Alkyl substituents triggered an unexpected formation of mono‐and dinuclear zirconium hydrazonate complexes: synthesis, characterization and their catalytic behavior toward ethylene polymerization

Abstract

Mononuclear zirconium complex 3a of the molecular identity [Zr[η2‐(C4H3O)C (Et) = NNPh]Cl3(THF)2], dinuclear zirconium complexes 3b [{Zr[η2‐(C4H3O)C(i‐Pr) = NNPh]2}2(μ2‐Cl)3(μ3‐Cl)2Li(Et2O)] and 3c [{Zr[η2‐(C4H3O)C(t‐Bu) = NNPh]2}2Cl2(μ2‐Cl)2] have been synthesized by the treatment of lithium salt of (C4H3O)C(R) = NNHPh (R = CH3CH2, 1a; R = (CH3)2CH, 1b; R = (CH3)3C, 1c), with different molar ratios of anhydrous zirconium tetrachloride. Of these, complex 3b was formed with lithium adduct and no such adduct was found in complex 3c. Compound 1a and all the zirconium complexes (3a‐3c) were structurally characterized by single‐crystal X‐ray diffraction studies. Thus, it revealed that each hydrazonato ligand acts in a strained η2‐coordination fashion for the three zirconium complexes. The molecular structures of the three zirconium complexes (3a‐3c) reveal the existence of intramolecular hydrogen bonding interactions. Interestingly, complexes 3a and 3b assemble into a two‐dimensional network structure through intermolecular hydrogen‐bonding interactions. Upon activation with methylaluminoxane (MAO), all the complexes namely 3a, 3b, and 3c exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylene with narrow molecular weight distributions.

Synthesis of Ultrahigh Molecular Weight Ethylene-Based (Co)polymers with Titanium Complexes Bearing Nonsymmetric Amine-bis(phenolate) Ligands

“…On the other hand, high to ultrahigh molecular weight polyethylene (PE) and polyolefin thermoplastic elastomer (POE) or linear low density PE (LLDPE) have attracted much attention because these unique polymers have outstanding physical and mechanical properties . So far, some well-defined nonmetallocene complexes of group 4 transition metals have been reported to generate linear ultrahigh molecular weight PE (UHMWPE). – However, relatively rare complexes of this type have been reported to catalyze ethylene/1-olefin copolymerization to produce copolymers with high to ultrahigh molecular weights. – …”