Boron Arylations of Subporphyrins with Aryl Zinc Reagents

Article abstract of DOI:10.1002/chem.201504719

Boron arylations of B-(methoxo)triphenylsubporphyrin have been developed with a combined use of ArZnI-LiCl and trimethylsilyl chloride. Aryl zinc reagents bearing bromo, cyano, amide, and ester groups can be employed for the B-arylation reaction to provide the corresponding B-arylated subporphyrins in moderate yields. Postmodifications of B-arylated subporphyrins have been demonstrated without loss of the B-C bond. These modifications include conversion of the cyano group into a benzoyl group with PhMgBr, hydrolysis of the ester group to give B-(4-carboxyphenyl)subporphyrin, and Pd-catalyzed Suzuki-Miyaura coupling of the 4-bromophenyl group to give a 1,4-phenylene-bridged subporphyrin-Zn^II porphyrin hybrid that displays intramolecular excitation energy transfer from the subporphyrin to the porphyrin. The newly synthesized B-arylated subporphyrins have been fully characterized by NMR, UV/Vis absorption and fluorescence spectroscopies, mass spectrometry, electrochemical measurements, and X-ray diffraction analysis.

Full text of DOI:10.1002/chem.201504719

DOI: 10.1002/chem.201504719
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Porphyrinoids |Hot Paper|
Boron Arylations of Subporphyrins with Aryl Zinc Reagents
Ryota Kotani, Kota Yoshida, Eiji Tsurumaki, and Atsuhiro Osuka*[a]
Abstract: Boron arylations of B-(methoxo)triphenylsubpor-
phyrin have been developed with a combined use of
ArZnI·LiCl and trimethylsilyl chloride. Aryl zinc reagents bear-
ing bromo, cyano, amide, and ester groups can be em-
ployed for the B-arylation reaction to provide the corre-
sponding B-arylated subporphyrins in moderate yields. Post-
modifications of B-arylated subporphyrins have been dem-
onstrated without loss of the BÀC bond. These modifications
include conversion of the cyano group into a benzoyl group
with PhMgBr, hydrolysis of the ester group to give B-(4-car-
boxyphenyl)subporphyrin, and Pd-catalyzed Suzuki–Miyaura
coupling of the 4-bromophenyl group to give a 1,4-phenyl-
ene-bridged subporphyrin–ZnII porphyrin hybrid that dis-
plays intramolecular excitation energy transfer from the sub-
porphyrin to the porphyrin. The newly synthesized B-arylat-
ed subporphyrins have been fully characterized by NMR, UV/
Vis absorption and fluorescence spectroscopies, mass spec-
trometry, electrochemical measurements, and X-ray diffrac-
tion analysis.
was prepared from b-hexabromosubporphyrin[6b] and exhibited
a large two-photon absorption cross-section, and tris(1,4-
benzodithiino)subporphyrin were prepared from b-hexachloro-
subporphyrin and displayed a large association constant to
capture C60.[6c]
Introduction
In recent years, subporphyrins, ring-contracted porphyrin cous-
ins coordinating a boron atom in the central cavity with
a bowl-shaped distorted 14p aromatic system, have emerged
as promising functional pigments in light of their tunable pho-
tophysical and electrochemical properties, high fluorescence
quantum yields, and large nonlinear optical responses.[1] Ra-
tional fabrications of subporphyrins have been accomplished
mostly at the meso- and b-positions so far. meso-Aryl substitu-
ents of subporphyrins can rotate rather freely to provide large
substituent effects, and the introduction of various meso-aryl
substituents has led to the creation of subporphyrins possess-
ing versatile electronic properties.[2] Along this strategy, many
A3-type meso-aryl-substituted subporphyrins have been pre-
pared. Representative examples include meso-(oligo-
phenyleneethynylene)-substituted subporphyrins[3] that display
expanded p-conjugated chromophores and meso-(4-amino-
phenyl)-substituted subporphyrins[4] that exhibit remarkable
quinonoidal contributions. meso-Bromosubporphyrin has been
used for the synthesis of lower symmetry A2B-type subpor-
phyrins, some of which undergo efficient electron-transfer and
excitation-energy-transfer reactions.[5] b-Mono- and perhaloge-
nations of subporphyrins have been demonstrated, and the re-
sultant b-halogenated subporphyrins underwent various sub-
stitution reactions to provide the corresponding products.[6] As
interesting examples, b-hexaphenylethynylated subporphyrin
In contrast, chemical modifications of the axial group of sub-
porphyrins have been only poorly explored.[7] Recently, we re-
ported subporphyrin B-hydrides by the reaction of B-
(methoxo)triphenylsubporphyrin 1 with diisobutylaluminum
hydride as a rare example of porphyrinoid borohydrides.[7c] We
also succeeded in the isolation of subporphyrinatoborenium
cation 2+ as a salt with a carborane anion, [CH6B11Br6]À, which
was shown to be a planar structure (Scheme 1).[7a] The boreni-
um cation 2+ was then converted into B-phenylated subpor-
phyrin 3 upon treatment with PhLi. Shortly after this work, B-
arylations of 1 were achieved by reactions with organomagne-
[a] R. Kotani, K. Yoshida, Dr. E. Tsurumaki, Prof. Dr. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
Fax: (+81)75-753-3970
E-mail: osuka@kuchem.kyoto-u.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504719.
Scheme 1. Synthesis of B-phenylated subporphyrin 3.
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sium reagents as a more facile synthetic route to B-arylated
subporphyrins.[8] However, the scope of this B-arylation is limit-
ed because of the high nucleophilicity of aryl magnesium bro-
mides. It is desirable to expand the scope of the axial aryl
groups of subporphyrins, including various functional groups.
We thus examined B-arylation reactions of subporphyrins with
aryl zinc reagents because aryl zinc reagents are milder carbon
nucleophiles with much wider functional-group compatibility
than aryl magnesium reagents.[9]
reaction time gave a better result (Table 1, entry 6). Moreover,
B-phenylation with a lower amount of PhZn reagent (5 equiv)
at room temperature gave a cleaner reaction mixture, from
which the separation of 3 was easier, with a 77% yield after
isolation (Table 1, entry 7). A further decrease in the amount of
PhZn reagent (1.5 equiv) lowered the yield of 3 (Table 1,
entry 8). Therefore, we concluded that the reaction conditions
in entry 7 in Table 1, (5 equiv of PhZn reagent, 20 equiv of
TMSCl, THF as solvent, room temperature, 16 h) were the best.
In the course of the optimization of the reaction conditions,
we noticed that the B-trimethylsiloxy-substituted subporphyrin
4 was formed as a side product (Table 1, entries 2 and 5–8).
Side product 4 was isolated and its structure was elucidated
by X-ray crystallographic analysis (see the Supporting Informa-
Results and Discussion
ArZnI·LiCl reagents (hereafter abbreviated as ArZn reagents)
were prepared by direct insertion of Zn powder into iodoar-
enes in the presence of LiCl.[10] As an initial attempt, B-phenyla-
tion of 1 with 20 equivalents of PhZn reagent was carried out
under the same conditions as those used for B-arylation of
1 with Grignard reagents (Table 1, entry 1). However, this at-
1
tion). The H NMR spectrum of 4 displays a singlet due to the
TMS group at d=À1.10 ppm, which is high-field shifted by the
strong diatropic ring current of the subporphyrin. The 11B NMR
spectrum of 4 displays a singlet at d=À16.7 ppm, which is
high-field shifted relative to that of 1 (d=À15.3 ppm)[2c] due
to the larger electron-donating effect of the trimethylsiloxy
group.
Table 1. B-Phenylation of 1 with phenylzinc reagent.
With the optimized reaction conditions in hand, we then
synthesized novel B-aryl-substituted subporphyrins (Scheme 3).
B-(4-Cyanophenyl)-, B-(4-(ethoxycarbonyl)phenyl)-, B-(4-(piperi-
dine-1-carbonyl)phenyl)-, and B-(4-bromophenyl)-substituted
subporphyrins 5–8 were obtained in moderate yields by the
reaction of 1 with the corresponding ArZn reagents. The yields
of 5–7 were lower than that of 3, presumably because of the
poorer nucleophilicity of ArZn reagents bearing electron-with-
drawing groups. Furthermore, we examined postmodifications
of the B-aryl substituents. Nucleophilic addition of PhMgBr
(10 equiv) to 5 at 608C followed by hydrolysis with aqueous
HCl provided B-(4-(benzoyl)phenyl)-substituted subporphyrin 9
in 42% yield. When treated with PhMgBr under reflux condi-
tions, 1 was converted into 3, whereas 5 was not converted
into 3, which indicated that the axial BÀC bond is more robust
than the BÀO bond under these conditions. Hydrolysis of the
ester group in subporphyrin 6 under basic conditions provided
B-(4-carboxyphenyl)-substituted subporphyrin 10 in 87% yield.
Finally, 1,4-phenylene-bridged subporphyrin–porphyrin hybrid
11 was synthesized in 79% yield by the Suzuki–Miyaura cross-
coupling reaction of 8 with 5-(4’,4’,5’,5’-tetramethyl-1’,3’,2’-di-
oxaboran-2-yl)-10,20-diphenylporphyrinto zinc(II)[12] with the
aid of a SPhos Pd G2 precatalyst.[13]
Entry
Lewis acid
n[a]
T
[8C]
t
[h]
Yield of 3[b]
[%]
1[c]
2
3
4
5
6
7
8
none
TMSCl
ZnI2
ZnBr2
TMSCl
TMSCl
TMSCl
TMSCl
20
20
20
20
20
20
5
reflux
60
60
60
RT
RT
RT
RT
1
1
1
1
1
5
81
N.D.
N.D.
[d]
[d]
57
74
16
16
16
79 (77[e]
66
)
1.5
1
[a] n: Equivalents of PhZn reagent. [b] Yields were determined by H NMR
spectroscopy with diphenylmethane as an internal standard. [c] Dioxane
was used as a solvent. [d] N.D.: not determined. [e] Yield of isolated prod-
uct.
tempt resulted in a low yield of B-phenylsubporphyrin 3, and
starting material 1 was mostly recovered, probably due to the
low nucleophilicity of the PhZn reagent. In order to activate
1 for nucleophilic attack of the PhZn reagent, we examined
the addition of 20 equivalents of TMSCl, because the presence
of a Lewis acid facilitated boron axial exchange reactions.[11]
This indeed improved the yield of 3 dramatically (Scheme 2;
Table 1, entry 2), although Lewis acids such as ZnI2 and ZnBr2
were not effective for the B-phenylation (Table 1, entries 3 and
4). If the reaction was carried out at room temperature, the
yield of 3 dropped to 57% (Table 1, entry 5), although a longer
Single crystals suitable for X-ray diffraction analysis were ob-
tained by slow recrystallizations from CH2Cl2/methanol solu-
tions of 5, 6, and 8, from benzene/n-heptane solutions of 7
and 10, from a CH2Cl2/n-hexane solution of 9, and from
a CHCl3/n-hexane solution of 11. The crystal structures are
shown in Figure 1 (see also the Supporting information). The
axial BÀC bond lengths of 5–11 were in the range of 1.61–
1.63 Š, which are similar to those in B-aryl subporphyrins previ-
ously reported.[8] The bowl depths, which are defined as the
distance from the mean plane of the peripheral six b carbon
atoms to the center boron atom, are in the range of 1.31–
1.43 Š. It is likely that the bowl depths are variable and
depend upon the packing structures. Carboxylic acid 10 re-
Scheme 2. B-Phenylation of 1 with phenylzinc reagent. TMSCl: trimethylsilyl
chloride.
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bonding. In hybrid 11, the ZnII porphyrin and subporphyrin
parts are linked through a 1,4-phenylene bridge with a center-
to-center (zinc-to-boron) distance of 9.32 Š.
1
The H NMR spectrum of B-(4-bromophenyl)subporphyrin 8
shows a singlet at d=8.16 ppm due to the six b protons, a set
of three signals at d=8.06, 7.70, and 7.61 ppm due to the
meso-phenyl protons, and two doublets at d=6.44 and
4.50 ppm due to the axial B-phenylene protons. Similarly, the
1H NMR spectra of the other B-aryl subporphyrins (5–7 and 9–
11) show the aromatic protons in the B-aryl groups at high-
field chemical shifts (2,6-protons at d=4.3–5.0 ppm and 3,5-
protons at d=6.5–7.2 ppm), which indicate diatropic ring cur-
rents due to the 14p-electronic aromatic circuits (see also the
1
Supporting Information). The H NMR spectrum of subporphyr-
in–porphyrin hybrid 11 exhibits signals due to the Ha and Hb
protons at d=5.01 and 7.17 ppm, respectively, which reflect
the diatropic ring currents of the subporphyrin and porphyrin.
The electrochemical potentials of 5–11 were measured by
cyclic voltammetry and differential-pulse voltammetry in
CH2Cl2 containing 0.10m nBu4NPF6 as a supporting electrolyte
(see Table 2 and the Supporting Information). Subporphyrin
Table 2. Oxidation and reduction potentials of subporphyrins 1, 3, and
5–11 (vs. the ferrocene/ferricenium ion pair). Supporting electrolyte:
nBu4NPF6 (0.10m); working electrode: glassy carbon; counter electrode:
platinum wire; reference electrode: Ag/AgClO4; scan rate: 0.05 VsÀ1
.
[a]
Eox.2
[V]
Eox.1
[V]
Ered.1
[V]
Ered.2
[V]
Eox.1ÀEred.1
[eV]
1[b]
3[b]
5
6
7
8
9
10
11
0.82
0.58
0.72
0.67
0.65
0.66
0.65
0.66
0.30[c]
À1.84
2.66
2.59
2.79
2.80
2.77
2.62
2.73
2.77
2.22
À2.01
À2.07[c]
À2.13[c]
À2.12[c]
À1.96
À2.08[c]
À2.11[c]
À1.92[c]
0.65[c]
À2.03[c]
[a] Electrochemical HOMO–LUMO gap. [b] Ref. [2c]. [c] Determined by dif-
ferential-pulse voltammetry.
1 shows reversible reduction and oxidation potentials at À1.84
and 0.82 V.[8] However, B-phenylsubporphyrin 3 exhibits reversi-
ble reduction and oxidation potentials at lower potentials of
À2.01 and 0.58 V, respectively, which reflect the electron-do-
nating phenyl substituent rather than the methoxy group.[7a]
Subporphyrins 5–10 exhibit similar reversible oxidation poten-
tials to 3, although their reduction waves are irreversible
except for that of 8. The electrochemical HOMO–LUMO gaps
for 5–10 are larger than that for 3, in contrast to those of sub-
porphyrins bearing electron-donating B-aryl groups.[8] These re-
sults are consistent with density functional theory calculations
performed at the B3LYP/6-311G(d) level by using the Gaussi-
an 09 package (see the Supporting Information).[14] Subpor-
phyrin–porphyrin hybrid 11 shows a first one-electron oxida-
tion at 0.30 V and a second two-electron oxidation at 0.65 V.
The two-electron oxidation process has been interpreted in
Scheme 3. Synthesis of B-arylated subporphyrins and their subsequent con-
versions. SPhos Pd G2: 2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl Pd
second-generation catalyst.
vealed a face-to-face dimeric packing structure, in which two
subporphyrin molecules are connected by hydrogen-bonding
interactions with the carboxylic groups (Figure 1g). Both inter-
molecular O···O distances are 2.615 Š. The C=O and CÀO bond
lengths on the CO2H part of 10 are 1.228(4) and 1.306(4) Š,
values that are slightly longer and shorter than the corre-
sponding C=O and CÀO bond lengths in ester 6 (1.208(2) and
1.3437(19) Š), respectively, and indicate effective hydrogen
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Figure 1. X-Ray crystal structures of (a) 5, (b) 6, (c) 7, (d) 8, (e) 9, (f) 10, and (h) 11. (g) Dimeric packing structure of 10. Thermal ellipsoids are set to 50% proba-
bility level. Hydrogen atoms except for the OH proton in 10 and solvent molecules are omitted for clarity.
terms of overlap of the first oxidation of the subporphyrin unit
and the second oxidation of the Zn porphyrin unit. The first
and the second reductions of 11 were observed at À1.92 and
À2.03 V, respectively, as reversible waves, which indicates the
electronic deconjugation nature of the subporphyrin and por-
phyrin units.
Figure 2a, the absorption spectrum of 11 is almost the super-
position of those of 3 and 5,10,15-tris(3,5-di-tert-butylphenyl)-
porphyrinatozinc(II) (12), which indicates negligible electronic
interaction in the ground state. The fluorescence spectrum of
11 taken for excitation of the subporphyrin at 386 nm shows
The UV/Vis absorption and fluorescence spectra of 5–10 are
quite similar to those of 3 and reveal Soret-like bands in the
range of 383–384 nm, Q-like bands at around 506 nm, and
fluorescence maxima at around 540 nm with quantum yields
of FF =0.12–0.13 (Table 3).[8] 4-Bromophenyl-substituted sub-
porphyrin 8 shows a similar fluorescence quantum yield, de-
spite the presence of the bromine substituent. As shown in
Table 3. Optical properties of subporphyrins 1, 3, and 5–11 measured in
CH2Cl2.
[a]
[a]
l [nm] (e [105 mÀ1 cmÀ1])
lem [nm]
FF
1[b]
3[c]
5
6
7
8
9
10
372 (1.66)
385 (1.55)
383 (1.57)
384 (1.47)
384 (1.46)
384 (1.40)
384 (1.41)
384 (1.43)
386 (1.78)
506 (0.15)
460 (0.12)
481 (0.10)
479 (0.09)
478 (0.09)
478 (0.09)
479 (0.09)
478 (0.09)
478 (0.09)
414 (5.00)
542 (0.20)
485 (0.09)
507 (0.15)
507 (0.13)
506 (0.14)
506 (0.14)
506 (0.13)
506 (0.13)
506 (0.13)
517
0.13
0.16
0.12
0.13
0.13
0.12
0.13
0.12
545
541
540
543
542
543
541
476 (0.10)
545, 584, 634
(584, 634)[d]
0.02[c]
(0.03)[d]
11
[a] Fluorescence spectra were recorded upon excitation at the peak
maxima of Soret-like bands of subporphyrins (372–386 nm). [b] Ref. [2c].
[c] Ref. [7a]. [d] Values in brackets were obtained upon excition at
414 nm.
Figure 2. (a) UV/Vis absorption spectra and (b) fluorescence spectra of sub-
porphyrins 3, subporphyrin–porphyrin dyad 11, and porphyrin 12 in CH2Cl2.
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performed with silica gel 60 F254. Preparative separations were per-
formed with silica gel chromatography (Wako gel C-300). Redox
potentials were measured on an ALS electrochemical analyzer
model 660.
decreased fluorescence (545 nm) due to the subporphyrin and
increased fluorescence (584 and 634 nm) due to the ZnII–por-
phyrin; this reveals intramolecular excitation energy transfer
from the subporphyrin moiety to the porphyrin moiety. From
a comparison of the fluorescence spectra of 3 and 11, the
quantum efficiency for the energy transfer of 11 is estimated
to be FET =0.97, which is slightly smaller than that (FET ꢀ1.00)
of a previously reported meso-phenylene-bridged subporphyr-
in–porphyrin dyad.[15] If 11 was excited at 414 nm, which corre-
sponds to the Soret band of the porphyrin moiety, only the
fluorescence from the porphyrin unit was observed with FF =
0.03.
General procedure for the synthesis of ArZn reagents
ArZn reagents used in the reactions were prepared according to
reference [10].
General procedure for the synthesis of B-arylated subpor-
phyrins
A solution of 1 (ꢀ60 mmol) in THF (1 mL) was cooled to 08C with
an ice bath. After dropwise addition of TMSCl (0.15 mL, 1.2 mmol)
through a syringe, a THF solution ofArZnI·LiCl (0.30 mmol) was
added to the mixture, and the solution was stirred for 16 h at
room temperature. The reaction mixture was poured onto water
and extracted with AcOEt. The organic layer was washed with
brine and dried over Na2SO4, and the solvent was removed under
reduced pressure. The crude product was separated by silica gel
column chromatography. Recrystallization furnished the corre-
sponding B-arylated subporphyrin.
Conclusion
We have developed a new synthetic protocol for B-aryl subpor-
phyrins by using aryl zinc reagents in the presence of tri-
methylsilyl chloride. Zinc reagents attached to electron-with-
drawing groups are available for the reaction, to provide the
corresponding B-aryl subporphyrins 5–8 in moderate yields.
Postmodifications of the B-aryl substituents were demonstrat-
ed to give novel subporphyrins 9–11 without loss of the BÀC
bond. Newly synthesized subporphyrins 5–11 were all fully
characterized by 1H and 11B NMR spectra and mass spectra,
and X-ray diffraction analysis. The electrochemical and photo-
physical properties of 5–10 are comparable to those of 3. Sub-
porphyrin–porphyrin hybrid 11 exhibits efficient intramolecular
energy transfer at excited states. As demonstrated, this syn-
thetic protocol allowed for the synthesis of a wider range of
subporphyrins bearing various axial boron subsituents and,
hence, opens a way to novel functional subporphyrins. Further
applications of this method to more elaborated subporphyrin-
based molecular systems are actively being pursued in our lab-
oratory.
Phenyl(5,10,15-triphenyllsubporphyrinato)boron(III) (3): Accord-
ing to the general procedure, 3 was prepared from 1 (29.9 mg,
59.6 mmol) and ArZnI·LiCl (Ar: phenyl; 0.98m, 0.31 mL, 0.30 mmol).
The crude product was separated by silica gel column chromatog-
raphy (eluent: n-hexane/CH2Cl2, 3:1). Recrystallization from CH2Cl2/
MeOH furnished 3 (25.0 mg, 77%) as an orange solid. The chemical
properties of 3 were in accordance with those previously reporte-
d.[8a]
Trimethylsiloxo(5,10,15-triphenylsubporphyrinato)boron(III) (4):
This compound was obtained as a side product under the above
B-arylation conditions. Selective preparation of 4 was as follows:
B-(Hydroxo)triphenylsubporphyrin (20.1 mg, 41.2 mmol) in THF
(1 mL) was added to TMSCl (0.10 mL, 0.80 mmol), and the mixture
was stirred for 30 min at room temperature. The crude product
was purified by silica gel column chromatography (eluent: n-
hexane/CH2Cl2, 4:1). Recrystallization from CH2Cl2/n-hexane fur-
nished 4 (8.4 mg, 36%) as an orange solid. A single crystal suitable
for X-ray diffraction analysis was prepared by slow recrystallization
from CH3Cl/n-heptane. 1H NMR (600 MHz, CDCl3): d=8.09–8.07
(12H, b and meso-Ph ortho), 7.71 (t, J=7.8 Hz, 6H, meso-Ph meta),
7.61 (t, J=7.7 Hz, 3H, meso-Ph para), and À1.10 ppm (s, 9H, tri-
methyl); 11B NMR (193 MHz, CDCl3): d=À16.7 ppm (s, 1B).
Experimental Section
General information
All reagents and solvents were of commercial reagent grade and
were used without further purification unless noted. THF and diox-
ane were purified with a solvent purification system before use. H,
11B, and 13C NMR spectra were recorded on a JEOL ECA-600 spec-
1
4-Cyanophenyl(5,10,15-triphenylsubporphyrinato)boron(III) (5):
According to the general procedure, 5 was prepared from
trometer. Chemical shifts were expressed as the d scale in ppm rel-
ative to the internal standard CHCl3 (d=7.26 ppm for H, and d=
1 (31.5 mg, 62.8 mmol) and ArZnI·LiCl (Ar: 4-cyanophenyl; 0.78m,
0.40 mL, 0.31 mmol). The crude product was separated by silica gel
column chromatography (eluent: n-hexane/CH2Cl2/diethyl ether,
8:4:1). Recrystallization from CH2Cl2/MeOH furnished 5 (18.3 mg,
51%) as an orange solid. A single crystal suitable for X-ray diffrac-
tion analysis was prepared by slow recrystallization from CH2Cl2/
MeOH. 1H NMR (600 MHz, CDCl3): d=8.18 (s, 6H, b), 8.06 (d, J=
8.2 Hz, 6H, meso-Ph ortho), 7.71 (t, J=7.8 Hz, 6H, meso-Ph meta),
7.63 (t, J=7.8 Hz, 3H, meso-Ph para), 6.59 (d, J=8.2 Hz, 2H, axial-
Ar meta), 4.69 ppm (d, J=8.7 Hz, 2H, axial-Ar ortho); 11B NMR
(193 MHz, CDCl3): d=À16.7 ppm (s, 1B); 13C NMR (150 MHz,
CDCl3): d=140.5, 137.2, 133.3, 129.9, 129.2, 128.9, 128.0, 122.6,
120.8, 119.4, 109.2 ppm (no signal was observed for the carbon
atom directly bonded to the boron atom); HR-APCI TOF-MS: m/z
calcd for C40H2511BN4 [M+H]+: 573.2252; found: 573.2269; UV/Vis
1
77.16 ppm for 13C) and an external standard BF3·OEt2 in CDCl3 (d=
0.00 ppm for 11B). Spectroscopic grade solvents were used for all
spectroscopic studies without further purification. UV/Vis absorp-
tion spectra were recorded on a Shimadzu UV-2500 spectrometer.
Fluorescence spectra were recorded on a Shimadzu RF-5300PC
spectrometer. Absolute fluorescence quantum yields were deter-
mined on a HAMAMATSU C9920–02S instrument. High-resolution
atmospheric-pressure-chemical-ionization time-of-flight mass spec-
troscopy (HR-APCI-TOF-MS) was performed on a BRUKER micrOTOF
model by using positive mode. X-Ray data were taken at À1808C
with a Rigaku XtaLAB P200 apparatus and two-dimensional PILA-
TUS 100 K/R detector with CuKa radiation (l=1.54187 Š). The
structures were solved by the SIR-97 direct method and refined
with the SHELXL-97 program.[16] Thin-layer chromatography was
(in CH2Cl2):
l
(e)=383 (157000), 479 (9000), 507 nm
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(14000 mÀ1 cmÀ1); fluorescence (in CH2Cl2, lex =383 nm); lmax
541 nm, FF =0.12.
=
CH2Cl2): l (e)=384 (140000), 479 (9000), 506 nm (13000 mÀ1 cmÀ1);
fluorescence (in CH2Cl2, lex =384 nm); lmax =542 nm, FF =0.12.
4-(Ethoxycarbonyl)phenyl(5,10,15-triphenylsubporphyrinato)bor-
on(III) (6): According to the general procedure, 6 was prepared
from 1 (29.8 mg, 59.4 mmol) and ArZnI·LiCl (Ar: 4-(ethoxycarbonyl)-
phenyl; 0.64m, 0.49 mL, 0.30 mmol). The crude product was sepa-
rated by silica gel column chromatography (eluent: n-hexane/
CH2Cl2/diethyl ether, 8:4:1). Recrystallization from CH2Cl2/MeOH fur-
nished 6 (20.8 mg, 56%) as an orange solid. A single crystal suita-
ble for X-ray diffraction analysis was prepared by slow recrystalliza-
Synthesis of 4-(benzoyl)phenyl(5,10,15-triphenylsubporphyr-
inato)boron(III) (9)
PhMgBr in THF solution (0.50 mL, 0.50 mmol) was added to a solu-
tion of 5 (28.6 mg, 50.0 mmol) in THF (1 mL), and the solution was
stirred for 4 h at 608C. 1m aqueous HCl (1 mL) was added, and the
mixture was stirred for 20 min at room temperature. The reaction
mixture was poured onto water and extracted with AcOEt. The or-
ganic layer was washed with brine and dried over Na2SO4, and the
solvent was removed under reduced pressure. The crude product
was separated by silica gel column chromatography (eluent: n-
hexane/CH2Cl2/diethyl ether, 10:3:1). Recrystallization from CH2Cl2/
MeOH furnished 9 (13.3 mg, 42%) as an orange solid. A single crys-
tal suitable for X-ray diffraction analysis was prepared by slow re-
1
tion from CH2Cl2/MeOH. H NMR (600 MHz, CDCl3): d=8.17 (s, 6H,
b), 8.07 (d, J=7.3 Hz, 6H, meso-Ph ortho), 7.70 (t, J=7.8 Hz, 6H,
meso-Ph meta), 7.62 (t, J=7.3 Hz, 3H, meso-Ph para), 7.00 (d, J=
8.2 Hz, 2H, axial-Ar meta), 4.71 (d, J=8.3 Hz, 2H, axial-Ar ortho),
4.06 (q, J=7.2 Hz, 2H, CH2), 1.12 ppm (t, J=6.9 Hz, 3H, CH3);
11B NMR (193 MHz, CDCl3): d=À16.5 ppm (s, 1B); 13C NMR
(150 MHz, CDCl3): d=166.8, 140.5, 137.4, 133.4, 128.8, 128.7, 127.9,
127.4, 122.5, 120.7, 120.6, 60.3, 14.3 ppm (no signal was observed
for the carbon atom directly bonded to the boron atom); HR-APCI-
TOF-MS: m/z calcd for C42H3011BN3O2 [M+H]+: 620.2511; found:
620.2502; UV/Vis (in CH2Cl2): l (e)=384 (147000), 478 (9000),
506 nm (14000 mÀ1 cmÀ1); fluorescence (in CH2Cl2, lex =384 nm):
lmax =540 nm, FF =0.13.
1
crystallization from CH2Cl2/n-hexane. H NMR (600 MHz, CDCl3): d=
8.18 (s, 6H, b), 8.06 (d, J=6.8 Hz, 6H, meso-Ph ortho), 7.71 (t, J=
7.8 Hz, 6H, meso-Ph meta), 7.62 (t, J=7.3 Hz, 3H, meso-Ph para)
7.39 (m, 3H, axial-COPh), 7.25 (t, J=7.8 Hz, 2H, axial-COPh), 6.77
(d, J=8.3 Hz, 2H, axial-Ar meta), 4.64 ppm (d, J=8.3 Hz, 2H, axial-
Ar ortho); 11B NMR (193 MHz, CDCl3): d=À16.6 ppm (s, 1B);
13C NMR (150 MHz, CDCl3): d=196.6, 140.5, 137.8, 137.3, 135.0,
133.3, 131.8, 129.7, 128.8, 128.6, 128.5, 128.1, 127.9, 122.5,
120.7 ppm (no signal was observed for the carbon atom directly
bonded to the boron atom); HR-APCI-TOF-MS: m/z calcd for
C46H3011BN3O [M+H]+: 652.2562; found: 652.2521; UV/Vis (in
CH2Cl2): l (e)=384 (141000), 478 (9000), 506 nm (13000 mÀ1 cmÀ1);
fluorescence (in CH2Cl2, lex =384 nm): lmax =543 nm, FF =0.13.
4-(Piperidine-1-carbonyl)phenyl(5,10,15-triphenylsubporphyrina-
to)boron(III) (7): According to the general procedure, 7 was pre-
pared from 1 (30.2 mg, 60.2 mmol) and ArZnI·LiCl (Ar: 4-(pyperi-
dine-1-carbonyl)phenyl; 0.76m, 0.39 mL, 0.30 mmol). The crude
product was separated by silica gel column chromatography
(eluent: n-hexane/CH2Cl2/EtOAc, 8:1:1). Recrystallization from
CH2Cl2/MeOH furnished 7 (21.0 mg, 53%) as an orange solid. A
single crystal suitable for X-ray diffraction analysis was prepared by
Synthesis of 4-carboxyphenyl(5,10,15-triphenylsubporpyri-
nato)boron(III) (10)
1
slow recrystallization from benzene/n-heptane. H NMR (600 MHz,
CDCl3): d=8.16 (s, 6H, b), 8.08 (d, J=7.6 Hz, 6H, meso-Ph ortho),
7.72 (t, J=7.7 Hz, 6H, meso-Ph meta), 7.61 (t, J=7.3 Hz, 3H, meso-
Ph para), 6.32 (d, J=8.3 Hz, 2H, axial-Ar meta), 4.64 (d, J=7.7 Hz,
2H, axial-Ar ortho), 3.43 (m, 2H, piperidyl), 2.87 (m, 2H, piperidyl),
1.54–1.46 (m, 4H, piperidyl), 1.20 ppm (m, 2H, piperidyl); 11B NMR
(193 MHz, CDCl3): d=À16.4 ppm (s, 1B); 13C NMR (150 MHz,
CDCl3): d=170.6, 140.5, 137.5, 133.8, 133.4, 128.8, 128.7, 127.9,
124.6, 122.4, 120.6, 48.5, 42.8, 26.4, 25.8, 24.6 ppm (no signal was
observed for the carbon atom directly bonded to the boron atom);
HR-APCI-TOF-MS: m/z calcd for C45H3511BN4O [M+H]+: 659.2984;
found 659.2988; UV/Vis (in CH2Cl2): l (e)=384 (146000), 478
(9000), 506 nm (14000 mÀ1 cmÀ1); fluorescence (in CH2Cl2, lex =
384 nm): lmax =543 nm, FF =0.13.
1m aqueous KOH (1 mL) was added to a solution of 6 (25.3 mg,
40.8 mmol) in THF (1 mL) and MeOH (0.5 mL), and the mixture was
stirred for 6 h at 608C. The solution was quenched by addition of
1m aqueous HCl (2 mL). The reaction mixture was poured onto
water and extracted with AcOEt. The organic layer was washed
with brine and dried over Na2SO4, and the solvent was removed
under reduced pressure. The crude product was separated by silica
gel column chromatography (eluent: n-hexane/CH2Cl2/AcOEt,
2:1:1). Recrystallization from CH2Cl2/n-hexane furnished 10
(21.1 mg, 87%) as an orange solid. A single crystal suitable for X-
ray diffraction analysis was prepared by slow recrystallization from
benzene/n-heptane. 1H NMR (600 MHz, CDCl3): d=12.5–10.5 (br,
1H, CO2H), 8.18 (s, 6H, b), 8.06 (d, J=6.9 Hz, 6H, meso-Ph ortho),
7.69 (t, J=7.3 Hz, 6H, meso-Ph meta), 7.60 (t, J=7.4 Hz, 3H, meso-
Ph para), 6.98 (d, J=8.3 Hz, 2H, axial-Ar meta), 4.69 ppm (d, J=
8.2 Hz, 2H, axial-Ar ortho); 11B NMR (193 MHz, CDCl3): d=
À16.7 ppm (s, 1B); 13C NMR (150 MHz, CDCl3): d=171.3, 140.5,
137.3, 133.3, 128.8, 128.7, 128.0, 127.9, 126.5, 122.5, 120.7 ppm (no
signal was observed for the carbon atom directly bonded to the
boron atom); HR-APCI-TOF-MS: m/z calcd for C40H2611BN3O2 [M+
H]+: 592.2198; found: 592.2206; UV/Vis (in CH2Cl2): l (e)=384
(143000), 478 (9000), 506 nm (13000 mÀ1 cmÀ1); fluorescence (in
CH2Cl2, lex =384 nm); lmax =541 nm, FF =0.12.
4-Bromophenyl(5,10,15-triphenylsubporphyrinato)boron(III) (8):
According to the general procedure,
8 was prepared from
1 (29.9 mg, 59.6 mmol) and ArZnI·LiCl (Ar: 4-bromophenyl; 0.70m,
0.43 mL, 0.30 mmol). The crude product was separated by silica gel
column chromatography (eluent: n-hexane/CH2Cl2/diethyl ether,
8:4:1). Recrystallization from CH2Cl2/MeOH furnished 8 (29.5 mg,
79%) as an orange solid. A single crystal suitable for X-ray diffrac-
tion analysis was prepared by slow recrystallization from CH2Cl2/
MeOH. 1H NMR (600 MHz, CDCl3): d=8.16 (s, 6H, b), 8.06 (d, J=
6.8 Hz, 6H, meso-Ph ortho), 7.70 (t, J=7.3 Hz, 6H, meso-Ph meta),
7.61 (t, J=7.4 Hz, 3H, meso-Ph para), 6.44 (d, J=8.3 Hz, 2H, axial-
Ar meta), 4.50 ppm (d, J=8.7 Hz, 2H, axial-Ar ortho); 11B NMR
(193 MHz, CDCl3): d=À16.4 ppm (s, 1B); 13C NMR (150 MHz,
CDCl3): d=140.5, 137.4, 133.4, 130.6, 129.3, 128.8, 127.9, 122.4,
120.6, 120.1 ppm (no signal was observed for the carbon atom di-
rectly bonded to the boron atom); HR-APCI-TOF-MS: m/z calcd for
C39H2511BN379Br [M+H]+: 626.1404; found: 626.1386; UV/Vis (in
Synthesis of subporphyrin–porphyrin dyad 11
A solution of 8 (44.1 mg, 70.4 mmol), 5-pinacolatoboryl-10,20-di-
phenylporphyrin (42.1 mg, 71.5 mmol), SPhos Pd G2 catalyst
(5.0 mg, 6.9 mmol), and K3PO4 (45.0 mg, 212 mmol) in THF (1.3 mL)
and H2O (30 mL) was stirred for 24 h at 608C. The reaction mixture
Chem. Eur. J. 2016, 22, 3320 – 3326
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was poured onto water and extracted with AcOEt. The organic
layer was washed with brine and dried over Na2SO4, and the sol-
vent was removed under reduced pressure. The crude product was
separated by silica gel column chromatography (eluent: n-hexane/
CH2Cl2/diethyl ether, 4:1:1). Recrystallization from CH2Cl2/MeOH fur-
nished 11 (59.8 mg, 79%) as a purple solid. A single crystal suitable
for X-ray diffraction analysis was prepared by slow recrystallization
from CHCl3/n-hexane. 1H NMR (600 MHz, CDCl3): d=10.16 (s, 1H,
porphyrin-meso), 9.32 (d, J=4.6 Hz, 2H, porphyrin-b), 9.00 (d, J=
4.6 Hz, 2H, porphyrin-b), 8.74 (d, J=4.6 Hz, 2H, porphyrin-b), 8.46
(d, J=4.6 Hz, 2H, porphyrin-b), 8.29 (s, 6H, subporphyrin-b), 8.22
(d, J=7.3 Hz, 6H, subporphyrin-meso-Ph ortho), 8.13 (d, J=6.9 Hz,
4H, porphyrin-meso-Ph ortho), 7.76 (t, J=7.8 Hz, 6H, subporphyrin-
meso-Ph meta), 7.73–7.69 (m, 6H, porphyrin-meso-Ph meta and
para), 7.65 (t, J=7.3 Hz, 3H, subporphyrin-meso-Ph para), 7.17 (d,
J=7.8 Hz, 2H, axial-Ar meta), 5.01 ppm (d, J=7.8 Hz, 2H, axial-
phenylene ortho); 11B NMR (193 MHz, CDCl3): d=À16.2 ppm (s,
1B); 13C NMR (150 MHz, CDCl3): d=150.0, 149.9, 149.8, 142.8,
140.8, 139.9, 137.7, 134.6, 133.5, 132.9, 132.5, 132.4, 132.1, 131.6,
131.5, 131.3, 128.8, 127.9, 127.5, 126.9, 126.6, 122.5, 122.4, 120.8,
120.4 ppm (no signal was observed for the carbon atom directly
bonded to the boron atom); HR-APCI-TOF-MS: m/z calcd for
C71H4411BN764Zn [M+H]+: 1070.3127; found: 1070.3075; UV/Vis (in
CH2Cl2): l (e): 386 (178000), 414 (500000), 476 (10000), 506
(15000), 542 nm (20000 mÀ1 cmÀ1); fluorescence (in CH2Cl2, lex =
386 nm): lmax =545, 584, 634 nm, FF =0.03; (in CH2Cl2, lex =
414 nm): lmax =584, 634 nm, FF =0.02.
Acknowledgements
This work was supported by JSPS KAKENHI (Grant numbers
25220802 and 25620031).
Keywords: boron–carbon bonds · energy transfer · organozinc
reagents · porphyrinoids · subporphyrins
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Received: November 24, 2015
Published online on January 27, 2016
Chem. Eur. J. 2016, 22, 3320 – 3326
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim