Pyrazolylimine iron and cobalt, and pyrazolylamine nickel complexes: Synthesis and evaluation of nickel complexes as ethylene oligomerization catalysts

Nickel Catalyzed Olefin Oligomerization and Dimerization

Brought to life more than half a century ago and successfully applied for high-value petrochemical intermediates production, nickel-catalyzed olefin oligomerization is still a very dynamic topic, with many fundamental questions to address and industrial challenges to overcome. The unique and versatile reactivity of nickel enables the oligomerization of ethylene, propylene, and butenes into a wide range of oligomers that are highly sought-after in numerous fields to be controlled. Interestingly, both homogeneous and heterogeneous nickel catalysts have been scrutinized and employed to do this. This rare specificity encouraged us to interlink them in this review so as to open up opportunities for further catalyst development and innovation. An in-depth understanding of the reaction mechanisms in play is essential to being able to fine-tune the selectivity and achieve efficiency in the rational design of novel catalytic systems. This review thus provides a complete overview of the subject, compiling the main fundamental/industrial milestones and remaining challenges facing homogeneous/heterogeneous approaches as well as emerging catalytic concepts, with a focus on the last 10 years.

Ni-Based Complexes in Selective Ethylene Oligomerization Processes

Linear alpha-olefins are widely used in the petrochemical industry and the world demand for these compounds increases annually. At present, the main method for producing linear alpha-olefins is the homogeneous catalytic ethylene oligomerization. This review presents modern nickel catalysts for this process, mainly systems for obtaining of one of the most demanded oligomer—1-butene—which is used for the production of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE). The dependence of the catalytic performance on the composition and the structure of the used activated complexes, the electronic and coordination states of the nickel center was considered.

Electron-density distributions in selected ferrocenyl-pyrazolyl late transition-metal complexes

⁵⁷Fe Mössbauer spectroscopy has been used to study electronic dispersions in complexes of Fe, Co, Ni and Pd anchored onto 3-ferrocenyl-5-methylpyrazolylmethylenepyridine and 3-ferrocenylpyrazolylmethylenepyridine ligands.

Ethylene oligomerization studies by nickel(ii) complexes chelated by (amino)pyridine ligands: experimental and density functional theory studies

Activation of (amino)pyridine nickel(ii) complexes 1–4 with either EtAlCl₂ or methylaluminoxane (MAO), produced active ethylene oligomerization catalysts to afford mostly butenes and hexenes and octenes as minor products.

A comparative synthetic, magnetic and theoretical study of functional M₄Cl₄ cubane-type Co(II) and Ni(II) complexes

We describe the synthesis, structures, and magnetochemistry of new M4Cl4 cubane-type cobalt(II) and nickel(II) complexes with the formula [M(μ3-Cl)Cl(HL·S)]4 (1: M = Co; 2: M = Ni), where HL·S represents a pyridyl-alcohol-type ligand with a thioether functional group, introduced to allow subsequent binding to Au surfaces. Dc and ac magnetic susceptibility data of 1 and 2 were modeled with a full spin Hamiltonian implemented in the computational framework CONDON 2.0. Although both coordination clusters 1 and 2 are isostructural, with each of their transition metal ions in a pseudo-octahedral coordination environment of four Cl atoms and N,O-donor atoms of one chelating HL·S ligand, the substantially different ligand field effects of Co(II) and Ni(II) results in stark differences in their magnetism. In contrast to compound 1 which exhibits a dominant antiferromagnetic intramolecular coupling (J = -0.14 cm(-1)), 2 is characterised by a ferromagnetic coupling (J = +10.6 cm(-1)) and is considered to be a single-molecule magnet (SMM), a feature of special interest for future surface deposition studies. An analysis based on density functional theory (DFT) was performed to explore possible magnetostructural correlations in these compounds. Using a two-J model Hamiltonian, it revealed that compound 1 has four positive and two (small) negative J(Co···Co) isotropic interactions leading to a S(HS) = 6 ground state. Taking into account the magnetic anisotropy, one would recover a M(S) = 0 ground state since D > 0 from computations. In 2, all the J constants are positive and, in this framework, the zero-field splitting energy characterising the axial anisotropy was estimated to be negative (D = -0.44 cm(-1)). The computational results are consistent with compound 2 being an SMM.

Synthesis and characterization of a new nonanuclear Ni(II) cluster from a pyridyl-alcohol ligand

The reaction of one equivalent of 2-methyl-1-(pyridin-2-yl)propan-2-ol (HL) with two equivalents of [Ni(OAc)2·4H2O] in methanol afforded the nonanuclear coordination cluster [Ni9(HL-κ(2)N,O)4(OAc-κ(2)O)2(μ2-OAc-κ(1)O)2(μ2-OAc-κ(2)O,O')4(μ3-OAc-κ(2)O;κ(2)O,O')2(μ3-OMe)8] (1). All nickel ions are hexacoordinated and show a slightly distorted octahedral coordination geometry. This unusual centrosymmetric coordination cluster can be described as constituted by two cubane moieties connected by a linker comprising a nickel atom, situated on the inversion centre, four bridging acetates and two triply-bridging acetates. Each cubane contains four Ni(II) centres and four triply-bridging methoxide anions, two of the Ni(II) centres are N,O-chelated by the ligand HL, another Ni(II) is chelated by an acetate ligand and the fourth Ni(II) centre is connected to the exo-cubane Ni(II) through three acetate ligands which each have a different bonding mode: μ2-κ(2)O,O', μ2-κ(1)O, and μ3-κ(1)O;κ(2)O,O'. The magnetic and catalytic properties for ethylene oligomerization of the unusual complex have been investigated.