Chalcogenide-capped triiron clusters [Fe3(CO)9(μ3-E)2], [Fe3(CO)7(μ3-CO)(μ3-E)(μ-dppm)]and [Fe3(CO)7(μ3-E)2(μ-dppm)] (E = S, Se) as proton-reduction catalysts

Chalcogenide-capped triiron clusters [Fe-3(CO)(7)(mu(3)-CO)(mu(3)-E)(mu-dppm)] and [Fe-3(CO)(7)(mu(3)-E)(2)(mu-dppm)] (E = S, Se) have been examined as proton-reduction catalysts. Protonation studies show that [Fe-3(CO)(9)(mu(3)-E)(2)] are unaffected by strong acids. Mono-capped [Fe-3(CO)(7)(mu(3)-CO)(mu(3)-E)(mu-dppm)] react with HBF4. Et2O but changes in IR spectra are attributed to BF3 binding to the face-capping carbonyl, while bicapped [Fe-3(CO)(7)(mu(3)-CO)(mu(3)-E)(mu-dppm)] are protonated but in a process that is not catalytically important. DFT calculations are presented to support these protonation studies. Cyclic voltammetry shows that [Fe-3(CO)(9)(mu(3)-E)(2)]exhibits two reduction waves, and upon addition of strong acids, protonreduction occurs at a range of potentials. Mono-chalcogenide clusters [Fe-3(CO)(7)(mu(3)-CO)(mu(3)-E)(mu-dppm)] (E = S, Se) exhibit proton-reduction at ca. -1.85 (E = S) and -1.62 V (E = Se) in the presence of p-toluene sulfonic acid (p-TsOH). Bicapped [Fe-3(CO)(7)(mu(3)-E)(2)(mu-dppm)] undergo quasi-reversible reductions at -1.55 (E = S) and -1.45 V (E = Se) and reduce p-TsOH to hydrogen but protonated species do not appear to be catalytically important. Current uptake is seen at the first reduction potential in each case, showing that [Fe-3(CO)(9)(mu(3)-E)(2)(mu-dppm)](-) are catalytically active but a far greater response is seen at ca. -1.9 V being tentatively associated with reduction of [H2Fe3(CO)(7)(mu(3)-E)(2)(mu-dppm)](+). In general, selenide clusters are reduced at slightly lower potentials than sulfide analogues and show slightly higher current uptake under comparable conditions. (C) 2018 Elsevier B.V. All rights reserved.