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

Abstract Chalcogenide-capped triiron clusters [Fe 3 (CO) 7 (μ 3 -CO)(μ 3 -E)(μ-dppm)] and [Fe 3 (CO) 7 (μ 3 -E) 2 (μ-dppm)] (E = S, Se) have been examined as proton-reduction catalysts. Protonation studies show that [Fe 3 (CO) 9 (μ 3 -E) 2 ] are unaffected by strong acids. Mono-capped [Fe 3 (CO) 7 (μ 3 -CO)(μ 3 -E)(μ-dppm)] react with HBF 4 .Et 2 O but changes in IR spectra are attributed to BF 3 binding to the face-capping carbonyl, while bicapped [Fe 3 (CO) 7 (μ 3 -E) 2 (μ-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 (μ 3 -Se) 2 ] exhibits two reduction waves, and upon addition of strong acids, proton-reduction occurs at a range of potentials. Mono-chalcogenide clusters [Fe 3 (CO) 7 (μ 3 -CO)(μ 3 -E)(μ-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 (μ 3 - E) 2 (μ - 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) 7 (μ 3 - E) 2 (μ - dppm)] - are catalytically active but a far greater response is seen at ca. - 1.9 V being tentatively associated with reduction of [H 2 Fe 3 (CO) 7 (μ 3 -E) 2 (μ-dppm)] + . In general, selenide clusters are reduced at slightly lower potentials than sulfide analogues and show slightly higher current uptake under comparable conditions.