Reactions of Model Complexes with

At -1 V (vs. AgjAgCl), this cation reduces protons to H2 with perfect Faradaic efficiency. The corresponding bis-phosphine complex, Fe2(SR)2(PMe3)2(CO)4 also exhibits good catalytic activity in the presence of excess protons [46]. Cyclic voltam-metric experiments indicate that the diphosphine derivatives are less catalytically active than the phosphine-cyanide complex [46, 50]. This difference is possibly attributable to the ability of the CN to convey a proton to the Fe-H-Fe group. 

The azadithiolate-containing hexacarbonyl Fe2[(SCH2)2NCH2CgH4Br)](CO)i5 also catalyzes hydrogen evolution [43]. Due to the presence of six CO ligands, this complex is more easily reduced than the substituted derivatives, operating at 0.9 V vs. AgjAgCl (Fig. 12.6). 

After protonation of the pendant amine, catalysis involves reduction of the diiron unit, which then sustains a second protonation to give an iron hydride, which couples, presumably intramolecularly, with the ammonium center to liberate H2. 

High-spin binuclear ferrous thiolates, e.g. [Fe2(SEt)g] , are imlikely to display reactivity relevant to hydrogenase, i.e. coordination of CO, H2, [51, 52]. The 

This mixed-valence species, however, decomposes rapidly at ambient temperatures. 

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Figure 6 Reaction of model complexes with molecular oxygen.

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