Colloidal Supported Metal Nanoparticles (CSMNs) as Effective Nanocatalysts for Liquid-Phase Suzuki Cross-Coupling Reactions

We investigate the catalytic activity obtained for three types of nanocatalysts: colloidal supported metal nanoparticles (CSMNs) prepared with silica colloids in solution that are air-dried, CSMNs prepared with dry silica colloids resuspended in doubly deionized water that are air-dried, and palladium nanoparticles loaded onto bulk silica dispersed in doubly deionized water that are air-dried. The three types of catalysts are prepared with and without the aminopropyltriethoxysilane (APTES) linker for a total of six different catalysts that are tested for the liquid-phase cross-coupling reaction between phenylboronic acid and iodobenzene to form biphenyl. TEM images and EDS spectra were obtained for the six different catalysts to see if the palladium nanoparticles are covalently attached to the functionalized silica colloids and functionalized bulk silica supports and to see if the palladium nanoparticles are adsorbed onto the unfunctionalized silica colloids and unfunctionalized bulk silica supports. The six different catalysts are tested for the Suzuki reaction between phenylboronic acid and iodobenzene to form biphenyl. The CSMNs prepared using unfunctionalized wet silica colloids reacted with palladium nanoparticles that are air-dried resulted in the highest catalytic activity. In the case of the nanocatalysts prepared using the APTES linker for covalent attachment of the palladium nanoparticles to the wet silica colloids or bulk silica dispersed in doubly deionized water that are air-dried, there is lower catalytic activity compared to their counterparts prepared without the use of the APTES linker. This suggests that the APTES could be acting as a catalyst poison resulting in lower catalytic activity for the Suzuki reaction between phenylboronic acid and iodobenzene to form biphenyl compared to unfunctionalized CSMNs.