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The Equatorial Ligand Effect on the Properties and Reactivity of Iron(V) Oxo Intermediates
Author(s) -
Pattanayak Santanu,
Cantú Reinhard Fabián G.,
Rana Atanu,
Gupta Sayam Sen,
de Visser Sam P.
Publication year - 2019
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.201900708
Subject(s) - reactivity (psychology) , chemistry , electron paramagnetic resonance , ligand (biochemistry) , photochemistry , reaction rate constant , catalytic cycle , catalysis , resonance (particle physics) , resonance raman spectroscopy , metal , electronic effect , reaction rate , raman spectroscopy , crystallography , kinetics , organic chemistry , nuclear magnetic resonance , medicine , biochemistry , physics , alternative medicine , receptor , pathology , quantum mechanics , particle physics , optics
High‐valent metal oxo oxidants are common catalytic‐cycle intermediates in enzymes and known to be highly reactive. To understand which features of these oxidants affect their reactivity, a series of biomimetic iron(V) oxo oxidants with peripherally substituted biuret‐modified tetraamido macrocyclic ligands were synthesized and characterized. Major shifts in the UV/Vis absorption as a result of replacing a group in the equatorial plane of the iron(V) oxo species were found. Further characterization by EPR spectroscopy, ESI‐MS, and resonance Raman spectroscopy revealed differences in structure and the electronic configuration of these complexes. A systematic reactivity study with a range of substrates was performed and showed that the reactions are affected by electron‐withdrawing substituents in the equatorial ligand, which enhance the reaction rate by almost 10 16 orders of magnitude. Thus, the long‐range electrostatic perturbations have a major influence on the rate constant. Finally, computational studies identified the various electronic contributions to the rate‐determining reaction step and explained how the equatorial ligand periphery affects the properties of the oxidant.