2-Benzimidazolyl-N-phenylquinoline-8-carboxamide Chromium(III) Trichlorides: Synthesis and Application for Ethylene Oligomerization and Polymerization

Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

The depicted cobalt catalysts bearing ortho-fluorine and fluorinated ortho-benzhydryl substituents displayed a preference for forming highly linear PE waxes; DFT studies have been used to probe this selectivity.

Chromium complexes supported by the bidentate PN ligands: synthesis, characterization and application for ethylene polymerization

Chromium-based complexes are among the most important catalysts in the field of ethylene polymerization and oligomerization. Heterogeneous Cr Phillips catalysts account for more than one-third of the commercialized high density polyethylene (HDPE). In this contribution, chromium complexes, LCrCl3 (Cr1-Cr4: L = 2,6-R1-4-R2-C6H2-N[double bond, length as m-dash]CH-C6H4-2-PPh2; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = iPr, R2 = H; Cr4: R1 = Ph2CH, R2 = iPr), have been synthesized and characterized by elemental analysis, ESI and IR spectroscopy. The molecular structures of Cr3 and Cr4 are defined by X-ray diffraction, revealing a distorted octahedral geometry around the chromium center in both structures. In the presence of an aluminum cocatalyst, complexes Cr1-Cr4 show moderate to high activities toward ethylene polymerization. The nature of the catalysts and various reaction conditions, such as the nature and the amount of cocatalyst, reaction time and temperature, are investigated in detail. The results show that the title complexes have good thermal stability and the substituents on the ligands significantly affect the catalytic properties. Particularly, complex Cr4 can produce HDPE with a high molecular weight up to 68.3 × 104 g mol-1 due to the suppression of the chain transfer/termination by the introduction of bulky Ph2CH groups.

Chromium(III) complexes with 1,2,4-diazaphospholide and 2,6-bis(N-1,2,4-diazaphosphol-1-yl) pyridine ligands: synthesis, X-ray structural characterization, EPR spectroscopy analysis, and magnetic susceptibility studies

Three chromium(III) 1,2,4-diazaphospholide complexes were prepared: 3,5-di-tert-butyl-1,2,4-diazaphospholide chromium(III) dichloride [(η 2-3,5-tBu2dp)Cr(THF)2Cl2] (1), 3,5-di-phenyl-1,2,4-diazaphospholide chromium(III) dichloride [(η 2-3,5-Ph2dp)Cr(THF)2Cl2] (2), and 2,6-bis(N-1,2,4-diazaphosphol-1-yl)pyridine chromium(III) trichloride {[2,6-bis(N-1,2,4-diazaphosphol-1-yl)pyridine]CrCl3} (3). X-ray diffraction analysis has shown that these six-coordinate complexes each have a pseudo-octahedral configuration. Electron paramagnetic resonance (EPR) spectroscopy data for complex 1 for the paramagnetic S = 3/2 system (d 3 electron configuration) confirm a Cr(III) center in the octahedral coordination environment. The magnetic susceptibility of complex 1 followed the Curie–Weiss law well between 25 and 300 K. The magnetic moment of 1 was found to be close to the spin-only magnetic moment expected for three unpaired electrons (3.87 μB).

Nickel(ii) complexes chelated by 2,6-pyridinedicarboxamide: syntheses, characterization, and ethylene oligomerization

Ni(ii) complexes chelated by a neutral tridentate amide ligand are conveniently prepared and are highly active for ethylene oligomerization.

Transition metal complexes bearing tridentate ligands for precise olefin polymerization

This review covers key developments in the design of post-metallocene transition metal complexes (precatalysts) bearing tridentate chelating ligands and their application in olefin polymerization.

Ethylene oligomerization promoted by chromium complexes bearing pyrrolide–imine–amine/ether tridentate ligands

Chromium complexes bearing pyrrolide–imino-amine/ether tridentate ligands have been synthesized and their catalytic behavior in ethylene oligomerization has been investigated. Drastic changes in selectivity have been observed upon slight variation of the MAO-to-Cr ratio.

Interaction of chromium(III) with a N,N'-disubstituted hydroxylamine-(diamido) ligand: a combined experimental and theoretical study

Reaction of hydroxylamine hydrochloride with prop-2-enamide in dichloromethane in the presence of triethylamine resulted in the isolation of the N,N'-disubstituted hydroxylamine-(diamido) ligand, 3,3'-(hydroxyazanediyl)dipropanamide (Hhydia). The ligand Hhydia was characterized by multinuclear NMR, high-resolution electrospray ionization mass spectrometry (ESI-MS), and X-ray structure analysis. Interaction of Hhydia with trans-[Cr(III)Cl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [Cr(III)(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[Cr(III)Cl2(Hhydia)2]Cl·2H2O (2·2H2O). The X-ray structure analysis of 1 revealed that the chromium atom in [Cr(III)(Hhydia)2](3+) is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, θ, in [Cr(III)(Hhydia)2](3+) is 54.5(6)(0), that is, very close to an ideal octahedron. The intramolecular hydrogen bonds developed between the N-OH group of the first ligand and the amidic oxygen atom of the second ligand and vice versa contribute to the overall stability of the cation [Cr(III)(Hhydia)2](3+). The reaction rate constant of the formation of Cr(III) complexes 1·2H2O and 2·2H2O was found to be 8.7(±0.8) × 10(-5) M(-1) s(-1) at 25 °C in methyl alcohol and follows a first-order law kinetics based on the biologically relevant ligand Hhydia. The reaction rate constant is considerably faster in comparison with the corresponding water exchange rate constant for the hydrated chromium(III). The modification of the kinetics is of fundamental importance for the chromium(III) chemistry in biological systems. Ultraviolet-visible and electron paramagnetic resonance studies, both in solution and in the solid state, ESI-MS, and conductivity measurements support the fact that, irrespective of the solvent used in the interaction of Hhydia with trans-[Cr(III)Cl2(H2O)4]Cl·2H2O, the ionization isomers[Cr(III)(Hhydia)2]Cl3·2H2O (1·2H2O) and cis/trans-[Cr(III)Cl2(Hhydia)2]Cl·2H2O (2·2H2O) are produced.The reaction medium affects only the relevant percentage of the isomers in the solid state. The thermodynamic stability of the ionization isomers 1·2H2O and cis/trans-2·2H2O, their molecular structures as well as the vibrational spectra and the energetics of the Cr(III)- Hhydia/hydia(-) were studied by means of density functional theory calculations and found to be in excellent agreement with our experimental observations.