Polymeric salicylaldimine ligands

Strong interest in late transition metal olefin polymerization catalysts resulted in the development of new five-coordinate Fe and Co systems (69) that afford highly linear, crystalline, high-density polyethylene.587-589 A new class of single-component, neutral Ni catalysts based on salicylaldimine ligands (70) was reported to be active in the polymerization of ethylene 590,591... 

In 1998, Grubbs and co-workers [83, 84] reported on a new type of neutral Ni(II) complexes with salicylaldimin ligands (32). With these catalysts low-branched polyethylenes were obtained with a narrow molecular weight distribution. The copolymerization of ethylene and norbomene is possible. Fe and Co catalysts were used for the linear polymerization of ethylene by Gibson [85] and Brookhart [86] independently (33). Activities of 10 TONs were reported. The polyethylenes obtained are highly crystalline with a broad molecular weight distribution. 

The pooled library of salicylaldimine-titanium products was combined with MAO and 150 ml toluene in a pressure vessel, and screened at 20 °G under 2.7 atm of propylene for 6h. Although 90% of the polymers produced were determined to be atactic through extraction experiments with diethylether, the remaining 10% of the polymers produced were found to contain insoluble syndiotactic polypropylene. Small subsets of the complex libraries were then resynthesized and screened in order to ascertain the particular metal-ligand combination responsible for the stereocontrol. The authors concluded the study by identifying and isolating a new syndiospecific propylene polymerization catalyst 2. 

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