Palladium complexes bearing aromatic Bis-aldimine N^N^N pincer ligands; activity as catalysts in the hydrogenation of carbon dioxide

Abstract

CO2 hydrogenation can serve as an avenue for the use of CO2 as a C1 carbon source whiles simultaneously serving as a means of hydrogen ‘storage’. Herein we report on the synthesis of new pyridine-2,6-bis(methanylylidene)bis(CH = NR)- palladium chloridecomplexes were(R = Ph, p-Br-C6H4, 2,6-dimethyl-C6H3). All the complexes were fully characterized by 1H NMR, 13C NMR, FT-IR, elemental analysis, mass spectrometry and single-crystal X-ray diffraction studies where appropriate. This work sought to investigate and discuss the role of substituents in respect of electronic effects, choice of pincer ligand system backbone, and steric effects of the substituents and the role it has on the hydrogenation of CO2. These pincer complexes were investigated as catalysts in the hydrogenation of CO2 and were found to be efficient in the direct catalytic carbon dioxide hydrogenation to formate with the highest TON at 520.