Cobalt- and Rhodium-Corrole-Triphenylphosphine Complexes Revisited: The Question of a Noninnocent Corrole

Article abstract of DOI:10.1021/acs.inorgchem.7b01828

A reinvestigation of cobalt-corrole-triphenylphosphine complexes has yielded an unexpectedly subtle picture of their electronic structures. UV-vis absorption spectroscopy, skeletal bond length alternations observed in X-ray structures, and broken-symmetry DFT (B3LYP) calculations suggest partial Co^II-corrole^?2- character for these complexes. The same probes applied to the analogous rhodium corroles evince no evidence of a noninnocent corrole. X-ray absorption spectroscopic studies showed that the Co K rising edge of Co[TPC](PPh₃) (TPC = triphenylcorrole) is red-shifted by ～1.8 eV relative to the bona fide Co(III) complexes Co[TPC](py)₂ and Co[TPP](py)Cl (TPP = tetraphenylporphyrin, py = pyridine), consistent with a partial Co^II-corrole^?2- description for Co[TPC](PPh₃). Electrochemical measurements have shown that both the Co and Rh complexes undergo two reversible oxidations and one to two irreversible reductions. In particular, the first reduction of the Rh corroles occurs at significantly more negative potentials than that of the Co corroles, reflecting significantly higher stability of the Rh(III) state relative to Co(III). Together, the results presented herein suggest that cobalt-corrole-triphenylphosphine complexes are significantly noninnocent with moderate Co^II-corrole^?2- character, underscoring - yet again - the ubiquity of ligand noninnocence among first-row transition metal corroles.

Full text of DOI:10.1021/acs.inorgchem.7b01828

Article
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Cite This: Inorg. Chem. 2017, 56, 14788−14800
Cobalt- and Rhodium-Corrole-Triphenylphosphine Complexes
Revisited: The Question of a Noninnocent Corrole
Sumit Ganguly,† Diemo Renz,† Logan J. Giles,‡ Kevin J. Gagnon,§ Laura J. McCormick,§
Jeanet Conradie,∥ Ritimukta Sarangi,*,‡ and Abhik Ghosh*,†
†Department of Chemistry, UiT − The Arctic University of Norway, N-9037 Tromsø, Norway
‡Structural Molecular Biology, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park,
California 94306, United States
§Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8229, United States
∥Department of Chemistry, University of the Free State, 9300 Bloemfontein, Republic of South Africa
S
* Supporting Information
ABSTRACT: A reinvestigation of cobalt−corrole−triphenylphosphine
complexes has yielded an unexpectedly subtle picture of their electronic
structures. UV−vis absorption spectroscopy, skeletal bond length
alternations observed in X-ray structures, and broken-symmetry DFT
(B3LYP) calculations suggest partial CoII−corrole•2− character for these
complexes. The same probes applied to the analogous rhodium corroles
evince no evidence of a noninnocent corrole. X-ray absorption
spectroscopic studies showed that the Co K rising edge of Co[TPC]-
(PPh3) (TPC = triphenylcorrole) is red-shifted by ∼1.8 eV relative to
the bona fide Co(III) complexes Co[TPC](py)2 and Co[TPP](py)Cl
(TPP = tetraphenylporphyrin, py = pyridine), consistent with a partial
CoII−corrole•2− description for Co[TPC](PPh3). Electrochemical
measurements have shown that both the Co and Rh complexes
undergo two reversible oxidations and one to two irreversible reductions. In particular, the first reduction of the Rh corroles
occurs at significantly more negative potentials than that of the Co corroles, reflecting significantly higher stability of the Rh(III)
state relative to Co(III). Together, the results presented herein suggest that cobalt−corrole−triphenylphosphine complexes are
significantly noninnocent with moderate CoII−corrole•2− character, underscoringyet againthe ubiquity of ligand
noninnocence among first-row transition metal corroles.
As in a number of other cases, the first inkling that Co-PPh3
corroles may not be true Co(III) complexes came from their
optical spectra. Over a long series of studies,5−7,10−16,19−30 we
have established that the Soret absorption maxima of
noninnocent meso-tris(para-X-phenyl)corrole (TpXPC) deriv-
atives redshift markedly with increasingly electron-donating
character of the para substituent X. The Soret maxima of
innocent metallotriarylcorroles, in contrast, do not exhibit such
a sensitivity to X. An examination of the literature readily
established that the Soret maxima of Co[TpXPC](PPh3)
redshift significantly in response to increasingly electron-
donating X groups.32,33 Accordingly, we undertook a
comprehensive reinvestigation of these complexes, employing
UV−vis spectroscopy, electrochemistry, X-ray absorption and
emission spectroscopies (XAS, XES), and DFT calculations.
For comparison, we also investigated the β-octabrominated
cobalt series Co[Br8TpXPC](PPh3) and the rhodium series
Rh[TpXPC](PPh3). Together, the results paint a remarkably
INTRODUCTION
■
Half a century after the term was coined,1 noninnocent ligands
continue to fascinate inorganic chemists.2,3 Not only have
important new examples of such ligands emerged in recent
years, they have also been recognized for their important role in
redox catalysis.4 The phenomenon is particularly widespread in
the currently fast-developing field of metallocorroles, where a
large number of complexes exhibit varying degrees of corrole•2−
character.5 Thus, while copper6−15 and chloroiron7,16−18
corroles were recognized as noninnocent early on, new
examples of noninnocent metallocorrole systems such as
FeNO19,20 and Fe2(μ-O)21 corroles are also accumulating at a
steady rate.22 (Examples of innocent metallocorroles include
CrO and MoO corroles,23 TcO24 and ReO25 corroles, RuN26
and OsN27 corroles, and Au28−30 corroles.) In this study, we
have evaluated the potential noninnocent character of cobalt−
corrole−triphenylphosphine31−33 complexes and compared
them with their rhodium analogues.34,35 The question is an
important one, because cobalt corroles are of increasing
importance in a number of technological applications such as
hydrogen evolution from water36−38 and ligand sensing.39−42
Received: July 18, 2017
Published: December 6, 2017
© 2017 American Chemical Society
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subtle picture of the electronic structure of these complexes, as
described below.
B. Single-Crystal X-ray Structures. Because several X-ray
structures have already been reported for Co−triarylcorrole−
PPh3 complexes,44−46,53,54 no attempt was made to crystallo-
graphically characterize the Co[TpXPC](PPh3) series. X-ray
structures were obtained for the novel β-octabrominated
complex Co[Br8TpCF3PC](PPh3), and for two Rh corroles,
Rh[TPC](PPh3) and Rh[TpOMePC](PPh3). Figure 2 presents
graphical representations of the three structures, and Tables 1
and 2 list key crystallographic data and geometrical parameters,
respectively. A summary of pertinent structural data from the
literature is given in Table 3.
RESULTS AND DISCUSSION
■
A. Synthesis and Proof of Composition. Figure 1 depicts
the three series of compounds investigated herein. For the
The Co−N and Rh−N bond distances in the structures
obtained here are in good accord with literature values (Table
3).49 The Co−N distances (∼1.88 0.01 Å) are about 0.08−
0.09 Å shorter than the Rh−N distances (∼1.965 0.01 Å),
which is somewhat smaller than the differences in Shannon−
Prewitt ionic radii for the two low-spin M(III) ions (Co, 54.5
Å; Rh, 66.5 Å)50,51 and in Pyykko’s single-bond covalent radii
̈
(Co, 1.11 Å; Rh, 1.25 Å).52 Comparison with noncorrole X-ray
structures suggests that these discrepancies largely reflect
unusually short Rh−N distances in Rh corroles, evidently a
result of the sterically constricted nature of the corrole N4
cavity. Careful examination of the M−N4, M−Cα8, and M−Cβ8
displacements and saddling dihedrals shows that the macro-
cycle conformation is planar to slightly saddled for the majority
of the Co complexes and mildly domed for the Rh complexes
(Table 3). Both the Co and Rh corroles, however, exhibit
similar M−N4 out-of-plane distances, ∼0.26−0.28 Å for Co and
∼0.27−0.31 Å for Rh.35,45 The crystal packing of the complexes
varies; thus, both partially cofacial dimers (e.g., Figure 2b) and
unstacked (e.g., Figure 2e) are observed for different complexes.
C. UV−Vis Spectroscopy. By now, the optical criterion for
ligand noninnocence, i.e., the sensitivity of the Soret maxima of
meso-triarylcorrole complexes to the para substituents X, is
well-established.5 The criterion applies well to a variety of Fe
and Cu corroles, where the noninnocent character of the
corrole ligand has also been established with additional
spectroscopic and computational methods. Certain Ag15 and
Pt22 corroles were also recognized as noninnocent via this
criterion. On the other hand, the Soret maxima of innocent
metallotriarylcorroles, including CrO, MoO, TcO, ReO, RuN,
OsN, and Au corroles, are essentially invariant with respect to
the para substituent X.5 Against this backdrop, the optical
spectra of the group 9 metallocorroles described here (Figure 3
and Table 4) make for an interesting story.
All three series of metallocorroles investigated here exhibit
split or double-humped Soret bands. In the case of
Co[TpXPC](PPh3), the higher energy peak, which corre-
sponds to the overall band maximum, exhibits a strong
sensitivity to X, shifting from 371 nm for Co[TpNO2PC]-
(PPh3) to 399 nm for Co[TpOMePC](PPh3). In contrast, the
Soret maxima of the Rh[TpXPC](PPh3) are essentially
invariant with respect to X. According to the aforementioned
optical criterion, these results strongly suggest that the
Co[TpXPC](PPh3) series is noninnocent, with significant
CoII−corrole•2− character, whereas the analogous Rh series is
innocent, i.e., RhIII−corrole3−. Such a scenario is analogous to
Cu and Ag15 triarylcorroles and to FeNO and RuNO26
triarylcorroles; in both of these cases, the first-row transition
metal complexes are strongly noninnocent, whereas the second-
row complexes are essentially innocent.
Figure 1. Complexes investigated in this study.
Co[TpXPC](PPh3) series, four of the five complexes
investigated (X = NO2, H, Me, and OMe) have been previously
reported and were resynthesized for this study.32,33 The
Co[Br8TpXPC](PPh3) series, except for Co[Br8TPC](PPh3)
(TPC = triphenylcorrole),43 and the Rh[TpXPC](PPh3) series
both consist of new compounds. The synthetic protocols
ranged from modifications of literature procedures to
essentially new procedures, as described below.
Cobalt insertion into corroles has traditionally been
accomplished in alcoholic solvents, particularly methanol, in
the presence of an added axial ligand.31,32,32,33,44−46 Several of
the free-base corroles needed in this study, including
H3[TpXPC] (X ≠ CF3) and all H3[Br8TpXPC] ligands,
however, were found to be poorly soluble in methanol. The
use of THF avoided the solubility problems, and complete Co
insertion took place smoothly at 45−50 °C in about 90 min for
both the TpXPC and Br8TpXPC series.
For the rhodium corroles reported here, an essentially new
synthetic protocol was devised. A first attempt, inspired by a
similar method used by Gray et al.47 for the preparation of
iridium-tris(pentafluorophenyl)corrole-PPh3, involved the re-
action of free base triarylcorroles with an excess of [Rh-
(cod)2Cl]2 in refluxing THF under an inert atmosphere and in
the presence of excess PPh3 and dry K2CO3. Except for X =
CF3, however, this procedure failed for all the other free base
H3[TpXPC] ligands. Fortunately, changing the solvent to 2:1
dichloromethane/ethanol and using much smaller quantities of
both the metal source (1.5 equiv) and PPh3 (1 equiv) provided
facile access to all four Rh[TpXPC](PPh3) complexes at room
temperature and without any provision for an inert atmosphere.
Somewhat similar conditions (albeit with no ethanol) have also
been previously used by Collmann et al. for the synthesis of
various Rh-corrole-amine complexes.48
Proof of purity and composition of the products came from
clean thin-layer chromatograms, ESI-MS, fully assigned
1
diamagnetic H NMR spectra, elemental analyses for all new
compounds that withstood warming and rigorous drying, and,
for three compounds, single-crystal X-ray structures.
The Soret envelope of the Co[Br8TpXPC](PPh3) series is
red-shifted by approximately 30 nm relative to the non-
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Figure 2. Selected views of X-ray structures. Co[Br8TpCF3PC](PPh3): (a) top and (b) side views. (c) Rh[TpOMePC](PPh3). Rh[TPC](PPh3): (d)
single molecule and (e) packing diagram.
brominated Co[TpXPC](PPh3) series. Unfortunately, the
Soret bands of the brominated complexes consist of two
closely spaced humps, which cannot be accurately deconvo-
luted. It is clear, nevertheless, that the substituent effect of X is
relatively muted in the brominated series, relative to the
nonbrominated series. A parallel may be drawn to analogous
behavior of Fe[TpXPC](NO) and Fe[Br8TpXPC](NO);
substituent effects on the Soret maxima for the latter series
are much more muted than those in the former.19,20 As noted
before, the lack of substituent sensitivity of the Soret maxima in
the brominated series most likely reflects the inability of the
meso-aryl groups to conjugate with the corrole as a result of the
steric constraints imposed by the β-bromines.20
D. DFT Calculations.56,57 DFT calculations support the
above interpretations. Thus, B3LYP/STO-TZP calculations
yielded a broken-symmetry spin density profile for Co[TPC]-
2
II
•2−
̂
(PPh3) (⟨S ⟩ = 0.58), consistent with a Co −corrole
description (Figure 4), as well as a surprisingly small singlet−
triplet splitting of only 0.14 eV. (It may be worth adding for the
uninitiated reader that these broken symmetry densities are not
real and hence do not manifest themselves as peak broadenings
1
in the H NMR spectra; they are nevertheless an excellent and
efficient way of visualizing the antiferromagnetically coupled
nature of the complexes.) In contrast, analogous calculations on
Rh[TPC](PPh3) yielded only a closed-shell solution as well as
a larger singlet−triplet splitting of 0.69 eV, indicating an
unambiguous Rh(III) ground state that is energetically well-
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Table 1. Crystallographic Data for Co[Br8TpCF3PC](PPh3), Rh[TPC](PPh3), and Rh[TpOMePC](PPh3)
sample
Co[Br8TpCF3PC](PPh3)
Rh[TPC](PPh3)
Rh[TpOMePC](PPh3)
chemical formula
formula mass
crystal system
space group
λ (Å)
C58H27F9Br8N4PCo
1680.01
monoclinic
C2/c
C55H38N4PRh
888.77
C58H44O3N4PRh
978.85
triclinic
monoclinic
P21/c
P1
̅
0.7749
0.7749
8.5019(4)
13.1646(7)
18.1789(9)
94.102(3)
92.306(3)
97.775(3)
2
0.7749
a (Å)
19.9698(12)
23.7533(13)
28.7932(15)
90
12.1715(4)
20.0064(7)
18.2451(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
96.104(3)
90
98.228(2)
90
γ (deg)
Z
8
4
V (Å3)
13580.6(13)
100(2)
2008.22(17)
100(2)
4397.1(3)
100(2)
temperature (K)
density (g/cm3)
measured reflections
unique reflections
parameters
restraints
1.643
1.470
1.479
134476
30310
84124
24858
14381
16042
734
550
607
1
0
0
Rint
0.045
0.0625
0.0547
θ range (deg.)
R1, wR2 all data
S (GoF) all data
max/min res. dens. (e/Å3)
2.213−36.070
0.0355/0.0845
1.066
2.178−35.825
0.0512/0.0982
1.037
2.152−36.001
0.0416/0.1030
1.034
1.144/−1.048
1.189/−1.417
1.976/−0.650
evidence of such bond length alternation (Figure 5), lending
credence to partial CoII−corrole•2− character for the complex.
E. Electrochemistry.58 Table 5 lists the redox potentials for
the various complexes studied, and Figure 6 depicts two
representative cyclic voltammograms. All the complexes exhibit
two reversible oxidations and one to two irreversible reductions
in CH2Cl2 with 0.1 M TBAP. The redox potentials of the
Co[Br8TpXPC](PPh3) series are generally about 450 mV
upshifted relative to those of the Co[TpXPC](PPh3) series.
The Co[TpXPC](PPh3) and Rh[TpXPC](PPh3) series exhibit
similar oxidation potentials, but significantly different reduction
potentials, with the Rh complexes undergoing reduction at
some 400 mV more negative potentials. The irreversibility of
the reductions may be reasonably attributed to the dissociation
of PPh3 from the M(II) reduced state, i.e., {MII[TpXPC]}−.59
The fact that the Co complexes are substantially easier to
reduce than their Rh analogues is consistent with the greater
accessibility of the Co(II) state,60 consistent with the DFT
results described above.
Table 2. Selected Crystallographic Geometry Parameters (Å)
for Co[Br8TpCF3PC](PPh3), Rh[TPC](PPh3), and
Rh[TpOMePC](PPh3)
Co[Br8TpCF3PC]
Rh[TPC]
(PPh3)
Rh[TpOMePC]
distances
(PPh3)
(PPh3)
M(1)−N(1)
M(1)−N(2)
M(1)−N(3)
M(1)−N(4)
M(1)−P(1)
1.8758(17)
1.9026(17)
1.8940(17)
1.8838(17)
2.2248(6)
1.9437(18)
1.9691(18)
1.9724(18)
1.9499(19)
2.2098(6)
1.9572(17)
1.9730(17)
1.9643(16)
1.9443(17)
2.2150(5)
0.3171(9)
M(1)−
0.2623(10)
0.2788(10)
4Nplane
separated from potential valence isomers. Not unexpectedly,
pure functionals do not yield broken-symmetry solutions for
either complex, but the same trend in singlet−triplet energy
separation is observed. Thus, BP86 calculations yield singlet−
triplet energy separations of 0.62 and 1.30 eV for the Co and
Rh complexes, respectively.
F. X-Ray Absorption Spectroscopy.61−63 Cobalt K-edge
XAS data were obtained for Co[TPC](PPh3) and compared
with those of the presumptive bona fide Co(III) complexes
Co[TPC](py)2 and Co[TPP](py)Cl64 (TPP = tetraphenylpor-
phyrin, Figure 7). The metal K-edge (rising edge) energy
position is generally a good indicator of the charge on the
absorbing metal ion.65 Figure 7 (top inset) shows that the rising
edge inflection point occurs at 7718.2, 7720.0, and 7720.4 eV
for Co[TPC](PPh3), Co[TPP](py)Cl, and Co[TPC](py)2,
respectively. The rising-edge region reflects transitions to states
that are higher in energy than both Co 3d based orbitals and
low-lying ligand orbitals that participate in back-bonding
interactions with Co 3d orbitals. Therefore, this region is not
directly affected by the field strength exerted by the ligands and
is dominated by changes in charge on the metal ion. The sharp
increase (>1.8 eV) in the rising-edge energy on going from
One flaw of the broken-symmetry B3LYP calculations was
that they yielded an overly long Co−P distance of 2.40 Å for
CoII−corrole•2−. Inclusion of Grimme’s dispersion corrections
in the B3LYP calculations or the use of a pure functional, with
or without the dispersion correction, yielded realistic Co−P
distances of ∼2.25 Å. For these reasons, TDDFT simulations of
the X-ray absorption spectra of Co[TPC](PPh3) (and reference
compounds) were carried out with the B3LYP functional
employing BP86 optimized geometries, as described below.
Regardless of the functional used, the optimized geometry of
Co[TPC](PPh3) revealed small but unmistakeable skeletal
bond length alternations in the bipyrrole half of the macrocycle,
a structural feature that has recently been recognized as a
characteristic of corrole•2− radicals.5 Remarkably, a previously
reported crystal structure of Co[TPC](PPh3) also shows clear
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Table 3. Comparison of Key Distances (Å) and Dihedrals (χ1−χ3) for Co/Rh−Corrole−PPh3 Complexes Reported in the
Literature
d(M−
N1/4
d(M−
N2/3
d(M− d(M− d(M− d(M−
complex
CCSD
BAQPUF
)
)
P)
N4)
Cα8)
Cβ8)
χ1
χ2
χ3
conformation
ref
av
av
a
Co[TPFPC](PPh3)
Co[TPC](PPh3)
1.872
1.866
1.866
1.886
1.889
1.880
2.205
2.201
2.217
0.262
0.280
0.289
0.309
0.361
0.341
0.375
0.471
0.437
1.5
1.2
4.8
18.3
20.6
11.0
7.4 planar
22.6 planar
6.0 planar
44
44
53
KIMQOM
b
b
Co[T2,4Cl2PC](PPh3)
SUCMOU
(molecule 1)
Co[T2,4Cl2PC](PPh3)
SUCMOU
(molecule 2)
1.866
1.868
1.868
1.846
1.917
1.832
1.880
1.880
1.882
1.890
1.905
1.869
1.879
1.898
2.216
2.204
2.205
2.217
2.207
2.239
2.225
0.289
0.286
0.277
0.292
0.300
0.261
0.262
0.360
0.384
0.373
0.360
0.389
0.341
0.269
0.477
0.523
0.507
0.460
0.446
0.433
0.296
2.4
0.2
5.2
17.5
19.1
0.8
16.3 planar
53
54
54
55
43
43
c
Co[T2ClPC](PPh3)
CAHJIH
CAJKEG
LAMTAX
22.3 slightly
domed
22.3 slightly
domed
13.7 slightly
saddled
16.9 slightly
saddled
d
Co[TDFPC](PPh3)
0.6
Co[10−2,6Cl2P-5,15-
11.3
0.1
e
(3NO2P)2C](PPh3)
f
Co[Br8TNPC](PPh3)
QIQCUO
(molecule 1)
4.6
QIQCUO
(molecule 2)
51.1
8.2
1.7
17.5 saddled
Co[Br8TpCF3PC](PPh3)
4.8
10.2 slightly
saddled
This
work
a
Rh[TPFPC](PPh3)
MELBUA
this work
1.964
1.947
1.972
1.971
2.222
2.210
0.277
0.279
0.440
0.400
0.670
0.563
6.3
0.8
20.2
23.0
21.3 domed
27.6 domed
35
Rh[TPC](PPh3)
This
work
Rh[TpOMePC](PPh3)
this work
1.951
1.969
2.215
0.317
0.459
0.670
0.5
23.2
11.7 domed
This
work
a
b
c
TPFPC = 5,10,15-tris(pentafluorophenyl)corrole. T2,4Cl2PC = tris(2,4-dichlorophenyl)corrole. T2ClPC = 5,10,15-tris(2-chlorophenyl)corrole.
d
e
f
TDFPC = tris(2,6-difluorophenyl)corrole. 10-2,6Cl2P-5,15-(3NO2P)2C = 10-(2,6-dichlorophenyl)-5,15-bis(3-nitrophenyl)corrole. TNPC =
5,10,15-tris(4-nitrophenyl)corrole.
Figure 3. UV−vis spectra in dichloromethane for (a) Co[TpXPC](PPh3), (b) Rh[TpXPC](PPh3), (c) Co[Br8TpXPC](PPh3), and (d)
Co[TpCF3PC](PPh3) and Co[Br8TpCF3PC](PPh3).
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Table 4. Soret λmax (nm) for Co and Rh Corroles Studied
Table 5. Redox Potentials (V vs. SCE) of Co/Rh−Corrole−
PPh3 Complexes Studied
para substituent X
complex
Eox2
Eox1
Ered‑irrev1
Ered‑irrev2
complex
NO2
371
CF3
H
Me
OMe
a
Co[TpNO2PC](PPh3)
Co[TpCF3PC](PPh3)
Co[TPC](PPh3)
1.11
1.09
1.02
1.00
0.94
1.28
1.21
1.18
1.17
0.96
0.85
0.80
0.77
0.71
0.65
0.54
0.52
0.51
1.08
0.99
0.97
0.97
0.53
0.46
0.42
0.41
−0.61
−0.82
−0.85
−0.89
−0.91
−0.32
−0.38
−0.43
−0.48
−1.24
−1.34
−1.37
−1.48
−1.19
Co[TpXPC](PPh3)
Co[Br8TpXPC](PPh3)
Rh[TpXPC](PPh3)
385
421
431
387
412
429
392
418
430
399
423
427
−1.74
−1.77
Co[TpMePC](PPh3)
Co[TpOMePC](PPh3)
Co[Br8TpCF3PC](PPh3)
Co[Br8TPC](PPh3)
Co[Br8TpMePC](PPh3)
Co[Br8TpOMePC](PPh3)
Rh[TpCF3PC](PPh3)
Rh[TPC](PPh3)
−1.96
−1.10
−1.17
−1.23
−1.35
Rh[TpMePC](PPh3)
Rh[TpOMePC](PPh3)
a
The reversible reduction peak might also correspond to reduction of
p-NO2Ph groups of Co[TpNO2PC](PPh3) as observed by Kadish et
al.33
Figure 4. Broken-symmetry B3LYP/STO-TZP spin density profile
(contour 0.006 e/Å3) for Co[TPC](PPh3).
Co[TPC](PPh3) to Co[TPP](py)Cl and Co[TPC](py)2 is
indicative of a higher positive charge on the Co atom in the
latter two complexes. It is important to note, however, that the
rising-edge energy is also affected by structural factors such as
long-range multiple scattering, ligand type, structural changes
due to changes in the metal spin state (high-spin versus low-
spin), metal−ligand distances, etc. In particular, a high-atomic-
number ligand tends to shift the rising edge to lower energies.
Thus, the large 2.2-eV shift between Co[TPC](PPh3) and
Co[TPC](py)2 is at least partially attributable to the presence
of a heavier axial ligand in Co[TPC](PPh3). For an evaluation
of metal oxidation state, a better comparison is provided by
Co[TPC](PPh3) and Co[TPP](py)Cl, both of which have a
third-period axial ligand. The 1.8 eV downshift of the rising
edge in Co[TPC](PPh3), relative to Co[TPP](py)Cl, thus is
consistent with a lower positive charge on the Co center in the
former complex.
Figure 6. Cyclic voltamograms of M[TpCF3PC](PPh3) (M = Co, Rh)
measured in CH2Cl2 with 0.1 M TBAP in. Scan rate: 100 mV/s.
ligand field strength.66 The expanded pre-edge region (bottom
inset, Figure 7) shows that pre-edge intensity weighted average
energy (IWAE) values of Co[TPP](py)Cl and Co[TPC](py)2
are at 7710.2 and 7709.9 eV, whereas the corresponding value
for Co[TPC](PPh3) is 7709.7 eV. These data indicate either a
slight weakening of the ligand field or a lower charge on the Co
center. The overall ligand field is expected to be weaker for
The Co K-pre-edge region, which arises from electric-dipole-
forbidden, quadrupole-allowed 1s → 3d transitions, affords
important information about the metal site symmetry and the
Figure 5. Skeletal bond distances (Å) for Co[TPC](PPh3). Left: broken-symmetry B3LYP. Right: X-ray structure (CCDC: KIMQOM).
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the Co center. In contrast, the complexes Co[TPC](PPh3),
Co[TPC](py)2, and Co[TPP](py)Cl all exhibit symmetric
spectra with maxima at 7648.9, 7649.0, and 7649.1 eV,
respectively, suggestive of a Co(III)-like ground state. A
comparison of the Kβvalence region (bottom inset, Figure 8)
reflects large differences in metal−ligand interactions among
the four complexes, consistent with differences in both ligand
type and coordination number.72
The apparent discrepancy between XAS rising-edge shift and
the energy of the XES Kβ1,3 feature can be explained on the
basis of covalent interactions between the Co and the ligands
and the influence of delocalization of Co 3d character into the
ligand orbitals, which in turn can influence the energy position
of the XES spectra. Recently, DeBeer et al. have demonstrated
that metal−ligand covalence can have a significant influence on
the splitting between the Kβ′ and the Kβ1,3 features,73 especially
if it leads to significant reduction in metal character in the
primarily metal d-based orbitals. This conclusion was reached
on the basis of an analysis of a series of Fe complexes for which
a significant redshift of the Kβ1,3 feature was observed on going
from the relatively ionic [FeF6]3− to the much more covalent
[Fe(SR)4]− complex.
For a low-spin S = 0 Co(III) species, the Kβ′−Kβ1,3 splitting
is 0 eV, since there is no metal 3p−3d exchange interaction. For
low-spin Co(II), this splitting is given by e2(4G1 + 42G3),
where e2 is the Stevens orbital reduction factor for the eg
orbitals and 4G1 + 42G3 is the Co p−d exchange interaction
energy per spin pair, which has been calculated to be 7.425 eV
for a free Co(II) ion (see Table S16, ref 73). In order to obtain
the Stevens orbital reduction factors, DFT calculations were
carried out on Co[TPC](PPh3), Co[TPC](py)2, Co[TPP]-
(py)Cl, and [Co(TPP)], as detailed in the Experimental
Section. TDDFT calculations were also carried out for the Co
1s → 3d transitions and were found to yield a reasonably good
simulation of the experimental Co K pre-edge XAS spectra, as
shown in Figure 9.
Figure 7. Normalized Co K-edge XAS spectra of Co[TPC](PPh3)
(black), Co[TPP](py)Cl (blue), and Co[TPC](py)2 (red). The top
inset depicts the first derivative spectra, where the first inflection
points of the rising edge region are marked with an asterisk. The
bottom inset shows the expanded pre-edge region.
Co[TPC](PPh3), which has only five ligands relative to six in
Co[TPC](py)2 and Co[TPP](py)Cl, but the shift in pre-edge
energy position is likely to reflect a combination of weakening
ligand field and a decrease in the charge on the Co center (as
indicated by the shift of the rising-edge postion to lower
energies).
G. X-Ray Emission Spectroscopy.67,68 To determine the
electronic structure of Co[TPC](PPh3) with greater certainty,
we carried out comparative Co Kβ XES measurements on
Co[TPC](PPh3), Co[TPC](py)2, and Co[TPP](py)Cl as well
as the Co(II) complex Co[TPP].69 The spectra consist of the
Co Kβ1,3 and the Co Kβ′ features, with the Co Kβ′ feature
gaining intensity via 3p−3d exchange interactions. These
features are strongly influenced by the number of unpaired
electrons at the Co center.70 In the case of S = 1/2 Co(II), the
unpaired 3d electron results in a small increase in the Co Kβ′
intensity at ∼7638 eV and a splitting of the Kβ′ and the Kβ1,3
features. The latter results in a blueshift of the Kβ1,3 feature, as
may be seen for Co[TPP] in Figure 8, thus affording a means
for distinguishing between S = 1/2 Co(II) and S = 0 Co(III).71
Figure 8 shows that the Co Kβ1,3 emission spectrum of
Co[TPP] consists of a distinct, asymmetric feature with a
maximum at 7649.8 eV. The asymmetry results from a low-
lying Kβ′ feature due to the presence of an unpaired electron at
Figure 9. Comparison of TDDFT 1s → 3d spectra (dotted lines) with
the experimental Co K pre-edge XAS data (solid lines) for
Co[TPC](PPh3) (black), Co[TPP](py)Cl (blue), Co[TPC](py)2
(red), and Co[TPP] (light green).
The above experimentally calibrated DFT calculations
provided the Co 3d contributions to the eg orbitals via the
Lowdin method and thereby also the Stevens orbital reduction
̈
2
2
2
factors (Table 6). Table 6 shows that both the dz and dx −y
Figure 8. Normalized Co K-edge XES spectra of Co[TPC](PPh3)
(black), Co[TPP](py)Cl (blue), Co[TPC](py)2 (red), and Co[TPP]
(light green). The top inset shows the expanded Kβ1,3 region, and the
bottom inset shows the expanded Kβvalence region.
orbitals engage in covalent interactions with the TPP and TPC
ligands and that the interaction is especially strong for
Co[TPC](PPh3), leading to greater reduction in its calculated
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Co[TPP]. DFT calculations provided a rationale for this
paradox in terms of a high degree of metal−ligand covalence in
Co[TPC](PPh3) relative to the other compounds. These
results emphasize that spin state assignments based simply on
the energy of the Kβ1,3 feature may be erroneous, especially for
highly covalent systems such as Co[TPC](PPh3).
Table 6. Stevens Reduction Factors (e) Obtained from the
Sum of the DFT Lowdin d Populations
̈
Co[TPC]
(py)2
Co[TPP](py)
Co[TPC]
(PPh3)
Co[TPP]
Cl
2
2
(α+β)3dz
155.8
139.0
294.8
0.54
124.3
123.7
248.0
0.38
127.5
127.3
254.7
83.2
109.3
192.5
0.23
2
(α+β)3dx −y
total
e2
EXPERIMENTAL SECTION
0.41
■
a
Materials. All reagents and solvents were used as purchased unless
otherwise noted. CHROMASOLV HPLC-grade n-hexane and
dichloromethane were used as solvents for column chromatography.
Silica gel 150 (35−70 μm particle size, Davisil) was used as the
stationary phase for flash chromatography, and silica gel 60 preparative
thin-layer chromatographic (PTLC) plates (20 × 20 cm, 0.5 mm thick,
Merck) were used for final purification of the products. Triphenyl-
phosphine was recrystallized from hot methanol and stored under
nitrogen. Cobalt(II) acetate tetrahydrate, Co(OAc)2·4H2O, obtained
from Merck, and bis[chloro(1,5-cyclooctadiene)rhodium(I)], [Rh-
(cod)2Cl]2, obtained from Sigma-Aldrich, were both used as received.
Anhydrous dichloromethane for electrochemistry was prepared by
distillation after predrying with CaH2 and stored over 3 Å molecular
sieves. The starting materials, the free base corroles H3[TpXPC] and
free base β-octabromocorroles H3[Br8TpXPC] (X = CF3, H, Me,
OMe), were synthesized as previously reported.74,75
ΔE (eV)
4.2
1.8
a
ΔE is calculated by using the calculated Co p−d exchange interaction
energy of 7.425 eV and is calculated for the low-spin d7 species.
e2 value. Like the remainder of our studies, these calculations
thus also ascribe significant CoII−corrole•2− character to the
Co[TPC](PPh3) complex. A hypothetical and simplistic view
of Co[TPC](PPh3) as purely CoII−corrole•2− and an e2 value
of 0.23 leads to a calculated Kβ′−Kβ1,3 splitting of 1.8 eV,
which is 2.4 V lower than that of Co[TPP] and consistent with
the observed blueshift of Kβ1,3 feature of the latter complex.
Since the Kβ′ feature is weak for low-spin d7 species and
weakens further and crawls under the main Kβ1,3 feature with
increased metal−ligand covalence, an experimental estimation
of ΔE is difficult. The ∼0.9 eV shift between the Kβ1,3 features
of [Co(TPP)] and [Co(TPC)]PPh3, however, may be viewed
as reasonably consistent with theory, as it is just under half the
calculated value of 2.4 eV. In other words, even if Co[TPC]-
(PPh3) were a full-fledged CoII−corrole•2− species, its main
Kβ1,3 feature should be significantly red-shifted relative to
Co[TPP] because of strong metal−ligand covalence in
Co[TPC](PPh3). Thus, although the XES data are not
diagnostic of the Co oxidation state in Co[TPC](PPh3), they
are consistent with a highly covalent electronic structure with
partial CoII−corrole•2− character and thus also with the XAS
data.
Instrumentation. Ultraviolet−visible spectra were recorded on an
Agilent Cary 8454 UV−visible spectrophotometer in CH2Cl2. Cyclic
voltammetry experiments were performed with an EG&G Princeton
Applied Research Model 263A potentiostat equipped with a three-
electrode system consisting of a glassy carbon working electrode, a
platinum wire counterelectrode, and a saturated calomel reference
electrode (SCE). Tetrakis(n-butyl)ammonium perchlorate (Sigma-
Aldrich, TBAP), recrystallized three times from absolute ethanol,
vacuum-dried at 40 °C for 2 days, and kept in a desiccator for further
drying for at least 2 weeks, was used as the supporting electrolyte. The
reference electrode was separated from bulk solution by a fritted-glass
bridge filled with the solvent/supporting electrolyte mixture. All
potentials were referenced to the SCE. A scan rate of 100 mV/s was
used. The anhydrous dichloromethane solutions were purged with
argon for at least 5 min prior to electrochemical measurements, and an
argon blanket was maintained over the solutions during the
measurements. 1H NMR spectra were recorded on a 400 MHz
Bruker Avance III HD spectrometer equipped with a 5 mm BB/1H
(BB = 19F, 31P−15N) SmartProbe in CDCl3 and referenced to residual
CHCl3 (7.26 ppm), all at room temperature. High resolution
electrospray ionization (HR-ESI) mass spectra were recorded on an
LTQ Orbitrap XL spectrometer.
Synthesis of Cobalt−Triarylcorrole−Triphenylphosphine
Complexes. A detailed procedure is described below for the synthesis
of cobalt−tris(4-trifluoromethylphenyl)corrole−triphenylphosphine,
Co[TpCF3PC](PPh3). A similar procedure was also followed for the
synthesis of the other Co complexes, except for details of the
chromatographic purifications, which are specified separately. Cobalt
corroles with electron-donating para substituents (X = Me and OMe)
were found to be somewhat unstable in contact with the silica gel used
for column chromatography, which may have led to comparatively
lower yields for these complexes.
Synthesis of Co[TpCF3PC](PPh3). To a THF solution (10 mL) of
free-base tris(4-trifluoromethylphenyl)corrole (0.025 g, 0.034 mmol)
in a 25-mL round-bottomed flask was added Co(OAc)2·4H2O (5
equiv, 0.042 g, 0.17 mmol) and NaOAc (15 equiv, 0.042 g, 0.51
mmol), and the resulting solution was stirred at room temperature for
5 min. Triphenylphosphine (5 equiv, 0.045 g, 0.17 mmol) was then
added, and stirring was continued at 45 °C for 90 min, during which
the color of the solution turned from green to dark red. After removal
of the solvent by rotary evaporation, the dark residue obtained was
chromatographed on a silica gel column (height 12 cm) with 5:1 n-
hexane/dichloromethane as eluent. The product eluted as an intense,
dark red band, which was collected and evaporated to dryness. The
resulting solid was further purified by PTLC using 3:1 n-hexane/
CONCLUSION
■
A multitechnique reinvestigation of cobalt−corrole−triphenyl-
phosphine complexes has suggested that they are not true
Co(III) complexes, as long supposed, but are noninnocent with
partial CoII−corrole•2− character. Thus, the Soret maxima of
Co[TpXPC](PPh3) redshift markedly with increasing electron-
donating character of the meso-aryl para substituent X, a key
signature of corrole radical states. In contrast, the Soret maxima
of Rh[TpXPC](PPh3) are essentially invariant with respect to
the para substituent X, indicating an innocent RhIII−corrole3−
description. This argument is supported by DFT B3LYP
calculations on Co[TPC](PPh3), which yielded a broken-
symmetry ground-state spin density profile consistent with a
CoII−corrole•2− description as well as a singlet−triplet gap of
only 0.15 eV. In contrast, analogous calculations on Rh[TPC]-
(PPh3) yielded a fully spin-paired ground state and a much
higher singlet−triplet gap of 0.94 eV. Skeletal bond length
alternations in the X-ray structure of Co[TPC](PPh3) (but not
the analogous Rh complexes) are also suggestive of a corrole
radical. XAS measurements also revealed that the Co K rising
edge of Co[TPC](PPh3) is some 1.8 eV lower than those of
the presumptive, genuine Co(III) complexes Co[TPP](py)Cl
and Co[TPC](py)2, consistent with a lower positive charge on
the metal in Co[TPC](PPh3). In apparent contrast to these
findings, Co[TPC](PPh3 ), Co[TPC](py)2 , and
Co[TPP](py)Cl were all found to exhibit near-identical Kβ1,3
emission maxima that are red-shifted by 0.8 0.1 eV relative to
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CH2Cl2 as eluent. The front red band consisted of pure Co-
0.012 mmol, 56%). UV−vis (CH2Cl2) λmax [nm, ε × 10−4 (M−1
cm−1)]: 407 (6.22), 412 (6.29), 584 (1.60). 1H NMR (CDCl3, 25 °C):
δ 7.85 (d, J = 7.7 Hz, 1H, meso-aryl), 7.81 (d, J = 7.6 Hz, 2H, meso-
aryl), 7.71−7.63 (m, 3H, meso-aryl), 7.60−7.46 (m, 6H, meso-aryl),
7.33 (d, J = 7.6 Hz, 1H, meso-aryl), 7.25−7.18 (m, 3H, p-H of PPh3),
7.01 (d, J = 7.6 Hz, meso-aryl), 6.92−6.86 ((m, 6H, m-H of PPh3),
4.95−4.87 (m, 6H, o-H of PPh3). HRMS (major isotopomer) [M]+:
1475.4889 (exptl), 1475.4931 (calcd).
Synthesis of Co[Br8TpMePC](PPh3). Silica gel column chroma-
tography with 3:1 n-hexane/CH2Cl2 followed by PTLC with 2:1 n-
hexane/CH2Cl2 as eluent afforded pure Co[Br8TpMePC](PPh3) (0.02
g, 0.013 mmol, 62%). UV−vis (CH2Cl2) λmax [nm, ε × 10−4 (M−1
cm−1)]: 418 (5.94), 583 (1.58). 1H NMR (CDCl3, 25 °C): δ 7.71 (d. J
= 7.6 Hz, 1H, meso-aryl), 7.67 (d, J = 7.6 Hz, 2H, meso-aryl), 7.40−
7.27 (m, 6H, meso-aryl), 7.22−7.16 (m, 4H, meso-aryl and p-H of PPh3
overlapping), 6.92−6.84 (m, 8H, overlapping meso-aryl and m-H of
PPh3), 4.94−4.86 (m, 6H, o-H of PPh3), 2.61 (overlapping s, 9H,
5,10,15-Me protons). HRMS (major isotopomer) [M]+: 1517.5397
(exptl), 1517.5402 (calcd).
[TpCF3PC](PPh3) (0.029g, 81%). UV−vis (CH2Cl2) λmax [nm, ε ×
1
10−4 (M−1 cm−1)]: 385 (5.76), 411 (sh, 4.84), 560 (1.19). H NMR
(CDCl3, 25 °C): δ 8.73 (d, J = 4.4 Hz, 2H, β-pyrrolic), 8.36 (d, J = 4.8
Hz, 2H, β-pyrrolic), 8.20 (br s, 2H, meso-aryl), 8.12 (s, 1H, meso-aryl),
8.10 (d, J = 4.8 Hz, 2H, β-pyrrolic), 8.03 (d, J = 4.4 Hz, 2H, β-
pyrrolic), 7.93−7.85 (m, 5H, meso-aryl), 7.82 (d, J = 8.04 Hz, 1H,
meso-aryl), 7.66 (br s, 2H, meso-aryl), 7.41 (d, J = 7.96 Hz, 1H, meso-
aryl), 7.12−7.06 (m, 3H, p-H of PPh3), 6.75−6.67 (m, 6H, m-H of
PPh3), 4.68−4.60 (m, 6H, o-H of PPh3). HRMS (major isotopomer)
[M]+: 1048.1788 (exptl), 1048.1782 (calcd). Elemental analysis found
(calcd): C, 66.58 (66.42); H, 3.72 (3.36); N, 5.19 (5.34).
Synthesis of Co[TpMePC](PPh3). Silica gel column chromatog-
raphy with n-hexane/CH2Cl2 (3:2) as eluent afforded 0.026 g (0.029
mmol, 66%) of Co[TpMePC](PPh3). UV−vis (CH2Cl2) λmax [nm, ε
1
× 10−4 (M−1 cm−1)]: 392 (5.33), 563 (0.99). H NMR (CDCl3, 25
°C): δ 8.57 (d, J = 4.4 Hz, 2H, β-pyrrolic), 8.33 ((d, J = 4.76 Hz, 2H,
β-pyrrolic), 8.10 (d, J = 4.76 Hz, 2H, β-pyrrolic), 8.03 (d, J = 4.4 Hz,
2H, β-pyrrolic), 8.02−7.94 (broad-m, 2H, meso-aryl), 7.89 (d, J = 7.7
Hz, 1H, meso-aryl), 7.50−7.32 (m, 8H, meso-aryl), 7.27 (s, 1H, meso-
aryl), 7.07−7.00 (m, 3H, p-H of PPh3), 6.74−6.66 (m, 6H, m-H of
PPh3), 4.77−4.69 (m, 6H, o-H of PPh3), 2.57 (s, 6H, 5,15-Me), 2.56
(s, 3H, 10-Me). HRMS (major isotopomer) [M]+: 886.2630 (exptl),
886.2630 (calcd).
Synthesis of Co[Br8TpOMePC](PPh3). Silica gel column
chromatography with n-hexane/CH2Cl2 (2:3, then 1:2) followed by
PTLC with 1:3 n-hexane/CH2Cl2 as eluent afforded pure Co-
[Br8TpOMePC](PPh3) (0.023 g, 0.0146 mmol, 73%). UV−vis
(CH2Cl2) λmax [nm, ε × 10−4 (M−1 cm−1)]: 393 (sh, 5.14), 423
1
Synthesis of Co[TpOMePC](PPh3). Silica gel column chromatog-
raphy with n-hexane/CH2Cl2 (1:1, then 1:2) as eluent afforded 0.0225
g (0.024 mmol, 59%) of Co[TpOMePC](PPh3). UV−vis (CH2Cl2)
(6.49), 584 (1.72). H NMR (CDCl3, 25 °C): δ 7.74−7.65 (m, 3H,
meso-aryl), 7.24−7.17 (m, 4H, meso-aryl and p-H of PPh3 overlapping),
7.13−7.02 (m, 6H, meso-aryl), 6.93−6.85 (m, 8H, overlapping meso-
aryl and m-H of PPh3), 4.93−4.85 (m, 6H, o-H of PPh3), 4.02
(overlapping s, 9H, 5,10,15-OMe). HRMS (major isotopomer) [M]+:
1565.5242 (exptl), 1565.5250 (calcd).
1
λmax [nm, ε × 10−4 (M−1 cm−1)]: 399 (7.13), 565 (1.27). H NMR
(CDCl3, 25 °C): δ 8.58 (d, J = 4.4 Hz, 2H, β-pyrrolic), 8.34 (d, J =
4.76 Hz, 2H, β-pyrrolic), 8.11 (d, J = 4.76 Hz, 2H, β-pyrrolic), 8.04 (d,
J = 4.4 Hz, 3H, overlapping β-pyrrolic and meso-aryl), 7.91 (d, J = 7.9
Hz, 1H, meso-aryl), 7.51 (s, 2H, meso-aryl), 7.29 (d, J = 7.8 Hz, 1H,
meso-aryl), 7.20−6.99 (m, 10H, overlapping meso-aryl and p-H of
PPh3), 6.75−6.65 (m, 6H, m-H of PPh3), 4.79−4.66 (m, 6H, o-H of
PPh3), 4.01 (s, 6H, 5,15-OMe), 4.0 (s, 3H, 10-OMe). HRMS (major
isotopomer) [M]+: 934.2475 (exptl), 934.2478 (calcd).
Synthesis of Co[TPC](py)2. A 50-mL round-bottomed flask
equipped with a magnetic stir bar was charged with free-base
triphenylcorrole (0.03 g, 0.057 mmol) dissolved in pyridine (10
mL). To this solution was added Co(OAc)2·4H2O (0.142 g, 0.57
mmol). The reaction flask was then fitted with a reflux condenser and
heated on an oil bath at 100 °C with stirring for 25−30 min.
Completion of the reaction was confirmed by UV−vis spectroscopy
and mass spectrometry. Upon cooling, the solution was rotary
evaporated under a high vacuum to yield a dark greenish-brown
residue. The residue was redissolved in a minimum volume of
dichloromethane containing a couple of drops of pyridine and was
chromatographed on a silica gel column (length 10 cm) with 1:1:0.02
n-hexane/dichloromethane/pyridine as eluent. The intense green front
running band was collected and identified as the title compound.
Recrystallization from a mixture of 3:1 n-hexane/DCM with a few
drops of pyridine afforded the pure product (0.0326 g, 0.044 mmol,
77%). UV−vis (CH2Cl2) λmax [nm, ε × 10−4 (M−1 cm−1)]: 388
(10.35). UV−vis (CH2Cl2, 0.5% pyridine) λmax [nm, ε × 10−4 (M−1
Synthesis of Cobalt−β-Octabromocorrole−Triphenylphos-
phine Complexes. A detailed procedure is described below for
Co[Br8TpCF3PC](PPh3); the other β-octabromocorrole complexes
were synthesized via a similar protocol, except for the chromatographic
purification, which is indicated separately for each complex. Accurate
elemental analyses could not be obtained for these complexes because
of decomposition on warming and rigorous drying and/or storage.
Synthesis of Co[Br8TpCF3PC](PPh3). To a THF (10 mL)
solution of free-base H3[Br8TpCF3PC] (0.025g, 0.018 mmol) in a
50-mL round-bottomed flask was added 5 equiv of Co(OAc)2·4H2O
(0.022 g, 0.09 mmol) and 5 equiv of triphenylphosphine (0.024g, 0.09
mmol), and the solution was stirred at 50 °C temperature while open
to the atmosphere. The progress of the reaction was monitored by
UV−vis spectroscopy and mass spectrometry. After 30−35 min, the
solvent was removed by rotary evaporation, and the dark brown
residue was chromatographed on a silica gel column with 4:1 n-
hexane/dichloromethane as eluent. The product eluted as a reddish-
brown band, which was collected and evaporated to dryness. Final
purification was carried out with PTLC using 7:3 n-hexane/CH2Cl2 as
eluent. The front brownish-yellow band contained pure product
Co[Br8TpCF3PC](PPh3) (0.025g, 82%). UV−vis (CH2Cl2) λmax [nm,
1
cm−1)]: 437 (6.86), 452 (6.03), 582 (0.95), 623 (3.09). H NMR
(benzene-d6, 25 °C): δ 9.05 (d, J = 4.3 Hz, 2H, β-pyrrolic), 8.93 (d, J =
4.6 Hz, 2H, β-pyrrolic), 8.76−8.70 (m, 4H, β-pyrrolic), 8.40−8.35 (m,
4H, 5,15-o/m-aryl), 8.30−8.25 (m, 2H, 10-o/m-aryl), 7.53−7.41 (m,
9H, 5,15, and 10-o/m/p-aryl), 5.08 (s, 2H, p-H of pyridine), 4.54 (s,
4H, m-H of pyridine), 3.18 (broad-s, 4H, o-H of pyridine). HRMS
(major isotopomers in the presence of a drop of pyridine, M =
C37H23N4Co): [M]+ (0.70) 582.1225 (exptl), 582.1249 (calcd); [M +
py]+ (1.00) 661.1676 (exptl), 661. 1671 (calcd); [M + 2 py]+ (0.30) =
740.2100 (exptl), 740.2093 (calcd).
1
ε × 10−4 (M−1 cm−1)]: 396 (5.82), 421 (5.94), 579 (1.49). H NMR
(CDCl3, 25 °C): δ 7.99 (d, J = 7.9 Hz, 1H, meso-aryl), 7.94 (d, J = 8.0
Hz, 2H, meso-aryl), 7.78−7.75 (m, 6H, meso-aryl), 7.39 (d, J = 7.9 Hz,
1H, meso-aryl), 7.27−7.22 (m, 3H, p-H of PPh3), 7.07 (d, J = 8.2 Hz,
2H, meso-aryl), 6.92−6.85 (m, 6H, m-H of PPh3), 4.87−4.79 (m, 6H,
o-H of PPh3). HRMS (major isotopomer) [M]+: 1679.4540 (exptl),
1679.4554 (calcd).
Needle-shaped X-ray quality crystals were obtained by slow
diffusion of MeOH vapor into a concentrated CHCl3 solution of the
complex over 1 week.
Synthesis of Rhodium−Corrole−Triphenylphosphine Com-
plexes. A detailed procedure is described below for the synthesis of
the rhodium−tris(4-trifluoromethylphenyl)corrole−triphenylphos-
phine complex, Rh[TpCF3PC](PPh3). A similar procedure was also
followed for the synthesis of the other Rh complexes, except for the
optimum methods for chromatographic purifications, which are
specified separately.
Synthesis of Rh[TpCF3PC](PPh3). To a solution of free base
tris(4-trifluoromethylphenyl)corrole (0.010 g, 0.014 mmol) in 2:1
dichloromethane/ethanol (15 mL) in a 50-mL round bottomed flask,
was added sequentially [Rh(cod)2Cl]2 (0.0103g, 0.021 mmol, 1.5
equiv), NaOAc (0.017g, 0.21 mmol, 15 equiv), and triphenyl
Synthesis of Co[Br8TPC](PPh3). Silica gel column chromatog-
raphy with 3:1 n-hexane/CH2Cl2 followed by PTLC with 2:1 n-
hexane/CH2Cl2 as eluent afforded pure Co[Br8TPC](PPh3) (0.018 g,
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phosphine (0.004g, 0.014 mmol, 1 equiv), and the mixture was stirred
at room temperature for about 30−35 min while open to the
atmosphere. Completion of the reaction was confirmed by UV−vis
spectroscopy and mass spectrometry. The solvent was then removed
by rotary evaporation, and the dark residue was chromatographed on a
silica gel column with 9:1 n-hexane/CH2Cl2 as eluent. A dark red band
that emerged second from the column was identified as containing
Rh[TpCF3PC](PPh3). Recrystallization from hexane afforded the pure
product (0.008 g, 0.007 mmol, 52%). UV−vis (CH2Cl2) λmax [nm, ε ×
10−4 (M−1 cm−1)]: 380 (sh) (1.93), 431 (4.45), 568 (1.39). 1H NMR
(CDCl3, 25 °C): δ 8.78 (d, J = 4.3 Hz, 2H, β-pyrrolic), 8.59 (d, J = 4.7
Hz, 2H, β-pyrrolic), 8.25 (d, J = 4.7 Hz, 2H, β-pyrrolic), 8.12 (d, J =
4.3 Hz, 2H, β-pyrrolic), 8.11−7.86 (m, 11H, meso-aryl), 7.51 (d, J =
7.8 Hz, 1H, meso-aryl), 7.08 (t, J = 7.3 Hz, 3H, p-H of PPh3), 6.74−
6.68 (m, 6H, m-H of PPh3), 4.42 (dd, J = 12.4, 7.8 Hz, 6H, o-H of
PPh3). HRMS (major isotopomer) [M]+: 1092.1498 (exptl),
1092.1505 (calcd). Elemental analysis found (calcd): C, 63.57
(63.75); H, 3.75 (3.23); N, 5.04 (5.13).
Synthesis of Rh[TPC](PPh3). Silica gel column chromatography
with 9:1 n-hexane/ethyl acetate as eluent followed by recrystallization
from 4:1 n-hexane/CH2Cl2 afforded the pure product (0.008 g, 0.009
mmol, 48%). UV−vis (CH2Cl2) λmax [nm, ε × 10−4 (M−1 cm−1)]: 381
(1.97), 429 (4.38), 566 (1.35). 1H NMR (CDCl3, 25 °C): δ 8.71 (d, J
= 4.3 Hz, 2H, β-pyrrolic), 8.58 (d, J = 4.7 Hz, 2H, β-pyrrolic), 8.25 (d,
J = 4.7 Hz, 2H, β-pyrrolic), 8.13 (d, J = 4.3 Hz, 2H, β-pyrrolic), 7.97
(br s, 5H, meso-aryl), 7.76−7.57 (m, 9H, meso-aryl), 7.47 (d, J = 6.9
Hz, 1H, meso-aryl), 7.04 (t, J = 7.6 Hz, 3H, p-H of PPh3), 6.77−6.66
(m, 6H, m-H of PPh3), 4.47 (dd, 6H, J = 12.3, 7.8 Hz, 6H, o-H of
PPh3). HRMS (major isotopomer) [M]+: 888.1866 (exptl), 888.1884
(calcd). Elemental analysis found (calcd): C, 73.71 (74.32); H, 4.53
(4.31); N, 6.33 (6.30).
in a nitrogen stream provided by an Oxford Cryostream 800 Plus.
Diffraction data were collected using a synchrotron with mono-
chromated radiation using a silicon (111) crystal at λ = 0.7749(1) Å.
The structures were solved using dual space methods using SHELXT76
and refined on F2 using SHELXL-2014.77 All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included at their
geometrically estimated positions. One bromine atom in Co-
[Br8TpCF3PC](PPh3) was found to be disordered and was modeled
over two sites with complementary occupancies. The two sites were
constrained to have equal Uij values.
Computational Methods. Ground state DFT calculations were
carried with the ADF program system,78 the B3LYP exchange-
correlation functional (20% Hartree−Fock exchange),79,80 and ZORA
STO-TZP basis sets, both with and without the Grimme’s D3
dispersion correction.81 DFT calculations related to the XAS/XES
measurements were carried out with the ORCA 3.0.3 program using
the BP86 optimized geometries followed by single-point spin-
unrestricted B3LYP calculations allowing for broken-symmetry
solutions. For the latter calculations, we used the core properties
basis sets as implemented in ORCA, viz. CP(PPP) for Co and the
Ahlrichs’s TZVP basis set for all other atoms. These calculations also
employed the conductor-like screening model (COSMO) with a
dielectric constant of 3.9 as well as appropriately fine grids and tight
SCF convergence criteria. For TDDFT calculations of Co K pre-edge
transitions, we set the number of roots at 40 and MaxDim at 400,
selected “doQuad True,” and did not calculate triplets. The TDDFT
calculations were carried out over the entire valence manifold and for
both spin-up (OrbWin = 0) and spin-down (OrbWin = 1) transitions.
The calculated transition energies were broadened with half-widths of
1.7 eV to account for core-hole lifetime and instrument broadening
and linearly upshifted by 164.5 eV for comparison with the
experimental spectra.
X-Ray Absorption Data Collection and Analysis. The Co K-
edge X-ray absorption spectra of Co[TPP], Co[TPP)(py)Cl, Co-
[TPC](py)2, and Co[TPC](PPh3) were collected at the Stanford
Synchrotron Radiation Lightsource under standard ring conditions of
3 GeV and ∼500 mA on the unfocused 20-pole 2 T wiggler side-
station 7−3, equipped with a Si(220) double crystal monochromator
for energy selection. The M0 mirror was not employed, and the
monochromator was detuned by ∼55% to eliminate contributions
from higher harmonics. All complexes were measured as solids ground
to a homogeneous powder in a BN matrix. The sample was placed in
Al spacers and wrapped in Kapton tape. During data collection, the
samples were maintained at a constant temperature of ∼10−15 K
using an Oxford liquid He cryostat. Co K-edge EXAFS data were
measured to k = 15 Å−1 (transmission mode) using ion-chamber
detectors. Internal energy calibration was accomplished by simulta-
neous measurement of the absorption of a Co-foil placed between the
second and third ionization chambers situated after the sample. The
data were calibrated to the first inflection point of the Co foil (7709.5
eV). Energy calibration, background correction, data averaging, and
normalization were accomplished with ATHENA, which is part of the
Demeter software package, version 0.9.24.82 The pre-edge region of
the data sets was fit using Peak-Fit (SigmaPlot).
X-Ray Emission Data Collection and Analysis. Co K-edge XES
spectra were measured on the 54-pole, 1-T wiggler beamline 6−2. A
liquid-nitrogen-cooled double crystal Si(111) monochromator was
used to set the incident energy at 9 keV. Vertical and horizontal
focusing mirrors were used to achieve a beam size of 150 × 400 mm.
Energy calibration was achieved with a Co foil. The first inflection
point of the foil spectrum was set at 7709.5 eV. Kβ X-ray emission
spectra were measured using the 533 reflection of five spherically bent
Si crystal analyzers in combination with a silicon drift detector aligned
in a Rowland geometry, as previously described.83 The overall energy
bandwidth of the X-ray emission spectrometer was ∼1.5 eV. The data
were normalized with respect to the Kα line intensity. The Kβ1,3 and
the Kβvalence spectra were recorded separately using different regions
with significant overlap between the two regions for accurate merging
of the two data sets. A higher number of Kβvalence scans was required to
achieve similar signal quality.
X-ray quality crystals were obtained by slow evaporation of a
concentrated solution of the complex in 3:1 n-hexane/CH2Cl2.
Synthesis of Rh[TpMePC](PPh3). Silica gel column chromatog-
raphy with 9:1 n-hexane/ethyl acetate as eluent followed by
recrystallization from 4:1 n-hexane/CH2Cl2 afforded the pure product
(0.009 g, 0.0097 mmol, 54%). UV−vis (CH2Cl2) λmax [nm, ε × 10−4
1
(M−1 cm−1)]: 381 (1.84), 430 (3.99), 567 (1.23). H NMR (CDCl3,
25 °C): δ 8.68 (d, J = 4.3 Hz, 2H, β-pyrrolic), 8.58 (d, J = 4.7 Hz, 2H,
β-pyrrolic), 8.25 (d, J = 4.7 Hz, 2H, β-pyrrolic), 8.13 (d, J = 4.3 Hz,
2H, β-pyrrolic), 7.92−7.80 (m, 5H, meso-aryl), 7.56−7.33 (m, 7H,
meso-aryl), 7.02 (t, J = 7.4 Hz, 3H, p-H of PPh3), 6.72−6.64 (m, 6H,
m-H of PPh3), 4.46 (dd, 6H, J = 12.2, 8.0 Hz, 6H, o-H of PPh3), 2.65
(s, 6H, 5,15-Me), 2.62 (s, 3H, 10-Me). HRMS (major isotopomer)
[M]+: 930.2374 (exptl), 930.2353 (calcd). Elemental analysis found
(calcd): C, 73.73 (74.84); H, 5.49 (4.76); N, 5.50 (6.02).
Synthesis of Rh[TpOMePC](PPh3). Silica gel column chromatog-
raphy with n-hexane/ethyl acetate (4:1 decreasing to 1:1) as eluent
followed by recrystallization from 3:1 n-hexane/CH2Cl2 afforded
0.0085g (0.0087 mmol) of pure Rh[TpOMePC](PPh3). Yield = 54%.
UV−vis (CH2Cl2) λmax [nm, ε × 10−4 (M−1 cm−1)]: 380 (3.1), 427
1
(6.06), 567 (2.06). H NMR (CDCl3, 25 °C): δ 8.68 (d, J = 4.3 Hz,
2H, β-pyrrolic), 8.58 (d, J = 4.7 Hz, 2H, β-pyrrolic), 8.25 (d, J = 4.7
Hz, 2H, β-pyrrolic), 8.11 (d, J = 4.3 Hz, 2H, β-pyrrolic), 7.87 (broad-d,
J = 8.0 Hz, 5H, meso-aryl), 7.35 (d, J = 8.1 Hz, 1H, meso-aryl), 7.29−
7.12 (m, 6H, meso-aryl), 7.02 (t, J = 7.2 Hz, 3H, p-H of PPh3), 6.71−
6.64 (m, 6H, m-H of PPh3), 4.45 (dd, J = 12.3 Hz, 7.8 Hz, 6H, o-H of
PPh3), 4.05 (s, 6H, 5,15-alkyl proton), 4.03 (s, 3H, 10-alkyl proton).
HRMS (ESI+,major isotopomer): [M]+ = 978.2197 (expt.), 978.2201
(calcd.). Elemental analysis found (calcd): C 69.07 (71.17), H, 4.83
(4.53), N, 5.61 (5.72).
X-ray quality crystals were obtained by slow diffusion of n-heptane
vapor into a concentrated benzene solution of the complex over 1
week.
Crystal Structure Determination. X-ray diffraction data were
collected on beamline 11.3.1 at the Advanced Light Source. Single
crystals were selected and coated in protective oil, before being
transferred onto a MiTeGen kapton micromount and transferred to a
Bruker D8 diffractometer fitted with a PHOTON100 CMOS detector
operating in shutterless mode. The samples were cooled to 100(2) K
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Inorganic Chemistry
Article
(7) Steene, E.; Dey, A.; Ghosh, A. β-Octafluorocorroles. J. Am. Chem.
Soc. 2003, 125, 16300−16309.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01828.
■
S
(8) Bruckner, C.; Brinas, R. P.; Krause Bauer, J. A. X-ray Structure
̈
̃
and Variable Temperature NMR Spectra of [meso-Triarylcorrolato]-
copper(III). Inorg. Chem. 2003, 42, 4495−4497.
(9) Broring, M.; Bregier, F.; Consul Tejero, E.; Hell, C.; Holthausen,
̈
1H NMR spectra, UV−vis spectra, cyclic voltammo-
grams, mass spectra, BP86 optimized coordinates (PDF)
M. C. Revisiting the Electronic Ground State of Copper Corroles.
Angew. Chem., Int. Ed. 2007, 46, 445−448.
(10) Thomas, K. E.; Wasbotten, I. H.; Ghosh, A. Copper β-
Octakis(Trifluoromethyl)Corroles: New Paradigms for Ligand Sub-
stituent Effects in Transition Metal Complexes. Inorg. Chem. 2008, 47,
10469−10478.
Accession Codes
CCDC 1535564−1535566 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(11) Alemayehu, A. B.; Conradie, J.; Ghosh, A. A First TDDFT
Study of Metallocorrole Electronic Spectra: Copper meso-Triarylcor-
roles Exhibit Hyper Spectra. Eur. J. Inorg. Chem. 2011, 2011, 1857−
1864.
(12) Alemayehu, A. B.; Hansen, L. K.; Ghosh, A. Nonplanar,
Noninnocent, and Chiral: A Strongly Saddled Metallocorrole. Inorg.
Chem. 2010, 49, 7608−7610.
(13) Thomas, K. E.; Conradie, J.; Hansen, L. K.; Ghosh, A. A
Metallocorrole with Orthogonal Pyrrole Rings. Eur. J. Inorg. Chem.
2011, 2011, 1865−1870.
(14) Berg, S.; Thomas, K. E.; Beavers, C. M.; Ghosh, A.
Undecaphenylcorroles. Inorg. Chem. 2012, 51, 9911−9916.
(15) Thomas, K. E.; Vazquez-Lima, H.; Fang, Y.; Song, Y.; Gagnon,
K. J.; Beavers, C. M.; Kadish, K. M.; Ghosh, A. Ligand Noninnocence
in Coinage Metal Corroles: A Silver Knife-Edge. Chem. - Eur. J. 2015,
21, 16839−16847.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: ritis@slac.stanford.edu.
*E-mail: abhik.ghosh@uit.no.
ORCID
Laura J. McCormick: 0000-0002-6634-4717
Abhik Ghosh: 0000-0003-1161-6364
Notes
■
The authors declare no competing financial interest.
(16) Steene, E.; Wondimagegn, T.; Ghosh, A. Electrochemical and
Electronic Absorption Spectroscopic Studies of Substituent Effects in
Iron(IV) and Manganese(IV) Corroles. Do the Compounds Feature
High-Valent Metal Centers or Noninnocent Corrole Ligands?
Implications for Peroxidase Compound I and II Intermediates. J.
Phys. Chem. B 2001, 105, 11406−11413; Addition/correction. J. Phys.
Chem. B 2002, 106, 5312−5312.
ACKNOWLEDGMENTS
■
This work was supported by grants 231086 and 262229 of the
Research Council of Norway (A.G.), the SSRL Structural
Molecular Biology (SMB) resource (R.S.), the Advanced Light
Source, Berkeley, California (L.J.M., K.J.G.), and the National
Research Fund of the Republic of South Africa (J.C.). The
SSRL SMB resource is supported by the National Institutes of
Health National Institute of General Medical Sciences
(NIGMS) through a Biomedical Technology Research
Resource P41 grant (P41GM103393) and by the DOE Office
of Biological and Environmental Research. The Advanced Light
Source is supported by the Director, Office of Science, Office of
Basic Energy Sciences of the U.S. Department of Energy under
Contract No. DE-AC02-05CH11231. L.J.G. was supported by a
postdoctoral fellowship from Stanford University.
(17) Zakharieva, O.; Schunemann, V.; Gerdan, M.; Licoccia, S.; Cai,
̈
S.; Walker, F. A.; Trautwein, A. X. Is the Corrolate Macrocycle
Innocent or Noninnocent? Magnetic Susceptibility, Mossbauer, 1H
̈
NMR, and DFT Investigations of Chloro- and Phenyliron Corrolates.
J. Am. Chem. Soc. 2002, 124, 6636−6648.
(18) Walker, F. A.; Licoccia, S.; Paolesse, R. Iron Corrolates:
Unambiguous Chloroiron(III) (Corrolate)2‑· π-Cation Radicals. J.
Inorg. Biochem. 2006, 100, 810−837.
(19) Vazquez-Lima, H.; Norheim, H. K.; Einrem, R. F.; Ghosh, A.
Cryptic Noninnocence: FeNO Corroles in a New Light. Dalton Trans.
2015, 44, 10146−10151.
(20) Norheim, H.-K.; Capar, J.; Einrem, R. F.; Gagnon, K. J.; Beavers,
C. M.; Vazquez-Lima, H.; Ghosh, A. Ligand Noninnocence in FeNO
Corroles: Insights from β-Octabromocorrole Complexes. Dalton
Trans. 2016, 45, 681−689.
REFERENCES
■
(1) Jørgensen, C. K. Differences between the Four Halide Ligands,
and discussion remarks on Trigonal-Bipyramidal Complexes, on
Oxidation States, and on Diagonal Elements of One-Electron Energy.
Coord. Chem. Rev. 1966, 1, 164−178.
(2) For a set of Inorganic Chemistry Forum articles, see: Chirik, P. J.
Preface: Forum on Redox-Active Ligands. Inorg. Chem. 2011, 50,
9737−9740.
(3) Kaim, W. Manifestations of Noninnocent Ligand Behavior. Inorg.
Chem. 2011, 50, 9752−9765.
(21) Ganguly, S.; Vazquez-Lima, H.; Ghosh, A. Wolves in Sheep’s
Clothing: μ-Oxo-Diiron Corroles Revisited. Chem. - Eur. J. 2016, 22,
10336−10340.
(22) Alemayehu, A. B.; Vazquez-Lima, H.; Beavers, C. M.; Gagnon,
K. J.; Bendix, J.; Ghosh, A. Platinum Corroles. Chem. Commun. 2014,
50, 11093−11096.
(23) Johansen, I.; Norheim, H.-K.; Larsen, S.; Alemayehu, A. B.;
Conradie, J.; Ghosh, A. Substituent Effects on Metallocorrole Spectra:
Insights from Chromium-Oxo and Molybdenum-Oxo Triarylcorroles.
J. Porphyrins Phthalocyanines 2011, 15, 1335−1344.
(24) Einrem, R. F.; Braband, H.; Fox, T.; Vazquez-Lima, H.; Alberto,
R.; Ghosh, A. Synthesis and molecular structure of 99Tc Corroles.
Chem. - Eur. J. 2016, 22, 18747−18751.
(25) Einrem, R. F.; Gagnon, K. J.; Alemayehu, A. B.; Ghosh, A.
Metal-Ligand Misfits: Facile Access to Rhenium-Oxo Corroles by
Oxidative Metalation. Chem. - Eur. J. 2016, 22, 517−520.
(26) Alemayehu, A. B.; Vazquez-Lima, H.; Gagnon, K. J.; Ghosh, A.
Stepwise Deoxygenation of Nitrite as a Route to Two Families of
(4) Lyaskovskyy, V.; de Bruin, B. Redox Non-Innocent Ligands:
Versatile New Tools to Control Catalytic Reactions. ACS Catal. 2012,
2, 270−279.
(5) Ghosh, A. Electronic Structure of Corrole Derivatives: Insights
from Molecular Structures, Spectroscopy, Electrochemistry, and
Quantum Chemical Calculations. Chem. Rev. 2017, 117, 3798−3881.
(6) Wasbotten, I. H.; Wondimagegn, T.; Ghosh, A. Electronic
Absorption, Resonance Raman, and Electrochemical Studies of Planar
and Saddled Copper(III) Meso-Triarylcorroles. Highly Substituent-
Sensitive Soret Bands as a Distinctive Feature of High-Valent
Transition Metal Corroles. J. Am. Chem. Soc. 2002, 124, 8104−8116.
14798
DOI: 10.1021/acs.inorgchem.7b01828
Inorg. Chem. 2017, 56, 14788−14800

Inorganic Chemistry
Article
Ruthenium Corroles: Group 8 Periodic Trends and Relativistic Effects.
Inorg. Chem. 2017, 56, 5285−5294.
(45) Simkhovich, L.; Goldberg, I.; Gross, Z. Easy Preparation of
Cobalt Corrole and Hexaphyrin and Isolation of New Oligopyrroles in
the Solvent-Free Condensation of Pyrrole with Pentafluorobenzalde-
hyde. Org. Lett. 2003, 5, 1241−1244.
(27) Alemayehu, A. B.; Gagnon, K. J.; Terner, J.; Ghosh, A. Oxidative
Metalation as a Route to Size-Mismatched Macrocyclic Complexes:
Osmium Corroles. Angew. Chem., Int. Ed. 2014, 53, 14411−14414.
(28) Alemayehu, A. B.; Ghosh, A. Gold Corroles. J. Porphyrins
Phthalocyanines 2011, 15, 106−110.
(46) Thomas, K. E.; Conradie, J.; Hansen, L. K.; Ghosh, A. Corroles
Cannot Ruffle. Inorg. Chem. 2011, 50, 3247−3251.
(47) Palmer, J. H.; Mahammed, A.; Lancaster, K. M.; Gross, Z.; Gray,
H. B. Structures and Reactivity Patterns of Group 9 Metallocorroles.
Inorg. Chem. 2009, 48, 9308−9315.
(48) Collman, J. P.; Wang, H. J. H.; Decreau, R. A.; Eberspacher, T.
A.; Sunderland, C. J. Synthesis and Characterization of RhIII corroles:
Unusual Reactivity Patterns Observed during Metalation Reactions.
Chem. Commun. 2005, 2497−2499.
(29) Rabinovich, E.; Goldberg, I.; Gross, Z. Gold(I) and Gold(III)
Corroles. Chem. - Eur. J. 2011, 17, 12294−12301.
(30) Thomas, K. E.; Alemayehu, A. B.; Conradie, J.; Beavers, C.;
Ghosh, A. Synthesis and Molecular Structure of Gold Triarylcorroles.
Inorg. Chem. 2011, 50, 12844−12851.
(31) Mahammed, A.; Giladi, I.; Goldberg, I.; Gross, Z. Synthesis and
Structural Characterization of a Novel Covalently-Bound Corrole
Dimer. Chem. - Eur. J. 2001, 7, 4259−4265.
(49) Thomas, K. E.; Alemayehu, A. B.; Conradie, J.; Beavers, C. M.;
Ghosh, A. The Structural Chemistry of Metallocorroles: Combined X-
ray Crystallography and Quantum Chemistry Studies Afford Unique
Insights. Acc. Chem. Res. 2012, 45, 1203−1214.
(32) Huang, S.; Fang, Y.; Lu, A.; Lu, G.; Ou, Z.; Kadish, K. M.
̈
Synthesis, Characterization and Solvent/Structural Effects on Spectral
and Redox Properties of Cobalt Triphenylcorroles in Nonaqueous
Media. J. Porphyrins Phthalocyanines 2012, 16, 958−967.
(33) Li, B.; Ou, Z.; Meng, D.; Tang, J.; Fang, Y.; Liu, R.; Kadish, K.
M. Cobalt triarylcorroles containing One, Two or Three Nitro
Groups. Effect of NO2 Substitution on Electrochemical Properties and
Catalytic Activity for Reduction of Molecular Oxygen in Acid Media. J.
Inorg. Biochem. 2014, 136, 130−139.
(50) Pyykko, P.; Atsumi, M. Molecular Single-Bond Covalent Radii
̈
for Elements 1−118. Chem. - Eur. J. 2009, 15, 186−197.
(51) Shannon, R. D. Revised Effective Ionic Radii and Systematic
Studies of Interatomic Distances in Halides and Chalcogenides. Acta
Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32,
751−767.
(52) Dronskowski, R. Computational Chemistry of Solid State
Materials; Wiley-VCH, 2007; pp 1−294.
(53) Tang, J.; Ou, Z.; Ye, L.; Yuan, M.; Fang, Y.; Xue, Z.; Kadish, K.
M. Meso-dichlorophenyl Substituted Co(III) corrole: A Selective
Electrocatalyst for the Two-Electron Reduction of Dioxygen in Acid
Media, X-ray Crystal Structure Analysis and Electrochemistry. J.
Porphyrins Phthalocyanines 2014, 18, 891−898.
(54) Rui, G.; Zhong-Ping, O.; Li-Na, Y.; Wen-Hao, H.; Zhao-Li, X.;
Ji-Jun, T.; Yuan-Yuan, F. Cobalt Triarylcorroles with Sterically
Hindered Halogenated Phenyl Rings: Synthesis, Crystal Structure
and Catalytic Activity for Electroreduction of Dioxygen. Chin. J. Struct.
Chem. 2016, 35, 1754−1763.
(55) Niu, Y.; Li, M.; Zhang, Q.; Zhu, W.; Mack, J.; Fomo, G.;
Nyokong, T.; Liang, X. Halogen Substituted A2B type Co(III)-
Triarylcorroles: Synthesis, Electronic Structure and Two Step
Modulation of Electrocatalyzed Hydrogen Evolution Reactions. Dyes
Pigm. 2017, 142, 416−428.
(56) Ghosh, A.; Wondimagegn, T.; Parusel, A. B. J. Electronic
Structure of Gallium, Copper, and Nickel Complexes of Corrole.
High-Valent Transition Metal Centers Versus Noninnocent Ligands. J.
Am. Chem. Soc. 2000, 122, 5100−5104.
(57) Ghosh, A.; Steene, E. High-Valent Transition Metal Centers and
Noninnocent Ligands in Metalloporphyrins and Related Molecules: A
Broad Overview Based on Quantum Chemical Calculations. JBIC, J.
Biol. Inorg. Chem. 2001, 6, 739−752.
(58) Fang, Y.; Ou, Z.; Kadish, K. M. Electrochemistry of Corroles in
Nonaqueous Media. Chem. Rev. 2017, 117, 3377−3419.
(59) Kadish, K. M.; Koh, W.; Tagliatesta, P.; Sazou, D.; Paolesse, R.;
Licoccia, S.; Boschi, T. Electrochemistry of rhodium and cobalt
corroles. Characterization of (OMC)Rh(PPh3) and (OMC)Co(PPh3)
where OMC is the Trianion of 2,3,7,8,12,13,17,18-Octamethylcorrole.
Inorg. Chem. 1992, 31, 2305−2313.
(60) El Murr, N.; Sheats, J. E.; Geiger, W. E., Jr.; Holloway, J. D.
Electrochemical Reduction Pathways of the Rhodocenium Ion.
Dimerization and Reduction of Rhodocene. Inorg. Chem. 1979, 18,
1443−1446.
(61) Palmer, J. H.; Lancaster, K. M. Molecular Redox: Revisiting the
Electronic Structures of the Group 9 Metallocorroles. Inorg. Chem.
2012, 51, 12473−12482.
(62) Sarangi, R.; Giles, L. J.; Thomas, K. E.; Ghosh, A. Ligand
Noninnocence in Silver Corroles: A XANES Investigation. Eur. J.
Inorg. Chem. 2016, 2016, 3225−3227.
(63) MacMillan, S. N.; Lancaster, K. M. X-ray Spectroscopic
Interrogation of Transition-Metal-Mediated Homogeneous Catalysis:
Primer and Case Studies. ACS Catal. 2017, 7, 1776−1791.
(34) Simkhovich, L.; Mahammed, A.; Goldberg, I.; Gross, Z.
Synthesis and Characterization of Germanium, Tin, Phosphorus,
Iron, and Rhodium Complexes of Tris(pentafluorophenyl)corrole, and
the Utilization of the Iron and Rhodium Corroles as Cyclopropanation
Catalysts. Chem. - Eur. J. 2001, 7, 1041−1055.
(35) Simkhovich, L.; Galili, N.; Saltsman, I.; Goldberg, I.; Gross, Z.
Coordination Chemistry of the Novel 5,10,15-Tris-
(pentafluorophenyl)corrole: Synthesis, Spectroscopy, and Structural
Characterization of Its Cobalt(III), Rhodium(III), and Iron(IV)
Complexes. Inorg. Chem. 2000, 39, 2704−2705.
(36) Dogutan, D. K.; McGuire, R., Jr.; Nocera, D. G. Electocatalytic
Water Oxidation by Cobalt(III) Hangman β-Octafluoro Corroles. J.
Am. Chem. Soc. 2011, 133, 9178−9180.
(37) Mondal, B.; Sengupta, K.; Rana, A.; Mahammed, A.;
Botoshansky, M.; Dey, S. G.; Gross, Z.; Dey, A. Cobalt Corrole
Catalyst for Efficient Hydrogen Evolution Reaction from H2O under
Ambient Conditions: Reactivity, Spectroscopy, and Density Functional
Theory Calculations. Inorg. Chem. 2013, 52, 3381−3387.
(38) Mahammed, A.; Mondal, B.; Rana, A.; Dey, A.; Gross, Z. The
Cobalt Corrole Catalyzed Hydrogen Evolution Reaction: Surprising
Electronic Effects and characterization of key reaction intermediates.
Chem. Commun. 2014, 50, 2725−2727.
(39) Yang, S.; Wo, Y.; Meyerhoff, M. E. Polymeric Optical Sensors
for Selective and Sensitive Nitrite Detection Using Cobalt(III) Corrole
and Rhodium(III) Porphyrin as Ionophores. Anal. Chim. Acta 2014,
843, 89−96.
(40) Guilard, R.; Gros, C. P.; Bolze, F.; Jerome, F.; Ou, Z.; Shao, J.;
Fischer, J.; Weiss, R.; Kadish, K. Alkyl and Aryl Substituted Corroles.
1. Synthesis and Characterization of Free Base and Cobalt Containing
Derivatives. X-ray Structure of (Me4Ph5Cor)Co(py)2. Inorg. Chem.
2001, 40, 4845−4855.
(41) Barbe, J.-M.; Canard, G.; Brandes, S.; Jerome, F.; Dubois, G.;
Guilard, R. Metallocorroles as Sensing Components for Gas Sensors:
Remarkable Affinity and Selectivity of Cobalt(III) corroles for CO vs.
O2 and N2. Dalton Trans. 2004, 1208−1214.
(42) Vazquez-Lima, H.; Conradie, J.; Ghosh, A. Metallocorrole
Interactions with Carbon Monoxide, Nitric Oxide, and Nitroxyl − A
DFT Study of Low-Energy Bound States. Inorg. Chem. 2016, 55,
8248−8250.
(43) Paolesse, R.; Nardis, S.; Sagone, F.; Khoury, R. G. Synthesis and
Functionalization of meso-Aryl-Substituted Corroles. J. Org. Chem.
2001, 66, 550−556.
(44) Paolesse, R.; Mini, S.; Sagone, F.; Boschi, T.; Jaquinod, L.;
Nurco, D. J.; Smith, K. M. 5,10,15-Triphenylcorrole: A Product from a
Modified Rothemund reaction. Chem. Commun. 1999, 1307−1308.
14799
DOI: 10.1021/acs.inorgchem.7b01828
Inorg. Chem. 2017, 56, 14788−14800

Inorganic Chemistry
Article
(64) This complex was synthesized as described in: Belghith, Y.;
Daran, J.-C.; Nasri, H. Chlorido(pyridine-κN)(5,10,15,20-tetraphenyl-
porphyrinato-κ4N)cobalt(III) chloroform hemisolvate. Acta Crystal-
logr., Sect. E: Struct. Rep. Online 2012, 68, m1104−m1105.
(65) Sarangi, R. X-ray Absorption Near-Edge Spectroscopy in
Bioinorganic Chemistry: Application to M−O2 systems. Coord. Chem.
Rev. 2013, 257, 459−472.
(66) Westre, T. E.; Kennepohl, P.; DeWitt, J. G.; Hedman, B.;
Hodgson, K. O.; Solomon, E. I. A Multiplet Analysis of Fe K-Edge
1s→3d Pre-Edge Features of Iron Complexes. J. Am. Chem. Soc. 1997,
119, 6297−6314.
(67) Glatzel, P.; Bergmann, U. High resolution 1s Core Hole X-ray
Spectroscopy in 3d Transition Metal Complexes − Electronic and
Structural Information. Coord. Chem. Rev. 2005, 249, 65−95.
(68) Bauer, M. HERFD-XAS and Valence-to-Core-XES: New Tools
to Push the Limits in Research with Hard X-Rays? Phys. Chem. Chem.
Phys. 2014, 16, 13827−13837.
(69) The complex was prepared as described in: Madura, P.; Scheidt,
W. R. Stereochemistry of Low-Spin Cobalt Porphyrins. 8. α,β,γ,δ-
Tetraphenylporphinatocobalt(II). Inorg. Chem. 1976, 15, 3182−3184.
́ ́ ́ ́
(70) Vanko, G.; Neisius, T.; Molnar, T.; Renz, F.; Karpati, S.; Shukla,
A.; de Groot, F. M. Probing the 3d Spin Momentum with X-ray
Emission Spectroscopy: The Case of Molecular-Spin Transitions. J.
Phys. Chem. B 2006, 110, 11647−11653.
(71) Pollock, C. J.; Delgado-Jaime, M. U.; Atanasov, M.; Neese, F.;
DeBeer, S. Kβ Mainline X-ray Emission Spectroscopy as an
Experimental Probe of Metal−Ligand Covalency. J. Am. Chem. Soc.
2014, 136, 9453−9463.
(72) Pollock, C. J.; DeBeer, S. Insights into the Geometric and
Electronic Structure of Transition Metal Centers from Valence-to-
Core X-ray Emission Spectroscopy. Acc. Chem. Res. 2015, 48, 2967−
2975.
(73) Pollock, C. P.; Delgado-Jaime, M. U.; Atanasov, M.; Neese, F.;
DeBeer, S. Kβ Mainline X-ray Emission Spectroscopy as an
Experimental Probe of Metal−Ligand Covalency. J. Am. Chem. Soc.
2014, 136, 9453−9463.
(74) Koszarna, B.; Gryko, D. T. Efficient Synthesis of meso-
Substituted Corroles in a H2O−MeOH Mixture. J. Org. Chem. 2006,
71, 3707−3717.
(75) Capar, J.; Berg, S.; Thomas, K. E.; Beavers, C. M.; Gagnon, K. J.;
Ghosh, A. Improved Syntheses of β-Octabromo-Meso-Triarylcorrole
Derivatives. J. Inorg. Biochem. 2015, 153, 162−166.
(76) Sheldrick, G. M. SHELXT - Integrated Space-Group and
Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv.
2015, 71, 3−8.
(77) Sheldrick, G. M. Crystal Structure Refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(78) The ADF program system uses methods described in: te Velde,
G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; van
Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. Chemistry with ADF. J.
Comput. Chem. 2001, 22, 931−967.
(79) Becke, A. D. Density-functional exchange-energy approximation
with correct asymptotic behaviour. Phys. Rev. A: At., Mol., Opt. Phys.
1988, 38, 3098−3100.
(80) Lee, C. T.; Yang, W. T.; Parr, R. G. Development of the Colle-
Salvetti correlation-energy formula into a functional of the electron-
density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(81) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and
accurate ab initio parametrization of density functional dispersion
correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010,
132, No. 154104.
(82) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS:
Data Analysis for X-ray Absorption Spectroscopy using IFEFFIT. J.
Synchrotron Radiat. 2005, 12, 537−541.
(83) Lee, N.; Petrenko, T.; Bergmann, U.; Neese, F.; DeBeer, S.
Probing Valence Orbital Composition with Iron Kβ X-ray Emission
Spectroscopy. J. Am. Chem. Soc. 2010, 132, 9715−9727.
14800
DOI: 10.1021/acs.inorgchem.7b01828
Inorg. Chem. 2017, 56, 14788−14800