Bioinspired Hydrogenase Models: The Mixed-Valence Triiron Complex [Fe3(CO)7(渭-edt)2] and Phosphine Derivatives [Fe3(CO)7鈥?i>x(PPh3
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- 作者：Ahibur Rahaman ; Shishir Ghosh ; David G. Unwin ; Sucharita Basak-Modi ; Katherine B. Holt ; Shariff E. Kabir ; Ebbe Nordlander ; Michael G. Richmond ; Graeme Hogarth
- 刊名：Organometallics
- 出版年：2014
- 出版时间：March 24, 2014
- 年：2014
- 卷：33
- 期：6
- 页码：1356-1366
- 全文大小：504K
- 年卷期：v.33,no.6(March 24, 2014)
- ISSN：1520-6041
文摘
The mixed-valence triiron complexes [Fe3(CO)7鈥?i>x(PPh3)x(渭-edt)2] (x = 0鈥?; edt = SCH2CH2S) and [Fe3(CO)5(魏2-diphosphine)(渭-edt)2] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an anti arrangement of the dithiolate bridges, and PPh3 substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF4路Et2O, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe3(CO)5(PPh3)2(渭-edt)2]+ and [Fe3(CO)5(魏2-diphosphine)(渭-edt)2]+, species which also result upon oxidation by [Cp2Fe][PF6]. The electrochemistry of the formally Fe(I)鈥揊e(II)鈥揊e(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe3(CO)5(PPh3)2(渭-edt)2] is oxidized at 鈭?.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between 鈭?.47 V for [Fe3(CO)7(渭-edt)2] and around 鈭?.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe2(CO)6(渭-edt)], [Fe3(CO)7(渭-edt)2] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron鈥搃ron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.