Scientists have sought the use of H2 as a renewable energy source for years, but as of now the cost of producing H2 outweighs the benefits. The development of diiron constructs that are synthetic analogues of the [FeFe]-hydrogenase active site as base metals for the proton reduction has attracted much attention recently. In our lab, N-heterocyclic carbenes, with allyl-ferrocenyl groups, have been prepared and attached to the diiron carbonyl models as a surrogate for the 4Fe4S cluster in the H-cluster. The 1-Imes analogue, see graphic, has almost identical ?(CO) IR bands, indicating that the pendant mesitylene or ferrocenyl groups have very little electronic influence on the neutral diiron complexes. However, the single irreversible cathodic event is some 250-300 mV more negative for the bis-ferrocenyl NHC as compared to the 1-Imes complex. In the anodic region, the 1-Imes has a prominent quasi-reversible wave at +510 mV. The 2Fc complex displays a reversible, apparently two electron process likewise shifted negatively as compared to the 1-Imes complex with a second reversible anodic wave at +780 mV. The ferrocenes of the neutral form (2Fc) shows no influence on the electronics of the [FeFe]-H2ase model complex as compared to 1-Imes. Four new complexes of this type have been prepared in order to establish the effects of a redox center, seated in the second coordination sphere, on the electronic and structural parameters of the 2Fe2S core. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/240nm/uploads/42755_figure_1_for_acs_2010_abstract.jpg' alt='' />

Diiron hydrogenase active site models outfitted with pendant redox-active units

247th National Meeting (2014)

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