Synthesis and Characterization of Diiron Thiadithiolate Complexes Related to the Active Site of [FeFe]‐Hydrogenases

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AbstractOn the basis of preparation of the known complex [Fe2(μ‐SCH2)2S(CO)6] (A) by a new method involving condensation of [(μ‐LiS)2Fe2(CO)6] with excess S(CH2Br)2, twelve new diiron thiadithiolates as mimics of the [FeFe]‐hydrogenase active site have been synthesized by substitution of the CO ligand and coordination at the central S atom of complex A with appropriate reagents. Treatment of A with 1 equiv. of the monodentate ligands PPh3 and [(η5‐C5H5)(η5‐Ph2PC5H4)Fe] in the presence of Me3NO and with 1 equiv. tBuNC and cyclohexyl isocyanide gave the single [2Fe3S]‐cluster‐containing monosubstituted complexes [Fe2(μ‐SCH2)2S(CO)5(L1)] (1, L1 = PPh3; 2, L1 = (η5‐C5H5)(η5‐Ph2PC5H4)Fe; 3, L1 = tBuNC; 4, L1 = C6H11NC), whereas the double [2Fe3S]‐cluster‐containing disubstituted complexes [{Fe2(μ‐SCH2)2S(CO)5}2(L2)] [5, L2 = 4,4′‐(Ph2P)2(C6H4)2; 6, L2 = trans‐Ph2PCH=CHPPh2; 7, L2 = 1,4‐(CN)2C6H4; 8, L2 = (η5‐Ph2PC5H4)2Fe; 9, L2 = (η5‐Ph2PC5H4)2Ru] were produced by reaction of A with 0.5 equiv. of the corresponding bidentate ligands in the presence of Me3NO. In addition, the single [2Fe3S]‐cluster‐containing complexes in which the central S atom is coordinated, [{Fe2(μ‐SCH2)2S(CO)6}{(η5‐MeC5H4)(CO)2Fe}(BF4)] (10), [{Fe2(μ‐SCH2)2S(CO)6}{Cr(CO)5}] (11), and [{Fe2(μ‐SCH2)2S(CO)6}{W(CO)5}] (12), could be obtained by reaction of complex A with the in situ prepared [{(η5‐MeC5H4)(CO)2Fe}(BF4)], [Cr(CO)5(thf)], and [W(CO)5(thf)], respectively. While complex 3 was found to be able to reduce the proton of the weak acid Et3NHCl to give H2, the X‐ray crystallographic study confirmed that (i) each P atom of the phosphane ligands in 1 and 8 occupies an apical position at the Fe atoms, (ii) the isocyanide ligand in 3 lies in a basal position of the Fe atom, and (iii) the (η5‐MeC5H4)(CO)2Fe, Cr(CO)5, and W(CO)5 units in 10–12 are linked to the central S atom of complex A by an equatorial bond from the two fused six‐membered rings of their [2Fe3S]‐cluster cores.