title: Hydrogen activation by biomimetic [NiFe]-hydrogenase model containing protected cyanide cofactors.
abstract: Described are experiments demonstrating incorporation of cyanide cofactors and hydride substrate into [NiFe]-hydrogenase (H2ase) active site models. Complexes of the type (CO)2(CN)2Fe(pdt)Ni(dxpe) (dxpe = dppe, 1; dxpe = dcpe, 2) bind the Lewis acid B(C6F5)3 (BAr(F)3) to give the adducts (CO)2(CNBAr(F)3)2Fe(pdt)Ni(dxpe), (1(BAr(F)3)2, 2(BAr(F)3)2). Upon decarbonylation using amine oxides, these adducts react with H2 to give hydrido derivatives [(CO)(CNBAr(F)3)2Fe(H)(pdt)Ni(dxpe)](-) (dxpe = dppe, [H3(BAr(F)3)2](-); dxpe = dcpe, [H4(BAr(F)3)2](-)). Crystallographic analysis shows that Et4N[H3(BAr(F)3)2] generally resembles the active site of the enzyme in the reduced, hydride-containing states (Ni-C/R). The Fe-H···Ni center is unsymmetrical with r(Fe-H) = 1.51(3) Å and r(Ni-H) = 1.71(3) Å. Both crystallographic and (19)F NMR analyses show that the CNBAr(F)3(-) ligands occupy basal and apical sites. Unlike cationic Ni-Fe hydrides, [H3(BAr(F)3)2](-) and [H4(BAr(F)3)2](-) oxidize at mild potentials, near the Fc(+/0) couple. Electrochemical measurements indicate that in the presence of base, [H3(BAr(F)3)2](-) catalyzes the oxidation of H2. NMR evidence indicates dihydrogen bonding between these anionic hydrides and R3NH(+) salts, which is relevant to the mechanism of hydrogenogenesis. In the case of Et4N[H3(BAr(F)3)2], strong acids such as HCl induce H2 release to give the chloride Et4N[(CO)(CNBAr(F)3)2Fe(Cl)(pdt)Ni(dppe)].
authors.affiliation: School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Manor
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Rauchfuss
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D001880:Boranes / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D003486:Cyanides / Q000737:chemistry* / Q000378:metabolism; D003901:Desulfovibrio / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism*; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular
chemical_list: D001880:Boranes; D003486:Cyanides; D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase
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