Ni(II) and Cu(II) complexes of phenoxy-ketimine ligands: Synthesis,structures and their utility in bulk ring-opening polymerization (ROP) of l-lactide

Synthetic, structural and catalysis studies of Ni(II) and Cu(II) complexes of a series of phenoxy-ketimine ligands with controlled variations of sterics, namely 2-[1-(2,6-diethylphenylimino)ethyl]phenol (1a), 2-[1-(2,6-dimethylphenylimino)ethyl]phenol (1b) and 2-[1-(2-methylphenylimino)ethyl]phenol (1c), are reported. Specifically, the ligands 1a, 1b and 1c were synthesized by the TiCl₄ mediated condensation reactions of the respective anilines with o-hydroxyacetophenone in 21–23% yield. The nickel complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Ni(II) (2a) and {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Ni(II) (2b), were synthesized by the reaction of the respective ligands 1a and 1b with Ni(OAc)₂ · 4H₂O in the presence of NEt₃ as a base in 71–75% yield. The copper complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Cu(II) (3a), {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Cu(II) (3b) and {2-[1-(2-methylphenylimino)ethyl]phenoxy}₂Cu(II) (3c) were synthesized analogously by the reactions of the ligands 1a, 1b and 1c with Cu(OAc)₂ · H₂O in 70–87% yield. The molecular structures of the nickel and copper complexes 2a, 2b, 3a, 3b and 3c have been determined by X-ray diffraction studies. Structural comparisons revealed that the nickel centers in 2a and 2b are in square planar geometries while the geometry around the copper varied from being square planar in 3a and 3c to distorted square planar in 3b. The catalysis studies revealed that while the copper complexes 3a, 3b and 3c efficiently catalyze ring-opening polymerization (ROP) of l-lactide at elevated temperatures under solvent-free melt conditions, producing polylactide polymers of moderate molecular weights with narrow molecular weight distributions, the nickel counterparts 2a and 2b failed to yield the polylactide polymer.     

Chloride-bridged Ni(II) complexes with ferromagnetic exchange interaction from thiazoline hydrazone derivative ligands

A novel ligand 2-acetyl-2-thiazoline acetylhydrazone (ATHAc) and two new chloride-bridged dimeric nickel(II) complexes containing thiazoline hydrazone derivative ligands, [{Ni(ATsc)(MeOH)}₂(μ-Cl)₂]Cl₂ (1) (ATsc = 2-acetyl-2-thiazoline semicarbazone) and [{Ni(ATHAc)(H₂O)}₂(μ-Cl)₂]Cl₂ (2), were prepared and structurally characterized by elemental analysis, single crystal X-ray diffraction, IR and UV–Vis spectroscopy. In addition, NMR spectroscopy for ATHAc and magnetic susceptibility measurements for nickel complexes were performed. The structure of nickel(II) complexes consists of dimeric molecules in which nickel ions are bridged by two chloride ligands. The coordination geometry around each nickel ion can be described as a distorted octahedron with each nickel atom coordinated to one thiazoline nitrogen atom, one imine nitrogen atom, one carbonyl oxygen atom, one oxygen atom (from a methanol molecule in 1 and from a water molecule in 2) and two bridge chloride ligands. The variable temperature magnetic susceptibility measurements of the complexes show the ferromagnetic behaviour in the solid state (J = 5.7(2) cm⁻¹ in 1; 6.6(3) cm⁻¹ in 2).     

Synthesis,molecular and crystalline architectures,and magnetic properties of neutral nickel(II)dicyanamide coordination polymers containing a symmetrical/unsymmetrical 1,2-diamine as an end-capping ligand

Two neutral nickel(II) coordination polymers [Ni(en)(dca)₂]_n (1) and [Ni(dmen)(dca)₂]_n (2) (en = ethylenediamine; dmen = N,N-dimethylethylenediamine; dca = dicyanamide) have been synthesized and X-ray crystallographically characterized. Each nickel(II) center in 1/2 adopts a distorted octahedral coordination environment with a NiN₆ chromophore ligated by two amine N atoms of the bidentate amine (en/dmen) and four nitrile N atoms of μ_1,5 bridged dca. The metal(II) centers are connected with each other through single μ_1,5 M–NCNCN–M bridges, resulting in a 2D layer structure with a (4,4) topology in 1 and a 3D network of topology (6,6) in 2. Multiple lateral N–H···N and C–H···N hydrogen bondings promote dimensionality. The magnetic susceptibility results of 1 and 2 at very low temperature support the zero-field splitting effect of the nickel(II) ions.     

Metal complexes derived from hydrazoneoxime ligands: III – Synthesis,characterization and electrospray ionization mass spectra of some nickel(II) complexes with aroylhydrazoneoximes

Five binuclear nickel(II) complexes [{Ni(L-R)}₂] derived from diacetylmonooxime aroylhydrazones (H₂L-R) have been prepared and characterized. In these complexes the oximate group functions as a bridge between the two nickel(II) ions. The corresponding octahedral bisligand complexes [Ni(HL-R)₂] have been also prepared and characterized. Reaction of [{Ni(L-R)}₂] with excess pyrazole (HPyr) afforded square planar [Ni(L-R)HPyr] complexes. The structure of [Ni(L-H)HPyr] (11), [Ni(L-CH₃O)HPyr] (13) and [Ni(L-Cl)HPyr] (14) have been determined by single-crystal X-ray diffraction. In these complexes, the Ni(II) is coordinated to the oximate nitrogen, hydrazone nitrogen and enolimine oxygen of the aroylhydrazoneoxime ligand, the fourth coordination site is occupied by pyrazole nitrogen. In 11 and 13 the molecular units are linked together by intramolecular NH?O hydrogen bonds forming a helical chain propagating along a and b axis respectively. The helical structure is stabilized by CH?O, CH?π and π?π noncovalent interactions. The structure of 14 consists of two independently crystallographic molecular units. The Ni1 molecular units are assembled together by CH?O and CH?Cl1 interactions forming a two dimensional sheet, while the Ni2 units are jointed together by CH?O and CH?C interactions forming a chain extending along b-axis which are enclosed between sheets of Ni1 units.     

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.     

2-Oxazoline/benzoxazole-1,10-phenanthrolinylmetal (iron, cobalt or nickel) dichloride: Synthesis, characterization and their catalytic reactivity for the ethylene oligomerization

Series of 2-benzoxazole-1,10-phenanthrolines (L1-L4) and 2-oxazoline-1,10-phenanthrolines (L5-L8) were synthesized and used as tridentate N^N^N ligands in coordinating with metal (nickel, cobalt or iron) chlorides. Their metal complexes, nickel(II) (Ni1-Ni8), cobalt(II) (Co1-Co8) and iron(II) (Fe1-Fe8), were characterized by elemental and IR spectroscopic analyses. The molecular structures of the ligand L2 and the complexes Ni3, Co1, Co3 and Fe2 have been determined by the single-crystal crystallography. The nickel complex Ni3 and iron complex Fe2 display an octahedral geometry, whereas cobalt complex Co1 is with a distorted bipyramidal geometry and Co3 as square pyramidal geometry. At 10 atm ethylene, all the complexes showed good activities in ethylene dimerization upon activation with appropriate aluminum cocatalysts; the nickel complexes gave the activity up to 3.11 × 10⁶ g mol⁻¹(Ni) h⁻¹ upon activation with diethylaluminum chloride (Et₂AlCl), meanwhile the cobalt and iron complexes showed activities up to 1.51 × 10⁶ g mol⁻¹(Co) h⁻¹ and 1.89 × 10⁶ g mol⁻¹(Fe) h⁻¹, individually, upon activation with modified methylaluminoxane (MMAO).     

A new type of chiral porphyrin: Organopalladium porphyrins with chiral chelating diphosphine ligands

Peripherally palladated Ni(II) porphyrins have been prepared using enantiopure chiral chelating diphosphines as supporting ligands on the attached Pd(II) fragment. Both enantiomers of the following complexes have been obtained in good yields, using oxidative addition of the bromoporphyrin starting material 5-bromo-10,20-diphenylporphyrinatonickel(II) (NiDPPBr (1)) to the [Pd⁰L] complex generated in situ from Pd₂dba₃ and the chiral ligand L: [PdBr(NiDPP)(CHIRAPHOS)] (2a,b) [CHIRAPHOS = 2,3-bis(diphenylphosphino)butane], [PdBr(NiDPP)(Tol-BINAP)] (3a,b) [Tol-BINAP) = 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] and [PdBr(NiDPP)(diphos)] [diphos = 1,2-bis(methylphenylphosphino)benzene] (4a,b). The induced asymmetry in the porphyrin was readily detected by ¹H NMR and CD spectroscopy. The porphyrin chiroptical properties are strongly dependent upon the structure of the chiral ligand, such that a monosignate CD signal, and symmetric and asymmetric exciton couplets were observed for 4a, 2b, and 3a,b, respectively.     

Self-assembly of 1D coordination polymers from nickel(II) tetraaza macrocycle and carboxylate ligands

Reactions of [Ni(L)]Cl₂ · 2H₂O (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with isophthalic acid (H₂isoph) and 1,3,5-cyclohexanetricarboxylic acid (H₃chtc) yield the 1D nickel(II) complexes {[Ni(L)(isoph)] · 3H₂O}_n (1) and {[Ni(L)(H-chtc)] · H₂O}_n (2). The structures were characterized by X-ray crystallography, spectroscopic and magnetic susceptibility. The crystal structures of the 1D chain compounds 1 and 2 show an elongated distorted octahedron about each nickel(II) ion. The magnetic behavior of two compounds exhibits weak intrachain antiferromagnetic interaction with J values of −0.93 cm⁻¹ for 1 and −1.28 cm⁻¹ for 2. The electronic spectra of the complexes are significantly affected by the nature of the carboxylate ligands.     

Acetamidine complexes as catalysts for ethylene polymerization

The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine (1a) and N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine (1b), and N,N′-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine (2), respectively. The addition of isomers (1a + 1b) to nickel (II) dibromide 2-methoxyethyl ether, (NiBr₂[O(C₂H₄OMe)₂]) gives a mixture of new nickel complexes, [NiBr₂{N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and [NiBr₂{N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N′-(2,6-dimethyl)-acetamidine}] (3b). Similarly, ligand 2 reacts with nickel (II) dibromide 2-methoxyethyl ether to afford the complex [NiBr₂{N,N´-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine}] (4). The structures of the ligands and nickel complexes have been determined by single crystal X-ray diffraction.The addition of MAO to these complexes generates catalytically active species for the homopolymerization of ethylene. The polymer products are high molecular weight (80-169 K). At temperatures of up to 60 °C both catalysts are a single site giving a monomodal molecular weight distribution. However, at 70 °C the mixture (3a + 3b) shows a bimodal molecular weight distribution.     

Structural and magnetic properties of metal complexes with pyridine-2,6-dicarboxylate and 5-(4-bromophenyl)-2,4′-bipyridine

A series of complexes has been synthesized based on pyridine-2,6-dicarboxylate (L1) as the bridging ligand and 5-(4-bromophenyl)-2,4′-bipyridine (L2) as the pendant with different metal ions such as Ni^II, Co^II, and Cu^II, under hydrothermal conditions. In nickel and cobalt complexes [M(L1)(L2)₂ · H₂O]_n (M = Ni²⁺ or Co²⁺), the metal ions are bridged by L1 to form 1D coordination zigzag polymeric chains with L2 pendants possessing hexa-coordinated distorted octahedral geometries. While the copper ions are penta-coordinated by L1 and L2 with distorted square pyramidal geometries forming the tetranuclear cluster with the formula [Cu₄(L1)₄(L2)₄] · 2H₂O. It has been found that both the structure and magnetic property of these complexes are metal ions dependent. Intramolecular antiferromagnetic interactions were observed in the nickel and cobalt 1D coordination polymers, while ferromagnetic coupling was found in the tetranuclear copper cluster. Density functional theory calculations suggested that the O–C–O bridges of L1 in a basal–apical mode are responsible for intracluster intermetallic ferromagnetic exchange for the tetranuclear copper cluster.     

Crystal structure, spectroscopy and magnetism of trinuclear nickel(II), cobalt(II) complexes and their solid solution

Four new complexes [Ni₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (1), [Co₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (2), [Ni₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (3), [Co₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (4) (L = 4-amino-3,5-dimethanyl-1,2,4-triazole) were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 and 2 are isomorphous; complex 3 and 4 are isomorphous. Four complexes all consist of the linear trinuclear cations ([M₃(μ-L)₆(H₂O)₆]⁶⁺ (M = Ni,Co) for 1 and 2; [M₃(μ-L)₆(H₂O)₄(CH₃OH)₂]⁶⁺ (M = Ni,Co) for 3 and 4), NO₃⁻ anions and crystallized water molecules. In the trinuclear cations, the central M(II) ions and two terminal M(II) ions are bridged by three triazole ligands. Other eleven solid solution compounds which are isomorphous with complex 3 and 4 were obtained by using different ratio of Ni(II) and Co(II) ions as reactants and ICP result indicates that ligand L has higher selectivity of Ni(II) ions than that of Co(II) ions. The magnetic analysis was carried out by using the isotropic spin Hamiltonian ? = −2J(?₁?₂ + ?₂?₃) (for complexes 1 and 3) and simultaneously considering the temperature dependent g factor (for complexes 2 and 4). Both the UV-Vis spectra and the magnetic properties of the solid solutions can be altered systematically by adjusting the Co(II)/Ni(II) ratio.     

Novel octahedral nickel(II) dithiocarbamates with bi- or tetradentate N-donor ligands: X-ray structures of [Ni(Bzppzdtc)(phen)2]ClO4 · CHCl3 and [Ni(Bz2dtc)2(cyclam)]

A series of novel octahedral nickel(II) dithiocarbamate complexes involving bidentate nitrogen-donor ligands (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) or a tetradentate ligand (cyclam = 1,4,8,11-tetraazacycloteradecane) of the composition [Ni(BzMetdtc)(phen)₂]ClO₄ (1), [Ni(Pe₂dtc)(phen)₂]ClO₄ (2), [Ni(Bzppzdtc)(phen)₂]ClO₄ · CHCl₃ (3), [Ni(Bzppzdtc)(phen)₂](SCN) (4), [Ni(BzMetdtc)(bpy)₂]ClO₄ · 2H₂O (5), [Ni(Pe₂dtc)(cyclam)]ClO₄ (6), [Ni(BzMetdtc)₂(cyclam)] (7), [Ni(Bz₂dtc)₂(cyclam)] (8) and [Ni(Bz₂dtc)₂(phen)] (9) (BzMetdtc = N,N-benzyl-methyldithiocarbamate(1-) anion, Pe₂dtc = N,N-dipentyldithiocarbamate(1-) anion, Bz₂dtc = N,N-dibenzyldithiocarbamate(1-) anion, Bzppzdtc = 4-benzylpiperazinedithiocarbamate(1-) anion), have been synthesized. Spectroscopic (electronic and infrared), magnetic moment and molar conductivity data, and thermal behaviour of the complexes are discussed. Single crystal X-ray analysis of 3 and 8 confirmed a distorted octahedral arrangement in the vicinity of the nickel atom with a N₄S₂ donor set. They represent the first X-ray structures of such type complexes. The catalytic influence of complexes 2, 3, 6, and 7 on graphite oxidation was studied and discussed.     

Synthesis and structural characterization of Ni(II) complexes containing a heterocyclic NO donor ligand

Five novel nickel(II) complexes have been successfully synthesized with a heterocyclic ligand, Opdac, [Ni(Opdac)₂]Cl₂ (1), [Ni(Opdac)₂(CH₃OH)₂]Br₂(CH₃OH)₂ (2), [Ni(Opdac)₂]I₂ (3), [Ni(Opdac)₂NO₃]NO₃ (4) and [Ni(Opdac)₂ClO₄]ClO₄ (5) where Opdac = 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3-one. All the complexes were characterized by elemental analysis, molar conductivity, CHN analysis, magnetic susceptibility measurements, spectroscopic studies and TG/DTA methods. In all the complexes, Opdac acts as a bidentate ligand coordinating to Ni(II) ion via the benzimidazole imine nitrogen and the pyrazolone oxygen atoms. The complexes 1 and 3 have a tetrahedral geometry while 2, 4 and 5 have an octahedral geometry around the Ni(II) center.     

Synthesis and crystal structure of two new heteropolynuclear [NiCdCdNi] and [NiCdNi] Schiff base complexes involving bridging chlorine and oxygen functions

Two new heteropolynuclear Schiff base complexes, [Ni₂Cd₂L₂Cl₂(μ-Cl)₂] (1) and [Ni₂CdL′₂Cl(H₂O)]ClO₄·H₂O (2) where L = [N,N′-bis(2-hydroxyacetophenylidene)]propane-1,2-diamine and L′ = [N,N′-bis(2-hydroxypropiophenylidene)]propane-1,2-diamine, have been synthesized by refluxing equimolar amounts of nickel perchlorate, cadmium chloride and the respective tetradentate Schiff base ligand, H₂L or H₂L′ in methanol medium. The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies on 1 reveal the presence of a bis(heterodinuclear) [Ni^IICd^II]₂ unit in which the two central cadmium ions are doubly chloro-bridged with each other and each of them is connected to a nickel(II) center through two phenolate oxygen bridges. In contrast, complex 2 contains a heterotrinuclear [Ni^IICd^IINi^II] unit in which the central cadmium ion is connected to two nickel(II) centers through two doubly bridging phenolate oxygen atoms. The Cd(II) ions in 1 and 2 adopt distorted, square pyramidal (CdO₂Cl₃) and octahedral (CdO₅Cl) geometries respectively. On the other hand, the Ni(II) ions in both 1 and 2 assume the same coordination geometry, i.e. a distorted square planar (NiO₂N₂) arrangement. Intermolecular C-H?Cl or O-H?Cl and O-H?O hydrogen bonding interactions are operative in the complexes to build up 2D supramolecular structures in their solid states.     

Structural variations in self-assembled cadmium benzoate complexes

A series of mixed ligand cadmium(II) complexes having 3,5-dimethylpyrazole and aromatic carboxylate are structurally characterized. The effect of substituent on aromatic ring and also the effect of composition on co-ordination behavior of these complexes are ascertained. Hydrogen bonded self-assembled mononuclear complexes are obtained from composition [Cd(L)₂(L_a)₂] where L_a = 3,5-dimethylpyrazole L = R–C₆H₄COO– [R = H (1), 2-Cl (2), 4-OH (3), 2-OH (4)]. The cadmium complex (5) having composition [Cd(L)₂(L_a)(H₂O)] (L = 2-NO₂–C₆H₄COO–) is tetra-nuclear. The complex has eight and six co-ordination around cadmium and self-assembles through hydrogen bonding leading to form extended chain structure. The four complexes (1–4) have six co-ordinated trigonal prismatic geometry around cadmium ions. Cadmium complexes having composition [Cd(L)₂(L_a)] such as R = 4-NO₂ (6), 4-Cl (7), and 1-naphthoate complex (8) are co-ordination polymers with seven co-ordination geometry around cadmium. In these co-ordination polymers different Cd–Cd distances are observed for alternate pair of cadmium ions. For example in the case of the co-ordination polymer of 4-nitro-benzoate complex the Cd–Cd distance between alternate pairs are 4.138 Å, and 3.748 Å. The 1-naphthoate complex having pyridine has composition [Cd(L)₂(L_b)₂](H₂O)] (9) where L_b = pyridine and L = 1-naphthoate has seven co-ordination with a distorted pentagonal bipyramid geometry.     

Synthesis,spectral, and structural investigation of [ML(NO3)2]: M = Co,Ni, Cu; L = N-(2-pyridylethyl)pyridine-2-methylketimine

Synthesis and structural characterization of distorted pentagonal bipyramidal Co(II), pseudo-octahedral Ni(II) and Cu(II) complexes of the type [ML(NO₃)₂], {L = N-(2-pyridylethyl)pyridine-2-methylketimine} are reported. Characterization includes elemental analysis, spectral, magnetism, and X-ray crystallographic studies. In case of cobalt (1) both the nitrates coordinate in bidentate fashion resulting overall distorted pentagonal bipyramidal geometry. In nickel (2) and copper (3) complexes, bivalent metal ion is coordinated by the three nitrogen atoms of the tridentate L with two pyridine-N occupying trans positions and amongst the two nitrates one coordinates in a bidentate fashion while other adopts a monodentate fashion. All the complexes exhibit d–d transitions in the visible region. Complex 1 is high-spin in nature and the X-band EPR spectra of 1, and 3 at room temperature and 77 K are reported.     

Co(II), Ni(II) and Zn(II)-orotate complexes with N-methylimidazole: Synthesis, crystal structures and antimicrobial activities

Three Co(II), Ni(II) and Zn(II) complexes of orotate with the N-methylimidazole ligand were synthesized and characterized by means of elemental and thermal analysis, magnetic susceptibilities, IR, UV-Vis spectroscopic and antimicrobial activity studies. The crystal structures of [Co(HOr)(H₂O)₂(Nmeim)₂]₃·H₂O (1), [Ni(HOr)(H₂O)₂(Nmeim)₂] (2) and [Zn(HOr)(H₂O)(Nmeim)₂] (3) were determined by the single crystal X-ray diffraction technique (H₃Or = orotic acid and Nmeim = N-methylimidazole). In complexes 1 and 2, the Co(II) and Ni(II) ions have distorted octahedral geometries with two Nmeim, one orotate and two aqua ligands. Complex 3 has a distorted trigonal bipyramidal geometry with two N-methylimidazole, one orotate and one aqua ligands. In the complexes, the orotate is coordinated to the metal(II) ions through the deprotonated nitrogen atom of the pyrimidine ring and the oxygen atom of the carboxylate group as a bidentate ligand. The complexes form a three-dimensional framework by hydrogen bonding, C-H?π and π?π stacking interactions. The MIC values of the complexes against selected microorganisms were determined to be in range 300-2400 μg/mL.     

Pyrazolyl iron, cobalt, nickel, and palladium complexes: synthesis, molecular structures, and evaluation as ethylene oligomerization catalysts

Reactions of [2-(3,5-dimethyl-pyrazol-1-yl)-ethanol] (L1) and [1-(2-chloro-ethyl)-3,5-dimethyl-1H-pyrazole] (L2) with Fe(II), Co(II), Ni(II), and Pd(II) salts gave the complexes [(L1)₂FeCl₂] (1), [(L1)₂CoCl₂] (2), [(L1)₂NiBr₂] (3), [(L1)₂Pd(Me)Cl] (5), [(L2)₂CoCl₂] (6), and [(L2)₂NiBr₂] (7). Whereas L2 behaves as a monodentate ligand, L1 can behave as either a monodentate or bidentate ligand depending on the nature of the metal centre. For palladium, L1 is monodentate in the solid state structure of 5 but bidentate in the structure of 4, obtained during attempts to crystallize 3. While the activation of iron, cobalt and palladium complexes with EtAlCl₂ did not produce active ethylene oligomerization catalysts, the nickel complexes 3 and 7 produced active ethylene oligomerization catalysts. Activities as high as 4329 kg/mol Ni h were obtained. Catalyst 3 produced mainly butenes (57%) and hexenes (43%); of which a combined 20% were converted to Friedel-Crafts alkylated-toluene. Catalyst 7, on other hand, produced mainly butenes (90%) and small amounts of hexenes (10%) which were then completely converted to the corresponding Friedel-Crafts alkylated-toluene products. This difference in product distribution in catalysis performed by complexes 3 and 7 is indicative of the role of the OH functionality in L1 on the EtAlCl₂ co-catalysts.     

Nickel(II) complexes bearing phosphinooxazoline ligands: Synthesis, structures and their ethylene oligomerization behaviors

A series of Ni(II) complexes 4a-f ligated by the unsymmetrical phosphino-oxazolines (PHOX) were synthesized and characterized by elemental analysis and IR spectroscopy, and the structures of complexes 4c-4e were confirmed by the X-ray crystallographic analysis. All derivatives showed distorted tetrahedron geometry by the nickel center and coordinative atoms. Upon activation with methylaluminoxane (MAO) or Et₂AlCl, these complexes exhibited considerable to high activity of ethylene oligomerization. The ligands environments and reaction conditions significantly affect their catalytic activities, while the highest oligomerization activity (up to 1.18 × 10⁶ g · mol⁻¹(Ni) · h⁻¹) was observed for 4d at 20 atm of ethylene. Incorporation of 2-4 equivalents of PPh₃ as auxiliary ligands in the 4a-f/MAO catalytic systems led to higher activity and longer catalytic lifetime.     

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.