Synthesis, reactivity, and spectroscopic properties of meso-triaryl-5- oxaporphyrins

Article abstract of DOI:10.1021/jo3010342

[meso-Triaryl-21,23-didehydro-23H-5-oxaporphyrinato](trifluoroacetato) zinc(II) was prepared by the reaction of meso-triarylbilindione with acetic anhydride and zinc acetate, and it was isolated as a trifluoroacetate salt. The X-ray crystallographic study demonstrated that the trifluoroacetate anion was coordinated to the zinc ion. [21,23-Didehydro-10,15,20-tris(4- methoxycarbonylphenyl)-23H-5-oxaporphyrinato](trifluoroacetato)zinc(II) 3a was dissolved in various organic solvents such as toluene, chloroform, diethyl ether, ethyl acetate, acetone, acetonitrile, methanol, DMSO, and DMF, although it readily reacted with alcohols and DMF to yield linear tetrapyrroles. The solubility of 3a in toluene was 4.2 ± 0.1 g dm^-3 at room temperature. 3a showed characteristic UV-vis absorption at 649 nm and fluorescence emission at 657 nm in chloroform. The fluorescence quantum yields of 3a, [21,23-didehydro-10,15,20-triphenyl-23H-5-oxaporphyrinato] (trifluoroacetato)zinc(II) (3c), and [21,23-didehydro-10,15,20-tris(4- methoxyphenyl)-23H-5-oxaporphyrinato](trifluoroacetato)zinc(II) (3b) were 0.071, 0.071, and 0.050, respectively. Reaction of 3a with EtOH afforded the zinc complex of 19-ethoxybilinone, and it proceeded 2 orders of magnitude faster than that of [β-octaalkyl-21,23-didehydro-23H-5-oxaporphyrinato]zinc(II). The reaction with alcohols was sensitive to steric bulk of the alcohols; the rate of reaction with i-PrOH was 2700 times faster than that of t-BuOH at 303 K. The reaction of [meso-triaryl-21,23-didehydro-23H-5-oxaporphyrinato]zinc(II) with water proceeded 3 orders of magnitude slower than that with EtOH.

Full text of DOI:10.1021/jo3010342

Article
pubs.acs.org/joc
Synthesis, Reactivity, and Spectroscopic Properties of meso-Triaryl-5-
oxaporphyrins
Kazuhisa Kakeya, Aya Nakagawa, Tadashi Mizutani,* Yutaka Hitomi, and Masahito Kodera
Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, and Center for Nanoscience Research,
Doshisha University, Kyotanabe, Kyoto 610-0321, Japan
S
* Supporting Information
ABSTRACT: [meso-Triaryl-21,23-didehydro-23H-5-oxa-
porphyrinato](trifluoroacetato)zinc(II) was prepared by the
reaction of meso-triarylbilindione with acetic anhydride and
zinc acetate, and it was isolated as a trifluoroacetate salt. The
X-ray crystallographic study demonstrated that the trifluor-
oacetate anion was coordinated to the zinc ion. [21,23-
Didehydro-10,15,20-tris(4-methoxycarbonylphenyl)-23H-5-
oxaporphyrinato](trifluoroacetato)zinc(II) 3a was dissolved in
various organic solvents such as toluene, chloroform, diethyl
ether, ethyl acetate, acetone, acetonitrile, methanol, DMSO,
and DMF, although it readily reacted with alcohols and DMF to yield linear tetrapyrroles. The solubility of 3a in toluene was 4.2
0.1 g dm−3 at room temperature. 3a showed characteristic UV−vis absorption at 649 nm and fluorescence emission at 657 nm
in chloroform. The fluorescence quantum yields of 3a, [21,23-didehydro-10,15,20-triphenyl-23H-5-oxaporphyrinato]-
(trifluoroacetato)zinc(II) (3c), and [21,23-didehydro-10,15,20-tris(4-methoxyphenyl)-23H-5-oxaporphyrinato]-
(trifluoroacetato)zinc(II) (3b) were 0.071, 0.071, and 0.050, respectively. Reaction of 3a with EtOH afforded the zinc complex
of 19-ethoxybilinone, and it proceeded 2 orders of magnitude faster than that of [β-octaalkyl-21,23-didehydro-23H-5-
oxaporphyrinato]zinc(II). The reaction with alcohols was sensitive to steric bulk of the alcohols; the rate of reaction with i-PrOH
was 2700 times faster than that of t-BuOH at 303 K. The reaction of [meso-triaryl-21,23-didehydro-23H-5-oxaporphyrinato]-
zinc(II) with water proceeded 3 orders of magnitude slower than that with EtOH.
respectively.8−10 The reaction of 5-oxaporphyrin with diol or
INTRODUCTION
■
triol was used to prepare bilinone dimers and trimers.11,12 The
Oxidation of iron porphyrin with O2 is an important pathway of
nucleophilic ring-opening of 5-oxaporphyrin complexes of
heme catabolism.1 Several intermediates are shown to be
Fe(II), Co(II), and Zn(II) was studied as a model reaction
involved such as 5-hydroxyporphyrin (oxophlorin) and 5-
oxaporphyrin Fe complex (verdoheme). Thus, preparation of 5-
oxaporphyrin and its spectroscopic properties and reactivity
attract interest in decades. Jackson, Kenner, and Smith reported
for verdoheme to biliverdin transformation.13
We previously reported that coupled oxidation of [meso-
tetraarylporphyrinato]iron(III) yielded both biladienone and
bilindione.14 It is well-known that two porphyrins, meso-
that oxidation of the iron complex of oxophlorin with O2 in
pyridine gave the oxaporphyrin iron complex.2 Saito and Itano
tetraphenylporphyrin and β-octaalkylporphyrin, have different
reactivity,15 since the electronic effects of alkyl groups are
reported that the iron complex of β-octaethyl-5-oxaporphyrin
different from those of phenyl groups and the substitution
pattern significantly affects the electronic structure of the
was prepared from octaethylbilindione by the reaction with
acetic anhydride, pyridine and iron sulfate.3 Fuhrhop and co-
porphyrin ring. meso-Tetraarylporphyrins have advantages over
workers described preparation of β-octaethyl-5-oxaporphyrin
β-octaalkylporphyrins with respect to a simpler synthetic route
zinc complex from β-octaethylbilindione by the reaction with
and facile control of electronic structure by introducing various
acetic anhydride or from octaethyloxophlorin by photochemical
oxidation.4 5-Oxaporphyrin Fe(II) complexes were prepared by
functional groups in the aryl groups. In addition, solubility of
meso-tetraphenylporphyrin was higher than β-octaethylporphyr-
coupled oxidation reaction of porphyrin iron complexes with
in in nonpolar solvents such as dichloromethane and toluene.16
In addition to previously reported studies of 5-oxaporphyrins
and bilindiones bearing β-octaalkyl substituents, investigations
of meso-substituted analogues should extend the scope of
tetrapyrrole chemistry, and such dyes should find applications
O2 in the presence of ascorbic acid or hydrazine.5 Preparation
of cobalt6 and copper7 complexes of 5-oxaporphyrin by
oxidation of porphyrins was also reported.
5-Oxaporphyrins are valuable precursors of linear tetrapyr-
roles because of the high reactivity toward nucleophiles. For
instance, [5-oxaporphyrinato]zinc(II) was allowed to react with
various nucleophiles such as alkoxide, Na2S, or NH3 to afford
19-alkoxybilinone, 5-thioniaporphyrin, and 5-azaporphyrin,
Received: May 23, 2012
Published: July 17, 2012
© 2012 American Chemical Society
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a
Scheme 1. Synthetic Route to [21,23-Didehydro-23H-5-oxaporphyrinato](trifluoroacetato)zinc(II) 3a−c
a
Reagents: (a) O2, ascorbic acid, pyridine in CHCl3 at rt; (b) 2 M HCl; (c) Ac2O, Zn(OAc)2, ethanol-free CHCl3, reflux; (d) 0.1%TFA.
in various fields. These tetrapyrrolic dyes find applications in
electronic functional materials,17 photofunctional materials,18
and scaffolds of supramolecular architectures.19 The goal of our
study is to clarify structural, spectroscopic, and chemical
properties of meso-triaryl derivatives of 5-oxaporphyrins and
bilinones. In this paper, we report preparation of meso-triaryl-
21,23-didehydro-23H-5-oxaporphyrins from bilindiones and
investigations into the electrophilic reactivities and spectro-
scopic properties.
RESULTS AND DISCUSSION
■
Figure 1. UV−vis spectra of 2a and 3a (1 × 10−5 M) in chloroform at
Synthesis of 5-Oxaporphyrins. meso-Triarylbilindione 2
298 K.
was prepared from [meso-tetraarylporphyrinato]iron(III) 1 by
the coupled oxidation reaction (Scheme 1).14a,c The reaction of
bilindione 2 with acetic anhydride and zinc acetate in ethanol-
free chloroform under refluxing conditions for 1 h afforded the
5-oxaporphyrin zinc complex in a quantitative yield.4b Three
[21,23-didehydro-23H-5-oxaporphyrinato]zinc(II) compounds
3a−c having 4-methoxycarbonylphenyl, 4-methoxyphenyl, and
phenyl groups on the meso positions were prepared.
Chromatographic purification on SiO2 using CH2Cl2/ace-
tone/TFA (20/1/0.1) as eluent gave [21,23-didehydro-23H-
5-oxaporphyrinato](trifluoroacetato)zinc(II) (3) as a green
solid.
5-Oxaporphyrin 3a was dissolved in various organic solvents
such as toluene, chloroform, dichloromethane, diethyl ether,
THF, ethyl acetate, acetone, acetonitrile, methanol, ethanol,
DMSO, and DMF, although it was not stable in alcohols and
DMF with spontaneous decomposition to yield linear
tetrapyrroles. It is interesting to note that 3a was slightly
soluble even in water and hexane. The solubility of 3a in
toluene was 4.2 0.1 g dm−3 at room temperature. Recently,
Dechaine and co-workers reported that solubility of β-
octaethylporphyrin and meso-tetraphenylporphyrin was 0.202
and 2.68 g dm−3 in toluene, respectively.16 The solubility of 3a
in toluene was higher than β-octaethylporphyrin and meso-
tetraphenylporphyrin.
degeneracy of the HOMO/LUMO of porphyrin is removed by
replacement of the meso carbon with oxygen, since the
molecular orbitals having large meso probabilities are
stabilized.21 Therefore, the Q-band is no longer a forbidden
transition. Second, the transition electric dipole moment along
the O5−C15 is intensified by the polarization due to the meso
oxygen. We performed time-dependent HF/6-31G(d,p)//HF/
6-31G(d,p) calculations of UV−vis spectra of 3a−c, and
transition energy, oscilator strength, and transition electric
dipole moment directions are listed in Tables S7−S9 (see the
Supporting Information). As shown in Tables S7−S9
(Supporting Information), the transition electric dipole mo-
ment direction of the Q-band is along the C10−C20 axis. Thus,
the first mechanism, where the removed degeneracy of
HOMO/LUMO caused the allowed Q-band, can account for
the intense Q-band. Another characteristic feature of the UV−
vis spectrum of 5-oxaporphyrin is the split B-band. As shown in
Tables S7−S9 (Supporting Information), the split B-band is
attributed to the perpendicularly polized two transitions, along
the O5−C15 axis and the C10−C20 axis. Thus, removal of
degeneracy of transitions along the C5−C15 axis and the C10−
C20 axis resulted in the split B-band.
The TOF-mass spectrum of 3a showed a peak at m/z 777
1
(M − CF3COO+) (M = C45H29F3N4O9Zn). The H NMR
The UV−vis spectra of 2a and 3a are shown in Figure 1. 5-
Oxaporphyrin 3a exhibited characteristic absorption peaks at
391 nm (B band) and 649 nm (Q-band). The spectrum is
similar to [β-octaethyl-5-oxaporphyrinato]zinc(II) reported by
Fuhrhop and co-workers, where the absorption maximum in
chloroform was 662 nm.4a The molar absorption coefficient of
the Q-band of 5-oxaporphyrin is ca. twice as large as that of
Q0−1 of zinc meso-tetraphenylporphyrin.20 There are two
possible mechanisms for the intensified Q-band. First, the
resonances of pyrrole β-protons of 3a appeared at 7.76, 7.92,
8.09, and 8.22 ppm, while those of bilindione 2a appeared at
6.26, 6.47, 6.69, and 6.94 ppm. The downfield shifts of these
protons of 3a by ca. 1.4 ppm as compared to 2a demonstrated
that these pyrrole β-protons have ring-current effects8 due to
the aromaticity of 5-oxaporphyrin. The 1H NMR resonances of
pyrrole β-protons of [5,10,15,20-tetrakis(4-methoxy-
carbonylphenyl)porphyrinato]zinc appeared at 8.8 ppm; thus,
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the aromaticity of 3a was lower than the zinc porphyrin. The
COSY experiments revealed that the resonances at 7.76 and
7.92 ppm are ascribed to the same pyrrole ring protons and
those at 8.09 ppm and 8.22 ppm to the same pyrrole ring
protons. The selected resonances in the 13C NMR of 3a
appeared at 120.0, 130.6, 130.8, 134.5, 135.9, 140.7, 143.0,
150.0, 154.6, 165.4, 166.76, and 166.81 ppm. The peaks at
166.76 and 166.81 ppm were correlated with methyl ester
protons at 4.04 and 4.06 ppm by the HMBC experiments;
therefore, the peaks at 166.76 and 166.81 ppm were ascribed to
the ester carbonyl carbons. Furthermore the HMBC experi-
ments indicated that the resonances at 8.09 and 8.22 ppm show
long-range coupling with the resonance at 165.4 ppm in the 13C
NMR. Because these 1D and 2D NMR experiments did not
give conclusive evidence to differentiate the pyrroles bridged by
cally, while the remaining nonhydrogen atoms were refined
anisotropically. The bond distances of 3a are shown in Figure
4a and also listed in Table S2 (see the Supporting Information).
Figure 4. Bond distances (Å) of 3a: (a) X-ray data and (b) ab initio
calculations at B3LYP/6-31G(d).
1
oxygen and the other pyrroles, we also used the H and 13C
NMR chemical shifts calculated with ab initio molecular orbital
to assign the resonances. On the basis of ab initio calculations
(HF/6-311+G(2d,p)) of NMR chemical shifts, the resonances
at 8.09, 8.22, and 165.4 ppm were assigned to H3, H2, and C4,
respectively. The resonance of C4 in the low magnetic field
implies that the C4 carbon is electron deficient as is discussed
below.
X-ray Crystallographic Studies of 3a. Crystals of 3a were
obtained by slow diffusion of cyclohexane to a solution of 3a in
toluene. The crystallographic studies revealed that the
CF3COO group was coordinated to the zinc, and the Zn−O
distance was 2.010 (4) Å. An ORTEP view of the complex is
shown in Figure 2. The 5-oxaporphyrin core was almost planar.
The bond distances between the ring oxygen and the adjacent
carbon atoms are 1.335(7) and 1.364(7) Å. This bond
distances were a bit longer than carbonyl groups: a typical
bond length of CO in the carbonyl group is 1.23 Å.
Ab initio molecular orbital calculations were performed to
gain further insights into the electronic structures of 5-
oxaporphyrin. The bond orders computed by ab initio
molecular orbital (B3LYP/6-31G(d)//B3LYP/6-31G(d)) are
shown in Figure S16 (Supporting Information). The bond
order between the ring oxygen and the adjacent carbon atoms
was 1.02. The bond orders between the ring oxygen and the
adjacent carbon in furan computed by the AM1 semiempirical
method22 and the Møller−Plesset (MP2) method23 were 1.10
and 0.98, respectively. In addition, the bond distance of furan
was studied by microwave24 and electron diffraction.25
According to the microwave experiment, the C−O bond
distance in furan is 1.36 Å. Comparisons of the bond distances
and bond orders between furan and 5-oxaporphyrin indicate
that the C−O bond in the macrocycle of 5-oxaporphyrin is
similar to that of furan.
For the bond order of the meso carbon to pyrrole α carbon,
the bond distance of C9−C10 was 1.379(7) Å and significantly
shorter than that of C10−C11 (1.422(7) Å). Therefore, the
C9−C10 bond had a larger bond order than the C10−C11
bond. Bond distances calculated using ab initio molecular
orbital theory at the B3LYP/6-31G(d) level for geometry
optimization are shown in Figure 4b. Figure 5 showed some
possible resonance structures of 5-oxaporphyrin (isomers I−
VI). The resonance structure I is most consistent with the
above discussion based on the bond distances determined by X-
ray crystallographic studies as well as the bond distances and
the bond orders computed with ab initio molecular orbital
theory. Moreover, the NBO charges of 3a are shown in Figure
S17 (Supporting Information). The C4 and C6 carbons were
relatively cationic, and the Zn ion was the most cationic in the
macrocycle of 5-oxaporphyrin. Therefore, the contribution
from the resonance structure III is also significant.
Figure 2. ORTEP view of 3a.
The zinc ion is displaced 0.56 Å out of the 5-oxaporphyrin
plane. The 5-oxaporphyrin plane is thus domed.13 The
displacements of each atom from the mean oxaporphyrin
core plane are shown in Figure 3. The phenyl groups are tilted:
the dihedral angles of C(pyrrole α)−C(meso)−C(phenyl
ipso)−C(phenyl ortho) are 60 − 66°. The structure displays
disorder in the location of the fluorine atoms of the ligand as
well as solvent atoms (hexane). These were refined isotropi-
X-ray structures of β-substituted 5-oxaporphyrin zinc
complexes have been reported previously.5c,8 Unfortunately,
the reported 5-oxaporphyrin structures display orientational
disorder that involves multiple sites for the oxa group, which
obscures small variation in bond lengths in regions near the
disordered oxa group. The structure of the β-octaethyl-5-
oxaporphyrin cobalt complex was determined without such
disorder, and it showed C−O bond distances of 1.340 and
1.348 Å and a C−O−C bond angle of 124.8°.26 Bond angles of
Figure 3. Perpendicular displacements of each atom of 3a out of the
mean oxaporphyrin core plane in units of pm.
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Figure 6. UV−vis spectral changes of 5.0 × 10−6 M of 3a in MeOH at
298 K. Spectra were recorded every 1 min.
were also obtained in a preparative scale by the reaction of 3a
or 3c with corresponding sodium alkoxide, and we confirmed
that they were identical with those obtained in the solvolysis
reactions. In the UV−vis spectrum, bilinone 7a showed λmax at
324, 404, and 645 nm in CHCl3. The TOF-mass spectrum of
1
7a showed a peak at 746 (M+, M = C44H34N4O8). In the H
NMR, the resonances of pyrrole β-protons of bilinone 7a
appeared at 6.24, 6.28, 6.39, 6.54, 6.59, 6.81, 6.95, and 7.15
ppm and the phenyl ortho protons appeared at 7.62, 7.71, and
7.75 ppm. The resonances at 3.73 ppm (3H) and 3.96 ppm
(9H) indicate that 7a has four methoxy groups. The peak at
3.73 ppm is assigned to the 19-methoxy group and the peaks at
3.96 ppm are to the methyl ester groups in the phenyl groups.
According to the NOESY spectra, following NOE correlations
were found: the resonances of pyrrole β-protons at 6.54 and
7.15 ppm (H-7, H-3) with that of the ortho phenyl protons at
7.62 ppm, the resonances of pyrrole β-protons at 6.59 and 6.95
ppm (H-12, H-8) with that of the ortho phenyl protons at 7.75
ppm, and the resonances of pyrrole β-protons at 6.39 and 6.81
ppm (H-13, H-17) with that of the ortho phenyl proton at 7.71
ppm. Based on these NOESY correlations, we identified that
bilinone 7a had (4Z,9Z,15Z) configuration.
The first-order rate constants of the ring-opening reaction of
3a in MeOH, EtOH, or i-PrOH at 30 °C were 0.0103, 0.075,
and 0.0082 s−1, respectively (Table 1 and Scheme 2). The half-
lives of 3a in these alcohols are in the range 10−90 s. By
contrast, the spectral changes of 5-oxaporphyrin 3a in t-BuOH
and in water were very slow. The reactivity of 3a toward
alcohols is, thus, primary > secondary ≫ tertiary. Therefore,
steric requirements of the transition state of the reaction are
rather severe. These results demonstrate that the 5-
oxaporphyrin can be used to functionalize hydroxy groups
regioselectively. The reaction of carbenium ions with alcohols
and water have been studied, where the reactivity decreases in
the order: MeOH > EtOH > i-PrOH > H2O > t-BuOH.29 The
ratio of the rate constant of reaction of a diphenylcarbenium
ion with i-PrOH to that with t-BuOH is 4.5, while the ratio of
the rates of reaction with 3a was 2700. Therefore, selectivity of
the reaction of 3a with sec- and tert-alcohols is much higher
than the diphenylcarbenium ion.
Figure 5. Resonance structures of 5-oxaporphyrin.
3a are listed in Table S3 (Supporting Information). The core
geometry of 3a is similar to that of the β-octaethyl-5-
oxaporphyrin cobalt complex.
Alcoholysis of Oxaporphyrins and Its Selectivity.
When the reaction of bilindione 2a with Ac2O/Zn(OAc)2
was performed in 1% ethanol-containing chloroform, two
products, 5-oxaporphyrin 3a and a less polar blue compound,
1
were obtained after acidic workup. H NMR and TOF-mass
spectroscopic data of the less polar blue compound suggested
that it is 19-ethoxybilinone 8a. If the reaction period was
shorter than 30 min, unreacted 3a was recovered (50%
recovery), while bilinone 8a was obtained as a major product in
61% yield in the longer reaction period. These observations
suggest that 3a is labile and reacted with a low concentration of
ethanol.
Although (β-substituted-5-oxaporphyrinato)zinc(II) has
been reported to react with various nucleophiles such as
alkoxide, amide, or thiolate anions4,27,28 to give a ring-opened
product, bilinone, no reaction was reported with alcohols. As
described below, 5-oxaporphyrin 3a reacted even with MeOH,
EtOH, i-PrOH, t-BuOH, and water, whose nucleophilicity
should be very low.
The UV−vis spectral changes of 3a in MeOH at 25 °C are
shown in Figure 6. When 3a was dissolved in MeOH, the
absorption of 3a at 388 and 639 nm decreased and new peaks
appeared at 334 and 801 nm. The UV−vis spectral changes
exhibited isosbestic points: it suggested that the reaction
yielded only zinc bilinone 4a exclusively. The MALDI TOF-MS
spectrum of the product exhibited peaks at 808.4, 809.4, 810.4,
811.4, 812.4, 813.4, 814.2, and 815.4 (m/z), and the isotopic
pattern was consistent with formation of both C44H32N4O8Zn+
(M) and MH+. Because 19-alkoxybilinone zinc complexes easily
demetalated in dilute acid, it was difficult to isolate them with
silica gel chromatography. After bilinone zinc complex 4a was
demetalated with 1 M HCl, the structure of 19-alkoxybilinone
7a was confirmed by 1H NMR, NOESY spectra, MALDI TOF-
MS, and UV−vis spectroscopy. Compounds 7a, 7c, 8a, and 9a
Conversion of iron 5-oxaporphyrin to bilindione attracts
interest as a model reaction of verdoheme to biliverdin
transformation catalyzed by heme oxygenase.1b,5b,30 Although
hydrolysis of 5-oxaporphyrin can yield bilindione, the
enzymatic reaction proceeds with consumption of one O2
molecule and four reducing equivalents.1 As shown in Table
1, the reaction rate of 3a with water is at least 2 orders of
magnitude slower than that with MeOH. Low nucleophilicity of
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Table 1. First-Order Rate Constants of the Ring-Opening Reaction of 3a−c in MeOH, in EtOH, and in i-PrOH
solvent
k/s−1, 3a (COOMe)
k/s−1, 3b (OMe)
k/s−1, 3c (H)
T (K)
EtOH
(7.5 0.5) × 10−2
(1.03 0.03) × 10−2
(8.2 0.3) × 10−3
(3.0 0.3) × 10−6
(8.6 1.0) × 10−5
(5.8 0.1) × 10−2
(4.6 0.1) × 10−3
(3.3 0.3) × 10−3
(1.0 0.1) × 10−3
(8.7 0.3) × 10−5
a
(1.1 0.1) × 10−2
(2.2 0.1) × 10−3
(3.2 0.1) × 10−4
a
303
303
303
303
303
298
298
MeOH
iso-PrOH
t-BuOH
b
H2O
a
a
EtOH
(2.1 0.2) × 10−3
(4.1 0.1) × 10−4
(9.0 0.2) × 10−3
(7.8 0.8) × 10−4
MeOH
a
b
Not determined. Hydrolysis was performed in 5%(v/v) CH3CN in water. Both the zinc complex of bilindione and the free base bilindione were
formed.
a
Scheme 2. Synthetic Route to 19-Alkoxybilinone Zinc Complexes 4−6 and Their Free Bases 7−9
a
Reagents: (a) various alcohols R2H; (b) 1 M HCl.
water could be one of reasons why the enzymatic trans-
formation is not a simple hydrolysis but a redox reactions.
Mechanism of the Ring-Opening Reaction. Balch and
co-workers31 proposed that the ring-opening reaction of 5-
oxaporphyrin with cyanide ion proceeds via a 4-cyano-5-
oxaporphyrin intermediate, followed by the bond cleavage of
C4−O5, to give 19-cyanobilinone. Recently theoretical
calculations of the ring-opening reaction of oxaporphyrin with
calculations at the B3LYP/6-31G(d) level. The optimized
geometries are shown in Figure 7, and the energies are listed in
Table 2. The energy (ΔE1) of the MeOH adduct intermediate
(11d) relative to the starting compounds was similar to that of
the i-PrOH adduct intermediate (11e), while the energy of t-
BuOH adduct intermediate (11f) was significantly higher. On
the other hand, the energy (ΔE2) of MeO-bilinone zinc
complex (12d) is much lower than those of both i-PrO-
NH2 , NMe2 , OH−, and CN− have been reported.32
According to the molecular orbital studies, an intermediate is
initially formed by nucleophilic attack of the anions to C4, and
it is then directly converted to a helical ring-opened zinc
complex by passing through a transition state. This mechanism
is schematically shown in Scheme 3 for the reaction with
alcohols.
−
−
We calculated the energies of 4-alkoxy-5-oxaporphyrins 11
and 19-alkoxybilinones 12 by ab initio molecular orbital
Scheme 3. Reaction of 5-Oxaporphyrin with Alcohol via
Alcohol Adducts (11) To Afford 19-Alkoxybilinone Zinc
Complexes (12)
Figure 7. Optimized geometry of (a) 11d, (b) 11f, (c) 12d, and (d)
12f at the B3LYP/6-31G(d) level.
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solvolysis of 3a in MeOH and in EtOH at 298 K were 0.029
and 0.039 eV, respectively. Kadish et al. reported that the
Hammett reaction constants ρ of the cation radical, dication,
anion radical and dianion formation reactions of para-
substituted tetraphenylporphyrins containing various metals in
the center were in the range 0.05−0.09 eV.34 Values of reaction
constants of 3a−c similar to those of one-electron transfer
indicate that nearly unit positive charge should be diminished in
the transition state of the reactions. The reaction mechanism
that cationic 5-oxaporphyrin 10 is converted to a neutral adduct
11, whose structure is similar to the transition state of the
reaction, is thus supported by the Hammett plot.
Table 2. Energies of 5-Oxaporphyrin Alcohol Adduct Zinc
Complexes (11) and 19-Alkoxybilinone Zinc Complexes
(12) Calculated by ab Initio (B3LYP/6-31G(d))
oxaporphyrin
alcohol adduct
(11) (au)
19-
a
b
ΔE1
alkoxybilinone
(12) (au)
ΔE2
(kcal mol−1
)
(kcal mol−1
)
MeOH
i-PrOH
t-BuOH
−2919.17727
−2997.81386
−3037.11831
24.1
25.5
33.8
−2919.20569
−2997.83848
6.3
10.1
10.4
−3037.15562
a
b
ΔE1 = E(11) + E(CF3COOH) − E(10) − E(ROH). ΔE2 = E(12) +
E(CF3COOH) − E(10) − E(ROH).
The first-order rate constants of ring-opening reaction with
alcohols were also determined in toluene. Table 3 summarizes
the rate constants of the nucleophilic ring-opening reaction of
3a−c by MeOH, EtOH, and i-PrOH at 303 K. In alcohols, the
reactivity decreases in the order EtOH > MeOH > i-PrOH ≫ t-
BuOH, while, in toluene, in the order MeOH ∼ EtOH > i-
PrOH. When 3a reacted with 1 M MeOH in acetonitrile at 303
K, the first-order rate constant of ring-opening reaction was
(1.4 0.2) × 10−4 s−1. The first-order rate constant in toluene
was about 5.4 times faster than in acetonitrile. A slower rate in
the polar solvent is consistent with the reaction mechanism that
a positive charge diminished in the transition state.
To compare the reactivity of meso-substituted oxaporphyrin
with that of β-substituted one, [3,7-bis(2-acetoxyethyl)-21,23-
didehydro-2,8,13,17-tetraethyl-12,18-dimethyl-23H-5-oxa-
porphyrinato](chloro)zinc(II) (13) was prepared by a
previously reported method.27a The first order rate constant
of the ring-opening reaction of 13 in EtOH at 30 °C was
0.00092 0.00001 s−1. Therefore, 13 is less reactive than 3a,
3b, and 3c. The electron-donating ability of eight alkyl groups
on the β-positions is thus stronger than three 4-methoxyphenyl
groups in the meso positions. Molecular orbital calculations at
B3LYP/6-31G indicated that the Mulliken atomic charges of
C4 and C6 of [2,3,7,8,12,13,17,18-octamethyl-5-oxa-
porphyrinato]zinc(II), 3a, and 3c were 0.475, 0.494, and
0.493 respectively, showing that the C4, C6 carbons of 3a and
3c are more electrophilic.
bilinone zinc complex (12e) and t-BuO-bilinone zinc complex
(12f). The rate constants listed in Table 1 indicate that the
ring-opening reactions of 3a−c with MeOH and i-PrOH have
transition states in similar energies while the ring-opening
reactions with t-BuOH have transition states with much higher
energy. Therefore, the structures of alcohol adducts 11d−f
seem to be a good approximation of the transition state of these
reactions.
Substituent Effects on the Reactivity of 5-Oxapor-
phyrins. The solvolysis reaction rates were compared for three
5-oxaporphyrins 3a−c to investigate electronic effects of
substituents on the ring-opening reaction rates. Table 1
summarizes the rate constants of solvolysis of 3a−c in either
MeOH, EtOH, or i-PrOH at 298 or 303 K. The Hammett plots
for the rate constants of solvolysis of 5-oxaporphyrins are
shown in Figure 8. The substituent constants σp were taken
UV−vis Absorption and Fluorescence Emission Spec-
tra of 5-Oxaporphyrins. Figure 9 compares UV−vis spectra
Figure 8. Hammett plots for the rate constants of the reaction of
oxaporphyrins with MeOH (black circle, 298 K; white circle, 303 K),
EtOH (black square, 298 K; white square, 303 K), and i-PrOH (white
triangle, 303 K). ρ/eV = 0.039 0.003 (EtOH at 298 K), 0.0375
0.0004 (EtOH at 303 K), 0.029 0.004 (MeOH at 298K), 0.028
0.001 (MeOH at 303 K), and 0.056 0.006 (i-PrOH at 303 K). σp
(COOMe) = 0.45, σp (H) = 0, σp (OMe) = −0.27.
from the literatures and the value of σp (COOEt) was used in
place of σp (COOMe).33 Since all three phenyl rings of 5-
oxaporphyrin are substituted, 3σp was used as the sum of the
substituent constant. Figure 8 demonstrates that the solvolysis
rates are linearly correlated with the substituent constants σp.
The positive slopes indicate that a positive charge diminishes in
the transition state. The Hammett reaction constants of the
Figure 9. UV−vis spectra of oxaporphyrins 3a−c in chloroform.
Table 3. First-Order Rate Constants of the Ring-Opening Reaction of 3a−c in 1 M MeOH, 1 M EtOH, and 1 M i-PrOH in
Toluene at 30 °C
nucleophile
k (s−1), 3a (COOMe)
k (s−1), 3b (OMe)
k (s−1), 3c (H)
EtOH
(3.65 0.04) × 10−4
(7.5 0.1) × 10−4
(7.8 0.4) × 10−5
(7.0 0.1) × 10−5
(7.3 0.4) × 10−5
(1.17 0.04) × 10−5
(1.83 0.05) × 10−4
(2.0 0.1) × 10−4
(4.0 0.4) × 10−5
MeOH
i-PrOH
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Article
of 5-oxaporphyrins 3a−c. 5-Oxaporphyrin substituted with
COOMe (3a) and unsubstituted phenyl groups (3c) exhibited
similar absorption spectra, while 5-oxaporphyrin substituted
with OMe (3b) showed a red-shifted B band.
Table 5. Fluorescence Data of Oxaporphyrin 3a in Various
Solvents
λem
λabs
(nm)
Stokes shift
(nm)
rel fluorescence
solvent
(nm)
intensity
To explore the electronic states, we performed time-
dependent HF calculations of 3a−c at the 6-31G(d,p) level,
without an axial ligand. The geometry was optimized at the
HF/6-31G(d,p) level. Absorption maxima, oscillator strengths,
CI configurations, and the transition electric dipole moment
directions are listed in Tables S7−S9 (Supporting Informa-
tion). The simulated UV−vis spectra of 3a−c based on the MO
calculations are shown in Figure S18 (Supporting Information).
These results indicate that the electron-donating OMe groups
have significant effects on the electronic states of 5-
oxaporphyrins. Table S10 (Supporting Information) lists
selected MO energies of 3a−c. The OMe substituents
particularly destabilized the HOMO-1 orbital.
toluene
THF
657
653
657
657
653
653
653
646
642
645
649
642
641
638
11
11
12
8
4.84
2.92
2.18
2.00
1.85
1.26
1.00
CH2Cl2
CHCl3
DMSO
acetone
CH3CN
11
12
15
reference compound.35 The fluorescence quantum yields of 3b
and 3c were 0.050 and 0.071, respectively. Compared to the
fluorescence quantum yield of tetraphenylporphyrin zinc
complex (ϕ = 0.033), the fluorescence quantum yields of 5-
oxaporphyrins were higher.35 Methoxy-substituted oxaporphyr-
in 3b showed a lower fluorescence quantum yield than 3a and
3c. Fluorescence spectrum of 3a showed a peak at 657 nm in
nonpolar solvents and 653 nm in polar solvents (Table 5).
Fluorescence intensity was higher in nonpolar solvents than in
polar solvents as shown in Figure 11. Stokes shifts of 3a were 8
to 15 nm and they were smaller than that of the porphyrin zinc
complex. Excitation of the Soret band at 400 nm also resulted
in the fluorescence at 657 nm, although the fluorescence
quantum yield was significantly lower.
Fluorescence spectra of 3a−c are shown in Figures 10 and
11, and spectroscopic data are listed in Tables 4 and 5. The
CONCLUSION
■
meso-Triarylbilindiones were converted into [meso-triaryl-21,23-
didehydro-23H-5-oxaporphyrinato]zinc(II) by refluxing them
with acetic anhydride and zinc acetate in chloroform, and they
were isolated as a CF3COO− salt. X-ray crystallographic studies
revealed that the CF3COO− is coordinated to the zinc. In spite
of its ionic structure, it is soluble in most of the organic
solvents, and the solubility in toluene was higher than meso-
tetraphenylporphyrin and β-octaethylporphyrin. Substituent
effects on the reactivity and spectroscopic properties were
studied for three [21,23-didehydro-23H-5-oxaporphyrinato]-
zinc(II) complexes. [meso-Triaryl-21,23-didehydro-23H-5-
oxaporphyrinato]zinc(II) is labile toward nucleophiles than
[β-octaalkyl-5-oxaporphyrinato]zinc(II) and reacted with weak
nucleophiles such as methanol, ethanol, and 2-propanol to give
bilinone zinc complexes having near-infrared absorption at 800
nm. The positive Hammett reaction constants for COOMe, H,
and OMe substituents in the phenyl rings are consistent with a
neutral adduct formation from the cationic reactant. Solvolysis
of [meso-triaryl-21,23-didehydro-23H-5-oxaporphyrinato]zinc-
(II) occurs rapidly in primary and secondary alcohols while
that in tertiary alcohol and water was slower by a factor of 102
to 103. The electron-donating substituents in the aryl groups
caused a significant red shift in electronic spectra, and the
fluorescence quantum yield was lower than that of [meso-
triphenyl-21,23-didehydro-23H-5-oxaporphyrinato]zinc(II),
while the electron-withdrawing substituents showed minor
effects on the electronic spectrum and the fluorescence
spectrum. Finally, [meso-triaryl-21,23-didehydro-23H-5-
oxaporphyrinato]zinc(II) is a fluorescent electrophile, easily
converted to the helical compound having near-infrared
absorption, and would find various applications to new
functional materials.
Figure 10. Fluorescence spectra of oxaporphyrin 3a−c at 298 K in
toluene where the samples were excited at 590 nm.
Figure 11. Fluorescence spectra of oxaporphyrin 3a in various solvents
at 298 K. The excitation wavelength was 590 nm.
Table 4. Fluorescence Data of Oxaporphyrins 3a−c in
Toluene
λem
(nm)
λabs
(nm)
Stokes shift
(nm)
fluorescence quantum
yield
3a (COOMe)
3b (OMe)
3c (H)
657
657
657
646
646
645
11
11
12
0.071
0.050
0.071
fluorescence quantum yield of 3a in toluene was determined to
be 0.071 by using tetraphenylporphyrin (ϕ = 0.13) as a
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The Journal of Organic Chemistry
Article
mmol), and acetic anhydride (0.14 mL, 1.5 mmol) in amylene-
stabilized chloroform (25 mL) was refluxed for 1 h. After being cooled
to room temperature, the reaction mixture was washed with water
twice, and the organic layer was dried over Na2SO4. Evaporation of the
solvent under reduced pressure gave a green solid. The product was
purified on silica gel chromatography using CH2Cl2/acetone/trifluoro-
acetic acid (20:1:0.1) as eluent. The green fractions were combined,
washed with water, dried over Na2SO4, and evaporated to yield 4.2 mg
of 3b (72%). 1H NMR (500 MHz, acetone-d6): δ = 4.04 (s, 3H; CH3),
4.05 (s, 6H; CH3), 7.29−7.33 (t, J = 8.60 Hz, 6H; phenyl), 7.83 (d, J =
4.60 Hz, 2H; pyrrole), 7.84−7.92 (d, J = 4.75 Hz, 6H; phenyl), 8.00
(d, J = 4.60 Hz, 2H; pyrrole), 8.16 (d, J = 4.60 Hz, 2H; pyrrole), 8.31
ppm (d, J = 4.60 Hz, 2H; pyrrole). 13C NMR (125 MHz, chloroform-
d): δ = 55.5 (CH3), 112.0, 118.8, 130.7, 131.0, 132.5, 134.5, 134.9,
137.4, 138.8, 142.3, 143.8, 150.6, 155.1, 160.2, 160.3, 164.9, 166.76,
166.81 ppm. 19F NMR (471 MHz, chloroform-d): δ = −75.5 ppm
(CF3COO). MS (MALDI-TOF): m/z = 693 [M-CF3COO]+; HRMS
(FAB): calcd for C40H29O4N464Zn m/z 693.1480, found 693.1454.
UV−vis (CH2Cl2, 25 °C): λmax (εmax) 437 (6.08 × 104), 587 (1.22 ×
104), 643 nm (6.42 × 104 M−1 cm−1).
EXPERIMENTAL SECTION
■
Molecular orbital calculations were performed using Gaussian 09
(Gaussian Inc.).36 Commercially available reagents were used as
received. Chromatographic separations of 5-oxaporphyrins and
bilinones were performed using silica gel 60N, spherical neutral with
particle size 40−50 μm. Ethanol-free chloroform was used to prepare
5-oxaporphyrin. Preparation of bilindiones 2a, 2b, and 2c was reported
elsewhere.14a,c Tetramethylsilane was used as an internal standard of
1H and 13C NMR spectra, and benzotrifluoride was used as an internal
standard (−63.7 ppm) of 19F NMR spectra. Assignments of 1H NMR
and 13C NMR were performed using 1H−1H COSY, NOESY, HMBC,
and HMQC spectra. A green plate crystal of 5-oxaporphyrin 3a was
obtained by slow diffusion of cyclohexane to a solution of 3a in
toluene. Crystal data and data collection parameters are given in Table
6.
Table 6. Crystallographic Data for Oxaporphyrin 3a
formula
C50H29F3N4O9Zn
952.14
V, Å3
Z
4446.99(16)
formula wt
4
[21,23-Didehydro-10,15,20-triphenyl-23H-5-oxa-
porphyrinato](trifluoroacetato)zinc(II) (3c). A solution of bilin-
dione 2c (16.5 mg, 0.0296 mmol), zinc acetate (11.0 mg, 0.0546
mmol), and acetic anhydride (0.6 mL, 6.35 mmol) in amylene-
stabilized chloroform (100 mL) was refluxed for 1 h. After being
cooled to room temperature, the reaction mixture was washed with
water twice, and the organic layer was dried over Na2SO4. Evaporation
of the solvent under reduced pressure gave a green solid. The product
was purified on silica gel chromatography using CH2Cl2/acetone/
trifluoroacetic acid (20:1:0.1) as eluent. The green fractions were
combined, washed with water, dried over Na2SO4, and evaporated to
color and
habit
green plate
T, K
113(2)
crystal
system
monoclinic
dcalcd (mg cm−3
)
1.422
space
group
P21/n
radiation (λ, Å)
μ, mm−1
Cu Kα
(1.54187)
a, Å
b, Å
21.2044(4)
10.4376(2)
1.415
range of
transmission
factors
0.6683 to
0.7448
a
c, Å
21.7778(5)
R1
0.0852
0.2359
0.986
1
yield 14.1 mg of 3c (66.5%). H NMR (500 MHz, dichloromethane-
b
α deg
β, deg
γ, deg
90
wR2
d2): δ = 7.63−7.74 (m, 9H; phenyl), 7.82 (d, J = 4.60 Hz, 2H;
pyrrole), 7.84−7.95 (m, 6H; phenyl), 7.98 (d, J = 4.60 Hz, 2H;
pyrrole), 8.05 (d, J = 4.50 Hz, 2H; pyrrole), 8.25 ppm (d, J = 4.50 Hz,
2H; pyrrole). 13C NMR (125 MHz, chloroform-d): δ = 112.8, 126.8−
127.4, 128.7, 128.8, 130.7, 132.5−133.4, 134.5, 137.2, 138.6, 138.8,
140.0, 142.0, 143.8, 150.4, 155.0, 165.1 ppm. 19F NMR (471 MHz,
chloroform-d): δ = −75.4 ppm (CF3COO). MS (MALDI-TOF): m/z
= 603 [M − CF3COO]+. HRMS (FAB): calcd for C37H23ON464Zn m/
z 603.1163, found 603.1142. UV−vis (CH2Cl2, 25 °C): λmax (εmax) 388
(4.80 × 104), 415 (5.52 × 104), 587 (1.03 × 104), 641 nm (5.44 × 104
M−1cm−1).
(4Z,9Z,15Z)-1,21-Dihydro-19-methoxy-5,10,15-tris(4-me-
thoxycarbonylphenyl)-23H-bilin-1-one (7a). A solution of
oxaporphyrin 3a (11.5 mg, 0.0129 mmol) and sodium methoxide
(3.0 mg, 0.0555 mmol) in anhydrous methanol (30 mL) was stirred at
room temperature for 30 min. The reaction mixture was quenched by
10% NH4Cl (20 mL), and chloroform (50 mL) was added. The
chloroform solution was washed with 1 M HCl twice and washed with
water, and the organic layer was dried over Na2SO4. Evaporation of the
solvent under reduced pressure gave a blue solid. The product was
purified on silica gel chromatography using chloroform as eluent to
yield 5.3 mg of 7a (55.3%). 1H NMR (500 MHz, acetone-d6): δ = 3.73
(s, 3H; OCH3), 3.96 (m, 9H; COOCH3), 6.24 (d, J = 4.80 Hz, 1H;
pyrrole H-18), 6.28 (d, J = 4.60 Hz, 1H; pyrrole H-2), 6.39 (d, J = 4.15
Hz, 1H; pyrrole H-13), 6.54 (d, J = 4.15 Hz, 1H; pyrrole H-7), 6.59 (s,
1H; pyrrole H-12), 6.81 (d, J = 4.80 Hz, 1H; pyrrole H-17), 6.95 (d, J
= 4.15 Hz, 1H; pyrrole H-8), 7.15 (d, J = 5.50 Hz, 1H; pyrrole H-3),
7.62 (d, J = 8.25 Hz, 2H; 5-phenylene H-2′), 7.71 (d, J = 8.25 Hz, 2H;
15-phenylene H-2′), 7.75 (d, J = 7.55 Hz, 2H; 10-phenylene H-2′),
8.13−8.34 (m, 6H; 5,10,15-phenylene H-3′), 10.27 (s, 1H; NH),
13.06 ppm (s, 1H; NH). 13C NMR (125 MHz, chloroform-d): δ =
52.30 (COOCH3), 52.36 (COOCH3), 52.41 (COOCH3), 55.7
(OCH3), 117.3, 119.7 (pyrrole C-13), 120.2 (pyrrole C-18), 123.8,
125.6 (pyrrole C-2), 127.8 (pyrrole C-7), 129.09, 129.14, 129.3, 129.6,
130.0, 130.2, 131.0, 131.1, 131.2, 132.1, 134.9 (pyrrole C-8), 136.58,
136.64 (pyrrole C-3), 138.3, 138.8 (pyrrole C-17), 141.1, 141.2, 141.4,
141.8, 142.3 (pyrrole C-4), 149.1 (pyrrole C-16), 151.9 (pyrrole C-9),
166.58 (COOCH3), 166.66 (COOCH3), 166.74 (COOCH3), 166.79
112.6870(10)
90
GOF
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = [∑[w(Fo − Fc )2]/
2
∑[w(Fo )2]]1/2
.
[21,23-Didehydro-10,15,20-tris(4-methoxycarbonylphenyl)-
23H-5-oxaporphyrinato](trifluoroacetato)zinc(II) (3a). A solu-
tion of bilindione 2a (23.2 mg, 0.0313 mmol), zinc acetate (11.0 mg,
0.0546 mmol), and acetic anhydride (0.6 mL, 6.35 mmol) in amylene-
stabilized chloroform (100 mL) was refluxed for 1 h. After being
cooled to room temperature, the reaction mixture was washed with
water twice, and the organic layer was dried over Na2SO4. Evaporation
of the solvent under reduced pressure gave a green solid. The product
was purified on silica gel chromatography using CH2Cl2/acetone/
trifluoroacetic acid (20:1:0.1) as eluent. The green fractions were
combined, washed with water, dried over Na2SO4, and evaporated to
yield 27.9 mg of 3a in a quantitative yield. 1H NMR (500 MHz,
chloroform-d): δ = 4.04 (s, 3H; CH3), 4.06 (s, 6H; CH3), 7.76 (d, J =
4.45 Hz, 2H; pyrrole H-12), 7.92 (d, J = 4.45 Hz, 2H; pyrrole H-13),
7.94−8.06 (m, 6H; 10,15,20-phenylene H-2′), 8.09 (d, J = 4.75 Hz,
2H; pyrrole H-3), 8.22 (d, J = 4.75 Hz, 2H; pyrrole H-2), 8.31 (d, J =
8.45 Hz, 2H; 15-phenylene H-3′), 8.34 ppm (d, J = 8.45 Hz, 4H;
10,20-phenylene H-3′). 13C NMR (125 MHz, chloroform-d): δ =
52.50 (CH3), 52.53 (CH3), 120.0 (pyrrole C-3), 128.2 (phenylene C-
3′), 128.5 (phenylene C-3′), 130.6 (meso), 130.8 (pyrrole C-12),
132.4−133.8 (phenylene C-2′), 134.5 (pyrrole C-13), 135.9 (meso),
138.6 (pyrrole C-2), 140.7, 143.0, 143.8 (pyrrole C-1), 144.3, 150.0
(pyrrole C-14), 154.6 (pyrrole C-11), 165.4 (pyrrole C-4), 166.76
(CO), 166.81 ppm (CO). 19F NMR (471 MHz, chloroform-d): δ
= −75.4 ppm (CF3COO). MS (MALDI-TOF): m/z = 777 [M −
CF3COO]+. HRMS (FAB): calcd for C43H29O7N464Zn m/z 777.1328,
found 777.1344. UV−vis (CH2Cl2, 25 °C): λmax (εmax) 323 (2.13 ×
104), 391 (3.89 × 104), 601 (1.05 × 104), 644 nm (4.57 × 104 M−1
cm−1).
[21,23-Didehydro-10,15,20-tris(4-methoxyphenyl)-23H-5-
oxaporphyrinato](trifluoroacetato)zinc(II) (3b). A solution of
bilindione 2b (4.5 mg, 0.0072 mmol), zinc acetate (2.6 mg, 0.014
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(pyrrole C-6), 170.2 (pyrrole C-1), 177.1 ppm (pyrrole C-19). MS
(MALDI-TOF): m/z = 746 [M]+. HRMS (FAB): calcd for
C44H34O8N4 m/z 746.2377, found 746.2356. UV−vis (CHCl3, 25
°C): λmax (εmax) 324 (3.69 × 104), 404 (4.36 × 104), 645 nm (1.90 ×
104 M−1 cm−1).
AUTHOR INFORMATION
Corresponding Author
*E-mail: tmizutan@mail.doshisha.ac.jp.
Notes
■
The authors declare no competing financial interest.
(4Z,9Z,15Z)-1,21-Dihydro-19-methoxy-5,10,15-triphenyl-
1
23H-bilin-1-one (7c). H NMR (500 MHz, chloroform-d): δ = 3.63
(s, 3H; OCH3), 6.18 (d, J = 4.75 Hz, 1H), 6.21 (d, J = 5.50 Hz, 1H),
6.43 (bs, 1H), 6.50 (d, J = 4.15 Hz, 1H), 6.61 (bs, 1H), 6.87 (d, J =
4.75 Hz, 1H), 6.84 (d, J = 3.45 Hz, 1H), 7.03 (d, J = 5.45 Hz, 1H),
7.38−7.57 (m, 15H), 10.18 ppm (s, 1H; NH), 12.83 ppm (s, 1H;
NH). 13C NMR (125 MHz, chloroform-d): δ =55.7, 118.7, 119.3,
119.9, 123.7, 124.9, 127.5, 127.76, 127.83, 128.0, 128.2, 128.4, 129.5,
130.6, 131.1, 131.3, 132.2, 134.8, 136.4, 136.6, 136.9, 137.0, 137.9,
138.5, 140.2, 141.1, 148.8, 152.0, 166.7, 170.3, 176.5 ppm. MS
(MALDI-TOF): m/z = 572 [M]+. HRMS (FAB): calcd for
C38H28O2N4 m/z 572.2212, found 572.2200. UV−vis (CHCl3, 25
°C): λmax (εmax) 328 (3.09 × 104), 402 (4.45 × 104), 637 nm (2.05 ×
104 M−1 cm−1).
(4Z,9Z,15Z)-1,21-Dihydro-19-ethoxy-5,10,15-tris(4-
methoxycarbonylphenyl)-23H-bilin-1-one (8a). 1H NMR (500
MHz, chloroform-d): δ = 1.11 (t, J = 6.90 Hz, 3H; CH3), 3.97 (m, 9H;
COOCH3), 4.07 (bs, 2H; OCH2), 6.18 (d, J = 4.60 Hz, 1H), 6.26 (d, J
= 5.75 Hz, 1H), 6.34 (bs, 1H), 6.47 (d, J = 4.60 Hz, 1H), 6.54 (bs,
1H), 6.79 (d, J = 5.15 Hz, 1H), 6.84 (d, J = 5.15 Hz, 1H), 7.00 (d, J =
5.75 Hz, 1H), 7.48 (d, J = 8.00 Hz, 2H), 7.63 (m,, 4H), 8.12−8.15 (m,
6H), 10.27 (s, 1H; NH), 12.89 ppm (s, 1H; NH). 13C NMR (125
MHz, chloroform-d): δ = 14.7, 52.3, 52.4, 64.7, 117.4, 119.6, 120.6,
123.9, 125.8, 127.7, 128.9, 129.1, 129.6, 130.0, 130.2, 131.1, 131.4,
132.1, 134.9, 136.5,135.6, 138.0, 138.9, 141.1, 141.4, 141.6, 141.8,
142.4, 149.4, 151.9, 166.6, 166.7, 166.8, 170.3, 176.7 ppm. MS
(MALDI-TOF): m/z = 760 [M]+. HRMS (FAB): calcd for
C45H36O8N4 m/z 760.2533, found 760.2551. UV−vis (CHCl3, 25
°C): λmax (εmax) 326 (3.90 × 104), 401 (4.82 × 104), 650 nm (1.99 ×
104 M−1 cm−1).
(4Z,9Z,15Z)-1,21-Dihydro-5,10,15-tris(4-methoxycarbonyl-
phenyl)-19-(1-methylethoxy)-23H-bilin-1-one (9a). 1H NMR
(500 MHz, acetone-d6): δ = 1.13 (d, J = 5.75 Hz 6H; CH3), 3.95
(m, 9H; COOCH3), 4.88 (m, 1H; CH), 6.19 (d, J = 4.60 Hz, 1H),
6.28 (dd, J = 5.75 Hz, 1.70 Hz, 1H), 6.34 (dd, J = 4.60 Hz, 2.3 Hz,
1H), 6.55 (d, J = 4.60 Hz, 1H), 6.59 (bs, 1H), 6.78 (d, J = 4.60 Hz,
1H), 6.93 (d, J = 4.60 Hz, 1H), 7.19 (dd, J = 5.75 Hz, 1.70 Hz, 1H),
7.64 (d, J = 8.00 Hz, 2H), 7.70 (d, J = 8.00 Hz, 2H), 7.73 (d, J = 8.00
Hz, 2H), 8.15−8.19 (m, 6H), 10.57 (s, 1H; NH), 12.87 ppm (s, 1H;
NH). 13C NMR (125 MHz, chloroform-d): δ = 22.0, 52.4, 72.4, 117.4,
121.1, 123.9, 125.7, 127.6, 129.1, 129.5, 130.1, 131.1, 131.3, 131.4,
132.2, 134.7, 136.4, 136.6, 137.8, 139.0, 141.0, 141.1, 141.4, 141.8,
149.6, 152.0, 166.6, 166.7, 166.8, 170.6, 176.0 ppm. MS (MALDI-
TOF): m/z = 774 [M]+, 731 [M − CH(CH3)2]+. HRMS (FAB): calcd
for C46H38O8N4 m/z 774.2690, found 774.2692. UV−vis (CHCl3, 25
°C): λmax (εmax) 324 (3.68 × 104), 401 (4.29× 104), 648 nm (2.28 ×
104 M−1 cm−1).
ACKNOWLEDGMENTS
■
This work was supported by “Creating Research Center for
Advanced Molecular Biochemistry”, Strategic Development of
Research Infrastructure for Private Universities, the Ministry of
Education, Culture, Sports, Science and Technology (MEXT),
Japan.
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ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR of 3a−c, 7a,c, 8a, and 9a; 13C NMR of 3a−c, 7a,c, 8a,
and 9a; NOESY NMR of 7a; UV−vis and MS spectral data of
4a−c, 5−c, 6a−c, 7b, 8b,c, and 9b,c; CIF file of 3a; selected
bond distances of 3a; selected bond angles of 3a; bond order of
3a; atomic coordinates of 3a−c optimized at the B3LYP/6-
31G(d) level; NBO charges of 3a; time-dependent RHF/6-
31G(d,p)//RHF/6-31G(d,p) calculations of the excited states
of 3a−c; selected MO energies (eV) of oxaporphyrins 3a−c.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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