Palladium(II) and platinum(II) based S^N^S and Se^N^Se pincer complexes as catalysts for CO₂ hydrogenation and N-formylation of diethylamine to diethylformamide

In this study, we report newly synthesized S^N^S and Se^N^Se tridentate platinum(II) and palladium(II) pincer complexes. These complexes have been evaluated as pre-catalysts in the hydrogenation of carbon dioxide to formate under basic conditions. These new molecular catalysts proved to be active in forming industrially valuable chemical intermediates like formate and diethylformamide from CO₂. The complexes are soluble in THF and insoluble in water enabling easy catalyst recovery from a biphasic mixture of THF/water solvent system after catalysis. The pincer ligands provide a robust framework for stabilizing the active centers through various catalytic cycle steps. Palladium(II) catalysts yielded formate with TONs as high as 1881, while Se^N^Se platinum(II)-based catalysts (C1, C2, and C3) catalyzed the hydrogenation of CO₂ to formate at TONs of 550, 421, and 1254, respectively, after 24 h. Similarly, the N-formylation of diethylamine using CO₂ and H₂ in the presence of C2 is effective with yields up to 71 %.