MOF-808 supported Pd Nanoparticles as heterogeneous catalyst: a non-inocent support for Suzuki-Miyaura cross-coupling reactions

GONZALO FERNÁNDEZ; IRINA DELLA CAGNOLETTA; SANDRA E. MARTÍN; ALEJANDRO M. GRANADOS; LAURA I. ROSSI; PAULA UBERMAN; ALEJANDRO M. FRACAROLI

Florianópolis

Conferencia; 15th Latin American Conference on Physical Organic Chemistry (CLAFQO-15); 2022

CLAFQO

Metal-organic frameworks (MOFs) are porous crystalline solids constructed by strong bonding between inorganic clusters and polyfunctional organic ligands. Among their attractive properties are its high permanent porosity, adjustable pore size, and the possibility of modifying their pore environments with crystallographic precision. As a result, MOFs have potential application in several different fields such as gas storage, drug transport in biological systems, separation processes, sensor construction and heterogeneous catalysis. In recent years, palladium nanoparticles (Pd NPs) have been successfully introduced into MOF to form highly active catalytic systems for cross-coupling reactions2 since its importance in organic synthesis.In this work, we employ a thermally and chemically stable Zr-based MOF themed MOF-808 featuring octahedrally shaped crystals with sizes between 500-600 nm. The MOF-808 crystals were characterized by TEM, SEM, PXRD, N2 adsorption among others. This material was used to grow Pd NPs with a ship-in-a-bottle method. For this, the palladium precursor, PdCl2, was diffused and subsequently reduced with ascorbic acid (L-AA) in presence of KBr as a modulating agent3. Variations in the reaction conditions allowed us to obtain an excess of Pd NPs in the pores rather than the external surface of the MOF crystals. The materials thus prepared (Pd@MOF-808) were evaluated in heterogeneous catalysis for Suzuki-Miyaura cross-coupling reactions.The catalytic activity, selectivity and recyclability of Pd@MOF-808 was studied using the Suzuki-Miyaura cross-coupling reaction of phenylboronic acid and 4-bromoacetophenone as a test reaction. Several reaction conditions were explored. The Pd@MOF-808 heterogeneous catalyst exhibited an excellent catalytic activity in methanol at a low temperature (65°C) with K2CO3 as base, achieving 98% of coupling product after only 6 hours. Given the importance of C-C bonds formation reactions in the field of organic chemistry, we have evaluated the recyclability of heterogeneous catalysts and the selectivity of substrates according to their size obtaining promising results.