Efficient Suppression of Chain Transfer and Branching via Cs-Type Shielding in a Neutral Nickel(II) Catalyst

An effective shielding of both apical positions of a neutral Ni-II active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a C-s-type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5x10(6) g mol(-1)) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3x10(5) turnovers h(-1)) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 degrees C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.