Aerobic Oxidation of Alcohols Catalyzed by in Situ Generated Gold Nanoparticles inside the Channels of Periodic Mesoporous Organosilica with Ionic Liquid Framework

Abstract

In situ generated gold nanoparticles inside the nanospaces of periodic mesoporous organosilica with an imidazolium framework (Au@PMO-IL) were found to be highly active, selective, and reusable catalysts for the aerobic oxidation of activated and nonactivated alcohols under mild reaction conditions. The catalyst was characterized by nitrogen adsorption–desorption measurement, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), elemental analysis (EA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst exhibited excellent catalytic activity in the presence of either Cs2CO3 (35 °C) or K2CO3 (60 °C) as reaction bases in toluene as a reaction solvent. Under both reaction conditions, various types of alcohols (up to 35 examples) including activated benzylic, primary and secondary aliphatic, heterocyclic, and challenging cyclic aliphatic alcohols converted to the expected carbonyl compounds in good to excellent yields and selectivity. The catalyst was also recovered and reused for at least seven reaction cycles. Data from three independent leaching tests indicated that amounts of leached gold particles were negligible (<0.2 ppm). It is believed that the combination of bridged imidazolium groups and confined nanospaces of PMO-IL might be a major reason explaining the remarkable stabilization and homogeneous distribution of in situ generated gold nanoparticles, thus resulting in the highly active and recyclable catalyst system.

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

“…Without further reduction, Au(III)@PMO-IL catalyzed the aerobic oxidation of benzyl alcohol to benzaldehyde in the presence of Cs 2 CO 3 and showed a wonderful catalytic activity with 99% conversion and >99% selectivity for benzaldehyde. 241 The high catalytic activity was attributed to the fact that alkyl imidazolium groups in the interior of mesochannels of Au@PMO-IL not only served as a handle for in situ generation and stabilization of PEGylation triethoxysilane; NaAsc: sodium ascorbate. 235 Reproduced with permission.…”

“…Without further reduction, Au( iii )@PMO-IL catalyzed the aerobic oxidation of benzyl alcohol to benzaldehyde in the presence of Cs 2 CO 3 and showed a wonderful catalytic activity with 99% conversion and >99% selectivity for benzaldehyde. 241 The high catalytic activity was attributed to the fact that alkyl imidazolium groups in the interior of mesochannels of Au@PMO-IL not only served as a handle for in situ generation and stabilization of gold nanoparticles from AuCl 4 − but also effectively prevented the leaching of Au species into solution during the reaction process. Hence, during catalysis, in situ formed Au NPs as the active species played a vital role in driving the reaction.…”

Improved catalytic performance by changing surface and textural properties of Ru supported bifunctional periodic mesoporous organosilicas in aerobic oxidation of alcohols

“…During the past decade, numerous metal-based heterogeneous catalysts, such as palladium, 9–19 ruthenium, 20–28 cobalt, 29–37 platinum, 38–45 gold, 46–57 copper, 58–69 vanadium, 70–72 and nickel, 73,74 have successfully been employed in the aerobic oxidation of alcohols to their corresponding carbonyl compounds. Among them, ruthenium-based catalysts, in either homogeneous or heterogeneous form, are the most reliable catalytic systems reported in this research area because of possessing wide range of oxidation states and displaying a high degree of selectivity and efficiency in the oxidation of a variety of structurally diverse alcohols.…”

Supported copper on a diamide–diacid-bridged PMO: an efficient hybrid catalyst for the cascade oxidation of benzyl alcohols/Knoevenagel condensation

“…24 They are a class of materials synthesized via a sol-gel process from an organobridged alkoxysilane in the presence of a surfactant. PMO materials can be prepared in the nanoscale; this property is very important especially for potential applications such as drugrelease, [25][26][27][28][29][30][31][32][33] sensors, chromatography, catalysis, and adsorption purposes. 20,28,34,35 Generally, the organosiloxane bridges determine the physical and chemical properties of the corresponding PMOs.…”