This paper reports an efficient heterogeneous catalyst system based on the immobilization of Pd nanoparticles on a silica-starch substrate (PNP-SSS). The PNP-SSS is found as a highly effective recyclable catalyst in Heck and copper-free Sonogashira reactions. The silica-starch substrate (SSS) can stabilize the Pd nanoparticles effectively so that it can provide a platform and prevent the aggregation of nanoparticles and their separation from the substrate surface. It also provides suitable catalytic sites for reactions in aqueous media. The Heck and copper-free Sonogashira reactions are performed in the presence of a small amount of this catalyst in water as a green solvent. The catalyst can be reused more than six times with almost consistent efficiency and can be recovered by simple filtration.

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An efficient ruthenium-catalyzed acceptorless dehydrogenative coupling reaction of primary alcohols with 2aminophenol for one-pot synthesis of benzoxazoles is introduced. The phosphine-functionalized magnetic nanoparticles (PFMNPs; Fe 3 O 4 @SiO 2 @PPh 2 ) as a magnetic recyclable phosphorus ligand in the presence of Ru 2 Cl 4 (CO) 6 was found to be an efficient heterogeneous catalytic system for promotion of the designed protocol. The reaction was carried out efficiently with a variety of substrates to give the corresponding products in moderate to good yields.

This study offers an example of using a silica–cyclodextrin (SCD) substrate for the capture of metal nanoparticles to prepare a novel nanocatalyst for catalytic organic reactions in water as a green solvent. Also, a simple and efficient method for the size control of palladium nanoparticles (PdNPs) using their immobilization on a SCD substrate was introduced. These new catalyst systems were fully characterized using some different techniques such as XRD, TEM, SEM, TGA, ICP, XPS, and FT-IR. The average size of immobilized PdNPs on silica α-, β-, and γ-CD substrates were obtained (10, 3, and 5 nm, respectively). The immobilized PdNPs on the silica β-CD substrate (PdNP-SβCD) was recognized as the best one for the Heck reaction in aqueous media. It seems that the anchored CD moieties on the silica surface can prevent removal of PdNPs and also their aggregations. Moreover, this substrate can provide appropriate catalytic sites for reactions in aqueous media; therefore, the PdNP-SβCD catalyst showed high activity in the Heck reaction in aqueous media.