Pd embedded on halloysite-cyclodextrin nanosponges hybrid: an efficient catalyst for promoting ligand and copper-free Sonogashira reaction

A novel hybrid was developed through covalent conjugation of halloysite nanoclay and cyclodextrin nanosponge and used for embedding Pd salt to afford Pd@Hal-CDNS with utility for promoting ligand and copper-free Sonogashira coupling reaction in aqueous media (Scheme 1). The reason behind this design was the fact that CDNS is composed of cyclodextrins with capability to encapsulate various guest molecules. On the other hand, Hal is an efficient support for immobilizing the catalysts. The formation of Pd@Hal-CDNS was confirmed by applying ICP-AES, TEM, SEM, TGA, XRD and FTIR analysis (Figure 1). CDNS could encapsulate the hydrophobic reagents and bring them near the catalytic active sites and allowed the reaction proceed in aqueous media. Notably, the catalyst was reusable up to five runs and could be recycled with negligible loss of catalytic activity and Pd leaching.