Oxygen-Atom Defect Formation in Polyoxovanadate Clusters via Proton-Coupled Electron Transfer

Abstract

The uptake of hydrogen atoms (H-atoms) into reducible metal oxides has implications in catalysis and energy storage. However, outside of computational modeling, it is difficult to obtain insight into the physicochemical factors that govern H-atom uptake at the atomic level. Here, we describe oxygen-atom vacancy formation in a series of hexavanadate assemblies via proton-coupled electron transfer, presenting a novel pathway for the formation of defect sites at the surface of redox-active metal oxides. Kinetic investigations reveal that H-atom transfer to the metal oxide surface occurs through concerted proton–electron transfer, resulting in the formation of a transient V III –OH 2 moiety that, upon displacement of the water ligand with an acetonitrile molecule, forms the oxygen-deficient polyoxovanadate-alkoxide cluster. Oxidation state distribution of the cluster core dictates the affinity of surface oxido ligands for H-atoms, mirroring the behavior of reducible metal oxide nanocrystals. Ultimately, atomistic insights from this work provide new design criteria for predictive proton-coupled electron-transfer reactivity of terminal M=O moieties at the surface of nanoscopic metal oxides.

Coordination-induced bond weakening of water at the surface of an oxygen-deficient polyoxovanadate cluster

“…Previous work from our group has shown that the BDFE(O–H) of reduced POV-alkoxide clusters can be approximated by monitoring the extent to which H-atom transfer occurs between various organic reagents and a cluster. 12,13 The observation of quantitative reduction of the POV suggests that the BDFE(O–H) of the cluster is sufficiently larger than that of DHP, establishing an effective minimum value of the BDFE(O–H) avg for the reduced cluster in THF. However, despite the fact that there exists a substantial library of known thermochemical parameters of PCET reagents, the BDFE(N–H) avg for DHP is not reported in THF.…”

“…9,10 To experimentally model mechanisms of PCET at MO x surfaces, researchers have turned to the investigation of their molecular analogues. [11][12][13][14][15][16] One class of compounds that is particularly well-suited for these studies is polyoxometalates (POMs). POMs are three-dimensional MO x assemblies composed of early transition metal oxyanions linked together by edge-or face-sharing oxide ligands.…”

Metal–Support Interactions in Molecular Single-Site Cluster Catalysts

“…Due to their synthetic tunability and homogeneous nature, atomically precise nanoclusters are advantageous for this purpose and can serve as both functional models and as platforms for new catalyst development. , Examples of molecular clusters that feature metal/support architectures exist, − such as the catalytically competent Au n ( SR ) m clusters in which the reactive surface gold atoms are chemically distinguished from those of the cluster core . While tuning cluster size − and the coordination environment of the active sites has been shown to modulate their catalytic activity, studies that identify the active site and systematically correlate how its identity impacts the metal/support interaction and the emerging catalytic activity are yet to materialize.…”

Quantitative UO bond activation in uranyl complexes via silyl radical transfer

“…9,10 More recently, PCET from molecular donors has been used to incorporate hydrogen atom equivalents into metal oxides, allowing for the activation of typically inert substrates by avoiding high-energy intermediates. 11,12 In a similar vein, silylium-coupled electron transfer presents an intriguing alternative to streamline the mechanism of UQO bond activation. Mashima and coworkers have demonstrated that the silyl transfer reagent, 1,4bis(trimethylsilyl)dihydropyrazine, Pyz(SiMe 3 ) 2 , called ''Mashima's reagent'', can facilitate the reduction of transition metals in high oxidation states.…”