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| - Nickel 2-Iminopyridine N-Oxide (PymNox) Complexes: Cationic Counterparts of Salicylaldiminate-Based Neutral Ethylene Polymerization Catalysts
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| - Nickel complexes with pyridine N-oxide based ligands are efficient catalysts for ethylene polymerization. Their structure and catalytic properties resemble those of salicylaldiminato catalysts. Some of these catalysts copolymerize ethylene and methyl acrylate.
- 2-Iminopyridine N-oxides (PymNox) constitute a promising class of ligands that can be considered as the neutral counterparts of the well-known salicylaldiminate system. A series of nickel PymNox complexes displaying different substitution patterns in the ligand have been synthesized, and their activity as ethylene polymerization catalysts has been studied. While an electron-donor group (OMe) at the remote position 4 of the pyridine ring causes a moderate decrease of the catalytic activity and increase of the polyethylene molecular weight, a strongly electron-withdrawing group (NO2) in this position shifts the catalyst selectivity from ethylene polymerization to oligomerization. The introduction of a phenyl substituent next to the pyridine nitrogen (position 6) causes a significant increase of the catalytic activity and the polymer molecular weight. Although aldimino PymNox catalysts are inactive in ethylene−methyl acrylate copolymerization, we observed that acetaldimino (displaying the Me-CNAr group) catalysts display a small but significant activity on this account, giving rise to copolymers incorporating ca. 1% methyl acrylate in their structure. The trends observed in the PymNox catalytic system are strongly reminiscent of those of nickel salicylaldiminates (although the former are considerably more active), demonstrating for the first time that substitution of the widely used phenoxo anionic group by the neutral pyridine N-oxide fragment is a useful possibility in the design of late transition metal catalysts for olefin polymerization.
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| - Nickel 2-Iminopyridine N-Oxide Complexes
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