Organoborane-Modified Silica Supports for Olefin Polymerization: Soluble Models for Metallocene Catalyst Deactivation

Treatment of silsesquioxane 1 with 3.3 equiv of the reactive organoboranes 2 [(C 6 F 5 ) 2 BX; X = H or Cl] provides the novel, trifunctional organoborane 3, which was characterized by spectroscopic means and single-crystal X-ray crystallography. Compound 3 is an effective cocatalyst for ethylene polymerization in combination with Cp 2 ZrMe 2 but only when these two compounds are combined in situ, in the presence of monomer, suggesting limited stability of the putative ion-pair derived from these compounds. Reaction of 3 with Cp 2 ZrMe 2 in toluene solution leads to formation of MeB(C 6 F 5 ) 2 - and Cp 2 Zr-functionalized silsesquioxane 5 at room temperature. Monitoring of this reaction by NMR spectroscopy at low temperatures indicates that the only ion-pair present is [Cp 2 ZrMe][Me 2 B(C 6 F 5 ) 2 ] ( 4 ), which results from reaction of Cp 2 ZrMe 2 with the byproduct MeB(C 6 F 5 ) 2 . Formation of 4 is reversible under these conditions, while production of 5 (from 3 and Cp 2 ZrMe 2 ) is not; the latter process occurs at a rate that exceeds that observed for independent decomposition of 4 to form Me 2 B(C 6 F 5 ) and Cp 2 Zr(C 6 F 5 )Me. These studies suggest that the active polymerization catalyst generated in situ from 3 and Cp 2 ZrMe 2 is probably ion-pair 4 .