Palladium (II) pyridylidene sulfonamides (PYSAs) for electrocatalytic reduction of CO₂

A new class of donor flexible nitrogen ligands, namely pyridylidene sulfonamides (PYSAs; N-(1-benzylpyridin-4(1H)-ylidene)benzene-sulfonamide, N-(1-benzylpyridin-4(1H)-ylidene)thiophene-2-sulfonamide, N-(1-benzylpyridin-4(1H)-ylidene)pyridine-2-sulfonamide and N-(1-benzylpyridin-4(1H)-ylidene)-8-quinoline-sulfonamide), were prepared from 4-amino-1-benzylpyridin-1-ium chloride and various aromatic sulfonyl chlorides. The treatment of PYSAs with [(CH₃CN)₂PdCl₂] afforded the corresponding Pd(II) complexes. The newly synthesized compounds were characterized by multinuclear ¹H and ¹³C NMR spectroscopy, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Their redox chemistry was then evaluated under an inert atmosphere of nitrogen and carbon dioxide, both in the presence and absence of protons. An apparent interaction of CO₂ with each Pd(II) catalyst was inferred by the collection of cyclic voltammograms and the enhancement of peak currents at respective peak potentials. All catalysts were robust under bulk electrolysis conditions over 3600 s.