivated alkynes was accomplished by NiII catalysis. Alkenyl phosphine products could be obtained with high regio- and enantioselectivity and easily derivatized to structurally diverse chiral phosphine compounds. Mechanistic studies on both Ni0-catalyzed Markovnikov addition and NiII-catalyzed anti-Markovnikov addition have been carried out by combining experimental and computational methods. In the Ni0 system, an allyl nickel complex was obtained as the catalyst resting state whose structure was unambiguously determined by single-crystal XRD analysis. A sequential hydrometallation, ligand exchange, and reductive elimination mechanism was elucidated corroboratively by DFT calculations. In the NiII system, the cationic secondary phosphine nickel complex serves as the active catalyst. A migratory insertion and protonation sequence was operative to accomplish anti-Markovnikov hydrophosphination.

Electronic Effect on Phenoxide Migration at a Nickel(II) Center Supported by a Tridentate Bis(phosphinophenyl)phosphido Ligand.

A phosphide nickel(II) phenoxide pincer complex (2) reacts with CO(g) to give a pseudo-tetrahedral nickel(0) monocarbonyl complex (3) possessing a phosphinite moiety. This metal-ligand cooperative (MLC) transformation occurs with a (PPP)Ni scaffold (PPP- = P[2-PiPr2-C6H4]2-), which can accommodate both square planar and tetrahedral geometries. The 2-electron reduction of a nickel(II) species induced by CO coordination involves group transfer to generate a P-O bond. For better mechanistic understanding, a series of nickel(II) phenolate complexes (2a-2e, XC6H4O- (X = OMe, Me, H, and CF3) and pentafluorophenolate) were prepared. Kinetic experimental data reveal that a phenolate species with an electron-withdrawing group reacts faster than those with electron-donating groups. The reaction kinetic experiments were conducted in pseudo-first order conditions at room temperature monitored by UV-vis spectroscopy. A pentafluorophenolate nickel(II) complex (2e) reveals instantaneous reactions even at -40 °C to give a nickel(0) monocarbonyl species (3e) and the reverse reaction is also possible. According to kinetic experiments, the rate determining step (RDS) would be the formation of a 5-coordinate intermediate 4 with a negative entropy value (ΔS‡ < 0), and a positive ρ value based on the Hammett plot indicates that the electron-deficient phenolate leads to a faster CO association. Furthermore, scramble experiments suggest that phenolate de-coordinates from the intermediate 4, which gives a (PPP)Ni-CO species 6. The cationic nickel monocarbonyl intermediate can possess a P--Ni(II), P•-Ni(I), or even a P+-Ni(0) character. Such an inner-sphere electron transfer is suggested when a π-acidic ligand such as CO coordinates to a metal ion. Another possible reaction is homolysis of a Ni-O bond to give P--Ni(I) or P•-Ni(0), when a phenoxyl radical is liberated. Considering the P-O bond formation, closed-shell nucleophilic and open-shell radical pathways are suggested. A phenolate pathway reveals a lower energy state for 2e relative to other complexes (2c and 2d), while its radical pathway undergoes via a higher energy state. Therefore, the formation of a P-O bond may occur with the binding of a closed-shell phenolate to the electron-deficient P center.

Synthesis of lightly branched ultrahigh-molecular-weight polyethylene using cationic benzocyclohexyl nickel catalysts

The ultra-fast chain propagation rate in this contribution can simultaneously promote an increase in molecular weight and a decrease in branching density to achieve lightly branched UHMWPEs (Mn up to 1846 kg mol−1).

Ethylene homo and copolymerization by phosphorus‐benzoquinone based homogeneous and heterogeneous nickel catalysts

AbstractThe low cost and high abundancy of nickel makes it highly attractive for both industrial and academic researchers in the field of polyolefin. However, the development of high performance nickel catalysts for ethylene homo and copolymerization is highly challenging. In this contribution, two novel cationic nickel catalysts with quinone backbone and sterically hindered aryl substituents on phosphine have been synthesized and supported on solid supports to prepare heterogeneous catalysts. The homogeneous catalysts showed high activity and high thermal stability in ethylene polymerization. After heterogenization of these catalysts, all the polymerization parameters (polymerization activity, thermal stability, and polymer molecular weight) were significantly improved. The heterogeneous catalyst can achieve activity of up to 3.26 × 106 g mol−1 h−1, along with polyethylene molecular weight of up to 81.8 × 104 g mol−1. More importantly, these homogeneous and heterogeneous catalysts can realize copolymerization of ethylene with a series of polar comonomers such as methyl 10‐undecenoate, 10‐undecenol, and 6‐chloro‐1‐hexene.

Improved hydrodeoxygenation of lignin-derived oxygenates and biomass pyrolysis oil into hydrocarbon fuels using titania-supported nickel phosphide catalysts

Biomass pyrolysis oil is a potentially essential renewable energy source that can serve as an alternative to petroleum-based fuels and chemicals. In this study, biomass pyrolysis oil was converted into petroleum-like deoxygenated hydrocarbons via catalytic hydrodeoxygenation using a titania-supported nickel phosphide catalyst. The phosphor precursor was added to several transition metals, including nickel, cobalt, copper, and iron, supported on titania. The formation of isolated nickel phosphide particles, which were active for complete hydrodeoxygenation, was confirmed by the characterization of prepared catalysts. As a model reactant of biomass pyrolysis oil, a mixture of alkyl-methoxyphenol compounds was hydrodeoxygenated to produce completely deoxygenated compounds, generating an 87% yield of cycloalkanes at 300 °C and 4 MPa H2 for a reaction time of 2 h. The hydrodeoxygenation of biomass pyrolysis oil also generated a 37.4% yield of hydrocarbon fuels. The high hydrodeoxygenation activity can be attributed to the synergy between the hydrogenating metals and the acid sites, which can be improved by electron transfer from a slightly cationic nickel to a slightly anionic phosphor. Furthermore, the addition of phosphor improved the formation of highly dispersed nickel particles, increasing the quantity of hydrogen-adsorbing surface metals. The observations in this study indicate that the efficient conversion of lignocellulose-derivatives into chemicals and fuels can be achieved using modified non-precious transition metal catalysts.

Nickel(i)-catalyzed (de)hydrogenative coupling of amines and alkyl heteroarenes with alcohols

A novel cationic nickel(i) complex exhibiting extremely high efficiency toward the (de)hydrogenative N-alkylation of amines and olefination of alkyl heteroarenes by alcohols is reported.

Structural and Electrochemical Studies of Cobalt(II) and Nickel(II) Coordination Polymers with 6-Oxonicotinate and 4,4′-Bipyridine

The 6-oxonicotinate (6-Onic) salts of a one-dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy), namely {[Co(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (1) and {[Ni(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,4′-bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {[M(4,4′-bpy)(H2O)4]2+}n (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N–H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R23(10) motif, the centrosymmetric tetrameric R24(8) and R24(12) motifs and the pentameric R45(12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II)).

Rationalizing Surface Electronic Configuration of Ni-Fe LDO by Introducing Cationic Nickel Vacancies as Highly Efficient Electrocatalysts for Lithium-Oxygen Batteries.

Cationic defect engineering is an effective strategy to optimize the electronic structure of active sites and boost the oxygen electrode reactions in lithium-oxygen batteries (LOBs). Herein, Ni-Fe layered double oxides enriched with cationic nickel vacancies (Ni-Fe LDO-VNi ) are first designed and studied as the electrocatalysts for LOBs. Based on the density functional theory calculation, the existence of nickel vacancy in Ni-Fe LDO-VNi significantly improves its intrinsic affinity toward intermediates, thereby fundamentally optimizing the formation and decomposition pathway of Li2 O2 . In addition, the number of eg electrons on each nickel site is 1.19 for Ni-Fe LDO-VNi , which is much closer to 1 than 1.49 for Ni-Fe LDO. The near-unity occupation of eg orbital enhances the covalency of transition metal-oxygen bonds and thus improves the electrocatalytic activity of Ni-Fe LDO-VNi toward oxygen electrode reactions. The experimental results show that the LOBs with Ni-Fe LDO-VNi electrode deliver low overpotentials of 0.11/0.29V during the oxygen reduction reaction/oxygen evolution reaction, respectively, large specific capacities of 13 933mA h g-1 and superior cycling stability of over 826 h. This study provides a novel approach to optimize the electrocatalytic activity of LDO through reasonable defect engineering.

Nonsymmetrical Benzene–Pyridine-Based Nickel Pincer Complexes Featuring Borohydride, Formate, Ethyl, and Nitrosyl Ligands

Nonsymmetrical nickel PCN pincer complexes [Ni(iPrPCNX)Cl] (X = NMe, CH2) are obtained by metalation of the benzene–pyridine-based pincer ligand iPrPCNX (X = NMe, CH2) with [Ni(dme)Cl2] (dme = 1,2-dimethoxyethane). These nickel species afforded the respective borohydride and ethyl complexes [Ni(iPrPCNX)L] (L = BH4, Et) upon treatment with NaBH4 and EtMgBr (or Et2Mg), respectively. Reacting [Ni(iPrPCNX)(κ2-BH4)] with CO2 gave the formate complexes [Ni(iPrPCNX)(OCHO)]. Treatment of [Ni(iPrPCNX)Cl] with the nitrosyl salt NOBF4 led to the formation of the unusual cationic square-pyramidal nickel nitrosyl pincer complexes [Ni(iPrPCNX)(NO)Cl]+ featuring a strongly bent NO ligand (∠Ni–N–O 128.5°). These systems can be described as {NiNO}10 according to the Enemark–Feltham convention. Despite of the bent nature of the NO ligand the νNO is observed at 1849 cm–1 which is more typical for a linear Ni–N–O arrangement. The structure of these complexes is rationalized by means of DFT calculations. The molecular structures of representative complexes are presented.

Oxidoborates Templated by Cationic Nickel(II) Complexes and Self-Assembled from B(OH)3

Several oxidoborates, self-assembled from B(OH)3 and templated by cationic Ni(II) coordination compounds, were synthesized by crystallization from aqueous solution. These include the ionic compounds trans-[Ni(NH3)4(H2O)2][B4O5(OH)4].H2O (1), s-[Ni(dien)2][B5O6(OH)4]2 (dien = N-(2-aminoethyl)-1,2-ethanediamine (2), trans-[Ni(dmen)2(H2O)2] [B5O6(OH)4]2.2H2O (dmen = N,N-dimethyl-1,2-diaminoethane) (3), [Ni(HEen)2][B5O6(OH)4]2 (HEen = N-(2-hydroxyethyl)-1,2-diaminoethane) (4), [Ni(AEN)][B5O6(OH)4].H2O (AEN = 1-(3-azapropyl) -2,4-dimethyl-1,5,8-triazaocta-2,4-dienato(1-)) (5), trans-[Ni(dach)2(H2O)2][Ni(dach)2] [B7O9(OH)5]2.4H2O (dach = 1,2-diaminocyclohexane) (6), and the neutral species trans-[Ni(en)(H2O)2{B6O7(OH)6}].H2O (7) (en = 1,2-diaminoethane), and [Ni(dmen)(H2O){B6O7(OH)6}].5H2O (8). Compounds 1–8 were characterized by single-crystal XRD studies and by IR spectroscopy and 2, 4–7 were also characterized by thermal (TGA/DSC) methods and powder XDR studies. The solid-state structures of all compounds show extensive stabilizing H-bond interactions, important for their formation, and also display a range of gross structural features: 1 has an insular tetraborate(2-) anion, 2–5 have insular pentaborate(1-) anions, 6 has an insular heptaborate(2-) anion (‘O+’ isomer), whilst 7 and 8 have hexaborate(2-) anions directly coordinated to their Ni(II) centers, as bidentate or tridentate ligands, respectively. The Ni(II) centers are either octahedral (1–4, 7, 8) or square-planar (5), and compound 6 has both octahedral and square-planar metal geometries present within the structure as a double salt. Magnetic susceptibility measurements were undertaken on all compounds.

Homogeneous-like Alkyne Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Cationic Nickel(II) Pyridinophane Complexes: Synthesis, Structures and Catalytic Activities for C–H Oxidation

A series of nickel(II) pyridinophane complexes were synthesized and characterized by X-ray crystallographic analysis. Their IR spectra supported the existence of mononuclear nickel(II) complexes in...

Neutral and cationic methallyl nickel complexes in alkene activation: a combined DFT, ESI-MS and chemometric approach

Herein, we report a comparative study of ethylene activation and 1-hexene isomerization carried out with isomeric neutral and cationic methallyl nickel complexes L1Ni(η3-C3H5) and [L1Ni(η3-C3H5)][B(ArF)4] in the presence of borane co-catalysts.