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 2 C 3 H 6 )(CO) 6 ( 2 ) in 68% yield. The analogous methyl-substituted complex, Fe 2 (μ-Se 2 C 3 H 5 CH 3 )(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-triselenacyclohexane ( 5 ) produced a mixture of Fe 2 (μ 2,κ-Se,C-SeCH 2 SeCH 2 )(CO) 6 ( 6 ), Fe 2 [(μ-SeCH 2 ) 2 Se](CO) 6 ( 7 ), and Fe 2 (μ-Se 2 CH 2 )(CO) 6 ( 8 ). Compounds 2, 3, 6, and 7 were characterized by IR, 1 H, 13 C, and 77 Se 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.