Vinyl polymerization of norbornene by nickel(II) complexes bearing β‐diketiminate ligands

Abstract

Norbornene polymerizations were carried out using nickel(II) bromide complexes CH{C(R)NAr} 2 NiBr (1, R = CH 3 , Ar = 2, 6− i Pr 2 C 6 H 3 ; 2, R = CH 3 , Ar = 2, 6-Me 2 C 6 H 3 ; 3, R = CF 3 , Ar = 2, 6− i Pr 2 C 6 H 3 ; 4, R = CF 3 , Ar = 2, 6-Me 2 C 6 H 3 ) in the presence of methylaluminoxane. Compound 3 is the most active norbornene polymerization catalyst of all the nickel complexes tested. The activity of theses catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. The resulting polynorbornenes are vinyl type by IR and NMR analyses.

Metal catalysts for the vinyl/addition polymerization of norbornene

“…The optimal Al/Ni ratio was shown to be 1500. Variation of the polymerization temperatures from 0 • C to 90 • C caused a steady increase in the activities, whereas the molecular weights of the PNB decreased at the same time [137].…”

Physico-chemical ageing of ethylene–norbornene copolymers: a review

“…The vinylic polymerization of norbornene with Pd(II) catalysts was patented in 1967, and much research has been done with different metal catalysts (Ni(II), Pd(II), Cr(III), Co(II), Cu(II)) [42][43][44][45][46]. In 1989, Kaminsky developed a process of synthesis using metallocene catalysts, in particular zirconocene and half-sandwich titanium methylaluminoxane (MAO) catalysts [47][48][49][50], allowing the development of a perfectly transparent material with a great rigidity, which was in the centre of several research efforts [35,[51][52][53][54][55][56][57][58][59][60].…”

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

“…[19] The 1 H and 13 C NMR spectra are very similar to those reported and also show no resonances assignable to double bonds. [11,18] The SEC measurements of several samples indicated that high-molecular weight polymers with a rather low polydispersity are formed. Unfortunately, a large number of polynorbornene samples could not be analyzed by size exclusion chromatography; due to the high molecular weight these polymers could not be dissolved in the commonly used chlorobenzene or 1,3,5-trichlorobenzene, even after stirring at elevated temperatures for several days.…”

“…[11] A reaction between the catalyst precursor and MAO in the presence of norbornene yields a nickel compound with a methyl ligand and a coordinated norbornene (A). The norbornene then inserts into the Ni-CH 3 bond to give the coordinatively unsaturated species B.…”

“…Proposed mechanism for the nickel catalyzed vinyl polymerization of norbornene (L = carbene ligand; PNB = polynorbornene). Adapted from Li et al [11] once a nickel catalyst starts the polymerization reaction, the rate of propagation is considerably higher than the rate of elimination. The low polydispersity measured for a number of polymers indicates that the catalyst operates through a single site active species, in line with the proposed mechanism.…”