Structural Models for the Bimetallic Site

The aforementioned work highlights the challenges associated with controlling the coordination behavior at Fe, both with regard to its penta-coordination and the presence of both CO and CN ligands. Numerous [Fe(CN)j (CO) J complexes have been prepared in recent years [85-87] this line of research could provide sources of the Fe(CO)(CN)2 fragment. Fmthermore, the spontaneous assembly of such Fe-CO-CN species is potentially relevant to the biosynthesis of the [NiFe] 

H2-ases. From the perspective of preparing functional models, it is unclear if these diatomic ligands play any direct catalytic role, thus their electronic influence might be adequately simulated with a facial tridentate ligand. 

Arguably the most advanced structural model for the active site is the species [Fe(NS3)CO]2Ni (Fig. 12.10), despite its trimetaUic nature. Each Fe center is five-coordinate, bearing CO Vqq = 1933 cm ) and bridged via a pair offhiolato ligands to a tetrahedral Ni(SR)4 center [91]. 

---