Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: synthesis, structures and ethylene polymerization behaviors of the group 4 complexes

Homogeneous Non-Metallocene Group 4 Metals Ligated with [N,N] Bidentate Ligand(s) for Olefin Polymerization

The development of catalysts has significantly advanced the progress of polyolefin materials. In particular, group 4 (Ti, Zr, Hf) non-metallocene catalysts ligated with [N,N] bidentate ligand(s) have garnered increasing attention in the field of olefin polymerization due to their structurally stability and exceptional polymerization behaviors. Ligands containing nitrogen donors are diverse and at the core of many highly active catalysts. They mainly include amidine, guanidinato, diamine, and various N-heterocyclic ligands, which can be used to obtain a series of new polyolefin materials, such as ultrahigh molecular weight polyethylene (UHWMPE), olefin copolymers (ethylene/norbornene and ethylene/α-olefin) with high incorporations, and high isotactic or syndiotactic polypropylene after coordination with group 4 metals and activation by cocatalysts. Herein, we focus on the advancements and applications of this field over the past two decades, and introduce the catalyst precursors with [N,N] ligand(s), involving the effects of ligand structure, cocatalyst selection, and polymerization conditions on the catalytic activity and polymer properties.

Synthesis of Pyridylimido Complexes of Tantalum and Niobium by Reductive Cleavage of the N═N Bond of 2,2'-Azopyridine: Precursors for Early-Late Heterobimetallic Complexes

We report the syntheses of 2-pyridylimido complexes of tantalum and niobium by N═N bond cleavage of 2,2'-azopyridine. Reaction of MCl5 (M = Ta and Nb) with 2,2'-azopyridine in the presence of 0.5 equiv of 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (abbreviated Si-Me-CHD) afforded a dark red solution (for Ta) and a dark blue solution (for Nb) with some insoluble precipitates. After removing the solids, another 0.5 equiv of Si-Me-CHD was added to each solution, giving [M(═Npy)Cl3]n (1a: M = Ta; 1b: M = Nb) through reductive cleavage of the N═N bond of 2,2'-azopyridine. The initial products of the above reactions were determined to be 2,2'-azopyridine-bridged dinuclear complexes, [(MCl4)2(μ-pyNNpy)] (2a: M = Ta; 2b: M = Nb), which were isolated by treating MCl5 with 2,2'-azopyridine and Si-Me-CHD in a 2:1:1 molar ratio. In 2a and 2b, the N═N bond was reduced to a single bond via two-electron reduction. Further reduction of complexes 2a and 2b with 1 equiv of Si-Me-CHD afforded complexes 1a and 1b. An anionic doubly μ-imido-bridged ditantalum complex, [nBu4N][Ta2(μ-Npy)2Cl7] (3a), was generated upon addition of nBu4NCl to complex 1a, while addition of nBu4NCl to niobium complex 1b gave a polymeric terminal imido complex, [nBu4N]n/2[{Nb(═Npy)Cl3}2(μ-Cl)]n/2 (3b). Complexations of 1a and 1b with 1 equiv of 2,2'-bipyridine resulted in the formation of mononuclear 2-pyridylimido complexes, M(═Npy)Cl3(bipy) (4a: M = Ta; 4b: M = Nb), whose main structural feature is intramolecular hydrogen bonding between the ortho hydrogen atom of 2,2'-bipyridine and the nitrogen atom of the pyridyl group on the imido ligand. Isolated 2-pyridylimido complexes 4a and 4b reacted with [RhCl(cod)]2 to produce the corresponding early-late heterobimetallic complexes, (bipy)MCl3(μ-Npy)RhCl(cod) (5a: M = Ta; 5b: M = Nb).

A pyridyl-substituted cyclodisilazane [(Apy)2(μ-SiMe)2] (ApyH2 = 2-aminopyridine)

The title compound, C14H20N4Si2 or [(Apy)2(μ-SiMe)2], systematic name 2-[2,2,4,4-tetramethyl-3-(pyridin-2-yl)-1,3,2,4-diazadisiletidin-1-yl]pyridine, was obtained as a side product from the reaction of 2-amino-pyridine with LiBu n followed by the addition of Me2NMe2SiCl in hexane. The compound was characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. The title compound lies about an inversion center at the centroid of the cyclodisilazane ring. The four-membered Si2N2 core is strictly planar with the two pyridyl rings placed centrosymmetrically on either side of the Si2N2 plane and are almost coplanar with the central four-membered ring.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. The catalytic behaviors of these zirconium complexes were investigated in the presence of MAO as a cocatalys.

Group IV compounds bearing a novel tridentate N-donor ligand: synthesis, structures and ethylene polymerization

In this paper, treatment of [PhN(CH₂)₃NC(Ph)NSiMe₃]₂Li₄·2Et₂O with group IV metal chlorides yields corresponding compounds 3–5. The catalytic behaviors of 3–5 were investigated in the presence of MAO as co-catalyst for ethylene polymerization.

Imido-pyridine Ti(IV) compounds: synthesis of unusual imido-amido heterobimetallic derivatives

The reaction of lithiated picolines and [TiCl3(η(5)-C5Me5)] leads to several bridging or terminal imido compounds, each of which can be selectively formed by controlling the stoichiometry and temperature. Specifically, the dinuclear imido-bridged [TiCl(η(5)-C5Me5)(μ-NR)]2 (1a, NR = 2-imido-3-picoline; 1b, NR = 2-imido-5-picoline) species and the unusual Ti-Li imido-amido heterobimetallic complex [{Li(THF)}{Ti(η(5)-C5Me5)(NR)(NHR)2}] (2a, NR = 2-imido-3-picoline; 2b, NR = 2-imido-5-picoline) were isolated. Compounds 2 are in effect the first structurally characterized examples of titanium(IV) coordinated to terminal imido-pyridines. DFT-D calculations for 2a denote a multiple bond character between titanium and the imido ligand and a strong polarization of the electron density by the alkali cation in spite of the lack of intermetallic bonding.

Theoretical investigation of the interaction between aromatic sulfur compounds and [BMIM](+)[FeCl4](-) ionic liquid in desulfurization: A novel charge transfer mechanism

In this work, interaction nature between a group of aromatic sulfur compounds and [BMIM](+)[FeCl4](-) have been investigated by density functional theory (DFT). A coordination structure is found to be critical to the mechanism of extractive desulfurization. Interaction energy and extractive selectivity follow the order: thiophene (TH)<dibenzothiophene (DBT)≈benzothiophene (BT). Alkylation of TH or BT (e.g. 3-methylthiophene, and 3-methylbenzothiophene) leads to a stronger interaction with ionic liquid, but steric hindrance effects of some alkylic derivatives (e.g. 2,7-dimethylbenzothiophene) lead to a weaker interaction with ionic liquid. The mechanism of extractive desulfurization is attributed to the charge transfer effect. During extractive desulfurization, electrons on aromatic sulfur compounds transfer into the Lewis part of ionic liquid, namely, [FeCl4](-). Furthermore, it is better to consider the Lewis acidity of Fe-containing ionic liquid by the whole unit (such as [FeCl4](-) and aromatic sulfur compounds (X)) rather than only Fe or S atom.

Zwitterionic group 4 aminophenolate catalysts for the polymerization of lactides and ethylene

A series of group 4 metal chloride complexes based on aminophenol ligands were synthesized and characterized by conventional spectroscopic techniques, elemental analysis and X-ray crystallography.

Amidinate group 4 complexes in the polymerization of olefins

The current perspective will present the use of amidinate group 4 complexes in α-olefin polymerizations.