Corroles that click : Modular synthesis of azido- and propargyl-functionalized metallocorrole complexes and convergent synthesis of a bis-corrole scaffold

Article abstract of DOI:10.1021/ic500714h

Bis-corroles have been prepared through a convergent synthesis using a copper-catalyzed azide-alkyne cycloaddition. Synthesis of the final homo- and heterobimetallic complexes has been achieved in three to four steps from commercially available materials in good overall yield. Meso-substituted corroles functionalized with a single azido or propargyl group were used as key starting materials. (C₆F₅)₂(p-O(CH ₂CCH)Ph)corroleH₃ (1) and ((C₆F ₅)₂(m-CH₂N₃)Ph)corroleH₃ (3) were metalated with copper or iron and attached by Huisgen azide-alkyne cycloaddition ( click reaction) first to small substrates and then to each other, demonstrating a convergent synthesis of bimetallic bis-corrole molecules.

Full text of DOI:10.1021/ic500714h

Article
pubs.acs.org/IC
Corroles That “Click”: Modular Synthesis of Azido- and Propargyl-
Functionalized Metallocorrole Complexes and Convergent Synthesis
of a Bis-corrole Scaffold
Heather L. Buckley,† Leah K. Rubin,† Mikołaj Chrominski,‡ Brendon J. McNicholas,†
́
Katherine H. Y. Tsen,† Daniel T. Gryko,‡,§ and John Arnold*,†
†Department of Chemistry, University of California, Berkeley, California 94720, United States
‡Institute for Organic Chemistry, Polish Academy of Sciences, Warsaw, Poland
§
Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland
S
* Supporting Information
ABSTRACT: Bis-corroles have been prepared through a
convergent synthesis using a copper-catalyzed azide−alkyne
cycloaddition. Synthesis of the final homo- and heterobime-
tallic complexes has been achieved in three to four steps from
commercially available materials in good overall yield. Meso-
substituted corroles functionalized with a single azido or
propargyl group were used as key starting materials. (C6F5)2(p-
O(CH2CCH)Ph)corroleH3 (1) and ((C6F5)2(m-CH2N3)Ph)-
corroleH3 (3) were metalated with copper or iron and
attached by Huisgen azide−alkyne cycloaddition (“click”
reaction) first to small substrates and then to each other,
demonstrating a convergent synthesis of bimetallic bis-corrole
molecules.
catalyst was an early motivator for this research.11 Imaging
agents and metal-based drugs are more effective if attached to a
INTRODUCTION
■
Interest in conjugated metallomacrocycles has rapidly increased
in recent years, due to their close analogy to biological
porphyrinoid systems and their potential application to real-
world problems. Lanthanide phthalocyanines have exhibited
biomolecule that provides targeted delivery to the site of
interest.21 Methods for covalently attaching corroles to other
substrates have been reported in the literature,22 but none have
seen widespread application.
single-molecule magnetism that may prove useful in molecular
Huisgen azide−alkyne cycloaddition,23−25 or “click” chem-
switches.1−5 Porphyrins have been used recently as high-
istry, has demonstrated utility both in surface attachment of
quantum-yield sensitizers in solar cells,6 in nonlinear optics,7
small molecules26−31 and in targeted delivery in biological
and in molecular-scale electroluminescence,8 among many
systems.30,32−35 In particular, both surfaces and biomolecules
other applications. While less studied than their 20-membered-
ring counterparts, metallocorrole complexes9 have demonstra-
are easily functionalized with azido groups, and so couplings
with alkynyl-functionalized small molecules are of great
ted excellent activity as oxygen reduction catalysts with
utility.36−40 The reaction takes place under mild conditions
potential applications in fuel cells,10−13 as well as other catalytic
activity for small-molecule/ion activation14,15 and detection of
and is tolerant of a wide range of functional groups. This makes
environmental toxins.16,17 Additionally, iron corroles have been
it ideal for attachment reactions of porphyrinoids, which are
often fragile with regard to strongly oxidizing conditions. The
shown to catalytically lower cholesterol levels and may be used
to prevent heart disease,18 in addition to both gallium and
phosphorus corroles being used as fluorescent reporters for
fact that the “click” reaction, when optimized, occurs in
quantitative yield is also an important attribute, considering
both the possibility of unreacted starting materials compromis-
tumor detection and treatment due to their high quantum
yields.19,20
ing device functionality and the high value of porphyrinoids as a
substrate. Indeed, several examples of azido- and alkynyl-
As potential applications of conjugated macrocycles and their
functionalized porphyrins have been used for click reactions in
metal complexes become increasingly prevalent, the question of
the literature.41−44 Further examples also exist where
how to practically incorporate these molecules into devices,
porphyrinoids have been attached to a surface by way of a
drugs, and sensors is often what limits the next step in their
development. Unattached small-molecule catalysts are imprac-
tical in a fuel cell or battery and need to be affixed to an
Received: March 27, 2014
electrode; interest in the use of corrole as an oxygen reduction
© XXXX American Chemical Society
A
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Article
“clicked” axial ligand.42 One example of a corrole functionalized
with an azido group was reported in 2005 as a synthetic
intermediate;45 this corrole has very recently been metalated
with gallium and attached to a BODIPY dye by way of Huisgen
azide−alkyne cycloaddition to demonstrate bidirectional
fluorescence resonance energy transfer.46 In addition, one
example of a corrole-functionalized with an alkynyl group has
been reported;47,48 while it was not used for “click” chemistry,
this species was used for a cross-coupling reaction between
corrole and coumarin units in order to study the optical
properties of the dyad.
One of the major advantages of the Gryko “A2B” synthesis of
corroles49 is that it allows more straightforward access to
conjugated macrocycles with a single meso substituent with
unique properties. In contrast, porphyrins with one unique
meso substituent50 (meso-substituted A3B porphyrins) are often
prepared by statistical synthesis, and existing examples of
alkynyl-substituted porphyrins have multiple alkynyl groups,41
creating the potential for a complex mixture of molecular
environments when these are attached to a surface.
Preparation of bisporphyrinoids is similarly challenged by the
use of statistical syntheses and is further plagued by
compounding low yields. Although several groups have
prepared interesting bis-corrole, bis-porphyrin, and porphyr-
in−corrole bimetallic complexes and demonstrated their
activity as small-molecule activation catalysts,10,51,52 the
reported yields are poor. In these unique cases the rigid
backbone of these complexes is important to their reactivity
and may not allow for the use of “click” chemistry. However,
convergent synthesis where two corroles are assembled
separately and then attached gives much better overall yields,
as well as allowing for separate coordination of two different
metals to produce a heterobimetallic complex.
Here we present the synthesis of two corrole ligands
functionalized with propargyl and azido groups, respectively.
These corroles are metalated with copper and iron and then
attached to small-molecule test substrates by Huisgen azide−
alkyne cycloaddition as a proof of concept. Finally, homo-
bimetallic (Cu2) and heterometallic (CuFe) bis-corrole
molecules are prepared in good yields by the same “click”
reaction.
Institute, Polish Academy of Sciences. UV−visible spectra were
determined with a Varian Cary 50 UV−vis spectrophotometer using a
1 mm quartz cell. Mass spectral data (ESI-MS, positive mode) were
obtained at the University of California, Berkeley, Microanalytical
Facility. Melting points were determined using sealed capillaries and
are uncorrected.
5-Pentafluorophenyldipyrromethane54 and 4-propargyloxybenzalde-
hyde55 were prepared according to literature procedures. 5,15-
Bis(pentafluorophenyl)-10-(4-methoxyphenyl)corrole ((C6F5)2(p-
OMePh)corroleH3; 4) was prepared according to a previously
reported procedure.49
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), triethylbenzy-
lammonium chloride (TEBA), and copper(I) acetate were purchased
from TCI and used as received. Sodium azide was purchased from
Acros and used as received. Copper(II) acetate, benzyl azide, and
propargyl alcohol were purchased from Aldrich and used as received.
3-Bromomethylbenzaldehyde, 2-(2-azidoethoxy)ethan-1-ol, and iron-
(II) bromide (bis(THF)) were obtained from commercial sources and
used as received. Tetraethylammonium tetrafluoroborate (TEABF4)
was purchased from Fluka and used as received. Tetra-n-
butylammonium tetrafluoroborate (TBABF4) was purchased from
Oakwood Products, Inc., and was purified by dissolving in ethyl
acetate, precipitating with pentane, filtering, and drying in vacuo
overnight.
Synthesis and Characterization of Compounds 1−15. 5,15-
Bis(pentafluorophenyl)-10-(4-propargyloxyphenyl)corrole.
(C6F5)2(p-O(CH2CCH)Ph)corroleH3 (1) was prepared according to
a modified literature procedure.49 5-Pentafluorophenyldipyrromethane
(3.12 g, 10 mmol) and 4-propargyloxybenzaldehyde (0.80 g, 5 mmol)
were dissolved in methanol (500 mL). Concentrated hydrochloric acid
(36%, 25 mL) was combined with 500 mL of distilled water, and the
acid solution was added to the methanol solution while stirring,
immediately producing a peach-colored suspension. The mixture was
stirred for 1 h at room temperature and then extracted with
chloroform. The organic extracts were combined, washed twice with
water, dried over sodium sulfate, filtered, and diluted with chloroform
to 1.25 L. DDQ (3.4 g, 15 mmol) was added, and the reaction mixture
was stirred overnight at room temperature. The solution was
concentrated to 200 mL by rotary evaporation, then filtered through
a short silica gel column (1:1 CH2Cl2/hexanes). The combined
eluents were concentrated to dryness. Column chromatography on
silica gel (1:1 CH2Cl2/hexanes, Rf = 0.62 in 1:1 CH2Cl2/hexanes)
provided the corrole with a minor impurity, which appears as a yellow
spot on the TLC plate. This impurity is removed by recrystallization of
the solid from hexanes, which is repeated until the yellow spot
disappears, yielding a purple solid (950 mg, 97% est. purity, 23%
yield). 1H NMR (500 MHz, CDCl3): δ 9.09 (d, J = 4.5 Hz, 2H), 8.71
(t, J = 4.3 Hz, 4H), 8.56 (d, J = 3.0 Hz, 2H), 8.11 (d, J = 8.5 Hz, 2H),
7.37 (d, J = 5.5 Hz, 2H), 4.96 (d, J = 2.5 Hz, 2H, OCH2CCH), 2.68 (t,
J = 2.3 Hz, 1H, OCH2CCH), −2.70 (br s, 3H, NH). 13C{1H} NMR
(125 MHz, CDCl3): δ 197.7, 157.6, 147.1, 145.1, 140.7, 138.9, 136.9,
135.6, 134.6, 127.8, 125.3, 117.6, 114.0, 113.8, 112.9, 78.8, 75.9, 56.1.
19F NMR (470 MHz, CDCl3): δ −137.9 (d, J = 18.8 Hz), −152.9 (s),
EXPERIMENTAL SECTION
■
General Considerations. Reactions were performed either using
standard Schlenk and N2-atmosphere glovebox techniques or under
ambient conditions on the laboratory bench, as noted. As much as
possible, flasks for synthesis were covered with aluminum foil to
reduce exposure to light throughout the procedures. When required,
solvents were dried by passing through a column of activated alumina
and degassed with nitrogen53 or using a Phoenix solvent drying system
commercially available from JC Meyer Solvent Systems.
−161.8 (t, J = 17.9 Hz). UV−vis (nm): 409, 561, 614. ESI-MS (+):
calcd 761.13937 for C40H18F10O1N4H, obsd 761.14109. Mp:
decomposition above 350 °C.
5,15-Bis(pentafluorophenyl)-10-(3-bromomethylphenyl)corrole.
((C6F5)2(mCH2Br)Ph)corroleH3 (2) was prepared according to a
modified literature procedure.49 5-Pentafluorophenyldipyrromethane
(1.56 g, 5 mmol) and 3-bromomethylbenzaldehyde (0.50 g, 2.5 mmol)
were dissolved in methanol (250 mL). Concentrated hydrochloric acid
(36%, 12.5 mL) was combined with 250 mL of distilled water, and the
acid solution was added to the methanol solution while stirring,
immediately producing a peach-colored suspension. The mixture was
stirred for 1 h at room temperature and then extracted with
chloroform. The organic extracts were combined, washed twice with
water, dried over sodium sulfate, filtered, and diluted with chloroform
to 1 L. DDQ (1.7 g, 7.5 mmol) was added, and the reaction mixture
was stirred overnight at room temperature. The solution was
concentrated to 200 mL by rotary evaporation, then filtered through
Purity of products was estimated by NMR spectroscopy, assuming
that aliphatic impurities, when not identifiable, had a molecular weight
1
of 100 and that a peak integrating to 1 in the H NMR spectrum
(relative to a corrole aromatic peak of area 2) had one equivalent of
impurity to one equivalent of corrole. In general this will overestimate
the concentration of impurity, and so the results given are conservative
and represent a minimum limit on purity and yield. Aromatic
impurities were compared to impurities observed in the 19F NMR
spectrum (where compounds were assumed to have a 1:1 mass ratio to
the corrole product) and in this case were assumed to be redundant.
Instrumentation. All NMR spectra were obtained at ambient
temperature in deuterated solvents using Bruker AVB-400 or AVQ-
400 spectrometers at the University of California, Berkeley, or on 400,
500, or 600 MHz NMR instruments at the Organic Chemistry
B
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a short silica gel column (1:1 CH2Cl2/hexanes). The combined
eluents were concentrated to dryness. Column chromatography on
silica gel (1:1 CH2Cl2/hexanes, Rf = 0.54 in 1:1 CH2Cl2/hexanes) and
subsequent concentration of the combined fractions yielded the pure
product as a purple microcrystalline solid (380 mg, 96% est. purity,
18% yield). 1H NMR (500 MHz, CDCl3): δ 9.12 (d, J = 4.2 Hz, 2H),
8.72 (dd, J = 18.4, 4.8 Hz, 4H), 8.58 (d, J = 4.7 Hz, 2H), 8.24 (m, 1H),
8.15−8.08 (m (dt, unresolved), 1H), 7.82−7.77 (m, 1H), 7.77−7.71
(m, 1H), 4.78 (s, 2H, CH2N3), −2.76 (br s, 3H, NH). 13C{1H} NMR
(125 MHz, CDCl3): δ 147.1, 145.1, 142.8, 141.8, 140.7, 138.9, 137.0,
136.9, 135.1, 134.7, 128.4, 127.8, 125.8, 117.5, 114.0, 112.6, 33.5. 19F
NMR (470 MHz, CDCl3): δ −137.1 (dd, J = 24.0, 8.0 Hz), −152.5 (t,
J = 21.2 Hz), −160.95 (td, J = 22.8, 7.8 Hz). UV−vis (nm): 409, 561,
612. ESI-MS (+): calcd 799.05497 for C38H17Br1F10N4, pbserved
799.05352. Mp: decomposition above 350 °C.
Bis(pentafluorophenyl)-10-(3-azidophenyl)corrole ((C6F5)2(m-
(CH2N3)Ph)corroleH3) (82 mg, 0.108 mmol) was dissolved in
CH2Cl2 (12 mL) under ambient conditions. Copper(II) acetate (58
mg, 0.323 mmol) was suspended in methanol (6 mL), and the
suspension added to the corrole solution. An additional 6 mL of
methanol was used in three portions to rinse residual copper(II)
acetate into the reaction mixture. The reaction was allowed to stir 30
min at room temperature and was monitored by thin-layer
chromatography (silica gel, 1:1 CH2Cl2/hexanes). Upon completion,
the solvent was removed by rotary evaporation, and the resulting solid
was purified by column chromatography (silica gel, 1:1 CH2Cl2/
hexanes, Rf = 0.70 in 1:1 CH2Cl2/hexanes). The product was isolated
1
as a brown solid (77 mg, 88% est. purity, 77% yield). H NMR (500
MHz, CDCl3): δ 7.97 (d, J = 4.0 Hz, 2H), 7.59−7.48 (m, 4H), 7.42 (d,
J = 4.3 Hz, 2H), 7.24−7.16 (m, 4H), 4.44 (s, 2H). 13C{1H} NMR
(125 MHz, CDCl3): δ 150.3, 149.5, 146.2, 144.9, 144.1, 142.6, 140.5,
138.8, 136.8, 135.6, 132.1, 130.3, 128.9, 126.6, 122.9, 111.7, 54.5. 19F
NMR (470 MHz, CDCl3): δ −141.8 (ddd, J = 32.7, 23.3, 7.2 Hz),
−157.1 (t, J = 21.2 Hz), −165.6 (tdd, J = 22.8, 15.3, 7.7 Hz). UV−vis
(nm): 406, 547. ESI-MS (+): calcd 821.0452 for C38H14Cu1F10N7,
obsd 821.0460. Mp: decomposition above 350 °C.
5,15-Bis(pentafluorophenyl)-10-(3-azidomethylphenyl)corrole.
((C6F5)2(m-CH2N3)Ph)corroleH3 (3) was prepared using 5,15-
bis(pentafluorophenyl)-10-(3-bromomethylphenyl)corrole (2) (150
mg, 0.188 mmol) dissolved in dry dimethylformamide (30 mL).
Sodium azide (13.4 mg, 0.207 mmol) and triethylbenzyl ammonium
chloride (TEBA) (4.3 mg, 0.019 mmol) were added, and the reaction
mixture was stirred overnight at room temperature.56 The reaction was
monitored by thin-layer chromatography (silica gel, 1:1 CH2Cl2/
hexanes). The reaction volume was diluted to 75 mL with chloroform.
The organic phase was washed twice with water and dried over sodium
sulfate, and the solvent removed by rotary evaporation. The solid was
dissolved in 10 mL of CH2Cl2, and the solvent again removed by
rotary evaporation to ensure complete removal of the dimethylforma-
mide. Column chromatography on silica gel (1:1 CH2Cl2/hexanes, Rf
= 0.49 in 1:1 CH2Cl2/hexanes) and subsequent concentration of the
combined fractions yielded the pure product as a purple microcrystal-
Copper(III) 5,15-Bis(pentafluorophenyl)-10-(4-methoxyphenyl)-
corrole. (C6F5)2(p-OMePh)corroleCu (7) was prepared according
to a modified literature procedure.57 5,15-Bis(pentafluorophenyl)-10-
(4-methoxyphenyl)corrole ((C6F5)2(p-OMePh)corroleH3; 4) (200
mg, 0.272 mmol) was dissolved in CH2Cl2 (50 mL) under ambient
conditions. Copper(II) acetate (148 mg, 0.815 mmol) was suspended
in methanol (20 mL), and the suspension added to the corrole
solution. An additional 30 mL of methanol was used in three portions
to rinse residual copper(II) acetate into the reaction mixture. The
reaction was allowed to stir 30 min at room temperature and was
monitored by thin-layer chromatography (silica gel, 1:1 CH2Cl2/
hexanes). Upon completion, the solvent was removed by rotary
evaporation, and the resultant solid was purified by column
chromatography (silica gel, 1:1 CH2Cl2/hexanes). The product was
1
line solid (106 mg, 92% est. purity, 69% yield). H NMR (500 MHz,
CDCl3): δ 9.10 (d, J = 4.0 Hz, 2H), 8.71 (d, J = 4.0 Hz, 2H), 8.67 (d, J
= 4.5 Hz, 2H), 8.56 (d, J = 2.5 Hz, 2H), 8.13 (m, 2H), 7.78 (m, 1H),
7.72 (m, 1H), 4.61 (s, 2H, CH2N3), −2.80 (br s, 3H, NH). 13C{1H}
(125 MHz, CDCl3): δ 162.3, 147.1, 145.1, 142.8, 141.9, 140.7, 136.9,
135.3, 134.5, 131.2, 128.8, 127.8, 125.8, 121.8, 117.6, 114.0, 112.6,
96.9, 54.8. 19F NMR (470 MHz, CDCl3): δ −137.9 (d, J = 18.8 Hz),
−152.9 (s), −161.8 (t, J = 17.9 Hz). UV−vis (nm): 409, 561, 613. ESI-
MS (+): calcd 761.1313 for C38H17F10N7, obsd 761.1307. Mp:
decomposition above 350 °C.
1
isolated as a brown solid (203 mg, 82% est. purity, 77% yield). H
NMR (400 MHz, CDCl3): δ 7.90 (br s, 2H) 7.52 (d, J = 8.0 Hz, 2H,
C6H2H2-OMe), 7.33 (br s, 2H), 7.06 (br s, 4H), 6.98 (d, J = 8.0 Hz,
2H, C6H2H2-OMe), 3.88 (s, 3H, OCH3). 19F NMR (376 MHz,
CDCl3): δ −136.2 (d, J = 18.8 Hz, 4F), −151.6 (t, J = 20.7 Hz, 2F),
−160.1 (quintet, J = 11.3 Hz, 4F). UV−vis (nm): 399, 430, 549. ESI-
MS (+): calcd 796.0377 for C38H15Cu1F10O1N4, obsd 796.0379. Mp:
decomposition above 350 °C.
C o p p e r ( I I I ) 5 , 1 5 - B i s ( p e n t a fl u o r o p h e n y l ) - 1 0 - ( 4 -
propargyloxyphenyl)corrole. (C6F5)2(p-O(CH2CCH)Ph)corroleCu
(5) was prepared according to a modified literature procedure.57
5,15-Bis(pentafluorophenyl)-10-(4-propargyloxyphenyl)corrole
((C6F5)2(p-O(CH2CCH)Ph)corroleH3) (50 mg, 0.066 mmol) was
dissolved in CH2Cl2 (10 mL) under ambient conditions. Copper(II)
acetate (36 mg, 0.197 mmol) was suspended in methanol (5 mL), and
the suspension added to the corrole solution. An additional 5 mL of
methanol was used in three portions to rinse residual copper(II)
acetate into the reaction mixture. The reaction was allowed to stir 30
min at room temperature and was monitored by thin-layer
chromatography (silica gel, 1:1 CH2Cl2/hexanes). Upon completion,
the solvent was removed by rotary evaporation and the resulting solid
purified by column chromatography (silica gel, 1:4 CH2Cl2/hexanes,
Rf = 0.75 in 1:1 CH2Cl2/hexanes). The product was isolated as a
purple-brown solid (50 mg, 80% est. purity, 74% yield). 1H NMR (500
MHz, CDCl3): δ 7.95 (d, J = 4.0 Hz, 2H), 7.55 (d, J = 8.4 Hz, 2H),
7.42 (d, J = 4.2 Hz, 2H), 7.26 (d, J = 5.7 Hz, 2H), 7.21 (d, J = 4.4 Hz,
2H), 7.09 (d, J = 8.4 Hz, 2H), 4.80 (d, J = 2.4 Hz, 2H), 2.59 (t, J = 2.3
Hz, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 158.4, 150.4, 149.6,
146.1, 145.0, 144.1, 142.6, 140.9, 139.0, 136.8, 132.6, 132.1, 129.8,
122.8, 114.6, 112.0, 78.3, 75.9, 55.9. 19F NMR (470 MHz, CDCl3): δ
−137.1 (dd, J = 23.6, 7.9 Hz), −152.5 (t, J = 18.8 Hz), −161.0 (td, J =
22.6, 7.9 Hz). UV−vis (nm): 399, 427, 548. ESI-MS (+): calcd
821.0455 for C40H15Cu1F10N4O1H, obsd 821.0496. Mp: decom-
position above 350 °C.
Iron(III) 5,15-Bis(pentafluorophenyl)-10-(4-propargyloxyphenyl)-
corrole Bis(diethyl ether). (C6F5)2(p-O(CH2CCH)Ph)corroleFe-
(Et2O)2 (8) was prepared according to a modified literature
procedure.58 5,15-Bis(pentafluorophenyl)-10-(4-propargyloxyphenyl)-
corrole ((C6F5)2(p-OMePh)corroleH3) (200 mg, 0.263 mmol) was
dissolved in dry dimethylformamide (30 mL) under nitrogen on a
Schlenk line. Iron(II) bromide(bis(THF)) (1.89 mg, 5.26 mmol) was
placed in another nitrogen-filled Schlenk flask, and the corrole solution
transferred by cannula. The resulting mixture was refluxed overnight at
110 °C, and the reaction monitored by thin-layer chromatography
(silica gel, 1:1 CH2Cl2/hexanes). Dimethylformamide was removed
under reduced pressure at 60 °C, and the resulting solid was triturated
twice with diethyl ether, which was subsequently removed under
reduced pressure to ensure complete removal of the dimethylforma-
mide. The compound was purified by column chromatography (silica
gel, 100% diethyl ether), and the combined organic fractions were
concentrated to 50 mL. Hydrazine (32 μL, 1.0 mmol) was added, and
the remaining solvent was removed under reduced pressure on a
Schlenk line to give the product as a red-brown solid (130 mg, 84%
1
est. purity, 44% yield). H NMR (400 MHz, C6D6, 23 °C): 19.73 (br
s), 7.49 (br s), 5.90 (br s), 3.27 (br), 1.11 (br s, Et2O), 0.90 (br s),
0.16 (br s, Et2O), −2.98 (br s), −58.78 (br s), −110.23 (br s). 19F
NMR (376 MHz, C6D6, 23 °C): δ −95.3 (br s, ortho-F), −149.7 (s,
para-F), −155.2 (s, meta-F). UV−vis (nm): 381, 551. ESI-MS (+):
calcd 813.0430 for C40H15F10Fe1N4O1, obsd 813.0457. Mp: decom-
position above 350 °C.
C o p p e r ( I I I ) 5 , 1 5 - B i s ( p e n t a fl u o r o p h e n y l ) - 1 0 - ( 3 -
azidomethylphenyl)corrole. ((C6F5)2(m-CH2N3)Ph)corroleCu (6)
was prepared according to a modified literature procedure.57 5,15-
C
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Iron(III) 5,15-Bis(pentafluorophenyl)-10-(4-methoxyphenyl)-
corrole Bis(diethyl ether). (C6F5)2(p-OMePh)corroleFe(Et2O)2 (9)
was prepared according to a modified literature procedure.58,59 5,15-
Bis(pentafluorophenyl)-10-(4-methoxyphenyl)corrole ((C6F5)2(p-
OMePh)corroleH3; 4) (74 mg, 0.1 mmol) was dissolved in dry
dimethylformamide (30 mL) under nitrogen on a Schlenk line.
Iron(II) bromide (720 mg, 2.0 mmol) was placed in another flask
under nitrogen, and the corrole solution transferred by cannula. The
resulting mixture was refluxed for 6 h at 110 °C, and the reaction
monitored by thin-layer chromatography (silica gel, 1:1 CH2Cl2/
hexanes). Dimethylformamide was removed under reduced pressure at
60 °C, and the resulting solid was triturated twice with diethyl ether,
which was subsequently removed under reduced pressure to ensure
complete removal of the dimethylformamide. The solid was extracted
with diethyl ether and filtered by cannula, and the solvent was
removed quickly under alternating nitrogen and vacuum to give a
brown solid (82 mg, 93% est. purity, 87% yield). 1H NMR (400 MHz,
C6D6, 23 °C): δ 8.68 (s), 7.73 (s), 6.18 (br s), 3.73 (s), 2.37 (s), 1.89
(s), 0.30, (s), −0.97 (br s), −34.35 (br s), −46.23 (br s), −104.68 (br
s). 19F NMR (376 MHz, C6D6, 23 °C): δ −100.5 (br s, ortho-F),
−149.5 (s, para-F), −155.7 (s, meta-F). UV−vis (nm): 376. ESI-MS
(+): calcd 789.0430 for C38H15F10Fe1N4 O1, obsd 789.0432. Mp:
decomposition above 350 °C.
Hz, 1H), 7.57−7.50 (m, 2H), 7.46−7.12 (m, 11H), 7.08 (d, J = 8.0
Hz, 2H), 5.56 (s, 2H), 5.30 (s, 2H). 19F NMR (376 MHz, CDCl3): δ
−136.2 (dd, J = 24.0, 8.0 Hz), −151.6 (t, J = −22.6 Hz), −160.1 (td, J
= 23.0, 7.9 Hz). UV−vis (nm): 400, 430, 550. ESI-MS (+): calcd
954.1095 for C47H22Cu1F10N7O1H, obsd 954.1107. Mp: decom-
position above 350 °C.
Iron(III) 5,15-Bis(pentafluorophenyl)-10-(4-oxymethyl-(1-benzyl-
1,2,3-triazol-4-yl)phenyl)corrole Bis(diethyl ether). (C6F5)2(p-O-
(CH2(C2HN3(CH2C6H5)))Ph)corroleFe(Et2O)2 (12) was prepared
as follows. Iron(III) 5,15-bis(pentafluorophenyl)-10-(4-
propargyloxyphenyl)corrole bis(diethyl ether) (33 mg, 0.034 mmol)
and benzyl azide (5 mg, 0.038 mmol) were placed in a dry 25 mL
Schlenk flask. The flask was evacuated and filled with nitrogen three
times, and dry CH2Cl2 (5 mL) was added by cannula. Copper(I)
acetate (catalytic, approximately 1 mg) was added, and the resulting
suspension was stirred for 15 min at room temperature.60 The reaction
was monitored by thin-layer chromatography (silica gel, 1:1 CH2Cl2/
hexanes). The solution was extracted twice with water to remove
excess azide. The combined extracts were dried over sodium sulfate
and filtered, and the solvent was removed by rotary evaporation. The
solid was purified by dry column vacuum chromatography (silica gel,
1:1 diethyl ether/hexanes). The product was dissolved in diethyl ether,
and 5 μL of hydrazine was added. The solvent was removed by slow
evaporation under a stream of nitrogen to isolate the compound as a
brown solid (22 mg, 89% est. purity, 52% yield). 1H NMR (400 MHz,
C6D6, 23 °C): δ 10.65 (br s), 9.58 (br s), 9.23 (br s), 8.65 (br s), 5.48
(br s), 4.98 (br s), 3.85 (br s), 3.21 (br s), 1.35 (br s, Et2O), 0.27 (br
Copper(III) 5,15-Bis(pentafluorophenyl)-10-(4-oxymethyl-(1-
ethoxyethanol-1,2,3-triazol-4-yl)phenyl)corrole. (C6F5)2(p-O-
(CH2(C2HN3(CH2CH2OCH2CH2OH)))Ph)corroleCu (10) was pre-
pared as follows. Copper(III) 5,15-bis(pentafluorophenyl)-10-(4-
propargyloxyphenyl)corrole (5) (150 mg, 0.182 mmol) and 2-(2-
azidoethoxy)ethan-1-ol (26 mg, 0.201 mmol) were placed in a dry 250
mL Schlenk flask. The flask was evacuated and filled with argon three
times, and dry CH2Cl2 (50 mL) was added by cannula. Copper(I)
acetate (catalytic, approximately 5 mg) was added, and the suspension
was stirred for 30 min at room temperature.60 The reaction was
monitored by thin-layer chromatography (silica gel, 1:1 CH2Cl2/
hexanes). The solution was extracted twice with water to remove
excess azide. The combined extracts were dried over sodium sulfate
and filtered, and the solvent was removed by rotary evaporation. The
resultant solid was purified by column chromatography (silica gel, 95:5
CH2Cl2/MeOH). The resulting solid was further purified by dry
column vacuum chromatography (99:1 CH2Cl2/MeOH). The product
s), 0.05 (br s, Et2O), −38.24 (br s), −50.08 (br s), −107.74 (br s). 19
F
NMR (376 MHz, C6D6, 23 °C): δ −92.9 (br s, ortho-F), −150.2 (s,
para-F), −155.5 (s, meta-F). UV−vis (nm): 410, 561. ESI-MS (+):
calcd 947.1148 for C47H22F10Fe1N4O7H, obsd 947.1153. Mp:
decomposition above 350 °C.
Copper(III) 5,15-Bis(pentafluorophenyl)-10-(3-methynyl-(4-meth-
anol-1,2,3-triazol-1-yl)phenyl)corrole. ((C6F5)2(m-CH2N3C2H-
(CH2OH))Ph)corroleCu (13) was prepared as follows. Copper(III)
5,15-bis(pentafluorophenyl)-10-(3-azidomethylphenyl)corrole (30
mg, 0.037 mmol) and propargyl alcohol (2.5 mg, 0.045 mmol) were
placed in a dry 25 mL Schlenk flask. The flask was evacuated and filled
with argon three times, and dry CH2Cl2 (5 mL) was added by cannula.
Copper(I) acetate (catalytic, approximately 1 mg) was added, and the
resulting suspension was stirred overnight at room temperature.60 The
reaction was monitored by thin-layer chromatography (silica gel, 1:1
CH2Cl2/hexanes). After completion, the solvent was removed by
rotary evaporation, and the resulting solid was purified by column
chromatography (silica gel, 98:2 CH2Cl2/MeOH, Rf = 0.32 in 98:2
CH2Cl2/MeOH) to yield a brown solid (14 mg, 94% est. purity, 41%
yield). 1H NMR (500 MHz, CDCl3): δ 7.97 (d, J = 4.2 Hz, 2H), 7.60−
7.40 (m, 6H), 7.23−2.10 (m, 5H), 5.60 (s, 2H), 4.79 (s, 2H), 2.22 (br
s, 1H). 13C{1H} NMR (125 MHz, CDCl3): δ 149.6, 148.1, 146.2,
144.2, 142.6, 140.6, 138.8 136.8, 134.9, 131.9, 131.2, 130.4, 129.2,
127.0, 125.3, 123.0, 121.6, 111.6, 108.5, 56.7, 53.9. 19F NMR (470
MHz, CDCl3): δ −136.9 to −137.2 (m), −152.2 (t, J = 21.2 Hz),
−160.8 (qd, J = 21.7, 8.0 Hz). UV−vis (nm): 304, 548. LR-MS: calcd
878.1 for C4H24Cu1F10N7O1, obsd 878.1. Mp: decomposition above
350 °C.
1-[(10-(3-Methylenephenyl))-5,15-bis(pentafluorophenyl)copper-
(III)corrole]-4-[(10-(4-oxymethylene))-5,15-bis(pentafluorophenyl)-
copper(III)corrole]triazole. Cu(corrole((C6F5)2(Ph))-p-O(CH2)-
(C2HN3)(CH2)-m-(Ph(C6F5)2corrole)Cu) (14) was prepared as
follows. Copper(III) 5,15-bis(pentafluorophenyl)-10-(4-
propargyloxyphenyl)corrole (25 mg, 0.030 mmol) and copper(III)
5,15-bis(pentafluorophenyl)-10-(3-azidomethylphenyl)corrole (25
mg, 0.030 mmol) were combined in a dry Schlenk flask under
nitrogen. Dry CH2Cl2 (5 mL) and copper(I) acetate (catalytic,
approximately 3 mg) were added, and the reaction was stirred
overnight at room temperature.60 The reaction was monitored by thin-
layer chromatography (silica, 1:1 CH2Cl2/hexanes). The solvent was
removed by rotary evaporation, and the resulting solid was purified by
column chromatography (silica gel, 1:1 CH2Cl2/hexanes, ramped to
100% CH2Cl2, ramped to 95:5 CH2Cl2/MeOH). The solvent was
1
was isolated as a brown solid (92 mg, 93% est. purity, 49% yield). H
NMR (600 MHz, CDCl3): δ 7.94 (d, J = 4.0 Hz, 2H), 7.87 (s, 1H,
N3C2H), 7.54 (d, J = 8.3 Hz, 2H), 7.42 (d, J = 4.3 Hz, 2H), 7.26 (d, J =
4.7 Hz, 2H), 7.21 (d, J = 4.5 Hz, 2H), 7.11 (d, J = 8.3 Hz, 2H), 5.31 (s,
2H, Ph-O-CH2), 4.61 (t, J = 5.0 Hz, 2H), 3.96−3.91 (m, 2H), 3.75−
3.68 (m, 2H), 3.61−3.56 (m, 2H), 1.26 (s, 1H). 13C{1H} NMR (125
MHz, CDCl3): δ 159.1, 149.6, 145.0, 144.1, 138.6, 136.9, 132.5, 132.1,
129.8, 124.0, 122.8, 114.5, 72.5, 69.3, 62.2, 61.7, 50.4. 19F NMR (470
MHz, CDCl3): δ −141.8 (dd, J = 24.0, 8.1 Hz), −157.2 (d, J = 23.5
Hz), −165.8 (td, J = 22.5, 7.7 Hz). UV−vis (nm): 399, 429, 549. ESI-
MS (+): calcd 951.1077 for C44H24Cu1F10N7O1, obsd 951.1073. Mp:
decomposition above 350 °C.
Copper(III) 5,15-Bis(pentafluorophenyl)-10-(4-oxymethyl-(1-ben-
zyl-1, 2, 3-triazol-4-yl)phenyl)corrole. (C6 F5 )2 (p-O-
(CH2(C2HN3(CH2C6H5)))Ph)corroleCu (11) was prepared as
follows. Copper(III) 5,15-bis(pentafluorophenyl)-10-(4-
propargyloxyphenyl)corrole (5) (25 mg, 0.030 mmol) and benzyl
azide (15 mg, 0.100 mmol) were placed in a dry 25 mL Schlenk flask.
The flask was evacuated and filled with nitrogen three times, and dry
CH2Cl2 (5 mL) was added by cannula. Copper(I) acetate (catalytic,
approximately 1 mg) was added, and the suspension was stirred for 30
min at room temperature.60 The reaction was monitored by thin-layer
chromatography (silica gel, 1:1 CH2Cl2/hexanes). The solution was
extracted twice with water to remove excess azide. The combined
extracts were dried over sodium sulfate and filtered, and the solvent
was removed by rotary evaporation. The product was purified by dry
column vacuum chromatography (silica gel, 98:2 CH2Cl2/MeOH),
and the solvent was removed under vacuum to give a brown
1
microcrystalline solid (25 mg, 86% est. purity, 72% yield). H NMR
(400 MHz, CDCl3): δ 7.93 (d, J = 4.4 Hz, 2H), 7.71 (dt, J = 7.4,3.7
D
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Scheme 1. Preparation of (a) Propargyl-, (b) Azido-, and (c) Methoxy-Functionalized Metallocorroles
removed under vacuum to give a brown microcrystalline solid (45 mg,
93% est. purity, 84% yield). 1H NMR (400 MHz, CD2Cl2): δ 8.04 (m,
4H), 7.75 (s, 1H), 7.62−7.40 (m, 10H), 7.24 (q, J = 5.1 Hz, 6H), 7.17
(d, J = 4.6 Hz, 2H), 7.08 (d, J − 8.3 Hz, 2H), 5.66 (s, 2H), 5.26 (s,
2H). 19F NMR (376 MHz, CD2Cl2): δ −137.1 to −137.4 (m), −152.4
to −152.8 (m), −160.8 to −161.2 (m). UV−vis (nm): 402, 550. ESI-
MS (+): calcd 1664.0727 for C78H29Cu2F20N11O1Na1, obsd
1664.0732; calcd 1680.0466 for C78H29Cu2F20N11O1K1, obsd
1680.0468. Mp: decomposition above 350 °C.
oborate in CH2Cl2. A three-electrode cell was used, with a glassy
carbon working electrode (3 mm diameter), a platinum mesh counter
electrode, and a Ag/Ag+ reference electrode. The reference electrode
consisted of a silver wire in a solution of 0.01 M AgNO3 and 0.1 M
TEABF4 in acetonitrile, separated from the bulk solution by a Vycor
frit. Electrolyte solutions were deoxygenated with nitrogen for at least
10 min before any compounds were added and were kept under a
blanket of nitrogen during analysis. Between measurements, the
working electrode was polished with 0.05 μm alumina and rinsed with
distilled water and acetonitrile.
1-[(10-(3-Methylenephenyl))-5,15-bis(pentafluorophenyl)copper-
(III)corrole]-4-[(10-(4-oxymethylene))-5,15-bis(pentafluorophenyl)-
iron(III)corrole(bis(acetonitrile))]triazole. Fe(CH3CN)2(corrole-
((C6F5)2(Ph))-p-O(CH2)(C2HN3)(CH2)-m-(Ph(C6F5)2corrole)Cu)
(15) was prepared as follows. Iron(III) 5,15-bis(pentafluorophenyl)-
10-(4-propargyloxyphenyl)corrole bis(diethyl ether) (24 mg, 0.025
mmol) and copper(III) 5,15-bis(pentafluorophenyl)-10-(3-
azidomethylphenyl)corrole (21 mg, 0.025 mmol) were combined in
a dry Schlenk flask under nitrogen. Dry CH2Cl2 (5 mL) and copper(I)
acetate (catalytic, approximately 3 mg) were added, and the reaction
was stirred overnight at room temperature.60 The reaction was
monitored by thin-layer chromatography (silica, CH2Cl2/hexanes).
The solvent was removed by rotary evaporation, and the resultant solid
was purified by column chromatography (silica gel, 1:1 CH2Cl2/
hexanes, ramped to 100% CH2Cl2, ramped to 95:5 CH2Cl2/MeOH).
The solvent was removed under vacuum, the solid was dissolved in
acetonitrile, and 5 μL of hydrazine was added. The solvent was
degassed with nitrogen and then removed under vacuum on the
Schlenk line to produce a brown solid (26 mg, 90% est. purity, 54%
All potentials are referenced to Ag/Ag+ (0.01 M Ag+). Potentials
reproduced from other publications have been converted from SCE to
Ag/Ag+ by subtracting 298 mV.61 All scans shown were taken at 100
mV/s, except for 15 (the Cu−Fe complex), which was not sufficiently
soluble in acetonitrile (although solubility was better in acetonitrile
than in CH2Cl2) and had to be measured at 500 mV/s to observe well-
resolved peaks. Currents are reported as current densities, calculated
using an electrode area of 0.071 cm2. Arrows on the voltammograms
(in the SI) indicate the direction of the first potential sweep.
RESULTS AND DISCUSSION
■
Previous research has emphasized the importance of electron-
withdrawing meso-substituents on corrole ligands.62 These
make the first oxidation potential more positive63 and enhance
the stability of the corrole toward light and oxygen.64 For this
reason, we chose 5-(pentafluorophenyl)dipyrromethane as a
key substrate. Combination of two equivalents of 5-
(pentafluorophenyl)dipyrromethane and one equivalent of 4-
propargyloxybenzaldehyde in a mixture of methanol and acidic
water at room temperature was followed by extraction with
chloroform and the addition of DDQ.49 After stirring overnight
at room temperature, column chromatography and recrystalli-
zation gave 5,15-bis(pentafluorophenyl)-10-(4-
propargyloxyphenyl)corrole ((C6F5)2(p-O(CH2CCH)Ph)-
corroleH3; 1) as a purple crystalline solid in 23% yield
(Scheme 1a).
1
yield). H NMR (400 MHz, CD3CN, 23 °C): δ 8.01−7.94 (m), 7.75
(d, J = 4 Hz), 7.65−7.40 (m), 7.1−4.6 (very br s), 5.81 (br s), 5.44 (s),
4.49 (s), 3.85 (s), 3.60 (s), 3.50 (s), 1.81 (s), 1.28 (s), −1.62 (br s),
−12.20 (br s), −32.12 (br s), −83.08 (br s). 19F NMR (376 MHz,
CD3CN, 23 °C): δ −117.7, −140.5, −158.0, −163.7, −165.2. UV−vis
(nm): 403, 552. ESI-MS (+): calcd 1635.0955 for
C78H30Cu1F20Fe1N11O1, obsd 1635.1101. Mp: decomposition above
350 °C.
Cyclic Voltammetry of Compounds 7, 9, 14, and 15. Cyclic
voltammetric measurements were performed with a Gamry Reference
600 potentiostat, using either 0.1 M tetraethylammonium tetrafluor-
oborate in acetonitrile or 0.1 M tetra-n-butylammonium tetrafluor-
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Following the same general procedure49 5,15-bis-
(pentafluorophenyl)-10-(3-bromomethylphenyl)corrole
((C6F5)2(m-(CH2Br)Ph)corroleH3; 2) was prepared in 18%
yield. The bromomethyl group was then converted to an
azidomethyl group by reaction with sodium azide in the
presence of triethylbenzyl ammonium chloride as a phase
transfer catalyst.56 This reaction was stirred overnight at room
temperature, and after aqueous extraction and column
chromatography 5,15-bis(pentafluorophenyl)-10-(3-
azidomethylphenyl)corrole ((C6F5)2(m-(CH2N3)Ph)-
corroleH3; 3) was isolated as a purple crystalline solid in 69%
yield (Scheme 1b). Free-base corroles 1, 2, and 3 have been
To test the reactivity of these species toward “click”
chemistry and to ascertain that the presence of coordinated
metals did not inhibit this reactivity, 5 was reacted with 2-(2-
azidoethoxy)ethan-1-ol and 5 and 8 were both reacted with
benzyl azide to produce 10 (49% yield), 11 (72% yield), and 12
(52% yield), respectively (Scheme 2).
Scheme 2. Test Reactions to Confirm Reactivity of
Propargyl-Functionalized Corroles 5 and 8 toward the
“Click” Reaction with Small Substrates
1
characterized by H, 13C, and 19F NMR spectroscopies, UV−
visible spectroscopy, and ESI mass spectrometry (see
Experimental Section). To our knowledge, these species
constitute only the second example in each case of of
alkynyl-functionalized47 (propargyl) and azido-functional-
ized45,46 corrole ligands.
Both 1 and 3, in addition to the previously reported 5,15-
bis(pentafluorophenyl)-10-(4-methoxyphenyl)corrole
((C6F5)2(p-OMePh)corroleH3; 4), were reacted with copper-
(II) acetate to form 5 (74% yield), 6 (77% yield), and 7 (77%
yield), respectively (Scheme 1).57 All three compounds have
1
been characterized by H and 19F NMR spectroscopies (5 and
6 were also characterized by 13C NMR spectroscopy; see the
SI), UV−visible spectroscopy, and ESI mass spectrometry (see
the Experimental Section). 7 was prepared primarily as a
reference compound for electrochemical characterization (see
below).
Compounds 1 and 4 were reacted with iron(II) bromide in
refluxing dimethylformamide under Schlenk conditions to
produce 8 (44% yield) and 9 (87% yield), respectively
(Scheme 1a).58 Unlike for the analogous trisperfluorophenyl-
corrole complexes, these compounds were sensitive to
oxidation to a bis-iron(IV)-bridged μ-oxo species and required
either anhydrous, air-free workup (9) or column chromatog-
raphy followed by reduction with hydrazine in diethyl ether (8)
to cleanly produce the paramagnetic iron(III) corrole species.
Both compounds have been characterized by 1H and 19F NMR
spectroscopies (see the SI), where their paramagnetically
shifted peaks are diagnostic and match closely with those
previously reported by Gross and co-workers for the para-
magnetic high-spin iron(III) trisperflouorophenyl corrole
bis(diethyl ether).58 Specifically, the broad signal at −95.3
ppm in the 19F NMR spectrum of 8 (−100.5 ppm in 9) can be
assigned to the ortho-fluorine atoms, while that at −149.7 ppm
(−149.5 ppm in 9) can be assigned to the para-fluorine and
that at −155.2 ppm (−155.7 ppm in 9) to the meta-fluorine
atoms. Differentiation of these compounds from the bis-
iron(IV)-bridged μ-oxo species is straightforward because the
latter displays five inequivalent diamagnetically shifted signals in
the 19F NMR spectrum. There are slight differences between
Similar to its precursor 8, 12 was reacted with hydrazine in
diethyl ether to cleanly isolate the iron(III) corrole species. To
a similar end, 6 was reacted with propargyl alcohol to produce
13 (41% yield) (Scheme 3). In all cases copper(I) acetate,
recently published as an excellent catalyst for azide−alkyne
cycloaddition,65 was used as a heterogeneous catalyst for this
reaction, and the compounds were isolated by column
chromatography. All three compounds were characterized by
1H and 19F NMR spectroscopies (and 10 by 13C NMR
spectroscopy; see the SI), UV−visible spectroscopy, and ESI
mass spectrometry (see the Experimental Section). The
paramagnetic NMR spectra of 12 are consistent with those
observed for 8 and with those reported in the literature.58
It should be noted that initial attempts were also made to
react the free-base corrole 1 with benzyl azide. These resulted
in very low yields of 5 and 11 among a mixture of species,
the chemical shifts of these compounds in both the 1H and 19
F
NMR spectra; these differences correspond to a very slight
difference in UV−visible absorption maxima between 8 (381
nm) and 9 (376 nm). As these compounds differ only by a
remote substituent (propargyl vs methoxy), the reasons for
these differences are unclear; however they may relate to the
slightly greater electronic-donating nature of the methoxy
group and subsequent inductive electron donation by the 10-
phenyl meso substitutent to the corrole ring. These compounds
were also characterized by ESI mass spectrometry (see the
Experimental Section).
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Scheme 3. Test Reactions to Confirm Reactivity of Azido-
Functionalized Corrole 6 toward the “Click” Reaction with
Small Substrates
Scheme 4. Synthesis of Homobimetallic (14) and
Heterobimetallic (15) Bis-corrole Complexes by a “Click”
Reaction
suggesting metalation of the free-base corrole by copper(I)
acetate. However, there was no indication of substitution of
iron with copper in reactions performed on 8, indicating that
metal exchange was not an issue in this case and that the
presence of redox-active iron(III) and copper(III) species does
not interfere with “click” reactivity.
Of greater interest than the ability to attach to small organic
substrates was the question of whether azido- and alkynyl-
derivatized corroles could be coupled with each other to
produce bis-corrole bimetallic species. To this end, 5 and 6
were reacted in the presence of copper(I) acetate to produce
bis-copper complex 14 in 84% yield (Scheme 4). The identity
of this compound as a single molecule (as opposed to a mixture
of the two starting materials) was confirmed by ESI-MS (see
environments (Figure 1), consistent with two bis-perfluorinated
copper(III) corroles that do not have any electronic
communication. Figure 1 also shows enlarged regions (inset)
for the ortho, para, and meta fluorine peaks for compounds 5, 6,
and 14. While the spectra cannot be overlaid directly due to
differences in solvent and magnetic field strength, comparison
of the complex peaks of 14 with those of its precursors shows
that the spectrum is consistent with two corrole rings in
diamagnetic environments. Additionally, the alkynyl proton
1
the Experimental Section). The H and 19F NMR spectra
suggest that there is no significant interaction between the two
corrole rings; unlike in several reported examples of “sandwich”
species where the corroles are cofacial with metals and bridging
ligands between them,66−68 no unusual shifts of the β-pyrollic
hydrogen atoms or the −C6F5 fluorine atoms are observed. If
the two rings interacted, then nonequivalency of the ortho and
meta fluorine atoms would be expected, and those on the inside
of the cofacial “sandwich” would be shifted upfield due to
shielding by added effects of two anisotropic corrole rings. The
19F NMR spectrum is notable in that it is clearly a superposition
of two sets of −C6F5 peaks in nearly identical chemical
1
observed in the H NMR spectrum of 5 is not present in 14,
but an additional singlet that integrates to 1H is observed at
7.75 ppm in the aromatic region (which otherwise looks very
much like a superposition of the spectra of 5 and 6), consistent
with formation of the triazole.
By a similar procedure, 8 and 6 were reacted in the presence
of copper(I) acetate to generate the heterobimetallic copper-
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Figure 1. 19F NMR spectrum of 14 (large spectrum), exhibiting typical chemical shifts for perfluorophenyl groups. Insets show ortho, para, and meta
fluorine peaks for compounds 5, 6, and 14.
(III) iron(III) bis-corrole complex 15 (54% yield). Analogous
to the iron(III) complex 12, hydrazine was added to convert
the product cleanly to an iron(III) species; in this case
acetonitrile was used as the coordinating solvent due to limited
Table 1. Assignment of Peaks in Cyclic Voltammograms of
14 and 15 and Comparison to Reference Compounds
a
ligand
corrole (solvent)
reduction(s)
CuIII/CuII FeIII/FeIV oxidation(s)
1
solubility of the larger molecule in diethyl ether. H and 19F
14 (CH2Cl2)
−0.21
−0.19
−0.23
0.74
b
b
b
NMR spectroscopies again suggest that there is minimal
interaction between the two metal centers, although broad
peaks from the paramagnetic iron(III) corrole do overlap the
peaks of the copper corrole in the 1H NMR spectrum,
precluding accurate integration of the sharp peaks. The
paramagnetically shifted peaks of the iron corrole in both the
1H and 19F NMR spectra of 15 are again consistent with those
15 (CH3CN)
0.04
0.6, 0.9
c
7 (CH2Cl2)
0.73, 1.33,
1.53
c
c
7 (CH3CN)
9 (CH2Cl2)
9 (CH3CN)
−0.22
0.62, 1.43
0.32, 1.00
0.29, 0.84
0.82, 1.26
−0.69
−0.76, −1.88
−2.00
−0.01
0.01
Cu(tpfc)
−0.09
−0.54
(CH2Cl2)69
previously reported for an iron(III) corrole species.58 In the 19
F
Cu(p-
0.35, 1.01,
1.29
NMR five peaks are observed (δ −117.7 (ortho-F-Fe(corrole)),
−140.5 (ortho-F-Cu(corrole)), −158.0 (possibly two peaks,
para-F’s), −163.7 (meta-F), −165.2 (meta-F)); it is likely that
two peaks are superimposed at −158 ppm due to slight
broadening of this peak; however integration is inaccurate in
the presence of a paramagnetic metal center. The meta-fluorine
peaks cannot be distinguished without more advanced NMR
spectroscopic studies.
OMePh)3corrole
(CH2Cl2)69
Fe(tpfc) (CH2Cl2)58 −1.08
0.44
(none
reported)
a
All voltages calculated as Epf − Epr at 0.1 V/s and reported in V vs
Ag/Ag+, unless otherwise indicated. Epf = peak potential in the forward
direction; Epr = peak potential in the reverse direction. Voltages
originally reported in SCE were converted to Ag/Ag+ by subtracting
298 mV.61 Data for 15 collected at 0.5 V/s due to low solubility.
b
Both 14 and 15 were characterized by cyclic voltammetry, as
were 7 and 9 for comparison. 14 shows a single reversible peak
at −0.21 V vs Ag/Ag+ in methylene chloride, corresponding to
the CuIII/CuII peaks of both copper centers (Figure S5, Table
1).69 This peak is at essentially the same potential with double
the current observed for 7 (−0.23 V vs Ag/Ag+) and occurs at a
Ligand oxidations were poorly resolved; peak potentials estimated.
Irreversible oxidations; reported as the oxidative peak potential.
c
potential 0.12 V more negative than the analogous peak in
previously reported copper(III) tris(perfluorophenyl) corrole
(Cu(tpfc)) and 0.33 V more positive than the previously
H
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Article
reported copper(III) tris(p-methoxyphenyl) corrole. These
numbers are consistent with the corresponding electron-
withdrawing and electron-donating natures of the corrole
ligands in 7, Cu(tpfc), and Cu(p-OMePh)3corrole.69 The
voltammogram of 14 also shows a quasireversible peak at 0.74
V vs Ag/Ag+ with an oxidative shoulder at 0.64 V (0.1 V/s) that
merges with the main peak at higher scan rates. These peaks
correspond to oxidation of the ligand and are again very similar
to the corresponding ligand oxidation observed for 7 but with
roughly double the current. The presence of a single peak for
the CuIII/CuII transition for 14 and the nearly identical ligand
oxidations for both 14 and 7 suggest that there is no interaction
or electronic communication between the two copper corroles
in 14, consistent with what is observed by NMR spectroscopy
and consistent with the fact that a recently reported corrole−
BODIPY dyad with click attachment exhibits only through-
space and not through-bond fluorescence resonance energy
transfer.46
Cyclic voltammetry of 15 in acetonitrile displays an oxidation
and a reduction consistent with the presence of both copper
and iron. The peak at −0.19 V vs Ag/Ag+ corresponds to the
CuIII/CuII couple and that at 0.04 V corresponds to FeIII/
FeIV;58 these are essentially the same peaks observed for the
two corresponding mononuclear species, 7 and 9 (Table 1). As
is the case with the CuIII/CuII peak, the FeIII/FeIV couple occurs
at a potential 0.40 V more negative than the analogous FeIII/
FeIV peak in Fe(tpfc).58 It should be noted that the
voltammograms of 14 and 15 were recorded in different
solvents due to solubility limitations. Similarly to 14, the
voltammogram of 15 shows oxidative peaks corresponding to
the oxidation of the ligand. Also analogous to 14, there is no
indication of interaction between the two metal centers, based
on the fact that the metal oxidations and reductions are
observed at essentially the same potentials as seen in the
monometallic analogues.
ACKNOWLEDGMENTS
■
The authors acknowledge Beata Koszarna, Mariusz Tasior, and
Jan Lewtak at Polish Academy of Sciences for helpful
discussions; Jerzy Chlistunoff at LANL for helpful discussions;
and the spectroscopy staff at the Polish Academy of Sciences
and UC Berkeley QB3 for routine analysis. H.L.B. acknowl-
edges the International Fulbright Science & Technology
fellowship and the UC Fees program for support. L.K.R.
acknowledges the NSF IGERT program (DGE-1144885).
B.J.M. acknowledges the Haas Scholars program at the
University of California, Berkeley. D.T.G. acknowledges the
EuroSolarFuels grant.
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AUTHOR INFORMATION
Corresponding Author
*Tel: 001 510 643 5181. E-mail: arnold@berkeley.edu.
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