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Snapshots of a Migrating H‐Atom: Characterization of a Reactive Iron(III) Indenide Hydride and its Nearly Isoenergetic Ring‐Protonated Iron(I) Isomer
Author(s) -
Drover Marcus W.,
Schild Dirk J.,
Oyala Paul H.,
Peters Jonas C.
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201909050
Subject(s) - chemistry , protonation , indene , hydride , reactivity (psychology) , ring (chemistry) , electron transfer , electron paramagnetic resonance , metal , atom (system on chip) , crystallography , stoichiometry , proton coupled electron transfer , proton , characterization (materials science) , photochemistry , stereochemistry , medicinal chemistry , ion , nanotechnology , organic chemistry , materials science , medicine , physics , alternative medicine , pathology , nuclear magnetic resonance , quantum mechanics , computer science , embedded system
Abstract We report the characterization of an S = 1 / 2 iron π‐complex, [Fe(η 6 ‐IndH)(depe)] + (Ind=Indenide (C 9 H 7 − ), depe=1,2‐bis(diethylphosphino)ethane), which results via C−H elimination from a transient Fe III hydride, [Fe(η 3 :η 2 ‐Ind)(depe)H] + . Owing to weak M−H/C−H bonds, these species appear to undergo proton‐coupled electron transfer (PCET) to release H 2 through bimolecular recombination. Mechanistic information, gained from stoichiometric as well as computational studies, reveal the open‐shell π‐arene complex to have a BDFE C‐H value of ≈50 kcal mol −1 , roughly equal to the BDFE Fe‐H of its Fe III −H precursor (Δ G °≈0 between them). Markedly, this reactivity differs from related Fe(η 5 ‐Cp/Cp*) compounds, for which terminal Fe III −H cations are isolable and have been structurally characterized, highlighting the effect of a benzannulated ring (indene). Overall, this study provides a structural, thermochemical, and mechanistic foundation for the characterization of indenide/indene PCET precursors and outlines a valuable approach for the differentiation of a ring‐ versus a metal‐bound H‐atom by way of continuous‐wave (CW) and pulse EPR (HYSCORE) spectroscopic measurements.