Efficient Route for Cyclic Olefin Polymerization:  Nonchelated Monodentate Benzimidazole Nickel(II) Complex Catalysts for Vinyl Polymerization of Norbornene

Abstract

We developed a series of nonchelated monodentate benzimidazole nickel complexes, bis [2-(2,6difluorophenyl) 4), upon activation with methylaluminoxane (MAO), which are found to be highly active for vinyl polymerization of norbornene (Nb). The polymerization activity displayed by 4 is as high as 1.68 × 10 9 g of PNb‚mol Ni -1 ‚h -1 at very high Nb/Ni ratio of 1 × 10 5 . Moreover a small amount of MAO is required to achieve such activity with high yield. The comparable high activity of 4.96 × 10 8 g of PNb‚mol Ni -1 ‚h -1 for the simplest complex 3 reveals the significance of nonchelation in this catalyst series. It is observed that the use of toluene as solvent inhibits the catalytic activity strongly. The in situ NMR analyses indicate that the ligand is still intact with the active species and hence the difference in activity is indeed being associated with the change in ligand.

Novel non-chelated cobalt(II) benzimidazole complex catalysts: Synthesis, crystal structures and cocatalyst effect in vinyl polymerization of norbornene

“…The coordination geometry around the cobalt is pseudotetrahedral similar observed to that of analogous nickel complexes [10]. The crystal structure of complex 2 consists of two solvent molecules per unit of the complex.…”

“…The ligands 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole (MOBPBI) and 2-(2,6-difluorophenyl)-1H-benzimidazole (DFPBI) have been synthesized according to the reported procedure [10], whereas the ligand 2-methyl-1H-benzimidazole (MBI) is used as received from the commercial sources. The neutral benzimidazole cobalt derivatives [CoCl 2 (MOBPBI) 2 (1)], [CoCl 2 (DFPBI) 2 (2)] and [CoCl 2 (MBI) 2 (3)] were prepared by reaction of CoCl 2 with the proper benzimidazole derivative in dichloromethane and purified by re-precipitation in diethyl ether.…”

“…Recently, we proposed [10] that nickel(II) monodentate benzimidazole complex catalysts in combination with MAO are the most active catalysts for vinyl polymerization of norbornene. Interestingly, we found that the cobalt(II) benzimidazole complexes show high structural analogy toward nickel(II) benzimidazole complexes at molecular level in solid state.…”

Metal catalysts for the vinyl/addition polymerization of norbornene

“…The lower activity of the system Ni-35/MAO was due to its lower steric demand and electronic poor nature. Catalyst Ni-36 was used for further investigation and it was found that the optimal polymerization temperature was 25 • C. Furthermore, the activity dramatically decreased by several orders of magnitude when the solvent was changed from the polar ODCB to a ODCB/toluene mixture [145].…”

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

“…[9] In the literature, two other types of nickel NHC complexes have been reported to be active as norbornene polymerization catalysts. Wang et al [20] reported activities up to 2.6 × 10 7 g (mol cat) −1 h −1 using a cationic nickel complex bearing two picolyl functionalized NHCs (1:Ni = 68 000, Al : Ni = 4500, 10 min at 80…”