Abstract
The azadithiolate complex Fe(2)[(SCH(2))(26)NMe](CO)(6) reacts with borane to give an initial 1:1 adduct, which spontaneously decarbonylates to give Fe(2)[(SCH(2))(2)NMeBH(3)](CO)(5). Featuring a Fe-H-B three-center, two-electron interaction, the pentacarbonyl complex is a structural model for H(2) complexes invoked in the [FeFe]-hydrogenases. The pentacarbonyl compound is a "σ complex", where a B-H σ bond serves as a ligand for iron. The structure of this σ complex was characterized by variable-temperature NMR spectroscopy and X-ray crystallography. Complementary to the 1:1 borane adduct is the quaternary ammonium complex [Fe(2)](SCH(2))(2)NMe(2)](CO)(6)](+), which was also characterized. It represents a kinetically robust analogue of the N-protonated amine cofactor, as indicated by its mild reduction potential.