Synthesis, characterization and electrocatalysis of diiron propanediselenolate derivatives as the active site models of [FeFe]-hydrogenases

As an extension of our study on the H-cluster model compounds, a series of diiron propanediselenolate (PDS)-type models have been successfully synthesized. Reaction of diselenol HSe(CH2)3SeH with Fe3(CO)12 in THF (tetrahydrofuran) at reflux gave the parent model compound [μ-Se(CH2)3Se-μ]Fe2(CO)6 (1) in 48% yield. Further reaction of 1 with PPh3 or PPh2H in the presence of Me3NO in MeCN at room temperature afforded the phosphine-monosubstituted model compounds [μ-Se(CH2)3Se-μ]Fe2(CO)5(L) (2, L = PPh3; 3, L = PPh2H) in 76% and 68% yields, respectively. Similarly, the N-heterocyclic carbene IMes-monosubstituted model compound [μ-Se(CH2)3Se-μ]Fe2(CO)5(IMes) (4) could be prepared in 46% yield by reaction of imidazolium salt IMes · HCl with n-BuLi followed by treatment of the resulting IMes ligand with 1 in THF at room temperature. Compounds 1–4 were fully characterized by elemental analysis and various spectroscopic methods. While the structures of 1–4 were further confirmed by X-ray crystallography, the comparative study of 1 and its analog [μ-S(CH2)3S-μ]Fe2(CO)6 demonstrates that 1 is a better catalyst for TsOH proton reduction to hydrogen under electrochemical conditions.