Bridged bisphenolate group IV metal complexes have been shown to be extremely active for the production of high molecular weight polypropylene and polyhexene at elevated temperatures.  A chelating bis-phenol ligand was prepared in ten steps from 2-bromo-4-tert-butyl-phenol.  This ligand reacts with tetrabenzyl hafnium or tetrabenzyl zirconium to generate chiral octahedral metal complexes that have been shown to be isostructural by x-ray crystallography.  Activation of these complexes with methyaluminoxane generated highly active catalysts for propylene polymerization.  The hafnium complexes generated more highly isotactic polypropylenes than the zirconium complexes ([mmmm] = 0.64 and 0.41, respectively) but the 13C NMR of the polypropylenes from both catalysts were consistent with stereodifferentiation by the chiral metal complexes accompanied by isolated mrrm stereoerrors.  These complexes are also highly active for the production of poly-hexene with a high degree of isotacticity, as well as the polymerization of other sterically demanding a-olefins such as 4-methyl-1-pentene and 4-vinyl-1-cyclohexene.

Bridged bisphenolate Group IV metal complexes for propylene and 1-hexene polymerization

239th National Meeting (2010)

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