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 PdCl 2 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 tetraethylorthosilicate, yielding an amorphous, sponge-like silica framework embedding the Pd nanoparticles. The resulting npPd@SiO 2 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@SiO 2 can considered one of the most active phosphine-free Pd solid catalysts reported to date.