Cyanide cofactors are well-established in [NiFe]-hydrogenases (H2-ases) but are noticeably absent in model compounds. Previous reports incorporating cyanide in [NiFe]-H2ase models have produced only structural models. Use of Lewis acids coordinated to cyanide convert previously unreactive compounds to active models. Complexes of the type (CO)2(CN)2Fe(pdt)Ni(dxpe), (dxpe = dppe; dcpe) bind the Lewis acid B(C6F5)3 (BArF3) to give the adducts (CO)2(CNBArF3)2Fe(pdt)Ni(dxpe). Decarbonylation of these adducts under a H2 atmosphere gives the hydrido derivatives Et4N[(CO)(CNBArF3)2Fe(pdt)(H)Ni(dxpe)]. Crystallographic analysis of Et4N[(CO)(CNBArF3)2Fe(pdt)(H)Ni(dppe)], which closely resembles the active site of the enzyme in the Ni-R state, revealed a highly unsymmetrical Fe-H-Ni center (rFe-H = 1.51(3), rNi-H = 1.71(3) �). Unlike previously reported cationic Ni-Fe hydrides, [(CO)(CNBArF3)2Fe(pdt)(H)Ni(dxpe)]? exhibit unusual properties indicative of their anionic character such as oxidizing at mild potentials (near ?0.10 V vs. Fc0/+) and engaging in dihydrogen bonding with weakly acidic ammonium salts.

Use of protected cyanide cofactors for hydrogen activation by biomimetic [NiFe]-hydrogenase models

246th National Meeting (2013)

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