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

On the basis of preparation of the known complex [Fe(2)(mu-SCH(2))(2)S(CO)(6)] (A) by a new method involving condensation of [(mu-LiS)(2)Fe(2)(CO)(6)] with excess S(CH(2)Br)(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 PPh(3) and [(eta(5)-C(5)H(5))(eta(5)-Ph(2)PC(5)H(4))Fe] in the presence of Me(3)NO and with 1 equiv. tBuNC and cyclohexyl isocyanide gave the single [2Fe3S]-cluster-containing monosubstituted complexes [Fe(2)(mu-SCH(2))(2)S(CO)(5)(L(1))] (1, L(1) = PPh(3); 2, L(1) = (eta(5)-C(5)H(5))(eta(5)-Ph(2)PC(5)H(4))Fe; 3, L(1) = tBuNC; 4, L(1) = C(6)H(11)NC), whereas the double [2Fe3S]-cluster-containing disubstituted complexes [{Fe(2)(mu-SCH(2))(2)S(CO)(5)}(2)(L(2))] [5, L(2) = 4,4'-(Ph(2)P)(2)(C(6)H(4))(2); 6, L(2) = trans-Ph(2)PCH=CHPPh(2); 7, L(2) = 1,4-(CN)(2)C(6)H(4); 8, L(2) = (eta(5)-Ph(2)PC(5)H(4))(2)Fe; 9, L(2) = (eta(5)-Ph(2)PC(5)H(4))(2)Ru] were produced by reaction of A with 0.5 equiv. of the corresponding bidentate ligands in the presence of Me(3)NO. In addition, the single On the basis of preparation of the known complex [Fe(2)(mu-SCH(2))(2)S(CO)(6)] (A) by a new method involving condensation of [(mu-LiS)(2)Fe(2)(CO)(6)] with excess S(CH(2)Br)(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 PPh(3) and [(eta(5)-C(5)H(5))(eta(5)-Ph(2)PC(5)H(4))Fe] in the presence of Me(3)NO and with 1 equiv. tBuNC and cyclohexyl isocyanide gave the single [2Fe3S]-cluster-containing monosubstituted complexes [Fe(2)(mu-SCH(2))(2)S(CO)(5)(L(1))] (1, L(1) = PPh(3); 2, L(1) = (eta(5)-C(5)H(5))(eta(5)-Ph(2)PC(5)H(4))Fe; 3, L(1) = tBuNC; 4, L(1) = C(6)H(11)NC), whereas the double [2Fe3S]-cluster-containing disubstituted complexes [{Fe(2)(mu-SCH(2))(2)S(CO)(5)}(2)(L(2))] [5, L(2) = 4,4'-(Ph(2)P)(2)(C(6)H(4))(2); 6, L(2) = trans-Ph(2)PCH=CHPPh(2); 7, L(2) = 1,4-(CN)(2)C(6)H(4); 8, L(2) = (eta(5)-Ph(2)PC(5)H(4))(2)Fe; 9, L(2) = (eta(5)-Ph(2)PC(5)H(4))(2)Ru] were produced by reaction of A with 0.5 equiv. of the corresponding bidentate ligands in the presence of Me(3)NO. In addition, the single [2Fe3S]-cluster-containing complexes in which the central S atom is coordinated, [{Fe(2)(mu-SCH(2))(2)S(CO)(6)}{(eta(5)-MeC(5)H(4))(CO)(2)Fe}(BF(4))] (10), [{Fe(2)(mu-SCH(2))(2)S(CO)(6)}{Cr(CO)(5)}] (11), and [{Fe(2)(mu-SCH(2))(2)S(CO)(6)}{W(CO)(5)}] (12), could be obtained by reaction of complex A with the in situ prepared [{(eta(5)-MeC(5)H(4))(CO)(2)Fe}(BF(4))], [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 Et(3)NHCl to give H(2), the X-ray crystallographic study confirmed that (i) each P atom of the phosphane ligands in I 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 (eta(5)-MeC(5)H(4))(CO)(2)Fe, 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.