Solution-Phase Synthesis of Platinum-Decorated Hydrogen\nTungsten Bronzes for Hydrogen Atom Transfer from Oxides to Molecules

Hydrogen bronzes can be used as hydrogen\ndonors for the broad class\nof reactions involving proton-coupled electron transfer (PCET). Here,\nwe describe a method to prepare platinum-decorated hydrogen tungsten\nbronzes, Pt@H<sub><i>x</i></sub>WO<sub>3</sub>·<i>n</i>H<sub>2</sub>O with <i>n</i> = 0, 1, and 2, by\nreacting the pristine oxides at modest temperatures with a mild reducing\nagent, H<sub>3</sub>PO<sub>2</sub>, and H<sub>2</sub>PtCl<sub>6</sub> in an aqueous solution. We explored the tunability and kinetics\nof this reaction and compared it with that of archetypal gas–solid\nhydrogen spillover. We demonstrate that the identity of the noble\nmetal affects the extent of bronze reduction. This suggests that the\nmechanism proceeds via the adsorption of a hydrogen-atom species on\nthe noble metal. Finally, we explored the ability of the Pt-decorated\nhydrogen tungsten bronzes to hydrogenate a model H<sup>+</sup>/e<sup>–</sup> acceptor, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO).\nThe bronze phases return to their fully oxidized states along with\nthe subsequent reduction of TEMPO to TEMPOH. Overall, this work demonstrates\na solution-phase method to obtain hydrogen bronzes, which can then\nbe used to perform hydrogen transfer reactions, providing a pathway\nfor the use of extended transition metal oxides as stoichiometric\nreagents for broad classes of hydrogenation reactions.