Grant Johnson - Redox chemistry in thin layers of organometallic complexes prepared using ion soft landing

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      Volume:   13

        Issue: 1

        Pages: 267-275


    Published: 2011


        Soft landing (SL) of mass-selected ions is used to transfer   catalytically-active metal complexes complete with organic   ligands from the gas phase onto an inert surface. This is part of   an effort to prepare materials with defined active sites and thus   achieve molecular design of surfaces in a highly controlled way.   Solution-phase electrochemical studies have shown that   V(IV)O(salen) reacts in the presence of acid to form   V(V)O(salen)(+) and the deoxygenated V(III)(salen)(+) complex-a   key intermediate in the four electron reduction of O(2) by   vanadium-salen. In this work, the V(V)O(salen)(+) and   [Ni(II)(salen) + H](+) complexes were generated by electrospray   ionization and mass-selected before being deposited onto an inert   fluorinated self-assembled monolayer (FSAM) surface on gold. A   time dependence study after ion deposition showed loss of O from   V(V)O(salen)(+) forming V(III)(salen)(+) over a four-day period,   indicating a slow interfacial reduction process. Similar results   were obtained when other protonated molecules were co-deposited   with V(V)O(salen)(+) on the FSAM surface. In all these   experiments oxidation of the V(III)(salen)(+) product occurred   upon exposure to oxygen or to air. The cyclic regeneration of   V(V)O(salen)(+) upon exposure to molecular oxygen and its   subsequent reduction to V(III)(salen)(+) in vacuum completes the   catalytic cycle of O2 reduction by the immobilized vanadium-salen   species. Moreover, our results represent the first evidence of   formation of reactive organometallic complexes on substrates in   the absence of solvent. Remarkably, deoxygenation of the   oxo-vanadium complex, previously observed only in highly acidic   non-aqueous solvents, occurs on the surface in the UHV   environment using an acid which is deposited into the inert   monolayer. This acid can be a protonated metal complex, e. g.   [Ni(II)(salen) + H](+), or an organic acid such as protonated   diaminododecane.

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