Reactivity and Improved Synthesis of Tetrafluoroargentate Salts

Abstract

Accessing the tetrafluoroargentate anion [AgF4]−, a powerful oxidizing agent, with the silver atom in the formal oxidation state +III, so far required the handling of elemental fluorine and anhydrous HF. Herein, we report a simple and safe method for generating tetrafluoroargentate salts on a preparative scale. Adding tetraalkylammonium halide salts, [NR4]X, or fluortetraphenylphosphorane, FPPh4 to silver difluoride in acetonitrile leads to the formation of the corresponding tetrafluoroargentate salt, [NR4][AgF4], or [PPh4][AgF4] and silver halide AgX via disproportionation. The reaction was monitored employing 19F and 109Ag NMR spectroscopy. In the single-crystal X-ray structure analysis, the expected square planar arrangement of the silver atom is observed, confirming the d8 configuration of the silver ion in the formal oxidation state +III. The fluorinating properties were demonstrated through the oxidation of bis(4-nitrophenyl)disulfide (aryl–S–S–aryl, with aryl = 4-NO2C6H4). The tetrafluoroargentate salt enables the oxidation of sulfur(I) to sulfur(VI), resulting in the formation of aryl-SF5. In strong contrast, treating the disulfide with AgF2 only results in the oxidation to the sulfur(IV) derivative, aryl-SF3, under the same conditions.