Privileged Role of Thiolate as the Axial Ligand in Hydrogen Atom Transfer Reactions by Oxoiron(IV) Complexes in Shaping the Potential Energy Surface and Inducing Significant H-Atom Tunneling

Johannes E. M. N. Klein*, Debasish Mandal, Wei-Min Ching, Dibyendu Mallick, Lawrence Que, Jr.*, Sason Shaik*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

23 Citations (Scopus)

Abstract

An H/D kinetic isotope effect (KIE) of 80 is found at -20 degrees C for the oxidation of 9,10-dihydroanthracene by [Fe-IV(O)(TMCS)](+), a complex supported by the tetramethylcyclam (TMC) macrocycle with a tethered thiolate. This KIE value approaches that previously predicted by DFT calculations. Other [Fe-IV(O)(TMC)(anion)] complexes exhibit values of 20, suggesting that the thiolate ligand of [Fe-IV(O)(TMCS)](+) plays a unique role in facilitating tunneling. Calculations show that tunneling is most enhanced (a) when the bond asymmetry between C-H bond breaking and O-H bond formation in the transition state is minimized, and (b) when the electrostatic interactions in the O---H---C moiety are maximal. These two factors which peak for the best electron donor, the thiolate ligand afford a slim and narrow barrier through which the H-atom can tunnel most effectively.

Original languageEnglish
Pages (from-to)18705-18713
Number of pages9
JournalJournal of the American Chemical Society
Volume139
Issue number51
DOIs
Publication statusPublished - 27-Dec-2017
Externally publishedYes

Keywords

  • ISOPENICILLIN-N-SYNTHASE
  • NONHEME FE(IV)O OXIDANTS
  • METHANE MONOOXYGENASE CATALYSIS
  • TRANSITION-METAL-COMPLEXES
  • ACTIVE-SITE ANALOGS
  • 2-STATE REACTIVITY
  • BOND-CLEAVAGE
  • ABSTRACTION REACTIVITY
  • OXIDATION REACTIONS
  • OXYGEN ACTIVATION

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