Synthesis, characterization and catalytic reactivity of pentacoordinate iron dicarbonyl as a model of the [Fe]-hydrogenase active site

Two mono iron complexes Fe(CO)2PR3(NN) (R = Cy (3), Ph (4), NN = o-phenylenediamine dianion ligand, N2H2Ph2–) derived from the ligand substitution of Fe(CO)3I2PR3 by the NN ligand were isolated and structurally characterized by single crystal X-ray diffraction. They have a similar first coordination sphere and oxidation state of the iron center as the [Fe]-hydrogenase active site, and can be a model of it. IR demonstrated that the effect of the NN ligand on the coordinated CO stretching frequencies was due to its excellent electron donating ability. The reversible protonation/deprotonation of the NN ligand was identified by infrared spectroscopy and density functional theory computation. The NN ligand is an effective proton acceptor as the internal base of the cysteine thiolate ligand in [Fe]-hydrogenase. The electrochemical properties of complexes 3, 4 were investigated by cyclic voltammograms. Complex 3 catalyzed the transfer hydrogenation of benzoquinone to hydroquinone effectively under mild conditions.

Graphical AbstractFe(CO)2PCy3(NN), (NN = phenylenediamine dianion ligand, N2H2Ph2–) exhibited interesting reversible protonation/deprotonation activity of the diimine ligand similar to the active site of Hmd. The catalytic transfer hydrogenation of benzoquinone to hydroquinone was catalyzed under mild conditions by this model complex with 89% conversion and 40% yield.Figure optionsDownload as PowerPoint slide