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

Abstract

Parent complex (μ-PDTe)Fe₂(CO)₆ (1, PDTe = μ-TeCH₂CH₂CH₂Te-μ) is prepared via a new synthetic route involving the reaction of (μ-Te₂)Fe₂(CO)₆ with Et₃BHLi, followed by treatment of (μ-LiTe)₂Fe₂(CO)₆ with Br(CH₂)₃Br in a 43% yield. Further reactions of 1 with 1 equiv of monophosphines in the presence of the decarbonylating agent Me₃NO afford the corresponding monophosphine-substituted complexes (μ-PDTe)Fe₂(CO)₅(L) (2, L = PPh₃; 3, PPh₂H; 4, PMe₃) in 37%–47% yields, whereas the N-heterocyclic carbene I_Mes-monosubstituted complex (μ-PDTe)Fe₂(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)Fe₂(CO)₄(dppm) (6) and (μ-PDTe)Fe₂(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 Me₃NO results in the formation of the corresponding diphosphine-bridged double-butterfly complexes [(μ-PDTe)Fe₂(CO)₅]₂(dppp) (8), [(μ-PDTe)Fe₂(CO)₅]₂(dppb) (9), and [(μ-PDTe)Fe₂(CO)₅]₂(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.