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Protonation and Proton‐Coupled Electron Transfer at S‐Ligated [4Fe‐4S] Clusters
Author(s) -
Saouma Caroline T.,
Morris Wesley D.,
Darcy Julia W.,
Mayer James M.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201500152
Subject(s) - protonation , chemistry , electron transfer , proton coupled electron transfer , redox , cluster (spacecraft) , photochemistry , dissociation (chemistry) , proton , reactivity (psychology) , coupled cluster , inorganic chemistry , organic chemistry , molecule , ion , physics , medicine , alternative medicine , quantum mechanics , pathology , computer science , programming language
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 [Fe 4 S 4 (SAr) 4 ] 2− ( 1 , SAr=S‐2,4‐6‐( i Pr) 3 C 6 H 2 ) leads to thiol dissociation, reversibly forming [Fe 4 S 4 (SAr) 3 L] 1− ( 2 ) and ArSH (L=solvent, and/or conjugate base). Solutions of 2 +ArSH react with the nitroxyl radical TEMPO to give [Fe 4 S 4 (SAr) 4 ] 1− ( 1 ox ) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster [Fe 4 S 4 (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.