A coordination driven self-assembled Pd6L8 nanoball catalyses copper and phosphine-free Sonogashira coupling reaction in both homogeneous and heterogeneous formats

Abstract

A Pd₆L₈ type coordination driven self-assembly was constructed using a tripodal ligand L (L = N¹,N³,N⁵-trimethyl-N¹,N³,N⁵-tris[(pyridin-4-yl)methyl]-1,3,5-benzene tricarboxamide) and palladium nitrate. The self-assembly was fully characterised using one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance spectroscopy, electrospray ionization-mass spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy and elemental analysis. Use of high resolution transmission electron microscopy (HR-TEM) analysis confirms the discrete nature of the assembly with a dimension of ∼2.8 nm, consistent with the density functional theory optimised structure. The assembly acts as an efficient homogeneous catalyst for a copper and phosphine free Sonogashira reaction under mild and aerobic conditions in aqueous medium. The catalyst shows equal efficiency for both electron deficient and electron rich aryl iodides and bromides and is also suitable for use with aliphatic alkynes. The utility of the catalyst as a reusable heterogeneous catalyst in toluene was assessed up to the 3rd cycle without any significant loss of catalytic activity.