Synthetic Optimization and Scale-Up of Imino–Amido Hafnium and Zirconium Olefin Polymerization Catalysts

Improved synthetic protocols were
developed for the safe, efficient,
and scalable preparation of imino–amido Hf and Zr complexes
that are precatalysts for olefin polymerizations. Facile syntheses
of four imino–amido complexes were achieved in high yields
by direct reactions of 4 equiv of MeMgBr with mixtures of the corresponding
bisimines or imine–amines and MCl4 (M = Hf, Zr).
These synthetic routes eliminate the use of the pyrophoric reagents
AlMe3 and n-BuLi used previously, avoid
cryogenic conditions, and lead to significant yield improvements.
Notably, competing reaction pathways between the bis-imine and MeLi
were observed. This led to the discovery of the selective addition
of MeMgBr to the bis-imine, which was successfully applied in the
synthesis of the imine–amine ligand.