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

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.
(© 2024 Wiley-VCH GmbH.)