Synthesis, Spectroscopy, and Structure of [FeRu(μ-dithiolate)(CN)(CO)].

The salt [K(18-crown-6)][Ru(CN)(CO)] ([K(18-crown-6)][]) was generated by the reaction of Ru(CH)(CO) with [K(18-crown-6)]CN. An initial thermal reaction gives [Ru(CN)(CO)], which, upon ultraviolet (UV) irradiation, reacts with a second equiv of CN. Protonation of [] gave [HRu(CN)(CO)] ([H]), which was isolated as a single isomer with mutually trans cyanide ligands. The complex -[Ru(pdt)(CN)(CO)] ([]) was prepared by the UV-induced reaction of [] with propanedithiol (pdtH). The corresponding iron complex -[Fe(pdt)(CN)(CO)] ([]) was prepared similarly. The pdt complexes [] and [] were treated with Fe(benzylideneacetone)(CO) to give, respectively, [RuFe (μ-pdt)(CN)(CO)] ([]) and [Fe(μ-pdt)(CN)(CO)] ([]). The pathway from [] to Fe complex [] implicates intermetallic migration of CN. In contrast, the formation of [] leaves the Ru(CN)(CO) center intact, as confirmed by X-ray crystallography. The structure of [] features a "rotated" square-pyramidal Fe(CO)(μ-CO) site. NMR measurements indicate that the octahedral Ru site is stereochemically rigid, whereas the Fe site dynamically undergoes turnstile rotation. Fe Mössbauer spectral parameters are very similar for rotated [] and unrotated Fe complex [], indicating the insensitivity of that technique to both the geometry and the oxidation state of the Fe site. According to cyclic voltammetry, [] oxidizes at ∼ -0.8 V vs Fc. Electron paramagnetic resonance (EPR) measurements show that 1e oxidation of [] gives an = 1/2 rhombic species, consistent with the formulation Ru(II)Fe(I), related to the H state of the [FeFe] hydrogenases. Density functional theory (DFT) studies reproduce the structure, H NMR shifts, and infrared (IR) spectra observed for []. Related homometallic complexes with both cyanides on a single metal are predicted to adopt rotated structures. These data suggest that [] is best described as Ru(II)Fe(0). This conclusion raises the possibility that for some reduced states of the [FeFe]-hydrogenases, the [2Fe] site may be better described as Fe(II)Fe(0) than Fe(I)Fe(I).