PNP-Chelated and -Bridged Diiron Dithiolate Complexes Fe2(μ-pdt)(CO)4{(Ph2P)2NR} Together with Related Monophosphine Complexes for the [2Fe]H Subsite of [FeFe]-Hydrogenases: Preparation, Structure, and Electrocatalysis

As the [2Fe](H) subsite models of [FeFe]-hydrogenases, a series of PNP-chelated and -bridged diiron dithiolate complexes 1a-f and 2a-f together with the three related monophosphine complexes 3a-c were prepared by the selective substitutions of the all-carbonyl complex Fe-2(mu-pdt)(CO)(6) (A, pdt = SCH2CH2CH2S) with aminodiphosphines (Ph2P)(2)NR (denoted as PNP) under different reaction conditions. The first UV irradiation of the toluene solutions of A with different PNP ligands (PNP = (Ph2P)(2)NR; R = (CH2)(3)Me, (CH2)(3)NMe2, (CH2)(3)Si(OEt)(3), C6H5, C6H4OMe-p, C6H4CO2Me-p) readily afforded the target PNP-chelated complexes Fe-2(mu-pdt)(CO)(4){(kappa(2)-Ph2P)(2)NR} (1a-f), while the reflux of xylene solutions of A with the aforementioned PNP ligands produced the PNP-bridged complexes Fe-2(mu-pdt)(CO)(4){(mu-Ph2P)(2)NR} (2a-f). Comparatively, treatments of A and one type of PNP ligand with N-aryl substituents R (R = C6H5, C6H4OMe-p, C6H4CO2Me-p) in MeCN at room temperature in the presence of the decarbonylating agent Me3NO center dot 2H(2)O formed the unexpected monophosphine complexes Fe-2(mu-pdt)(CO)(5){kappa(1)-Ph2P(NHR)} (3a-c) and the minor chelated complexes 1d-f. All of the complexes 1a-f, 2a-f, and 3a-c have been characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1a,b,d-f, 2b,d-f, and 3b by X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes la and 2a as a pair of representative isomers have been evaluated and compared by cyclic voltammetry in MeCN as solvent in the absence and presence of HOAc as a proton source.