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

Abstract

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.

Synthesis and Reactivity of Remarkably Stable and Nucleophilic Hydroxide-Bridged Dimetallic Nickel NHC Complexes

“…Stronger acids were detrimental to the stability of the Ni2 core. For example, addition of phenol (pKa = 10), NH4BF4 (pKa = 9.2), or formic acid (pKa = 3.75) to complex 2a induced cleavage of the dimeric structure and formation of the known 31,32 neutral bis(carbene) nickel(II) complex 5 in about 50% isolated yield (Fig. 5).…”

NHC‐Stabilized Nickel Olefin, Dialkyl, and Dicyanido Complexes

“…We also synthesized the complexes trans ‐[Ni( i Pr 2 Im Me ) 2 Br 2 ] 2 and trans ‐[Ni(Me 2 Im Me ) 2 Br 2 ] 4 in good yields using similar procedures. For the synthesis of a Me 2 Im‐stabilized dihalide nickel complex (Me 2 Im = 1,3‐dimethylimidazolin‐2‐ylidene) we adopted a procedure developed by Bowman et al for the synthesis of trans ‐[Ni(Me 2 Im) 2 I 2 ] 3 ,[6c], since the reactions of Me 2 Im with [Ni(dme)Br 2 ] leads to grey to brown mixtures containing elemental nickel and only traces of the desired product trans ‐[Ni(Me 2 Im) 2 Br 2 ]. Complexes 1–4 are air and water stable and can be stored in air for a prolonged time.…”

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The complexes (341), [124] (360), [306] (548), [306] (557), [306] (570−573), [174] (574), [175] (622−623), [306] (677) [204] and (785) [175] catalyzed norbornene polymerization in the presence of MAO. The complexes (327−332) [111] polymerized norbornene directly in the absence of any activator.…”