Polymer Microstructure Control in Catalytic Polymerization Exclusively by Electronic Effects of Remote Substituents

A series of (2-N,O)salicylaldiminato nickel methyl pyridine complexes 8a-h-pyr bearing 2,6-di-(4-R-phenyl)phenyl groups on the imine nitrogen and varying in the remote substituents [R=C8F17 (a), CF3 (b), F (7c), H (d), Me (e), tert.-butyl (f), OMe (g), and NMe2 (h)] were studied as precatalysts for ethylene polymerization. Complexes 8a-h-pyr catalyze the polymerization of ethylene to low molecular weight polyethylene. Decreasing molecular weight and increasing degrees of branching are observed in the order R=C8F17CF3>F>H>Me>MeO>tert-butyl>NMe2. X-Ray diffraction analysis of complex 8c-pyr and polymerization results obtained with complexes 8-pyr indicate that it is not the sterics but the electronics of the R group that control the polymer microstructure. This is a rare example of a polymerization catalyst in which substituents effects can clearly be traced to electronics exclusively