Preparation and characterization of acylhydrazone nickel(II) complexes and their catalytic behavior in vinyl polymerization of norbornene and oligomerization of ethylene

A series of salicylaldimine-based neutral Ni(II) complexes (3a-j) [ArN = CH(C 6 H 4 O)]Ni(PPh 3 )Ph [3a, Ar = C 6 H 5 ; 3b, Ar = C 6 H 4 F(o); 3c, Ar = C 6 H 4 F(m); 3d, Ar = C 6 H 4 F(p); 3e, Ar = C 6 H 3 F 2 (2,4); 3f, Ar = C 6 H 3 F 2 (2,5); 3g, Ar = C 6 H 3 F 2 (2,6); 3h, Ar = C 6 H 3 F 2 (3,5); 3i, Ar = C 6 H 2 F 3 (3,4,5); 3j, Ar = C 6 F 5 ] have been synthesized in good yield, and the structures of complexes 3a and 3i have been confirmed by X-ray crystallographic analysis. Using modified methylaluminoxane as a cocatalyst, these neutral Ni(II) complexes exhibited high catalytic activities for the vinylic polymerization of norbornene. It was observed that the strong electron-withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalyst activity for vinylic polymerization of norbornenes. In addition, catalyst activity, polymer yield and polymer molecular weight can also be controlled over a wide range by the variation of reaction parameters such as Al : Ni ratio, norbornene : catalyst ratio, monomer concentration, polymerization temperature and time.

Synthesis and characterization of novel neutral nickel complexes bearing fluorinated salicylaldiminato ligands and their catalytic behavior for vinylic polymerization of norbornene

Song

et al. 2008

Nickel N‐heterocyclic carbene complexes in the vinyl polymerization of norbornene

Berding

Lutz

Spek

et al. 2010

Vinyl polymerized norbornene has some useful properties such as good mechanical strength, optical transparency and heat resistance. Several transition metal complexes have been described in the literature as active catalysts for the vinyl polymerization of norbornene. We now report the use of three types of nickel(II) complexes with N-heterocyclic carbene (NHC) ligands in the catalytic vinyl polymerization of norbornene under a range of conditions. Specifically, two nickel complexes bearing a chelating bis(NHC) ligand, two nickel complexes bearing two chelating anionic N-donor functionalized NHC ligands as well as one diiodidonickel(II) complex with two monodentate NHC ligands were tested. The solid-state structure of bis(1,3-dimethylimidazol-2-ylidene)diiodidonickel(II), as determined by X-ray crystallography, is presented. The highest polymerization activity of 2.6 × 10 7 g (mol cat) −1 h −1 was observed using the latter nickel complex as catalyst, activated by methylaluminoxane. The norbornene polymers thus obtained are of high molecular weight but with rather low polydispersity.

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

Duan

Yuan

et al. 2020

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.