Design of highly robust halloysite nanoclay supported palladium complex as a highly active heterogeneous catalyst for construction of biaryls

Metal leaching, contamination of final product, lack of recovery, and limited reusability are important problems in catalyst systems. The best way to overcome these drawbacks is to design highly stable heterogeneous catalysts. Therefore, we prepared in this study a heterogeneous palladium catalyst (Hal-Pd) from halloysite nanoclay which is a natural, non-toxic, cheap, biocompatible and environmentally friendly clay with high surface area. Then, Hal-Pd was evaluated as a heterogeneous catalyst for Suzuki-Miyaura coupling reactions under solvent-free media. Hal-Pd catalyst showed high tolerance against different substituted aryl halides. Furthermore, Hal-Pd catalyst was easily recovered for the next runs, and it was reused at least ten times with a slight loss in product yield from 99% to 82%. It also showed very minimal level of Pd leaching. Besides its high catalytic activity, Hal-Pd catalyst presented some advantages such as operation simplicity, short reaction time, and high stability. This study shows that halloysite nanoclay can be an alternative catalyst support compared to other known support materials, and the newly designed Hal-Pd is an efficient catalyst that facilitates the synthesis of various biaryl compounds...