Dinuclear Nickel Complexes Research Articles

Alternating Copolymerization of Carbon Dioxide with Epoxides Using Highly Active Dinuclear Nickel Complexes: Catalysis and Kinetics.

A novel series of well-defined dicarboxylate dinuclear nickel complexes containing benzotriazole based 1,3-diamine-bisphenolate (1,3-DiBTP) ligands were readily synthesized through a one-pot procedure, which were highly active single-component catalysts for copolymerization of CO2 and epoxides. X-ray structural determination of dinickel complexes 1-11 indicates that the DiBTP ligand acted as a N,O,N,N,O,N-hexadentate framework to chelate two nickel atoms, and two carboxylates are nonequivalently coordinated. The best benzoate-bonded dinickel catalyst 6 displayed the effective activity for both high-pressure and 1 atm CO2-copolymerization of cyclohexene oxide (CHO) in a controllable manner. Noteworthily, a high turnover frequency up to 9600 h-1 could be reached at 140 °C and a CO2 pressure of 20.7 bar utilizing a low catalyst loading of 0.01 mol %, and the same copolymerization conditions were capable of producing narrowly dispersed poly(cyclohexene carbonate) (PCHC) having >99% polycarbonate selectivity. In addition to CO2/CHO copolymerization, 4-vinyl-1,2-cyclohexene oxide or cyclopentene oxide was also applied to efficiently copolymerize CO2 under conditions of 80 °C and 20.7 bar initial CO2 pressure. Kinetic studies of CO2/CHO copolymerization catalyzed by 6 were investigated. Such polymerization revealed first-order dependence for both catalyst 6 and CHO concentrations, and the activation energy for PCHC generation by 6 is 57.69 kJ mol-1. A possible polymerization mechanism for CO2-copolymerization of CHO was proposed based on kinetics and structural studies of the obtained polycarbonates.

Unveiling the urease like intrinsic catalytic activities of two dinuclear nickel complexes towards the in situ syntheses of aminocyanopyridines.

Designing metal complexes as functional models for metalloenzymes remains one of the main targets in synthetic bioinorganic chemistry. Furthermore, the utilization of the product(s) derived from the catalytic reaction for subsequent organic transformation that occurs in biological systems is an even more difficult challenge for biochemists. Urease, the most efficient enzyme known, catalyzes the hydrolysis of urea and it contains an essential dinuclear NiII cluster in the active site. Inspired by the catalytic properties of urease, two dinickel(ii) complexes viz. Ni2L12(OAc)2(H2O) (1) and Ni2L22(OAc)2(H2O) (2) [HL1 = 2,4-dimethyl-6-{[(2'-dimethyl aminoethyl)methylamino]methyl}-phenol and HL2 = 2,4-dichloro-6-{[(2'-dimethyl aminoethyl)methylamino]methyl}-phenol] have been synthesized and characterized in this report. Both the complexes have shown the urease kind of activity with the liberation of ammonia from urea in aqueous solution. The plausible mechanistic pathway and kinetics of the reactions have been studied. Besides, the liberated ammonia has been utilized in the one-pot synthesis of biologically active products like 2-amino-3-cyanopyridines and their derivatives in aqueous medium with excellent yields.

Phenoxido mediated antiferromagnetic and azide mediated ferromagnetic coupling in two dinuclear ferromagnetic nickel(ii) complexes with isomeric Schiff bases: a theoretical insight on the pathway of magnetic interaction

Two relatively rare mixed phenoxo and azide bridged dinuclear nickel(ii) complexes have been discussed. Both complexes show strong intermolecular hydrogen bonding interactions and exhibit ferromagnetic exchange coupling.

Exploration of Theoretical and Antioxidant Mimetic Activities of Binuclear Copper(II) and Nickel(II) Coordination Complexes

Three dinuclear copper(II) and nickel(II) complexes viz. [Cu2(La)(py)2]·(ClO4)2 (1), [Ni2(Lb)(ImH)2]·(ClO4)2 (2) and [Ni2(Lc)(H2O)2]·(ClO4)2 (3) were designed and synthesized using disulfide and auxiliary ligands as functional models for antioxidant superoxide dismutase enzyme (where, H2La-H2Lc = disulfide ligands bearing S-S bond, py = pyridine, ImH = imidazole). The disulfide ligands were synthesized by condensation reaction of 2-(2-(2-aminophenyl)disulfanyl)benzeneamine with 3-bromo-2-hydroxy-5-nitrobenzaldehyde; 5-bromo-2-hydroxybenzaldehyde and 3,5-dichloro- 2-hydroxybenzaldehyde, respectively. All the compounds were characterized by various spectrometry methods. The molecular docking study was performed against penicillin binding protein 4 (PBP4) active site pocket and E. coli DNA Gyrase B ATPase domain to evaluate the possible mechanism of antibacterial property of disulfide ligands. The results revealed that H2La-H2Lc possess higher binding affinity for active site of PBP4 and Gyrase B ATPase domain. The present study also demonstrated that disulfide compounds have potential to inhibit the PBP4 and Gyrase B ATPase domain and can be developed as lead compounds. In addition, antioxidant superoxide dismutase (SOD) activity is also discussed of these complexes. The antioxidant superoxide measurements show that complexes behave as superoxide mimic in alkaline nitro blue tetrazolium chloride (NBT) assay.

Synthesis, molecular docking studies, anticancer and antibacterial activities of some novel Dinuclear Nickel (II) Complexes 2, 4-Dihydroxy acetyl-4-Hydroxybenzoic Hydrazone

Substituted 2, 4-Dihydroxyacetyl-4-Hydroxybenzoic Hydrazone, which is known for their versatile biological activities, have been reported to show significant anti lung cancer activities. In the present study, a novel series of some 2, 4-Dihydroxyacetyl-4-Hydroxybenzoic Hydrazone ligands were complexed with Nickle and synthesized to develop more potent anti-cancer activities. The Ni complexes were synthesized in good to excellent yields, and equimolar solutions of 2, 4-dihydroxyacetophenone in methanol and 4-hydroxy benzoic hydrazide in hot aqueous ethanol were refluxed for two hours on a water bath and cooled. I.R., NMR and HRMS spectral analysis characterized the structures of all newly synthesized compounds. The title compounds were tested against a panel of Gram-positive and Gram-negative bacteria for in vitro antibacterial activity. The compounds were docked to BCL2 protein, an expressed protein of lung cancer for anti-cancer studies. All the title compounds were screened for anti-cancer activity using BCL2 lung protein based on insilico molecular docking studies, and the results showed IC50 value ranging between 40-45μg.

Cooperativity in Highly Active Ethylene Dimerization by Dinuclear Nickel Complexes Bearing a Bifunctional PN Ligand

In order to examine the possibility to promote cooperative effects on catalytic activity and selectivity in ethylene dimerization through ligand design, the bisphosphino-iminato ligands syn-L and a...

Visible‐Light‐Driven CO2 Reduction Catalyzed by a Dinuclear Nickel Complex

The utilization of synergy between two metal sites in dinuclear metal catalysts for CO2 reduction remains challenging. Herein, for the first time, we employ a dinuclear nickel complex as a molecular catalyst for visible‐light‐driven CO2 reduction with 99 % selectivity toward CO production. The photocatalytic mechanism was proposed based on the results of electrochemical measurements and fluorescent quenching experiments.

Dinuclear nickel(II) complexes with ONO-pincer and coordinated aquo ligands as a robust homogeneous water oxidation catalyst

A nickel(II) complex with the newly synthesized dicarboxamide ligand [H2LBZ][(CF3SO3)Cl] was explored as a water oxidation catalysis. All the synthesized compounds were characterized by IR and NMR spectroscopy, thermogravimetry, and single-crystal XRD analysis. The superior kinetics of the water oxidation reaction in the presence of the NiII catalyst was shown by an enhanced current of 4535 µA (pH 8) or 8900 µA (pH 10) at an overpotential of 186 mV in a cyclic voltammogram. Controlled potential electrolysis demonstrated that the catalyst was stable during the water oxidation experiment. These results are akin to those for other reported nickel catalysts.

Metal-to-Ligand Ratio Controlled Assembly of Two Ni(II) Complexes: Structures, Luminescent and Electrochemical Properties

Treatment of Ni(OAc)2·4 H2O with 3,4-pyrazoledicarboxylic acid (H3pdc) and imidazole (ImH) in different metal-to-ligand ratios afforded two dinuclear nickel(II) complexes, [Ni(Hpdc)(ImH)(H2O)2]2·4 H2O (1) and [Ni(Hpdc)(ImH)2(H2O)]2·2.5 H2O (2), which were characterized by elemental analysis (EA), IR spectra and X-ray diffraction analysis and thermogravimetric analysis (TGA). Both in 1 and 2, the dinickle unit [Ni2(µ2-Hdpc)2] with six-numbered Ni2N4 ring was formed by a pair of µ2-Hpdc2− ligands linked two Ni(II) ions in N,O-chelating and N‒N-bridging fashions. The dinuclear units in 1 and 2 were expanded to 2D layer structures though hydrogen-bonding interactions between coordination water molecules, ImH molecules and carboxylate oxygen atoms, whereas the lattice water molecules in 1 and 2 just embedded in the 2D layer through intermolecular hydrogen bonding interactions. Finally, the 2D sheets in 1 were further assembled to a 3D supramolecular architecture via intermolecular C–H⋯O hydrogen bond. Besides, the luminescent and electrochemical properties of two complexes have been reported. Two dinuclear nickel(II) complexes, [Ni(Hpdc)(ImH)(H2O)2]2·4 H2O (1) and [Ni(Hpdc)(ImH)2(H2O)]2·2.5 H2O (2), were obtained by assembling of a Ni(II) ion, 3,4-pyrazoledicarboxylic acid (H3pdc) and imidazole (ImH) in different metal-to-ligand ratios. In 1 and 2, the O(C, N)−H⋯O hydrogen bonds expanded the dinuclear complexes to 3D/2D supramolecular structures, respectively.

Nickel(II) Phosphane‐ and N‐heterocyclic Carbene Complexes with Tridentate, Dianionic [S,N,O]2– Ligands

Square‐planar dinuclear nickel(II) complexes containing [S,N,O]2– ligands formed by condensation of acetyl acetone or benzoyl acetone with cysteamine were prepared. These dimeric nickel(II) compounds undergo bridge‐cleavage reactions with the cage phosphine PTA (PTA = 1,3,5‐triaza‐7‐phosphaadamantane) or in situ generated N‐heterocyclic carbenes. The resulting diamagnetic, square planar NiII complexes were characterized by spectroscopic methods and X‐ray diffraction.

Catalysis and kinetics for alternating copolymerization of carbon dioxide with epoxides using dinuclear nickel catalysts of pyrazolyl based diamine-bisphenolate ligands

The synthesis of structurally well-characterized dinuclear nickel complexes bearing a new type of pyrazolyl based diamine-bisphenolate ligand was reported for the first time. Catalysis towards nickel-catalyzed copolymerization of CO2 with cyclohexene oxide (CHO) by these newly prepared bimetallic complexes was systematically investigated. Particularly, dinickel complex 4 supporting 2-nitrophenoxide coligands was demonstrated to effectively catalyze CO2-copolymerization of CHO, 4-vinyl-1,2-cyclohexene oxide or cyclopentene oxide, generating the corresponding CO2-based polycarbonates with >99% carbonate linkages under optimal conditions. Kinetic studies of CO2/CHO copolymerization revealed that such copolymerization catalysis is first-order in dinickel complex 4 and second-order in CHO concentration.

Competing H2 versus Intramolecular C–H Activation at a Dinuclear Nickel Complex via Metal–Metal Cooperative Oxidative Addition

Nickel(I) metalloradicals bear great potential for the reductive activation of challenging substrates but are often too unstable to be isolated. Similar chemistry may be enabled by nickel(II) hydrides that store the reducing equivalents in hydride bonds and reductively eliminate H2 upon substrate binding. Here we present a pyrazolate-based bis(β-diketiminato) ligand [LPh]3- with bulky m-terphenyl substituents that can host two Ni-H units in close proximity. Complexes [LPh(NiII-H)2]- (3) are prone to intramolecular reductive H2 elimination, and an equilibrium between 3 and orthometalated dinickel(II) monohydride complexes 2 is evidenced. 2 is shown to form via intramolecular metal-metal cooperative phenyl group C(sp2)-H oxidative addition to the dinickel(I) intermediate [LPhNiI2]- (4). While NiI species have been implicated in catalytic C-H functionalization, discrete activation of C-H bonds at NiI complexes has rarely been described. The reversible H2 and C-H reductive elimination/oxidative addition equilibrium smoothly unmasks the powerful 2-electron reductant 4 from either 2 or 3, which is demonstrated by reaction with benzaldehyde. A dramatic cation effect is observed for the rate of interconversion of 2 and 3 and also for subsequent thermally driven formation of a twice orthometalated dinickel(II) complex 6. X-ray crystallographic and NMR titration studies indicate distinct interaction of the Lewis acidic cation with 2 and 3. The present system allows for the unmasking of a highly reactive [LPhNiI2]- intermediate 4 either via elimination of H2 from dihydride 3 or via reductive C-H elimination from monohydride 2. The latter does not release any H2 byproduct and adds a distinct platform for metal-metal cooperative two-electron substrate reductions while circumventing the isolation of any unstable superreduced form of the bimetallic scaffold.

Three new dinuclear nickel(II) complexes with amine pendant-armed ligands: Characterization, DFT study, antibacterial and hydrolase-like activity

Herein, we report the synthesis and characterization of three new Ni(II) complexes, namely: [Ni2(H2LEt)(μ-OAc)2(H2O)]BPh4‧ClO4 (1), (H2LEt = 2-[(N-benzyl-N-2-pyridyl methylamine)]-4-methyl-6-[N-2(pyridylmethyl)aminomethyl)]-6((2-aminoethyl)amino)methyl phenol); [Ni2(H2LProp)(μ-OAc)2(H2O)](ClO4)2 (2), (H2LProp = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl]-6-((2-aminopropyl) amino)methylphenol); and [Ni2(LBut)(μ-OAc)2(H2O)](HCl)2 (3), (LBut = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl]-6-((2-aminobuthyl) amino)methylphenol). All of them were characterized through spectroscopic techniques (elemental analysis, IR, UV–Vis spectroscopy), ESI-MS, electrochemistry and potentiometric titration. Density functional theory (DFT) was used to better understand the electronic and molecular structure of these complexes. The hydrolytic activity of complexes 1–3 towards the 2,4-BDNPP substrate was analyzed and complex 2 presented the highest catalytic efficiency (kcat/KM) of the three, possibly due to a greater interaction with the substrate. The complexes were also screened for their antibacterial activities using both Gram-positive and Gram-negative bacterial strains by minimum inhibitory concentration and minimum bactericidal concentration methods.

A dinuclear nickel catalyst based on metal–metal cooperation for electrochemical hydrogen production

In the quest for efficient metal catalysts for hydrogen production, a new dinuclear nickel complex of formula [{(μ-2-thiazolethiolate)Ni(1,3-bis(diphenylphosphino)propane)}2](BF4)2 (2) has been synthesized. Complex 2 shows electrochemical catalytic behavior for hydrogen production with a overpotential of 0.26 V, a current efficiency of 59%, and a turnover number of 6.4. The lack of catalytic behavior of a related mononuclear complex under the same conditions suggests that the cooperation between the two Ni centers plays a pivotal role in the catalytic behavior.

A series of hydrogen bond mediated dinuclear nickel(II) complexes with reduced Schiff base ligands: An insight into the nature of their short intermolecular hydrogen bonds

A series of isostructural centrosymmetric hydrogen bonded dimeric nickel(II) complexes of general formula, [Ni2(HL)2(DMSO)2(H2O)2]X {where H2L = N2O4 donor reduced Schiff base ligand, [H2L1=(2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol) and H2L2=(2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)] and X = counter anion}, are synthesized and characterized by elemental analysis, infrared and electronic spectra. The structures of all complexes have been confirmed by single crystal X-ray diffraction analysis. Each complex forms O⋯H⋯O hydrogen bonded dimer in the solid state, where the O⋯O distance is very short, ranging from 2.424(3) to 2.437(3) Å. The hydrogen bonds are very strong as can be seen from the DFT estimated energy of these hydrogen bonds. Non-covalent interaction plot (NCI plot) index has been used to characterize them.

Dinuclear cobalt and nickel complexes of a mercaptoacetic acid substituted 1,2,4-triazole ligand: syntheses, structures and urease inhibitory studies.

Because of its versatile coordination modes and strong coordination ability, the mercaptoacetic acid substituted 1,2,4-triazole 2-{[5-(pyridin-2-yl)-4H-1,2,4-triazol-3-yl]sulfanyl}acetic acid (H2L) was synthesized and characterized. Treatment of H2L with cobalt and nickel acetate afforded the dinuclear complexes {μ-3-[(carboxylatomethyl)sulfanyl]-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-ido-κ2N1,N5:N2,O}bis[aqua(methanol-κO)cobalt(II)] methanol disolvate, [Co2(C9H6N4O2S)2(CH3OH)2(H2O)2]·2CH3OH (1), and {μ-3-[(carboxylatomethyl)sulfanyl]-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-ido-κ2N1,N5:N2,O}bis[diaquanickel(II)] methanol disolvate dihydrate, [Ni2(C9H6N4O2S)2(H2O)4]·2CH3OH·2H2O (2), respectively. Complex 1 crystallized in the monoclinic space group P21/c, while 2 crystallized in the tetragonal space group I41/a. Single-crystal X-ray diffraction studies revealed that H2L is doubly deprotonated and acts as a tetradentate bridging ligand in complexes 1 and 2. For both of the obtained complexes, extensive hydrogen-bond interactions contribute to the formation of their three-dimensional supermolecular structures. Hirshfeld surface analysis was used to illustrate the intermolecular interactions. Additionally, the urease inhibitory activities of 1, 2 and H2L were investigated against jack bean urease, where the two complexes revealed strong urease inhibition activities.

Visible-light-driven methane formation from CO2 in hydrous solution with a dinuclear nickel catalyst

The photocatalytic reduction of CO2 to CH4 in a hydrous solution was successfully achieved by a homogeneous molecular catalytic system involving two dinuclear nickel complex catalysts (i.e., [(dmbpy)2Ni2Cl4(H2O)2] (1) (dmbpy = 4,4′-dimethyl-2,2′-bipyridine) and [(bpy)2Ni2Cl4(H2O)2] (2) (bpy = 2,2′-bipyridine)), in the presence of [Ru(bpy)32+] or organic dye such as Eosin Y as a photosensitizer. Control and cyclic voltammetry experiments (CV) revealed that H2O could provide the H+ required for the conversion of CO2 into CH4 and ruled out CO as an intermediate in this reaction.

Catalytic Conversion of Atmospheric CO2 into Organic Carbonates by Nickel(II) Complexes of Diazepane-Based N4 Ligands.

Activation of CO2 and conversion into value-added products is an effective option to mitigate CO2 emission. The nickel(II) complexes [Ni(L1)](ClO4)2 1, [Ni(L2)](ClO4)2 2, and [Ni(L3)(CH3CN)2](Ph4B)2 3 of diazepane-based ligands [1,4-bis[(pyridin-2-yl-methyl)]-1,4-diazepane (L1), 1,4-bis[2-(pyridin-2-yl)ethyl]-1,4-diazepane (L2), and 4-bis[2-(quinoline-2-yl)-methyl]-1,4-diazepane (L3)] have been synthesized and structurally characterized. The complexes were employed as the catalysts for the conversion of atmospheric CO2 into organic carbonates in the absence of cocatalyst at 1 atm pressure. The single-crystal X-ray structures of 1 and 2 exhibit distorted square-planar geometry with almost identical Ni-N bond distances (1.891-1.946 Å). The geometry of the complexes rearranged into octahedral in acetonitrile, which was studied by paramagnetic 1H NMR and electronic spectra. The complexes selectively captured CO2 from the atmospheric air and readily converted epoxides into cyclic carbonates without any cocatalyst. They showed a maximum yield of 25% (TON, 500) using 1 atm air, which is drastically enhanced up to 89% (TON, 1780) using 1 atm pure CO2 gas. This is the highest catalytic efficiency reported for CO2 fixation using nickel-based catalysts to date. The CO2 fixation reaction without organic substrate showed the formation of carbonate-bridged dinuclear nickel(II) complexes. They showed characteristic absorption bands around 571-612 nm and were further confirmed by electrospray ionization mass spectrometry, IR, and single-crystal X-ray structures. The molecular structure of carbonate-bridged intermediates exhibited two Ni2+-centers with distorted square pyramidal geometries for 2a and 3a but distorted octahedral and square pyramidal geometries for 1a. The CO2 fixation reactions possibly proceeded via the formation of CO2-bound nickel species.

Synthesis, structural characterization, DFT calculations and biological properties of mono- and dinuclear nickel complexes with tetradentate transformed ligands by aerobic oxidative-coupling reactions

Reaction of nickel chloride with acetylacetone bis(salicylhydrazone) (L) (prepared in situ by condensation of acetylacetone with salicylhydrazide) in methanol results in the formation of air-sensitive nickel (II) complex of symmetrical tetradentate Schiff base [NiII(L)] (1). Air oxidation of 1 leads to the formation of dinuclear species [NiII(L-L)NiII] (2) where the ligand (L-L)4– is formed by oxidative C-C coupling at the central methylene group of the acetylacetone fragment of (L)2–. The same reaction in methanol/pyridine solution leads to oxidative C-N coupling forming a mesoionic [NiII(L-Py)](3). The use of Nickel acetylacetonate in methanol/pyridine or DMSO solution under aerobic conditions provide [NiII(L-O)(py)2](4), [NiII(L-O)(DMSO)2](5). In this case, the ligand (L)2– is partially oxidized to form (L-O) which is formed by oxidation of the central methylene group. The molecular structure of 1–5 have been determined by X-ray crystallography. The first three complexes 1, 2 and 3 have a square-planar geometry, while, 4 and 5 adopt octahedral geometry. In vitro antioxidant activities of compounds 1, 4 and 5 were evaluated against DPPH radical and hydrogen peroxide and were compared with standard antioxidant, ascorbic acid. Our results reveal that the three compounds exhibit excellent radical scavenging activities. DFT calculations have been performed on complexes 1–5 using the BP86 and B3LYP functionals to provide a complete rationalization of their structures and to describe their electronic structures elucidating the fundamental spin state and the Metal-Ligand interaction type.

The influence of the tertiary butyl group in the ligand frame on the catalytic activities, DNA cleavage ability and cytotoxicity of dinuclear nickel(II) complexes

Dinuclear phenoxo-bridged nickel complexes [Ni2(L1)H2O(CH3COO)](1) and [Ni2(L2)H2O(CH3COO)](2) (where L1H3° = 2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabutenyl]-3-enyl]-1,3-imidazolidine and L2H3° = 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-1,3-bis[4-(3,5-di-tert-butyl-2-hydroxyphenyl)-3-azabutenyl]-1,3-idazolidine, and H stands for dissociable protons) have been synthesized and characterized by different spectroscopic methods. Molecular structure of 2 was determined by X-ray crystallography. Redox properties of complexes 1 and 2 were investigated by cyclic voltammetric studies. As functional mimic of active site of galactose oxidase enzyme, complexes 1 and 2 were utilized for the oxidation of primary alcohol. Both the complexes exhibited catecholase activity. DNA interaction studies on complexes 1 and 2 were also investigated. Self-activated DNA cleavage activity of complex 2 was observed. The cytotoxicity of the complexes 1 and 2 was measured using a standard MTT assay and IC50 values for of 1 and 2 were found to be 21.92 µM and 20.69 µM on MCF-7 breast cancer cell line respectively.