Pd nanoparticles embedded in sponge-like porous silica as a Suzuki-Miyaura catalyst: Similarities and differences with homogeneous catalysts

Pd nanoparticles of homogeneous size were prepared by PdCl2 reduction with hydrazine in an inverse micelle microemulsion. These Pd nanoparticles were stabilized with dodecanethiol and 3-mercaptopropyltrimethoxysilane. The latter ligands were co-condensed with tetraethyl-orthosilicate, yielding an amorphous, sponge-like silica framework embedding the Pd nanoparticles. The resulting npPd@SiO2 exhibits significant catalytic activity for the demanding Suzuki coupling of electron-rich 4-bromoanisole and phenylboronic acid. The solid can be recovered and reused with only a gradual decrease in catalytic activity. Using the cross-coupling of 4-bromoacetophenone and phenylboronic acid, a total turnover number of 63,000 was obtained. npPd@SiO2 can considered one of the most active phosphine-free Pd solid catalysts reported to date. (C) 2007 Elsevier Inc. All rights reserved.