All-iron hydrogenase: synthesis, structure and properties of {2Fe3S}-assemblies related to the di-iron sub-site of the H-cluster

Tripodal dithiolate thioether ligands MeC(CH2SH)(2)CH2SR (R = Me or Ph) provide a route to {2Fe3S}-complexes and syntheses are described. X-Ray crystal structures for two {2Fe3S}-pentacarbonyl derivatives and that for the first carbonyl cyanide are reported, together with temperature dependent H-1-NMR, Mossbauer, FTIR and redox potential data. The NMR data establish fluctionality associated with inversion at the thioether sulfur in the carbonyl complexes. The Mossbauer data affirm that the coordination environment of the two iron atoms in a dicyanide bridging carbonyl intermediate are differentiated. Bridging carbonyl intermediates have been structurally and spectroscopically identified in resting and CO inhibited forms of the sub-site of all-iron hydrogenases; the observation of a thermally unstable {2Fe3S}-bridging carbonyl intermediate is discussed in this context.