Synthesis, Spectroscopy, and Structure of [FeRu(μ-dithiolate)(CN) 2 (CO) 4 ] 2 .

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 ] - ([H 1 ] - ), 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).