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

Abstract

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.