Electronic Structure of Manganese Corroles Revisited: X-ray Structures, Optical and X-ray Absorption Spectroscopies, and Electrochemistry as Probes of Ligand Noninnocence

Article abstract of DOI:10.1021/acs.inorgchem.8b00537

Presented herein is a detailed multitechnique investigation of ligand noninnocence in S = ³/₂ manganese corrole derivatives at the formal Mn^IV oxidation state. The Soret maxima of Mn[TpXPC]Cl (TpXPC = meso-tris(p-X-phenyl)corrole, where X = CF₃, H, Me, and OMe) were found to red-shift over a range of 37 nm with increasing electron-donating character of X. For Mn[TpXPC]Ph, in contrast, the complex Soret envelopes were found to be largely independent of X. These observations suggested a noninnocent corrole^·2--like ligand for the MnCl complexes and an innocent corrole^3- ligand for the MnPh complexes. Single-crystal X-ray structures of three Mn[TpXPC]Cl complexes revealed skeletal bond-length alternations indicative of a noninnocent corrole, while no such alternation was observed for Mn[TpOMePC]Ph. B3LYP density functional theory (DFT) calculations on Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities, consistent with an antiferromagnetically coupled Mn^III-corrole^·2- description. By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an essentially Mn^IV-corrole^3- description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of 0.6 eV for the Mn K-pre-edge of Mn[TpCF₃PC]Ph and a striking enhancement of the pre-edge intensity, relative to Mn[TpCF₃PC]Cl, consistent with a more oxidized, i.e., Mn^IV, center in Mn[TpCF₃PC]Ph. Time-dependent DFT calculations indicated that the enhanced intensity of the Mn K-pre-edge of Mn[TpCF₃PC]Ph results from the extra 3d_z² hole, which mixes strongly with the Mn 4p_z orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic voltammetry measurements revealed highly negative first reduction potentials for the Mn[TpXPC]Ph series (～-0.95 V) as well as large electrochemical HOMO-LUMO gaps of ～1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the Mn-Ph bond.

Full text of DOI:10.1021/acs.inorgchem.8b00537

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Electronic Structure of Manganese Corroles Revisited: X‑ray
Structures, Optical and X‑ray Absorption Spectroscopies, and
Electrochemistry as Probes of Ligand Noninnocence
Sumit Ganguly,† Laura J. McCormick,‡ Jeanet Conradie,§ Kevin J. Gagnon,‡ Ritimukta Sarangi,*,∥
and Abhik Ghosh*,†
†Department of Chemistry, UiTThe Arctic University of Norway, Tromsø N-9037, Norway
‡Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8229, United States
§Department of Chemistry, University of the Free State, Bloemfontein 9300, Republic of South Africa
∥Structural Molecular Biology (SMB), Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory,
Menlo Park, California 94306, United States
S
* Supporting Information
ABSTRACT: Presented herein is a detailed multitechnique investigation of
3
ligand noninnocence in S = /2 manganese corrole derivatives at the formal
MnIV oxidation state. The Soret maxima of Mn[TpXPC]Cl (TpXPC = meso-
tris(p-X-phenyl)corrole, where X = CF3, H, Me, and OMe) were found to red-
shift over a range of 37 nm with increasing electron-donating character of X. For
Mn[TpXPC]Ph, in contrast, the complex Soret envelopes were found to be
largely independent of X. These observations suggested a noninnocent
corrole•2−-like ligand for the MnCl complexes and an innocent corrole3−
ligand for the MnPh complexes. Single-crystal X-ray structures of three
Mn[TpXPC]Cl complexes revealed skeletal bond-length alternations indicative
of a noninnocent corrole, while no such alternation was observed for
Mn[TpOMePC]Ph. B3LYP density functional theory (DFT) calculations on
Mn[TPC]Cl yielded strong spatial separation of the α and β spin densities,
consistent with an antiferromagnetically coupled MnIII-corrole•2− description.
By comparison, relatively little spatial separation of the α and β spin densities was found for Mn[TPC]Ph, consistent with an
essentially MnIV-corrole3− description. X-ray absorption of near-edge spectroscopy (XANES) revealed a moderate blue shift of
0.6 eV for the Mn K-pre-edge of Mn[TpCF3PC]Ph and a striking enhancement of the pre-edge intensity, relative to
Mn[TpCF3PC]Cl, consistent with a more oxidized, i.e., MnIV, center in Mn[TpCF3PC]Ph. Time-dependent DFT calculations
2
indicated that the enhanced intensity of the Mn K-pre-edge of Mn[TpCF3PC]Ph results from the extra 3dz hole, which mixes
strongly with the Mn 4pz orbital. Combined with similar results on Fe[TPC]Cl and Fe[TPC]Ph, the present study underscores
the considerable potential of metal K-edge XANES in probing ligand noninnocence in first-row transition-metal corroles. Cyclic
voltammetry measurements revealed highly negative first reduction potentials for the Mn[TpXPC]Ph series (∼−0.95 V) as well
as large electrochemical HOMO-LUMO gaps of ∼1.7 V. The first reductions, however, are irreversible, suggesting cleavage of the
Mn−Ph bond.
manganese corroles.13,14 Accordingly, a major goal of the study
INTRODUCTION
■
was also to validate other key experimental methods, notably
In recent years, several families of iron1 and copper2−11 corroles
UV−vis spectroscopy, X-ray crystal structures, X-ray absorption
have provided paradigmatic examples of noninnocent ligands;
spectroscopy (XAS), and electrochemistry, as probes of ligand
i.e., the corrole ligand in these complexes has substantial
noninnocence in manganese corroles.
corrole•2− radical-dianion character.12 Against this backdrop,
this work presents a detailed analysis of ligand noninnocence in
manganese corroles, for which the phenomenon has been less
thoroughly explored. The study involved a multitechnique
Substituent effects of meso-aryl substituents on the Soret
maximum have often provided the first indication of a
noninnocent corrole in a given class of metallotriarylcorroles.
investigation of MnCl and MnPh (Ph = phenyl) meso-tris(p-X-
Special Issue: Applications of Metal Complexes with Ligand-
Centered Radicals
phenyl)corrole (TpXPC) derivatives, where X = CF3, H, Me,
1
and OMe (Figure 1). Unlike for iron corroles, H NMR and
electron paramagnetic resonance (EPR) spectroscopies do not
provide a detailed picture of the electron distribution in
Received: March 1, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b00537
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Forum Article
40% yield (relative to H3[TpOMePC]) with no particular
adjustment to the procedure.
Arylation of the MnCl corroles was also carried out following
a published protocol.34,35 Anhydrous dichloromethane sol-
utions of Mn[TpXPC]Cl derivatives were treated with an
excess of phenylmagnesium bromide under an inert atmos-
phere, leading to Mn[TpXPC]Ph corroles via ligand exchange.
The optimum reaction time was found to be about 7−8 min;
longer reaction times resulted in drastically reduced yields. The
MnPh products were obtained in 33−42% yield after aerobic
workup.
Both MnCl and MnPh corroles are only moderately stable
and are best stored in a freezer at under −50 °C. Under aerobic
conditions in solution, the MnPh corroles were found to
decompose rapidly via Mn−Ph bond cleavage [as judged from
electrospray ionization mass spectromety (ESI-MS) analyses],
visibly changing in color from reddish-brown to yellowish-green
in about 1 h. Thus, even column chromatography and
preparative thin-layer chromatography (PLC) over ∼30 min
under aerobic conditions resulted in a significant loss of
material due to decomposition. Warming and rigorous drying
of the solids also led to decomposition, frustrating our attempts
at obtaining accurate elemental analyses. Accordingly, the
sample purity was ascertained primarily by means of rapid
analytical thin-layer chromatography on short (∼4 cm) silica
gel strips and ESI-MS as well as, in a number of cases, single-
crystal X-ray structures.
Figure 1. Manganese corroles studied in this work.
Thus, for noninnocent TpXPC derivatives, electron-donating X
groups bring about distinct red shifts of the Soret
maximum.1−12 No such red shifts are observed for innocent
metallotriarylcorroles.15−21 The power of this simple optical
probe has been dramatically underscored in recent reinvesti-
gations of FeNO,22 (μ-oxo)diiron,23 and Co-PPh3 corrole
24
derivatives, which led us to reenvision these species as
fundamentally noninnocent. Preliminary studies of a set of
three Mn[TpXPC]Cl derivatives, where X = CF3, H, and CH3,
revealed significant shifts of the Soret maxima, leading us to
propose a MnIII-corrole•2− formulation for these com-
pounds.13,25 Presented below is a comparative study of the
Mn[TpXPC]Cl series, with X = CF3, H, CH3, and OMe, and
the new series Mn[TpXPC]Ph.
Optical Spectroscopy. As shown in Table 1 and Figure 2,
the Soret maxima of the Mn[TpXPC]Cl series red-shift
Table 1. Soret Absorption Maxima (nm) of Mn-, Fe-, Cu-,
and Au[TpXPC] Complexes in CH2Cl2
Very recently, we have found a subtle but characteristic
bond-length alternation in high-quality X-ray structures of
noninnocent metallocorroles.22,26,23,24 In view of the relative
paucity of structurally characterized manganese corroles at the
formal MnIV oxidation level, a number of single-crystal X-ray
structure determinations were performed as part of this study.
These fully substantiated the usefulness of high-quality X-ray
structures as a potential probe of ligand noninnocence.
XAS has long been used as a probe of oxidation state, but the
first applications to metallocorroles have only occurred
recently.27−29 For iron corroles, X-ray absorption near-edge
spectroscopy (XANES) has provided an excellent probe of
ligand noninnocence.30 In this study, we have carried out a
comparative XANES analysis of MnCl and MnPh corroles,
again with excellent results.
p-substituent
series
CF3
H
Me
OMe
ref
Mn[TpXPC]Cl
Mn[TpXPC]Ph
Fe[TpXPC]Cl
Fe[TpXPC]Ph
Fe[TpXPC](NO)
Cu[TpXPC]
423
398
401
384
385
407
419
433
394
410
383
390
410
418
442
389
419
383
400
418
420
460
387
426
385
416
434
420
this work
this work
1, 30
30
22
2
Au[TpXPC]
20
Finally, we have addressed the question of whether
electrochemical redox potentials are indicative of the innocent
or noninnocent character of a given class of metallocorroles.
Throughout, density functional theory (DFT) calcula-
tions31,32 have helped to interpret and contextualize the
experimental data, as described below.
RESULTS AND DISCUSSION
■
Synthesis of MnCl and MnPh Corroles. The Mn-
[TpXPC]Cl (X = CF3, H, Me, and OMe) derivatives were
synthesized following a previously reported procedure.33
Interaction of free-base triarylcorroles with Mn(OAc)2·4H2O
in N,N-dimethylformamide (DMF) at 165−170 °C for
approximately 45 min, followed by column chromatography,
yielded the pure manganese(III) corroles. The manganese(III)
corroles were then subjected to aerial oxidation in the presence
of 10% aqueous HCl, affording the MnCl corroles. The new
complex Mn[TpOMePC]Cl was obtained in approximately
Figure 2. Electronic absorption spectra (in dichloromethane) of
Mn[TpXPC]Cl derivatives.
dramatically from X = CF3 (423 nm) to X = OMe (460 nm)
series, strongly suggesting a noninnocent corrole.1,22−25
Extrapolating conclusions based on time-dependent DFT
B
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(TDDFT) calculations on copper corroles,36,37 we may
plausibly assign the key substituent-sensitive feature in the
complex Soret envelope to an aryl-to-corrole•2− ligand-to-
ligand charge-transfer (LL′CT) transition. For the new
compound Mn[TpOMePC]Cl, which has a pronounced split
Soret band, this LL′CT transition may be reasonably assigned
to the lower-energy peak with a maximum at 460 nm. For the
Mn[TpXPC]Ph series (Figure 3), the Soret maxima drift
and CISHAO35). The higher displacements for the MnCl
2
complexes facilitate antiferromagnetic coupling between the dz
electron of the high-spin MnIII center and the “a2u-type” corrole
radical. The question of such a spin coupling does not arise for
the d3 MnIV center in Mn-aryl corroles.
Figure 6 reveals a small but distinct bond-length alternation
in and around the bipyrrole unit of the three MnCl structures.
An analogous bond-length alternation is also found for other
structurally characterized halogenomanganese corroles (MIK-
WOU,41 TORMET,44 YAWQES,14 YAWQAO,14 GIFJEL,45
and XIDRUY42) but is essentially nonexistent in the X-ray
structure of Mn[TpOMePC]Ph (as well as CISGUH35 and
CISHAO35). We have recently shown that such a bond-length
alternation is indicative of a corrole a2u-type radical (allowing
ourselves to use D4h symbols for orbital symmetries that are
standard for porphyrins).22−24 DFT calculations also reproduce
this difference in the skeletal bond-length alternation between
Mn[TPC]Cl and Mn[TPC]Ph (Figure 4).
Interestingly, the X-ray structure of Mn[TpOMePC]Ph
revealed two symmetry-distinct molecules, each existing as a
slipped π-stacked dimer (Figure 7). Such π stacking is common
for porphyrinoid structures. No such stacking, however, was
observed for any of the three MnCl structures.
An attempt to structurally characterize a five-coordinate
manganese(III) complex led to an X-ray structure of Mn-
[TpCF3PC](py)2 (Figure 8). Unsurprisingly for a high-spin
manganese(III) complex, the Mn−N distances involving the
axial pyridines were found to be long2.4269(17) Å each
somewhat longer than that observed in the monopyridine
complexes Mn[OEC]py (2.277 Å)34 and Mn[TpNO2PC]Cl
(MIKWEK,41 2.385 Å). This finding is somewhat at odds with
spectrophotometric titration34,38,39 and mass spectrometric46,47
studies, which indicate that the major species in solution in the
presence of added pyridine is a five-coordinate manganese(III)
corrole with a single axially bound pyridine. As described below
and in the Supporting Information, however, XAS studies
suggest that both monopyridine and bispyridine adducts may
coexist, depending on the exact conditions.
XAS. Figure 9 depicts the Mn K-edge XAS data for the solid-
state compounds Mn[TpCF3PC]Cl, Mn[TpCF3PC]Ph, and
Mn[TpCF3PC](py)n (n = 1−2); the inset shows an expanded
view of the pre-edge region. The metal K-pre-edge spectra
result from 1s-to-3d electric-dipole-forbidden, quadrupole-
allowed transitions, and their energy positions and intensity
patterns are strongly modulated by changes in the electronic
structure. A comparative study of the pre-edge region, among
closely related molecular systems, can provide important insight
into electronic-structural differences. The K-pre-edge energy of
first-row transition metal complexes is strongly affected by the
overall ligand-field strength, and the pre-edge can gain intensity
via two mechanisms: (1) an increase in the number of metal 3d
holes and (2) an increase in metal 3d−4p mixing (associated
with a decrease in centrosymmetry).48,49 These general rules
are expected to apply well to the structurally similar, square-
pyramidal complexes examined here, which have the same TPC
ligand as the dominant contributor to the overall ligand field.50
The expanded Mn K-pre-edge region (Figure 9, inset) shows
that, upon going from the genuine manganese(III) species
Mn[TpCF3PC](py)n (n = 1−2) to Mn[TpCF3PC]Cl, the
intensity-weighted average energy (IWAE) position of the pre-
edge increases slightly from 6540.6 to 6540.8 eV and the total
intensity increases from 0.12 to 0.25 units, respectively. The
modest increases in the pre-edge energy and intensity are
Figure 3. Electronic absorption spectra (in dichloromethane) of
Mn[TpXPC]Ph derivatives.
somewhat erratically in the range 387−398 nm, but the overall
peak envelopes do not move. Furthermore, the higher-
wavelength shoulder of the Soret band, which all of the
complexes exhibit and which presumably corresponds to the
above-mentioned LL′CT transition, occurs at a fixed position,
strongly suggesting an innocent corrole ligand. These
conclusions are consistent with DFT(B3LYP/STO-TZP)
calculations on Mn[TPC]Cl and Mn[TPC]Ph. Thus, note
the much smaller minority spin populations on the corrole for
Mn[TPC]Ph, consistent with an essentially MnIV-corrole3−
description (Figure 4), compared with Mn[TPC]Cl.12
Importantly, these conclusions also nicely parallel those for
FeCl and FePh triarylcorroles.1,30
As shown in Figure 5, the UV−vis spectra of MnCl and
MnPh corroles differ markedly from those of manganese(III)
corroles. Thus, the UV−vis spectrum of Mn[TpCF3PC](py)n
in dichloromethane exhibits a split Soret band, with two peaks
of almost equal intensity at 408 and 430 nm. The characteristic
Q band around 650 nm is thought to be indicative of a single
axial pyridine ligand.34,38−40
X-ray Structures. Only a handful of manganese corroles
have been structurally characterized until now.14,34,35,41−43
Accordingly, a strong effort was made to determine single-
crystal X-ray structures for the manganese corroles synthesized
as part of this study. Five structures were successfully solved
(Table 2). Key structural parameters of the MnCl and MnPh
corroles are listed in Table 3 (along with literature
comparisons) and illustrated in Figure 6. The structures
underscore significant structural differences between the
MnCl and MnPh corroles.
Thus, Table 3 shows that halogenomanganese corroles
(including the previously reported structures MIKWOU,41
TORMET,44 YAWQES,14 YAWQAO,14 GIFJEL,45 and XI-
DRUY42) exhibit significantly larger out-of-plane Mn−N4
displacements than Mn-aryl corroles (including CISGUH35
C
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Figure 4. Comparative B3LYP/STO-TZP results for Mn[TPC]Cl and Mn[TPC]Ph. Top: Mulliken spin populations. Middle: Excess majority
(cyan) and minority (magenta) spin densities plotted with a contour of 0.03 e/Å3. Bottom: Skeletal bond distances (Å). Bond-length alternations are
indicated in color for Mn[TPC]Cl. meso-Phenyl groups have been omitted for clarity.
consistent with a MnIII center in both complexes, i.e., with a
MnIII(S=2)-corrole•2− electronic description for Mn-
[TpCF3PC]Cl. By comparison, the pre-edge energy position
of Mn[TpCF3PC]Ph is significantly blue-shifted and occurs at
6541.4 eV. The large increase in the pre-edge energy position is
also accompanied by a dramatic increase in the pre-edge
intensity (0.62 units). These results indicate either a significant
increase in metal 3d−4p mixing in Mn[TpCF3PC]Ph relative
to Mn[TpCF3PC]Cl or oxidation of the Mn center, which
2
would lead to a manganese(IV) species with an additional dz
hole.30 To delineate the role of these two factors, DFT
calculations with full geometry optimizations were carried out
Figure 5. Comparative electronic absorption spectra (in dichloro-
methane) of the Mn[TpCF3PC](L) complexes (L = py, Cl, and Ph).
on the above three compounds. Figure 10, which depicts the
unoccupied molecular orbital (MO) energy levels contributing
to the Mn pre-edge region (see Figures S7 and S8 and Table S1
D
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Table 2. Crystallographic Data for the Manganese Corroles Analyzed in This Work
Mn[TpMePC]Cl
Mn[TPC]Cl
Mn[TpCF3PC]Cl
Mn[TpOMePC]Ph
Mn[TpCF3PC](py)2
chemical formula
formula mass
cryst syst
C40H29ClMnN4
656.06
C37H23ClMnN4
613.98
C40H20ClF9MnN4
817.99
C46H34O3N4Mn
745.71
C50H30F9MnN6
940.74
monoclinic
P21/n
monoclinic
P21/n
triclinic
triclinic
monoclinic
C2/c
space group
λ (Å)
P1
̅
0.7749
P1
̅
0.7749
1.0332
0.7293
0.7749
a (Å)
15.8442(9)
12.4846(7)
16.5813(9)
90
8.2864(5)
15.8843(10)
21.0546(13)
90
8.2998(9)
11.6142(13)
18.151(2)
96.535(3)
91.747(3)
100.883(3)
2
10.1014(3)
13.6476(4)
25.4568(8)
94.755(2)
95.107(2)
90.353(2)
4
18.3531(9)
16.7778(8)
14.4477(7)
90
b (Å)
c (Å)
α (deg)
β (deg)
111.797(2)
90
90.063(3)
90
113.778(3)
90
γ (deg)
Z
4
4
4
Z′
1
1
2
0.5
V (Å3)
3045.4(3)
100(2)
1.431
2771.3(3)
100(2)
1704.6(3)
100(2)
3483.18(18)
100(2)
4071.2(4)
100(2)
1.535
temp (K)
density (g/cm3)
measured reflns
unique reflns
parameters
restraints
1.472
1.594
1422
26122
49491
19570
62858
26941
8496
8503
6235
12791
6233
418
408
561
979
324
0
33
50
0
0
Rint
0.0544
0.0616
0.0543
0.0638
0.0368
θ range (deg)
R1, wR2 (all data)
S(GOF) (all data)
max/min residual density (e/Å3)
2.208−47.232
0.1126, 0.2080
1.324
1.315−31.483
0.0397, 0.0899
1.083
1.961−28.977
0.0850, 0.1205
1.148
2.207−27.894
0.0479, 0.1174
1.046
1.871−33.655
0.0641, 0.1547
1.055
0.808/−0.954
0.450/−0.304
0.649/−0.618
0.469/−0.482
3.203/−0.694
Table 3. Selected Crystallographic Geometry Parameters for Manganese Corroles at the Formal MnIV Oxidation State
d(M−
N1/4
d(M−
N2/3
d(M− d(M−
complex
CCSD
chemical name
)
)
Lax)
N4)
ref
ave
ave
Mn[Et4Me2EtAc2C]
Cl
TORMET chloro-7,8,12,13-tetraethyl-2,18-bis[2-(methoxycarbonyl)ethyl]-3,17-
dimethylcorrolatomanganese, acetonitrile solvate
1.942
1.940
1.931
1.930
1.939
1.934
1.936
1.938
1.918
1.924
1.919
1.918
1.920
1.914
1.915
1.918
2.338
0.407 44
0.427 14
0.429 41
0.374 this
work
0.410 this
work
0.406 this
work
Mn[TPFPC]Cl
Mn[TpNO2PC]Cl
Mn[TpMePC]Cl
Mn[TPC]Cl
YAWQES
chloro-5,10,15-tris(pentafluorophenyl)corrolatomanganese, benzene
solvate
2.312
2.284
2.295
2.284
2.287
2.428
2.633
MIKWOU chloro-5,10,15-tris(4-nitrophenyl)corrolatomanganese, dichloromethane
solvate
chloro-5,10,15-tris(4-methylphenyl)corrolatomanganese
chloro-5,10,15-triphenylcorrolatomanganese
Mn[TpCF3PC]Cl
Mn[TPFPC]Br
Mn[Et8BTC]I
chloro-5,10,15-tris(4-trifluoromethylphenyl)corrolatomanganese
YAWQAO bromo-5,10,15-tris(pentafluorophenyl)corrolatomanganese, benzene
0.416 14
solvate
GIFJEL
iodo-2,3,7,8,12,13,17,18-octaethyl-5,15-bis(4-methylphenyl)
corrolatomanganese
0.361 45
Mn[Et8DPhC]I
Mn[Et8Me2C]Ph
XIDRUY
CISGUH
CISHAO
iodo-2,3,7,8,12,13,17,18-octaethyl-5,15-diphenylcorrolatomanganese
phenyl-2,3,8,12,17,18-hexaethyl-7,13-dimethylcorrolatomanganese
1.945
1.902
1.900
1.922
1.881
1.897
2.663
2.019
2.019
0.380 42
0.285 35
0.247 35
Mn[Et6Me2C](4-
C6H4Br)
4-bromophenyl-2,3,8,12,17,18-hexaethyl-7,13-
dimethylcorrolatomanganese
Mn[TpOMePC]Ph
phenyl-5,10,15-tris(4-methoxyphenyl)corrolatomanganese
1.905
1.902
1.892
1.901
2.025
2.021
0.291 this
Molecule 1
work
Mn[TpOMePC]Ph
Molecule 2
phenyl-5,10,15-tris(4-methoxyphenyl)corrolatomanganese
0.279 this
work
for additional details), shows that the lowest unoccupied
majority-spin MO of Mn[TpCF3PC]Cl is essentially a
“porphyrin a2u-type” corrole MO, with only a small
contribution from the Mn center, whereas the corresponding
calculations, which did a good job of simulating the intensity
profile of the pre-edge region of the three complexes in
question (Table 4 and Figure 11).
The above manganese complexes make for an interesting
comparison with Fe[TPC]Cl and Fe[TPC]Ph, which we
recently investigated with a combination of spectroscopic and
theoretical methods.30 Thus, Fe[TPC]Cl and Fe[TPC]Ph have
been described as FeIII(S=3/2)-corrole•2− and FeIV(S=1)-
corrole3−, respectively, which mirrors analogous descriptions
2
MO in Mn[TpCF3PC]Ph is Mn 3dz -based. The availability of
this additional hole, which mixes strongly with the Mn 4pz
orbital, would thus appear to be primarily responsible for the
dramatic increase in the pre-edge intensity in Mn[TpCF3PC]-
Ph. This assignment was explicitly confirmed by TDDFT
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Figure 6. Selected crystallographic geometry parameters (Å) for MnCl and MnPh corroles studied in this work. In the top three structures, longer
and shorter bond lengths are indicated in blue and red, respectively.
for their manganese counterparts. Moreover, the lowest
unoccupied majority-spin MOs of Fe[TPC]Cl and Fe[TPC]Ph
are corrole “a2u”- and Fe 3dz2-based, respectively, which
explains the very similar trends in the pre-edge energy positions
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reduction potentials reflects similar reduction processes for the
two metals:
Cl‐MIII‐corrole•2−/Cl‐MIII‐corrole3− (M = Mn, Fe)
Thin-layer spectroelectrochemical studies by Kadish and co-
workers, which revealed sharp Q bands for electroreduced
MnCl corroles,33,34 are suggestive of a fully aromatic reduced
state and thus are consistent with the above assignment.
In contrast, the first reduction potentials of Mn[TpXPC]Ph
occur at dramatically more negative potentials, at −0.95 0.05
V, relative to the MnCl and FeCl series and even the FePh
series (Table 4). In other words, the MnPh corroles are much
more thermodynamically resistant to one-electron reduction
than FePh corroles, consistent with the widespread prevalence
of many stable manganese(IV) complexes. A key difference
between the two metals, however, is that one-electron
reduction of the Mn[TpXPC]Ph series is irreversible (Figure
13),34 whereas the Fe[TpXPC]Ph series reduces reversibly.30 In
other words, the reduced MnPh center is less stable than the
reduced FePh center. This difference between the two metals
may be related to B3LYP calculations, indicating a significantly
higher minority spin density on the ipso-C of the σ-phenyl
group in MnPh corroles (about −0.27 in Figure 4) than on the
analogous C in FePh corroles (−0.15).12 That, along with the
fact that the Mn carries a majority spin population greater than
3.0 (Figure 4), strongly suggests that the Mn center has a
degree of MnIII character:
MnIV( ↑ ↑ ↑ ) − Ph ↔ MnIII( ↑ ↑ ↑ ↑ ) − Ph•( ↓ )
An interesting question concerns whether redox potentials,
by themselves, can provide a clue as to the ground-state
innocence or nonnoncence of a given metallocorrole family. It
may be tempting to interpret the present results as a “yes”. The
nonninnocent MnCl and innocent MnPh series reduce at very
different potentials and exhibit very different electrochemical
HOMO−LUMO gaps. In contrast, however, the reduction
potentials and electrochemical HOMO−LUMO gaps of
analogous FeCl and FePh corroles exhibit much more modest
differences.30 Great care therefore must be exercised in relating
redox potentials to the innocence or noninnocence of the
corrole ligand in the neutral complex.
Figure 7. Two views of π-stacking interactions of Mn[TpOMePC]Ph.
and intensities for the two metals. The energy-shifted
comparison depicted in Figure 12 is in full accord with this
picture, underscoring the usefulness of metal K-pre-edges as a
source of detailed electronic structural information.
Electrochemistry. The first oxidation potentials of the
Mn[TpXPC]Cl series occur in the range 0.93−1.17 V versus
the saturated calomel electrode (SCE) and are nearly identical
to those observed for Fe[TpXPC]Cl (Figure 13 and Table 5).
The first oxidation potential of the Mn[TpXPC]Ph series is
slightly lower, by about 250 mV (Figure 13 and Table 4).
Roughly speaking, the first oxidation potentials of all metal-
lotriarylcorroles hover around +1.0 V (Table 4).51 In contrast,
the first reduction potentials vary considerably among different
metallocorrole families, as described below.
The first reduction potentials of both the Mn[TpXPC]Cl
and Fe[TpXPC]Cl series occur at around 0.1 0.1 V, which
corresponds to an electrochemical highest occupied molecular
orbital (HOMO)−lowest unoccupied molecular orbital
(LUMO) gap (defined as the difference between the first
oxidation potential and the first reduction potential) of about
1.0 V. By comparison, the electrochemical HOMO−LUMO
gaps of metallocorroles with redox-inactive metal centers such
as Au,20 OsVIN,17 and ReVO16 are approximately twice as large,
2.0−2.2 V.52 It is reasonable to assume that the similar
CONCLUSION
■
The synthesis of the new series of manganese complexes,
Mn[TpXPC]Ph (X = CF3, H, Me, and OMe), has allowed an
extensive multitechnique comparison with the Mn[TpXPC]Cl
series and a detailed examination of the question of ligand
noninnocence in the two series. While the Soret bands of the
former series were found to exhibit only minor variations, the
Soret maxima of the latter series were found to red-shift by 37
nm from X = CF3 to X = OMe. These observations, which
parallel analogous observations for iron corroles, suggested a
noninnocent corrole•2− ligand for the MnCl complexes and an
innocent corrole3− ligand for the MnPh complexes. Single-
crystal X-ray structures of multiple Mn[TpXPC]Cl complexes
also revealed bond-length alternations characteristic of non-
innocent metallocorroles; no such bond-length alternation was
observed for Mn[TpOMePC]Ph. Spin-unrestricted DFT
calculations yielded spin-density profiles consistent with an
antiferromagnetically coupled MnIII-corrole•2− description for
Mn[TPC]Cl and a largely MnIV-corrole3− description for
Mn[TPC]Ph, albeit with a degree of MnIII−Ph• character. The
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Figure 8. Selected symmetry-distinct geometry parameters (Å) for Mn[TpCF3PC](py)2. The meso-aryl groups have been deleted for clarity.
The much more negative reduction potentials of the MnPh
complexes, relative to the MnCl complexes, also appear to be
consistent with an innocent corrole ligand and a relatively
stable MnIVPh center. XANES, applied here for the first time to
manganese corroles, nicely confirmed the above conclusions.
Thus, compared with Mn[TpCF3PC]Cl, the Mn K-pre-edge of
Mn[TpCF3PC]Ph was not only blue-shifted by 0.6 eV but also
was dramatically more intense. DFT and TDDFT calculations
showed that the enhanced intensity results from the extra d
hole in MnPh compound. This hole, which corresponds to the
2
LUMO, involves strong 3dz −4pz mixing, the key factor
underlying the dramatically enhanced pre-edge of Mn[TPC]Ph.
Along with similar measurements on iron corroles, the present
study underscores the considerable usefulness of XANES as a
probe of metal-ion oxidation state, and thereby of ligand
Figure 9. Normalized Mn K-edge XANES data for solid Mn-
[TpCF3PC]Cl (black), Mn[TpCF3PC]Ph (red), and Mn[TpCF3PC]-
noninnocence, in metallocorroles.
(py)n (blue). The inset displays an expanded view of the pre-edge
region.
EXPERIMENTAL SECTION
Materials. All reagents and solvents were used as purchased unless
otherwise noted. Silica gel 150 (35−70 μm particle size, Davisil) was
used as the stationary phase for flash chromatography, and silica gel 60
PLC plates (20 × 20 cm, 0.5 mm thick, Merck) were used for the final
purification of the products. CHROMASOLV HPLC-grade n-hexane
and dichloromethane were used as solvents for column chromatog-
raphy. Phenylmagnesium bromide (3.0 M in diethyl ether, Sigma-
Aldrich), Mn(OAc)2·4H2O (Merck), and pyridine (≥99%, Sigma-
Aldrich) were used as received. For electrochemical measurements,
■
calculations also reproduced the characteristic bond-length
alternation for Mn[TPC]Cl. Although these results are not
particularly surprising, their mutual consistency greatly bolsters
our faith in the experimental and computational methods
employed, viz., optical spectroscopy, X-ray crystallography, and
DFT calculations, as probes of ligand noninnocence in corroles.
H
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Figure 10. LUMO energy levels and contour plots for Mn[TpCF3PC]Cl and Mn[TpCF3PC]Ph. Only the Mn 3d-based MOs are shown, and ligand-
based MOs have been omitted for clarity.
Table 4. Experimental and Calculated (TDDFT) IWAE
a,b
Positions (eV) and Relative Intensities
Mn[TpCF3PC]
(py)n
Mn[TpCF3PC]Cl
Mn[TpCF3PC]Ph
calc
exp
calc
exp
calc
exp
IWAE
6372.2
1.0
6540.6
1.0
6372.3
2
6540.8
2.1
6372.7
6.3
6541.4
5.3
relative
intensity
a
The calculated and experimental intensities of solid Mn[TpCF3PC]-
(py)n have been set at 1.0 for the purpose of intercompound
b
comparison. For comparison with calculated TDDFT spectra,
experimental IWAE positions obtained by fitting the data were fit
with the Peakfit software (Sigmaplot).
commericially available anhydrous dichloromethane was predried with
CaH2, distilled, and stored over 3 Å molecular sieves. Tetrakis(n-
butyl)ammonium perchlorate (Sigma-Aldrich), recrystallized three
times from absolute ethanol, vacuum-dried at 40 °C for 2 days, and
stored in a desiccator for at least 2 weeks, was used as the supporting
electrolyte. The free-base corroles H3[TpXPC] (X = CF3, H, Me, and
OMe) were synthesized as previously reported.53
Figure 11. Comparison of the Mn K-pre-edge XAS data (solid lines)
for solid Mn[TpCF3PC](py)n (blue), Mn[TpCF3PC]Cl (black), and
Mn[TpCF3PC]Ph (red) with the TDDFT-calculated spectra on their
TPC analogues (dashed lines). The calculated spectra have been
linearly upshifted by 168.2 eV. The calculated intensities have been
scaled for graphical representation.
Instrumentation. UV−vis spectra were recorded on an Agilent
Cary 8454 UV−vis 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
counter electrode, and an SCE reference electrode. The reference
electrode was separated from the 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.
High-resolution mass spectrometry (HRMS) spectra were recorded on
an LTQ Orbitrap XL spectrometer.
Synthesis of Mn[TpCF3PC](py)n. A 50 mL round-bottomed flask
equipped with a magnetic stir-bar was charged with free-base tris(4-
trifluoromethylphenyl)corrole (0.044 g, 0.06 mmol) dissolved in
pyridine (15 mL). To this solution was added Mn(OAc)2·4H2O (10
equiv, 0.147 g, 0.60 mmol). The reaction flask was then fitted with a
reflux condenser and heated on an oil bath at 105 °C with stirring for
approximately 30 min, whereupon completion of metal insertion was
confirmed by UV−vis spectroscopy and/or mass spectrometry. Upon
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Table 5. Electrochemical Data (V) for the Compounds
Studied
series
X
Eox2
Eox1
Ered1
EHOMO−LUMO
ref
this
work
Mn[TpXPC]
CF3
1.17
0.23
0.94
Cl
H
1.05
1.00
0.93
0.10
0.07
0.06
0.95
0.93
0.87
1.76
Me
OMe
CF3
a
Mn[TpXPC]
1.27
0.86 −0.90
this
work
Ph
a
a
a
H
1.13
1.06
0.98
0.77 −0.95
0.73 −0.97
0.70 −0.99
1.72
1.70
1.68
0.99
1.05
1.05
0.94
1.20
Me
OMe
CF3
H
Fe[TpXPC]Cl
1.18
1.09
1.05
0.97
0.98
0.19
0.04
0.00
0.03
1, 30
Me
OMe
CF3
Figure 12. Comparison of the metal K-pre-edge XAS data for
Mn[TpCF3PC]Cl/Fe[TPC]Cl (black) and Mn[TpCF3PC]Ph/Fe-
[TPC]Ph (red), where the Mn and Fe data are indicated by solid
and dashed lines, respectively.
Fe[TpXPC]
(NO)
−0.22
22
H
0.86
0.84
0.83
0.92
0.82
0.78
0.76
0.89
0.76
0.70
0.65
0.94
0.80
0.78
0.76
−0.33
−0.36
−0.37
−0.27
−0.35
−0.37
−0.39
−0.08
−0.20
−0.23
−0.24
−1.29
−1.38
−1.42
−1.57
1.19
1.20
1.20
1.19
1.17
1.15
1.15
0.97
0.96
0.93
0.89
2.23
2.18
2.20
2.33
Me
OMe
Fe[TpXPC]Ph CF3
1.29
1.20
1.14
1.09
30
2
H
Me
OMe
Cu[TpXPC]
Au[TpXPC]
CF3
H
Me
OMe
CF3
H
20
1.35
1.35
1.32
Me
OMe
a
Peak potential for irreversible cathodic reduction.
HRMS (major isotopomers in the presence of a drop of pyridine; M =
C40H20N4F9Mn; [M + py]+): 861.1344 (exp), 861.1341 (calc). X-ray-
quality crystals were obtained by the slow evaporation of a
concentrated solution of the complex in 4:1 n-heptane/CHCl3
containing a few drops of pyridine, over 3−4 weeks.
Synthesis of MnCl Corroles. A detailed procedure is described
below for the synthesis of Mn[TpOMePC]Cl. A similar procedure was
also followed for the synthesis of the other manganese complexes,
except for details of the chromatographic purifications, which are
specified separately.
Synthesis of Mn[TpOMePC]Cl. A 100 mL two-neck round-
bottomed flask equipped with a magnetic stir-bar was charged with
free-base tris(4-methoxyphenyl)corrole (0.1 g, 0.16 mmol) and DMF
(40 mL). To the solution was added Mn(OAc)2·4H2O (10 equiv,
0.392 g, 1.6 mmol), and argon was bubbled through the solution for 5
min. The reaction flask was then fitted with a reflux condenser and
heated on an oil bath at 165−170 °C with stirring for approximately
45 min. Completion of the reaction was confirmed by UV−vis
spectroscopy and mass spectrometry. Upon cooling, the solution was
rotary-evaporated to dryness to yield a dark-brownish-green residue.
The residue was redissolved in a minimum volume of 1:1
dichloromethane/ethyl acetate and chromatographed on a silica gel
column (8−10 cm height) with 1:1 n-hexane/ethyl acetate as the
eluent. The front-running green band and the second reddish-brown
band were collected and combined; these contained the initially
formed manganese(III) corrole (as confirmed by ESI-MS).
Figure 13. Cyclic voltammograms for the manganese corroles studied:
Mn[TpXPC]Cl (top) and Mn[TpXPC]Ph (bottom).
cooling, the solution was rotary-evaporated to dryness under high
vacuum. The resulting dark-greenish-brown residue was redissolved in
a minimum volume of dichloromethane containing a couple of drops
of pyridine and chromatographed on a silica gel column (12 cm
height) with n-hexane/dichloromethane/pyridine (2:1:0.02) as the
eluent. The front-running, green band was collected and identified as
the title compound. Recrystallization from a mixture of approximately
5:1 n-hexane/dichloromethane with a few drops of pyridine afforded
the solid product (0.0425 g, 0.049 mmol, 81.7% based on n = 1),
which was used for XAS measurements. UV−vis [CH2Cl2; λmax, nm (ε
× 10−4, M−1cm−1)]: 408 (4.18), 430 (3.88), 506 (1.48), 658 (1.08).
The combined fraction was rotary-evaporated to dryness, and the
residue was redissolved in dichloromethane (25 mL). The dichloro-
methane solution of manganese(III) corrole was treated with 10%
aqueous HCl (3 × 25 mL), washed twice with distilled water, dried
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over anhydrous Na2SO4, and filtered, and the filtrate was rotary-
evaporated under vacuum to yield a dark-reddish-brown residue. The
residue was redissolved in a minimum volume of dichloromethane and
chromatographed on a silica gel column (10 cm height) with
dichloromethane and subsequently with 1:0.01 dichloromethane/
methanol as the eluent. The reddish-brown band was collected and
identified as pure Mn[TpOMePC]Cl (0.044 g, 0.062 mmol, 39% yield
relative to free-base H3[TpOMePC]). UV−vis [CH2Cl2; λmax, nm (ε ×
10−4, M−1cm−1)]: 330 (2.77), 394 (3.95), 460 (3.84), 533 (1.86).
HRMS (major isotopomer; [M]−):54 703.1314 (expt), 703.1314
(calc).
341 (3.21), 389 (4.8), 521 (1.16), 542 (1.36). HRMS (major
isotopomer; [M]+): 697.2150 (expt), 697.2158 (calc).
Synthesis of Mn[TPC]Ph. Silica gel column chromatography with
3:1 n-hexane/dichloromethane followed by PLC with 2:1 n-hexane/
dichloromethane as the eluent afforded pure Mn[TPC]Ph (0.018 g,
42%). UV−vis [CH2Cl2; λmax, nm (ε × 10−4, M−1 cm−1)]: 341 (3.5),
394 (5.15), 521 (1.3), 539 (1.4). HRMS (major isotopomer; [M]+):
655.1690 (expt), 655.1689 (calc).
Synthesis of Mn[TpCF3PC]Ph. Silica gel column chromatography
with 4:1 n-hexane/dichloromethane followed by PLC with 3:1 n-
hexane/dichloromethane as the eluent afforded pure Mn[TpCF3PC]-
Ph (0.016 g, 38%). UV−vis [CH2Cl2; λmax, nm (ε × 10−4, M−1 cm−1)]:
340 (3.4), 398 (5.36), 523 (1.36), 535 (1.35). HRMS (major
isotopomer; [M]+): 859.1315 (expt), 859.1311 (calc).
Synthesis of Mn[TpMePC]Cl. Silica gel column chromatography
with dichloromethane and subsequently with 1:0.005 dichloro-
methane/methanol as the eluent afforded the pure product (0.061 g,
Single-Crystal X-ray Structure Determinations. Data for all
compounds were collected on beamline 11.3.1 at the Advanced Light
Source, Lawrence Berkeley National Laboratory. The samples were
mounted on MiTeGen Kapton loops and placed in a 100(2) K
nitrogen cold stream provided by an Oxford Cryostream 700 Plus low-
temperature apparatus on the goniometer head of a Bruker D8
diffractometer equipped with a PHOTON100 CMOS detector (for
Mn[TpOMePC]Ph) or a PHOTONII CPAD detector (for the other
compounds) operating in shutterless mode. Diffraction data were
collected using synchrotron radiation monochromated using Si(111).
Approximate full-spheres of data were collected using a combination of
φ and ω scans. The crystals of Mn[TpCF3PC]Cl were found to be
twinned, and the components were separated using CELL_NOW.55
Absorption corrections were applied using SADABS56 or TWINABS57
(for Mn[TpCF3PC]Cl). The structures were solved by direct methods
(SHELXS58 for Mn[TPC]Cl) or intrinsic phasing (SHELXT59) and
refined by full-matrix least squares on F2 (SHELXL-201460) using the
ShelXle GUI.61 Appropriate scattering factors were applied using the
XDISP62 program within the WinGX suite.63 All non-H atoms were
refined anisotropically. H atoms were geometrically calculated and
refined as riding atoms. The Mn[TPC]Cl crystal was found to be
twinned using the TWINROTMAT routine in PLATON,64 and the
appropriate twin law was added to the model. The large residual peak
of the electron density in Mn[TpCF3PC](py)2 was identified as the
Mn site of a second orientation of the corrole unit, whose occupancy
was refined to 6% (see the CIF files for additional details). Additional
crystallographic information has been summarized in Table 2, and full
details can be found in the CIF files.
Mn K-Edge XAS Measurements. The Mn K-edge X-ray
absorption spectra of Mn[TpCF3PC]Cl, Mn[TpCF3PC]Ph, and
Mn[TpCF3PC](py)n were measured at the SSRL on the wiggler
BL9-3 under standard ring conditions of 3 GeV and ∼500 mA. A
Si(220) double-crystal monochromator was used for energy selection.
A harmonic rejection mirror was used and the monochromator
detuned by 10% to reject components of higher harmonics. During
data collection, the samples were maintained at a constant temperature
of ∼10 K using an Oxford liquid-helium cryostat. Mn K-edge XAS data
for Mn[TpCF3PC]Cl and Mn[TpCF3PC]Ph were measured in
transmission mode using ion chambers as detectors. A 100-element
germanium fluorescence detector from Canberra Industries was
employed for fluorescence data measurements on Mn[TpCF3PC]-
(py)n. For fluorescence measurements, the background signal was
suppressed using soller slits equipped with a chromium filter. The solid
samples were ground to a homogeneous powder in a BN matrix. The
homogeneous mixture was then placed in aluminum spacers and
wrapped in Kapton tape. Solution samples were transferred into 2 mm
Delrin XAS cells with 70 mm Kapton tape windows and immediately
frozen after preparation and stored under liquid N2. Internal energy
calibration was accomplished by simultaneous measurement of the
absorption of a manganese foil placed between two ionization
chambers situated after the sample. The first inflection point of the
foil spectrum was set at 6539.0 eV. The data presented here are 3-, 2-,
and 12-scan average spectra for Mn[TpCF3PC]Cl, Mn[TpCF3PC]Ph,
and Mn[TpCF3PC](py)n, respectively. At least two sweeps were
collected to ensure that no radiation damage was observed. Energy
calibration, background correction, data averaging, and normalization
0.09 mmol, 53% relative to H3[TpMePC]). UV−vis [CH2Cl2; λmax
,
nm (ε × 10−4, M−1 cm−1)]: 318 (2.56), 361 (3.08), 442 (4.71). HRMS
(major isotopomer; [M]−): 655.1467 (expt), 655.1467 (calc). X-ray-
quality crystals were obtained by the slow evaporation of a
concentrated solution of the complex in 4:1 n-hexane/dichloro-
methane, over 2 weeks.
Synthesis of Mn[TPC]Cl. Silica gel column chromatography with
dichloromethane and subsequently with 1:0.005 dichloromethane/
methanol (200 mL) as the eluent afforded the pure product (0.053 g,
0.086 mmol, 45% relative to H3[TPC]). UV−vis [CH2Cl2; λmax, nm (ε
× 10−4, M−1 cm−1)]: 315 (1.69), 363 (2.21), 433 (4.64). HRMS
(major isotopomer; [M]−): 613.1000 (expt), 613.0997 (calc). X-ray-
quality crystals were obtained by the slow evaporation of a
concentrated solution of the complex in 3:1 n-hexane/dichloro-
methane, over almost 2 weeks.
Synthesis of Mn[TpCF3PC]Cl. Silica gel column chromatography
with dichloromethane (3 × 500 mL) and subsequently with 1:0.005
dichloromethane/methanol (100 mL) as the eluent afforded the pure
product (0.062 g, 0.076 mmol, 54% relative to H3[TpCF3PC]). UV−
vis [CH2Cl2; λmax, nm (ε × 10−4, M−1 cm−1)]: 314 (1.59), 363 (2.29),
423 (5.10). HRMS (major isotopomer; [M]−): 817.0612 (expt), 817.
0619 (calc). X-ray-quality crystals were obtained by the slow
evaporation of a concentrated solution of the complex in 4:1 n-
heptane/CHCl3, over 3 weeks.
Synthesis of MnPh Corroles. A detailed procedure is described
below for the synthesis of Mn[TpOMePC]Ph. A similar procedure
was also followed for the synthesis of the other manganese complexes,
except for details of the chromatographic purifications, which are
specified separately.
Synthesis of Mn[TpOMePC]Ph. A 50 mL round-bottomed flask
equipped with a magnetic stir-bar was charged with Mn[TpOMePC]-
Cl (0.04 g, 0.057 mmol). Anhydrous dichloromethane (15 mL) was
added with a syringe under argon, and the mixture was stirred under
argon for 5 min. Phenylmagnesium bromide (114 μL, 6 equiv) was
then added with a syringe, and the mixture was stirred under argon for
7−8 min. The solution was then quenched with an excess of distilled
water and extracted with dichloromethane. The organic fraction was
dried with anhydrous MgSO4 and filtered, and the filtrate was
evaporated to dryness on a rotary evaporator under vacuum. The dark-
brown residue obtained was redissolved in a minimum volume of
dichloromethane and chromatographed on a silica gel column with 1:1
n-hexane/dichloromethane as the eluent. The product eluted as an
intense dark-red band, which was collected and evaporated to dryness.
Final purification was carried out with PLC using 1:2 n-hexane/
dichloromethane as the eluent. The front-running red band contained
pure Mn[TpOMePC]Ph (0.014 g, 33%). UV−vis [CH2Cl2; λmax, nm
(ε × 10−4, M−1cm−1)]: 341 (3.35), 387 (5.67), 429(sh) (3.8), 519
(1.26), 544 (1.54). HRMS (major isotopomer; [M]+): 745.2009
(expt), 745.2006 (calc). Needle-shaped, X-ray-quality crystals were
obtained by the slow diffusion of MeOH vapor into a concentrated
CHCl3 solution of the complex, over 1 week.
Synthesis of Mn[TpMePC]Ph. Silica gel column chromatography
with 3:1 n-hexane/dichloromethane followed by PLC with 3:2 n-
hexane/dichloromethane as the eluent afforded pure Mn[TpMePC]Ph
(0.0156 g, 37%). UV−vis [CH2Cl2; λmax, nm (ε × 10−4, M−1 cm−1)]:
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were carried out with ATHENA, which is part of the Demeter software
package, version 0.9.24.65
REFERENCES
■
(1) Steene, E.; Wondimagegn, T.; Ghosh, A. Electrochemical and
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carried out with the BP86 functional and a spin-unrestricted
formalism, allowing for broken-symmetry solutions, using the ORCA
3.0.3 program system.66,67 Ahlrich’s all-electron triple-ζ triple polar-
ization TZVPPP basis set was used for the Mn atom, and TZVPP was
used for all other atoms.68 All calculations were performed in a
dielectric continuum using the conductor-like screening model with
benzene as the solvent.69 Tight self-consistent-field (SCF) con-
vergence criteria were employed throughout. The SlowConv criterion
was employed. An SCF grid of 4 with no final grid was used. A higher
grid (grid 7) was used on the Mn atom. The optimized structures were
used for single-point calculations using the B3LYP functional (while
otherwise maintaining the same calculational parameters). Subse-
quently, B3LYP TDDFT calculations were performed to simulate the
Mn K pre-edge region (as implemented in the ORCA package). The
number of roots was set at 20, MaxDim was set at 200, “doQuad True”
was selected, and spin-flip transitions were not calculated. The
TDDFT calculations were performed over the entire valence manifold
and for both the spin-up (OrbWin = 0) and spin-down (OrbWin = 1)
transitions. The calculated energies and intensities were broadened
using the line-broadening script within ORCA to achieve half-widths of
1.5 eV to account for the core−hole lifetime and instrument
broadening. The calculated pre-edge energies were linearly upshifted
by 168.2 eV for comparison with the experimental spectra.
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ASSOCIATED CONTENT
* Supporting Information
■
(8) 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.
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00537.
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Undecaphenylcorroles. Inorg. Chem. 2012, 51, 9911−9916.
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in Coinage Metal Corroles: A Silver Knife-Edge. Chem. - Eur. J. 2015,
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EXAFS data, ESI-MS spectra, and details of DFT/
TDDFT calculations (PDF)
Accession Codes
CCDC 1826554−1826558 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.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: ritis@slac.stanford.edu (R.S.).
*E-mail: abhik.ghosh@uit.no (A.G.).
■
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Insights from Chromium-Oxo and Molybdenum-Oxo Triarylcorroles.
J. Porphyrins Phthalocyanines 2011, 15, 1335−1344.
ORCID
Laura J. McCormick: 0000-0002-6634-4717
Jeanet Conradie: 0000-0002-8120-6830
Abhik Ghosh: 0000-0003-1161-6364
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was supported by grants 231086 and 262229 of the
Research Council of Norway (AG) and the National Research
Fund of the Republic of South Africa (JC). This research used
resources of the Advanced Light Source, which is a DOE Office
of Science User Facility under contract no. DE-AC02-
05CH11231. The SSRL Structural Molecular Biology (SMB)
resource is supported by the NIH 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.
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