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Ligand Redox Non-Innocence in [Coᴵᴵᴵ(TAML)]0/‒ Complexes Affects Nitrene Formation

submitted on 28.10.2019 and posted on 30.10.2019 by Nicolaas P. van Leest, Martijn A. Tepaske, Jean-Pierre H. Oudsen, Bas Venderbosch, Niels R. Rietdijk, Maxime A. Siegler, Moniek Tromp, Jarl Ivar van der Vlugt, Bas de Bruin
The redox non-innocence of the TAML scaffold in cobalt-TAML (Tetra-Amido Macrocyclic Ligand) complexes has been under debate since 2006. In this work we demonstrate with a variety of spectroscopic measurements that the TAML backbone in the anionic complex [CoIII(TAMLred)]- is truly redox non-innocent, and that one-electron oxidation affords [CoIII(TAMLsq)]. Multi-reference (CASSCF) calculations show that the electronic structure of [CoIII(TAMLsq)] is best described as an intermediate spin (S = 1) cobalt(III) center that is antiferromagnetically coupled to a ligand-centered radical, affording an overall doublet (S = ½) ground-state. Reaction of the cobalt(III)-TAML complexes with PhINNs as a nitrene precursor leads to TAML-centered oxidation, and produces nitrene radical complexes without oxidation of the metal ion. The ligand redox state (TAMLred or TAMLsq) determines whether mono- or bis-nitrene radical complexes are formed. Reaction of [CoIII(TAMLsq)] or [CoIII(TAMLred)]- with PhINNs results in formation of [CoIII(TAMLq)(NNs)] and [CoIII(TAMLq)(NNs)2]-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron reduced Fischer-type nitrene radicals (NNs-) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV-Vis spectroscopy, high resolution mass spectrometry, magnetic moment measurements and supporting CASSCF calculations.


Netherlands Organization for Scientific Research (NWO TOP-Grant 716.015.001)

Netherlands Organization for Scientific Research (NWO VIDI grant 723.014.010)


Email Address of Submitting Author


University of Amsterdam


The Netherlands

ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare no competing financial interest.

Version Notes

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