Facile Conversion of syn-[Fe IV (O)(TMC)] 2+ into the anti Isomer via Meunier's Oxo–Hydroxo Tautomerism Mechanism

Jai Prakash, Yuan Sheng, Apparao Draksharapu, Johannes E.M.N. Klein, Christopher J. Cramer, Lawrence Que

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Abstract

The syn and anti isomers of [Fe IV (O)(TMC)] 2+ (TMC=tetramethylcyclam) represent the first isolated pair of synthetic non-heme oxoiron(IV) complexes with identical ligand topology, differing only in the position of the oxo unit bound to the iron center. Both isomers have previously been characterized. Reported here is that the syn isomer [Fe IV (O syn )(TMC)(NCMe)] 2+ (2) converts into its anti form [Fe IV (O anti )(TMC)(NCMe)] 2+ (1) in MeCN, an isomerization facilitated by water and monitored most readily by 1 H NMR and Raman spectroscopy. Indeed, when H 2 18 O is introduced to 2, the nascent 1 becomes 18 O-labeled. These results provide compelling evidence for a mechanism involving direct binding of a water molecule trans to the oxo atom in 2 with subsequent oxo–hydroxo tautomerism for its incorporation as the oxo atom of 1. The nonplanar nature of the TMC supporting ligand makes this isomerization an irreversible transformation, unlike for their planar heme counterparts.

Original languageEnglish (US)
Pages (from-to)1995-1999
Number of pages5
JournalAngewandte Chemie - International Edition
Volume58
Issue number7
DOIs
StatePublished - Feb 11 2019

Bibliographical note

Funding Information:
This work was supported by a grant from the U.S. National Science Foundation (CHE-1665391 to L.Q. and CHE-1361595 to C.J.C.). J.E.M.N.K. thanks the Alexander von Humboldt Foundation for a Feodor Lynen Research Fellowship. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper. We would also like to thank the Center for Information Technology of the University of Groningen for their support and for providing access to the Peregrine high-performance computing cluster.

Publisher Copyright:
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Keywords

  • iron
  • isomers
  • macrocycles
  • reaction mechanisms
  • tautomerism

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