Self-assembled Pd6L4 cage and Pd4L4 square using hydrazide based ligands: synthesis, characterization and catalytic activity in Suzuki–Miyaura coupling reactions

Abstract

A discrete Pd₆L₄ T_d-symmetric molecular cage and a discrete Pd₄L₄ square assembly were obtained using a coordination-driven self-assembly technique. The assembly, Pd₆L₄, was prepared via a face-directed method, utilising a ‘cis-clipped’ palladium(II) species and a new C₃ symmetric tripodal hydrazinic ligand. The Pd₄L₄ square assembly was prepared via an edge directed method, using the ‘cis-clipped’-palladium(II) species and a new C₂ symmetric dipodal hydrazinic ligand. Both assemblies were characterised using multinuclear NMR and ESI-MS spectroscopic techniques and elemental analysis. The size of the assemblies were assigned from HR-TEM measurements, while DOSY NMR analysis established the presence of single component species in solution. Optimised structures obtained using Hartree–Fock calculations are in conformity with the experimental results. Both the assemblies show significant catalytic activity as heterogeneous catalysts for Suzuki–Miyaura coupling reactions under mild, aerobic and phosphine free conditions in aqueous ethanolic medium.