Synthesis and characterization of palladium complexes containing tridentate ligands with PXP (X = C, N, O, S, As) donor sets and their evaluation as electrochemical CO2 reduction catalysts

Square-planar palladium complexes containing tridentate ligands with PXP (X = C, N, O, S, and As) donor sets have been prepared. For (Pd(POP-R)(CH₃CN)₂)(BF₄)₂ complexes (where POP-R is bis((diethylphosphine)ethyl)ether), bis((diphenylphosphino)ethyl)ether, or Bis((dicyclohexylphosphino)ethyl)ether), the POP-R ligands function as bidentate ligands. For all other complexes, the PXP ligands function as tridentate ligands. The dependence of the catalytic current on CO₂ and acid concentrations is consistent with the formation of a hydroxycarbonyl intermediate which decomposes in the presence of acid to form hydrogen as the catalytic product.