(585bm) Metal Nanoparticles Encapsulated in Melamine Dendrons Supported on MCM-41 and SBA-15

Dendrimer-encapsulated nanoparticles (DENs) have attracted interest since they were first introduced in 1998 [1]. This synthetic approach leads to well-defined sizes, compositions and structures of nanoparticles controlled by the dendrimer template. The nanoparticles formed have been investigated for numerous applications including catalysis, sensing, etc. DENs made in solution have been investigated for reactions such as Heck coupling, allyl alcohol hydrogenation, and electrocatalysis [2]. In this work we form metal nanoparticles using melamine dendrons grafted to mesoporous silica, building off prior work in our lab reporting the synthesis of well-defined dendrons grown off mesoporous silica.

This talk will describe the synthesis, characterization, and catalytic testing of Pd, Cu, and Au nanoparticles formed in dendrons on mesoporous silica. Thermogravimetric analysis (TGA), infrared spectroscopy, nitrogen porosimetry, and UV-Vis spectroscopy were used to confirm the target ligand loadings, that the ligands formed are the desired ligands, that the materials textural properties change as expected upon dendrimer formation, and monitor the metal uptake and reduction processes. These methods show that it is possible to make well-defined uniform nanoparticles using this approach; STEM measurements show that the Pd particles formed have a mean size of 2.4 nm with minimal polydispersity, and that the Cu and Au particles are both 3 nm in size.

Catalytic testing of the hybrid materials will also be reported. For the Pd-dendron samples the Heck reaction between n-butyl acrylate and bromobenzene (or iodobenzene) was performed and the materials demonstrate high conversion and selectivity to the target product (over 60% conversion of the halide and 40% selectivity to the target product after 24 h at 393 K). How metal loading and dendron generation impact reactivity will also be discussed.

In the case of Cu and Au samples the click reaction between benzyl azide and cyclohexylacetylene will be described. Results to date show over 70% conversion in 24 hours at room temperature with essentially quantitative selectivity to the desired product over Cu samples. The effect of metal loading, dendron generation, and how samples containing both gold and copper behave will be described.

In both of the reactions described above one has concerns around metal leaching. Our efforts in quantifying this using the hot filtrate test and a variety of solvents for the reaction will also be described.

References

1. Zhao, M., Sun, L. and Crooks, R. M., J. Am. Chem. Soc. 120, 4877 (1998).

2. Myers, V. S., Weir, M. G., Carino, E. V., Yancey, D. F., Pande, S. and Crooks, R. M., Chemical Science 2, 1632 (2011).

3. Acosta, E. J., Carr, C. S., Simanek, E. E. and Shantz, D. F., Advanced Materials 16, 985 (2004).

4. Yoo, S., Lunn, J. D., Gonzalez, S., Ristich, J. A., Simanek, E. E. and Shantz, D. F., Chemistry of Materials 18, 2935 (2006).