Halogen substituted A2B type Co(III)triarylcorroles: Synthesis, electronic structure and two step modulation of electrocatalyzed hydrogen evolution reactions

Article abstract of DOI:10.1016/j.dyepig.2017.02.049

Seven low symmetry A₂B type Co(III)triarylcorroles with electron withdrawing meso-aryl substituents have been synthesized and characterized. A detailed analysis of the optical and redox properties has been carried out by comparing their optical

Full text of DOI:10.1016/j.dyepig.2017.02.049

Accepted Manuscript
Halogen substituted A B type Co(III)triarylcorroles: Synthesis, electronic structure
2
and two step modulation of electrocatalyzed hydrogen evolution reactions
Yingjie Niu, Minzhi Li, Qianchong Zhang, Weihua Zhu, John Mack, Gertrude Fomo,
Tebello Nyokong, Xu Liang
PII:
S0143-7208(16)31492-9
10.1016/j.dyepig.2017.02.049
DYPI 5894
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 27 December 2016
Revised Date: 18 February 2017
Accepted Date: 20 February 2017
Please cite this article as: Niu Y, Li M, Zhang Q, Zhu W, Mack J, Fomo G, Nyokong T, Liang X,
Halogen substituted A B type Co(III)triarylcorroles: Synthesis, electronic structure and two step
2
modulation of electrocatalyzed hydrogen evolution reactions, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.02.049.
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ACCEPTED MANUSCRIPT
Halogen Substituted A2B Type Co(III)Triarylcorroles: Synthesis, Electronic
Structure and Two Step Modulation of Electrocatalyzed Hydrogen Evolution
Reactions
Yingjie Niu,†,# Minzhi Li,†,# Qianchong Zhang,†† Weihua Zhu*,† John Mack*,‡ Gertrude Fomo‡
Tebello Nyokong,‡ and Xu Liang*,†
†School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R.
China; ‡ Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa. ††State
Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005, P.
R. China
Corresponding Author
liangxu@ujs.edu.cn (X. L.); sayman@ujs.edu.cn (W. Z.); J.Mack@ru.ac.za (J. M.)
Author Contributions
# These authors contributed equally.
Keyword. A2B Corrole, Electronic Structure, TD-DFT Calculation, HER Reaction
Abstract
Seven low symmetry A2B type Co(III)triarylcorroles with electron withdrawing meso-aryl
substituents have been synthesized and characterized. A detailed analysis of the optical and
redox properties has been carried out by comparing their optical spectroscopy, electrochemistry
and spectroelectrochemistry to trends predicted in a series of DFT and TD-DFT calculations.
The results demonstrate that Co(III)corroles are highly effective catalysts for hydrogen evolution
reactions (HERs). Moreover, there is a marked enhancement in their homogenous catalytic
ability when halogen atoms are introduced at the B position, which demonstrates that facile
modifying the meso-aryl rings is a effective strategy for developing new HER catalysts. The
electrochemical results demonstrate that an unusual two step modulation of HER reactions can
be achieved by using singly and doubly electrochemical reduced cobalt triarylcorroles anions.
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Introduction
Metallo-corroles are ring-contracted porphyrin analogues with the presence of a direct
pyrrole-pyrrole bond, that have attracted significant interest in recent decades, due to the
stabilization of high-valence metal ions by various meso- and/or β-substituted ligands.[1] The
interest in corrole coordination chemistry is driven by the unusual structures and topologies of
these molecules[2] but also by their interesting properties, such as their electronic structures[3] and
magnetism[4], and potential applications such as bioimaging[5], biosensors[6], organocatalysis[7]
and electrocatalysis[8]. On the other hand, clean renewable energy sources that do not increase
atmospheric carbon dioxide levels are required to meet the ever increasing global demand for
energy. The use of hydrogen for energy storage so that supply from renewable energy sources
can be balanced with demand through the use of fuel cells has many advantages in this regard
and is widely considered to be the next generation energy source that will replace the use of
fossil fuels in many contexts.[9] There has been increasing interest in hydrogen evolution
reactions (HERs) that involve the electrochemical reduction of protons, due to the convenient
procedures that are involved and the availability of catalytic materials to convert electrical
energy to chemical energy through the generation of H2 gas[10]. Although platinum enables
highly efficient electrocatalysis, the use of less-expensive and more abundant transition metals
would be preferable.
Recent research interest has shown that complexes containing high-valent metal-centers
such as iron[11], cobalt[12], nickel[13] and molybdenum[14] are redox active for HER catalysis, but
their low catalytic efficiencies and insufficient stability in the concentrated acid environments
that are used in this context has limited further development of this field of research[15]
.
Although modulation of electrocatalyzed HER reactions has recently been reported for singly or
doubly reduced nickel porphyrin anions[13b], similar behavior has yet to be reported for
metallo-corroles. The key advantage of using corroles is that a trianionic ligand is formed when
a meso-carbon is removed from the porphyrin structure, which stabilizes the higher oxidation
states of first row transition metals, such as Co(III). The redox properties of corrole complexes
can be readily fine-tuned by modifying the meso-aryl rings, since corroles are formed by reacting
a meso-aryldipyrromethane with pyrrole and an appropriate arylaldehyde. This means that A2B
type low symmetry corroles (Scheme 1) are obvious candidates to study how the efficiency of
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HERs can be enhanced, since they can be easily be modified at the B meso-position by reacting a
series of different arylaldehydes with the meso-aryldipyrromethane precursor (Scheme 1). The
introduction of strongly electron-withdrawing halogen atoms is one possible approach, in this
regard. In this manuscript, the synthesis of a series of A2B type Co(III) corroles with different
halogenated meso-aryl groups at the B position, along with their structural characterizations, and
an analysis of their electronic structures and two steps modulation of HER reactions is described.
Results and Discussions
Free base corroles (2a-g) were synthesized according to literature procedures from a
reaction of dipyrromethane 1 and an arylaldehyde (Scheme 1)[16]. Co(III)PPh3 corroles (3a-g)
were then synthesized by a metal-insert reaction of 2a-g, cobalt acetate salt and
triphenylphosphine, and were purified by silica gel column chromatography and recrystallization.
MALDI-TOF MS for 3a revealed an intense parent peak at m/z = 672.21 (calcd. [M-PPh3]+ =
672.53), providing direct evidence that the Co(III)PPh3-5,15-(m-nitrophenyl)-10-phenylcorrole
target compound was successfully prepared. Similar parent peaks were observed for 3b-g.
The proton signals for the meso-substituents and pyrrole rings in the 1H NMR spectra of 3a-g lie
beyond 7.40 ppm, while the other three signals at 7.10, 6.70 and 4.50 ppm can be assigned to the
triphenylphosphine axial ligand (Figure S1). 19F NMR spectra contain a singlet peak at
−111.83 ppm for 3d, a triplet peak at −109.92 ppm for 3f, and a group of peaks at
−137.42~−138.05, −151.99, and −160.57 ppm for 3g which is consistent with the presence of
one, two, and five fluorine atoms, respectively (Figure S2).
The structure of the
Co(III)PPh3-corrole was unambiguously elucidated through an X-ray structural analysis on
single crystals of 3e obtained through the slow diffusion of hexane into a toluene solution
(Figure 1). The crystal adopts the Pca21 space group. The structure of 3e is similar to that of
metallotriarylcorrole[17], which also has a five-coordinate Co(III) ion. There is a small degree
of nonplanarity in the corrole ligand, which can be attributed to steric hindrance due to crystal
packing.
Optical spectra and TD-DFT calculations
When compared to the Q band absorption of Co(III)-triphenyl-corroles,[18] the introduction
of electron-withdrawing m-nitrophenyl substituents at the A2 5,15-positions results in a sizeable
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blue-shift of the Q band (3a: 561 and 584 nm, 3b: 562 and 586 nm, and 3c: 560 and 588 nm),
which depends on the electron-withdrawing ability of the meso-aryl rings (Figure 2). The
electronic structure and optical spectroscopy of porphyrinoids can be readily understood by using
Gouterman’s 4-orbital model[19] and Michl’s perimeter model[20] as conceptual frameworks,
through a consideration of the structural perturbations that are made to the molecular orbitals
(MOs) of a C16H162− parent hydrocarbon perimeter. The MOs are arranged in an ML = 0, ±1, ±2,
±3, ±4, ±5, ±6, ±7, 8 sequence in ascending energy in terms of their angular nodal properties.
The highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO)
have ML values of ±4 and ±5. Michl[19] referred to π-MOs derived from the HOMO and
LUMO of the parent perimeter with angular nodal planes that lie on the y-axis as a and -a,
respectively, while the corresponding MOs that have y-axis atoms with significant MO
coefficients are referred to as the s and -s MOs (Figure 3). This terminology facilitates the
comparison of trends observed in the MO energies of complexes of differing symmetries. The
four spin-allowed transitions between the a, s, -a and -s MOs provide the basis for Gouterman’s
4-orbital model, which consists of an allowed B transition (ꢀML = ±1) and a forbidden Q
transition (ꢀML = ±9).
In the context of 3a-g, introduction of a Co(III) ion with a d6 metal ion is predicted to introduce
an MO with significant 3dz2 character as the LUMO, while the s and a MOs have very similar
energies and form the HOMO and HOMO−1. The introduction of different B position
meso-aryl substituents is predicted to make relatively little difference to the energies of the
frontier MOs and hence the magnitudes of the HOMO−LUMO gaps, as is anticipated when
minor differences in the inductive effects of the aryl groups are involved. The trends observed
in the predicted MO energies are therefore consistent with the relatively minor changes that are
observed in the experimental and calculated optical spectra of 3a-g in CH2Cl2 (Figures 2 and 3).
The relatively weak absorption bands and the coupled pair of Faraday B0 terms in the 500−700
nm region (Figure 2) can be assigned to the Q transitions (Figure S3), while the main absorption
band at ca. 480 nm can be readily assigned to the B transitions. The +/− sign sequence in
ascending energy terms observed in the Faraday B0 terms in the Q band region (Figure 1) is the
pattern typically observed for corroles[18], since the separation of the MOs derived from the
LUMO of the parent perimeter (referred to as the ꢀLUMO value to use Michl’s terminology[19]
)
is greater than those derived from the HOMO level (the ꢀHOMO value[19]). The more complex
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sign sequence in the B band region is consistent with configurational interaction between the B
excited states and close-lying states with ππ* and ligand-to-metal charge transfer character
(Figure S3).
Electrochemistry
To gain a further insight into the electronic structures of 3a-g and the effect of solvent
polarity on the redox properties, cyclic voltammetry (CV) and differential pulse voltammetry
(DPV) measurements were carried out in both low polar o-dichlorobenzene (o-DCB) and high
polar dimethylformamide (DMF) containing 0.1 M tetra-n-butylammonium perchlorate
([NtBu]ClO4; TBAP) as a supporting electrolyte, so that redox potential (E ) values could be
½
clearly derived (Figure 4). The electrochemical behavior of 3a-g in these solvents is similar to
those reported for other Co(III)corrole and porphyrin complexes with regards to oxidation[21,22]
,
which is anticipated to only involve the corrole π-system because no other MOs lie close in
energy to the a and s MOs (Figure 3). The effect of reduction is more complex, however, due
to the presence of a 3d orbital associated with the central Co(III) ion and two MOs associated
with the meso-nitrophenyl rings in addition to the -a and -s MOs. Co(III)corroles with two
para-nitrophenyl rings have been reported to undergo a facile one-electron reduction to generate
a [Co(II)corrole]− species during the 1st reduction step, followed by a one-electron reduction on
the meso-nitrophenyl rings for the 2nd step and overlapping reduction processes on the
meso-nitrophenyl rings and at the metal center as the 3rd step[22b]. While there is a positive shift
of the oxidation curves and a negative shift of the reduction curves when the redox data are
compared to those that have been reported for regular Co(III)triphenyl-corroles[23], the redox
couple values that were obtained in DMF for the redox couples (Table 2) are broadly comparable
to those reported previously for A3 Co(III)corroles with three electron withdrawing
para-nitrophenyl rings[22b]. The poorly defined cathodic reduction peak and the negative shifts
of the E value for the Co(III)/Co(II) processes in the other solvents (Figure 4) are probably
½
caused by the loss of the PPh3 axial ligand and an associated reaction due to electron transfer.
When electron-withdrawing substituents are introduced at the meso-positions of Co(III)corroles,
there is a decrease in the electron density on the π-conjugation system of the corrole ligand and
this results in significantly easier reduction and more difficult oxidation[21]
.
The cyclic
voltammogram for 3a consists of a first reversible [Co(III)PPh3Corrole]/[Cu(II)Corrole]−
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reduction step at E = −0.51 V (in o-DCB). When halogen atoms are introduced on the B
½
position meso-aryl ring, little or no change is observed in the E value in o-DCB at −0.50 V for
½
3b, −0.50 V for 3c, −0.44 V for 3d, −0.48 V for 3e, −0.49 V for 3f, and −0.52 V for 3g. The
[Co(III)Corrole]/[Co(III)Corrole]+ first oxidation step also remains largely unchanged in o-DCB
with E values of 0.76 V for 3a, 0.78 V for 3b, 0.77 V for 3c, 0.85 V for 3d, 0.79 V for 3e, 0.74
½
V for 3f, and 0.81 V for 3g. The E1/2 values were found to change significantly when the
polarity of the solvent was increased, however. There is a positive shift of the E values, which
½
follows the trend in the electron-withdrawing ability of the halogenated meso-aryl rings on
moving from 3a to 3g. In DMF, the positively shifted 1st to 3rd reduction steps are observed at
−0.32, −1.02 and −1.54 V for 3a, and similar trends are observed in the electrochemical
properties of 3b-g (Figure 4). The trend observed in the gaps between the first reduction and
oxidation steps are consistent with the slight blue-shift of the main Q and B bands that is
observed spectroscopically for compounds with more strongly electron withdrawing B position
meso-aryl substituents (Figure 2) and predicted in theoretical calculations (Figure 3). The
significant decrease in the electron density of the Co(III)corrole π-system causes a slight increase
in the magnitude of the HOMO−LUMO gap.
Spectroelectrochemistry
Thin-layer UV-visible absorption spectroelectrochemical studies were carried out in
o-dichlorobenzene (o-DCB) and DMF containing 0.1 M TBAP to further characterize the
one-electron oxidized and reduced products. During the first reduction step, the main bands of
3a-g in the B region shift to ca. 420 nm (Figure 5). In o-DCB, there is a decrease in intensity at
384 nm in the B band region as the singly reduced species of 3a is formed, while a new band at
414 nm gains intensity, and a visible region band is observed at ca. 630 nm. This process can
be assigned to a metal-centered electron transfer and the removal of an axial ligand to form a
[Co(II)corrole]− species since the spectra are similar to those that have been previously reported
for the reduction of other Co(III)corroles[24] and oxidation at the metal ion would be anticipated
based on the predicted MO energies (Figure 3). Somewhat different spectral changes are
observed for 3b-g, since the B region bands of 3b-g undergo almost no shift in their λmax values
during the first reduction step, but the spectra are still consistent with Co(II) species. The
splittings in the B band region become smaller and there is an increase in intensity in the Q band
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region at ca. 600 nm. The first oxidation steps of 3b-g in o-DCB result are expected to result in
the formation of a ring-oxidized [Co(III)PPh3]+ π-cation species, since the HOMO is a π-MO
(Figure 3). A similar set of spectral changes is observed in each case. There is a decrease in
intensity in the Q and B band regions, while there is increased intensity beyond 680 nm and in
the NIR region, as would normally be expected after the formation of a π-cation[24]. When the
solvent polarity was increased by using DMF rather than o-DCB, some spectral changes were
observed (Figure 6). In contrast, there are significant differences in the spectral changes
observed during the first oxidation steps.
HER Catalysis
Stability in acidic environments has been a key concern in the design of new HER catalysts,
and the improved acid tolerance has been reported in several systems[25]. Analysis of the
electrocatalyzed HERs was only carried out for 3a-d and 3g, due to the poor solubility of 3e and
3f in CH3CN. Similar electrochemical and spectroelectrochemical properties were observed in
CH3CN (Figure S4-S5). The stability of 3a-d and 3g in concentrated TFA solutions in CH3CN
has been evaluated (Figure 7). Co(III)PPh3-corroles and TFA (1:4 molar ratio) were mixed in
CH3CN, and were carefully kept in the dark so the stability of 3a-d and 3g could be verified by
measuring the electronic absorption spectra for 4 h. Negligible spectral changes were observed.
This demonstrates that the A2B type Co(III)triarylcorroles are suitable for use as HER catalysts.
The most important parameters when considering the efficiency of the HERs are the kinetic
reactivity (icat/ip) and onset potentials (Figure 9). The addition of TFA to homogeneous
Co(III)corrole solutions in CH3CN induced catalytic waves at potentials close to the first
(CoIII/CoII) and 3rd (CoII/CoI) reduction couples. When the concentration of TFA is increased
from 1.0−6.0 eq in the 3a solution, a clear increase in the icat/ip ratio is observed at the first
CoIII/CoII couple (Figure 8). When the TFA concentration is increased further, a significant
increase is also observed close to the wave for the second CoII/CoI couple, clearly demonstrating
that there is usual two step modulation of the HER. In a similar manner, in the data for 3g,
which contains a pentafluorophenyl-substituent, in the presence of 1.0−4.0 eq of TFA, the icat/ip
ratio is significantly increased to a constant value near the CoIII/CoII couple, while at over 5.0 eq,
there is a significant increase at the CoII/CoI couple. In the case of 3a-d and 3g, there is a clear
increase in the icat/ip ratio based on the electron-withdrawing ability of the B position
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meso-substituent, which demonstrates that its electron withdrawing properties have a significant
influence on the HER catalysis. In addition, the catalytic wave increases in amplitude when the
acid concentration is increased and progressively shifts to more negative potentials. In the
current study, 3g was found to be the most efficient catalyst, followed by 3d, 3c and 3b with 3a
being the least reactive, since it contains no electron-withdrawing halogen atoms.
Conclusion
A series of seven meso-substituted A2B type Co(III)PPh3-meso-triarylcorroles containing
different halogenated meso-aryl-substituents at the B position have been synthesized and
characterized. A detailed analysis of the UV-visible absorption and MCD spectra, cyclic and
differential pulse voltammetry measurements, in situ thin-layer electroelectrochemical
characterizations, and the results of DFT and TD-DFT calculations has been carried out to
identify trends in the redox and optical properties. The results demonstrate that A2B Co(III)
corroles are highly effective catalysts for HER applications. When the number of fluorine atoms
on the meso-aryl substituents is increased, the catalysis of HERs is significantly enhanced. This
demonstrates that the introduction of different meso-aryl rings into the structures of low
symmetry A2B corroles is a useful strategy for modulating the efficiency of these reactions.
Clear evidence for two step modulation of the HER was observed during the electrochemical
measurements.
Experimental Section
General
1H and 19F NMR spectra were recorded on a Bruker AVANCE 400 spectrometer (operating
1
at 400.03 MHz) using the residual solvent as an internal reference for the H NMR spectra (δ =
7.26 ppm for CDCl3, δ = 5.32 ppm for CD2Cl2). All reagents and solvents were of commercial
reagent grade and were used without further purification except where noted. Cyclic
voltammetry was performed in a three-electrode cell using Chi-730D electrochemistry station.
A glassy carbon disk electrode was utilized as the working electrode while a platinum wire and a
saturated calomel electrode (SCE) were employed as the counter and reference electrodes,
respectively.
UV-visible spectroelectrochemical measurements were performed with a
home-made optically transparent thin-layer cell with Pt mesh as the working electrode. The
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potential was applied using a Chi-730D potentiostat. UV-visible spectra were recorded with a
HP 8453A diode array spectrophotometer. All electrochemical and spectroelectrochemical
measurements were carried out under a nitrogen atmosphere. Magnetic circular dichroism
(MCD) spectra were recorded on a JASCO J-815 spectrodichrometer equipped with a JASCO
electromagnet, which produces magnetic fields of up to 1.6 T (1 T = 1.0 tesla) with both parallel
and antiparallel fields. The conventions of Piepho and Schatz are used to describe MCD
intensity and the Faraday terms[26]
.
X-ray crystal structure
Single crystal X-ray diffraction quality crystal of 3e was grown from the mix solution of
CHCl3 and MeOH. The single crystal data of 3e was collected using Saturn724 Mo-Kα radiation
(λ = 0.71073 Å). The structures were solved by direct methods, and non-hydrogen atoms were
refined anisotropically by least-squares on F2 using the SHELXTL-97 program.[27] Hydrogen
atoms of the molecule were generated geometrically (C-H, 0.96 Å). CCDC number: 1515533
contain the supplementary crystallographic data for 3e. It can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Theoretical calculations
Optimized geometries were calculated for 3a-g by using the B3LYP functional of the
Gaussian 09 software package[28] with 6-31G(d) basis sets. TD-DFT calculations were carried
out in a similar manner by using the CAM-B3LYP functional, which includes an increasing
fraction of Hartree-Fock (HF) exchange as the interelectronic separation increases so that a
long-range correction is introduced. This is expected to provide more accurate results for
transitions in which there is significant charge transfer in the electronic excited states,[17] as is
likely to be the case in the spectra of 3a-g.
Synthesis and Characterizations
Synthesis
of
Co(III)PPh3-5,15-(m-nitrophenyl)-10-phenylcorrole
(3a):
5,15-(m-nitrophenyl)-10-phenylcorrole (0.05 mmol, 0.0308 g), CoAc2 (0.25 mmol, 0.0623 g) and
triphenylphosphine (0.25 mmol, 0.0656 g) was dissolved in a mixture of 5 mL CH2Cl2 and 20
mL methanol, which was then stirred and heated at 75 ℃ under N2 for 1 h. After removal of the
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solvent, the residue was further purified by Al2O3 gel chromatography (eluent: CH2Cl2/Hexane =
1:1), and the target compound was obtained in 86.3% yield (0.0290 g). MALDI-TOF-mass:
m/z = 672.21 (calcd. [M-PPh3]+ = 672.53). IR (KBr, v, cm-1): 3448 (s), 3060 (m), 2968 (w),
2922 (w), 2854 (w), 2362 (w), 1598 (w), 1571 (w), 1561 (w), 1529 (vs), 1504 (m), 1481 (w),
1437 (s), 1409 (w), 1347 (vs), 1321 (s), 1280 (w), 1224 (w), 1165 (w), 1090 (w), 1054 (s), 1018
(s), 987 (s), 924 (w), 883 (w), 845 (m), 807 (m), 786 (m), 743 (s), 719 (m), 709 (s), 693 (m), 663
(w), 521 (s). 1H NMR (CDCl3, 298K): δH, ppm 9.00 (1H, s), 8.78 (2H, s), 8.56 (2H, m), 8.33 ~
8.15 (7H, m), 8.02 (3H, d, J = 4 Hz), 7.87 ~ 7.83 (2H, t, J1 = 8 Hz, J2 = 8 Hz), 7.69 ~ 7.60 (3H,
m), 7.42 ~ 7.40 (1H, d, J = 7.2 Hz), 7.17 (3H, s), 6.77 (6H, s), 4.71 ~ 4.66 (6H, dd, J1 = 8.4 Hz, J2
= 10 Hz).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-(p-bromophenyl)corrole (3b). The synthetic
procedure for 3b is similar to that for 3a, with 5,15-(m-nitrophenyl)-10-(p-bromophenyl)corrole
used instead.
The target compound was obtained in 80.1% yield (0.0301 g).
MALDI-TOF-mass: m/z = 752.08 (calcd. [M-PPh3]+ = 751.43). IR (KBr, v, cm-1): 3442 (s),
3064 (w), 2967 (w), 2924 (w), 2863 (w), 2372 (w), 1571 (w), 1560 (w), 1529 (vs), 1503 (m),
1481 (m), 1459 (m), 1436 (s), 1410 (w), 1349 (vs), 1320 (m), 1280 (w), 1226 (w), 1164 (w),
1090 (m), 1072 (m), 1054 (s), 1019 (s), 1011 (m), 986 (m), 930 (w), 876 (w), 844 (m), 805 (s),
786 (m), 763 (w), 741 (m), 721 (m), 713 (s), 695 (m), 652 (w), 521 (s), 508 (w). 1H NMR
(CDCl3, 298K): δH, ppm 8.96 (1H, s), 8.78 (2H, s), 8.55 ~ 8.53 (2H, d, J = 7.6 Hz), 8.41~8.20
(7H, m), 8.00 (3H, s), 7.85 ~ 7.69 (5H, m), 7.26 ~ 7.14 (3H, m), 6.73 (6H, s), 4.64 ~ 4.60 (6H, t,
J1 = 8.8 Hz, J2 = 9.6 Hz).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-(p-chlorophenyl)corrole (3c). The synthetic
procedure for 3c is similar to that for 3a, with 5,15-(m-nitrophenyl)-10-(p-chlorophenyl)corrole
2c used instead.
The target compound was obtained in 82.3% yield (0.0291g).
MALDI-TOF-mass: m/z = 705.63 (calcd. [M-PPh3]+ = 706.98). IR (KBr, v, cm-1): 3448 (s), 3061
(m), 2960 (w), 2855 (w), 2365 (w), 1571 (w), 1561 (w), 1528 (vs), 1507 (m), 1436 (s), 1410 (w),
1349 (vs), 1320 (m), 1225 (w), 1163 (w), 1090 (s), 1054 (s), 1018 (s), 986 (s), 926 (w), 877 (w),
844 (m), 805 (s), 786 (m), 763 (w), 741 (s), 715 (s), 706 (s), 694 (m), 521 (s), 504 (w). 1H NMR
(CDCl3, 298K): δH, ppm 8.96 (1H, s), 8.78 (2H, d, J = 3.2 Hz), 8.55~8.53 (2H, d, J = 7.2 Hz),
8.42~8.33 (5H, m), 8.20 (2H, d, J = 4.8 Hz), 8.00 (2H, d, J = 3.2 Hz), 7.92 ~ 7.90 (1H, m), 7.85
~ 7.81 (2H, t, J1 = 8 Hz, J2 = 8 Hz), 7.61 ~ 7.52 (3H, m), 7.13 (3H, s), 6.74 (6H, s), 4.65~4.60
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(6H, m).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-(p-fluorophenyl)corrole (3d). The synthetic
procedure for 3d is similar to that for 3a, with 5,15-(m-nitrophenyl)-10-(p-fluorophenyl)corrole
2d used instead.
The target compound was obtained in 81.4% yield (0.0281g).
MALDI-TOF-mass: m/z = 690.00 (calcd. [M-PPh3]+ = 690.52). IR (KBr, v, cm-1): 3448 (s),
3064 (m), 2967 (w), 2924 (w), 2362 (w), 1571 (w), 1560 (w), 1529 (vs), 1511 (s), 1481 (w),
1437 (m), 1349 (vs), 1320 (m), 1224 (m), 1157 (m), 1091 (m), 1054 (s), 1018 (s), 987 (m), 926
(w), 881 (w), 844 (m), 807 (m), 786 (m), 763 (w), 741 (m), 720 (w), 708 (m), 694 (m), 652 (w),
598 (w), 540 (w), 522 (s). 1H NMR (CDCl3, 298K): δH, ppm 9.00 (1H, s), 8.78 (2H, s), 8.57 ~
8.55 (2H, d, J = 9.2 Hz), 8.33 ~ 8.25 (6H, m), 8.02 (3H, d, J = 4 Hz), 7.87 ~ 7.85 (2H, t, J1 = 8
Hz, J2 = 8 Hz), 7.71 ~ 7.55 (3H, m), 7.42 ~ 7.40 (1H, d, J = 7.2 Hz), 7.16 (3H, s), 6.77 (6H, s),
4.71~4.66 (6H, m). 19F NMR (CDCl3, 298K): δF, ppm −115.02 (1F, s).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-(2,6-dichlorophenyl)corrole (3e). The
synthetic
procedure
for
3e
is
similar
to
that
for
3a,
with
5,15-(m-nitrophenyl)-10-(2,6-dichlorophenyl)corrole 2e used instead. The target compound
was obtained in 76.6% (0.0284 g). MALDI-TOF-mass: m/z = 740.41 (calcd. [M-PPh3]+ =
741.42). IR (KBr, v, cm-1): 3424 (m), 3065 (w), 2957 (w), 2923 (w), 2868 (w), 2364 (w), 1572
(w), 1556 (w), 1529 (vs), 1509 (s), 1480 (m), 1427 (s), 1407 (w), 1374 (w), 1349 (vs), 1320 (s),
1282 (w), 1246 (w), 1226 (w), 1189 (m), 1161 (w), 1090 (s), 1074 (w), 1053 (s), 1018 (s), 987
(s), 924 (m), 882 (w), 846 (m), 824 (w), 807 (m), 793 (s), 778(w), 760 (m), 742 (m), 712 (s), 693
(s), 649 (w), 635 (w), 618 (w), 521 (s). 1H NMR (CDCl3, 298K): δH, ppm 9.03 (1H, s), 8.54 ~
8.52 (5H, d, J = 7.6 Hz), 8.30 (3H, s), 8.12 (2H, d, J = 4.8 Hz), 8.01 (2H, s), 7.83 (3H, s), 7.66 ~
7.57 (3H, m), 7.10 (3H, s), 6.73 (6H, s), 4.74 ~ 4.70 (6H, tt, J1 = 7.6 Hz, J2 = 10.8 Hz).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-(2,6-difluorophenyl)corrole (3f). The synthetic
procedure
for
3f
is
similar
to
that
for
3a,
with
5,15-(m-nitrophenyl)-10-(2,6-difluorophenyl)corrole 2f used instead. The target compound was
obtained in 80.4% yield (0.0285 g). MALDI-TOF-mass: m/z = 708.72 (calcd. [M-PPh3]+ =
708.52). IR (KBr, v, cm-1): 3449 (s), 3111 (m), 1622 (m), 1584 (w), 1574 (w), 1558 (w), 1530
(vs), 1481 (w), 1462 (m), 1434 (m), 1400 (w), 1384 (s), 1349 (vs), 1320 (w), 1272 (m), 1194 (w),
1164 (w), 1090 (m), 1053 (s), 1018 (s), 999 (s), 987 (m), 928 (w), 881 (w), 845 (m), 824 (w),
805 (m), 781 (m), 763 (w), 739 (w), 715 (m), 707 (m), 693 (m), 652 (w), 581 (w), 521 (s), 509
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(w). 1H NMR (CDCl3, 298K): δH, ppm 9.01 (1H, s), 8.65 (2H, s), 8.54 ~ 8.52 (2H, d, J = 8 Hz),
8.46 ~ 8.22 (7H, m), 8.05 (2H, d, J = 4 Hz), 7.84 ~ 7.82 (2H, t, J1 = 8 Hz, J2 = 8 Hz), 7.72~7.65
(1H, m), 7.26~7.22 (2H, m), 7.09 (3H, s), 6.73 (6H, s), 4.71 ~ 4.66 (6H, m).
Synthesis of Co(III)PPh3-5,15-(m-nitrophenyl)-10-pentafluorophenylcorrole (3g). The synthetic
procedure for 3g is similar to that for 3a, with 5,15-(m-nitrophenyl)-10-pentafluorophenylcorrole
2g used instead.
The target compound was obtained in 83.1% yield (0.0317 g).
MALDI-TOF-mass: m/z = 761.26 (calcd. [M-PPh3]+ = 762.49). IR (KBr, v, cm-1): 3430 (m),
3066 (m), 2956 (w), 2922 (w), 2865 (w), 2364 (w), 1649 (w), 1613 (w), 1573 (w), 1526 (vs),
1486 (s), 1448 (m), 1433 (m), 1384 (w), 1373 (w), 1349 (vs), 1321 (m), 1302 (w), 1281 (w),
1231 (w), 1188 (w), 1165 (m), 1089 (m), 1052 (s), 1019 (s), 987 (s), 951 (s), 931 (w), 910 (w),
883 (w), 846 (m), 824 (w), 805 (m), 771 (m), 761 (s), 741 (m), 730 (w), 719 (m), 708 (s), 693
(m), 617 (w), 598 (w), 521 (s). 1H NMR (CDCl3, 298K): δH, ppm 9.00 (1H, s), 8.71 (2H, s),
8.56 ~ 8.54 (2H, d, J = 8 Hz), 8.45 ~ 8.19 (7H, m), 8.08 (2H, d, J = 4 Hz), 7.87 ~ 7.85 (2H, t, J1
= 8 Hz, J2 = 8 Hz), 7.11 (3H, s), 6.73 (6H, s), 4.65 ~ 4.60 (6H, tt, J1 = 7.6 Hz, J2 = 11.2 Hz). 19F
NMR (CDCl3, 298K): δF, ppm −137.42 ~ −138.44 (2F, tt), −153.77 (1F, t), −161.91 ~ −162.24
(2F, d).
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FIGURES.
Figure 1. X-ray single crystal structure of 3e, top (left) and side view (right). The thermal
ellipsoids were scaled to the 50% probability level. Solvent molecules in both views and the
axial ligand in the top view were omitted for clarity.
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Figure 2. UV-visible absorption (bottom) and magnetic circular dichorism (MCD, top) spectra of
Co(III)PPh3triarylcorroles 3a-g at room temperature in CH2Cl2.
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Figure 3. The angular nodal patterns of the frontier MOs of 3g (TOP), including the a, s, -a and
-s MOs of Michl’s perimeter model highlighted with thicker black lines, the 3dz2 MO shown with
green lines and two MOs that are localized on the A2 position meso-aryl rings due to the presence
of the nitro substituents. MO energies predicted for the parent Co(III)triphenylcorrole (noNO2)
and 3a-g with the CAM-B3LYP functional and 6-31G(d) basis sets for a series of B3LYP
optimized geometries (Bottom). Black squares and diamonds are used to highlight the a/-a and
s/-s MOs, respectively, while green lines are used to highlights MOs with significant 3d orbital
character. Red diamonds are used to denote the HOMO−LUMO gap values, which are plotted
against a secondary axis.
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Figure 4. CV and DPV measurements of 3a-g at room temperature in o-dichlorobenzene
(o-DCB, left) and DMF (right) containing 0.1 M [NnBu4]+[ClO4]− (TBAP) as a supporting
electrolyte.
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Figure 5. In situ spectroelectrochemical measurements of 3a-g at room temperature in
o-dichlorobenzene containing 0.1 M [NnBu4]+[ClO4]− (TBAP) as a supporting electrolyte.
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Figure 6. In situ spectroelectrochemical measurements of 3a-g at room temperature in DMF
containing 0.1 M [NnBu4]+[ClO4]− (TBAP) as a supporting electrolyte.
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Figure 7. UV-visible spectra of Co(III)PPh3-5,15-(m-nitrophenyl)-10-arylcorroles 3a-d and 3g at
room temperature in the absence and presence of 4.0 eq of TFA in CH3CN.
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Figure 8. Reductive cyclic voltammetry of 3a-3d and 3g in CH3CN in the presence of 1.0−9.0
eq of TFA with 0.1 M TBAP as the supporting electrolyte.
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Figure 9. Plot of the icat/ip values of 3a-d and 3g for the 1st (left) and 3rd reduction (right) steps
upon addition of TFA in CH3CN containing 0.1 M TBAP. All of the values are derived from
CV measurements.
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SCHEMES.
Scheme 1. Synthesis of Co(III)PPh3-meso-triarylcorroles.
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TABLES.
Table 1. Crystal data of 3e.
Sample-Temperature
Data
(K)
Space group
a (Å)
Pca21
21.034(2),
16.6280(17),
14.3910(15)
90.00, 90.00, 90.00
5033.2(9)
4
b (Å)
c (Å)
α, β, γ (˚)
V (Å3)
Z
F(000)
2128
µ (mm-1)
Observed reflections
(I>2σ(I))
Independent
reflections
R1
0.534
20554
8474
0.1595
0.2911
wR2
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Table 2. Redox potentials of 3a-g in o-DCB and DMF containing 0.1M TBAP.
Ox2
Ox2
Red1
Red2
Red3
2nd E1/2
(V)
1.20
0.88
0.84
1.22
0.92
−
1st E1/2
1st E1/2
1st E1/2
1st E1/2
(V)
No.
Solvent
(V)
(V)
(V)
o-DCB
DMF
0.75
0.69
0.62
0.78
0.69
0.67
0.77
0.68
0.63
0.85
0.72
0.63
0.79
0.86
−
−0.51
−0.32
−0.48
−0.50
−0.36
−0.42
−0.50
−0.38
−0.46
−0.44
−0.29
−0.46
−0.48
−0.32
−
−1.09
−1.03
−1.13
−1.11
−1.07
−1.13
−1.11
−1.10
−1.13
−1.05
−1.03
−1.14
−1.09
−1.01
−
−1.67
−1.54
−1.67
−1.77
−1.67
−1.58
−1.64
−1.64
−1.69
−1.58
−1.52
−1.73
−1.65
−1.48
−
3a
CH3CN
o-DCB
DMF
3b
3c
3d
3e
3f
CH3CN
o-DCB
DMF
1.16
0.90
0.85
1.29
0.90
0.86
1.24
−
CH3CN
o-DCB
DMF
CH3CN
o-DCB
DMF
CH3CN
o-DCB
DMF
−
1.23
−
0.74
0.71
−
−0.49
−0.47
−
−1.10
−1.08
−
−1.65
−1.70
−
CH3CN
o-DCB
DMF
−
1.28
−
0.81
0.71
0.75
−0.52
−0.36
−0.33
−1.10
−1.07
−1.04
−1.65
−1.63
−1.57
3g
CH3CN
1.01
Supporting Information.
1
The experimental details, H and 19F NMR spectra, calculated electronic absorption and MCD
spectra, electrochemical and spectroelectrochemical measurements in CH3CN are available free
of charge via the Internet.
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Funding Sources
Financial support was provided by Natural Science Foundation of China (No. 21171076) and
Natural Science Foundation of Jiangsu Province (No. BK20160499) to XL and WZ and an NRF
of South Africa CSUR grant (uid: 93627) to JM.
ACKNOWLEDGMENT
The theoretical calculations were carried out at the Centre for High Performance Computing in
Cape Town.
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