Synthesis and characterization of 2-(2-benzhydrylnaphthyliminomethyl)pyridylnickel halides: formation of branched polyethylene

A series of 2-(2-benzhydrylnaphthyliminomethyl)pyridine derivatives (L1–L3) was prepared and used to synthesize the corresponding bis-ligated nickel(II) halide complexes (Ni1–Ni6) in good yield. The molecular structures of representative complexes, namely the bromide Ni3 and the chloride complex Ni6, were confirmed by single crystal X-ray diffraction, and revealed a distorted octahedral geometry at nickel. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all nickel complex pre-catalysts exhibited high activities (up to 2.02 × 10⁷ g(PE) mol⁻¹(Ni) h⁻¹) towards ethylene polymerization, producing branched polyethylene of low molecular weight and narrow polydispersity. The influence of the reaction parameters and the nature of the ligands on the catalytic behavior of the title nickel complexes were investigated

2-{2,6-Bis[bis(4-fluorophenyl)methyl]-4-chlorophenylimino} -3-aryliminobutylnickel(II) bromide complexes: Synthesis, characterization, and investigation of their catalytic behavior

The series of 2-{2,6-bis[di(4-fluorophenyl)methyl]-4-chlorophenylimino}-3- aryliminobutane derivatives (L1-L5) and their nickel(II) dibromide complexes (Ni1-Ni5) were synthesized, and all organic compounds were fully characterized by the Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis, while the nickel complexes were characterized by FT-IR spectroscopy, elemental analysis, as well as by single-crystal X-ray diffraction for two representative examples, namely Ni1 and Ni4. A distorted tetrahedral geometry was observed for these four-coordinate nickel complexes. Upon the activation with either Methylaluminoxane or modified methylaluminoxane as co-catalyst, all nickel complex precatalysts showed very high activity toward ethylene polymerization with activities of up to 10 7 g(PE)·mol -1 (Ni)·h -1 , and afforded highly branched polyethylene with a bimodal distribution. © 2014 Elsevier B.V

Beneficial influence of nanocarbon on the aryliminopyridylnickel chloride catalyzed ethylene polymerization

A series of 1-aryliminoethylpyridine ligands (L1―L3) was synthesized by condensation of 2-acetylpyridine with 1-aminonaphthalene, 2-aminoanthracene or 1-aminopyrene, respectively. Reaction with nickel dichloride afforded the corresponding nickel (II) chloride complexes (Ni1–Ni3). All compounds were fully characterized and the molecular structures of Ni1 and Ni3 are reported. Upon activation with methylaluminoxane (MAO), all nickel complexes exhibit high activities for ethylene polymerization, producing waxes of low molecular weight and narrow polydispersity. The presence of multi-walled carbon nanotubes (MWCNTs) or few layer graphene (FLG) in the catalytic medium can lead to an increase of productivity associated to a modification of the polymer structure

Reversible H_2 Addition across a Nickel−Borane Unit as a Promising Strategy for Catalysis

We report the synthesis and characterization of a series of nickel complexes of the chelating diphosphine-borane ligands ArB(o-Ph_2PC_6H_4)_2 ([^(Ar)DPB^(Ph)]; Ar = Ph, Mes). The [^(Ar)DPB^(Ph)] framework supports pseudo-tetrahedral nickel complexes featuring η^2-B,C coordination from the ligand backbone. For the B-phenyl derivative, the THF adduct [^(Ph)DPB^(Ph)]Ni(THF) has been characterized by X-ray diffraction and features a very short interaction between nickel and the η^2-B,C ligand. For the B-mesityl derivative, the reduced nickel complex [^(Mes)DPB^(Ph)]Ni is isolated as a pseudo-three-coordinate “naked” species that undergoes reversible, nearly thermoneutral oxidative addition of dihydrogen to give a borohydrido-hydride complex of nickel(II) which has been characterized in solution by multinuclear NMR. Furthermore, [^(Mes)DPB^(Ph)]Ni is an efficient catalyst for the hydrogenation of olefin substrates under mild conditions

Metal complexes as potential ligands : the deprotonation of aminephenolate metal complexes

The cationic nickel, copper and zinc complexes of tris-(2-hydroxybenzyl)-aminoethylamine (H6TrenSal) have been deprotonated using potassium hydroxide. The nickel complex can be sequentially deprotonated to form a series of compounds namely, [(H6TrenSal)Ni]+, [(H6TrenSal)Ni] and "[(H6TrenSal)Ni]K". The latter is isolated as a mixture of species namely [{(H6TrenSal)Ni}K(EtOH)]2, [{(H6TrenSal)Ni}K(EtOH)2-μ-OH2]2 and [{(H6TrenSal)Ni}K(EtOH)2-μ-EtOH]2, which co-crystallise in a roughly 50:27.5:22.5 ratio. In contrast the deprotonation of [(H6TrenSal)M]+ (M = Cu, Zn) results in the formation of tetrameric complexes [({(H6TrenSal)Ni}K(OH2)2)4(μ4-OH2)]

Synthesis and C−C Coupling Reactivity of a Dinuclear Ni^I−Ni^I Complex Supported by a Terphenyl Diphosphine

Mono- and bimetallic complexes of nickel supported by a terphenyl diphosphine have been synthesized. The reported complexes show diverse metal−arene interactions in the solid state. Reactions of an o,o′-biphenyldiyl dinickel complex with CO and dichloroalkanes lead to fluorene derivatives, indicating the formation of carbon−carbon bonds at a bimetallic moiety

Synthesis, characterization and ethylene polymerization behaviour of binuclear nickel halides bearing 4,5,9,10-tetra(arylimino)pyrenylidenes

Pyrene-4,5,9,10-tetraone was prepared via the oxidation of pyrene, and reacted with various anilines to afford a series of 4,5,9,10-tetra(arylimino)pyrenylidene derivatives (L1–L4). The tetraimino-pyrene compounds L1 and L2 were reacted with two equivalents of (DME)NiBr₂ in CH₂Cl₂ to afford the corresponding dinickel bromide complexes (Ni1 and Ni2). The organic compounds were fully characterized, whilst the bi-metallic complexes were characterized by FT-IR spectra and elemental analysis. The molecular structures of representative organic and nickel compounds were confirmed by single-crystal X-ray diffraction studies. These nickel complexes exhibited high activities towards ethylene polymerization in the presence of either MAO or Me₂AlCl, maintaining a high activity over a prolonged period (longer than previously reported dinickel complex pre-catalysts). The polyethylene obtained was characterized by GPC, DSC and FT-IR spectroscopy and was found to possess branched features

Nickel-Mediated Hydrogenolysis of C–O Bonds of Aryl Ethers: What Is the Source of the Hydrogen?

Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)aryl methyl ethers. A Ni(0) complex containing Ni–arene interactions adjacent to the aryl–O bond was isolated. Heating led to aryl–O bond activation and generation of a nickel aryl methoxide complex. Formal β-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving β-H elimination from a nickel alkoxide rather than cleavage of the Ni–O bond by H_2

Ni(II) binding to the Human Tool Like Receptor (HTLR4)

Nickel allergy is the most frequent cause of contact hypersensitivity (burning, redness, itching, swelling and even blisters) in industrialized countries, with 30% of population being affected. Contact allergy is commonly induced by nickel ions present in nickel-containing jewelry such as rings and earrings, as well as in nickel-containing cellular telephones. Ni(II) seems to trigger an inflammatory response by activating human Toll-like-Receptor 4 (hTLR4) [1-4]. Species-specific activation, as in this case, requires distinct sequence motifs that are present in humans but not in mouse, a species not sensitive to nickel-induced allergies. A sequence containing three histidine residues, H431, and the non-conserved H456 and H458, localized in the C-terminus, could be identified as the specific region of human TLR4 responsible for nickel responses. It has been proposed that the imidazole side chain of the histidine residues H456 and H458 may provide a potential binding site for this metal because they are located at an optimal distance to interact with Ni(II) ions, whereas H431 is located further apart. The aim of our research was to verify the possibility of metal binding to the sequence containing the three histidines supposedly involved in nickel response. The chosen segment was the 32aa peptide FQH431SNLKQMSEFSVFLSLRNLIYLDISH456TH458TR, which was studied in order to understand both its binding properties and the thermodynamic stability of its metal complexes. Formation equilibria of Ni(II) complexes have been investigated in aqueous solution and in a wide pH range. Protonation and complex-formation constants have been potentiometrically determined; complex-formation models and species stoichiometry have been checked by means of UV-Vis absorption and CD spectroscopy and investigation through multidimensional and eteronuclear NMR spectroscopy. The predominant species for a 1:1 peptide/Ni(II) molar ratio was obtained at physiological pH and showed an effective binding of the metal to the target sequence