Synthetic {2Fe2S} - and {2Fe3S}]-models of the [FeFe]-hydrogenase active site

Daraosheh, Ahmad

Part A: In order to elucidate the influence of phosphite or phosphine ligands on the structure of the [2Fe3S]-cluster related to the active site of [FeFe]-hydrogenases, substitution studies of CO-ligands in Fe2(μ-S2(C3H6)2S-μ)(CO)5 (1) by P(OMe)3 or PMe3 have been investigated. The reaction of 1 with one equivalent of trimethylphosphite afforded the kinetically controlled product Fe2(μ-S2(C3H6)2S)(CO)5P(OMe)3 (2) or the thermodynamically controlled product Fe2(μ-S2(C3H6)2S-μ)(CO)4P(OMe)3 (3). Moreover, Fe2(μ-S2(C3H6)2S)(CO)4[P(OMe)3]2 (4) or Fe2(μ-S2(C3H6)2S)(CO)4[PMe3]2 (5) were obtained from the reactions of 1 with excess of P(OMe)3 or PMe3. The novel complexes have been characterized by IR, 1H, 13C, 31P NMR spectroscopy, mass spectrometry, elemental analysis and X-ray single crystal structure analysis. Part B: The reactions of triiron dodecacarbonyl with thiobenzophenone (a) as well as 9H-thioxanthene-9-thione (b) were investigated under different conditions. In the case of 1:1 molar ratio of triiron dodecacarbonyl and a or b, the ortho-metallated complexes Fe2(CO)6(µ,,S, SCH(C6H5)C6H4-2) (6) and Fe2(CO)6(µ,,S,SCH(C6H4)-S-C6H3-2) (7) were obtained as major products, respectively. In contrast, the treatment of triiron dodecacarbonyl with excess of a or b, respectively, afforded two bioinspired models for the active site of the [FeFe]-hydrogenase, Fe2(CO)6(µ-SCH(C6H5)C6H4S-µ) (8) and Fe2(CO)6(µ SCH(C6H4) S C6H3S µ) (9), respectively. In addition to these complexes, the two reactions also afforded Fe2(CO)6(µ-SC(C6H5)2)S-µ) (10) and Fe2(CO)6(µ-SC(C6H4-S-C6H4)S-µ) (11). Furthermore, [Fe2(CO)6(µ-SCH(C6H5)2)]2(µ4-S) (12) was isolated from the reaction of Fe3(CO)12 with a. The molecular structures of all new complexes were determined from spectroscopic and analytical data and the crystal structures for 6 and 9-12 were obtained. A plausible mechanism for the formation of the isolated complexes involving dithiirane derivatives as key intermediates is proposed. Herein, thioketones a and b act as sulfur transfer reagents. The electrochemical experiments showed that complex 8 behaves as a catalyst for the electrochemical reduction of protons from acetic acid.

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Daraosheh, Ahmad: Synthetic {2Fe2S} - and {2Fe3S}]-models of the [FeFe]-hydrogenase active site. 2012.

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