Synthesis of Functionalized Perfluorinated Porphyrins for Improved Spin Switching

Article abstract of DOI:10.1021/acs.joc.5b01524

We have established a method to synthesize perfluorinated meso-phenylporphyrins with one phenyl group bearing a substituent in the ortho position. These novel electron-deficient porphyrins are interesting for model enzymes, catalysis, photodynamic therapy, and electron transfer. The key step is the synthesis of an iodine-substituted porphyrin and its Suzuki cross coupling with boronic acid derivatives. We applied the novel strategy to synthesize a highly electron-deficient, azopyridine-substituted Ni-porphyrin that undergoes an improved ligand-driven coordination-induced spin-state switch.

Full text of DOI:10.1021/acs.joc.5b01524

Brief Communication
pubs.acs.org/joc
Synthesis of Functionalized Perfluorinated Porphyrins for Improved
Spin Switching
M. Dommaschk,† C. Nather,‡ and R. Herges*,†
̈
†Otto-Diels-Institut fur Organische Chemie, Christian-Albrechts-Universitat, Otto-Hahn-Platz 4, 24098 Kiel, Germany
̈
̈
‡Institut fur Anorganische Chemie, Christian-Albrechts-Universitat, Otto-Hahn-Platz 6/7, 24098 Kiel, Germany
̈
̈
S
* Supporting Information
ABSTRACT: We have established a method to synthesize
perfluorinated meso-phenylporphyrins with one phenyl group
bearing a substituent in the ortho position. These novel
electron-deficient porphyrins are interesting for model
enzymes, catalysis, photodynamic therapy, and electron
transfer. The key step is the synthesis of an iodine-substituted
porphyrin and its Suzuki cross coupling with boronic acid
derivatives. We applied the novel strategy to synthesize a
highly electron-deficient, azopyridine-substituted Ni−porphyr-
in that undergoes an improved ligand-driven coordination-
induced spin-state switch.
ickel−porphyrins are known to change their spin state
a higher association constant to axial ligands.2 For the
realization of the PDL concept, therefore, meso-tetrakis-
(pentafluorophenyl)nickel(II)porphyrin (Ni−TPPF20, 1) was
used as the square-planar Ni complex. Ni−TPPF20 is one of the
most electron-deficient porphyrins.3 The RP concept is also
based on meso-tetraarylporphyrins; however, one of the ortho
positions of the aryl groups is equipped with an azopyridine
unit as the switching ligand (Figure 2). So far, the synthesis of
N
upon coordination of axial ligands, which is also known
as a coordination-induced spin-state switch (CISSS).1,2 Ni−
porphyrins without axial ligands and square planar geometry
are always diamagnetic (low spin, LS, S = 0). Upon axial
coordination of ligands, square-pyramidal and octahedral
complexes are formed which are paramagnetic (high spin,
HS, S = 1). The process is fully reversible and can be controlled
by light (LD-CISSS) using photochromic azopyridines as free
ligands (photo-dissociable ligands, PDL)3 or azopyridines
covalently attached to the Ni−porphyrin (record player, RP
concept) (Figure 1).4 The systems are designed in such a way
Figure 2. Association of the axial ligand to the Ni−porphyrin by
untethered free 3-phenylazopyridine (2) (PDL concept, left) and by
intramolecular coordination (RP concept, right).
Figure 1. Spin-state switching using PDLs (left) and the RP concept
(right).
that only one of the two azopyridine configurations coordinates
to the Ni ion (trans isomer for PDL, cis isomer for RP), whereas
the other isomer does not. Consequently, isomerization of the
azo group changes the coordination number and thereby
switches the spin state of the nickel.
The switching efficiency (diamagnetic to paramagnetic)
depends on the association constants of the axial ligands to
the porphyrin. Generally, a strong coordination of the binding
isomer is advantageous to achieve a high conversion to the high
spin state. It is known that electron-deficient porphyrins exhibit
RP systems has been performed via the “mixed aldehyde
synthesis”. Consequently, in previous designs, only three of the
four meso positions are substituted with electron-withdrawing
pentafluorophenyl groups (Figure 2), which give rise to an
incomplete intramolecular coordination. Only 74% of cis-RP 3
Received: July 3, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b01524
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Brief Communication
is in the paramagnetic, coordinated form (300 K, acetone-d6),
and 26% remain noncoordinating and diamagnetic.
Scheme 2. Synthesis of the Porphyrin Mixtures 13−15 and
the Corresponding Nickel Derivatives 1, 16, and 17
Perfluorination of the fourth meso position, to which the
tether is attached, should enhance the intramolecular
association. Thus, we developed a novel strategy to prepare
porphyrins with three pentafluorophenyl substituents and one
ortho-substituted tetrafluorophenyl substituent. With an iodine
at this position, aryl substituents such as azopyridines can be
introduced using cross-coupling reactions. A further advantage
of this strategy compared to the mixed aldehyde approach is the
fact that the yields are considerably higher with respect to the
functional unit, which should be introduced.
The starting material is the commercially available 1,2,3,4-
tetrafluorobenzene (4). It is known that metalation of 4 is
possible with n-butyllithium (n-BuLi).5 The metalated species 5
is well characterized.6 At temperatures higher than −40 °C,
lithium fluoride is eliminated and an aryne is formed. At lower
temperatures, 5 is stable and can react with electrophiles. We
were able to obtain the formylated product 6 by addition of
ethyl formate (Scheme 1) in analogy to the reaction of the
Scheme 1. Synthesis of 9
possible products from 6 to 3, prefabricated meso-
(pentafluorophenyl)dipyrromethane (12) (synthesized from
pentafluorobenzaldehyde (11) and pyrrole) was used instead of
pyrrole as one of the three components.12 The resulting
porphyrins TPPF20 (13), TPPF19I (14), and TPPF18I2 (15)
cannot be separated and therefore are used as a mixture. The
yields correspond to the statistical product distribution of 1:2:1.
The porphyrin mixture was metalated quantitatively with
nickel(II) acetylacetonate (Ni(acac)2) yielding a Ni−porphyrin
mixture of Ni−TPPF20 (1), Ni−TPPF19I (16), and Ni−
TPPF18I2 (17).
The porphyrin mixtures 13−15 and the corresponding Ni
compounds 1, 16, and 17 were used for Suzuki cross-coupling
reactions13 with pinacol boronic ester 19 to prepare record
player molecules 20 and 21 (Scheme 3). Compound 19 was
synthesized by a Miyaura borylation reaction14 with the
brominated phenylazopyridine 18 as starting material.4 Note
regioisomer 1,2,4,5-tetrafluorobenzene.7 Formylation with
dimethylformamide (DMF) failed because the aryne formation
is faster than the reaction with DMF. The lithiation/
formylation sequence is the first one-pot preparation of
2,3,4,5-tetrafluorobenzaldehyde (6) from commercially avail-
able 1,2,3,4-tetrafluorobenzene (4). Thus far, it has been
obtained by Grignard reaction from the less accessible 1-
bromo-2,3,4,5-tetrafluorobenzene8 or by Swern oxidation of the
corresponding benzylic alcohol.9 2,3,4,5-Tetrafluorobenzalde-
hyde (6) rapidly oxidizes under air to the corresponding
carboxylic acid. To prevent oxidation and to allow metalation,
the crude aldehyde was immediately protected with ethylene
glycol yielding 2-(2,3,4,5-tetrafluorophenyl)-1,3-dioxolane (7)
with an overall yield of 73% over three steps from 1,2,3,4-
tetrafluorobenzene (Scheme 1). Compound 7 was metalated
with n-BuLi in analogy to the corresponding carboxylic acid.10
Addition of iodine gave the 2-(2-iodo-3,4,5,6-tetrafluorophen-
yl)-1,3-dioxolane (9) with a yield of 91% (Scheme 1). A
structural analysis of 9 is available in the Supporting
Information.
Scheme 3. Miyaura Borylation of Phenylazopyridine 18
Yields Pinacol Boronic Ester 19, Which Is Utilized for
Suzuki Cross-Coupling Reaction with Porphyrins 14 and 16
To Prepare the Record Players 20 and 21
Deprotection of dioxolane 9 to the corresponding aldehyde
was achieved quantitatively with AcOH/HCl. The (iodo,
tetrafluorophenyl) tris(pentafluorophenyl) porphyrin 14 was
prepared by the mixed aldehyde synthesis also known as the
Lindsey method (Scheme 2).11 To reduce the number of
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DOI: 10.1021/acs.joc.5b01524
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The Journal of Organic Chemistry
Brief Communication
that separation of the porphyrins is not possible before the
cross-coupling reaction.
EXPERIMENTAL SECTION
■
General Experimental Methods. Tetrahydrofuran was dried and
The improved coordination of perfluorinated RP 21
(compared to the parent system 3) can be observed by NMR
spectroscopy. The intramolecular association was quantified by
distilled from sodium/benzophenone. All compounds were charac-
1
terized using H, 13C and, if possible, 19F NMR spectroscopy. The
signals were assigned using 2D spectroscopy. For H and 13C NMR
1
1
signal assignment we performed HSQC and HMBC. For 19F signal
the H NMR shift of the pyrrole protons. The maximum shift
assignment we applied 19F COSY.
(100% paramagnetic complex) for 3 and 21 is identical (∼53
ppm). The latter was measured by addition of an excess of an
axial ligand (pyridine-d5). The diamagnetic shift (∼9 ppm) is
known from the trans isomer and the corresponding Zn−
porphyrin.4 The equilibrium between the paramagnetic and
Synthesis of 2-(2,3,4,5-Tetrafluorophenyl)-1,3-dioxolane (7).
1,2,3,4-Tetrafluorobenzene (4) (10.0 g, 7.09 mL, 66.6 mmol) was
mixed with tetrahydrofuran (200 mL) and cooled to −78 °C. n-
Buthyllithium (30 mL, 75.0 mmol, 2.5 M in hexane) was slowly added,
and the reaction mixture was stirred for another 1 h at −78 °C. Ethyl
formate (27 mL, 333 mmol) was slowly added, and the mixture was
allowed to warm to room temperature overnight. Diethyl ether (500
mL) was added. The organic layer was washed with water three times
and dried over magnesium sulfate, and the solvent was removed under
reduced pressure. Crude product of 2,3,4,5-tetrafluorobenzaldehyde
(3) (12.4 g) was obtained as a pale yellow liquid. The crude product
was mixed with benzene (500 mL) and ethylene glycol (12.4 g, 200
mmol). p-Toluenesulfonic acid monohydrate (111 mg, 0.583 mmol)
was added, and the benzene water mixture was removed by azeotropic
distillation. The residue was treated with triethylamine (2 mL) and
diethyl ether (200 mL). The organic layer was successively washed
with saturated sodium carbonate, diluted sodium carbonate solution,
and water. The organic phase was dried over magnesium sulfate, and
the solvent was removed under reduced pressure. The crude product
(11.8 g yellow liquid) was purified by vacuum distillation (bp 105 °C,
0.7 mbar) to obtain 2-(2,3,4,5-tetrafluorophenyl)-1,3-dioxolane (7)
(10.8 g, 48.6 mmol, 73%) as a colorless liquid. n20D = 1.4561. FT-IR: ν
= 2892 (m), 1635 (w), 1524 (s), 1488 (vs), 1406 (m) 1371 (m), 1265
(w), 1194 (w), 1134 (s), 1103 (w), 1030 (s), 973 (s), 946 (vs), 868
1
diamagnetic conformer is faster than the H NMR time scale.
Hence, an average shift is observed that is directly proportional
to the amount of the paramagnetic complex. By irradiation with
light of 500 nm 61% of the cis-isomer was obtained, which is
the same percentage as for the parent system 3. Hence, the
perfluorination does not influence the photochromism. As
expected, the pyrrole protons of the perfluorinated RP 21 (X =
F) resonate at lower fields as those of the parent system 3 (X =
H) (Figure 3). The average shift rises from 41.7 to 48.2 ppm
(m), 757 (m), 708(m), 616 (m), 560 (w), 499 (w) cm−1. H NMR
1
(500 MHz, 300 K, CDCl3): δ = 7.04 (m, 1H, Ar-H), 5.90, (s, 1H,
CHO2), 4.02−3.91 (m, 4H, CH2) ppm. 13C NMR (125 MHz, 300 K,
CDCl3): δ = 147.1 (dddd, 1J = 247 Hz, 2J = 10.2 Hz, 3J = 3.7 Hz, 4J =
1.9 Hz, C5), 146.1 (dddd, 1J = 250 Hz, 2J = 10.9 Hz, 3J = 3.8 Hz, 4J =
1.7 Hz, C2), 141.0 (dddd, 1J = 255 Hz, 2J = 16.8, 12.2 Hz, 3J = 3.3 Hz,
1
2
3
Figure 3. Equilibrium between the dia- (cis-RPdia) and paramagnetic
(cis-RPpara) conformations of the perfluorinated RP 21 (X = F) and of
the parent system 3 (X = H). Average shift is the average chemical
shift of the four pyrrole protons; cis-RPpara is the percentage of the
paramagnetic cis isomer relative to the total amount of cis isomer.
C4), 140.7 (dddd, J = 254 Hz, J = 16.5, 12.3 Hz, J = 3.6 Hz, C3),
122.3 (dddd, 2J = 11.6 Hz, 3J = 5.9, 3.9 Hz, 4J = 0.7 Hz, C1), 109.0 (dt,
3
2J = 20.5 Hz, J = 3.7 Hz, C6), 97.7 (m, CHO2), 65.6 (s, CH2) ppm.
19F NMR (470 MHz, 300 K, CDCl3): δ = −139.14 (ddd, 3J = 20.9 Hz,
4
3
5
5J = 13.1 Hz, J = 2.4 Hz, 1F, F-5), −145.00 (ddd, J = 20.3 Hz, J =
13.1 Hz, 4J = 3.9 Hz, 1F, F-2), −154.92 (td, 3J = 20.1 Hz, 4J = 3.9 Hz,
1F, F-4), −153.73 (td, 3J = 19.9 Hz, 4J = 2.4 Hz, 1F, F3) ppm. MS (EI,
TOF): m/z = 222 (67) [M]+, 203 (45) [M − F]+, 178 (100) [M −
C2H4O]+. HRMS (EI, TOF-Q) m/z: [M]+ calcd for C9H6F4O2
222.0304, found 222.0305.
(acetone-d6), which corresponds to 15% higher percentage of
the paramagnetic cis isomer (cis-RPpara). The overall switching
efficiency (diamagnetic to paramagnetic) has increased from
45% to 54%.
Synthesis of 2-(2-Iodo-3,4,5,6-tetrafluorophenyl)-1,3-dioxo-
lane (9). 2-(2,3,4,5-Tetrafluorophenyl)-1,3-dioxolane (7) (9.29 g, 41.8
mmol) was mixed with tetrahydrofuran (150 mL) and cooled to −78
°C. n-Buthyllithium (18.4 mL, 46.0 mmol, 2.5 M in hexane) was added
within 1 h whereby the solution became pale red. The mixture was
stirred for another 1 h at −78 °C. Iodine (11.7 g, 46.0 mmol) was
dissolved in tetrahydrofuran (50 mL) and slowly added with a syringe
pump within 1.5 h. Finally, the color of iodine did not disappear upon
addition. The reaction mixture was allowed to warm to room
temperature and added to diethyl ether (300 mL). The organic layer
was washed with diluted sodium carbonate and saturated sodium
thiosulfate and once again with diluted sodium carbonate solution.
Than it was dried over magnesium sulfate, and the solvent was
removed under reduced pressure. A pale yellow solid was obtained
which was dissolved in a minimum amount of dichloromethane. By
addition of pentane the product 9 precipitated as a fluffy, colorless
solid (13.2 g, 37.9 mmol, 91%). Crystals for structure analysis were
obtained by vapor diffusion of pentane in a saturated solution of 9 in
dichloromethane. Mp: 128.3 °C. FT-IR: ν = 2909 (m), 1627 (w),
1506 (s), 1470 (m), 1395 (m), 1353 (w), 1337 (m), 1270 (w), 1170
(w), 1148 (s), 1094 (m), 1070 (m), 1017 (w), 994 (m), 964 (s), 950
(vs), 925 (s), 809 (s), 753 (m), 724 (m), 652 (w), 624 (s), 617 (m),
In summary, we present a novel, modular approach to
prepare highly electron-deficient functionalized porphyrins. Key
intermediates are the porphyrins TPPF19I (14) and Ni−
TPPF19I (16). Cross-coupling reactions were used to function-
alize these porphyrins as demonstrated by the synthesis of
perfluorinated RP 21, a Ni−porphyrin that exhibits an
improved LD-CISSS. Our approach provides access to a
number of perfluorinated mono meso-o-phenyl-functionalized
porphyrins which have not been described so far and which are
difficult to prepare by the established mixed aldehyde synthesis.
TPPF19I (14) is a suitable building block to tether various
functional groups, particularly axial ligands. Besides spin
switching, metalated derivatives of such porphyrins are of
broad interest as model enzymes15 and for catalysis,16
photodynamic therapy (PDT),17 and electron-transfer pro-
cesses.18
C
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The Journal of Organic Chemistry
Brief Communication
519 (w) cm−1. 1H NMR (500 MHz, 300 K, CDCl3): δ = 6.06 (s, 1H,
CHO2), 4.18−3.96 (m, 4H, CH2) ppm. 13C NMR (125 MHz, 300 K,
CDCl3): δ = 147.2 (dddd, 1J = 242 Hz, 2J = 11.0 Hz, 3J = 4.3 Hz, 4J =
2.0 Hz, C3), 146.8 (dddd, 1J = 257 Hz, 2J = 11.1 Hz, 3J = 3.9 Hz, 4J =
2.0 Hz, C6), 141.0 (dddd, 1J = 255 Hz, 2J = 17.3, 12.3 Hz, 3J = 3.7 Hz,
mmol) dissolved in dichloromethane (100 mL) was added, and the
mixture was stirred for 14 h. p-Chloranil (1.50 g, 6.09 mmol) was
added, and the mixture was stirred under reflux for 4 h. The solvent
was removed under reduced pressure, and the crude product was
purified by column chromatography (cyclohexane/chloroform = 1:1,
Rf = 0.45). The mixture of three porphyrins (13−15) was obtained as
a purple solid (555 mg, 513 μmol, 18% assuming a 1:2:1 porphyrin
mixture). HRMS (EI, TOF-Q) m/z: [M]+ calcd for C44H10F20N4
974.059, found 974.055; [M]+ calcd for C44H10F19IN4 1081.964, found
1081.961; [M]+ calcd for C44H10F18I2N4 1189.871, found 1189.866.
The metal-free porphyrin mixture (13−15) (229 mg, 212 μmol),
pinacol boronic ester 19 (157 mg, 0.51 mmol), and tetrakis-
(triphenylphosphine)palladium(0) (∼10 mg) were dissolved in a
toluene (6.5 mL)/ethanol (2 mL) mixture under nitrogen atmosphere.
Potassium carbonate (232 mg, 1.68 mmol) dissolved in 1.5 mL of
water was added, and the mixture was stirred overnight at 80 °C.
Water (50 mL) was added, and the aqueous layer was extracted twice
with dichloromethane. The combined organic layers were dried over
magnesium sulfate, and the solvent was removed under reduced
pressure. The crude product was purified by column chromatography
(cyclohexane/ethyl acetate = 7:3, Rf = 0.15). The product was
obtained as a purple solid (46 mg, 40.4 μmol, 38% assuming a 1:2:1
porphyrin mixture as starting material). Mp: 216.2 °C. FT-IR (layer):
ν = 3316 (w), 1651 (w), 1516 (s), 1495 (s), 1391 (m), 1080 (w),
1066 (m), 1043 (m), 1026 (w), 987 (vs), 917 (vs), 801 (s), 768 (m),
754 (s), 722 (m), 700 (s), 645 (w) cm−1. 1H NMR (500 MHz, 300 K,
acetone-d6): δ = 9.51 (s, br, 2H, H-Por), 9.36 (s, br, 2H, H-Por),
1
2
3
C5), 140.3 (dddd, J = 259 Hz, J = 19.7, 12.8 Hz, J = 3.9 Hz, C4),
122.9 (dm, 2J = 9.6 Hz, C1), 105.1 (dd, 3J = 4.6 Hz, 4J = 2.3 Hz, CH),
2
3
5
78.5 (dt, J = 24.9 Hz, J = 3.3 Hz, C2), 66.2 (d, J = 1.2 Hz, CH2)
ppm. 19F NMR (470 MHz, 300 K, CDCl3): δ = −113.04 (ddd, J =
3
23.3 Hz, 5J = 9.8 Hz, 4J = 3.9 Hz, 1F, F-3), −140.52 (ddd, 3J = 20.3 Hz,
5J = 9.8 Hz, J = 5.2 Hz, 1F, F-6), −151.29 (td, J = 21.5 Hz, J = 5.2
4
3
4
Hz, 1F, F-4), −153.73 (td, 3J = 19.9 Hz, 4J = 3.9 Hz, 1F, F-5) ppm. MS
(EI, TOF): m/z = 348 (100) [M]+, 303 (31) [M − C2H4O]+, 275 (6)
[M − C3H5O2]+, 221 (20) [M − I]+. Anal. Calcd for C9H5F4O2I: C,
31.06; H, 1.45. Found: C, 31.21; H, 1.47.
Synthesis of 2-Iodo-3,4,5,6-tetrafluorophenylbenzaldehyde
(10). 2-(2-Iodo-3,4,5,6-tetrafluorophenyl)-1,3-dioxolane (9) (1.01 g,
2.90 mmol) was dissolved in acetic acid (25 mL). After dropwise
addition of concentrated hydrochloric acid (6 mL), the mixture was
stirred for 3 h. Ethyl acetate (200 mL) was added. The organic layer
was washed with water and saturated sodium carbonate solution and
dried over magnesium sulfate. The solvent was removed under
reduced pressure. The obtained aldehyde (883 mg, 2.90 mmol, > 99%)
is sensitive to oxidation and therefore was directly used for the
1
porphyrin synthesis. H NMR (500 MHz, 300 K, CDCl3): δ = 10.05
(s, 1H, CH) ppm. 13C NMR (125 MHz, 300 K, CDCl3): δ = 188.1
(m, CH), 149.2 (dddd, 1J = 267 Hz, 2J = 11.1 Hz, 3J = 3.7 Hz, 4J = 2.4
Hz, C3), 147.9 (dddd, 1J = 245 Hz, 2J = 11.1 Hz, 3J = 4.4 Hz, 4J = 1.5
3
9.32−9.27 (m, 4H, H-Por), 8.64 (s, 1H, NCH), 8.60 (d, J = 4.5 Hz,
1
2
3
4
3
Hz, C6), 144.0 (dddd, J = 267 Hz, J = 19.7, 12.7 Hz, J = 3.9 Hz,
1H, NCH), 7.78 (t, J = 1.7 Hz, 1H, N2CCH), 7.50 (d, J = 8.1 Hz,
1
2
3
C5), 140.9 (dddd, J = 259 Hz, J = 16.2, 12.5 Hz, J = 3.3 Hz, C4),
1H, NCHCHCH), 7.44 (dm, 3J = 7.9 Hz, 1H, N2CCH), 7.30 (dd, 3J =
2
3
2
3
3
4
119.9 (dd, J = 7.2 Hz, J = 3.8 Hz, C1), 78.4 (dd, J = 25.5 Hz, J =
4.7 Hz, C2) ppm. 19F NMR (470 MHz, 300 K, CDCl3): δ = −113.29
(ddd, 3J = 23.1 Hz, 5J = 10.6 Hz, 4J = 4.8 Hz, 1F, F-3), −142.84 (ddd,
8.1, 4.5 Hz, 1H, NCHCH), 7.01 (ddd, J = 7.9 Hz, J = 2.0, 1.1 Hz,
1H, N2CCHCHCH), 7.54 (t, 3J = 7.9 Hz, 1H, N2CCHCH), −3.01 (s,
2H, H-N) ppm. 13C NMR (125 MHz, 300 K, acetone-d6): δ = 152.8
(NCH), 151.0 (N2C(CH)2), 148.0 (NCHCN2), 147.2 (NCH), 133.9
(N2CCHCH), 133.6 (N2CHC), 129.4 (N2CCHCH), 127.0
(NCHCHCH), 124.8 (NCHCH), 124.5 (N2CCHC), 123.9
(N2CCHCHCH) ppm, C atoms of the porphyrin and of the
perfluorinated meso phenyl substituents cannot be assigned. 19F
NMR (470 MHz, 300 K, acetone-d6): δ = −137.19 (ddd, 3J = 23.2 Hz,
5J = 11.9 Hz, 4J = 3.5 Hz, 1F, F-o′-C), −139.72 (dd, 3J = 23.8 Hz, 5J =
7.9 Hz, 2F, F-o′-A), −139.82 to −139.94 (m, 4F, F-o-A, F-o-B, F-o′-B),
3J = 19.8 Hz, 5J = 10.6 Hz, 4J = 8.7s Hz, 1F, F-6), −143.89 (ddd, J =
3
23.1, 19.1 Hz, 4J = 8.7 Hz, 1F, F-4), −152.45 (td, 3J = 19.5 Hz, 4J = 4.8
Hz, 1F, F-5) ppm.
Synthesis of 3-(3-(Pinacol boronic ester)phenylazo)pyridine
(19). A solution of 3-(3-bromophenylazo)pyridine (18) (1.00 g, 3.82
mmol) and potassium acetate (748 mg, 7.62 mmol) in dioxane (40
mL) was dried over molecular sieves (3 Å) by heating to 120 °C for 4
h. Bis(pinacolato)diboron (1.07 g, 4.20 mmol) and bis-
(triphenylphosphine)palladium(II) dichloride (140 mg, 0.20 FT-
IRded and the solution was kept at 100 °C overnight without stirring.
After cooling the molecular sieve and all solid components were
filtered off. The volume of the filtrate was doubled with water and
extracted twice with dichloromethane. The combined organic layers
were dried over magnesium sulfate and the solvent was removed under
reduced pressure. The crude product was purified by column
chromatography (cyclohexane/ethyl acetate =6:4, Rf = 0.15). The
product was obtained as an orange solid (1.05 g, 3.40 mmol, 89%).
Mp: 86.6 °C. FT-IR (layer): ν = 2975 (m), 1422 (m), 1356 (s), 1333
(s), 1273 (w), 1213 (w), 1139 (s), 1064 (m), 967 (w), 918 (w), 851
(m), 817 (s), 698 (vs), 676 (m), 618 (w), 566 (w), 538 (m), 512 (w)
cm−1. 1H NMR (500 MHz, 300 K, CDCl3): δ = 9.21 (dd, 4J = 2.3, 5J =
0.5 Hz, 1H, H-2), 8.70 (dd, 3J = 4.7 Hz, 4J = 1.6 Hz 1H, H-6), 8.37 (m,
1H, H-8), 8.14 (ddd, 3J = 8.2 Hz, 4J = 2.3, 1.6 Hz, 1H, H-4), 8.02 (ddd,
3J = 7.9 Hz, 4J = 2.3, 1.2 Hz, 1H, H-12), 7.95 (dt, 3J = 7.3 Hz, 4J = 1.2
3
5
4
−142.78 (ddd, J = 22.2 Hz, J = 11.9 Hz, J = 3.1 Hz, 1F, F-m-C),
−155.44 (t, 3J = 20.5 Hz, 2F, F-p-A), −155.49 (t, 3J = 20.2 Hz, 1F, F-p-
B), −156.80 (td, 3J = 21.0 Hz, 4J = 3.5 Hz, 1F, F-p-C), −159.23 (td, 3J
= 21.8 Hz, 4J = 3.1 Hz, 1F, F-m′-C), −164.18 (td, 3J = 22.2 Hz, 5J = 8.0
Hz, 2F, F-m′-A), −164.46 to −164.61 (m, 4F, F-m-A, F-m-B, F-m′-B)
ppm. HRMS (EI, TOF-Q) m/z: [M]+ calcd for C55H18F19N7
1137.1320, found 1137.1350.
Synthesis of Record Player 21. The metal-free porphyrin
mixture (150 mg, 139 μmol) and nickel(II) acetylacetonate (360
mg, 1.40 mmol) were dissolved in toluene (30 mL) and stirred under
reflux for 4 d. The solvent was removed under reduced pressure, and
the crude product was purified by column chromatography (cyclo-
hexane/ethyl acetate = 3:1, Rf = 0.30). The mixture of three Ni−
porphyrins (1, 16, and 17) was obtained as a purple solid (156 mg,
137 μmol, 99% assuming a 1:2:1 Ni−porphyrin mixture). HRMS (EI,
TOF-Q) m/z: [M]+ calcd for C44H8F20N4Ni 1029.978, found
1029.974; [M]+ calcd for C44H8F19IN4Ni 1137.884, found 1137.880;
[M]+ calcd for C44H8F18I2N4Ni 1245.790, found 1245.785. The Ni−
porphyrin mixture (1, 16, 17) (156 mg, 137 μmol), pinacol boronic
ester 19 (103 mg, 333 μmol), and tetrakis(triphenylphosphine)-
palladium(0) (∼10 mg) were dissolved in a toluene (6.5 mL)/ethanol
(2 mL) mixture under nitrogen atmosphere. Potassium carbonate (151
mg, 1.09 mmol) dissolved in 1.5 mL of water was added, and the
mixture was stirred overnight at 80 °C. Water (50 mL) was added, and
the aqueous layer was extracted twice with dichloromethane. The
combined organic layers were dried over magnesium sulfate, and the
solvent was removed under reduced pressure. The crude product was
purified by column chromatography (cyclohexane/ethyl acetate = 2:1,
Rf = 0.20). The product was obtained as a purple solid (49.2 mg, 41.9
Hz, 1H, H-10), 7.54 (t, 3J = 7.6 Hz, 1H, H-11), 7.45 (ddd, 3J = 8.2, 4.7
5
Hz, J = 0.5 Hz, 1H, H-5), 1.38 (s, 12H, CH3) ppm. 13C NMR (125
MHz, 300 K, CDCl3): δ = 152.1 (C7), 151.7 (C6), 148.1 (C3), 147.5
(C2), 138.2 (C10), 130.7 (C9), 129.7 (C8), 128.8 (C11), 127.1 (C4),
125.6 (C12), 124.1 (C5), 25.1 (CH3) ppm. MS (EI, TOF): m/z = 319
(29) [M]+, 203 (100) [PhBPin]+. Anal. Calcd for C17H20BN3O2: C,
66.04; H, 6.52; N, 13.59. Found: C, 65.71; H, 6.80; N, 13.52.
Synthesis of Metal-Free Record Player 20. 2-Iodo-3,4,5,6-
tetrafluorophenylbenzaldehyde (10) (883 mg, 2.90 mmol) and
pentafluorophenylbenzaldehyde (11) (568 mg, 2.90 mmol) were
dissolved in dichloromethane (700 mL) under nitrogen atmosphere.
Boron trifluoride diethyl etherate (280 μL, 0.50 mmol) was added
dropwise. Pentafluorophenyl dipyrromethane (12) (1.81 g, 5.81
D
DOI: 10.1021/acs.joc.5b01524
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Brief Communication
μmol, 62% assuming a 1:2:1 Ni−porphyrin mixture as starting
material). Mp: 209.0 °C. FT-IR (layer): ν = 2980 (w), 1652 (w), 1518
(s), 1486 (s), 1346 (m), 1079 (m), 1061 (m), 1025 (w), 985 (vs), 937
(3) (a) Thies, S.; Sell, H.; Schutt, C.; Bornholdt, C.; Nather, C.;
̈
̈
Tuczek, F.; Herges, R. J. Am. Chem. Soc. 2011, 133, 16243−16250.
(b) Thies, S.; Sell, H.; Bornholdt, C.; Schutt, C.; Kohler, F.; Tuczek,
̈
̈
1
(vs), 800 (m), 760 (s), 732 (w), 701 (s), 644 (m) cm−1. H NMR
F.; Herges, R. Chem. - Eur. J. 2012, 18, 16358−16368.
(500 MHz, 300 K, acetone-d6): δ = 9.60 (s, br, 2H, H-Por), 9.41 (s, br,
6H, H-Por), 9.28 (s, br, 1H, NCH), 9.21 (s, br, NCH), 9.15 (s, br,
NCHCHCH), 7.53 (s, 1H, N2CCH), 7.44 (d, 3J = 7.9 Hz, 1H,
(4) (a) Venkataramani, S.; Jana, U.; Dommaschk, M.; Sonnichsen, F.
̈
D.; Tuczek, F.; Herges, R. Science 2011, 331, 445−448. (b) Dom-
maschk, M.; Schutt, C.; Venkataramani, S.; Jana, U.; Nather, C.;
̈
̈
3
3
NCHCH), 7.27 (d, J = 7.9 Hz, 1H, N2CCH), 7.06 (d, J = 7.9 Hz,
Sonnichsen, F. D.; Herges, R. Dalton Trans. 2014, 43, 17395−17405.
̈
1H, N2CCHCHCH), 6.81 (t, 3J = 7.9 Hz, 1H, N2CCHCH) ppm. 13
C
(c) Dommaschk, M.; Peters, M.; Gutzeit, F.; Schutt, C.; Nather, C.;
Sonnichsen, F. D.; Tiwari, S.; Riedel, C.; Boretius, S.; Herges, R. J. Am.
̈
̈
NMR (125 MHz, 300 K, acetone-d6): δ = 152.0 (N2C), 134.0
(N2CCH), 133.1 (N2CCHC), 129.9 (N2CCHCH), 124.2 (N2CCH),
124.0 (N2CCHCHCH) ppm, C atoms of the pyridine, porphyrin, and
the perfluorinated meso aryl substituents are not detectable because of
the low concentration and slight paramagnetism due to intermolecular
coordination. 19F NMR (470 MHz, 300 K, acetone-d6): δ = −136.97
(dd, 3J = 21.2 Hz, 5J = 10.8 Hz, 1F, F-o′-C), −139.59 to −139.69 (m,
3F, F-o′-A, F-o′-B), −139.96 to −140.06 (m, 3F, F-o-A, F-o-B),
−142.76 (dd, 3J = 21.6 Hz, 5J = 10.8 Hz, 1F, F-m-C), −155.60 (t, 3J =
20.4 Hz, 2F, F-p-A), −155.63 (t, 3J = 20.4 Hz, 1F, F-p-B), −156.92 (t,
̈
Chem. Soc. 2015, 137, 7552−7555.
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2385−2389.
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(b) Leroy, J.; Schollhorn, B.; Syssa-Magale, J.-L.; Boubekeur, K.;
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Palvadeau, P. J. Fluorine Chem. 2004, 125, 1379−1382.
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4719−4727.
3
3J = 21.5 Hz, 1F, F-p-C), −159.07 (t, J = 21.3 Hz, 1F, F-m′-C),
−164.13 (td, 3J = 21.6 Hz, 5J = 7.5 Hz, 2F, F-m′-A), −164.42 (td, 3J =
22.3 Hz, 5J = 7.8 Hz, 1F, F-m′-B), −164.46 to −164.59 (m, 3F, F-m-A,
F-m-B) ppm. UV−vis (MeCN): λmax (lg ε) = 311 (4.547), 403
(5.390), 523 (4.234), 556 (4.125) nm. HRMS (EI, TOF-Q) m/z:
[M]+ calcd for C55H16F19N7Ni 1193.0517, found 1193.0528.
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2840−2845.
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7508−7510.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.5b01524.
CCDC-1409964 contains the supplementary crystallographic
data for compound 9. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.
(15) (a) Kumar, D.; Tahsini, L.; Visser, S. P. d.; Kang, H. Y.; Kim, S.
J.; Nam, W. J. Phys. Chem. A 2009, 113, 11713−11722. (b) Rebelo, S.
L.; Pereira, M. M.; Monsanto, P. V.; Burrows, H. D. J. Mol. Catal. A:
Chem. 2009, 297, 35−43. (c) Sainna, M. A.; Kumar, S.; Kumar, D.;
Fornarini, S.; Crestoni, M. E.; de Visser, S. P. Chem. Sci. 2015, 6,
1516−1529.
1H, 13C, 19F, and 2D NMR spectra of new compounds
and crystal structure data for 2-(2-iodo-3,4,5,6-tetraphen-
yl)-1,3-dioxolane (9) (PDF)
X-ray cystallographic data for compound 9 (CIF)
(16) (a) Cunningham, I. D.; Basaleh, A.; Gazzaz, H. A. Dalton Trans.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rherges@oc.uni-kiel.de.
■
2012, 41, 9158−9160. (b) Baran, J. D.; Gronbeck, H.; Hellman, A. J.
̈
Am. Chem. Soc. 2014, 136, 1320−1326. (c) Castro, K. A. D. F.;
Simoes, M. M. Q.; Neves, M. G. P. M. S.; Cavaleiro, J. A. S.; Wypych,
F.; Nakagaki, S. Catal. Sci. Technol. 2014, 4, 129−141.
Notes
(17) (a) Samaroo, D.; Vinodu, M.; Chen, X.; Drain, C. M. J. Comb.
The authors declare no competing financial interest.
Chem. 2007, 9, 998−1011. (b) Kral
Dolensky, B.; Vasek, P.; Pouckova,
ek, P.; Dvorak, M.; Kral, V. J. Med. Chem. 2008, 51, 5964−5973.
́
ova,
́
J.; Bríza, T.; Moserova,
́
I.;
́
̌
́
P.; Kejík, Z.; Kaplan
́
ek, R.;
ACKNOWLEDGMENTS
■
Martas
́
́
́
The authors gratefully acknowledge funding from the
Collaborative Research Center SFB 677 Function by Switching
and a scholarship from the Fonds der Chemischen Industrie for
M.D.
(18) (a) Gobeze, H. B.; Das, S. K.; D’Souza, F. J. Phys. Chem. C 2014,
118, 16660−16671. (b) Das, S. K.; Song, B.; Mahler, A.; Nesterov, V.
N.; Wilson, A. K.; Ito, O.; D’Souza, F. J. Phys. Chem. C 2014, 118,
3994−4006.
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E
DOI: 10.1021/acs.joc.5b01524
J. Org. Chem. XXXX, XXX, XXX−XXX