Pd(0) Nanoparticles Supported Organofunctionalized Clay Driving C-C Coupling Reactions under Benign Conditions through a Pd(0)/Pd(II) Redox Interplay

Abstract

This work describes the grafting of montmorillonite clay with two organic moieties containing amine and phenyl groups, followed by Pd(0) metal nanoparticle loading, which acted as the active center toward the C-C coupling reactions, through a Pd(0)/Pd(H) redox interplay under benign conditions. Various characterization techniques revealed that the functional groups get strongly attached to the clay surface through its surface hydroxyl groups via covalent bond and 3-5 nm sized Pd(0) nanoparticles get uniformly decorated and stabilized through the organic amine moieties. The catalyst gave 97 and 96% biphenyl yield in Suzuki-Miyaura and Ullmann coupling reactions, respectively, without evidence of leached Pd in five to six runs. After this the catalytic activity decreased, but not to a marginal extent. This could be ascribed to a homogeneous catalytic process following a "release and catch" mechanism resulting in the agglomeration of Pd particles as evidenced from the TEM (transmission electron microscopy) analysis of the eight times recycled catalyst.