Described are experiments demonstrating incorporation of cyanide cofactors and hydride substrate into [NiFe]-hydrogenase (H(2)ase) active site models. Complexes of the type (CO)(2)(CN)(2)Fe(pdt)Ni(dxpe) (dxpe = dppe, 1; dxpe = dcpe, 2) bind the Lewis acid B(C6F5)(3) (BAr3F) to give the adducts (CO)(2)(CNBAr3F)(2)Fe(pdt)Ni(dxpe), (1(BAr3F)(2), 2(BAr3F)(2)). Upon decarbonylation using amine oxides, these adducts react with H-2 to give hydrido derivatives [(CO)(CNBAr3F)(2)Fe(H)(pdt)Ni-(dxpe)](-) (dxpe = dppe, [H3(BAr3F)(2)](-); dxpe = dcpe, [H4(BAr3F)(2)](-)). Crystallographic analysis shows that Et4N[H3(BAr3F)(2)] generally resembles the active site of the enzyme in the reduced, hydride-containing states (Ni-C/R). The Fe-H center dot center dot center dot Ni center is unsymmetrical with r(Fe-H) = 1.51(3) angstrom and r(Ni-H) = 1.71(3) angstrom. Both crystallographic and F-19 NMR analyses show that the CNBAr3F- ligands occupy basal and apical sites. Unlike cationic Ni-Fe hydrides, [H3(BAr3F)(2)](-) and [H4(BAr3F)(2)](-) oxidize at mild potentials, near the Fc(+/0) couple. Electrochemical measurements indicate that in the presence of base, [H3(BAr3F)(2)](-) catalyzes the oxidation of H-2. 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(BAr3F)(2)], strong acids such as HCl induce H-2 release to give the chloride Et4N[(CO)(CNBAr3F)(2)Fe(Cl)(pdt)Ni-(dppe)].