Mechanistic Insights on the Controlled Switch from Oligomerization to Polymerization of 1‑Hexene Catalyzed by an NHC-Zirconium Complex

The
benzimidazolylidene zirconium complex 1 switches
from an oligomerization (without additive) to a polymerization catalyst
by addition of an L-type ligand such as trimethylphosphine, while
larger phosphines or amines completely inhibit catalysis. On the basis
of the regioselectivity of the oligomers/polymers obtained, the time
profiles of reactions as a function of added ligand, and the molecular
structures of several cationic zirconium complexes, we propose a mechanistic
framework for interpreting this complex catalytic behavior.