Borane-Induced Dehydration of Silica and the Ensuing Water-Catalyzed Grafting of B(C₆F₅)₃ To Give a Supported, Single-Site Lewis Acid, SiOB(C₆F₅)₂

A supported, single-site Lewis acid, SiOB­(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 Brønsted 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 <i>in situ</i> by borane-induced dehydration of silanol pairs, the adduct (C₆F₅)₃B·OH₂ hydrolyzes to afford C₆F₅H and (C₆F₅)₂BOH. The latter reacts with the surface hydroxyl groups of silica to yield SiOB­(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 (α-iminocarboxamidato)­nickel­(II) complex, was explored

Single-Step Delamination of a MWW Borosilicate Layered Zeolite Precursor under Mild Conditions without Surfactant and Sonication

Layered borosilicate zeolite precursor ERB-1P (Si/B = 11) is delaminated via isomorphous substitution of Al for B using a simple aqueous Al­(NO₃)₃ treatment. Characterization by PXRD shows loss of long-range order, and TEM demonstrates transformation of rectilinear layers in the precursor to single and curved layers in the delaminated material. N₂ physisorption and base titration confirm the expected decrease of micropore volume and increase in external surface area for delaminated materials relative to their calcined 3D zeolite counterpart, whereas FTIR and multinuclear NMR spectroscopies demonstrate synthesis of Brønsted acid sites upon delamination. Comparative synthetic studies demonstrate that this new delamination method requires (i) a borosilicate layered zeolite precursor, in which boron atoms can be isomorphously substituted by aluminum, (ii) neutral amine pore fillers instead of rigid and large quaternary amine SDAs, and (iii) careful temperature control, with the preferred temperature window being around 135 °C for ERB-1P delamination. Acylation of 2-methoxynaphthalene was used as a model reaction to investigate the catalytic benefits of delamination. A partially dealuminated delaminated material displays a 2.3-fold enhancement in its initial rate of catalysis relative to the 3D calcined material, which is nearly equal to its 2.5-fold measured increase in external surface area. This simple, surfactant- and sonication-free, mild delamination method is expected to find broad implementation for the synthesis of delaminated zeolite catalysts