Synthesis and Scale-up of Imino–Enamido Hafnium and Zirconium Olefin Polymerization Catalysts

New imino–enamido hafnium and zirconium trimethyl complexes were prepared in high yield by reacting a mixture of an imino–enamine ligand and hafnium or zirconium tetrachloride with four equivalents of methylmagnesium bromide in toluene. A significantly improved imine formation reaction in the final step of the ligand synthesis was developed that involves the reaction between the keto–enamine and a reagent formed in situ by mixing 0.55 equivalents of titanium tetrachloride and 5.5 equivalents of n-butylamine. Ethylene/1-octene polymerization evaluations at 120 °C revealed that polymerization characteristics of the imino–enamido hafnium and zirconium trimethyl derivatives were very similar to those of the tribenzyl analogues. A scale-up of the hafnium trimethyl derivative, performed on a 255 g scale, was accomplished in an overall yield of 57% in four steps starting with commercially available cyclohexa-1,2-dione. Hafnium and zirconium complexes derived from two isomeric imino–enamine ligands each resulted in very high molecular weight ethylene/1-octene copolymers, which differ significantly, however, in the level of incorporated octene. These features make these new catalysts good candidates for the preparation of olefin block copolymers via chain-shuttling polymerization.