Ferrocenyl Dithiophosphonate Ag(I) Complexes: Synthesis, Structures, Luminescence, and Electrocatalytic Water Splitting Tuned by Nuclearity and Ligands

Abstract The heterometallic [Ag(I)/Fe(II)] molecular electrocatalysts for hydrogen production were introduced here to recognize the mutual role of metallic nuclearity and ligand engineering. A series of ferrocenyl dithiophosphonate stabilized mononuclear [Ag(PPh 3 ) 2 {S 2 PFc(OR)}] {where R=Me ( 1 ), Et ( 2 ), n Pr ( 3 ), i Pr ( 4 ), i Amyl ( 5 ); Fc=Fe ( ɳ 5 ‐C 5 H 4 ) ( ɳ 5 ‐C 5 H 5 )} and dinuclear [Ag(PPh 3 ){S 2 PFc(OR}] 2 {where R=Et ( 2 a ), and n Pr ( 3 a )} complexes were synthesized and characterized by SCXRD, NMR ( 31 P and 1 H), ESI‐MS, UV‐Vis, and FT‐IR spectroscopy. The comparative electrocatalytic HER behavior of 1 – 5 and 2 a – 3 a showed effective current density of 1 mA/cm 2 with overpotentials ranging from 772 to 991 mV, demonstrating the influence of extended and branched carbon chains in dithiophosphonates and metallic (mono‐/di−) nuclearity, which correlates with documented tetra‐nuclear [Ag 4 (S 2 PFc(O n Pr) 4 ], 6 . DFT study suggests the coordinated ( μ 1 ‐S) site of ligands is the reactivity center and the adsorption energy of intermediate [H*‐SM] varies with the engineering of ligand and nuclearity. A catalytic mechanism using mononuclear ( 1 ) and di‐nuclear ( 2 a ) was proposed with the assistance of DFT. Each complex, being the first example of Ag(I) dithiophosphonates, exhibits intense photoluminescence with high quantum yields ranging from 33 % to 67 %. These results link the lower nuclearity structures to their physical and catalytic properties.