Synthesis and characterization of diiron diselenolato complexes including Iron Hydrogenase models

Diiron diselenolato complexes have been prepared as models of the active site of [FeFe]-hydrogenases. Treatment of Fe ₃(CO) ₁₂ with 1 equiv of 1,3-diselenocyanatopropane (1) in THF at reflux afforded the model compound Fe ₂(μ-Se ₂C ₃H ₆)(CO) ₆ (2) in 68% yield. The analogous methyl-substituted complex, Fe ₂(μ-Se ₂C ₃H ₅CH3)(CO) ₆ (3), was obtained from the reaction of Fe ₃(CO) ₁₂ with the in situ generated compound 3-methyl-1,2-diselenolane (4). In contrast, the reaction of Fe ₃(CO) ₁₂ with 1,3,5-triselenacy-clohexane (5) produced a mixture of Fe ₂(μ ²,k-Se,C-SeCH ₂SeCH ₂)(CO) ₆ (6), Fe ₂[(μ- SeCH ₂) ₂Se](CO) ₆ (7), and Fe ₂(μ- Se ₂CH ₂)(CO) ₆ (8). Compounds 2, 3, 6, and 7 were characterized by IR, ¹H, ¹³C, and ⁷⁷Se NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray single-crystal structure analysis. The He I and He II photoelectron spectra for 3 are reported, and the electronic structure is further analyzed with the aid of DFT computations. The calculated reorganization energy of the cation of 3 to the "rotated" structure, which has a semibridging carbonyl ligand, is less than that of the analogous complexes with sulfur instead of selenium. Complexes 2 and 3 have been proved to be catalysts for electrochemical reduction of protons from the weak acids pivalic and acetic acid, respectively, to give hydrogen.