Improved syntheses of β-octabromo-meso-triarylcorrole derivatives

Article abstract of DOI:10.1016/j.jinorgbio.2015.07.017

In spite of significant applications as starting materials for a variety of metallocorrole derivatives, free-base β-octabromo-meso-triarylcorroles continue to be viewed as inaccessible. The reasons range from the need for tedious column-chromatographic pu

Full text of DOI:10.1016/j.jinorgbio.2015.07.017

Improved syntheses of β-octabromo-meso-triarylcorrole derivatives
Jan Capar, Steffen Berg, Kolle E. Thomas, Christine M. Beavers, Kevin
J. Gagnon, Abhik Ghosh
PII:
DOI:
Reference:
S0162-0134(15)30044-1
doi: 10.1016/j.jinorgbio.2015.07.017
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Journal of Inorganic Biochemistry
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Accepted date:
19 April 2015
13 July 2015
19 July 2015
Please cite this article as: Jan Capar, Steffen Berg, Kolle E. Thomas, Chris-
tine M. Beavers, Kevin J. Gagnon, Abhik Ghosh, Improved syntheses of β-
octabromo-meso-triarylcorrole derivatives, Journal of Inorganic Biochemistry (2015), doi:
10.1016/j.jinorgbio.2015.07.017
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Capar et. al.
Bioinorganic methods
Improved syntheses of -octabromo-meso-triarylcorrole derivatives
Jan Capar,a Steffen Berg,a Kolle E. Thomas,a Christine M. Beavers,b Kevin J. Gagnon,b
and Abhik Ghosh*,a
aDepartment of Chemistry and Center for Theoretical and Computational Chemistry
University of Tromsø, 9037 Tromsø, Norway; Email: abhik.ghosh@uit.no
bAdvanced Light Source, Lawrence Berkeley National Laboratory, Berkeley,
CA, USA
Abstract. In spite of significant applications as starting materials for a variety of
metallocorrole derivatives, free-base -octabromo-meso-triarylcorroles continue to be viewed as
inaccessible. The reasons range from the need for tedious column-chromatographic purification
to limitations of the reductive demetallation protocol for selected systems. Here we report that
column chromatography may be entirely avoided for a number of -octabromo-meso-tris(p-X-
phenyl)corrole derivatives, where X = CF3, NO2, F, H, CH3, and OCH3; instead, analytically
pure products may be obtained by recrystallization from chloroform/methanol. In addition, we
have presented an optimized synthesis of the heretofore inaccessible, sterically hindered ligand
-octabromo-meso-tris(2,6-dichlorophenyl)corrole, H3[Br8TDCPC], via reductive demetallation
of the corresponding Mn(III) complex. With our earlier report of tris(pentafluorophenyl)corrole,
H3[Br8TPFPC], a comprehensive set of optimized synthetic protocols are thus in place for a good
number of -octabromo-meso-triarylcorrole ligands. Furthermore, we have illustrated the use of
these ligands by synthesizing the iron complexes Fe[Br8TDCPC]Cl and Fe[Br8TDCPC](py)2, of
which the latter lent itself to single-crystal X-ray structure determination.
Keywords: reductive demetallation, corrole, metallocorrole, octabromocorrole, iron
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Introduction. Over a decade has elapsed since copper-octabromo-meso-tris(p-X-
phenyl)corroles, Cu[Br8TpXPC] (X = CF3, H, CH3, OCH3), were synthesized via direct
bromination of -unsubstituted copper triarylcorroles, Cu[TpXPC].1 Subsequently, the reductive
demetallation method also afforded octabrominated free-base corroles, H3[Br8TpXPC] (Figure
1).2,3 Since then, both copper and free-base octabromocorroles have seen important applications.4
Thus, the copper complexes have been derivatized to copper -octakis(trifluoromethyl)-meso-
triarylcorroles, Cu[(CF3)8TpXPC],5 and to copper undecaarylcorroles,6 both by means of
palladium coupling reactions. The octabrominated free-base corroles were used to synthesize the
first gold7,8 corroles and also unique diboron corroles,9 the latter differing markedly with respect
to both chemical structure and conformation from -unsubstituted diboron corroles.10 Despite
these significant advances, applications of -octabromo-meso-triarylcorroles have languished for
a variety of reasons. In this study, we have addressed some of these problems and present
protocols providing greatly improved access to several of these ligands.
Figure 1. Standard synthetic route to -octabromo-meso-tris(p-X-phenyl)corrole derivatives.
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Tedious column-chromatographic purification, a common bane of porphyrin chemistry, is
also a problem for both Cu[Br8TpXPC] and H3[Br8TpXPC] derivatives. A key result of this
study is that, for X = CF3, NO2, F, H, CH3, and OCH3, column chromatography may be largely
or entirely averted, with analytically pure products obtained simply via recrystallization. Detailed
protocols are given below for Cu[Br8TPC] and H3[Br8TPC] (TPC = meso-triphenylcorrole).
Another difficulty in this area is that the original reductive demetallation procedure fails
for certain copper -octabromocorroles. Thus, we failed to efficiently demetallate copper
tris(pentafluorophenyl)corrole, Cu[TPFPC], and its -octabromo derivative, Cu[Br8TPFPC].
Taking a cue from another early demetallation protocol by Chang and coworkers,11 where
manganese corroles were demetallated with SnCl2/CH2Cl2/HCl, we successfully demetallated
3
Mn[Br8TPFPC] in up to 86% yield. Recently, we have also reported a high-quality single-crystal
X-ray structure of the free base H3[Br8TPFPC].12
In the same vein, Dehaen and coworkers failed to cleanly demetallate copper -octabromo-
meso-tris(2,6-dichlorophenyl)corrole, Cu[Br8TDCPC], with SnCl2/HCl in 2:1
acetonitrile/dichloromethane, obtaining partially debrominated free-base corroles instead.13 The
13
same conditions did lead to demetallation of Cu[Cl8TDCPC], albeit in poor yield (20%). Thus,
as of today, the highly desirable, sterically hindered ligand H3[Br8TDCPC] has not been
reported. Here we report an optimized protocol for the synthesis of this ligand via demetallation
of the corresponding manganese complex, Mn[Br8TDCPC], which has been recently reported by
Gross and coworkers (Figure 2).14
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Capar et. al.
Figure 2. Synthesis of free-base and iron Br8TDCPC derivatives.
Finally, to illustrate the use of H3[Br8TDCPC] as a ligand, we describe its conversion to
two iron complexes – Fe[Br8TDCPC]Cl and Fe[Br8TDCPC](py)2 (py = pyridine; see Figure 2).
These are the first examples of iron -octabromocorroles. The latter complex also lent itself to
single-crystal X-ray structure determination, as described below.
Experimental section. Materials. Unless otherwise mentioned, all reagents and solvents
were obtained from Sigma-Aldrich. Silica gel (DAVISIL® LC150A 35-70µm) was used as the
stationary phase in all flash chromatographic purification. The -unsubstituted free bases
15
15
1
H3[TpXPC] and H3[TDCPC] and the corresponding copper complexes were prepared as
previously described. The Cu complexes Cu[TDCPC] and Cu[Br8TDCPC] were synthesized
16
13
14
according to Dehaen and coworkers. The Mn complexes Mn[TDCPC] and Mn[Br8TDCPC]
were synthesized according to procedures reported by Gross and coworkers. The analytical data
for all known compounds mentioned below were fully consistent with published literature
,
1 15
values.
Instrumentation. UV-visible spectra were recorded on an HP 8453 spectrophotometer. All
NMR spectra (400 MHz for 1H and 376 MHz for 19F) were recorded on a Mercury Plus Varian
spectrometer at 298K in THF-d8. The 1H NMR spectra were referenced to δ = 3.58 ppm
(residual protons in THF-d8) and the 19F NMR spectra were referenced to 2,2,2-trifluoroethanol-
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d3 (δ = -77.8). High Resolution Mass Spectra (HRMS) were recorded on an LTQ Orbitrap XL
spectrometer.
Synthesis and purification of Cu[Br8TPC]. The synthetic procedure employed is slightly
1
modified relative to that reported earlier. To Cu[TPC] (0.105 g, 0.179 mmol) dissolved in
CHCl3 (50 mL) was added dropwise a solution of 275 L (5.34 mmol) of liquid bromine
dissolved in CHCl3 (20 mL) over a period of 30-40 minutes, followed by stirring for 1 h, all at
room temperature. Pyridine (474 μL) dissolved in CHCl3 (20 mL) was then added dropwise over
a period of 30-40 minutes, followed by stirring for an additional hour. The reaction was stopped
by washing the reaction mixture twice with 20% w/v sodium metabisulfite (Na2S2O5, 90 mL).
The organic layer was dried with anhydrous sodium sulfate, filtered, and rotary-evaporated to
dryness. The entire procedure was repeated 5 times.
The crude Cu[Br8TPC] thus obtained could be purified with column chromatography on
silica gel, with eluents of gradually increasing polarity, ranging from 1:1 CH2Cl2/hexane through
pure CH2Cl2 to pure CHCl3. Evaporation of the brown bands resulted in a 52% yield of
Cu[Br8TPC]. In all, the column chromatography required about 1 L of CH2Cl2 and 2 L of CHCl3.
The time-consuming and solvent-wasting nature of the column chromatography
prompted us to investigate recrystallization as an alternative method of purification. In the final,
successful protocol, crude Cu[Br8TPC], obtained from all 5 preparations, was combined and
redissolved in a minimum volume of CHCl3 and layered with an equal volume of methanol. The
precipitated Cu[Br8TPC] was filtered after 1-2 days, washed with methanol, and dried to give a
combined yield of 0.556 g of the final product (51% relative to 0.525 g Cu[TPC], i.e. from all 5
batches). Although this product is suitable for further chemical transformations, a second
recrystallization was carried out to yield 0.505 g of analytically pure product (46% relative to
,
1 15
0.525 g Cu[TPC]), which was characteried as previously reported.
Synthesis and purification of H3[Br8TPC]. Demetallation of Cu[Br8TPC] was carried out
2
essentially according to the original literature procedure for reductive demetallation. A 50-mL
round-bottomed flask equipped with a magnetic stirrer was charged with Cu[Br8TPC] (63 mg,
0.052 mmol) and anhydrous FeCl2 (31.1 mg, 0.245 mmol). Concentrated H2SO4 (2 mL) was
added dropwise under stirring. The solution was alternately stirred for 30 min and sonicated for
30 min for a total of 2 h. The reaction mixture was then quenched with distilled water, washed 3-
4 times with saturated aqueous NaHCO3, and extracted with CHCl3. The organic phase was dried
with anhydrous Na2SO4 and filtered and the filtrate was rotary-evaporated to dryness.
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The original method of purification involved column chromatography with 1:1
2
CH2Cl2/hexane as eluent. This process was both tedious and required large quantities of solvent.
In the new method, crude H3[Br8TPC] was dissolved in a minimum volume of CHCl3 and
layered with an equal volume of methanol. After standing for 1-2 days, the solution was filtered
to yield purified H3[Br8TPC] in 53% yield (32 mg). A second recrystallization yielded the
,
1 15
analytically pure free base (29 mg), which was characteried as previously reported.
Synthesis and purification of para-substituted Cu[Br8TpXPC] (X = CH3, OCH3, CF3 and
1
F). Copper -octabromo-meso-triarylcorroles with para-X-substituted meso aryl groups could
also be effectively purified by the recrystallization method described above. The optimum
CHCl3/methanol ratios, however, varied somewhat with X, being 1:2 for X = F and 1:3 for X =
CH3, OCH3, and CF3. The times required for crystallization were also somewhat longer, i.e. at
least 2 days, compared with Cu[Br8TPC].
For X = NO2, exposure to methanol led to decomposition of the Cu[Br8T(p-NO2-P)C].
Fortunately, recrystallization could be achieved over a period of 2 days by layering a saturated
CHCl3 solution with an equal volume of hexane.
Full spectroscopic details of the Cu[Br8TpXPC] derivatives with X = F and NO2 have not
been published to date and accordingly are presented below.
Characterization of Cu[Br8TpFPC]. Yield 72%. UV-vis (CH2Cl2): λmax, nm (ε x 10-4,
M-1cm-1): 445 (10.19), 649 (0.65). 1H NMR: δ 7.58 (dd, 4H, 5,15-o or -m, 4-FPh), 7.52 (dd, 2H,
10-o or -m, Ph), 7.28 – 7.17 (overlapping triplets, 4H, J = 8.8 Hz, 5,15-m or –o and 2H, J = 8.8
Hz,10-m or -o Ph). 19F NMR (THF-d8): δ -110.81 to -110.93 (m, 1F, 10-p-F, Ph); -110.99 to -
111.11 (m, 2F, 5,15-p-F, Ph). MS (ESI–, major isotopomer): M– = 1271.3785 (expt), 1271.3706
(calcd).
Characterization of Cu[Br8TpNO2PC]. Yield 98.5%. UV-Vis (CH2Cl2): UV-Vis
(CH2Cl2): λmax, nm (ε x 10-4, M-1cm-1): 439 (7.15), 644 (0.67). 1H NMR: δ 8.36 (d, 4H, 3J = 8Hz,
5,15-m or -o, 4-NO2Ph); 8.31 (d, 2H, 3J = 8Hz,10-m or -o, 4-NO2Ph); 7.82 (d, 4H, 3J = 8 Hz,
5,15-o or -m, 4-NO2Ph); 7.76 (d, 2H, 3J = 8Hz, 10-o or -m). MS (ESI–, major isotopomer): [M]–
= 1352.3518 (expt), 1352.3542 (calcd). Elemental analysis: 33.23% C (calcd 32.84%), 1.22% H
(calcd 0.89%), 7.49% N (calcd 7.24%).
Recrystallization of H3[Br8TpXPC]. Purification of the para-substituted free bases
H3[Br8TpXPC] by means of recrystallization was somewhat less efficient, relative to
H3[Br8TPC]. A good strategy leading to analytically pure octabromocorrole free bases involved
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an initial column chromatography followed by crystallization from CHCl3/methanol (or
CHCl3/hexane), as described above.
Synthesis of H3[Br8TDCPC]. Two different syntheses of H3[Br8TDCPC] are described
below, with the first clearly much more successful than the second.
Demetallation of Mn[Br8TDCPC]. Into a 25-mL round-bottomed flask were placed
Mn[Br8TDCPC] (20 mg, 0.014 mmol) and 10 equiv anhydrous FeCl2 (17.9 mg, 0.14 mmol,
Sigma-Aldrich). Concentrated H2SO4 (95-97%, 2.5 mL, Merck) was added. The mixture was
then stirred at room temperature. The progress of the reaction was monitored by taking very
small amounts of the reaction mixture into a small vial, adding distilled water, extracting with
CH2Cl2, washing once with saturated aqueous NaHCO3, and monitoring with UV-vis
spectroscopy, followed by TLC and comparing with the starting material. After 1.5 h, the
reaction was quenched by carefully pouring the mixture into distilled H2O (300 mL), followed
by extraction with CH2Cl2. The green organic phase was washed once with distilled water and
then twice with saturated aqueous NaHCO3. The organic phase was dried with anhydrous
Na2SO4 and filtered and the filtrate was rotary-evaporated to dryness. The residue was
chromatographed on a silica gel column with n-hexane/CH2Cl2 (5:1, followed by 1:1) as eluent
to afford the pure free base. Yield: 14.45 mg (75%). UV-vis (CH2Cl2) λmax, nm (ε x 10-4, M-1
cm-1): 441 (4.70), 590 (0.73), 624 (0.49), 677 (0.42). 1H NMR (400 MHz, CDCl3) δ, ppm: 7.56-
7.66 (m, 9H, aryl), 0.85 (brs, 3H, NH). MS (HR-ESI, major isotopomer): [M]+ = 1364.27 (expt),
1364.26 (calcd).
Demetallation of Cu[Br8TDCPC]. Into a 25-mL round-bottomed flask were placed
Cu[Br8TDCPC] (5.5 mg, 0.00386 mmol) and 5 equiv of anhydrous FeCl2 (2.45 mg, 0.0193
mmol, Sigma-Aldrich). Concentrated H2SO4 (95-97%, 2 mL, Merck) was added. The mixture
was alternately stirred and sonicated at 50 °C. The progress of the reaction was monitored by
UV‑vis spectroscopy. After 4 h the reaction mixture was cooled down to r. t. and the reaction
was quenched by pouring the mixture into 300 mL distilled H2O, then extracted with CH2Cl2.
The green organic phase was washed once with distilled water and then twice with saturated
aqueous NaHCO3. The organic phase was dried with anhydrous Na2SO4, filtered and rotary-
evaporated to dryness. The residue obtained was chromatographed on a silica gel column first
with 5:1 n-hexane/CH2Cl2 to get the recovered [Cu[Br8TDCPC], then with 2:1 n-hexane/CH2Cl2
to collect 0.7 mg of the pure free-base in 14% yield.
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Synthesis of Fe[Br8TDCPC]Cl. Iron insertion into free-base H3[Br8TDCPC] was carried
out essentially according to the procedure reported by Gross and coworkers.17,18 Free-base
H3[Br8TDCPC] (0.030 g, 0.022 mmol) and anhydrous FeCl2 (0.056 g, 0.44 mmol, 20 equiv)
were dissolved in dry DMF (25 mL) under argon. The mixture was heated to reflux and the
reaction mixture was monitored by thin-layer chromatography. After the solution had been
refluxed for 40 min, no more starting material was detected with thin-layer chromatography and
heating was discontinued. Upon cooling to room temperature, the reaction mixture was rotary
evaporated to dryness. The residue was dissolved in diethyl ether and chromatographed on a
short column of silica gel with diethyl ether as eluent. After the evaporation of the diethyl ether,
the product was dissolved in CH2Cl2, washed twice with 2.0 M aqueous HCl, and then twice
with water. The organic phase was dried with anhydrous Na2SO4, followed by rotary evaporation
of the solvent. After chromatography on a short column of silica gel with CH2Cl2 as eluent, pure
Fe[Br8TDCPC]Cl was obtained in 92% yield (0.029 g, 0.020 mmol). UV-vis (CH2Cl2) λmax, nm
(ε x 10-4, M-1cm-1): 419 (4.31), 566 (0.68). 1H NMR (400 MHz, CDCl3) δ 10.56 (s, 1H, 10-para),
9.16 (s, 4H, 5,15-meta), 8.32 (s, 2H, 5,15-para), -4.52 (s, 2H, 10-meta). MS (HR-ESI, major
isotopomer: [M – Cl]+ = 1416.30 (expt), 1416.29 (calcd).
Synthesis of Fe[Br8TDCPC](py)2. Iron insertion was carried out exactly as described
above for Fe[Br8TDCPC]Cl. Thus, free-base H3[Br8TDCPC] (0.030 g, 0.022 mmol) and
anhydrous FeCl2 (0.056 g, 0.44 mmol, 20 equiv) were dissolved in dry DMF (25 mL) under
argon. The reaction mixture was heated to reflux and monitored by TLC. Heating was
discontinued after no more starting material could be detected by TLC, in about 40 min. After
rotary evaporation of the solvent, the residue was dissolved in diethyl ether and chromatographed
on a short column of silica gel with diethyl ether as eluent. The iron-corrole dietherate
(characterized only by means of mass spectrometry) thus obtained was dissolved in a minimum
volume of diethyl ether/n-heptane containing a few drops of pyridine. Crystallization over
several hours led to Fe[Br8TDCPC](py)2 in 90% yield (0.031 g, 0,0198 mmol). X-ray quality
crystals were obtained by recrystallization of Fe[Br8TDCPC](py)2 by diffusion of n-heptane into
a concentrated benzene solution (over 3-4 weeks). UV-vis (CH2Cl2): λmax, nm (ε x 10-4, M-1.cm-1)
425 (6.71), 573 (1.14), 780 (0.37). 1H NMR (400 MHz, CDCl3): δ 9.59 (s, 2H), 7.61 (s, 4H),
7.41 (s, 3H). (The axial pyridines exhibited complex dynamic behavior in the 1H NMR and could
not be readily assigned.) MS (HR-ESI, major isotopomer): [M]+ = 1575.26 (expt), 1575.49
(calcd).
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X-ray structure determination of Fe[Br8TDCPC](py)2. X-ray data were collected on
beamline 11.3.1 at the Advanced Light Source, Lawrence Berkeley National Laboratory. A 115
x 110 x 10 µm3 green plate was mounted on a MiTeGen® kapton loop 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 an APEXII CCD detector.
Diffraction data were collected for synchrotron radiation monochromated with silicon(111) to a
wavelength of 0.9322(1) Å. An approximate full-sphere of data was collected with 0.3° scans.
The structure was solved by intrinsic phasing (SHELXT) and refined by full-matrix least squares
on F2 (SHELXL-2014). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were geometrically calculated and refined as riding atoms. Key crystal data are as follows.
Empirical formula: C56.44H33.05Br8Cl6FeN6; formula weight: 1703.04. Crystal system:
monoclinic. Space group P21/n. Unit cell dimensions: a = 16.316(5) Å, b = 18.168(5) Å, c =
19.625(6) Å,  = 90°,  = 94.533(4)°,  = 90°, and V = 5799(3) Å3. Reflections collected: 40077;
independent reflections: 6091 [R(int) = 0.0858]. Final R indices [I > 2(I)]: R1 = 0.0597, wR2 =
0.1207. R indices (all data): R1 = 0.0969, wR2 = 0.1388. Additional details may be obtained
from the crystallographic information file provided as Supporting Information.
Discussion. Our key findings may be summarized as follows.
Even by the standards of porphyrin and corrole chemistry, where column
chromatography is the standard method of purification, the column chromatography of many
2
Br8TpXPC derivatives is unusually tedious. The compounds ‘tail’ badly and accordingly
purification demands both long times and prodigious quantities of solvent. In the new protocols
outlined above, we have completely averted column-chromatographic purification for all
Cu[Br8TpXPC] (X = CF3, NO2, F, H, CH3, and OCH3) derivatives. Recrystallization was found
to work effectively for all such complexes, saving a lot of both time and solvent.
Recrystallization was also found to be valuable for the purification of the corresponding free
bases 3[Br8TpXPC].
We have presented optimized procedures for the synthesis of the new, sterically hindered
free-base corrole, H3[Br8TDCPC], and for its complexation to iron. The two iron complexes
reported are the first examples of iron octabromocorroles. Applications in areas such as
biomimetic catalysis of atom and group transfer reactions may now be expected.19 A few
interesting physical properties of the new iron complexes are pointed out below.
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Extensive 1H NMR, DFT and ab initio computational studies have established that FeCl
triarylcorroles are generally best described as an intermediate-spin S = 3/2 Fe(III) center
antiferromagnetically coupled to a corrole•2– radical leading to an overall S = 1 ground
state.20,21,22,23,24 Walker and coworkers, however, have emphasized that the nature of the spin
coupling is sensitive to the displacement of the iron above the corrole N4 plane. Thus, for the
undecasubstituted complex octamethyltriphenylcorrolatoiron chloride, Fe[Me8TPC]Cl, the spin
coupling is ferromagnetic, leading to an unusual S = 2 ground state. At this point, the spin state
of Fe[Br8TDCPC]Cl (i.e., S = 1 or 2) has not been determined; such a determination will be
carried out and reported in due course.
Figure 3 depicts the thermal ellipsoid plot for Fe[Br8TDCPC](py)2. The Fe-N distances
involving the anionic corrole nitrogens, averaging around 1.91 Å, are shorter than those
involving the axial pyridines, which average around 2.02 Å. These distances are typical of low-
spin Fe(III) complexes with all-nitrogen coordination and similar to those found for
Fe[TDCPC](py)2. An interesting feature of the present structure is that the 2,6 C-H bonds on the
axial pyridines act as hydrogen bond donors toward the chlorines of the 5,15-dichlorophenyl
groups. As shown in Figure 4, the C-H…Cl hydrogen bond distances all lie in the range 3.54-3.82
Å. Despite the low energies associated with such interactions, the presence of four such
interactions per molecule apparently stabilize the observed conformation, where the two axial
pyridines and the 5,15-dichlorophenyl groups are all roughly coplanar.
Figure 3. Thermal ellipsoid plot for Fe[Br8TDCPC](py)2. Selected distances: Fe1-N1 1.893(9) Å;
Fe1-N2 1.934(10) Å; Fe1-N3 1.930(9) Å; Fe1-N4 1.884(10) Å; Fe-Npy 2 2.032(9) Å.
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Figure 4. C-H…Cl hydrogen bonding interactions in Fe[Br8TDCPC](py)2.
Concluding remarks. As a result of this work, improved syntheses are now available
that afford near-gram quantities of several free-base -octabromo-meso-triarylcorroles, including
H3[Br8TpXPC] (X = CF3, NO2, F, H, CH3, and OCH3) and ~100 mg of the sterically hindered
ligand H3[Br8TDCPC]. To this list may be added the perhalogenated ligand H3[Br8TPFPC],
3
which we reported in our earlier work. Furthermore, we have illustrated the use of these ligands
by synthesizing the first iron octabromocorroles. We look forward to seeing additional
applications of these ligands in the synthesis of new reagents, catalysts, and materials with novel
properties.
Acknowledgement. This project was supported by FRINATEK projects 163054 and
231086 of the Research Council of Norway and by the Advanced Light Source, Berkeley,
California. The Advanced Light Source is supported by the Director, Office of Science, Office of
Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-
05CH11231.
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References
Graphical abstract
Improved synthetic protocols are presented for several free-base -octabromo-meso-tris(p-X-
phenyl)corroles (X = CF3, NO2, F, H, CH3, and OCH3), along with a synthesis of the heretofore
inaccessible free-base -octabromo-meso-tris(2,6-dichlorophenyl)corrole. The latter has also
been complexed to provide the first iron octabromocorrole derivatives.
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512.
4 For a review on corrole applications, see: I. Aviv-Harel, Z. Gross, Chem. Eur. J. 15 (2009)
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