Ligand-induced substrate steering and reshaping of [Ag2(H)]+ scaffold for selective CO2 extrusion from formic acid

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Abstract
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, [LAg2(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, HO2CH, 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. [Ag2(H)]+and [Ph3PAg2(H)]+react with formic acid yielding Lewis adducts, while [(Ph3P)2Ag2(H)]+is unreactive. Using bis(diphenylphosphino)methane (dppm) reshapes the geometry of the binuclear Ag2(H)+scaffold, triggering reactivity towards formic acid, to produce [dppmAg2(O2CH)]+and H2. Decarboxylation of [dppmAg2(O2CH)]+via CID regenerates [dppmAg2(H)]+. These gas-phase insights inspired variable temperature NMR studies that show CO2and H2production at 70 °C from solutions containing dppm, AgBF4, NaO2CH and HO2CH.

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