Structural and Spectroscopic Features of Mixed Valent FeIIFeI Complexes and Factors Related to the Rotated Configuration of Diiron Hydrogenase

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• 作者：Chung-Hung Hsieh ; 脰zlen F. Erdem ; Scott D. Harman ; Michael L. Singleton ; Edward Reijerse ; Wolfgang Lubitz ; Codrina V. Popescu ; Joseph H. Reibenspies ; Scott M. Brothers ; Michael B. Hall ; Marcetta Y. Darensbourg
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：August 8, 2012
• 年：2012
• 卷：134
• 期：31
• 页码：13089-13102
• 全文大小：736K
• 年卷期：v.134,no.31(August 8, 2012)
• ISSN：1520-5126

文摘

The compounds of this study have yielded to complementary structural, spectroscopic (M枚ssbauer, EPR/ENDOR, IR), and computational probes that illustrate the fine control of electronic and steric features that are involved in the two structural forms of (渭-SRS)[Fe(CO)₂PMe₃]₂^0,+ complexes. The installation of bridgehead bulk in the 鈭扴CH₂CR₂CH₂S鈥?dithiolate (R = Me, Et) model complexes produces 6-membered FeS₂C₃ cyclohexane-type rings that produce substantial distortions in Fe^IFe^I precursors. Both the innocent (Fc⁺) and the noninnocent or incipient (NO⁺/CO exchange) oxidations result in complexes with inequivalent iron centers in contrast to the Fe^IFe^I derivatives. In the Fe^IIFe^I complexes of S = 1/2, there is complete inversion of one square pyramid relative to the other with strong super hyperfine coupling to one PMe₃ and weak SHFC to the other. Remarkably, diamagnetic complexes deriving from isoelectronic replacement of CO by NO⁺, {(渭-SRS)[Fe(CO)₂PMe₃] [Fe(CO)(NO)PMe₃]⁺}, are also rotated and exist in only one isomeric form with the 鈭扴CH₂CR₂CH₂S鈥?dithiolates, in contrast to R = H (Olsen, M. T.; Bruschi, M.; De Gioia, L.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 2008, 130, 12021鈭?2030). The results and redox levels determined from the extensive spectroscopic analyses have been corroborated by gas-phase DFT calculations, with the primary spin density either localized on the rotated iron in the case of the S = 1/2 compound, or delocalized over the {Fe(NO)} unit in the S = 0 complex. In the latter case, the nitrosyl has effectively shifted electron density from the Fe^IFe^I bond, repositioning it onto the spin coupled Fe鈥揘鈥揙 unit such that steric repulsion is sufficient to induce the rotated structure in the Fe^II-{Fe^I(^{鈥?/sup>NO)}8 derivatives.}