Organosilicas with Chiral Bridges and Self-Generating Mesoporosity

Abstract

Amine-functionalized, chiral mesoporous organosilicas were prepared from a rationally designed precursor, which combines the functions of a network builder, a chiral latent functional group, and a porogen in one molecule. The precursors are formed by a convenient enantioselective hydroboration using (S)-monoisopinocampheylborane on an ethylene-bridged silica precursor. These precursors do selforganize when hydrolysis of their inorganic moiety takes place via an aggregation of their organic moiety into hydrophobic domains. After a condensation-ammonolysis sequence mesoporous organosilicas functionalized with chiral amine groups are obtained, with the complete chiral functionalities located at the pore wall surface and therefore accessible to chemical processes. The pore size of the resulting organosilicas can be fine-tuned using different organic moieties attached to the boron group in the first step. While a wormlike arrangement of pores is observed for the pure precursor, common surfactants can be admixed to further control and tailor the resulting mesoporous system. In certain phase ranges, also chiral periodic mesoporous organosilicas can be obtained.

Periodic Mesoporous Organosilica Materials: Self‐Assembly of Carbamothioic Acid‐Bridged Organosilane Precursors

“…Therefore, these materials have greater potential applications than the conventional siliceous mesoporous materials in catalysis, [4] adsorption, [5] and nanostructure templating. [6] So far, there have been many reports on the preparation of PMOs, but the resulting PMO materials are mainly limited to a few types of alkane, [7][8][9] alkene, [10,11] phenyl, [12] and aromatic bridging functional groups. [13,14] The synthesis of PMOs was also attempted from precursors with large bridging groups, such as bipyridine, biphenylene, tetraazacyclotetradecane, and Schiff base complexes, [15][16][17][18] but these attempts often led to PMOs with a small percentage of bridging groups.…”

Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications

“…A similar methodology to obtain pure chiral PMOs was further developed by Thomas et al 181 They obtained a PMO View Online material with chiral amines (52) incorporated into the framework. They showed the optical activity of the resulting material by circular dichroism measurements, confirming the chiral character of the amine groups.…”

Funktionsmaterialien: von harten zu weichen porösen Netzwerken

“…B. durch Herauslösen der organischen Gruppe aus den Netzwerken mit Flusssäure und Analyse der verbleibenden organischen Gruppe mithilfe von HPLC an chiraler Phase. [87] Auch konnte die optische Aktivität der Proben direkt an den PMOs gemessen werden, indem die Pulver entweder in einem isorefraktiven Lö-sungsmittel [85,86] oder als KBr-Presslinge mit Circulardichroismus(CD)-Spektroskopie untersucht wurden. [88] Die Zugabe eines unchiralen, sauren Chromophors (Benzoesäure) zum chiralen, Amin-funktionalisierten PMO 2 und eine anschließende CD-Messung zeigten eine induzierte optische Aktivität des Chromophors, wodurch der Nachweis erbracht wurde, dass die chirale funktionelle Gruppe für in die Poren eindringende Substrate zugänglich ist.…”