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Wright RJ, Lim C, Tilley TD: Diiron proton reduction catalysts possessing electron-rich and electron-poor naphthalene-1,8-dithiolate ligands. Chemistry. 2009 Aug 24;15(34):8518-25.
The diiron complexes [Fe (2)(CO)(6)(1,8-S (2)-2,4,5,7-Cl (4) C (10) H (2))] (3), [Fe (2)(CO)(6)(1,8-S (2) C (10) H (6))] (4), and [Fe (2)(CO)(6)(1,8-S (2)-2,7-tBu (2) C (10) H (4))] (5) were synthesized in moderate yield from naphthalene-1,8-dithiols and [Fe (3)(CO)(12)]. They were characterized by IR, (1) H and (13) C NMR spectroscopy and 3 and 4 were characterized by X-ray crystallography. They contain a butterfly Fe (2) S (2) core with Fe-Fe distances of 2.529 (1) (3) and 2.506 (1) A (4). Cyclic voltammetry (CH (2) Cl (2)/nBu (4) PF (6)) revealed two one-electron reductions, at potentials more positive than those for the related [Fe (2)(CO)(6)(S (CH (2))(3) S)] (1), and one one-electron oxidation. The first reduction of the electron poor 3 (-1.60 V vs Fc/Fc (+)) is 240 mV more positive than the first reduction of the electron rich 5 (-1.84 V). Electrochemical studies revealed that 3-5 facilitate the proton reduction of p-toluenesulfonic acid. The rates of catalysis, with a 95% confidence limit, are 2.4+/-0.8 (1), 5.2+/-0.8 (3), 3.1+/-1.1 (4), 2.9+/-0.6 (5), and 4.5+/-0.2 h (-1) for the related [Fe (2)(CO)(6)(1,2-S (2) C (6) H (4))]. The rates were determined by bulk electrolysis at -1.70 V (Fc/Fc (+)), which correspond to an overpotential of 1.05 V for p-toluenesulfonic acid. |
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