Characterization of Complex-B ([Fe(κ-cys)(CN)(CO)]), Biosynthetic Precursor to the [FeFe]-Hydrogenase Active Site, and Related Complexes.

The preparation, spectroscopy, and structure are described for [Fe(κ-cys)(CN)(CO)] ([]). Otherwise known as complex-B, this coordination complex is an early intermediate in the biosynthesis of the active site of the [FeFe]-hydrogenases. As confirmed by X-ray crystallography, the complex is octahedral with a tridentate cysteinate ligand. The octahedron is completed with two CO ligands and CN, which is trans to thiolate. A second isomer is observed in solution. Complex [] was prepared by treating [Fe(succinimido)(Br)(CN)(CO)] ([]) with cysteinate. From [] the related penicillamine and homocysteine complexes were also prepared. A practical reagent for probing the biosynthetic role of complex-B, called Syn-B-Br, can be produced in good yield from []. Complex [] is prepared by oxidative addition of -bromosuccinimide to [Fe(CN)(CO)]. The work is complemented by CO exchange experiments and DFT calculations.