Borane-Induced Dehydration of Silica and the Ensuing Water-Catalyzed Grafting of B(C6F5)3 To Give a Supported, Single-Site Lewis Acid, 鈮iOB(C6F5

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• 作者：Ying-Jen Wanglee ; Jerry Hu ; Rosemary E. White ; Ming-Yung Lee ; S. Michael Stewart ; Philippe Perrotin ; Susannah L. Scott
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：January 11, 2012
• 年：2012
• 卷：134
• 期：1
• 页码：355-366
• 全文大小：586K
• 年卷期：v.134,no.1(January 11, 2012)
• ISSN：1520-5126

文摘

A supported, single-site Lewis acid, 鈮iOB(C₆F₅)₂, was prepared by water-catalyzed grafting of B(C₆F₅)₃ onto the surface of amorphous silica, and its subsequent use as a cocatalyst for heterogeneous olefin polymerization was explored. Although B(C₆F₅)₃ has been reported to be unreactive toward silica in the absence of a Br酶nsted base, we find that it can be grafted even at room temperature, albeit slowly. The mechanism was investigated by ¹H and ¹⁹F NMR, in both the solution and solid states. In the presence of a trace amount of H₂O, either added intentionally or formed in situ by borane-induced dehydration of silanol pairs, the adduct (C₆F₅)₃B路OH₂ hydrolyzes to afford C₆F₅H and (C₆F₅)₂BOH. The latter reacts with the surface hydroxyl groups of silica to yield 鈮iOB(C₆F₅)₂ sites and regenerate H₂O. When B(C₆F₅)₃ is present in excess, the resulting grafted boranes appear to be completely dry, due to the eventual formation of [(C₆F₅)₂B]₂O. The immobilized, tri-coordinate Lewis acid sites were characterized by solid-state ¹¹B and ¹⁹F NMR, IR, elemental analysis, and C₅H₅N-TPD. Their ability to activate two molecular C₂H₄ polymerization catalysts, Cp₂ZrMe₂ and an (伪-iminocarboxamidato)nickel(II) complex, was explored.