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

An effective shielding of both apical positions of a neutral Ni active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a C -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 (5×10  g mol ) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3×10  turnovers h ) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 °C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.