Aminopolycarboxyl-modified Ag2S nanoparticles: Synthesis, characterization and resonance light scattering sensing for bovine serum albumin

A novel method was proposed to prepare a series of functionalized Ag₂S nanoparticles capped with various aminopolycarboxylic acids. The as-prepared Ag₂S nanoparticles were characterized by UV-vis, FTIR, resonance light scattering spectra (RLS) and transmission electron microscopy (TEM). Based on the RLS intensities enhanced by BSA-induced Ag₂S nanoparticles aggregation, a sensitive RLS method for the detection BSA at nanogram levels was established. The detection limits for BSA are between 8.6 and 112.6 ng mL⁻¹, depending on the different capping agents. The effects of various capping agents on the detection limits of BSA have been investigated. The detection limit is found to be dependent on the stability constant (log K_MY) of the silver-aminopolycarboxyl complexes.     

(Fluoroalkyl)phosphine complexes of nickel(0) and cobalt(I)

The synthesis of a series of (fluoroalkyl)phosphine complexes of nickel is reported. Treatment of (cod)₂Ni with dfepe (dfepe=(C₂F₅)₂PCH₂CH₂P(C₂F₅)₂) yields (dfepe)Ni(cod) (1), which has been structurally characterized. Treatment of 1 with CO or bipy results in the formation of (dfepe)Ni(CO)₂ (2) and (dfepe)Ni(bipy) (3), respectively. Addition of excess dfepe to 1 results in incomplete cod displacement to form (dfepe)₂Ni (4). The homoleptic complex 4 may be independently prepared in high yield by reduction of (acac)₂Ni with (ⁱBu)₃Al in the presence of butadiene and excess dfepe. Solvation of (dfepe)Ni(cod) in acetonitrile gives a new complex tentatively identified as (dfepe)Ni(MeCN)₂ (6), whereas dissolution of (dfepe)₂Ni in acetonitrile leads to a mixture of 6 and the partial displacement product (dfepe)(η¹-dfepe)Ni(MeCN) (5). In contrast to (R₃P)₄Ni(0) phosphine and phosphite complexes, which undergo protonation by strong anhydrous acids such as HCl, H₂SO₄ and CF₃CO₂H to give (R₃P)₄Ni(H)⁺ products, Treatment of (dfepe)₂Ni with neat CF₃CO₂H or excess HOTf in dichloromethane gave no spectroscopic evidence for (dfepe)₂Ni(H)⁺. Exposure for extended periods leads to dfepe loss and decomposition to Ni(II) products. The synthesis of the first cobalt complex of dfepe, (dfepe)Co(CO)₂H, is also reported.     

Synthesis of two-coordinate iron aryloxides and their reactions with organic azide: Intramolecular C-H bond amination

The synthesis and reaction of homoleptic iron(II) complexes with 2,6-di-adamantyl-substituted aryloxides [OC₆H₂-2,6-Ad-4-R]⁻ ([OAr^AdR]⁻, Ad = adamantyl, R = Me, ⁱPr) are described. Monomeric two-coordinate iron aryloxides Fe(OAr^AdR)₂ (R = Me, 1; ⁱPr, 2) were synthesized by the reaction of Fe[N(SiMe₃)₂]₂ with 2 equiv of HOAr^AdR. Treatment of 1 and 2 with 1-azidoadamantane resulted in intramolecular insertion of an adamantyl nitrene into a methylene C-H bond of the aryloxide adamantyl substituent, yielding the corresponding amine-aryloxide complexes Fe(OAr^AdR)(OAr^AdR-NHAd) (R = Me, 3; ⁱPr, 4). Molecular structures of all these complexes are reported.     

Transformation of a ditopic Schiff base nickel(II) nitrate complex into an unsymmetrical Schiff base complex by partial hydrolytic degradation: structural and density functional theory studies

A new Schiff base complex [Ni(H₂L¹)(NO₃)](NO₃) (1) (H₂L¹ = 3-[N,N′-bis-2-(5-bromo-3-(morpholinomethyl) salicylideneamino) ethyl amine]) was synthesized from reaction of the ditopic ligand H₂L¹ with Ni(NO₃)₂ in anhydrous MeOH. Complex 1 is stable in the solid state, but prone to hydrolysis. Recrystallization of 1 from wet MeOH led to the isolation of a novel unsymmetrical complex [Ni(HL²)(NO₃)](NO₃) (2) (HL² = 2-[(2-(2-aminoethylamino) ethylimino) ethyl)-5-bromo-3-(morpholino methyl) salicylidene amine]). X-ray single-crystal analysis of complex 2 showed that complex 1 had undergone partial decomposition of one imine bond. In contrast, the Schiff base complex [Ni(HL³)](NO₃) (3) (H₂L³ = N,N′-bis(5-methyl-salicylidene) diethylenetriamine) was stable in wet methanol, and the single-crystal structure of 3 showed that the Ni(II) center was coordinated in an unsymmetrical square planar geometry. Density functional theory calculations were performed in order to obtain a geometry-optimized model of complex 1, in which the Ni(II) center was coordinated in a similar manner as that in complex 3. The thermodynamic parameters were calculated, in order to rationalize the difference in hydrolytic reactivity between complexes 1 and 3.     

Synthesis and crystal structure of maleonitriledithiolate metal complexes with N-methylacridine as cations

The synthesis of [N-MeA]₂[M(mnt)₂] (N-MeA=N-methylacridine; M=Ni (II), Zn (II), Cu (II) and Cd (II); mnt=maleonitriledithiolate) and crystal structure analysis of the Ni (1) and Zn (2) complexes are reported. The conductivities of almost all the complexes under 4 MPa pressure are above 10⁻⁵ S cm⁻¹, which are characteristic of intrinsic semi-conductors. The complexes exhibit charge transfer transitions in both their absorption spectra and fluorescence spectroscopy.     

Synthesis and crystal structures of Ni(II), Cu(II) and μ-oxo-Fe(III) complexes of a salen type ligand: Mononuclear versus multinuclear complex formation

The nickel, copper and iron complexes of bis(salicylidene)-meso-1,2-diphenylethylendiaminato (mdpSal^2?) and their propensity to form multinuclear complexes similar to those observed for Co(mdpSal) are reported. The syntheses of the primary compounds were carried out with M(OAc)₂·xH₂O (M = Fe, Ni or Cu) and mdpSalH₂ in methanol. The Ni and Cu reactions resulted in the isolation of mononuclear Ni(mdpSal) (1) and Cu(mdpSal) (2) complexes. Both species 1 and 2 adopt approximate square planar geometries in the monoclinic space group P2₁/n and are iso-structural to the previously reported Co(mdpSal). Although structurally similar, neither 1 nor 2 exhibit comparable reactivity as reported for the cobalt analogue of mdpSal^?2 in forming multinuclear complexes. The iron reaction yielded a μ-oxo species [Fe(mdpSal)]₂O (3) in which each iron center is oxidized to +3 and ligated to one mdpSal^2? ligand frame with each iron center adopting distorted square pyramid geometry. In addition, Co(Salophen) (4) (SalophenH₂ = N,N′-bis(salicylidene)-1,2-phenylenediamine) has been synthesized and its reactivity assessed and compared to Co(mdpSal). Complexes 1–3 have been characterized by X-ray crystallography as well as UV–Vis and IR spectroscopy. A detailed comparison of the structural and spectral characteristics of the iso-structural complexes 1 and 2 with Co(mdpSal) are presented along with a discussion of factors that contributed to the unique reactivity observed for [Co(mdpSal)].     

Syntheses,characterization, and antimicrobial properties of nickel(II) dithiocarbamate complexes containing NiS4 and NiS2PN moieties

Three Ni(II) dithiocarbamate complexes, [Ni(buphdtc)₂] (1), [Ni(buphdtc)(PPh₃)(NCS)] (2) and [Ni(buphdtc)(PPh₃)(NC)] (3) (where bu = butyl and ph = phenyl), were synthesized and characterized by elemental analysis, UVvis, and FTIR spectroscopies. Complexes 1 and 2 were further characterized by single-crystal X-ray structural analysis. The single-crystal X-ray structural analysis indicates a slightly distorted square planar geometry. In 2 and 3, the influences of the auxiliary ligands (PPh₃, NCS, and NC) on their steric and electronic properties were observed. Thermal studies of the complexes showed decomposition starting at 250–300 °C, leading to formation of nickel sulfide phases around 400 °C. The complexes were screened against some bacteria strains, Staphylococcus aureus, Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli, Klebsiella oxytoca and Pseudomonas aeruginosa, and two fungi species, Aspergillus niger and Fusarium oxysporum. The complexes showed moderate-to-strong antimicrobial potentials, with [Ni(buphdtc)₂] (1) displaying the best antimicrobial activity. Fluconazole and streptomycin were used as reference drugs for antifungal and antibacterial assays, respectively.     

Studies on Co(II) and Cu(II) complexes of a ligand derived from 1,3-phenylenediamine and 5-bromosalicylaldehyde synthesis, characterisation, thermal properties and use as new precursors for preparation cobalt and copper oxide nano-particles

A symmetric tetradentate Schiff base ligand, N,N′-bis(5-bromosalicylaldehyde)-1,3-phenylenediamine [(Brsal)₂-1,3-phen) and its Cu(II) and Co(II) complexes with general formula M₂((Brsal)₂-1,3-phen)₂, where M=Co (1) and Cu (2)], have been synthesized and characterized by elemental analyses and FTIR spectroscopy. In addition, Schiff base ligand has been characterized by ¹HNMR spectroscopy. Thermogravimetric analysis of the ligand and its metal complexes reveals their thermal stability and decomposition pattern.     

Syntheses,crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2′-bipyridine and TCNQ

From the aqueous-methanolic systems Ni(NO₃)₂ – LiTCNQ – 5,5′-dmbpy and Ni(NO₃)₂ – LiTCNQ – 4,4′-dmbpy three novel complexes [Ni(5,5′-dmbpy)₃](TCNQ)₂ (1), [Ni(4,4′-dmbpy)₃](TCNQ)₂ (2) and [Ni(4,4′-dmbpy)₃]₂(TCNQ-TCNQ)(TCNQ)₂∙0.60H₂O (3), were isolated in single crystal form. The new compounds were identified using chemical analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compositions and have shown that their ionic structures contain the complex cations [Ni(5,5′-dmbpy)]²⁺ (1) or [Ni(4,4′-dmbpy)]²⁺ (2 and 3). The anionic parts of the respective crystal structures 1–3 are formed by TCNQ^⋅- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)^2- with a C-C distance of 1.663(5) Å. The supramolecular structures are governed by weak hydrogen bonding interactions. The variable-temperature (2–300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQ^⋅- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)^2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQ^⋅- anion-radicals.     

General theoretical analysis of three-connected polyhedral molecules and their capped derivatives

The synthesis of the half-sandwich compound Na[(C₅H₅)Ni{P(S)(CH₃)₂}₂] is described. The anions [(C₅H₅)Ni{P(S)R₂}₂]^?, 1a (R = OCH₃) and 1b (R = CH₃) react as bidentate sulfur ligands with [Ni₂(C₅H₅)₃]⁺, giving nickelocene and weakly paramagnetic dinuclear complexes of the type [(C₅H₅)Ni{P(S)R₂}₂Ni(C₅H₅)] (2a,b). In these compounds, the P(S)R₂ units form NiPSNi bridges in such a fashion as to generate a (C₅H₅)NiP₂ and a (C₅H₅)NiS₂ unit. A temperature-dependent singlettriplet spin equilibrium is observed, which is essentially localized on the (C₅H₅)NiS₂ side. Accordingly, the position of the cyclopentadienyl peak of the (C₅H₅)Ni unit bound to the two sulfur donor centers displays a very large temperature dependence in the ¹H NMR spectra. MO model calculations (EHT) for P(S)H₂^?, [(C₅H₅)Ni{P(S)H₂}₂]^? (1c), [(C₅H₅)Ni{P(S)H₂}₂Ni(C₅H₅)] (2c) and its isomer 3c allow the observed spin crossover to be explained as a consequence of the pronounced π-donor properties of the sulfur centers and allow predictions for related complexes.The green complexes 2a,b isomerize completely and irreversibly in a first-order reaction to yield the diamagnetic red compounds [{(C₅H₅)NiP(S)R₂}₂] (3a,b), in which each (C₅H₅)Ni unit is coordinated to one P and one S donor atom. The rate constant of isomerization of 2a, k (7.6 ± 0.3) × 10^?4s^?1 at 306 K, and the energy of activation, E_a 76 kJ mol^?1, have been determined. The rate of isomerization is independent of the solvent, and crossover experiments verify that the isomerization is an intramolecular process without involvement of the monomeric units [(C₅H₅)NiP(S)R₂].     

Syntheses and X-ray crystallographic studies of {[Ni(en)2(pot)2]0.5CHCl3} and [Ni(en)2](3-pytol)2

Two novel Ni(II) complexes {[Ni(en)₂(pot)₂]0.5CHCl₃} (3) {pot = 5-phenyl-1,3,4-oxadiazole-2-thione} (1) and [Ni(en)₂](3-pytol)₂ (4) {3-pytol = 5-(3-pyridyl)-1,3,4-oxadiazole-2-thiol} (2) have been synthesized using en as coligand. The metal complexes have been characterized by physical and analytical techniques and also by single crystal X-ray studies. The complexes 3 and 4 crystallize in monoclinic system with space group P21/a and P121/c, respectively. The complex 3 has a slightly distorted octahedral geometry with trans (pot)⁻ ligands while 4 has a square planar geometry around the centrosymmetric Ni(II) center with ionically linked trans (3-pytol)⁻ ligands. The π?π (face to face) interaction plays an important role along with hydrogen bondings to form supramolecular architecture in both complexes.     

Synthesis and properties of nickel(II) and copper(II) complexes of a di-N-acetamide tetraaza macrocycle

The syntheses of the hexadentate ligand 2,13-bis(acetamido)-5,16-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane (L²) and its complexes with Ni(II) and Cu(II) are described. Crystal structures of H₂L²·2HClO₄ (1), [Ni(L²)](ClO₄)₂ (2) and [Cu(L²)](ClO₄)₂ (3) are reported. The two pendant acetamide groups of the macrocyclic ligand 1 are trans to each other and the absolute configuration is a trans-IV in the solid state. The crystal structures of 2 and 3 revealed an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two oxygen atoms of the pendant acetamide groups at the axial positions. The nickel(II) and copper(II) ions are located at an inversion center. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the presence of the pendant arms.     

Nickel(II) complexes of the type [RM(oxam)MR] (oxam: oxalamidinate, R=n-butyl, n-hexyl): the first binuclear n-alkyl nickel complexes

The reaction between one equivalent of [(acac)Ni(A)Ni(acac)] (A: N¹,N²-bis(2-pyridylmethyl)-N³,N⁴-bis-(2,4,6-trimethylphenyl)oxalamidinate) and two equivalents of R-Li (R=n-butyl; n-hexyl) results in the formation of the binuclear complexes [(R-Ni)(A)(Ni-R)] (1: R=n-butyl: 2=n-hexyl). Both compounds were characterized by ¹H- and ¹³C-NMR spectroscopy, elemental analysis, and mass spectroscopy. X-ray single diffraction studies of single crystals of 1 and 2 show that symmetrical binuclear complexes are formed in which the two Ni(II) centers are connected by the oxalamidinato bridging ligand A in a planar-square environment. No agostic interactions between the β-hydrogens of the n-alkyl groups and the metal centers were observed. DTA- and DTG-investigations show, that 1 and 2 are surprisingly thermally stable (decomposition temperature of 1: 188 °C under formation of butenes). Heating up a 1:1 mixture of 1 and 2 in toluene results in the formation of octane, decane and dodecane indicating an intermolecular transfer reaction of the n-alkyl-groups in solution. CV measurements display that the oxam complexes [(R-M)(A)(M-R)] (M=Ni, R=CH₃ (3), Ph (4), CCH (6), CCPh (7); M=Pd, R=CH₃ (5) are reversibly reduced in two steps indicating electronic interactions between the two metal centers.     

Synthesis,crystal structures and spectral studies of square planar nickel(II) complexes containing an ONS donor Schiff base and triphenylphosphine

Five mononuclear nickel(II) complexes, viz. [Ni(L1)(PPh₃)] (1), [Ni(L2)(PPh₃)] (2), [Ni(L3)(PPh₃)] (3), [Ni(L4)(PPh₃)] (4) and [Ni(L5)(PPh₃)] (5) (where L1, L2, L3, L4 and L5 are dianions of N-(2-mercaptophenyl)salicylideneimine, 5-methyl-N-(2-mercaptophenyl)salicylideneimine, 5-chloro-N-(2-mercaptophenyl)salicylideneimine, 5-bromo-N-(2-mercaptophenyl)salicylideneimine and N-(2-mercaptophenyl)naphthylideneimine, respectively), have been synthesized and characterized by means of elemental analysis, electronic, IR, ¹H, ¹³C and ³¹P NMR spectroscopy. Single crystal X-ray analysis of two of the complexes (1 and 5) has revealed the presence of a square planar coordination geometry (ONSP) about nickel. The crystal structures of the complexes are stabilized by intermolecular π–π stacking between the ligands (L) and by various C–H···π interactions.     

Novel nickel(II) and copper(II) complexes with phenoxy-imidazole ligands: Syntheses, crystal structures and norbornene addition polymerization

The novel nickel(II) (1) and copper(II) (2) complexes bearing 2′-(4′,6′-di-tert-butylhydroxy-phenyl)-1,4,5-triphenyl imidazole ligand have been synthesized and characterized. The molecular structure analyses of complexes 1 and 2 indicated that Ni(II) centre in 1 adopts a distorted tetrahedral coordination geometry with a dihedral angle of 85.2° between Ni(1)O(1)N(1) plane and Ni(1)O(1A)N(1A) plane, while the Cu(II) centre in 2 represents a distorted square planar coordination geometry with a cis-N₂O₂ arrangement of the donor atoms, the dihedral angle being 32° between Cu(1)O(1)N(1) plane and Cu(1)O(1A)N(1A) plane. After activation with methylaluminoxane (MAO), both Ni(II) and Cu(II) complexes can be used as catalysts for the addition polymerization of norbornene (NB). The polynorbornenes (PNBs) are produced with very high polymerization activity (10⁸ g PNB mol⁻¹ Ni h⁻¹) for Ni(II) complex and moderate catalytic activity (10⁵ g PNB mol⁻¹ Cu h⁻¹) for Cu(II) complex, respectively. The high molecular weight polynorbornenes (10⁶) are obtained for complexes 1 and 2. Moreover, the distinct effects of polymerization temperature and Al/M ratio on catalytic activities and molecular weights of polymers are discussed.     

Square planar Ni(II) thiosemicarbazone complexes as functional models for carbon monoxide dehydrogenase

Two Ni(II) complexes, [Ni(dmoTSCH)Cl] (1) and [Ni(dmoPhTSCH)Cl] (2) of the tridentate thiosemicarbazone ligands diacetylmonooxime thiosemicarbazone (dmoTSCH₂) and diacetylmonooxime (4-phenyl)thiosemicarbazone (dmoPhTSCH₂) have been synthesized. X-ray crystal structure of [Ni(dmoTSCPhTSCH)Cl] (2) indicates that the Ni(II) assumes a square planar geometry in the complexes, with the ligand coordinated in a monoanionic N,N,S donor mode and the fourth coordination position of Ni(II) is occupied by a chloride ion. Cyclic and differential pulse voltammetric experiments suggest that the Ni(II) complexes can undergo a two electron reduction at about ?1.0V. It is shown that the Ni(II) complexes in DMF or DMSO solutions can mimic CO-dehydrogenase activity by oxidizing CO to CO₂ in presence of a base like NaOAc and a sacrificial electron acceptor like methyl viologen and the colour of the resultant MV^.+ can be used to monitor the reaction.     

Binding modes of a dimethyliminopentanone ligand on nickel pre-catalysts toward olefin polymerization

Nickel complexes prepared using a 4-(2,6-diisopropylphenylimino)-3,3-dimethylpentan-2-one ligand framework are shown. The potassium salt of the ligand is obtained by deprotonation with KH in diethyl ether. Potassium 4-(2,6-diisopropylphenylimino)-3,3-dimethyl-pent-2-en-2-olate can then be reacted with Ni(PMe₃)₂(η¹-CH₂Ph)Cl to yield 4-(2,6-diisopropylphenylimino)-3,3-dimethyl-pent-2-en-2-olato-κ¹O](η¹-CH₂Ph)(PMe₃)₂Ni (1). The potassium salt of the ligand can also be reacted with Ni(PMe₃)(η³-CH₂Ph)Cl to yield bis(4-(2,6-diisopropylphenylimino)-3,3-dimethyl-pent-2-en-2-olato-κ²N,O](η¹-CH₂Ph)₂Ni₂ (2) or 4-(2,6-diisopropylphenylimino)-3,3-dimethyl-pent-2-en-2-olato-κ²N,O](η¹-CH₂Ph)(PMe₃)Ni (3), depending on the reaction conditions. The addition of five equivalents of B(C₆F₅)₃ to 1, 2, or 3 yields catalytically active species for the homopolymerization of ethylene. The polymer products are described by a single molecular weight distribution, consistent with the presence of a single active site.     

Chiral resolution of l- and d-alanine and a racemic macrocyclic nickel(II) complex: synthesis and crystal structures

The reactions of a racemic four-coordinate Ni(II) complex [Ni(rac-L)](ClO₄)₂ with l- and d-alanine in acetonitrile/water gave two six-coordinate enantiomers formulated as [Ni(RR-L)(l-Ala)](ClO₄)·2CH₃CN (1) and [Ni(SS-L)(d-Ala)](ClO4) (2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane, Ala^? = alanine anion), respectively. Evaporation from the remaining solutions gave two four-coordinate enantiomers characterized as [Ni(SS-L)](ClO₄)₂ (S-3) and [Ni(RR-L)](ClO₄)₂ (R-3), respectively. Single-crystal X-ray diffraction analyses of complexes 1 and 2 revealed that the Ni(II) atom has a distorted octahedral coordination geometry, being coordinated by four nitrogen atoms of L in a folded configuration, plus one carboxylate oxygen atom and one nitrogen atom of l- or d-Ala^? in mutually cis-positions. Complexes 1 and 2 are supramolecular stereoisomers, constructed via hydrogen bonding between [Ni(RR-L)(l-Ala)]⁺ or [Ni(SS-L)(d-Ala)]⁺ monomers to form 1D hydrogen-bonded zigzag chains. The homochiral natures of complexes 1 and 2 have been confirmed by CD spectroscopy.     

Hydrothermal and sonochemical synthesis of a nano-sized nickel(II) Schiff base complex as a precursor for nano-sized nickel(II) oxide; spectroscopic, catalytic and antibacterial properties

The Ni(II) complexes [Ni(L)₂](ClO₄)₂ (1) and [Ni(L)₂(NO₃)₂] (2), where L is the Schiff base ligand of 4,5,9,13,14-pentaaza-benzo[b] triphenylene, were synthesized and characterized by physico-chemical and spectroscopic methods. Nano-sized particles of (1) were prepared both by sonochemistry (3) and solvothermal (4) methods. NiO nanoparticles were obtained by calcination of the nano-structure complexes at 500 °C. The structures of the nano-sized compounds were characterized by X-ray powder diffraction and scanning electron microscopy. The thermal stabilities of the bulk complexes (1–2) and nano-sized particles (3–4) were studied by thermogravimetric and differential scanning calorimetry. The catalytic activities of complexes of (1–4) are reported. The free Schiff base and its Ni(II) complexes have been screened for antibacterial activities against three Gram-positive bacteria. The metal complexes are more active than the free Schiff base. Electrochemical studies show that the Ni complexes undergo irreversible reduction in MeCN solution.     

Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12-16/MAO systems is up to 3.3 × 10⁴ g mol⁻¹ h⁻¹ whereas for 17-24/MAO systems it is up to 4.94 × 10⁵ g mol⁻¹ atm⁻¹ h⁻¹. The influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh₃/Ni molar ratio on catalytic activity was investigated.