The [FeFe]-Hydrogenase enzyme is capable of reducing protons to dihydrogen at a rate of 6000/sec.  Bioinorganic chemists have focused on synthesis and characterization of the 2Fe active site of the enzyme, which consists of a single azadithiolate ligand as well as three carbonyl and two cyanide ligands.  This active site is bound to a 4Fe4S cluster buried in the core of the protein.  A recent study of the biosynthesis of this unique 2Fe cluster has found that a (�-(SCH-2)2X)[Fe2(CO)4(CN)2]2- model complex can bind the 4Fe4S cluster of the scaffold protein (HydF) through a bridging cyanide, previously unknown in biology.1  In order to gain insight into this intermediate, a hydrogenase active site mimic was bound to a model of the 4Fe4S cluster through a cyanide bridge.  A variety of (?5-C-5H5)FeII(CO)x(CN)y(THF)zn- �piano stool� complexes were chosen to model the 4Fe4S cluster.    Combinations of these piano stool compounds, [CpFe(CO)-2THF]+, CpFe(CO)-2CN, and [CpFe(CN)-2CO]-, and 2Fe site models, such as (�-S(CH-2)3S)[Fe2(CO)6-], (�-S(CH-2)3S)[Fe2(CO)5CN]-, and (�-S(CH-2)3S)[Fe2(CO)4(CN)2]2- were used to target either CpFeII(�-CN)FeIFeI or CpFeII(�-NC)FeIFeI bridging species.  The individual precursors were prepared according to literature methods.2-7  The most successful attempt to prepare the three iron constructs resulted from combining CpFe(CO)-2THF+ with (�-S(CH-2)3S)[Fe2(CO)5CN]- to yield a complex with the bridging cyanide.  Infrared spectroscopy in the diatomic region, particularly v(CN) IR data indicates the bridging of cyanide from the 2Fe model complex to the CpFeII piano stool complex.   Complexes were identified primarily through FTIR spectroscopy, but also using 1H/13C NMR, Mass Spectroscopy, and X-Ray diffraction.

Molecular assemblies as mimics of the complete H-cluster in diiron hydrogenase

247th National Meeting (2014)

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