Protonation and Proton‐Coupled Electron Transfer at S‐Ligated [4Fe‐4S] Clusters |
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| Authors: | Dr Caroline T Saouma Wesley D Morris Julia W Darcy Prof James M Mayer |
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| Institution: | 1. Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195 (USA);2. Department of Chemistry, University of Utah, 315 S 1400 E Room 2020, Salt Lake City, UT 84112 (USA);3. Department of Chemistry, Yale University, 225 Prospect St., PO Box 208107, New Haven, CT 06520 (USA) |
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| Abstract: | Biological Fe‐S] clusters are increasingly recognized to undergo proton‐coupled electron transfer (PCET), but the site of protonation, mechanism, and role for PCET remains largely unknown. Here we explore this reactivity with synthetic model clusters. Protonation of the arylthiolate‐ligated 4Fe‐4S] cluster Fe4S4(SAr)4]2? ( 1 , SAr=S‐2,4‐6‐(iPr)3C6H2) leads to thiol dissociation, reversibly forming Fe4S4(SAr)3L]1? ( 2 ) and ArSH (L=solvent, and/or conjugate base). Solutions of 2 +ArSH react with the nitroxyl radical TEMPO to give Fe4S4(SAr)4]1? ( 1ox ) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster Fe4S4(SAr)3(HSAr)]1? ( 1‐H ). Similar reactions with this and related clusters proceed comparably. An understanding of the PCET thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states. |
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| Keywords: | [Fe‐S] cluster enzyme mechanism iron PCET electron transfer |
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