Synthesis, characterization, and electrochemical properties of diiron propaneditellurolate (PDTe) complexes as active site models of [FeFe]-hydrogenases.

Parent complex (μ-PDTe)Fe(2)(CO)(6) (1, PDTe = μ-TeCH(2)CH(2)CH(2)Te-μ) is prepared via a new synthetic route involving the reaction of (μ-Te(2))Fe(2)(CO)(6) with Et(3)BHLi, followed by treatment of (μ-LiTe)(2)Fe(2)(CO)(6) with Br(CH(2))(3)Br in a 43% yield. Further reactions of 1 with 1 equiv of monophosphines in the presence of the decarbonylating agent Me(3)NO afford the corresponding monophosphine-substituted complexes (μ-PDTe)Fe(2)(CO)(5)(L) (2, L = PPh(3); 3, PPh(2)H; 4, PMe(3)) in 37%-47% yields, whereas the N-heterocyclic carbene I(Mes)-monosubstituted complex (μ-PDTe)Fe(2)(CO)(5)(I(Mes)) (5) can be prepared in a 26% yield by treatment of 1 with the in situ generated I(Mes) from the 1,3-bis(mesityl)imidazolium salt I(Mes)·HCl and n-BuLi. While the diphosphine-bridged single-butterfly complexes (μ-PDTe)Fe(2)(CO)(4)(dppm) (6) and (μ-PDTe)Fe(2)(CO)(4)(dppn) (7) can be prepared in 28% and 21% yields by treatment of 1 with 1 equiv of the corresponding diphosphines in refluxing xylene, treatment of 1 with 0.5 equiv of diphosphines in the presence of Me(3)NO results in the formation of the corresponding diphosphine-bridged double-butterfly complexes (μ-PDTe)Fe(2)(CO)(5)(dppp) (8), (μ-PDTe)Fe(2)(CO)(5)(dppb) (9), and (μ-PDTe)Fe(2)(CO)(5)(dppf) (10) in 25-37% yields. All the new substituted model complexes 2-10 are characterized by combustion analysis and spectroscopy, and particularly for 2, 3, 5, and 7-10, by X-ray crystallography. In addition, a comparative study on the electrochemical and electrocatalytic properties of the PDTe-type model complexes 1 and 7 with their corresponding selenium and sulfur analogs are reported.