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(CH(2))(3)SeH with Fe(3)(CO)(12) in THF (tetrahydrofuran) at reflux gave the parent model compound [micro-Se(CH(2))(3)Se-micro]Fe(2)(CO)(6) (1) in 48% yield. Further reaction of 1 with PPh(3) or PPh(2)H in the presence of Me(3)NO in MeCN at room temperature afforded the phosphine-monosubstituted model compounds [micro-Se(CH(2))(3)Se-micro]Fe(2)(CO)(5)(L) (2, L=PPh(3); 3, L=PPh(2)H) in 76% and 68% yields, respectively. Similarly, the N-heterocyclic carbene I(Mes)-monosubstituted model compound [micro-Se(CH(2))(3)Se-micro]Fe(2)(CO)(5)(I(Mes)) (4) could be prepared in 46% yield by reaction of imidazolium salt I(Mes).HCl with n-BuLi followed by treatment of the resulting I(Mes) 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 [micro-S(CH(2))(3)S-micro]Fe(2)(CO)(6) demonstrates that 1 is a better catalyst for TsOH proton reduction to hydrogen under electrochemical conditions.