Ligand-induced substrate steering and reshaping of [Ag(2)(H)](+) scaffold for selective CO(2) extrusion from formic acid

Metalloenzymes preorganize the reaction environment to steer substrate(s) along the required reaction coordinate. Here, we show that phosphine ligands selectively facilitate protonation of binuclear silver hydride cations, [LAg(2)(H)](+) by optimizing the geometry of the active site. This is a key step in the selective, catalysed extrusion of carbon dioxide from formic acid, HO(2)CH, with important applications (for example, hydrogen storage). Gas-phase ion-molecule reactions, collision-induced dissociation (CID), infrared and ultraviolet action spectroscopy and computational chemistry link structure to reactivity and mechanism. [Ag(2)(H)](+) and [Ph(3)PAg(2)(H)](+) react with formic acid yielding Lewis adducts, while [(Ph(3)P)(2)Ag(2)(H)](+) is unreactive. Using bis(diphenylphosphino)methane (dppm) reshapes the geometry of the binuclear Ag(2)(H)(+) scaffold, triggering reactivity towards formic acid, to produce [dppmAg(2)(O(2)CH)](+) and H(2). Decarboxylation of [dppmAg(2)(O(2)CH)](+) via CID regenerates [dppmAg(2)(H)](+). These gas-phase insights inspired variable temperature NMR studies that show CO(2) and H(2) production at 70 °C from solutions containing dppm, AgBF(4), NaO(2)CH and HO(2)CH.