Conformational Mobility and Pendent Base Effects on Electrochemistry of Synthetic Analogues of the [FeFe]-Hydrogenase Active Site

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• 作者：Danielle J. Crouthers ; Jason A. Denny ; Ryan D. Bethel ; David G. Munoz ; Marcetta Y. Darensbourg
• 刊名：Organometallics
• 出版年：2014
• 出版时间：September 22, 2014
• 年：2014
• 卷：33
• 期：18
• 页码：4747-4755
• 全文大小：606K
• ISSN：1520-6041

文摘

Dynamic NMR (¹³C and ¹H) studies of (渭-SCH₂XCH₂S)[Fe(CO)₃]₂ complexes (X = CR₂, NR) were utilized to examine the fluxional processes that are important in the [FeFe]-hydrogenase active site models, where an open site for proton/hydrogen binding, achieved by configurational mobility of the Fe(CO)₃ unit, is required for electrocatalysis of proton reduction. In order to interrogate the effects of fluxional mobility on electrochemical response to added acid, energy barriers for the CO site exchange in Fe(CO)₃ rotors were determined for nitrogen- and carbon-based bridgehead complexes. The effect of the methyl substituent in both the NH/NCH₃ and CH₂/C(CH₃)₂ cases is to lower the Fe(CO)₃ rotational activation barrier relative to the NH or CH₂ analogues. Although the C(CH₃)₂ case has the lowest Fe(CO)₃ rotational barrier, its performance as a proton reduction electrocatalyst is 2-fold less than that for the X = NR species, indicating the proton-directing effect of the pendent base on catalytic efficiency.