Abstract
Ultra-small mesoporous silica nanoparticles (MSNs) have been synthesized at room temperature with particle sizes ranging from 28 to 45 nm. These MSNs have been employed as heterogeneous supports for palladium and gold nanocatalysts. The colloidal nature of the MSNs is highly useful for catalytic applications as it allows for better mass transfer properties and a more uniform distribution of the nanocatalysts in solution. The two nanocatalysts were evaluated in the cycloisomerization of alkynoic acids and demonstrated to produce the corresponding alkylidene lactones in good to excellent yields under mild conditions. In addition to their high activity, the catalysts exhibit low degree of metal leaching and straight-forward recycling, which highlight the practical utility of MSNs as supports for nanocatalysts.
Highlights
Transition metal-based catalysis has played a central role in advancing the field of organic synthesis, by allowing for the development of new types of reactions that have not been possible a Authors to whom correspondence should be addressed
The work in nanocatalysis has been greatly facilitated by the rapid progress in the field of nanotechnology during the past decades, which has provided a variety of size- and shape-selective methods for synthesizing metal nanoparticles.2e, 3 some challenges still remain in the synthesis of nanosized transition metal particles, where one of the most crucial issues concerns how to prevent the nanoparticles from aggregating during the catalytic conditions, which generally translates into reduced catalytic activity over time
N2 adsorption/desorption indicated a typical type IV isotherm of the mesoporous silica nanoparticles (MSNs) with a specific surface area of 331 m2 g−1, a total pore volume of 1.83 cm3 g−1 contributed by both mesopores and macropores (Figure S2). 3D electron tomography was performed on Pd loaded MSNs, and the reconstructured tomogram clearly showed that the mesopores are open to the external surface of the MSNs (Movie S1 and Figure S3)
Summary
Transition metal-based catalysis has played a central role in advancing the field of organic synthesis, by allowing for the development of new types of reactions that have not been possible a Authors to whom correspondence should be addressed. The two nanocatalysts were evaluated in the cycloisomerization of alkynoic acids and demonstrated to produce the corresponding alkylidene lactones in good to excellent yield under mild conditions. In addition to their high activity, the catalysts exhibit low degree of metal leaching and straight-forward recycling, which highlight the practical utility of MSNs as supports for nanocatalysts.
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