Pd(II) complexes with amide-based macrocycles: syntheses, properties and applications in cross-coupling reactions

This work shows Pd(II) complexes in a set of 13-membered amide-based macrocyclic ligands varied by the placement of e(-)-donating and e(-)-withdrawing substituents on the ligand framework. Ligands constitute a N-4 square-planar cavity and optimally house the Pd(II) ion. The solution-state structure via NMR and absorption spectra substantiates the solid-state structure obtained by crystallography. The electrochemical studies display the impact of electronic substituents on ligands that significantly influence the redox properties and also shift the locus of oxidation. These complexes were used in the Suzuki and Heck cross-coupling reactions. The moderate cross-coupling reaction results are due to limited redox accessibility that can be improved either by using substrates with a better leaving group or by placing electron-withdrawing substituents on the macrocyclic ligands.