Pyridinecarboxamidato−Nickel(II) Complexes

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.

Ni(ii) complexes bearing pyrrolide-imine ligands with pendant N-, O- and S-donor groups: synthesis, structural characterization and use in ethylene oligomerization

Nickel complexes bearing pyrrolide-imine ligands with pendant N-, O- and S-donor groups have been synthesized and their catalytic behavior in ethylene oligomerization has been investigated.

Well-defined phosphino-phenolate neutral nickel(ii) catalysts for efficient (co)polymerization of norbornene and ethylene

With B(C₆F₅)₃as a singular cocatalyst, a series of phosphino-phenolate neutral nickel catalysts were found to be highly efficient for norbornene (co)polymerization. High molecular weight (co)polymers with good solubility in common organic solvents were obtained.

Targeting polyethylene waxes: 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridylnickel halides and their use as catalysts for ethylene polymerization

The title complexes exhibited high activities toward ethylene polymerization, producing branched polyethylene waxes.

8-(2-Cycloalkylphenylimino)-5,6,7-trihydro-quinolylnickel halides: polymerizing ethylene to highly branched and lower molecular weight polyethylenes

Cycloalkyl-modified 8-arylimino-5,6,7-trihydroquinolylnickel pre-catalysts highly polymerize ethylene into branched polyethylene waxes.

Ethylene polymerization by 2-iminopyridylnickel halide complexes: synthesis, characterization and catalytic influence of the benzhydryl group

A series of 2-(2-benzhydrylbenzenamino)pyridine ligands (L1–L13) was synthesized and used as bidentate N^N ligands with nickel halides to afford the corresponding nickel dihalide complexes L(2)Ni(2)Cl(4) C1–C13 and L(2)NiBr(2) D1–D13. All ligands and complexes were characterized by IR and NMR spectroscopy, and by elemental analysis. The molecular structures of the representative complexes C1·2CH(3)OH, C5·2H(2)O, D4, D7 and D9 were confirmed by single-crystal X-ray diffraction studies. Upon activation with either methylaluminoxane (MAO) or ethylaluminium sesquichloride (Et(3)Al(2)Cl(3), EASC), these nickel pre-catalysts exhibited high activities (up to the range of 10(7) g mol(-1) (Ni) h(-1)) towards ethylene polymerization, producing branched polyethylenes with narrow polydispersity.

Synthesis and characterization of an unsymmetrical cobalt(III) active site analogue of nitrile hydratase

The design, synthesis, and characterization of an unsymmetrical diamidato-dithiol ligand (H(4) 1, where the hydrogen atoms represent deprotonatable amide and thiol protons) and its cobalt(III) complex, a synthetic analogue of the cobalt-containing nitrile hydratase enzyme family, are reported. The ligand was prepared in 24% yield from an overall eight-step synthetic pathway following a modified protocol established in our laboratory that includes two peptide couples using O-(1H-benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate as the coupling agent. The ligand and all precursors were characterized by NMR spectroscopy and elemental analysis. The cobalt nitrile hydratase synthetic analogue complex [NBu(4)][Co(1)] was prepared on deprotonating ligand H(4) 1 to [1](4-) on addition of 5 equiv of NaH in N,N-dimethylformamide and adding 1 equiv of CoCl(2) at -40 °C under a N(2) atmosphere followed by oxidizing the complex by stirring it overnight open to dry air. The complex [NBu(4)][Co(1)] was isolated after counterion exchange with 1 equiv of NBu(4)Cl followed by crystallization from MeCN/Et(2)O in 71% yield. The structure of the complex was confirmed by X-ray diffraction analysis. Cyclic voltammetry studies on [NBu(4)][Co(1)] in a 0.1 M [NBu(4)][PF(6)]/MeCN solution showed a quasi-reversible reduction potential at -1.1 V (vs. Ag/AgCl), and magnetic susceptibility investigations indicated the complex is paramagnetic in both the solid and the solution states as determined from inverse-Gouy and Evans NMR methods, respectively.

2-(1H-2-Benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylnickel Complexes: Synthesis, Characterization, and Ethylene Oligomerization

A series of tridentate N,N,N-nickel complexes bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines was synthesized and characterized by elemental and IR spectroscopic analysis. The molecular structures of representative complexes were determined by single-crystal diffraction, and these were found to have a six-coordinate distorted octahedral geometry around the Ni centre. On treatment with Et2AlCl, all nickel complexes exhibited good catalytic activities up to 106 g mol–1(Ni) h–1 for ethylene oligomerization with major dimerization. The steric and electronic effects on catalytic activities of metal complexes as well as the influence of various reaction parameters were carefully investigated.

Alpha-iminocarboxamidato nickel complexes

Polyolefins constitute a vast class of macromolecules that range from everyday plastics to sophisticated materials used as hip-replacement joints and in bulletproof vests. By tailoring the molecular structure of the backbone, researchers can tune the bulk properties of these materials for specific product applications. Transition-metal complexes that mediate the polymerization of ethylene, 1-alkenes, and related monomers provide an important tool for industrial preparation. Although commercially viable options exist for large-scale manufacturing, it is not possible to achieve all desirable polymer targets using these methods. For example, the copolymerization of ethylene with co-monomers bearing polar functionalities under living conditions, where there is high activity and minimum chain transfer and termination, is not available at this scale. Also, given the magnitude of polyolefin production, we anticipate a need to more efficiently manage chemical resources. For these reasons, new metal/catalyst combinations and methods for their applications continue to be an active area of research in both academic and industrial laboratories. This Account focuses on the chemistry of alpha-iminocarboxamidato complexes of nickel carried out in our laboratories. Such complexes can serve as precursors to zwitterionic or neutral active species, depending upon the mode of activation. We have successfully applied the zwitterionic systems in the tandem action of multiple active sites to yield branched polyethylene from ethylene alone; a coordinated effort of catalysts that is reminiscent of metabolic pathways. These polymerizations show many of the characteristics of living polymerizations. The neutral initiators allow for the controlled preparation of copolymers containing ethylene and functionalized co-monomers and can be used to access higher order polymer architectures, such as block, tapered, and pseudo-tetrablock copolymers. Many of these polymers are not readily available using other catalytic methods. In this Account, we first provide a historical narrative of developments leading to ligands derived from the alpha-iminocarboxamide framework. Second, we explore how structural variations of this ligand system are readily obtained and how they can be used to provide insight into the mechanism of activation and for controlling polymerization reactions. We conclude by describing emerging applications, particularly in the area of graft copolymers.