Multifunctional imino-amido based asymmetrical ligands with Pd(II) for electrochemical CO2 reduction

Abstract

In this work, four new Pd(II) complexes with multifunctional and asymmetrical nitrogen donor chelates are reported for electrochemical CO₂ reduction. The anionic amido and neutral imino ligand arms were connected via rigid aromatic framework in ligand to achieve flexible electron donation for palladium. Further, imino arm of ligand was substituted with various electron donating aryl groups to study the subtle variations of inductive and resonance effects on palladium centred electro-catalysis. The successful synthesis of Pd(II) complexes were verified by various spectroscopic techniques namely ¹H NMR, ¹³C NMR, FTIR, MS and by elemental analysis. It was found out that palladium complexes with extended conjugation and more electron donor substituents on ligands caused an enhancement in electrochemical reduction of CO₂ to synthesis gas (TOF of 282s^-1). Multifunctional ligand features such as proton shuttles and hydrophobic groups were introduced to achieve high selectivity for CO (TOF of 194s^-1 by [Pd(L³)₂] Where L³ = (E)-2-((2-(cyclohexylamino) pyridin-3-ylimino)methyl)naphthalen-2-ol).