Improving the Performance of Heterogeneous Borane Cocatalysts by Pretreatment of the Silica Support with Alkylaluminum Compounds

Well-defined silica supported aluminum hydride: another step towards the utopian single site dream?

“…Reaction of TIBA also led to the formation of silicon hydride(s) species characterized by a broad ν (Si–H) band at 2100–2200 cm –1 . 39 , 55 , 56 Based on DFT calculations ( vide infra ), the presence of these silicon hydrides is explained by a β-H elimination from one of the isobutyl fragment to the Al center of [ SiO–Al–[CH 2 CH(CH 3 ) 2 ] 2 . Then, the Al–H intermediate thus formed reacts with adjacent silicon bridges to form silicon hydride.…”

“…The type of reaction between alkyl aluminum compounds (AlR 3 , R = Me, 29 – 34 Et, 35 iBu…) and silica surface still remains not elucidated despite its huge applications as a co-catalyst for olefins polymerization. 36 – 39 Because many aluminum alkyls exist in solution as dimers or trimers, we have chosen triisobutylaluminum (TIBA) because it is a monomer, 40 with the hope it will remain monomeric once it is grafted to the surface. A preliminary account of this chemistry was started on mesoporous silica SBA15 700 .…”

“…and silica surface still remains not elucidated despite its huge applications as a co-catalyst for olens polymerization. [36][37][38][39] Because many aluminum alkyls exist in solution as dimers or trimers, we have chosen triisobutylaluminum (TIBA) because it is a monomer, 40 with the hope it will remain monomeric once it is graed to the surface. A preliminary account of this chemistry was started on mesoporous silica SBA15 700 .…”

“Bound but Not Gagged”Immobilizing Single-Site α-Olefin Polymerization Catalysts

“…Recently, a third synthetic route to heterogeneous trityl borates has been reported . Gulari and co-workers found that the Brønsted acid s FAB-1 reacts with trityl chloride under facile conditions, room temperature, and in the absence of light (step 6, Scheme ), eliminating HCl to form the supported trityl borate.…”

“…Boranes and borates have also been immobilized and used as cocatalysts. − Whereas physisorbed, tethered, and grafted boron species have been reported, so far only silica-grafted boranes 258c,538 and borates 539 have been modeled. Representative examples are the neutral silsesquioxane tris(borane), R 7 Si 7 O 12 [B(C 6 F 5 ) 2 ] 3 , and the silsesquioxane−borato ammonium salt, {[( c -C 5 H 9 ) 7 Si 7 O 13 ]B(C 6 F 5 ) 3 } - {PhN(H)Me 2 } + (Figure ).…”