Silica-grafted borato cocatalysts for olefin polymerization modeled by silsesquioxane-borato complexes

The syntheses and reactivity studies of silsesquioxane-borato complexes are described. Treatment of B(C6F5)(3) with (c-C5H9)(7)Si8O12(OH) and (c-C5H9)(7)Si7O9(OH)(3) in the presence of a Bronsted base yields the silsesquioxane-borates X+{[(C-C5H9)(7)Si8O13]B(C6F5)3}(-) (1a, X+ = PhN(H)Me-2(+); 1b, X+ = Et3NH+) and X+{[(c-C5H9)(7)Si-7(OH)(2)O-10]B(C6F5)(3)}(-) (1b, X+ = PhN-(H)Me-2(+); 2b, X+ = Et3NH+), respectively. When the more nucleophilic base pyridine is used, (C6F5)(3)B . NC5H5 (3) is formed instead, demonstrating the competition between B(C6F5)(3) and H+ to react with the amine. The dimethylaniline in 1a and 2a is readily exchanged by NEt3 to form 1b and 2b. With the nucleophilic Lewis base NC5H5, the B-O bond in 1a and 2a is split, yielding (C6F5)(3)B . NC5H5 (3) and the free silsesquioxanes. Complexes 1 and 2 rapidly undergo hydrolysis under formation of the hydroxyl complexes X+{(C6F5)(3)BOH}(-) (4a, X+ = PhN(H)Me-2(+); 4b, X+ = Et3NH+). Likewise, alcoholysis of 1a and 2a with i-PrOH yields the alkoxide {PhN(H)Me-2}(+) {i-PrOB(C6F5)(3)}(-) (5)- The B-O bond is only moderately stable toward early-transition-metal alkyls. Nevertheless, Cp2Zr(CH2Ph)(2) + 1a and Zr(CH2Ph)(4) + 2a form single-site ethylene polymerization catalysts. Detailed reactivity studies demonstrated that both B-O and B-C bond splitting plays a crucial role, as not 1a and 2a, but their decomposition product B(C6F5)(3) is the actual cocatalyst. The solid-state structures of 1a and 4b were determined by single-crystal X-ray analysis.