Abstract
The preparation, spectroscopy, and structure are described for [Fe(κ(3)-cys)(CN)(CO)(2)](-) ([2](-)). 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 [2](-) was prepared by treating [Fe(succinimido)(Br)(CN)(CO)(3)](-) ([1](-)) with cysteinate. From [1](-) 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 [1](-). Complex [1](-) is prepared by oxidative addition of N-bromosuccinimide to [Fe(CN)(CO)(4)](-). The work is complemented by (13)CO exchange experiments and DFT calculations.