Undecaphenylcorroles

Article abstract of DOI:10.1021/ic301388e

A first major study of undecaphenylcorrole (UPC) derivatives is presented. Three different Cu-UPC derivatives with different para substituents X (X = CF₃, H, CH₃) on the β-aryl groups were synthesized via Suzuki-Miyaura coupling of Cu[Br₈TPC] and the appropriate arylboronic acid. A single-crystal X-ray structure of the X = CF₃ complex revealed a distinctly saddled macrocycle conformation with adjacent pyrrole rings tilted by ～60-66° relative to one another (within the dipyrromethane units), which is somewhat higher than that observed for β-unsubstituted Cu-TPC derivatives but slightly lower than that observed for Cu[Br₈TPC] (～70°) derivatives. Electrochemical and electronic absorption measurements afforded some of the first comparative insights into meso versus β substituent effects on the copper corrole core. The Soret maxima of the Cu-UPC complexes (～440-445 nm), however, are comparable to those of Cu[Br₈TPC] derivatives and are considerably red-shifted relative to Cu-TPC derivatives. Para substituents on the β-phenyl groups were found to tune the redox potentials of copper corroles more effectively than those on meso-phenyl substituents, a somewhat surprising observation given that neither the HOMO nor LUMO has significant amplitudes at the β-pyrrolic positions.

Full text of DOI:10.1021/ic301388e

Article
pubs.acs.org/IC
Undecaphenylcorroles
Steffen Berg,† Kolle E. Thomas,† Christine M. Beavers,‡ and Abhik Ghosh*,†
†Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, 9037 Tromsø, Norway
‡Advanced Light Source (ALS), Lawrence Berkeley National Laboratory (LBNL), Berkeley, California 94720-8229, United States
S
* Supporting Information
ABSTRACT: A first major study of undecaphenylcorrole (UPC) derivatives is presented.
Three different Cu-UPC derivatives with different para substituents X (X = CF3, H, CH3)
on the β-aryl groups were synthesized via Suzuki−Miyaura coupling of Cu[Br8TPC] and
the appropriate arylboronic acid. A single-crystal X-ray structure of the X = CF3 complex
revealed a distinctly saddled macrocycle conformation with adjacent pyrrole rings tilted
by ∼60−66° relative to one another (within the dipyrromethane units), which is some-
what higher than that observed for β-unsubstituted Cu-TPC derivatives but slightly lower
than that observed for Cu[Br8TPC] (∼70°) derivatives. Electrochemical and electronic
absorption measurements afforded some of the first comparative insights into meso versus
β substituent effects on the copper corrole core. The Soret maxima of the Cu-UPC
complexes (∼440−445 nm), however, are comparable to those of Cu[Br8TPC] derivatives
and are considerably red-shifted relative to Cu-TPC derivatives. Para substituents on the β-
phenyl groups were found to tune the redox potentials of copper corroles more effectively
than those on meso-phenyl substituents, a somewhat surprising observation given that
neither the HOMO nor LUMO has significant amplitudes at the β-pyrrolic positions.
formation of metal−metal-bonded dimers, a common occur-
rence with second- and third-row transition metals.4,5 A third and
crucial motivation for this study is that corroles, as trianionic
ligands, support fundamentally different transition-metal chem-
istry, including different coordination, oxidation, and spin states,
relative to the dianionic porphyrins.6 These considerations led us
to initiate a systematic study of UPC derivatives. Except for an
isolated report on copper undecakis(p-chlorophenyl)corrole,7
these fascinating ligands and their complexes remain virtually
unexplored. We present here Suzuki−Miyaura8 coupling-based
syntheses of three Cu-UPC derivatives with varying p-X-
substituted (X = CF3, H, CH3; Figure 2) β-aryl groups, Cu[(4-
XPh)8TPC] (TPC = meso-triphenylcorrole). The syntheses are
convenient and apparently quite general; preliminary experi-
ments indicate that other UPC derivatives, including the free-
base ligands and various metal complexes, should also be
accessible via an analogous strategy.
INTRODUCTION
■
Like their porphyrin counterparts,1,2 sterically hindered corroles
such as undecaphenylcorrole (UPC) derivatives (Figure 1) are of
The copper complexes reported herein are of considerable
interest in their own right. Uniquely among metallocorroles,
which are generally planar (regardless of peripheral steric crowd-
ing),6 copper corroles exhibit inherent saddling (even in the
absence of a sterically hindered set of substituents). This saddling
2
2
is primarily an electronic effect, a result of a copper (dx −y )−
corrole (“a2u”) orbital interaction (Figure 3),9 but it is accen-
tuated by sterically hindered substituents.10,11 The molecular
structure of a Cu-UPC derivative is thus of considerable interest,
and we report here the first such X-ray structure. Electrochemical
and electronic absorption studies on the new compounds also
Figure 1. Space-filling model of Cu-UPC as a paradigm of a sterically
hindered metallocorrole.
interest for many reasons. They offer, for example, the potential
for shape-selective catalysis.3 They also promise novel
coordination complexes, which might be too unstable in the
absence of a sterically protective ligand environment. The
sterically hindered ligands should effectively preclude the
Received: June 28, 2012
Published: September 6, 2012
© 2012 American Chemical Society
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the corrole and one hexane molecule. The copper corrole is
bisected by a crystallographic C2 axis, aligned along the Cu−C10
(meso) vector. The structure, including all of the CF3 groups
(somewhat remarkably), is fully ordered. The corroles stack
upon each other along the c axis (space group C2/c). Their
sterically hindered nature and helical shape, however, result in a
pocket containing two hexane molecules, with an inversion-
related corrole closing the pocket.
The copper corrole macrocycle exhibits a fairly strongly
saddled conformation. The two symmetry-distinct saddling
dihedrals C8−C9−C9′−C8′ and C3−C4−C6−C7 are 60.1 and
66.0°, respectively (see Figure 4). Qualitatively, the conforma-
tion resembles that of other copper corroles and of various DPP
derivatives. The origin of the saddling, however, is very different
for corroles, relative to porphyrins. For DPP derivatives,15 the
saddled geometries are a consequence of their sterically hindered
nature. By contrast, steric hindrance is almost never sufficient
for bringing about saddling in metallocorroles, as illustrated
by several sterically hindered, undecasubstituted metallocor-
roles with planar macrocyclic cores (see ref 6c for a detailed
discussion). As mentioned, copper corroles are an important
exception in this regard in that they are inherently saddled on
electronic grounds.9 As shown in Figure 3, saddling allows some
of the electron density of a corrole “a2u-type” highest occupied
molecular orbital (HOMO; using porphyrin nomenclature) to
flow into the empty dx −y orbital of the formally trivalent metal
center. The copper center is thus not true CuIII but has sig-
nificant CuII character. The degree of saddling observed for
Cu[(4-CF3Ph)8TPC] is significantly higher than that observed
for Cu-TPC derivatives and marginally smaller than what is
found for Cu[Br8TPC] derivatives.6c,9,10 In other words, the
β-aryl groups accentuate the saddling relative to β-H, but not
quite as much as β-Br groups.
Figure 2. Cu[(4-XPh)8TPC] derivatives reported in this study.
shed significant light on β-substituent effects on metallocorroles.
Relatively little is known about the subject because, compared
with meso-aryl substituents, β substituents on porphyrins and
corroles are not as easily manipulated. To date, we have reported
five different Cu-TPC series with varying β substituents, viz., Ph,
H, Br,12 F,13 and CF3.14 A comparison of the five series affords
unique insight into the interplay of electronic and steric effects on
metallocorroles.
The new UPC derivatives were synthesized from Cu-
[Br8TPC]12 and the appropriate arylboronic acid in refluxing
toluene under anerobic conditions with Pd2(dba)3·CH2Cl2 (dba =
dibenzylidene acetone) as the catalyst. Except for the catalyst,
these conditions are similar to those used in early syntheses of
dodecaphenylporphyrins (DPPs) by Muzzi et al.2a The use of
Pd(PPh3)4, the catalyst used by these authors, however, led to
significantly longer reaction times. Aerobic conditions led to
drastically lower yields. The reaction appeared to be faster with
more electron-donating p-X groups on arylboronic acid, taking
approximately 1.5, 2.0, and 2.5 days for X = CH3, H, and CF3,
respectively (progress being monitored with electrospray
ionization mass spectrometry). The yields, however, exhibited
an opposite dependence on X: 41, 56, and 82% for CH3, H, and
CF3, respectively.
2
2
b. Electrochemistry. Figure 5 presents the cyclic voltammo-
grams of the three Cu-UPC derivatives studied and Table 1 the
corresponding redox potentials. Clearly, the para substituents on
the β-aryl groups exercise a significant effect on both the
oxidation and reduction potentials, which may be modeled by
Hammett-type equations, as follows:16
E
1/2ox1/V = 0.35σp + 0.71
RESULTS AND DISCUSSION
■
a. Molecular Structure of Cu[(4-CF3Ph)8TPC]·2C6H14.
Small X-ray-quality crystals, with dimensions of 0.06 × 0.01 ×
0.01 mm3, were obtained for one of the complexes, Cu[(4-
CF3Ph)8TPC], and the structure could be solved at the ALS,
Berkeley, CA (Figure 4). The asymmetric unit consists of half of
E1/2red1/V = 0.49σp + 0.43
Recalling that there are eight β-aryl groups, the substituent effect
per β-aryl group is given by
Figure 3. Frontier orbitals (OLYP/TZP) of Cu-TPC: (a) LUMO; (b) HOMO.
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Figure 4. Left and top right: Thermal ellipsoid diagrams (two different views at the 50% probability level) for Cu[(4-CF3Ph)8TPC]. Bottom right:
Stacking of two inversion-related corroles. The structures on the right side have been viewed along the b axis (parallel to the molecular C2 axes).
Distances (Å): Cu−N1 1.897, Cu−N2 1.902. Dihedrals (deg): C2−C1−C1−C2 40.9, C3−C4−C6−C7 60.1, C8−C9−C9′−C8′ 66.0, the primed
atoms are the C2-related counterparts of the corresponding unprimed atoms.
dE1/2red1
dσ
1
8
0.49 V
8
=
= 61 mV
For comparison, the effect of a para substituent in the meso-
triarylcorrole series, Cu[T(4-XP)C], is given by12
dE1/2ox1
dσ
1
3
= 32 mV
dE1/2red1
dσ
1
3
= 23 mV
Para substituents on β-aryl groups thus are more effective at
tuning the electronic character of the copper corrole core than
para substituents on meso-aryl groups. This result is somewhat
unexpected, given that both the HOMO and lowest unoccupied
molecular orbital (LUMO) of copper corroles have large
amplitudes at the meso positions but only small ones at the β
positions. A plausible explanation is that the electronic effects of aryl
substituents have a large through-space, electrostatic component.
In concert with our earlier contributions on metallocorroles,16
this study affords some of the first detailed insights into
β-substituent effects on copper corroles. The first oxidation and
reduction potentials of the five Cu[X8TPC] (X = Ph, H, Br, F,
CF3) derivatives are listed in Table 2, along with Hammett
substituent constants,17 Charton’s steric parameters (νX),17 and
the corrole saddling dihedral (ω, defined as the C8−C9−C9′−C8′
Figure 5. Cyclic voltammograms of Cu[(4-XPh)8TPC] (X = CF3, H,
CH3) in CH2Cl2.
Table 1. Cu-UPC Redox Potentials (V vs SCE) in CH2Cl2
complex
E1/2ox1
E1/2ox2
E1/2red1
E1/2red2
Cu[(4-CF3Ph)8TPC]
Cu-UPC
0.89
0.70
0.65
1.36
1.25
1.23
−0.17
−0.45
−0.50
−0.90
−0.89
−0.91
Cu[(4-CH3Ph)8TPC]
dE1/2ox1
dσ
1
8
0.35 V
8
=
= 44 mV
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time-dependent density functional theory (TDDFT) calcula-
tions, these shifts reflect aryl-to-Cu charge-transfer character in
the Soret region. As shown in Figure 6, the corresponding shift
Table 2. Redox Potentials of Cu[X8TPC] (V vs SCE) as a
Function of the β Substituents X
+
−
X
σp
σp
σp
E1/2ox1 E1/2red1
νX
ω (deg)
Ph
H
−0.01
0.00
0.15
0.06
0.53
−0.18
0.00
0.02
0.00
0.70
0.76
1.14
1.15
1.39
−0.45
−0.20
0.12
1.66
0.00
0.65
0.27
0.91
66
469
6810
Br
F
0.23
0.25
a
−0.07
n.a.
−0.03
0.65
0.22
na
CF3
0.26
8511
a
na = not available.
or C8−C9−C11−C12 torsion). Compared with the Cu[(4-
XPh)8TPC] derivatives discussed above, the complexes listed in
Table 2 are more diverse, not only in terms of the electronic char-
acter of the β substituents but also in terms of their steric character,
which leads to substantial differences in saddling across the five
molecules. Overall, both E1/2ox1 and E1/2red1 vary over a wide range,
nearly 700 mV. An interesting question concerns whether we can
analyze and model the interplay of the substituent electronic
effects and macrocycle distortion.
Figure 6. Electronic absorption spectra of Cu[(4-XPh)8TPC] in
CH2Cl2, with those of Cu[T(4-XP)C] also shown for comparison (top
right).
Not surprisingly, when steric effects and nonplanar distortions are
ignored, the redox potentials exhibit poor-to-modest correlation with
the Hammett σp constants of the β substituents (as reflected in R2):
for Cu[(4-XPh)8TPC] is much smaller, only about 5 nm between
X = CF3/H and CH3. Unfortunately, although TDDFT
calculations have provided crucial qualitative insights into copper
corrole spectra, they (as they are implemented to date) do a poor
job of reproducing the Soret shifts.19 At this point, therefore, we
report these results simply as an interesting observation, without
attempting to rationalize them.
The absolute values of the Soret maxima (in nm) of the
Cu[(4-XPh)8TPC] derivatives are roughly similar to those of
Cu[Br8T(4-XP)C] and significantly higher than those of Cu[T(4-
XP)C]. The nonplanar distortion of the Cu[(4-XPh)8TPC] series,
however, is intermediate between that of Cu[T(4-XP)C] and that
of the Cu[Br8T(4-XP)C] series. The roughly 30-nm red shift of
the Soret maxima of the Cu-UPC series relative to the Cu-TPC
series thus appears to be attributable in part to a difference in
macrocycle conformation and in part to β-aryl electronic effects,
the latter suggesting that certain of the key molecular orbitals
involved in Soret-region transitions have significant β-aryl
character.
E
1/2ox1/V = 0.35σp + 0.71
R2 = 0.71
R2 = 0.44
E1/2red1/V = 0.49σp − 0.43
Including the saddling dihedral as a variable in a bilinear analysis
led to a good fit for oxidation potentials but less so for reduction
potentials:18
E1/2ox1 = 1.167σp + 0.00090ω + 0.7436
R2 = 0.99
R2 = 0.77
E1/2red1 = 1.482σp − 0.00752ω + 0.1802
+
−
Using the Hammett constants σp and σp did not result in
significantly improved fits. Thus, we cannot yet offer a simple
equation describing the redox potentials of Cu-TPC derivatives
as a function of the β substituents X, especially when the
electronic and steric character of X varies widely.
The electrochemical data (Tables 1 and 2) do, however, afford
a rather clear comparison of the electronic character of the UPC
ligands. Cu-UPC and Cu-TPC derivatives are oxidized with
comparable ease, but the former are significantly more resistant
to reduction. As sterically hindered catalysts for oxidative pro-
cesses, therefore, metallo-UPC derivatives with electron-with-
drawing β-aryl groups are likely to be more rugged and effective.
c. Electronic Absorption Spectra. The Soret maxima of
various Cu-TPC derivatives shift sensitively as a function of the
para substituents on meso-aryl groups (Table 3).19 From X = CF3
CONCLUSION
■
In summary, we have described a first major study of UPC
derivatives, including the first crystal structure of such a species.
Some of the key conclusions are: (a) The degree of saddling
observed for Cu[(4-CF3Ph)8TPC] (60−66° within the dipyrro-
methane units) is higher than that observed for β-unsubstituted
Cu-TPC derivatives (45−50°) but slightly lower than that for
Cu[Br8TPC] derivatives (70°). (b) The Soret maxima of the
Cu-UPCs, interestingly, are similar to those of Cu[Br8TPC]
derivatives and are redshifted by some 30 nm relative to those of
Cu-TPCs. (c) Para substituents on the β-phenyl groups tune the
redox potentials of copper corroles more effectively than those
on meso-phenyl substituents, while the opposite applies for Soret
maxima.
Table 3. Comparison of meso- vs p-XPh β-Substituent Effects
on Soret λmax (nm)
X =
complex
CF3
H
F
CH3
Cu[(4-XPh)8TPC]
Cu[T(4-XP)C]
441
407
436
na
441
413
439
459
443
412
445
462
445
418
453
471
The simple and effective syntheses described here open the
door for much new, exciting work on UPC derivatives. Pre-
liminary experiments indicate that both the free-base forms and
other metal complexes of UPCs should be accessible via a
Suzuki−Miyaura-based approach. Investigations into the reac-
tivity and catalytic behavior of metallo-UPCs are then an obvious
next step. Another line of inquiry concerns the dynamics of
Cu[Br8T(4-XP)C]
Cu[(CF3)8T(4-XP)C]
to CH3, the Soret maximum of Cu[T(4-XP)C] red-shifts by
11 nm and that of Cu[Br8T(4-XP)C] by 17 nm. According to
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1
2
646 (0.52). H NMR (CD2Cl2): δ 7.08 (d, J = 8.4 Hz, 4H, 2,18-m,
CF3Ph), 6.99 (d, 2J = 8.4 Hz, 4H, 2,18-o, CF3Ph), 6.97 (dd, 2J = 8.4 Hz,
3J = 1.2 Hz, 2H, 10-o, Ph), 6.94 (d, 2J = 7.8 Hz, 4H, 3,17-m, CF3Ph), 6.89
(d, 2J = 8.4 Hz, 4H, 7,13-m, CF3Ph), 6.85−6.83 (m, 4H, 5,15-o, Ph, 4H,
8,12-m, CF3Ph), 6.80 (d, 2J = 7.8 Hz, 4H, 3,17-o, CF3Ph), 6.73 (tt, 2J =
7.8 Hz, 3J = 1.2 Hz, 2H, 5,15-p, Ph), 6.67−6.62 (m, 1H, 10-p, Ph, 8H, 7,
8,12,13-o, CF3Ph), 6.46 (t, 2J = 7.8 Hz, 4H, 5,15-m, Ph), 6.42 (t, 2J = 7.8
Hz, 2H, 10-m, Ph).19F NMR: δ −63.29 (bs, 6F), −63.33 (bs, 6F),
−63.45 to −63.42 (overlapping bs, 12F). MS (HR-ESI major isotopo-
mer): M+ = 1739.27 (expt), 1739.27 (calcd). Elem anal. Found (calcd):
C, 64.35 (64.20); H, 2.91 (2.72); N, 3.16 (3.22).
Cu-UPC derivatives and of other sterically hindered copper
corroles. Because of saddling, these are inherently chiral
chromophores, which we have only synthesized in racemic
form to date.10,11,20 Detailed studies of the energetics and
geometric pathway of the enantiomerization process are
underway in our laboratory and will be reported in due course;
isolation of the pure enantiomers and their characterization by
various chiroptical methods are similarly other important goals.
EXPERIMENTAL SECTION
■
Copper 2,3,5,7,8,10,12,13,15,17,18-Undecaphenylcorrole,
Cu-UPC. The reaction was complete after 2 days (49 h). The residue
was passed through a silica gel column (14 × 3 cm) with 3:1 n-hexane/
CH2Cl2. The first two bands (brown and yellow) were impurities. The
next dark-brown band was the desired product and was eluted with 0.8 L
of the eluent. The yellow impurity band that followed was discarded.
The product was further purified by PLC with 3:1 n-hexane/CH2Cl2,
where pure Cu[UPC] appeared as the last brown band (11.1 mg, 56%).
UV−vis (CH2Cl2): λmax, nm (ε × 10−4, M−1 cm−1): 441 (3.51), 548
(0.44), 643 (0.29). 1H NMR (CD2Cl2): δ 7.06 (dd, 2J = 8.4 Hz, 3J = 1.2
Hz, 2H, 10-o, Ph), 6.92 (dd, 2J = 8.4 Hz, 3J = 1.2 Hz, 4H, 5,15-o, Ph),
6.86−6.82 (m, 6H, 2,18-m and -p, Ph), 6.80−6.77 (m, 4H, 2,18-o, Ph),
6.69−6.52 (m, 10H, 3,17-o, -m, and -p; 2H, 5,15-p; 10H, 7,13-o, -m,
and -p; 1H,10-p; 10H, 8,12-o, -m, and -p, Ph), 6.46−6.40 (m, 6H,
5,10,15-m, Ph). MS (HR-ESI major isotopomer): M+ = 1194.37 (expt),
1194.37 (calcd). Elem anal. Found (calcd): C, 85.59 (85.37); H, 4.80
(4.64); N, 4.45 (4.68).
Copper 2,3,7,8,12,13,17,18-Octakis(4-methylphenyl)-
5,10,15-triphenylcorrole, Cu[(4-CH3Ph)8TPC]. The reaction was
complete after 1.5 days (39 h). After workup, the brown residue
obtained was chromatographed on a silica gel column (14 × 3 cm) with
3:1 n-hexane/CH2Cl2 as the eluent. The first brown band was an
impurity, but the next brown band was the desired complex. It gradually
faded out to yellow and was completely eluted with 1.1 L of the eluent. A
red impurity band followed thereafter and was discarded. The product
was purified by PLC with 4:1 n-hexane/CH2Cl2. The last brown band
Materials. All reagents and solvents were used as purchased.
Toluene was predried by distillation from CaH2 and then distilled from
sodium-benzophenone. Silica gel 60 (0.04−0.063 mm particle size;
230−400 mesh, Merck) was used for flash chromatography. Silica gel 60
preparative thin-layer chromatographic plates (20 × 20 cm; 0.5 mm
thick, Merck) were used for the final purification of the new complexes.
The starting material Cu[Br8TPC] was synthesied as previously
reported.12
Instrumentation. Ultraviolet−visible (UV−vis) spectra were
recorded on an HP 8453 spectrophotometer. Cyclic voltammetry was
performed with an EG&G model 263A potentiostat having a three-
electrode system: a glassy carbon working electrode, a platinum wire
counter electrode, and a saturated calomel reference electrode (SCE).
Tetra(n-butyl)ammonium perchlorate, recrystallized twice from absolute
ethanol and dried in a desiccator for at least 2 weeks, was used as the
supporting electrolyte. The reference electrode was separated from the
bulk solution by a fritted-glass bridge filled with a solvent/supporting
electrolyte mixture. All potentials were referenced to the SCE. The
anhydrous dichloromethane solutions were purged with argon for at least
5 min prior to measurements. An argon blanket was maintained over the
1
solutions during the electrochemical measurements. H NMR spectra
(600 MHz) were recorded in CD2Cl2 (referenced to 5.30 ppm) at 298 K
on a Varian Inova spectrometer equipped with a cryogenically cooled
inverse triple-resonance probe. 19F NMR spectra (376 MHz) were
acquired at 298 K and referenced to 2,2,2-trifluoroethanol-d3 (δ =
−77.8 ppm) on a Mercury Plus Varian spectrometer. High-resolution
electrospray ionization (HR-ESI) mass spectra were recorded on an LTQ
Orbitrap XL spectrometer.
was pure Cu[(4-CH3Ph)8TPC] (8.8 mg, 41%). UV−vis (CH2Cl2): λmax
,
nm (ε × 10−4, M−1 cm−1): 445 (2.64), 644 (0.20). 1H NMR (CD2Cl2): δ
6.98 (dd, 2J = 7.8 Hz, 3J = 1.2 Hz, 2H, 10-o, Ph), 6.83 (d, 2J = 7.2 Hz, 4H,
5,15-o, Ph), 6.73 (d, 2J = 7.8 Hz, 4H, 2,18-o, tolyl), 6.68 (tt, 2J = 7.2 Hz,
3J = 1.2 Hz, 2H, 5,15-p, Ph), 6.63 (tt, 2J = 7.8 Hz, 3J = 1.2 Hz, 1H, 10-p,
Ph), 6.59 (d, 2-J = 7.8 Hz, 4H, 2,18-m, tolyl), 6.56 (d, 2J = 7.2 Hz, 4H,
3,17o, tolyl), 6.47−6.36 (m, 8H, 7, 8, 12,13-o, tolyl; 12H, 3,7,8,12,13,17-
m, tolyl, 6H, 5,10,15-m, Ph), 2.14 (s, 6H, 2,18-p-CH3, tolyl), 2.01 (s, 6H,
3,17-p-CH3, tolyl), 1.98 (s, 6H, 7,13-p-CH3, tolyl) 1.94 (s, 6H, 8, 12-p-
CH3, tolyl). MS (HR-ESI, major isotopomer): M+ = 1307.49 (expt),
1307.50 (calcd). Elem anal. Found (calcd): C, 85.53 (85.39); H, 5.67
(5.47); N, 4.19 (4.28).
General Procedure for the Synthesis of Undecaarylcorroles.
Cu[Br8TPC] (20 mg), arylboronic acid (40 equiv), potassium carbonate
(40 equiv), and Pd2(dba)3·CHCl3 (0.1 equiv) were introduced into a
50-mL three-necked, round-bottomed flask fitted with a reflux condenser
and a magnetic stirring bar. The reaction setup was degassed with argon,
followed by the addition of dry toluene (10 mL). The suspension was
purged with argon for 10 min and stirred at 100−105 °C under argon for
1.5−2.5 days. Progress of the reaction was monitored by mass spectrometry.
After complete consumption of octabromocorrole, the product mixture
was cooled to room temperature, diluted with 10 mL of CH2Cl2,
and washed with saturated aqueous NaHCO3 and then with distilled
water. The CH2Cl2 phase was dried with anhydrous Na2SO4, filtered,
and evaporated. The brown residue obtained was purified by silica gel
column chromatography with an n-hexane/CH2Cl2 mixture as the
eluent. The product eluted as an intense brown band, which was
collected and evaporated to dryness. The residue obtained was purified
by preparative thin-layer chromatography (PLC), as detailed below
for each corrole. Spectroscopic data are also fully indicated, except
for certain HHJ’s, which could not be discerned because of overlapping
peaks.20
Copper 2,3,7,8,12,13,17,18-Octakis[4-(trifluoromethyl)-
phenyl]-5,10,15-triphenylcorrole, Cu[(4-CF3Ph)8TPC]. The reac-
tion was complete after 2.5 days (62 h). The brown residue obtained
after workup was chromatographed on a silica gel column (14 × 3 cm)
with 3:1 n-hexane/CH2Cl2 as the eluent. The complex was collected as
the first brown band that faded into yellow after eluting with 0.8 L of the
eluent. The corrole residue was further purified by PLC with 4:1 n-
hexane/CH2Cl2. The last brown band was pure Cu[(4-CF3Ph)8TPC]
(23.5 mg, 82%). The complex was crystallized as tiny brownish needles
over 1 week by diffusion of CH3OH into a CH2Cl2 solution. UV−vis
(CH2Cl2): λmax, nm (ε × 10−4, M−1 cm−1): 442 (6.00), 546 (0.83),
X-ray Structure Determination of Cu[(4-CF3Ph)8TPC]·2C6H14.
A dichroic red-blue needle of dimensions 0.06 × 0.01 × 0.01 mm3 was
mounted in the 100(2)-K nitrogen cold stream provided by an Oxford
Cryostream low-temperature apparatus on the goniometer head of a
Bruker D85 diffractometer equipped with an Apex II CCD detector on
Beamline 11.3.1 at the ALS, Berkeley, CA. Diffraction data were
collected using synchrotron radiation monochromated with sili-
con(111) to a wavelength of 0.8856(1) Å. A full sphere of data, to
2θ = 63°, was collected using 0.3° ω scans. A multiscan absorption
correction was applied using the program SADABS 2008/1. The data
consist of 36315 reflections collected, of which 7223 were unique
[R(int) = 0.0645] and 4843 were observed [I > 2σ(I)]. The space group
was determined and the structure was solved by direct methods
(SHELXT) and refined by full-matrix least squares on F2 (SHELXL-97)
using 608 parameters and zero restraints. The asymmetric unit contains
half of the copper corrole and one hexane molecule. The whole corrole is
generated by a 2-fold axis. The hydrogen atoms on the carbon atoms
were generated geometrically and refined as riding atoms with C−H =
0.95−0.99 Å, Uiso(H) = 1.2Ueq(C) for aromatic carbon atoms and
Uiso(H) = 1.5Ueq(C) for CH3 groups. The maximum and minimum
peaks in the final difference Fourier map were +1.023 and −0.563 e Å−3.
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dx.doi.org/10.1021/ic301388e | Inorg. Chem. 2012, 51, 9911−9916

Inorganic Chemistry
Article
Crystal data: C105H75F24N4Cu, Mw = 1912.23, monoclinic, C2/c, a =
25.4620(13) Å, b = 25.8918(12) Å, c = 16.2468(9) Å, β = 128.316(3)°,
V = 8403.7(7) Å3, T = 100(2) K, Z = 4, R1 [I > 2σ(I)] = 0.0550, wR2
(all data) = 0.1592, GOF (on F2) = 1.039.
(16) Substituent effects on copper corroles have been examined
electrochemically in a number of papers from our laboratory12−14 but
most notably in: Ou, Z.; Shao, J.; Zhao, H.; Ohkubo, K.; Wasbotten, I.
H.; Fukuzumi, S.; Ghosh, A.; Kadish, K. M. J. Porphyrins Phthalocyanines
2004, 8, 1236−1247.
(17) Williams, A. Free Energy Relationships in Organic and Bioorganic
Chemistry; Royal Society of London: London, 2003; pp 1−297.
(18) We have preferred to use the saddling dihedral over Charton’s νX
parameter because the latter, essentially a radius most appropriate
for three-dimensional groups, is not particularly meaningful for planar
β-aryl substituents. The steric effects of the β-aryl groups are far lower
than that implied by the very high νX value shown in Table 2.
(19) Substituent effects on the electronic absorption spectra of copper
corroles have been examined in a number of papers from our
laboratory12−14 but most notably in: (a) Alemayehu, A. B.; Conradie,
J.; Ghosh, A. Eur. J. Inorg. Chem. 2011, 12, 1857−1864. (b) Alemayehu,
A. B.; Conradie, M. M.; Ghosh, A. J. Porphyr. Phthalocya. 2012, 16,
695−704.
ASSOCIATED CONTENT
* Supporting Information
Details of the synthesis and characterization, including X-ray
analysis. This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: abhik.ghosh@uit.no.
Notes
■
The authors declare no competing financial interest.
(20) The temperature-dependent NMR dynamics of the Cu-UPC
derivatives is of significant interest. At room temperature, the ortho or
meta protons on each aryl group are equivalent, as a result of phenyl
rotation.2a DFT calculations suggest that enantiomerization via saddling
inversion entails a rather high activation barrier. A full exposition of
these results will follow shortly in a separate paper on the subject.
ACKNOWLEDGMENTS
■
This work was supported by the Research Council of Norway
and the ALS, LBNL. We thank Drs. Arnfinn Kvarsnes and Johan
Isaksson for assistance with the NMR measurements and
Dr. Jeanet Conradie for assistance with graphics and data analysis.
REFERENCES
■
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