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Redox potentials of high-valent iron-, cobalt-, and nickel-oxido complexes: evidence for exchange enhanced reactivity

The ferrocene titration method has been employed to determine the one-electron reduction potentials of a series of oxido-iron(IV), oxido-cobalt(IV) and oxido/hydroxido-nickel(III) complexes based on the same tetradentate TMG3tren ligand (TMG3tren=tris[2-(N-tetramethylguanidyl)ethyl]amine). The S=2 g...

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Bibliographic Details
Main Authors: Comba, Peter (Author) , Rensland, Anna-Maria (Author) , Pfaff, Florian Felix (Author) , Ray, Kallol (Author)
Format: Article (Journal)
Language:English
Published: 2020
In: Israel journal of chemistry
Year: 2020, Volume: 60, Issue: 10/11, Pages: 957-962
ISSN:1869-5868
DOI:10.1002/ijch.202000038
Online Access:Verlag, kostenfrei, Volltext: https://doi.org/10.1002/ijch.202000038
Verlag, kostenfrei, Volltext: https://onlinelibrary.wiley.com/doi/abs/10.1002/ijch.202000038
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Author Notes:Peter Comba, Anna-Maria Löhr, Florian Pfaff, and Kallol Ray
Description
Summary:The ferrocene titration method has been employed to determine the one-electron reduction potentials of a series of oxido-iron(IV), oxido-cobalt(IV) and oxido/hydroxido-nickel(III) complexes based on the same tetradentate TMG3tren ligand (TMG3tren=tris[2-(N-tetramethylguanidyl)ethyl]amine). The S=2 ground state of the [(TMG3tren)FeIV=O]2+ complex allows an exchange enhanced reactivity, which enables it to perform efficient oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions with a low one-electron reduction potential of 270 mV vs. SCE. In the absence of exchange enhanced reactivity, the OAT and HAA abilities of the S=3/2 [(TMG3tren)CoIV−O(Sc(OTf)3)]2+, S=1/2 [(TMG3tren)NiIII−O(H)]2+ and the previously reported S=1 [(TMC)(CH3CN)FeIV=O]2+ and [(N4Py)FeIV=O]2+ complexes can be directly correlated to their reduction potentials. Notably, [(N4Py)FeIV=O]2+ and [(TMG3tren)FeIV=O]2+ exhibit similar OAT and HAA reactivities although the reduction potential of [(N4Py)FeIV=O]2+ is 0.24 V more positive than that of [(TMG3tren)FeIV=O]2+. The present study therefore provides experimental evidence for exchange enhanced reactivity and rationalizes nature's choice for employing S=2 oxido-iron(IV) cores to achieve difficult oxidation reactions at biologically viable potentials.
Item Description:First published: 25 May 2020
Gesehen am 10.11.2021
Physical Description:Online Resource
ISSN:1869-5868
DOI:10.1002/ijch.202000038

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