Synthesis and Characterization of Diiron Diselenolato Complexes Including Iron Hydrogenase Models

Abstract

Diiron diselenolato complexes have been prepared as models of the active site of [FeFe]-hydrogenases. Treatment of Fe3(CO)12 with 1 equiv of 1,3-diselenocyanatopropane (1) in THF at reflux afforded the model compound Fe2(μ-Se2C3H6)(CO)6 (2) in 68% yield. The analogous methyl-substituted complex, Fe2(μ-Se2C3H5CH3)(CO)6 (3), was obtained from the reaction of Fe3(CO)12 with the in situ generated compound 3-methyl-1,2-diselenolane (4). In contrast, the reaction of Fe3(CO)12 with 1,3,5-triselenacyclohexane (5) produced a mixture of Fe2(μ2,κ-Se,C-SeCH2SeCH2)(CO)6 (6), Fe2[(μ-SeCH2)2Se](CO)6 (7), and Fe2(μ-Se2CH2)(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.