Abstract
The salt [K(18-crown-6)](2)[Ru(CN)(2)(CO)(3)] ([K(18-crown-6)](2)[1]) was generated by the reaction of Ru(C(2)H(4))(CO)(4) with [K(18-crown-6)]CN. An initial thermal reaction gives [Ru(CN)(CO)(4)](-), which, upon ultraviolet (UV) irradiation, reacts with a second equiv of CN(-). Protonation of [1](2-) gave [HRu(CN)(2)(CO)(3)](-) ([H1](-)), which was isolated as a single isomer with mutually trans cyanide ligands. The complex cis,cis,cis-[Ru(pdt)(CN)(2)(CO)(2)](2-) ([2](2-)) was prepared by the UV-induced reaction of [1](2-) with propanedithiol (pdtH(2)). The corresponding iron complex cis,cis,cis-[Fe(pdt)(CN)(2)(CO)(2)](2-) ([3](2-)) was prepared similarly. The pdt complexes [2](2-) and [3](2-) were treated with Fe(benzylideneacetone)(CO)(3) to give, respectively, [RuFe (μ-pdt)(CN)(2)(CO)(4)](2-) ([5](2-)) and [Fe(2)(μ-pdt)(CN)(2)(CO)(4)](2-) ([4](2-)). The pathway from [3](2-) to Fe(2) complex [4](2-) implicates intermetallic migration of CN(-). In contrast, the formation of [5](2-) leaves the Ru(CN)(2)(CO) center intact, as confirmed by X-ray crystallography. The structure of [5](2-) features a "rotated" square-pyramidal Fe(CO)(2)(μ-CO) site. NMR measurements indicate that the octahedral Ru site is stereochemically rigid, whereas the Fe site dynamically undergoes turnstile rotation. (57)Fe Mössbauer spectral parameters are very similar for rotated [5](2-) and unrotated Fe(2) complex [4](2-), indicating the insensitivity of that technique to both the geometry and the oxidation state of the Fe site. According to cyclic voltammetry, [5](2-) oxidizes at E(1/2) ∼ -0.8 V vs Fc(+/0). Electron paramagnetic resonance (EPR) measurements show that 1e(-) oxidation of [5](2-) gives an S = 1/2 rhombic species, consistent with the formulation Ru(II)Fe(I), related to the H(ox) state of the [FeFe] hydrogenases. Density functional theory (DFT) studies reproduce the structure, (1)H NMR shifts, and infrared (IR) spectra observed for [5](2-). Related homometallic complexes with both cyanides on a single metal are predicted to not adopt rotated structures. These data suggest that [5](2-) is best described as Ru(II)Fe(0). This conclusion raises the possibility that for some reduced states of the [FeFe]-hydrogenases, the [2Fe](H) site may be better described as Fe(II)Fe(0) than Fe(I)Fe(I).