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)(3)SeH with Fe-3(CO)(12) in THF (tetrahydrofuran) at reflux gave the parent model compound [mu-Se(CH2)(3)Se-mu[Fe-2(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 [mu-Se(CH2)(3)Se-mu[Fe-2(CO)(5)(L) (2, L - PPh3; 3, L = PPh2H) in 76% and 68% yields, respectively. Similarly, the N-heterocyclic carbene I-Mes-monosubstituted model compound [mu-Se(CH2)(3)Se-mu]Fe-2(CO)(5)(I-Mes) (4) could be prepared in 46% yield by reaction of imidazolium salt I-Mes center dot 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 structure of 1-4 were further confirmed by X-ray crystallography, the comparative study of 1 and its analog [mu-S(CH2)S-mu]Fe-2(CO)(6) demonstrates that 1 is a better catalyst for TsOH proton reduction to hydrogen under electrochemical conditions. (C) 2009 Elsevier Inc. All rights reserved.