National Institute Of Materials Physics - Romania

TEMPO stable free radical has been supported on porous silica nanoparticles in different ways and the resulted materials have been tested as heterogeneous oxidation catalyst of three benzylic alcohols using air as final oxidant and nitrosonium tetrafluoroborate as cocatalyst. Good to excellent yields were obtained. The catalytic system consists in fact in two coupled cycles, NO/NO2 and TEMPO+/TEMPO, able to convert under mild conditions (room temperature, air, metal and halogen free condition) alcohols into aldehydes or ketones. Under these conditions, supported TEMPO on silica nanoparticles containing gold clusters lowers the efficiency of the catalyst.

A bimodal (micro/mesoporous) COF was synthesized by coupling tetrakis-1,3,5,7-(4'-iodophenyl) adamantane with 4,4'-diethynylbiphenyl following a Sonogashira protocol. The COF preparation strategy led, however, to the incomplete recovery of the palladium catalyst and ICP-OES analysis indicated that around 0.1 wt% palladium remained inside the pores. Noteworthily, the remnant palladium catalyst is still accessible and can be valorised in additional catalytic reactions like the hydrogenation of nitrostyrene. Further deposition of 0.5 wt% active metals (like palladium or gold) enhanced the catalytic activity and tuned the catalyst selectivity with respect to analogous metal catalysts prepared using active carbon as a support. The resulting COF-supported metal NPs are stable and recyclable catalysts. Under normal conditions, this COF is also able to adsorb large amounts of weak electrophilic gases like carbon dioxide.