The oxidation state of the redox noninnocent tetra-amido macrocyclic ligand (TAML) scaffold was recently shown to affect the formation of nitrene radical species on cobalt(III) upon reaction with PhINNs [

The redox noninnocence 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 [Co III (TAML red )] − is truly redox noninnocent and that one-electron oxidation affords [Co III (TAML sq )]. Multireference (CASSCF) calculations show that the electronic structure of [Co III (TAML sq )] 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 = 1 / 2 ) 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 (TAML red or TAML sq ) determines whether mono-or bis-nitrene radical complexes are formed. Reaction of [Co III (TAML sq )] or [Co III (TAML red )] − with PhINNs results in the formation of [Co III (TAML q )(N • Ns)] and [Co III (TAML q )(N • Ns) 2 ] − , respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron-reduced Fischer-type nitrene radicals (N • Ns − ) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV−vis spectroscopy, highresolution mass spectrometry, magnetic moment measurements, and supporting CASSCF calculations.

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 <b>[Co^III(TAML^red)]^-</b> is truly redox non-innocent, and that one-electron oxidation affords <b>[Co^III(TAML^sq)]</b>. Multi-reference (CASSCF) calculations show that the electronic structure of <b>[Co^III(TAML^sq)]</b> 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 (TAML^red or TAML^sq) determines whether mono- or bis-nitrene radical complexes are formed. Reaction of <b>[Co^III(TAML^sq)]</b> or <b>[Co^III(TAML^red)]^-</b> with PhINNs results in formation of <b>[Co^III(TAML^q)(N^•Ns)]</b> and <b>[Co^III(TAML^q)(N^•Ns)₂]^-</b>, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron reduced Fischer-type nitrene radicals (N^•Ns^-) 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. <br>

Cr-catalyzed ethene trimerization is an industrially important process to produce 1-hexene. Despite its industrial relevance, the changing oxidation state and the structural rearrangements of the metal center during the catalytic cycle remain unclear. In this study, we have investigated the active species in a [(R-SN (H)SÀ R)CrCl 3 ] (R = C 10 H 21 ) catalyzed ethene trimerization system using a combination of spectroscopic techniques (XAS, EPR and UV/VIS) and DFT calculations. Reaction of the octahedral Cr III complex with modified methylaluminoxane (MMAO) in absence of ethene gives rise to the formation of a square-planar Cr II complex. In the presence of ethene (1 bar), no coordination was observed, which we attribute to the endergonic nature of the coordination of the first ethene molecule. Employing an alkyne as a model for ethene coordination leads to the formation of a dinuclear cationic Cr III alkyne complex. DFT calculations show that a structurally related dinuclear cationic Cr III ethene complex could form under catalytic conditions. Comparing a mechanism proceeding via mononuclear cationic Cr II /Cr IV intermediates to that proceeding via dinuclear cationic Cr II /Cr III intermediates demonstrates that only the mechanism involving mononuclear cationic Cr II /Cr IV intermediates can correctly explain the observed product selectivity.[a] B.

In [Fe–Fe] hydrogenase mimic systems the ene-1,2-dithiolene ligands play an important role in the stabilisation of the redox-active metal center.