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

Article abstract of DOI:10.1021/jacs.9b11715

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^a￠Ns)] and [Co^III(TAML^q)(N^a￠Ns)₂]^-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron-reduced Fischer-type nitrene radicals (N^a￠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.

Full text of DOI:10.1021/jacs.9b11715

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Article
III
0/#
Ligand Redox Non-Innocence in [Co(TAML)]
Complexes Affects Nitrene Formation
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, and Bas de Bruin
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b11715 • Publication Date (Web): 17 Dec 2019
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Ligand Redox Non-Innocence in [CoIII(TAML)]0/‒ Complexes
Affects Nitrene Formation
Nicolaas P. van Leest,† Martijn A. Tepaske,† Jean-Pierre H. Oudsen,§ Bas Venderbosch,§ Niels R.
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Rietdijk,† Maxime A. Siegler,‡ Moniek Tromp,§ Jarl Ivar van der Vlugt†,* and Bas de Bruin†,*
†Homogeneous, Supramolecular and Bio-Inspired Catalysis Group and §Sustainable Materials Characterization Group, van ’t
Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098XH Amsterdam, The Neth-
erlands
‡Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
KEYWORDS: Ligand redox non-innocence. Ligand-to-substrate single-electron transfer. Nitrene radical. Cobalt. TAML.
ABSTRACT: 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)].
Multireference (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)(NNs)] and [CoIII(TAMLq)(NNs)2], respectively. Herein, ligand-to-substrate single-electron trans-
fer 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.
electron to produce a nitrene radical (NR) complex with sin-
gle-electron population of the π symmetric Co‒N antibonding
INTRODUCTION
The use of base metals and redox non-innocent (or redox-
active) ligands in radical-type carbene, oxo and nitrene transfer
reactions has evolved as a powerful tool for the direct function-
alization of (unactivated) C‒H bonds and olefins.1 The func-
tionalized products of these reactions are motifs in pharmaceu-
ticals and agrochemicals, and are therefore highly valued.2
N-group transfer reactivity is an efficient way to afford the di-
rect synthesis of e.g. secondary amines and aziridines, of which
the synthesis otherwise typically requires harsh reaction condi-
tions or multiple steps.3 Generation of the essential catalytic
metal-nitrene intermediates has been achieved with second and
third row transition metals (Ru,4 Rh,5 Pd,6 Ag7 and Au8) as well
as more abundant base metals (Mn,9 Fe,10 Co,11 Ni12 and Cu13).
orbital. Interestingly, reaction of cobalt(II)-porphyrins with imi-
noiodinanes (PhINNs, Ns = nosyl) led to formation of bis-
nitrene radical species with two one-electron reduced Fischer-
type nitrenes, wherein the second nitrene is reduced via ligand-
to-substrate SET. Intrigued by these nitrene transfer catalysts,
we became interested in the possibility of nitrene radical for-
mation on square planar cobalt(III) platforms involving solely
ligand-to-substrate single electron transfer,15 by studying sys-
tems containing redox-active ligands for which metal-to-sub-
strate SET is difficult or even impossible.
When searching for suitable redox-active macrocyclic tetraden-
tate ligand platforms that enforce a square planar coordination
geometry around cobalt in an oxidation state higher than +II,
we decided to investigate the Tetra-Amido Macrocyclic Ligand
(TAML) platform designed by the group of Collins.16 The gen-
eral structure of a TAML that met the aforementioned require-
ments is depicted in Scheme 1. Moreover, the potential redox
non-innocence of TAML and related o-phenylenedicarboxam-
ido complexes has been proposed in the literature, and for clar-
ity we will follow the nomenclature as presented in Scheme 1
for the fully reduced tetra-anion (red), mono-oxidized tri-ani-
onic ligand-centered radical (sq) and fully oxidized di-anion
(q).16,17
Our group, in collaboration with the Zhang group, has stud-
ied the formation and reactivity of nitrene adducts of cobalt(II)-
porphyrin complexes, which are competent catalysts for a range
of (enantioselective) amination and aziridination reac-
tions.11a,11d-j,14 The mono-nitrene species generated on cobalt
upon reaction with an organic azide is most accurately de-
scribed as a one-electron reduced Fischer-type nitrene radi-
cal.14b This interesting electronic structure is the result of metal-
to-substrate single-electron transfer (SET), wherein cobalt is
oxidized from CoII to CoIII, and the nitrene is reduced by one
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Figure 1. Interpretation of the ligand (non-)innocence in cobalt-TAML complexes in chronological order. HFI = hyperfine interaction.
Scheme 1. General structure of the TAML scaffold and the
potential redox non-innocence of the backbone. X1 = Cl, H,
NO2, OMe. X2 = Cl, H. R = Et, Me, F.16
Co(TAML)-based imido- or nitrene-complexes have been re-
ported to date. Moreover, contrary to chemistry with iron, the
existence of TAML-centered redox processes in cobalt com-
plexes is still under debate (Figure 1).
Collins et al.21 reported the synthesis and characterization
of an anionic [CoIII(TAMLred)] complex with a diamidophenyl
backbone in 1991. The anionic parent complex was character-
ized as a triplet with an S = 1 Co center and a fully reduced
o-phenylenedicarboxamido ligand. Oxidation of this complex
afforded a neutral S = ½ system, for which crystallographic
bond metrics indicated single-electron oxidation of the ligand
and electron paramagnetic resonance (EPR) data hinted at a co-
balt-centered radical (Figure 1). This data was interpreted in
1998 as corresponding to an S = 1 cobalt(III) center antiferro-
magnetically coupled to a ligand-centered radical ([CoIII(TAM-
Lsq)]).28 Ghosh et al.29 reported an elaborate density functional
theory (DFT) study on the ligand non-innocence of multiple
variations of the TAML backbone, and suggested that the elec-
tronic structure of [CoIII(TAMLsq)] is better described as
[CoIV(TAMLred)] (Figure 1). Their assignment was based on the
Mulliken spin density, which was solely localized on cobalt.
Collins and coworkers18 critically re-interpreted these spin den-
sities as being evidence of an S = 1 CoIII center. It should be
noted that multireference post-Hartree-Fock methods were not
accessible at the time, and possible broken-symmetry solutions
were apparently not explored. As such, optional antiferromag-
netic coupling between an S = 1 Co center and a ligand-centered
radical could have remained hidden in the applied DFT calcu-
lations.
Iron complexes of these TAML activators have found wide-
spread use in oxidation chemistry, and TAML complexes with
Cr, Mn, Fe, Co, Ni and Cu have been reported with many vari-
ations of the TAML scaffold.16,18 Interestingly, ligand-centered
oxidation of an [FeV(TAMLred)(NTs)] complex was shown to
afford [FeV(TAMLsq)(NTs)], which is a more active nitrene
transfer species towards activated C‒H bonds (bond dissocia-
tion energy between 75 and 80 kcal mol-1) and thioanisole than
the reduced analogue.19 A similar trend was observed for a man-
ganese-imido complex, wherein [MnV(TAMLred)(NMes)]‒
(Mes = mesityl) proved to be unreactive, while the metal-cen-
tered oxidized complex [MnVI(TAMLred)(NMes)] could be used
for hydrogen atom transfer reactions and nitrene transfer to thi-
oanisole.20 Apparently the redox activity of the TAML ligand
varies from complex to complex, depending on the metal and
other ligands, and both metal- and ligand-centered redox pro-
cesses can be used to influence nitrene-transfer reactivity.
Innocent behavior of the TAML scaffold was claimed in an
electrochemical study reported in 2014,30 as well as in the char-
Specific [CoIII(TAMLred)] complexes21 have been used for
electrochemical water oxidation22,23 and oxygen reduction,24 cy-
cloaddition of CO2 to epoxides,25 electrochemical sensing of
H2O2,26 oxo transfer to C‒H bonds27 and electron-transfer reac-
tions.28 However, to the best of our knowledge, no nitrene trans-
fer reactions or stoichiometric reactions leading to formation of
acterization of
a
Lewis-acid stabilized oxo-complex
[CoIV(TAMLred)(O)].27 The TAMLred and CoIV oxidation states
in a Sc3+-bound [CoIV(TAMLred)(O)]2- complex were based on
UV-Vis, EPR, XAS (X-ray absorption spectroscopy) and
EXAFS (extended X-ray absorption fine structure) studies, in
combination with DFT calculated Mulliken spin densities.27 On
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contrary,
TAML-centered
redox-activity
in
on the (electronic) structure of the targeted nitrene (rad-
ical) species? (See Figure 2B).
[CoIII(TAMLq)(OH)] was claimed in 2018 on the basis of UV-
Vis, EPR and XPS (X-ray photoelectron spectroscopy) stud-
ies.23
(3) In case the TAML ligand platform is indeed redox-ac-
tive, can we use this feature for ligand-to-substrate SET
to produce nitrene radical species at square planar co-
balt(III) species? (See Figure 2B).
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The main findings of the investigations presented in this paper
are summarized in Figure 2C.
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RESULTS AND DISCUSSION
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Ligand-Centered Oxidation of [CoIII(TAMLred)]. The
parent [CoIII(TAMLred)] complex was obtained according to
an adapted literature procedure.21,31 After a five-step synthetic
procedure to obtain the ligand (TAMLH4), coordination of CoII
to the fully deprotonated ligand (generated using n-BuLi) and
aerobic oxidation afforded Li[CoIII(TAMLred)], or
PPh4[CoIII(TAMLred)] after salt metathesis with PPh4Cl
(Scheme 2). Crystals suitable for singe crystal X-ray diffraction
(XRD) analysis of TAMLH4 and PPh4[CoIII(TAMLred)] were
grown by vapor diffusion of pentane into concentrated THF so-
lutions of the ligand or complex, respectively. The solid state
structure of PPh4[CoIII(TAMLred)] displays a square planar ge-
ometry around cobalt and a non-coordinating THF molecule in
the crystal lattice. As expected, and in accordance with litera-
ture,21 analysis of the crystallographic bond metrics (see Sup-
porting Information) of the diamidophenyl ring in TAMLH4
and PPh4[CoIII(TAMLred)] supports the preservation of aroma-
ticity upon coordination to cobalt, with the ligand being fully
reduced ((TAMLred)4-) and the metal adopting the CoIII oxida-
tion state. The effective magnetic moment of PPh4[CoIII(TAM-
Lred)], as determined via the Evans’ method,32 indicated a triplet
(S = 1) ground state (µeff = 2.94 µB). This is in accordance with
literature and expected for an intermediate spin CoIII center with
two parallel metal-centered unpaired electrons.21 The DFT op-
timized structure of [CoIII(TAMLred)] in the triplet state at the
BP86/def2-TZVP level of theory is consistent with these obser-
vations and the calculated bond metrics closely match the ex-
perimental bond lengths (see SI).
Scheme 2. (A): Formation of Li[CoIII(TAMLred)] and
PPh4[CoIII(TAMLred)] from TAMLH4. Thermal displace-
ment ellipsoid plots (50% probability level) of TAMLH4 (B)
and PPh4[CoIII(TAMLred)] (C). H-atoms (except for NH)
and lattice solvent (THF for PPh4[CoIII(TAMLred)]) re-
moved for clarity.
Figure 2. (A): Electronic structure questions regarding the redox
non-innocence of the TAML scaffold. (B): Possible electronic
structures of the targeted nitrene species. The ligand color-coding
is as presented in Scheme 1. (C): Main findings with the assignment
of the TAML scaffold being redox non-innocent in the coordination
sphere of cobalt and its influence on nitrene (radical) formation.
Given i) the contrasting descriptions of ligand and cobalt
oxidation states in [Co(TAML)] complexes, ii) our interest in
generating cobalt-nitrene radical intermediates via ligand-to-
substrate SET and iii) the previous characterization of
[Fe(TAML)(imido)], [Mn(TAML)(imido)] and [Co(TAML)-
(oxo)] complexes, we set out to answer the following research
questions:
(1) Is the ligand in [Co(TAML)] complexes redox non-
innocent and can the different assignments in literature
be reconciled? (See Figure 2A).
(2) Can the [Co(TAML)] platform be used to generate (cat-
alytically competent) cobalt-nitrene (radical) species,
and what is the influence of the (ligand) oxidation state
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Electrochemical oxidation of PPh4[CoIII(TAMLred)] in
CH2Cl2 (Scheme 3A) using cyclic voltammetry displays three
characteristic for a net S = ½ system with unpaired electron den-
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sity on cobalt (giso = 2.22) (Figure 3A). EPR measurements at
10 K in a toluene glass showed a rhombic signal with gx = 2.03,
gy = 2.16, gz = 2.54 and partially unresolved cobalt hyperfine
interactions (HFIs) (Figure 3B). The inclusion of 59Co (I = 7/2
nucleus) HFIs (ACox = 5.0 MHz, ACoy = 50.0 MHz, ACoz = 20.0
MHz) is necessary for accurate simulation of the spectrum. The
DFT calculated cobalt HFIs are overestimated (B3LYP/def2-
fully reversible redox events at E = 1.18 , +0.53 and +1.13 V
½
vs. Fc+/0, which are attributed to metal-centered reduction
(CoIII/II) and two ligand-centered oxidations (TAMLred/sq and
TAMLsq/q) respectively (vide infra).33 UV-Vis spectroelectro-
chemical (UV-Vis-SEC) monitoring of the oxidation event at
+0.53 V vs. Fc+/0 shows disappearance of PPh4[CoIII(TAM-
Lred)] (λmax = 510 nm) and concomitant appearance of the char-
acteristic absorption band of [CoIII(TAMLsq)] (λmax = 623 nm)
with an isosbestic point at 545 nm (Scheme 3B).21,23,34,35 For
clarity we already assigned the electronic structure of
[CoIII(TAMLsq)] in the following descriptions. In the following
sections we will further elaborate on the measurements and cal-
culations leading to this assignment.
TZVP: gx = 2.04, gy = 2.25, gz = 2.26, ACox = 166.3 MHz, ACo
y
= 199.8 MHz, ACoz = 641.3 MHz), which we attribute to the er-
roneous description of multireference systems with DFT meth-
ods (vide infra). Interestingly, the isotropic X-band EPR spec-
trum measured in MeCN (Figure 3C) revealed an eight-line pat-
tern at giso = 2.00, attributed to hyperfine coupling with cobalt
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(ACo = 36.0 MHz) in [CoIII(TAMLsq)(MeCN)], which is in
iso
excellent agreement with the DFT calculated parameters
Chemical oxidation of TAML complexes with ceric ammo-
nium nitrate ((NH4)2[Ce(NO3)6]) typically requires excess oxi-
dant and large volumes of solvent to extract the product.21 For
purple colored PPh4[CoIII(TAMLred)] and Li[CoIII(TAM-
(B3LYP/def2-TZVP: giso = 2.00, ACo = 34.2 MHz). Notably,
iso
this species has a single-reference doublet electronic structure
with the unpaired electron residing in a cobalt-ligand * orbital
(strongly delocalized over cobalt and the ligand; see SI).
Lred)], oxidation with a stoichiometric amount of thianthrenium
36
tetrafluoroborate ((Thi)BF4) (Eo = 0.86 V vs. Fc+/0
)
cleanly
½
afforded the blue colored [CoIII(TAMLsq)] complex (Scheme
3C). A UV-Vis titration gave identical data as the UV-Vis-SEC
monitoring of the oxidation event at +0.53 V vs. Fc+/0 (Scheme
3D).
Scheme 3. (A): Cyclic voltammogram of PPh4[CoIII(TAM-
Lred)] in DCM (see SI for details). (B): UV-Vis-SEC oxida-
tion of PPh4[CoIII(TAMLred)] in DCM (see SI for details).
(C): Oxidation of [CoIII(TAMLred)] to [CoIII(TAMLsq)] with
(Thi)BF4. (D): UV-Vis titration of PPh4[CoIII(TAMLred)] in
DCM (0.15 mM) with increasing amounts of (Thi)BF4.
Figure 3. (A): X-band EPR spectrum of [CoIII(TAMLsq)] in ben-
zene at r.t. (black line: microwave freq. 9.390167 GHz, mod. amp.
4 G, power 2.518 mW) and CH2Cl2 (blue line: microwave freq.
9.3966 GHz, mod. amp. 5 G, power 2.000 mW) with giso = 2.22.
(B): experimental (black) and simulated (blue) X-band EPR spec-
trum of [CoIII(TAMLsq)] in toluene at 10 K. Microwave freq.
9.365984 GHz, mod. amp. 4 G, power 2.000 mW. Simulation pa-
rameters: gx = 2.03, gy = 2.16, gz = 2.54, ACox = 5.0 MHz, ACo
=
y
50.0 MHz, ACo = 20.0 MHz, linear A-strain 0.018 (z direction),
z
quadratic A strain 18 (x direction) and 2 (y direction). (C): Ex-
perimental (black) and simulated (blue) X-band EPR spectrum of
[CoIII(TAMLsq)(MeCN)] at r.t. in MeCN and DFT (BP86/def2-
TZVP/disp3) optimized structure. Microwave freq. 9.3886 GHz,
mod. amp. 3 G, power 0.7962 mW. Simulated (calculated;
B3LYP/def2-TZVP)) parameters: giso = 2.00 (2.00) and ACo
=
iso
36.0 (34.2) MHz.
The cobalt oxidation state of the four-coordinate complexes
was further investigated using Co K-edge X-ray near edge
structure (XANES) analysis. The Co K-edge XANES spectra
of PPh4[CoIII(TAMLred)] and [CoIII(TAMLsq)] in toluene are
compared in Figure 4. The edge position (determined at the
half-step height) was 7721 eV for both complexes. Both spectra
are identical, which is in line with the same oxidation state
(+III) and similar coordination geometry of cobalt in the two
The effective magnetic moment of [CoIII(TAMLsq)] (µeff
=
1.88 µB, Evans’ method) was found to be consistent with an
overall net doublet (S = ½) ground state. Room temperature
(r.t.) X-band EPR studies in CH2Cl2 or toluene reveal a signal
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the complex causes increased stabilization of the cobalt d-orbit-
complexes. The +III oxidation state of cobalt was already found
in PPh4[CoIII(TAMLred)] (according to XRD-derived bond
metric analysis, vide supra) and the observed edge position is
equal to a related [CoIII(TAML)]‒ complex.27 The shoulder at
approximately 7715 eV in the Co K-edge XANES spectra is
typical for square planar Co complexes, including square planar
Co-porphyrin complexes and a related cobalt-TAML com-
plex.14b,27 The main edge feature arises primarily from 1s → 4p
electron transitions, whereas the feature at 7715 eV is com-
monly assigned to 1s → 4pz and ligand to metal charge transfer
(LMCT) shakedown transitions.37
als compared to the parent anionic complex, which increases
overlap between the dxz and Lπ orbitals (Figure 5B). Due to this
stabilization, the bonding and antibonding combinations of the
dxz and Lπ orbitals are comprised of substantial contributions
from both dxz and Lπ. As a result of three orbitals being close in
energy, significant population of the Lπ-dxz antibonding combi-
nation (occupancy 0.64) from the dxz+Lπ bonding combination
(occupancy 1.38) occurs, while the dyz orbital is singly occupied
(1.07). The net-doublet ground state of the neutral [CoIII(TAM-
Lsq)] complex is thus best described as an S = 1 CoIII center that
is antiferromagnetically coupled to an S = ½ TAML-centered
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radical, leading to
a
net-doublet system with
a
(dxy)2.00(dz²)2.00(dxz+Lπ)1.38(dyz)1.07(Lπ-dxz)0.64 electronic structure,
in agreement with the early interpretation of Collins.28 Excita-
tion energies derived from the CASSCF(13,12) calculation re-
vealed that the absorption band observed at λmax = 623 nm
(Scheme 3B and D) is indeed characteristic for the ligand-cen-
tered radical. The corresponding calculated excitation (at 625
nm) is comprised of ligand-centered Lπ→ Lπ-dxz and metal-to-
ligand (dxz+Lπ→ Lπ-dxz and dyz→ Lπ-dxz) charge-transfer pro-
cesses, with the ligand-centered radical orbital being the accep-
tor in all cases.
Figure 4. Co-K edge XANES analysis of PPh4[CoIII(TAMLred)]
(black) and [CoIII(TAMLsq)] (red) in toluene.
In agreement with previous studies,27,29 DFT calculations
with various GGA and hybrid functionals (BP86, B3LYP, PBE
and OPBE; see SI for details) gave unsatisfactory results for the
Co(TAML)-type complexes under investigation. An illustrative
example of the problem encountered with DFT is found in the
challenging description of the net-doublet ground state of the
[CoIII(TAMLsq)] complex. Distinguishing between a genuine
CoIV complex and a multireference electronic structure solution
involving antiferromagnetic coupling between an S = 1 CoIII
center and a TAML ligand-centered radical (as indicated by the
B3LYP broken symmetry DFT solution) is very difficult, if not
impossible, when relying only on single reference computa-
tional methods (such as DFT).38 We therefore decided to turn to
multireference N-Electron Valence State Perturbation Theory
(NEVPT2)-corrected Complete Active Space Self Consistent
Field (CASSCF) calculations for a proper description of the
electronic structures of the Co(TAML)-type complexes de-
scribed in this paper.39
CASSCF calculations were initiated on the anionic
[CoIII(TAMLred)] complex by inclusion of all cobalt d-orbitals
and those ligand π-orbitals (Lπ) that could have an interaction
with cobalt. In the final CASSCF(14,13) calculation, all initial
orbitals were preserved in the active space, except for the dxy
orbital, which is uncorrelated (occupancy of 2.00).40 A selection
of the most relevant active orbitals with their occupancies (in
parentheses) is given in Figure 5A. Löwdin population analysis
of the electronic configuration of the d-shell gave
(dxy)2.00(dz²)1.99(dyz)1.02(dxz)1.02, consistent with the assigned +III
oxidation state of cobalt. Notably, the Lπ orbital at 0.268 Eh
has a weak bonding interaction with the dxz orbital and is fully
filled (occupancy 1.91), consistent with the fully reduced oxi-
dation state of the ligand.
CASSCF(13,12) calculations on the neutral [CoIII(TAM-
Lsq)] complex included a similar active space as for the parent
anionic complex, and revealed substantial multi-reference char-
acter. The uncorrelated dz² and dxy orbitals (occupancy 2.00)
were not preserved in the active space.40 The reduced charge on
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of [Co(TAML)(NNs)2] (2.75 µB) and [Co(TAML)(NNs)]
Figure 5. Relevant active orbitals and occupancies (in parenthesis)
of NEVPT2-corrected CASSCF(14,13) on [CoIII(TAMLred)] (A)
and CASSCF(13,12) on [CoIII(TAMLsq)] (B).
1
2
3
4
5
6
7
(1.53 µB) are consistent with formation of (net) triplet (S = 1)
and doublet (S = ½) systems, respectively. For clarity, we al-
ready included the assigned oxidation states of the ligand and
cobalt for the anionic bis-nitrene ([CoIII(TAMLq)(NNs)2]) and
neutral mono-nitrene ([CoIII(TAMLq)(NNs)]) in Scheme 4 and
Figure 6 and the following text. In the next sections we will fur-
ther elaborate on the measurements and calculations leading to
these assignments.
The combined data from magnetic moment measurements,
EPR, UV-Vis and XANES spectroscopy and NEVPT2-
CASSCF calculations reveal that oxidation of [CoIII(TAM-
Lred)] is ligand-centered, giving rise to the formation of
[CoIII(TAMLsq)], wherein cobalt retains its +III oxidation state.
Synthesis
and
Characterization
of
8
9
[CoIII(TAMLq)(NNs)2] and [CoIII(TAMLq)(NNs)] via
Ligand-to-Substrate SET. With a proper understanding of
their electronic structure, confirming that both complexes are
square planar cobalt(III) species featuring a redox-active ligand,
but in two different ligand oxidation states, we next set out to
investigate nitrene formation at the anionic [CoIII(TAMLred)]
and neutral [CoIII(TAMLsq)] complexes. We were particularly
interested in exploring the influence of the ligand oxidation
state on the structure and overall composition of the targeted
nitrene adducts.
Scheme 4. Synthesis of bis-nitrene (radical) complex
PPh4[CoIII(TAMLq)(NNs)2] and mono-nitrene (radical)
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complex [CoIII(TAMLq)(NR)] (R
=
Ns, Ts) from
PPh4[CoIII(TAMLred)] and [CoIII(TAMLsq)], respectively.
Addition of one equivalent of the nitrene precursor PhINNs
to PPh4[CoIII(TAMLred)] in CH2Cl2 at r.t. led to a mixture of
starting material, mono-nitrene adduct [Co(TAML)(NNs)]
and trace amounts of bis-nitrene adduct [Co(TAML)(NNs)2],
as revealed by negative mode electrospray ionization high res-
olution mass spectrometry (ESI-HRMS) analysis. Upon addi-
tion of ten equivalents PhINNs to PPh4[CoIII(TAMLred)] in
CH2Cl2 or toluene at r.t., quantitative formation of bis-nitrene
species [Co(TAML)(NNs)2] was achieved, based on ESI-
HRMS and UV-Vis analysis (Scheme 4 and Figure 6A,B).41
While bis-nitrene formation was readily achieved for the ani-
onic complex upon addition of an excess of PhINNs, addition
of ten equivalents of PhINNs to the neutral complex
[CoIII(TAMLsq)] in CH2Cl2 or toluene at r.t. led to quantitative
formation
of
only
the
mono-nitrene
species
[Co(TAML)(NNs)], as shown by ESI-HRMS and UV-Vis
analysis (Scheme 4 and Figure 6C, D). Also the addition of the
alternative nitrene source PhINTs (ten equivalents) to
[CoIII(TAMLsq)] in CH2Cl2 or toluene at room temperature led
to formation of mono-nitrene complex [Co(TAML)(NTs)], ac-
cording to ESI-HRMS data. The effective magnetic moments
Figure 6. (A): UV-Vis spectrum of PPh4[CoIII(TAMLq)(NNs)2] (red) upon reaction of PPh4[CoIII(TAMLred)] (150 µM in CH2Cl2, black)
with 10 equivalents of PhINNs. (B) ESI-HRMS spectrum (black) and simulated spectrum (red) for [CoIII(TAMLq)(NNs)2]. (C): UV-Vis
spectrum of [CoIII(TAMLq)(NNs)] (blue), formed by addition of 10 equivalents of PhINNs to [CoIII(TAMLsq)] (78 µM in CH2Cl2, black).
(D) ESI-HRMS spectrum (black) and simulated spectrum (blue) for [CoIII(TAMLq)(NNs)].
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five- or a six-coordinated cobalt complex can be made. This was
As can be expected for an integer spin system, the anionic
also observed in related CoIII(porphyrin)-mono- and bis-nitrene
complexes that displayed an octahedral coordination environ-
ment, with an axial co-ligand (NsNH2, NsNH, H2O, or solvent)
present in case of the mono-nitrene species.14b Moreover, an ad-
ditional low intensity pre-edge feature at 7711 eV is observed
clearly for [CoIII(TAMLq)(NNs)] (insert in Figure 8). The pre-
bis-nitrene complex [CoIII(TAMLq)(NNs)2] is X-band EPR si-
lent, both at r.t. and at 10 K. The neutral mono-nitrene complex
[CoIII(TAMLq)(NNs)] displays an isotropic EPR signal (Figure
2
3
4
7A) at giso = 2.091 at r.t., showing well-resolved 59Co (ACo
=
iso
89.5 MHz) and poorly resolved (but necessary for accurate sim-
ulation) 14N (ANiso = 18.9 MHz) HFIs. The anisotropic low tem-
perature (20 K) EPR spectrum of [CoIII(TAMLq)(NNs)] rec-
orded in a toluene glass displays a slightly rhombic signal with
a small g-anisotropy and multiple hyperfine coupling interac-
tions, consistent with a net-doublet ground state (Figure 7B).42
The r.t. EPR spectrum of [CoIII(TAMLq)(NTs)] proved to be
similar to that of [CoIII(TAMLq)(NNs)] (see SI).
5
6
7
8
edge
feature
in
the
XANES
spectrum
of
PPh4[CoIII(TAMLq)(NNs)2] is not well-resolved due to mod-
erate data quality caused by low solubility of the complex.
These pre-edge features arise from 1s→3d transitions, and in
centrosymmetric (i.e. square planar and octahedral) complexes
these transitions are weak due to quadrupole transitions.14b
However, symmetry breaking enables 3d–4p–hybridization of
metal atomic orbitals, causing the pre-edge to gain intensity due
to dipole-allowed transitions. It thus seems that
[CoIII(TAMLq)(NNs)] bears an unidentified sixth coordinating
co-ligand (octahedral coordination geometry), but is not fully
centrosymmetric. However, similar low-intensity pre-edge fea-
tures have been observed in a five-coordinate cobalt-TAML
complex27 and therefore a square pyramidal coordination
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around
cobalt
cannot
be
fully
excluded
for
[CoIII(TAMLq)(NNs)].
Figure
8.
Co-K
edge
XANES
analysis
of
PPh4[CoIII(TAMLq)(NNs)2] (black) and [CoIII(TAMLq)(NNs)]
(red) in toluene. Insert: zoom of the pre-edge feature for
[CoIII(TAMLsq)(NNs)].
Figure 7. (A): Experimental (black) and simulated (blue) X-band
EPR spectrum of [CoIII(TAMLq)(NNs)] at r.t. in toluene. Micro-
wave freq. 9.3716 GHz, mod. amp. 2.000 G, power 6.325 mW.
Consistent with the abovementioned experimental results,
DFT calculations (BP86, def2-TZVP, disp3, m4 grid) indicate
that formation of the neutral mono-nitrene complex
[CoIII(TAMLq)(NNs)] (S = ½; ΔGo298K = 20.3 kcal mol-1) from
[CoIII(TAMLsq)] (S = ½; reference point) is energetically more
favorable than formation of the neutral bis-nitrene adduct
[Co(TAML)(NNs)2] (S = ½; ΔGo298K = 14.5 kcal mol-1). How-
ever, the corresponding formation energies of the anionic
mono-and bis-nitrene complexes [CoIII(TAMLsq)(NNs)]
(S = 1; ΔGo298K = 27.9 kcal mol-1) and [CoIII(TAMLq)(NNs)2]
Simulated parameters: giso = 2.091, ACo = 89.5 (34.2) MHz and
iso
AN
=
18.9 MHz. (B): X-band EPR spectrum of
iso
[CoIII(TAMLq)(NNs)] in toluene glass at 20 K. Microwave freq.
9.376 GHz, mod. amp. 2.000 G, power 6.325 mW.
The
Co
K-edge
XANES
spectra
for
PPh4[CoIII(TAMLq)(NNs)2] and [CoIII(TAMLq)(NNs)] are
shown in Figure 8. As was observed for the parent complexes
PPh4[CoIII(TAMLred)] and [CoIII(TAMLsq)], the edge position
for both cobalt-nitrene complexes is detected at 7721 eV, sug-
gesting that the cobalt centers in all four complexes have the
same overall +III oxidation state. Interestingly, the intense
shoulder absorption at 7715 eV observed in the spectra of
PPh4[CoIII(TAMLq)(NNs)2] and [CoIII(TAMLq)(NNs)] (cor-
responding to 1s → 4p + LMCT shakedown transitions charac-
teristic for square planar cobalt complexes), is no longer visible
in the nitrene adducts, thus suggesting that both complexes un-
dergo changes in coordination number and/or geometry. Solely
based on Co K-edge XANES data, no differentiation between a
(S = 1; ΔGo
= 29.9 kcal mol-1) from [CoIII(TAMLred)]
298K
(S = 1; reference point) are nearly equal (see SI).
NEVPT2-corrected CASSCF calculations were performed
to accurately describe the electronic structure of the nitrene spe-
cies. All cobalt d-orbitals, ligand Lπ and nitrene localized p-or-
bitals were included in the active spaces. CASSCF(14,13) cal-
culations on [CoIII(TAMLq)(NNs)2] showed that the dxy or-
bital is not preserved in the active space (occupancy 2.00)40 and
that the dz² orbital forms bonding (nitrene-N1 and -N2 localized,
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occupancy 1.94) and antibonding (mostly dz² localized, occu-
mono-nitrene and the anionic bis-nitrene complexes, without
1
2
3
4
5
6
7
8
oxidation of cobalt and without changing the net total spin state
of the complex. The redox events clearly occur on the TAML
backbone (electron donor) and the nitrene (electron acceptor),
wherein the former undergoes one-electron or two-electron ox-
idation to accommodate one or two nitrene radical(s) on the
CoIII-center.
pancy 0.07) combinations with the nitrene N푝 orbitals. The dyz
z
and dxz orbitals are both filled (occupancies 1.97 and 1.95, re-
spectively) and the Lπ-dxz (occupancy 0.10) is virtually empty.
Given that the Lπ orbital was doubly-filled in [CoIII(TAM-
Lred)] (vide supra), this implies that formation of
[CoIII(TAMLq)(NNs)2] from [CoIII(TAMLred)] is associated
with two-electron oxidation of the ligand. Interestingly, both
nitrene nitrogen atoms bear a single unpaired electron in their
N푝 /N푝 orbitals (both occupancies 1.00). The electronic struc-
y
x
9
ture is thus best described as (dxy)2.00(dyz)1.97(dxz)1.95(Np1
+
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z
Np2 + dz )1.94(Np2
)
1.00(Np1 1.00, consistent with a CoIII center,
)
2
z
x
y
fully oxidized TAML backbone (TAMLq) and two one-electron
reduced Fischer-type nitrene radical substrates (NNs).43
Moreover, the cobalt(III) center has undergone a spin transition
from intermediate spin in [CoIII(TAMLred)] to low spin in
[CoIII(TAMLq)(NNs)2] upon formation of the bis-nitrene
radical species. As a result, the net total spin state does not
change in the process, and remains a triplet spin state (S = 1).
The most relevant active orbitals and their occupation numbers
are shown in Figure 9A. In addition, excitation energies derived
from the CASSCF(14,13) calculation revealed that no intense
absorption bands are expected in the 400-850 nm region (see
SI), consistent with the experimental spectrum depicted in Fig-
ure 6A.
The complex bears some resemblance to the previously re-
ported cobalt-porphyrin bis-nitrene ([CoIII(TPP)(NNs)2])14
and ruthenium-porphyrin bis-imido ([RuVI(TPP)(NTs)2])44
complexes (TPP = tetraphenylporphyrin). The ruthenium bis-
imido complex is formed exclusively via metal-centered oxida-
tion processes. However, while in the cobalt-porphyrin com-
plex double nitrene-radical formation is the result of combined
metal-to-substrate and (porphyrin) ligand-to-substrate SET
processes, formation of [CoIII(TAMLq)(NNs)2] is an entirely
(double) ligand-to-substrate single-electron transfer process.
In a very similar fashion, CASSCF(13,12) calculations on
[CoIII(TAMLq)(NNs)] reveal π (dyz+Np ) and σ (dz²+Np )
y
z
bonding interactions between cobalt and the nitrene, with occu-
pations of 1.93 and 1.86 electrons respectively.45 The dxz orbital
is filled (occupancy 1.91) and the formerly half-filled Lπ-dxz or-
bital is now unoccupied (occupancy 0.12), indicating single-
electron oxidation of the ligand (i.e. from TAMLsq to TAMLq).
The single unpaired electron of the complex is mainly localized
on the nitrene moiety (Np -dyz, occupancy 1.06), again con-
y
sistent with [CoIII(TAMLq)(NNs)] being a Fischer-type
nitrene radical complex with a net -bond order between cobalt
and the nitrene of ~0.5.43 As for the anionic bis-nitrene complex,
the neutral mono-nitrene complex is generated via ligand-to-
substrate SET. Once again the cobalt(III) ion does not change
its oxidation state in the process, but it does undergo a spin flip
from intermediate spin in [CoIII(TAMLsq)] to low spin in
[CoIII(TAMLq)(NNs)]. The most relevant active orbitals and
their occupations are shown in Figure 9B. Notably, neither
[CoIII(TAMLq)(NNs)2] nor [CoIII(TAMLq)(NNs)] show
significant multi-reference character.
Figure 9. Most relevant active orbitals and occupancies (in paren-
thesis)
([CoIII(TAMLq)(NNs)2],
([CoIII(TAMLq)(NNs)], bottom) calculations.
of
NEVPT2-corrected
CASSCF(14,13)
CASSCF(13,12)
top) and
Interestingly, ligand-to-substrate SET combined with a
metal-based spin flip effectively leads to a shift of the spin den-
sity from the metal to the nitrene nitrogen(s) in both the neutral
Intrigued by the influence of the ligand oxidation state on
the structure of the nitrene species, the mono- and bis-nitrene
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low spin (S = 0) at the cobalt(III) center effectively results in a
species were probed for catalytic nitrene transfer reactivity in
the benchmark aziridination of styrene (Scheme 5).1a,3 A re-
markable difference in yield of aziridine product 1 was ob-
served when using PPh4[CoIII(TAMLred)] (64%) or
[CoIII(TAMLsq)] (35%) as the catalyst in nitrene transfer reac-
tions from PhINNs to styrene, suggesting that the anionic bis-
nitrene and neutral mono-nitrene exhibit markedly different ac-
tivity and/or stability properties. A thorough investigation on
the applicability and mechanisms of PPh4[CoIII(TAMLred)]
and [CoIII(TAMLsq)] as aziridination catalysts is the subject of
current investigations, that will be reported in due time. At this
point it is worth mentioning that for cobalt-TAML complexes
the reduced (anionic) [CoIII(TAMLred)] species are apparently
more effective nitrene-transfer catalysts than the corresponding
oxidized (neutral) [CoIII(TAMLsq)] species, while for iron- and
manganese TAML complexes the reverse was observed.19,20
shift of the spin density from the metal to the nitrene moieties,
without oxidation of cobalt and without changing the net total
spin state of the complex.
1
2
3
4
5
6
7
8
Preliminary catalytic styrene aziridination reactions using
PPh4[CoIII(TAMLred)] or [CoIII(TAMLsq)] as the catalyst re-
veal remarkable differences in activity/stability between the
two systems. More elaborate studies on the underlying mecha-
nisms, synthetic applicability and differences between the two
complexes in nitrene transfer catalysis will be reported in the
near future.
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ASSOCIATED CONTENT
Supporting Information. Experimental details, synthetic proce-
dures, relevant NMR, EPR, HRMS, XRD, UV-Vis, electrochemi-
cal and XANES data, geometries (xyz coordinates) of stationary
points (DFT) and description of the CASSCF calculations. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Scheme 5. Catalytic aziridination of styrene to afford 1
using PPh4[CoIII(TAMLred)] and [CoIII(TAMLsq)].
AUTHOR INFORMATION
Corresponding Author
*Dr. Ir. J. I. van der Vlugt. j.i.vandervlugt@uva.nl
*Prof. Dr. B. de Bruin. b.debruin@uva.nl
Notes
The authors declare no competing financial interest.
CONCLUSIONS
In this work we have conclusively shown that the ligand in
Co(TAML) complexes is redox-active. Oxidation of
Funding Sources
NWO TOP-Grant 716.015.001 to BdB.
[CoIII(TAMLred)]
using
(Thi)BF4
cleanly
affords
[CoIII(TAMLsq)] via ligand-centered oxidation, with the elec-
tronic structure being best described as an intermediate spin
(S = 1) cobalt(III) center that is antiferromagnetically coupled
to a ligand-centered radical (S = ½).
ACKNOWLEDGMENT
Financial support from The Netherlands Organization for Scientific
Research (NWO TOP-Grant 716.015.001 to BdB and NWO VIDI
grant 723.014.010 to MT) is gratefully acknowledged. Ed Zuidinga
is thanked for HRMS measurements and Lars Grooten is thanked
for preliminary UV-Vis studies. The authors thank the staff of the
beamline B18, Diamond Light Source (proposal number SP22432)
in Didcot, UK for support and access to their facilities.
Interestingly,
cobalt-nitrene
adducts
of
PPh4[CoIII(TAMLred)] and CoIII(TAMLsq) can be cleanly
generated from PhINNs via ligand-to-substrate single-electron
transfer to afford PPh4[CoIII(TAMLq)(NNs)2] and
[CoIII(TAMLq)(NNs)], respectively. CASSCF calculations
revealed that both nitrene complexes are best described as one-
electron reduced Fischer-type nitrene radicals. The formation of
a bis-nitrene adduct of PPh4[CoIII(TAMLred)] is attributed to
the availability of two electrons within the reduced TAML
framework for double ligand-to-substrate SET, whereas only
one electron can be used for ligand-to-substrate SET on
[CoIII(TAMLsq)], which therefore affords the mono-nitrene
adduct. Intriguingly, in both cases the combination of ligand-to-
substrate SET and a spin flip from intermediate spin (S = 1) to
ABBREVIATIONS
CASSCF, Complete Active Space Self Consistent Field; DCM, di-
chloromethane; DFT, density functional theory; EPR, electron par-
amagnetic resonance; HFI, hyperfine interaction; Ns, nosyl; r.t.,
room temperature; TAML, tetra-amido macrocyclic ligand;
XANES, X-ray near edge structure.
Das, B. G.; Kuijpers, P. F.; Sinha, V.; de Bruin, B. Application
of Stimuli-Responsive and “Non-Innocent” Ligands in Base
Metal Catalysis. In Non-Noble Metal Catalysis Molecular Ap-
proaches and Reactions; Wiley-VCH Verlag GmbH & Co.
KGaA: Weinheim Germany, 2018; pp 1‒31. (d) Lu, H.; Zhang,
X. P. Catalytic C‒H functionalization by metalloporphyrins: re-
cent developments and future directions. Chem. Soc. Rev. 2011,
40, 1899‒1909. (e) Lyaskovskyy, V.; de Bruin, B., Redox Non-
innocent Ligands – Versatile New Tools to Control Catalytic Re-
actions. ACS Catalysis, 2012, 2, 270–279.
REFERENCES
(1) (a) van Leest, N. P.; Epping, P. F. J.; van Vliet, K. M.; Lankelma,
M.; van den Heuvel, E. J.; Heijtbrink, N.; Broersen, R.; de Bruin,
B. Single-Electron Elementary Steps in Homogeneous Organo-
metallic Catalysis. In Advances in Organometallic Chemistry;
Elsevier: London UK, 2018; Vol. 70, pp 71‒180. (b) Broere, D.
L. J.; Plessius, R.; van der Vlugt, J. I. New avenues for ligand-
mediated processes ‒ expanding metal reactivity by the use of
redox-active catechol, o-aminophenol and o-phenylenediamine
ligands. Chem. Soc. Rev. 2015, 44, 6886‒6915. (c) Chirila, A.;
(2) Hili, R.; Yudin, A. K. Making carbon-nitrogen bonds in biologi-
cal and chemical synthesis. Nat. Chem. Biol. 2006, 2, 284‒287.
9
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Journal of the American Chemical Society
Page 10 of 12
(10) (a) Bagh, B.; Broere, D. L. J.; Sinha, V.; Kuijpers, P. F.; van
(3) (a) Kuijpers, P. F.; van der Vlugt, J. I.; Schneider, S.; de Bruin,
B. Nitrene Radical Intermediates in Catalytic Synthesis. Chem.
Eur. J. 2017, 23, 13819‒13829. (b) Park, Y.; Kim, Y.; Chang, S.
Transition Metal-Catalyzed C–H Amination: Scope, Mecha-
nism, and Applications. Chem. Rev. 2017, 117, 9247‒9301. (c)
Shin, K.; Kim, H.; Chang, S. Transition-Metal-Catalyzed C–N
Bond Forming Reactions Using Organic Azides as the Nitrogen
Source: A Journey for the Mild and Versatile C–H Amination.
Acc. Chem. Res. 2015, 48, 1040‒1052.
(4) (a) Intrieri, D.; Carminati, D. M.; Gallo, E. Recent advances in
C–H bond aminations catalyzed by ruthenium porphyrin com-
plexes. J. Porphyrins Phthalocyanines 2016, 20, 1‒14. (b) Zardi,
P. Caselli, A.; Macchi, P.; Ferretti, F.; Gallo, E. Synthesis of Bi-
ologically Relevant Compounds by Ruthenium Porphyrin Cata-
lyzed Amination of Benzylic C–H Bonds. Organometallics
2014, 33, 2210‒2218. (c) Fantauzzi, S.; Gallo, E.; Caselli, A.;
Ragaini, F.; Casati, N.; Macchi, P.; Cenini, S. The key interme-
diate in the amination of saturated C–H bonds: synthesis, X-ray
characterization and catalytic activity of Ru(TPP)(NAr)2 (Ar =
3,5-(CF3)2C6H3). Chem. Commun. 2009, 3952‒3954.
(5) (a) Guthikonda, K.; When, P. M.; Caliando, B. J.; Du Bois, J.
Rh-catalyzed alkene oxidation: a highly efficient and selective
process for preparing N-alkoxysulfonyl aziridines. Tetrahedron
2006, 62, 11331‒11342. (b) Liang, C.; Robert-Peillard, F.; Fruit,
C.; Müller, P.; Dodd, R. H.; Dauban, P. Efficient Diastereoselec-
tive Intermolecular Rhodium-Catalyzed C‒H Amination. An-
gew. Chem. Int. Ed. 2006, 45, 4641‒4644. (c) Espino, C. G.;
When, P. M.; Chow, J.; Du Bois, J. Synthesis of 1,3-Difunction-
alized Amine Derivatives through Selective C−H Bond Oxida-
tion. J. Am. Chem. Soc. 2001, 123, 6935‒3936. (d) Roizen, J. L.;
Zalatan, D. N.; De Bois, J. Selective Intermolecular Amination
of C‒H Bonds at Tertiary Carbon Centers. Angew. Chem. Int. Ed.
2013, 52, 11343-11346.
(6) (a) Broere, D. L. J.; de Bruin, B.; Reek, J. N. H.; Lutz, M.;
Dechert, S.; van der Vlugt, J. I. Intramolecular Redox-Active
Ligand-to-Substrate Single-Electron Transfer: Radical Reactiv-
ity with a Palladium(II) Complex. J. Am. Chem. Soc. 2014, 136,
11574‒11577. (b) Broere, D. L. J.; van Leest, N. P.; de Bruin,
B.; Siegler, M. A.; van der Vlugt, J. I. Reversible Redox Chem-
istry and Catalytic C(sp3)–H Amination Reactivity of a Paramag-
netic Pd Complex Bearing a Redox-Active o-Aminophenol-De-
rived NNO Pincer Ligand. Inorg. Chem. 2016, 55, 8603‒8611.
(c) Okamoto, K.; Oda, T.; Kohigashi, S.; Ohe, K. Palladium‐Cat-
alyzed Decarboxylative Intramolecular Aziridination from 4H‐
Isoxazol‐5‐ones Leading to 1‐Azabicyclo[3.1.0]hex‐2‐enes. An-
gew. Chem. Int. Ed. 2011, 50, 11470‒11473.
Leest, N. P.; de Bruin, B.; Demeshko, S.; Siegler, M. A.; van der
Vlugt, J. I. Catalytic Synthesis of N-Heterocycles via Direct
C(sp3)–H Amination Using an Air-Stable Iron(III) Species with
a Redox-Active Ligand. J. Am. Chem. Soc. 2017, 139, 5117‒
5124. (b) Avenier, F.; Latour, J.-M. Catalytic aziridination of
olefins and amidation of thioanisole by a non-heme iron com-
plex. Chem. Commun. 2004, 1544‒1545. (c) Fingerhut, A.; Ser-
dyuk, O. V.; Tsogoeva, S. B. Non-heme iron catalysts for epox-
idation and aziridination reactions of challenging terminal al-
kenes: towards sustainability. Green Chem. 2015, 17, 2042‒
2058. (d) Correa, A.; Mancheño, O. G.; Bolm, C. Iron-catalysed
carbon–heteroatom and heteroatom–heteroatom bond forming
processes. Chem. Soc. Rev. 2008, 37, 1108‒1117. (e) Hennessy,
E. T.; Betley, T. A. Complex N-Heterocycle Synthesis via Iron-
Catalyzed, Direct C‒H Bond Amination. Science 2013, 340,
591‒595. (f) Iovan, D. A.; Betley, T. A. Characterization of Iron-
Imido Species Relevant for N-Group Transfer Chemistry. J. Am.
Chem. Soc. 2016, 138, 1983‒1993. (g) Patra, R.; Coin, G.; Cas-
tro, L.; Dubourdeaux, P.; Clémancey, M.; Pécaut, J.; Lebrun, C.;
Maldivi, Latour, J.-M. Rational design of Fe catalysts for olefin
aziridination through DFT-based mechanistic analysis. Catal.
Sci. Technol. 2017, 7, 4388‒4400. (h) Klotz, K. L.; Slominksi,
L. M.; Hull, A. V.; Gottsacker, V. M.; Mas-Ballesté, R.; Que, L.
Jr.; Halfen, J. A. Non-heme iron(II) complexes are efficient ole-
fin aziridination catalysts. Chem. Commun. 2007, 2063‒2065. (i)
Klotz, K. L.; Slominski, L. M.; Riemer, M. E.; Phillips, J. A.;
Halfen, J. A. Mechanism of the Iron-Mediated Alkene Aziridi-
nation Reaction: Experimental and Computational Investiga-
tions. Inorg. Chem. 2009, 48,801‒803. (j) Chandrachud, P. P;
Bass, H. M.; Jenkins, D. M. Synthesis of Fully Aliphatic Aziri-
dines with a Macrocyclic Tetracarbene Iron Catalyst. Organo-
metallics 2016, 35, 1652‒1657. (k) Nakanishi, M.; Salit, A.-F.;
Bolm, C. Iron-Catalyzed Aziridination Reactions. Adv. Synth.
Catal. 2008, 350, 1835‒1840.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(11) (a) Kuijpers, P. F.; Tiekink, M. J.; Breukelaar, W. B.; Broere, D.
L. J.; van Leest, N. P.; van der Vlugt, J. I.; Reek, J. N. H.; de
Bruin, B. Cobalt-Porphyrin-Catalysed Intramolecular Ring-
Closing C−H Amination of Aliphatic Azides: A Nitrene-Radical
Approach to Saturated Heterocycles. Chem. Eur. J. 2017, 23,
7945‒7952. (b) Goswami, M.; Geuijen, P.; Reek, J. N. H.; de
Bruin, B. Application of [Co(Corrole)]‒ Complexes in Ring-
Closing C‒H Amination of Aliphatic Azides via Nitrene Radical
Intermediates. Eur. J. Inorg. Chem. 2018, 617‒626. (c) Baek, Y.;
Betley, T. A. Catalytic C–H Amination Mediated by Dipyrrin
Cobalt Imidos. J. Am. Chem. Soc. 2019, 141, 7797‒7806. (d) Jin,
L.-M.; Lu, H.; Cui, Y.; Lizardi, C. L.; Arzua, T. N.; Wojtas, L.;
Cui, X.; Zhang, X. P. Selective radical amination of aldehydic
C(sp2)–H bonds with fluoroaryl azides via Co(II)-based metallo-
radical catalysis: synthesis of N-fluoroaryl amides from alde-
hydes under neutral and nonoxidative conditions. Chem. Sci.
2014, 5, 2422‒2427. (e) Lu, H.; Jiang, H.; Wojtas, L.; Zhang, X.
P. Angew. Chem. Int. Ed. 2010, 49, 10192‒10196. (f) Ruppel, J.
V.; Kamble, R. M.; Zhang, X. P. Selective Intramolecular C‒H
Amination through the Metalloradical Activation of Azides:
Synthesis of 1,3-Diamines under Neutral and Nonoxidative Con-
ditions. Org. Lett. 2007, 9, 4889‒4892. (g) Jin, L.-M.; Xu, X.;
Lu, H.; Cui, X.; Wojtas, L.; Zhang, X. P. Effective Synthesis of
Chiral N-Fluoroaryl Aziridines through Enantioselective
Aziridination of Alkenes with Fluoroaryl Azides. Angew. Chem.
Int. Ed. 2013, 52, 5309‒5313. (h) Gao, G.-Y.; Jones, J. E.; Vyas,
R.; Harden, J. D.; Zhang, X. P. J. Cobalt-Catalyzed Aziridination
with Diphenylphosphoryl Azide (DPPA): Direct Synthesis of N-
Phosphorus-Substituted Aziridines from Alkenes. Org. Chem.
2006, 71, 6655‒6658. (i) Subbarayan, V.; Ruppel, J. V.; Zhu, S.;
Perman, J. A.; Zhang, X. P. Highly asymmetric cobalt-catalyzed
aziridination of alkenes with trichloroethoxysulfonyl azide
(TcesN3). Chem. Commun. 2009, 4266‒4268. (j) Gao, G.-Y.;
Harden, J. D.; Zhang, X. P. Cobalt-Catalyzed Efficient Aziridi-
nation of Alkenes. Org. Lett. 2005, 7, 3191‒3193. (k) Caselli, A.;
Gallo, E.; Fantauzzi, S.; Morlacchi, S.; Ragaini, F.; Cenini, S.
Allylic Amination and Aziridination of Olefins by Aryl Azides
(7) (a) Llaveria, J.; Beltrán, Á.; Díaz-Requejo, M. M.; Matheu, M.
I.; Castillón, S.; Pérez, P. J. Efficient Silver-Catalyzed Regio-
and Stereospecific Aziridination of Dienes. Angew. Chem. Int.
Ed. 2010, 49, 7092‒7095. (b) Rigoli, J. W.; Weatherly, C. D.;
Alderson, J. M.; Vo, B. T.; Schomaker, J. M. Tunable, Chemose-
lective Amination via Silver Catalysis. J. Am. Chem. Soc. 2013,
135, 17238‒17241. (c) Dolan, N. S.; Scamp, R. J.; Yang, T.;
Berry, J. F.; Schomaker, J. M. Catalyst-Controlled and Tunable,
Chemoselective Silver-Catalyzed Intermolecular Nitrene Trans-
fer: Experimental and Computational Studies. J. Am. Chem. Soc.
2016, 138, 14658‒14667. (d) Cui, Y.; He, C. Efficient Aziridi-
nation of Olefins Catalyzed by a Unique Disilver(I) Compound.
J. Am. Chem. Soc. 2003, 125, 16202‒16203.
(8) Li, Z.; Ding, X.; He, C. Nitrene Transfer Reactions Catalyzed by
Gold Complexes. J. Org. Chem. 2006, 71, 5876‒5880.
(9) (a) Minakata, S.; Ando, T.; Nishimura, M.; Ryu, I.; Komatsu, M.
Novel Asymmetric and Stereospecific Aziridination of Alkenes
with a Chiral Nitridomanganese Complex. Angew. Chem. Int.
Ed. 1998, 37, 3392‒3394. (b) Nishikori, H.; Katsuki, T. Catalytic
and highly enantioselective aziridination of styrene derivatives.
Tetrahedron Lett. 1996, 37, 9245‒9248. (c) Yang, J.; Weinberg,
R.; Breslow, R. The hydroxylation and amidation of equilenin
acetate catalyzed by chloro[5,10,15,20-tetrakis(pentafluoro-
phenyl)porphyrinato]manganese(III). Chem. Commun. 2000,
531‒532.
10
ACS Paragon Plus Environment

Page 11 of 12
1
Journal of the American Chemical Society
Catalyzed by CoII(tpp): A Synthetic and Mechanistic Study. Eur.
J. Inorg. Chem. 2008, 3009‒3019.
(18) Popescu, D.-L.; Chanda, A.; Stadler, M.; Tiago de Oliveira, F.;
Ryabov, A. D.; Münck, E.; Bominaar, E. L.; Collins, T. J. High-
valent first-row transition-metal complexes of tetraamido (4N)
and diamidodialkoxido or diamidophenolato (2N/2O) ligands:
Synthesis, structure, and magnetochemistry. Coord. Chem. Rev.
2008, 252, 2050‒2071.
(12) (a) Wiese, S.; Aguila, M. J. B.; Kogut, E.; Warren, T. H. β-
Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Iso-
cyanides. Organometallics 2013, 32, 2300‒2308. (b) Iluc, V. M.;
Miller, A. J. M.; Anderson, J. S.; Monreal, M. J.; Mehn, M. P.;
Hillhouse, G. L. Synthesis and Characterization of Three-Coor-
dinate Ni(III)-Imide Complexes. J. Am. Chem. Soc. 2011, 133,
13055‒13063. (c) Kogut, E.; Wiencko, H. L.; Zhang, L.;
Cordeau, D. E.; Warren, T. H. A Terminal Ni(III)−Imide with
Diverse Reactivity Pathways. J. Am. Chem. Soc. 2005, 127,
11248‒11249.
2
3
4
5
6
7
8
9
(19) (a) Hong, S.; Sutherlin, K. D.; Vardhaman, A. K.; Yan, J. J.;
Park, S.; Lee, Y.-M.; Jang, S.; Lu, X.; Ohta, T.; Ogura, T.; Solo-
mon, E. I.; Nam, W. A Mononuclear Nonheme Iron(V)-Imido
Complex. J. Am. Chem. Soc. 2017, 139, 8800‒8803. (b) Hong,
S.; Lu, X.; Lee, Y.-M.; Seo, M. S.; Ohta, T.; Ogura, T.; Clé-
mancey, M.; Maldivi, P.; Latour, J.-M. Sarangi, R.; Nam, W.
Achieving One-Electron Oxidation of a Mononuclear Nonheme
Iron(V)-Imido Complex. J. Am. Chem. Soc. 2017, 139, 14372‒
14375.
(20) Shi, H.; Xie, J.; Lam, W. W. Y.; Mab, W.-L.; Mak, C.-K.; Yiu,
S.-M.; Lee, H. K.; Lau, T.-C. Generation and Reactivity of a
One-Electron-Oxidized Manganese(V) Imido Complex with a
Tetraamido Macrocyclic Ligand. Chem. Eur. J. 2019, 25,
12895–12899.
(21) Collins, T. J.; Powell, R. D.; Slebodnick, C.; Uffelman, E. S. Sta-
ble highly oxidizing cobalt complexes of macrocyclic ligands. J.
Am. Chem. Soc. 1991, 113, 8419‒8425.
(22) Das, D.; Pattanayak, S.; Singh, K. K.; Garai, B.; Gupta, S. S.
Electrocatalytic water oxidation by a molecular cobalt complex
through a high valent cobalt oxo intermediate. Chem. Commun.
2016, 52, 11787‒11790.
(23) Du, H.-Y.; Chen, S.-C.; Su, X.-J.; Jiao, L.; Zhang, M.-T. Redox-
Active Ligand Assisted Multielectron Catalysis: A Case of CoIII
Complex as Water Oxidation Catalyst. J. Am. Chem. Soc. 2018,
140, 1557‒1565.
(24) Nasini, U. B.; Gartia, Y.; Ramidi, P.; Kazi, A.; Shaikh, A. U.;
Ghosh, A. Oxygen reduction reaction catalyzed by cobalt(III)
complexes of macrocyclic ligands supported on multiwalled car-
bon nanotubes. Chem. Phys. Lett. 2013, 566, 38‒43.
(25) Ghosh, A.; Ramidi, P.; Pulla, S.; Sullivan, S. Z.; Collom, S. L.;
Gartia, Y.; Munshi, P.; Biris, A. S.; Noll, B. C.; Berry, B. C. Cy-
cloaddition of CO2 to Epoxides Using a Highly Active Co(III)
Complex of Tetraamidomacrocyclic Ligand. Catal. Lett. 2010,
137, 1‒7.
(26) Parnell, C. M.; Watanabe, F.; Nasini, U. B.; Berry, B. C.; Mitch-
ell, T.; Shaikh, A. U.; Ghosh, A. Electrochemical sensing of hy-
drogen peroxide using a cobalt(III) complex supported on carbo-
naceous nanomaterials. J. Electroanal. Chem. 2015, 740, 37‒44.
(27) Hong, S.; Pfaff, F. F.; Kwon, E.; Wang, Y.; Seo, M.-S.; Bill, E.;
Ray, K.; Nam, W. Spectroscopic Capture and Reactivity of a
Low-Spin Cobalt(IV)-Oxo Complex Stabilized by Binding Re-
dox-Inactive Metal Ions. Angew. Chem. Int. Ed. 2014, 53,
10403‒10407.
(13) (a) van Vliet, K. M.; Polak, L. H.; Sieglet, M. A.; van der Vlugt,
J. I.; Fonseca Guerra, C.; de Bruin, B. Efficient Copper-Cata-
lyzed Multicomponent Synthesis of N-Acyl Amidines via Acyl
Nitrenes. J. Am. Chem. Soc. 2019, 141, 15240‒15249. (b)
Carsch, K. M.; DiMucci, I. M.; Iovan, D. A.; Li, A.; Zheng, S.-
L.; Titus, C. J.; Lee, S. J.; Irwin, K. V.; Nordlund, D.; Lancaster,
K. M.; Betley, T. A. Synthesis of a copper-supported triplet
nitrene complex pertinent to copper-catalyzed amination. Sci-
ence 2019, 365, 1138‒1143. (c) Evans, D. A.; Faul, M. M.; Bilo-
deau, M. T.; Anderson, B. A.; Barnes, D. M. Bis(oxazoline)-cop-
per complexes as chiral catalysts for the enantioselective aziridi-
nation of olefins. J. Am. Chem. Soc. 1993, 115, 5328‒5329. (d)
Li, Z.; Quan, R. W.; Jacobsen, E. N. Mechanism of the
(Diimine)copper-Catalyzed Asymmetric Aziridination of Al-
kenes. Nitrene Transfer via Ligand-Accelerated Catalysis. J. Am.
Chem. Soc. 1995, 117, 5889‒5890. (e) Gephart, R. T. III; War-
ren, T. H. Copper-Catalyzed sp3 C–H Amination. Organometal-
lics 2012, 31, 7728‒7752. (f) Lebel, H.; Parmentier, M. Copper-
catalyzed enantioselective aziridination of styrenes. Pure Appl.
Chem. 2010, 82, 1827‒1833. (g) Mairena, M. A.; Díaz-Requejo,
M. M.; Belderraín, R. R.; Nicasio, M. C.; Trofimenko, S.; Pérez,
P. J. Copper-Homoscorpionate Complexes as Very Active Cata-
lysts for the Olefin Aziridination Reaction. Organometallics
2004, 23, 253‒256. (h) Bagchi, V.; Paraskevopoulou, P.; Das, P.;
Chi, L.; Wang, Q.; Choudhury, A.; Mathieson, J. S.; Cronin, L.;
Pardue, D. B.; Cundari, T. R.; Mitrikas, G.; Sanakis, Y.; Stav-
ropoulos, R. A Versatile Tripodal Cu(I) Reagent for C–N Bond
Construction via Nitrene-Transfer Chemistry: Catalytic Perspec-
tives and Mechanistic Insights on C–H Aminations/Amidina-
tions and Olefin Aziridinations. J. Am. Chem. Soc. 2014, 136,
11362‒11381. (i) Ren, Y.; Cheaib, K.; Jacquet, J.; Vezin, H.;
Fensterbank, L.; Orio, M.; Blanchard, S.; Desage-El Murr, M.
Copper-Catalyzed Aziridination with Redox-Active Ligands:
Molecular Spin Catalysis. Chem. Eur. J. 2018, 24, 5086‒5090.
(14) (a) Lyaskovskyy, V.; Suarez, A. I. O.; Lu, H.; Jiang, H.; Zhang,
X. P.; de Bruin, B. Mechanism of Cobalt(II) Porphyrin-Cata-
lyzed C–H Amination with Organic Azides: Radical Nature and
H-Atom Abstraction Ability of the Key Cobalt(III)–Nitrene In-
termediates. J. Am. Chem. Soc. 2011, 113, 12264‒12273. (b)
Goswami, M.; Lyaskobskyy, V.; Domingos, S. R.; Buma, W. J.;
Woutersen, S.; Troeppner, O.; Ivanović-Burmazović, I.; Lu, H.;
Cui, X.; Zhang, X. P. Reijerse, E. J.; DeBeer, S.; van Schoone-
veld, M. M.; Pfaff, F. F.; Ray, K.; de Bruin. B. Characterization
of Porphyrin-Co(III)-‘Nitrene Radical’ Species Relevant in Cat-
alytic Nitrene Transfer Reactions. J. Am. Chem. Soc. 2015, 137,
5468‒5479.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(28) Patterson, R. E.; Gordon-Wylie, S. W.; Woomer, C. G.; Norman,
R. E.; Weintraub, S. T.; Horwitz, C. P.; Collins, T. J. Electron-
Transfer Oxidation by Phase-Separating Reagents. Inorg. Chem.
1998, 37, 4748‒4750.
(29) Conradie, M. M.; Conradie, J. Gosh, A. A DFT overview of high-
valent iron, cobalt and nickel tetraamidomacrocyclic ligand
(TAML) complexes: The end of innocence?. J. Inorg. Biochem.
2006, 100, 620‒626.
(30) Saavedra Díaz, R. O.; Le Lagedec, R.; Shen, L. Q.; Ryabov, A.
D. In search for chelating TAMLs (tetraamido macrocyclic lig-
ands) with peripheral bidentate donor centers: a cobalt(III) com-
plex of the 3,3′-(2,2′-bipyridindiyl)-tailed TAML. J. Coord.
Chem. 2014, 67, 3909‒3919.
(15) van der Vlugt, J. I. Radical-Type Reactivity and Catalysis by Sin-
gle-Electron Transfer to or from Redox-Active Ligands. Chem.
Eur. J. 2019, 25, 2651‒2662.
(16) Collins, T. J.; Ryabov, A. D. Targeting of High-Valent Iron-
TAML Activators at Hydrocarbons and Beyond. Chem. Rev.
2017, 117, 9140‒9162.
(31) Ramidi, P.; Sullivan, S. Z.; Gartia, Y.; Munshi, P.; Griffin, W.
O.; Darsey, J. A.; Biswas, A.; Shaikh, A. U.; Ghosh, A. Catalytic
Cyclic Carbonate Synthesis Using Epoxide and Carbon Dioxide:
Combined Catalytic Effect of Both Cation and Anion of an Ionic
CrV(O) Amido Macrocyclic Complex. Ind. Eng. Chem. Res.
2011, 50, 7800‒7807.
(32) (a) Evans, D. F. The determination of the paramagnetic
susceptibility of substances in solution by nuclear magnetic
resonance. J. Chem. Soc. 1959, 2003–2005. (b) Deutsch, J. L.;
Poling, S. M. The determination of paramagnetic susceptibility
(17) Dutta, S. K.; Beckmann, U.; Bill, E.; Weyhermuller, T.;
Wieghardt, K. 1,2-Bis(pyridine-2-carboxamido)benzenate(2−),
(bpb)2-:ꢀ A Noninnocent Ligand. Syntheses, Structures, and
Mechanisms of Formation of [(n-Bu)4N][FeIV2(μ-N)(bpb)2(X)2]
‒
(X
=
CN‒, N3 ) and the Electronic Structures of
[MIII(bpbox1)(CN)2] (M = Co, Fe). Inorg. Chem. 2000, 39, 3355‒
3364.
11
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Journal of the American Chemical Society
Page 12 of 12
(39) (a) Angeli, C.; Cimiraglia, R.; Evangelisti, S.; Leininger, T.;
by NMR: A physical chemistry experiment. J. Chem. Educ.
1969, 46, 167–168. (c) Piguet, C. Paramagnetic Susceptibility by
NMR: The "Solvent Correction" Removed for Large
Paramagnetic Molecules. J. Chem. Educ. 1997, 74, 815–816. (d)
Sur, S. K. Measurement of magnetic susceptibility and magnetic
moment of paramagnetic molecules in solution by high-field
fourier transform NMR spectroscopy. J. Magn. Reson. 1989, 82,
169–173. (e) Grant, D. H. Paramagnetic Susceptibility by NMR:
The "Solvent Correction" Reexamined. J. Chem. Educ. 1995, 72,
39. (f) Hoppeé, J. I. Effective magnetic moment. J. Chem. Educ.
1972, 49, 505. (g) Bain, G. A.; Berry, J. F. Diamagnetic
Corrections and Pascal's Constants. J. Chem. Educ. 2008, 85,
532–536.
Malrieu, J.-P. Introduction of n-electron valence states for mul-
tireference perturbation theory. J. Chem. Phys. 2001, 114,
10252‒10264. (b) Angeli, C.; Cimiraglia, R.; Malrieu, J.-P. N-
electron valence state perturbation theory: a fast implementation
of the strongly contracted variant. Chem. Phys. Lett. 2001, 350,
297‒305. (c) Angeli, C.; Cimiraglia, R.; Malrieu, J.-P. n-electron
valence state perturbation theory: A spinless formulation and an
efficient implementation of the strongly contracted and of the
partially contracted variant. J. Chem. Phys. 2002, 117, 9138‒
9153.
1
2
3
4
5
6
7
8
9
(40) We attempted to rotate the uncorrelated orbital(s) back in the ac-
tive space. However, this was unsuccessful. Moreover, inclusion
of orbitals with occupancy 2.00 in the active space should be
avoided. Aravena, D.; Atanasov, M.; Chilkuri, V. G.; Guo, Y.;
Jung, J.; Maganas, D.; Mondal, B.; Schapiro, I.; Sivalingam, K.;
Ye, S.; Neese, F. CASSCF Calculations in ORCA (4.2): A Tuto-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(33) Notably, a previous study (see ref. 23) on the electrochemical
behavior of Na[CoIII(TAMLred)] in MeCN only displayed one re-
versible oxidation event, whereas the second oxidation was
found to be irreversible.
(34) Mak, S.-T.; Wong, W.-T.; Yam, V. W.-W.; Lai, T.-F.; Che, C.-
M. Cobalt(III) alkyl complexes of 1,2-bis(2-pyridinecarboxam-
ido)benzene (H2bpb) and 4,5-dichloro-1,2-bis(2-pyridinecarbox-
amido)benzene (H2bpc) and X-ray crystal structures of
[Co(bpc)(CH2CH2CMe=CH2)(H2O)] and [Co(bpb)Et(H2O)]. J.
Chem. Soc. Dalton Trans. 1991, 1915‒1922.
rial
Introduction
[Online].
https://or-
caforum.kofo.mpg.de/app.php/dlext/?cat=4 (accessed Septem-
ber 17, 2019).
(41) CASSCF calculations demonstrated that no intense characteristic
absorption bands are expected in the 400-850 nm region. See the
CASSCF section on [CoIII(TAMLq)(NNs)2]‒.
(42) Accurate simulation of the experimental spectrum proved to be
challenging and was unsuccessful.
(35) CASSCF calculations demonstrated that the absorption band at
623 nm is dominated by ligand-centered ππ* and metal-to-lig-
and charge-transfer excitations. See the CASSCF section on
[CoIII(TAMLsq)] for more details.
(36) (a) Connelly, N. G.; Geiger, W. E. Chemical Redox Agents for
Organometallic Chemistry. Chem. Rev. 1996, 96, 877‒910. (b)
Boduszek, B.; Shine, H. J. Preparation of solid thianthrene cation
radical tetrafluoroborate. J. Org. Chem. 1988, 53, 5142‒4143.
(37) Lahanas, N.; Kucheryavy, P.; Lockard, J. V. Spectroscopic Evi-
dence for Room Temperature Interaction of Molecular Oxygen
with Cobalt Porphyrin Linker Sites within a Metal–Organic
Framework. Inorg. Chem. 2016, 55, 10110‒10113.
(43) Olivos Suarez, A.I.; Lyaskovskyy, V.; Reek, J.N.H.; van der
Vlugt, J.I.; de Bruin, B. Nitrogen-Centred Ligand Radical Com-
plexes; Classification, Spectroscopic Features, Reactivity and
Catalytic Applications. Angew. Chem. Int. Ed. 2013, 52, 12510–
12529.
(44) (a) Au, S.-M.; Fung, W.-H.; Cheng, M.-C.; Che, C.-M.; Peng, S.-
M. Synthesis, characterisation and reactivity of novel bis(to-
syl)imidoruthenium(VI) porphyrin complexes; X-ray crystal
structure of a tosylamidoruthenium(VI) porphyrin. Chem. Com-
mun. 1997, 1655–1656. (b) Au, S.-M.; Huang, J.-S.; Yu, W.-Y.;
Fung, W.-H.; Che, C.-M. Aziridination of Alkenes and Ami-
dation of Alkanes by Bis(tosylimido)ruthenium(VI) Porphyrins.
A Mechanistic Study. J. Am. Chem. Soc. 1999, 121, 9120–9132.
(45) See the SI for a description of CASSCF calculated UV-Vis exci-
tation energies and EPR g-values.
(38) Cramer, C. J. Essentials of Computational Chemistry: Theories
and Models. 2nd ed; John Wiley & Sons Ltd: West Sussex UK,
2004; pp 205‒210.
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