Ligand Noninnocence in Cobalt Dipyrrin-Bisphenols: Spectroscopic, Electrochemical, and Theoretical Insights Indicating an Emerging Analogy with Corroles

Article abstract of DOI:10.1021/acs.inorgchem.8b03006

Three cobalt dipyrrin-bisphenol (DPPCo) complexes with different meso-aryl groups (pentafluorophenyl, phenyl, and mesityl) were synthesized and characterized based on their electrochemistry and spectroscopic properties in nonaqueous media. Each DPPCo unde

Full text of DOI:10.1021/acs.inorgchem.8b03006

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Ligand Noninnocence in Cobalt Dipyrrin−Bisphenols: Spectroscopic,
Electrochemical, and Theoretical Insights Indicating an Emerging
Analogy with Corroles
†
‡
‡
‡
Wenqian Shan, Nicolas Desbois, Sandrine Pacquelet, Stephane Brandes, Yoann Rousselin,‡
́
̀
Jeanet Conradie,§ Abhik Ghosh,*,∥ Claude P. Gros,*,‡ and Karl M. Kadish*,†
†Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States
‡
́
́
́
Institut de Chimie Moleculaire de l’Universite de Bourgogne (ICMUB), UMR CNRS 6302, Universite de
́
Bourgogne-Franche-Comte, 9 avenue Alain Savary, B.P. 47870, 21078 Dijon, Cedex, France
§Department of Chemistry, University of the Free State, Bloemfontein 9300, Republic of South Africa
∥Department of Chemistry, UiTThe Arctic University of Norway, Tromsø N-9037, Norway
S
* Supporting Information
ABSTRACT: Three cobalt dipyrrin−bisphenol (DPPCo)
complexes with different meso-aryl groups (pentafluorophenyl,
phenyl, and mesityl) were synthesized and characterized based
on their electrochemistry and spectroscopic properties in
nonaqueous media. Each DPPCo undergoes multiple
oxidations and reductions with the potentials, reversibility,
and number of processes depending on the specific solution
conditions, the specific macrocyclic substituents, and the type
and number of axially coordinated ligands on the central
cobalt ion. Theoretical calculations of the compounds with
different coordination numbers are given in the current study
in order to elucidate the cobalt-ion oxidation state and the
innocence or noninnocence of the macrocyclic ligand as a function of the changes in the solvent properties and degree of axial
coordination. Electron paramagnetic resonance spectra of the compounds are obtained to experimentally assess the electron
spin state. An X-ray structure of the six-coordinate complex is also presented. The investigated chemical properties of DPPCo
compounds under different solution conditions are compared to those of cobalt corroles, where the macrocycle and metal ion
also possess formal 3− and 3+ oxidation states in their air-stable forms.
ble free-base corroles (CorH3; Chart 1), a class of tetrapyrrole
ligands whose chemistry has grown dramatically over the last
two decades.10−13 Herein we report a detailed electrochemical,
spectroscopic, and quantum-chemical study of DPPCo
complexes that provides strong support for a DPP−corrole
analogy, indeed a simple case of an isolobal analogy,14 which in
time may prove to be a significant driver of new discoveries in
the DPP field.
INTRODUCTION
The free-base dipyrrin−bisphenols (DPPH3; Chart 1), an
emerging class of hybrid pyrrole-based ligands, are of interest
■
Chart 1. Structures of Free-Base Dipyrrin−Bisphenol and
Corrole Ligands
Until now, there have been two major studies of four-
coordinate (abbreviated as 4c) DPPCo derivatives.1,2 The
authors of one paper,1 Thomas and co-workers, formulated the
neutral cobalt dipyrrin−bisphenols as (DPP•2−)CoII and the
corresponding singly oxidized complex as (DPP−)CoII (both
reasonable formulations, in our view), while in another paper,2
the authors mainly focused on the catalytic reactivity of the
DPPCo complexes. These authors, however, did not character-
ize the ionized states of the compounds after oxidation or
for a variety of reasons,1−9 perhaps most notably for the fact
that several DPPM derivatives (M = Co,1,2 Ni,1 Cu,3 or Pt4)
have been found to exist as metal-radical assemblies, i.e., as
(DPP•2−)MII, as opposed to (DPP3−)MIII. In terms of both
their formally trianionic character and their propensity to yield
noninnocent metal-radical assemblies, DPPH3 ligands resem-
Received: October 23, 2018
© XXXX American Chemical Society
A
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reduction, nor did they explore the axial ligation chemistry of
the complexes. As part of this work, we have synthesized three
DPPCo derivatives, 1−3, as four-coordinate complexes in the
solid state and investigated their electrochemical and
spectroscopic properties in four different nonaqueous solvents,
one of which is noncoordinating [dichloromethane (CH2Cl2)]
and three of which are coordinating [benzonitrile (PhCN),
dimethyl sulfoxide (DMSO), and pyridine]. The three
compounds are depicted in Chart 2 and referred to hereafter
similarities may foreshadow important applications of the DPP
derivatives in areas where metallocorroles already play a
significant role, for examples, in catalytic group-transfer
chemistry21 (such as epoxidations,22,23 aziridinations,24,25 and
cyclopropanations26) and chemical sensing of small molecules
such as carbon monoxide (CO)27−29 or nitrite.30
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The DPP complexes
1−3 were synthesized via modification of a previously reported
protocol.2 The synthetic route is shown in Scheme 1. The acid-
catalyzed condensation of 2-(2-methoxyphenyl)pyrrole and
aldehyde in methylene chloride, followed by subsequent
oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone,
afforded the dipyrrin precursor.31 Deprotection of the phenol
moieties with boron tribromide (BBr3) then quantitatively
afforded the free-base dipyrrin−bisphenol precursors
(DPPH3).6 The target DPPCo complexes 1−3 were prepared
by the reaction of DPPH3 with Co(OAc)2·4H2O.
Chart 2. Structures of the Investigated DPPCo Complexes
1−3
1H NMR spectra (Figures S1−S3) and mass spectrometry
(MS) measurements (Figures S4−S9) were carried out to
confirm the structures reported in Chart 2. A perfect match
was observed between the experimental high-resolution MS
(HR-MS) spectra (Figures S4−S6) of compounds 1−3 and
the simulated ionic patterns. Electrospray ionization (ESI)-MS
spectra have also been registered in the presence of pyridine or
NH3·H2O (Figures S7−S9). In both cases, the molecular peaks
corresponding to the six-coordinate species (e.g., bis-py and
bis-NH3 species) are clearly observed, proving that the DPPCo
complexes 1−3 can also lead to six-coordinate species in the
presence of NH3 or pyridine, as previously reported in the case
of cobalt corrole complexes.18,32
UV−Visible Spectroscopy. Before the redox reactions
were carried out, the UV−visible spectrum of each neutral
compound 1−3 was measured in one noncoordinating solvent
(CH2Cl2) and three coordinating solvents (PhCN, DMSO,
and pyridine). Examples of the obtained spectra are given in
Figure 1 for a 10−3 M solution of compounds 1−3 in four
solvents containing 0.1 M tetrabutylammonium perchlorate
(TBAP), and a summary of the spectral data under these
conditions is given in Table 1.
as (F5Ph)DPPCo (1), (Ph)DPPCo (2), and (Mes)DPPCo
(3), where F5Ph, Ph, and Mes refer to the pentafluorophenyl,
phenyl, and mesityl groups at the meso-position of the DPP
ligand, respectively. By examining three different DPPCo
derivatives under different solution conditions, we are able to
document the rich coordination chemistry of the DPPCo
complexes, which have previously been examined only in one
noncoordinating solvent, CH2Cl2.1
Like cobalt porphyrins15,16 and corroles,12,17,18 the DPPCo
complexes examined are expected to undergo several reduction
and oxidation processes involving the Co center, the DPP π
system or a combination of both. Here we have used a
comprehensive set of UV−visible spectroelectrochemical
measurements to characterize the neutral, cationic, and anionic
states of the complexes. The measurements underscore the
importance of axial ligands, which greatly influence whether a
given redox process occurs in a metal- or ligand-centered
manner. Density functional theory (DFT) calculations with
three different exchange-correlation functionals on 2 (Chart 2)
were also carried out and provide additional details on the
nature of the low-energy states of the complex for the various
charge and coordination states.
Each spectrum is characterized by an intense band at 311−
329 nm, two to three intense overlapping bands at 554−693
nm, and one less intense band at wavelengths between these
two major absorption peaks. For example, all three investigated
Our results indicate extensive parallels between the low-
energy states of the DPPCo and CorCo complexes.19,20 These
Scheme 1. Synthetic Route To Obtain DPPCo Complexes 1−3
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Figure 1. UV−visible spectra of 1−3 (∼10−3 M) in four solvents containing 0.1 M TBAP.
Table 1. UV−Visible Spectral Data for 1−3 (∼10−3 M) in
CH2Cl2, PhCN, DMSO, or Pyridine Containing 0.1 M
TBAP
is 4−9 nm in PhCN, 13−49 nm in DMSO, and 39−69 nm in
pyridine. The first intense band is at similar wavelengths in
CH2Cl2, PhCN, and DMSO (around 316, 320, and 312 nm for
compounds 1−3, respectively), but this band is red-shifted by
5−13 nm in pyridine compared to the other solvents.
Considering the known solvent-binding ability of the Co
metal center in similar compounds,17,18,32 those red shifts and
the appearance of the additional band might correspond to the
axial coordination of a solvent molecule at the Co center in the
DPPCo complex.
Moreover, as seen in Figure 1, the UV−visible spectra of
compounds 2 and 3, which have meso-phenyl and mesityl
groups, are almost identical with each other in the same
solvent. These spectra differ from that of 1, which has a highly
electron-withdrawing meso-F5Ph group and is characterized by
visible bands that are 21−43 nm red-shifted compared to
compounds 2 and 3, with the exact value depending on the
specific solvent.
In order to investigate the possible binding of the solvent
molecules to DPPCo, the UV−visible spectral changes of 3 in
CH2Cl2 were measured during titration with DMSO and
pyridine. The binding constants were calculated as log K1 =
1.51 and 6.55, respectively, for the addition of a single solvent
molecule using nonlinear curve fitting (Figures S10 and S11).
A second set of spectral changes were not observed under the
experimental conditions on the time scale of both titrations. As
seen in Figures S10a and S11a, the major absorption bands of
the DPP derivatives in the neat solvents (627 nm in DMSO
and 658 nm in pyridine) are red-shifted compared to those of
the last spectra during the titration (18 nm shift from 609 nm
in the DMSO titration and 54 nm shift from 604 nm in the
pyridine titration). This contrasts with that seen in neat PhCN
(at 607 nm), where the major absorption band at the end of
the titration is the same as that in neat PhCN. This indicates
λmax, nm (ε × 10−4, M−1 cm−1
)
meso-
solvent
CH2Cl2
substituent
compd
Soret region
316 (1.6)
visible region
F5Ph
1
596 (1.2),
624 (1.2)
Ph
2
3
1
2
3
1
2
3
1
2
3
320 (1.8)
311 (1.8)
574 (1.1),
603 (1.2)
572 (1.4),
602 (1.6)
602 (1.1),
633 (1.4)
580 (0.9),
607 (1.3)
580 (1.2),
607 (1.7)
645 (1.1),
670 (1.1)
587 (0.7),
627 (1.1)
587 (0.8),
627 (1.3)
Mes
F5Ph
Ph
PhCN
DMSO
Py
316 (1.5),
434 (0.5)
319 (1.4),
414 (0.5)
312 (1.5),
414 (0.5)
315 (1.5),
471 (0.5)
321 (1.6),
445 (0.5)
313 (1.5),
443 (0.5)
329 (1.4),
473 (0.7)
325 (1.5),
461 (0.7)
Mes
F5Ph
Ph
Mes
F5Ph
Ph
649 (0.9),
693(1.2)
613 (0.8),
658 (1.2)
613 (0.7),
658 (1.2)
Mes
323 (1.4),
461 (0.6)
compounds have bands at 414−473 nm in PhCN, DMSO, or
pyridine, but this band is not seen in the noncoordinating
CH2Cl2 solvent. In addition, the major visible bands of
compounds 1−3 in the three coordinating solvents are red-
shifted compared to the corresponding bands in CH2Cl2. The
magnitude of the wavelength shift compared to that in CH2Cl2
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that five-coordinate (abbreviated as 5c) species are the major
derivatives of DPPCo compounds in PhCN and in the solution
mixture at the end of both titration experiments, while six-
coordinate (abbreviated as 6c) species can exist in neat DMSO
and neat pyridine.
Interestingly, when measuring the UV−visible spectrum of
compounds 1−3 in pyridine, a slow transformation was
observed to occur between two different forms of the DPPCo
complexes. To study the kinetics of this transformation, the
UV−visible spectral changes of compounds 1−3 in pyridine
were recorded as a function of time and kinetic plots were
constructed in order to determine the reaction order of the
transformation. Examples of the spectral changes and
corresponding plots are given in Figure 2.
with the calculated rate constants for conversion between two
states of compounds 1−3.
Table 2. Spectral Data for Compounds 1−3 (∼10−5 M) in
Pyridine and a CH2Cl2/Pyridine Mixture and Slopes of the
Kinetic Plots
λmax, nm
Soret
region
visible
region
slope =
a
b
compd
solution condition CN
−k
(F5Ph)
CH2Cl2/2000
equiv of Py
neat Py (initial)
5c 316,
464
5c 316,
464
6c 329,
473
5c 320,
435
5c 320,
435
6c 325,
461
5c 312,
430
5c 312,
430
600, 627
604, 632
649, 693
575, 604
583, 608
613, 658
575, 604
580, 607
613, 658
DPPCo (1)
neat Py (final)
−0.18
−0.24
−0.07
(Ph)DPPCo
(2)
CH2Cl2/2000
equiv of Py
neat Py (initial)
neat Py (final)
(Mes)DPPCo CH2Cl2/2000
(3)
equiv of Py
neat Py (initial)
neat Py (final)
6c 323,
461
a
b
CN = coordination numbers of 5c and 6c. Conversion between two
forms only occurs in neat pyridine (Py).
As shown in Table 2 and Figure 2, the major visible bands of
1−3 are red-shifted by 50 to 61 nm during the transformation
from 5c to 6c. Red shifts are also seen for the other bands. The
reaction rate constant for compound 3, which has an electron-
donating (mesityl) group on the meso position, is 0.07, which
is much smaller than the 0.24 value for compound 2 (Ph) and
the 0.18 value for compound 1 (F5Ph). The electron-donating
group decreases the rate of the transformation processes.
Considering the possible equilibrium between (DPP•2−)CoII
and (DPP3−)CoIII, the slow conversion from 5c to 6c can be
proposed to involve a change of the electronic configurations,
as shown in Scheme 2. The 5c form can be assigned to the
complex (DPP•2−)CoII(Py), while the 6c form corresponds to
the complex (DPP3−)CoIII(Py)2. All of the data suggest the
reactions in Scheme 2.
Figure 2. (a) UV−visible spectral changes of 3 (∼10−5 M) in
pyridine, from t = 0 (assigned as 5c) to 90 min (assigned as 6c), after
dissolution of the compound in solution. (b) Plot of the absorbance at
607 and 658 nm versus time (min). (c) Correlation between the
natural logarithm of the concentration of the initial 5c compound 3
versus time (min).
As seen in Figure 2a, the initial spectrum of 3 when
dissolved in pyridine has two major bands at 580 and 607 nm,
but after 90 min, the most intense band has shifted from 607 to
658 nm while the less intense band has disappeared. The initial
spectrum is assigned as a 5c form of DPPCo and the final
spectrum as a 6c form. Well-defined isosbestic points can be
seen at 506 and 624 nm in Figure 2, which indicate the
absence of a spectrally detectable intermediate between the 5c
and 6c forms on the time scale of the measurement. The
changes in absorbance at 607 nm for state 5c and at 658 nm
for state 6c are plotted versus time in Figure 2b, while Figure
2c shows a plot of ln [5c] versus time, which was calculated
from the absorbance band at 607 nm. As shown in Figure 2c,
there is a linear relationship between the natural logarithm of
the calculated concentration of the 5c reactant versus time,
with a slope of −0.07. The linearity of the slope indicates that
this transformation process involves a first-order chemical
reaction. Similar transformations also can be seen for
compounds 1 and 2, and a summary of the spectral data
under different solution conditions is given in Table 2, along
Scheme 2. Transformations among the 4c−6c Forms of
Compounds 1−3
To confirm the axial ligation of two pyridine molecules on
1
the DPPCo complexes, TGA (Figure S12) and H NMR
spectroscopy (Figure S1) were measured for the chemically
synthesized bis(pyridine)-ligated (F5Ph)DPPCo(Py)2
[1(Py)2]. According to TGA, the measured weight loss
(Δm) of the bis-ligated compounds was 21.0% compared to
the calculated value 22.3% for two pyridine molecules. More
evidence is given in the following DFT Calculations section of
the manuscript.
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Notably, 6c species can also partially exist in neat DMSO as
mentioned above. However, the complete transformation from
5c (with one axial DMSO molecule) to 6c (with two axial
DMSO molecules) species was not observed either in neat
DMSO or during the titration of DMSO in CH2Cl2. A
transformation from 5c to 6c was also not observed on the
experimental time scale during titration with pyridine.
compound 1 in the four utilized solvents is given in Figure
3, and a summary of measured potentials for the major redox
reactions of these three complexes is given in Table 3.
Table 3. Half-Wave or Peak Potentials (E1/2 or Ep, V vs
SCE) of DPPCo Complexes 1−3 in Four Solvents
Containing 0.1 M TBAP
Electrochemistry. The first step in characterizing the
electrochemistry of compounds 1−3 was to obtain cyclic
voltammograms in the coordinating and noncoordinating
solvents and then to relate changes in the observed redox
potentials to changes in the spectroscopic properties of the
neutral, electroreduced, and electrooxidized forms of the
compounds. As described on the following pages, two major
reductions and two major oxidations can be observed for DPP
derivatives, as schematically shown in Scheme 3.
potential (V vs SCE)
meso-
solvent
CH2Cl2
substituent
compd Ox 2
Ox 1
Red 1
Red 2
a
F5Ph
Ph
Mes
F5Ph
Ph
Mes
F5Ph
Ph
Mes
F5Ph
Ph
1
2
3
1
2
3
1
2
3
1
2
3
1.10
1.00
1.04
1.03
1.01
1.02
0.92
0.85
0.83
0.65
0.57
0.56
0.13
0.08
0.07
0.05
0.04
−1.40
−1.46
−1.52
−1.37
−1.51
−1.55
−1.30
−1.43
−1.46
−1.40
−1.52
−1.55
a
a
b
PhCN
DMSO
Py
0.56
b
0.51
b
0.51
0.02
0.46
0.44
0.41
0.54
0.48
0.49
−0.10
−0.13
−0.13
−1.02
−1.12
−1.16
Scheme 3. Major Redox Reactions of DPPCo Complexes
a
a
a
Mes
a
b
Peak potentials (Epc) for irreversible redox processes. Potentials
were taken from multiple scans at a scan rate of 500 mV s−1.
The DPPCo complex with tert-butyl groups was reported
earlier to undergo two reversible oxidations and one reversible
reduction in CH2Cl2 containing 0.1 M TBAP, all three of
which were assigned to electron transfers at the DPP ligand.1
However, the currently examined DPPCo complexes 1−3
show three or four oxidations and several reductions, with the
exact number depending on the specific electrochemical
solvent. An example of the cyclic voltammograms for
Solvent Effect on the Redox Potentials. As shown in Figure
3, the first reduction of compound 1, labeled as Red 1, shifts
from E1/2 = 0.13 V in CH2Cl2 to 0.05 V in PhCN and then to
−0.10 V in DMSO. Similar positive shifts of the potentials are
also seen for two major oxidations of compound 1 as well as
for the related redox reactions of compounds 2 and 3. As seen
in Figure 3, the cyclic voltammogram of compound 1 in
Figure 3. Cyclic voltammograms of compound 1 for the redox reactions in (a) CH2Cl2, (b) PhCN, (c) DMSO, and (d) pyridine containing 0.1 M
TBAP.
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Figure 4. Cyclic voltammograms of compound 1 (∼10−3 M) under different solution conditions: (a) at room temperature (r.t.), (b) at −60 °C in
CH2Cl2, (c) at r.t. in PhCN containing 100 equiv of added CH3I; (d) in PhCN without CH3I.
Figure 5. UV−visible spectral changes of compound 1 during the (a) first oxidation, (b) first reduction, and (c) second reduction in four different
solvents.
pyridine is quite different from the cyclic voltammograms in
the other three solvents; namely, there is one reversible
oxidation at E1/2 = 0.54 V, one irreversible reduction at Ep =
−1.02 V, and one reversible reduction at E1/2 = −1.40 V. The
earlier described spectroscopic data of compounds 1−3 in
pyridine suggest the binding of two Py axial ligands and a
proposed electron configuration of (DPP3−)CoIII(Py)2. This is
consistent with the electrochemical behavior of the three
compounds in this solvent.
Effect of Meso-Substituents. In all four solvents, compound
1 is easier to reduce and harder to oxidize than compounds 2
and 3 because of the highly electron-withdrawing F5Ph− group
on the meso-position of the dipyrrin ligand. For example, in
CH2Cl2, E1/2 for the first reduction is shifted positively by 50
mV compared with the same electrode reactions of compound
2, while an 80 mV positive shift is seen for the first oxidation of
compound 1. The substituent effect is even larger for the
second reduction in all four solvents. The difference in E1/2
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Scheme 4. Proposed Mechanism for Redox Reactions of the DPPCo Complexes 1−3 in Different Solvents (S = PhCN or
DMSO for 5c Complexes and Pyridine for 6c Complexes)
Figure 6. Spin-density plots for selected states of 4c 2: (a) state C; (b) state D; (c) state F; (d) state I; (e) state J. The states, indicated in capital
letters, are defined in Table 4.
between the second reductions of compounds 1 and 2 ranges
from 60 to 130 mV depending on the solvent.
Examples of the time-resolved spectral changes for compound
1 are given in Figure 5, and the proposed mechanism for all
major redox reactions of this compound is given in Scheme 4.
Although spectra of the neutral compounds vary with a
change of the solvent, the spectra of the one-electron-reduced
species (Figure 5b) are almost independent of the solvent and
are characterized by bands at 626−639 and 362−374 nm. The
similarity in the UV−visible spectra after the first electron
addition of each compound under different solution conditions
indicates that the electrophilic properties (binding properties)
of the four investigated solvents have little to no effect on the
one-electron-reduced species. According to the previous study
on a related cobalt dipyrrin complex,1 the reactant in the first
reduction can be assigned as (DPP•2−)CoII, which would then
be reduced to (DPP3−)CoII, as shown in Scheme 4.
The spectra of the two-electron-reduced species (Figure 5c)
are also identical with each other in PhCN, DMSO, and
pyridine but not in CH2Cl2, where, as indicated by the cyclic
voltammetry curves, a chemical reaction occurs between the
doubly reduced DPP derivatives and the solvent. During the
second reduction, the intense visible bands of the one-electron-
reduced species at 626−639 nm decrease in intensity while
“Extra” Reductions in CH2Cl2. Unlike in other solvents, the
second reduction of compounds 1−3 in CH2Cl2 is irreversible,
and an additional irreversible reduction is observed at more
negative potential. A similar irreversibility is also seen upon
reduction of cobalt(II) porphyrins15,33 and electrogenerated
cobalt(II) corroles34 in CH2Cl2, and this was explained by a
chemical reaction between the low-oxidation-state electron-
reduction product and the CH2Cl2 solvent.
Cyclic voltammograms illustrating the reduction of com-
pound 1 under different solution conditions are given in Figure
4. As seen in the figure, an extra reduction is not observed at
−60 °C in CH2Cl2 compared to that seen at room
temperature, and it is also not observed in PhCN where the
doubly reduced dipyrrin complexes are stable. The cyclic
voltammogram at −60 °C in CH2Cl2 is quite similar to that in
PhCN, providing evidence for a reaction of the doubly reduced
species with the CH2Cl2 solvent.
Spectroelectrochemical Studies. The spectral changes
that occurred during each redox reaction were monitored by
UV−visible spectroelectrochemistry in the different solvents.
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Table 4. Selected DFT Results for the 4c−6c States of 2
c
all-electron occupations (α//β)
Erel (eV)
B3LYP-
D3
a
b
state CN point group
q
S
a1
a2
b1
b2
description
OLYP
B3LYP
A
B
C
D
E
F
G
H
I
4c
C2v
0
0
0
0
0
1
0
54//54
54//53
54//53
54//54
54//53
54//54
54//53
54//53
54//54
54//53
54//54
8//8
8//9
9//8
9//8
9//8
8//8
8//8
9//8
9//8
9//9
9//9
39//39
39//39
39//39
39//39
40//39
39//39
39//39
39//39
39//39
39//39
39//39
17//17
17//17
17//17
17//16
17//16
17//16
17//17
17//16
17//17
17//17
17//16
LS Co(III)
0.136
0.180
0.043
0.000
0.662
6.031
6.027
6.462
−2.489
−2.322
−1.947
0.707
0.033
0.000
0.100
0.361
6.345
6.198
6.643
−2.673
−2.714
−2.392
0.704
0.033
0.000
0.098
0.363
6.342
6.160
6.638
−2.653
−2.712
−2.391
21
0
1
1
LS dz Co(II), L(•2−); antiferro
21
LS dz Co(II), L(•2−); ferro
IS Co(III), L(3−)
2
IS Co(II), L(•2−); ferro
IS Co(III), L(•2−); antiferro
1
/
2
2
2
2
2
2
1
3
1
1
1
21
1
/
/
/
/
/
LS dz Co(II), doubly oxidized L(−)
1
IS Co(III), L(•2−); ferro
1
−1
−1
−1
LS dπ Co(II), L(3−)
21
J
LS dz Co(II), L(3−)
1
K
LS dπ′ Co(II), L(3−)
all-electron occupations
c
(α//β)
Erel (eV)
a
b
state
CN
point group
q
S
a′
a′′
description
OLYP
B3LYP
B3LYP-D3
L
5c
Cs
0
0
0
0
0
0
1
83//83
84//83
84//83
84//82
83//83
84//83
84//82
84//83
56//56
55//56
56//55
57//55
56//55
55//55
56//55
56//56
LS Co(III)
0.442
0.208
0.000
0.482
6.026
5.692
5.984
−2.070
0.441
0.054
0.000
0.188
6.232
0.343
0.076
0.000
0.217
6.149
5.904
6.227
−2.489
21
M
N
O
P
LS dz Co(II), L(•2−); antiferro
21
LS dz Co(II), L(•2−); ferro
2
HS Co(II), L(•2−); ferro
LS Co(III), L(•2−)
1
1
/
2
1
21
Q
R
S
1
/
LS dz Co(II), doubly oxidized L(−)
5.897
2
3
1
/
IS Co(III), L(•2−); ferro
6.229
2
1
21
−1
/
LS dz Co(II), L(3−)
−2.486
Erel (eV)
2
c
all-electron occupations (α//β)
a
b
state CN
point group
q
S
a1
a2
b1
b2
description
OLYP
B3LYP
B3LYP-D3
T
U
V
6c
C2v
0
0
1
0
1
71//71
72//71
71//71
72//71
12//12
12//11
12//11
12//12
42//42
42//42
42//42
42//42
35//35
35//35
35//35
35//35
LS Co(III), L(3−)
IS Co(III), L(3−)
LS Co(III), L(•2−)
0.069
0.000
5.426
0.000
0.306
5.518
−1.957
0.000
0.387
5.528
−1.728
1
/
2
1
21
W
−1
/
LS dz Co(II), L(3−)
2
a
b
c
CN = coordination number. ferro = ferromagnetically coupled; antiferro = antiferromagnetically coupled. The energy zero level for each
molecule and each functional is indicated in boldface.
new bands grow in at 511−515 nm. The decrease in the
intensity of the major absorption bands indicates a loss of
conjugation in the DPP ligand upon the second electron
addition. At the same time, new bands at 803−809 nm are
seen in the spectra when measured in PhCN, DMSO, or
pyridine, and those bands can be considered to be diagnostic
criteria for a redox reaction involving the ligand.
DFT Calculations. Spin-unrestricted DFT calculations
were undertaken for 2 to aid in the assignment of the neutral,
cationic, and anionic states, as well as to evaluate the issue of
ligand noninnocence and potential similarities with cobalt
corroles. Three different, well-tested methods were employed:
OLYP, B3LYP, and B3LYP-D3. Appropriate symmetry
constraints were used for the 4c form (C2v), monopyridine-
ligated 5c form (Cs), and bis(pyridine)-ligated 6c form (C2v) so
as to allow for an examination of different electronic
configurations with different numbers of electrons in each
irreducible representation. The results allow for a number of
insights, which are shown in Figures 6−8, Table 4, and Figures
S13−S15.
Co(II) states are easily discernible in the spin-density plots by
2
a dz -shaped blob on the Co center. Note also the characteristic
bond distance alternations on the ligand in states with DPP•2−
radicals (Figure S13).
For the 4c cationic complex, the calculations suggest two
possible candidates for the ground state. The first is a low-spin
Co(II) state with a doubly oxidized DPP ligand (state G). The
second is an intermediate-spin Co(III) state with a
2
22
1
1
dxy dz dxz dyz configuration with some spin delocalization to
the ligand (state F, Figure 6c). The reader may verify that a
dimple in the z direction at the Co atom in the spin-density
plot is consistent with the absence of an unpaired electron in
2
the Co dz orbital.
For the neutral 5c complex, the calculations indicate a
ferromagnetically coupled, S = 1 CoIIDPP•2− state with a high
degree of certitude (based on the mutual consistency of the
three DFT methods), with the corresponding antiferromag-
netically coupled state a couple of tenths of an electronvolt
higher (state N, Figure 7a). An analogous electronic
configuration, albeit with antiferromagnetic coupling, has also
been considered plausible for 5c cobalt corrole monopyridine
adducts (state M, Figure 7b). The preference for ferromagnetic
coupling in the present compound is thought to be a reflection
of the relative orthogonality of the Co 3d orbitals and the
ligand highest occupied molecular orbital.
The calculations clearly indicate S = 1 states as the key
contenders for the ground state of the neutral 4c complex, viz.,
a low-spin Co(II) state with a ferromagnetically coupled
DPP•2− radical (state C, Figure 6a) and an intermediate-spin
Co(III) state with an antiferromagnetically coupled DPP•2−
radical (state D, Figure 6b). The reader may note that low-spin
H
DOI: 10.1021/acs.inorgchem.8b03006
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. Spin-density plots for selected states of 5c 2(Py): (a) state
N; (b) state M; (c) state Q; (d) state S. The states, indicated in
capital letters, are defined in Table 4.
Figure 8. Spin-density plots for selected states of 6c 2(Py)2: (a) state
U; (b) state V. The states, indicated in captal letters, are defined in
Table 4.
In view of the difficulty of describing long-range charge-
transfer excitations in metallocorroles with time-dependent
DFT calculations, we have refrained from undertaking such
calculations in the present study. However, the presence of a
significant quantity of spin density at the meso-C in several of
the DPPCo states examined is qualitatively consistent with our
finding that meso substituents indeed have a significant
influence on the UV−visible spectra.
For the cationic 5c complex, the different calculational
methods also proved mutually consistent, predicting a Co(II)
center in association with a doubly oxidized ligand, a possibility
that has also been entertained for 5c cobalt corrole cations
(albeit without explicit computational support; state Q, Figure
7c).
For the 6c complex, the calculations unsurprisingly predict a
low-spin Co(III) center for the neutral state (state U, Figure
8a) and a low-spin Co(III) center associated with a ligand
radical for the cation (state U, Figure 8b). Thus, binding of a
second pyridine results in a major electronic reorganization
from a (DPP•2−)CoII state to a low-spin Co(III) state, which
may explain the slow spectral change observed upon
dissolution of the 4c complex in pyridine.
EPR Spectroscopy. In order to directly assess the
electronic spin state, EPR experiments were run at 293 and
100 K in dichloromethane (Figure S16) for 3. At 293 K,
compound 3 gave an almost silent spectrum (Figure S16a),
indicating that the cobalt complex is either in a diamagnetic
Co(III) form or that it has an S = 0 spin state due to a strong
antiferromagnetic coupling between Co(II) and the anion
radical in the cobalt(II) corrole(2•−) formalism. After cooling
to 100 K (Figure S16b), a radical-like pattern centered at g =
2.012 appears with a large broadening and a multiline
morphology due to the hyperfine coupling of the single
electron with the Co center. At least 7 of the 8 theoretical
For the anionic 4c complex, the calculations indicate two
potential contenders for the ground state, both of which may
be described as low-spin Co(II) (states I and J, Figure 6d,e). In
2
one of the them, the unpaired electron resides in the Co(dz )
orbital (state J, Figure 6e), whereas in the other, the unpaired
electron occupies an a2-symmetry Co dπ orbital (state J, Figure
6e). For the 5c and 6c anions (states S and W), in contrast, the
calculations exhibit a much clearer preference for a low-spin
7
expected lines (ICo = /2) are observed. Then it seems clear
that the cobalt(II) corrole(2•−) formalism is favored with an
electron delocalization over both the ligand and metal center.
After the addition of pyridine, a spectral shape typical of a
radical complex centered at g = 2.004 is obtained (Figure
S16c), with a small broadening of the single line (fwhh ≈ 7 G).
This central line is probably assigned to a radical impurity
because of overoxidation of 3 in the presence of strong axial
donors like pyridine, with the six-coordinate 3(Py)2 being
more oxidizable than the four-coordinate 3. In addition, this
line is flanked by one broad signal with a low intensity at the
left side of the radical signal, which is assigned to the excited
triplet state, with the second transition band being overlapped
by the more intense radical line. The low intensity of the triplet
state agrees with a large singlet−triplet gap, inducing a weak
2
Co(II) state with the unpaired electron in the Co dz orbital.
B3LYP-D3 calculations do, however, indicate significantly
elongated Co−Npy bond distances of 2.228 Å for the 5c anion
(Figure S14d for B3LYP) and 2.323 Å for the 6c anion,
compared with a distance of 1.989 Å for the 6c, low-spin
Co(III) neutral state (with the corresponding B3LYP distances
for the three states being 2.309, 2.460, and 2.010 Å,
respectively). There is thus a good chance that pyridines are
essentially detached in the anionic 6c state and a 4c or 5c low-
21
spin dz Co(II) state is the dominant anionic form under
experimental conditions, in agreement with our conclusions
based on UV−visible spectroelectrochemical measurements.
I
DOI: 10.1021/acs.inorgchem.8b03006
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
bridge of low porosity, which contained the solvent/supporting
electrolyte mixture. All potentials measured by cyclic voltammetry
were referenced to the SCE.
thermally accessible excited triplet state. This result is
confirmed by recording the EPR spectrum at 100 K that
shows a very low intensity of the lines assigned to the triplet
state (Figure S16d).
Crystal Structure Analysis. Single clear dark-violet
needle-shaped crystals of 1 were recrystallized from a mixture
of chloroform and heptane with 1 drop of aqueous NH4OH by
slow evaporation. An X-ray diffraction experiment was carried
out to determine the crystallographic structure (Figure 9). As
Spectroscopically monitored titrations with acid or base were
carried out in a 1.0 cm glass cell. Thin-layer UV−visible
spectroelectrochemical experiments were carried out with the
Honeycomb spectrochemical cell by Pine Research Instrumentation.
Potentials were applied and monitored with an EG&G PAR model
173 potentiostat. Time-resolved UV−visible spectra were recorded
with a Hewlett-Packard model 8453 diode-array spectrophotometer.
High-purity N2 from Trigas was used to deoxygenate the solution and
kept over the solution during each electrochemical and spectroscopic
experiment.
1
CDCl3 and C6D6 were used as solvents for the H NMR spectra,
which were recorded on a Bruker AVANCE III spectrometer (500
MHz). The measurements were made at the PACSMUB-WPCM
technological platform, which relies on the Institut de Chimie
́
́
Moleculaire de l’Universite de Bourgogne and Welience TM, a
Burgundy University private subsidiary. Chemical shifts were
expressed in parts per million. NH3·H2O was added to enhance the
resolution of the spectra. MS spectra were recorded on a Bruker
Ultraflex Extreme MALDI Tandem TOF mass spectrometer using
DCTB as the matrix or on a LTQ Orbitrap XL (Thermo) instrument
in the ESI mode (for the HR-MS spectra). Low-resolution MS
(LRMS) spectra were recorded on a Thermo Scientific MSQ Plus
single quadrupole mass spectrometer equipped with an ESI source. All
LRMS spectra were recorded in the positive mode (ESI+) using the
following parameters: full scan, 250−1250 amu; data type, centroid;
needle voltage, 3.0 kV; detector voltage, 1100 V; probe temperature,
350 °C; cone voltage, 10 or 75 V; scan time, 1 s. Sample preparation:
cobalt dipyrrins were prepared in tetrahydrofuran (THF) and were
directly analyzed by ESI-MS (direct infusion mode with a syringe
pump; cone voltage, 75 V). To assess the chelation of NH3 and
pyridine molecules, 2 μL of an aqueous NH3 solution (25% in water,
v/v) or pyridine was added to a dilute sample prior to injection
through a direct infusion mode (cone voltage, 10 V). Thermogravi-
metric analyses (TGA) were recorded using a Netzsch STA 409 PC
thermal analyzer. The samples were heated from 298 to 1273 K with a
heating rate of 10 K min−1 under a flow of nitrogen (30 mL min−1)
and oxygen (10 mL min−1). The measurements were made at the
PACSMUB-WPCM technological platform. Continuous-wave EPR
spectra were recorded on a Bruker ELEXSYS 500 spectrometer. The
instrument was equipped with a 4122 SHQE/0405 X-band resonant
cavity operating at 9.43 GHz, a X-band high-power dual gun-oscillator
bridge, and a quartz cryostat. The experiments were run at 293 or 100
K with a stream of nitrogen. The temperature was regulated with an
ER 4131VT accessory. All apparatuses as well as the data acquisition
were controlled using Xepr software. The magnetic field was swept
from 250 to 360 mT through 2048 points. Spectra were recorded at 6
mW power, 100 kHz frequency modulation, 0.5 mT modulation
amplitude, 10 ms time constant, and 40 ms conversion time. Samples
were dissolved in dichloromethane and spectra recorded in both
liquid (293 K) and frozen (100 K) solutions, before and after the
addition of 1 drop of pyridine.
Figure 9. ORTEP view of compound 1. Thermal ellipsoids are
depicted at 50% probability. The water molecule and disordered
chloroform are omitted for clarity.
seen in the figure, 1 was crystallized in a C2/c centrosymmetric
group with a water molecule and a disordered chloroform
molecule (Figure S16). The six-coordinate DPPCo complex
was found to coordinate with both the N and O atoms of the
DPP unit and two axial ammonia ligands, which are in the
apical position. Detailed information for the crystallographic
data collection and refinement are given in the Supporting
Information.
As shown in Figure 9, the octahedral geometry is similar to
that reported in a previous publication for bis(ammonia)-
coordinated cobalt corrole complexes,32 and this gives
additional evidence that DPP is an analogue to the corrole
ligand. In order to make this comparison in detail, the
geometric parameters of both structures, (F5Ph)DPPCo-
(NH3)2 in this work and (o,o-Cl2Ph)3CorCo(NH3)2 in the
previous publication,32 are given in Table 5. Despite structural
differences between the two ligands (dipyrrinbisphenol and
corrole), the distances and bond angles in the two cobalt
complexes are of the same order of magnitude as those seen in
the table. DPP is shown to be an excellent analogue of corrole,
and it is thus expected to form some similar metal complexes.
Synthesis of Compound 1. Compound 1 was prepared in 94%
yield (44.0 mg, 80.0 μmol). Starting from free-base pentafluor-
ophenyl−dipyrrin−bisphenol (42.1 mg, 85.2 μmol),6 triethanolamine
(34.4 μL) and a solution of Co(OAc)2·4H2O (21.2 mg, 85.2 μmol) in
5 mL of a mixture of methanol/chloroform (1:3) were mixed with 26
mL of a mixture of methanol/chloroform (1:3) at room temperature
overnight. Then water was added (30 mL), and the product was
extracted with chloroform, dried over MgSO4, and evaporated to
EXPERIMENTAL SECTION
■
Chemicals. Dichloromethane (CH2Cl2, 99.8%) from EMD
Chemicals Inc. was used for electrochemistry without further
purification. Benzonitrile (PhCN) was purchased from Sigma-Aldrich
Chemical Co. and distilled over P2O5 under vacuum prior to use.
Dimethyl sulfoxide (DMSO), pyridine (Py; HPLC), and tetra-n-
butylammonium perchlorate (TBAP), used as the supporting
electrolyte, were purchased from Sigma-Aldrich Chemical Co.
Instrumentation. Cyclic voltammetry was carried out with an
EG&G model 173 potentiostat/galvanostat. A homemade three-
electrode electrochemistry cell was used, consisting of a glassy carbon
working electrode (diameter = 0.3 mm), a platinum wire counter
electrode, and a saturated calomel reference electrode (SCE). The
SCE was separated from the bulk of the solution by a fritted-glass
1
dryness under vacuum. H NMR (300 MHz, CDCl3 + 1 drop of
ΝΗ3·Η2Ο): δ 7.53 (d, 2H, J = 7.0 Hz), 7.39 (d, 2H, J = 8.0 Hz), 7.13
(m, 4H), 6.81 (d, 2H, J = 4.0 Hz), 6.64 (t, 2H, J = 7.0 Hz), 1.75 (brs,
6H, 2NH3 ). MS (MALDI-TOF, DCTB). Calcd for
C27H12CoF5N2O2: m/z550.01. Found: m/z 549.68 ([M]•+). HR-
MS (ESI). Calcd for C27H12CoF5N2O2: m/z 550.0145. Found: m/z
550.0129 ([M]•+). MS (ESI, THF + 1 drop of NH3·H2O). Calcd for
C27H13CoF5N2O2: m/z 551.0 Found: m/z 551.1 ([M + H]+). Calcd
J
DOI: 10.1021/acs.inorgchem.8b03006
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 5. Comparison of Selected Geometric Distances (Å) and Angles (deg) of Compound 1 and the Previous Cobalt Corrole
Complex32
for C27H13CoF5N2O2·2NH3: m/z 585.2 ([M + H + 2NH3]+). Found:
m/z 585.1. MS (ESI, THF + 1 drop of pyridine). Calcd for
C27H12CoF5N2O2·1py: m/z 629.1. Found: m/z 629.1 ([M + py]•+).
Calcd for C27H12CoF5N2O2·2py: m/z 708.1. Found: m/z 708.0 ([M
+ 2py]•+).
mesityl−dipyrrin−bisphenol8 (25.5 mg, 57.7 μmol) and Co(OAc)2·
4H2O (24.6 mg, 57.7 μmol). 1H NMR (300 MHz, CDCl3 + 1 drop of
NH3·H2O): δ 7.52 (d, 2H, J = 7.5 Hz), 7.35 (d, 2H, J = 8 Hz), 7.09
(m, 2H), 7.01 (d, 2H, J = 4.5 Hz), 6.96 (s, 2H), 6.73 (d, 2H, J = 4.5
Hz), 6.60 (t, 2H, J = 7.5 Hz), 2.37 (s, 3H), 2.07 (s, 6H), 1.78 (brs,
6H, 2NH3). MS (MALDI-TOF, DCTB). Calcd for C30H23CoN2O2:
m/z 502.11. Found: m/z 501.79 ([M]•+). HR-MS (ESI). Calcd for
C30H23CoN2O2: m/z 502.1086. Found: m/z 502.1075 ([M]•+). MS
(ESI, THF + 1 drop of NH3·H2O). Calcd for C30H24CoN2O2: m/z
503.1. Found: m/z 503.0 ([M + H]+). Calcd for C30H23CoN2O2·
2NH3: m/z 537.2. Found: 536.9 ([M + 2NH3]•+). MS (ESI, THF + 1
drop of pyridine). Calcd for C30H24CoN2O2·1py: m/z 582.2. m/z
582.3 ([M + H + py]•+). Calcd for C30H24CoN2O2·2py: m/z 661.2.
Found: m/z 661.3 ([M + H + 2py]+).
Single-Crystal X-ray Diffraction. All experimental data are
detailed in the Supporting Information. CCDC 1880078 for
compound 1, containing the supplementary crystallographic data for
this paper, can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
Synthesis of the 1(Py)2 Complex. Compound 1 (10 mg) was
dissolved in dichloromethane (10 mL), 2 drops of pyridine were
added, and the solution was evaporated. 1H NMR (300 MHz, C6D6):
δ 8.43 (brs, 4H, py), 7.96 (brs, 2H), 7.63 (brs, 2H), 7.31 (brs, 4H),
6.86 (brs, 2H), 6.71 (brs, 2H), 6.34 (brs, 2H, py), 6.08 (brs, 4H, py).
Pyridine content determined by TGA (see Figure S11): Δm (calcd for
2 py ligated) = 21.0% (calcd 22.3%). Tonset = 55 °C. Tend = 240 °C.
Synthesis of Compound 2. Compound 2 was prepared in 86%
yield (39.1 mg, 84.9 μmol), as described for 1, starting from free-base
phenyl−dipyrrin−bisphenol (40.0 mg, 98.9 μmol)8 and Co(OAc)2·
4H2O (14.4 mg, 98.9 μmol). 1H NMR (300 MHz, CDCl3 + 1 drop of
NH3·H2O): δ 7.50 (m, 7H), 7.39 (d, 2H, J = 7.5 Hz), 7.10 (m, 4H),
6.93 (m, 2H), 6.63 (m, 2H), 1.72 (brs, 6H, 2NH3). MS (MALDI-
TOF, DCTB). Calcd for C27H17CoN2O2: m/z 460.06. Found: m/z
459.69 ([M]•+). HR-MS (ESI). Calcd for C27H17CoN2O2: m/z
460.0617. m/z 460.0609 ([M]•+). MS (ESI, THF + 1 drop of NH3·
H2O). Calcd for C27H17CoN2O2: m/z 460.1. Found: m/z 460.1
([M]•+). Calcd for C27H18CoN2O2·2NH3: m/z 495.1. Found: m/z
495.0 ([M + H + 2NH3]+). MS (ESI, THF + 1 drop of pyridine).
Calcd for C27H17CoN2O2·1py: m/z 539.1. Found: m/z 539.0 ([M +
py]•+). Calcd for C27H17CoN2O2·2py: m/z 618.2. Found: m/z 618.2
([M + 2Py]•+).
CONCLUSION
■
In summary, three cobalt dipyrrin−bisphenol complexes with
different meso-aryl substituents have been synthesized, and
their spectroscopic and electrochemical properties character-
ized in both noncoordinating and coordinating solvents. The
various charge, spin, and axial ligation states have also been
examined by means of DFT calculations. The experimental and
Synthesis of Compound 3. Compound 3 was prepared in 94%
yield (27.1 mg, 53.9 μmol), as described for 1, starting from free-base
K
DOI: 10.1021/acs.inorgchem.8b03006
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
computational studies, together, afford detailed insight into the
question of ligand noninnocence in the DPPCo complexes.
The facile reduction potentials (E1/2 ∼ 0.0 V vs SCE) of the
complexes in noncoordinating (CH2Cl2) and weakly coordi-
nating (PhCN and DMSO) solvents are suggestive of a
(DPP•2−)CoII formulation for the neutral complexes, a
conclusion that is consistent with the DFT calculations. This
contrasts with that seen in pyridine, where the complexes are
reduced at significantly more negative potentials (E1/2 ∼ −1.0
V), thus indicating a 6c low-spin Co(III) center that is quite
resistant to reduction. The fact that the one-electron-reduced
state exhibits similar optical spectra in all four solvents appears
to indicate a common 4c or 5c (DPP3−)CoII state throughout,
again consistent with the DFT calculations. Our spectral
studies do not allow a definitive assignment of the cationic
states. DFT calculations, however, indicate a (DPP−)CoII state
with a doubly oxidized DPP ligand for the 5c complexes and a
(DPP•2−)CoIII state with a low-spin Co(III) center for the 6c
complexes. A ferromagnetically coupled, S = 1 (DPP•2−)CoII
description for the 5c monopyridine complex also provides an
explanation for the observed slow binding of a second pyridine
ligand, leading to the 6c low-spin cobalt(III) bis(pyridine)
complex.
Jeanet Conradie: 0000-0002-8120-6830
Abhik Ghosh: 0000-0003-1161-6364
Claude P. Gros: 0000-0002-6966-947X
Karl M. Kadish: 0000-0003-4586-6732
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Support was provided by the Robert A. Welch Foundation (to
K.M.K. under Grant E-680), the CNRS (Grant UMR UB-
CNRS 6302), the Research Council of Norway (to AG under
́
́
Grant 262229), the Universite de Bourgogne Franche-Comte,
the FEDER-FSE Bourgogne 2014/2020 (European Regional
́
Development Fund), and the Conseil Regional de Bourgogne
through the PARI II CDEA project. The authors also warmly
thank Prof. Anthony Romieu (IUF, UBFC, ICMUB, UMR
CNRS 6302) for recording the LRMS ESI spectra of cobalt
dipyrrin complexes.
REFERENCES
■
(1) Kochem, A.; Chiang, L.; Baptiste, B.; Philouze, C.; Leconte, N.;
Jarjayes, O.; Storr, T.; Thomas, F. Ligand-Centered Redox Activity in
Cobalt(II) and Nickel(II) Bis(phenolate)-Dipyrrin Complexes. Chem.
- Eur. J. 2012, 18, 14590−14593.
The (DPP•2−)CoII, (DPP3−)CoII, and (DPP−)CoII formu-
lations of the neutral, anionic, and cationic states of the 5c
complexes exactly parallel the (Cor•2−)CoII, (Cor3−)CoII, and
(Cor−)CoII formulations proposed for the analogous charged
states of 5c CorCo monopyridine adducts. The ground-state
(DPP•2−)CoII description is analogous to that proposed for
CorCo, CorCo(PPh3), and CorCo(CO), as well as to that for
the MnCl, FeCl, FeNO, Fe2(μ-O), Cu, and Pt corrole
derivatives.11 These extensive parallels between DPP and
corrole potentially presage a bright future for transition-metal
DPP complexes in areas such as catalytic transformations and
small molecule sensing, where metallocorroles are already
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03006.
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1H NMR and MS spectra for 1−3, UV−visible spectral
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Accession Codes
CCDC 1880078 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: abhik.ghosh@uit.no.
*E-mail: Claude.Gros@u-bourgogne.fr.
*E-mail: kkadish@uh.edu.
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ORCID
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Stephane Brandes: 0000-0001-6923-1630
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DOI: 10.1021/acs.inorgchem.8b03006
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