Effects of an axial amino ligand on the spectroscopic and electrochemical properties of amino(methoxo)-(tetraphenylporphyrinato)antimony(V) complexes

Article abstract of DOI:10.1246/bcsj.81.583

We investigated the effects of an axial amino ligand on the spectroscopic and electrochemical properties of alkylamino(methoxo)(tetraphenylporphyrinato) antimony(V) bromide 1 and anilino(methoxo)(tetraphenylporphy-rinato)antimony(V) bromide 2. Fluorescence measurements of 1 and 2 showed that their fluorescence quantum yields were lower than that of dihydroxo(tetraphenylporphyrinato) antimony(V) bromide (3) due to intramolecular electron transfer (ET) from the axial amino ligand to the excited porphyrin ring. Fluorescence was enhanced by the addition of a proton, which was caused by the protonation of the axial nitrogen atom, thereby preventing ET. From the titration curves of fluorescence quantum yield (φ_f)versus proton concentration, we estimated the acid dissociation constants (pK_a) for the conjugate acid of the axial amino ligand of 1 to be 4.41-5.03. The reduction potentials (E _1/2^red) of 2 depended strongly on the electronic effect of the p-substituents (X) on the axial aniline group whereas the E _1/2^red methoxo(p-substituted-phenoxo) (tetraphenylporphyrinato)antimony(V) bromide was little affected by the p-substituents on the phenoxo ligand. These observations were interpreted as reflecting the participation of the axial amino ligand in the LUMO, calculated for 2 by the PM3 method.

Full text of DOI:10.1246/bcsj.81.583

Ó 2008 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 81, No. 5, 583–589 (2008)
583
Effects of an Axial Amino Ligand on the Spectroscopic
and Electrochemical Properties of Amino(methoxo)-
(tetraphenylporphyrinato)antimony(V) Complexes
Shin-ichiro Tsunami,1 Kousuke Tanaka,2 Jin Matsumoto,2
ꢀ2
Tsutomu Shiragami, and Masahide Yasuda2
1Miyazaki Prefecture Environmental Science Association, 6258-20 Tayoshi, Miyazaki 880-0911
2Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki,
Gakuen-Kibanadai, Miyazaki 889-2192
Received October 1, 2007; E-mail: t0g109u@cc.miyazaki-u.ac.jp
We investigated the effects of an axial amino ligand on the spectroscopic and electrochemical properties
of alkylamino(methoxo)(tetraphenylporphyrinato)antimony(V) bromide 1 and anilino(methoxo)(tetraphenylporphy-
rinato)antimony(V) bromide 2. Fluorescence measurements of 1 and 2 showed that their fluorescence quantum yields
were lower than that of dihydroxo(tetraphenylporphyrinato)antimony(V) bromide (3) due to intramolecular electron
transfer (ET) from the axial amino ligand to the excited porphyrin ring. Fluorescence was enhanced by the addition
of a proton, which was caused by the protonation of the axial nitrogen atom, thereby preventing ET. From the titration
curves of fluorescence quantum yield (ꢀf) versus proton concentration, we estimated the acid dissociation constants
(pKa) for the conjugate acid of the axial amino ligand of 1 to be 4.41–5.03. The reduction potentials (E1=2red) of 2
red
depended strongly on the electronic effect of the p-substituents (X) on the axial aniline group whereas the E1=2 of
methoxo(p-substituted-phenoxo)(tetraphenylporphyrinato)antimony(V) bromide was little affected by the p-substituents
on the phenoxo ligand. These observations were interpreted as reflecting the participation of the axial amino ligand in the
LUMO, calculated for 2 by the PM3 method.
Recently, the synthesis and characterization of metallo-
porphyrin complexes have been extensively investigated
X
R1 R2
N
from the viewpoint of light-energy conversion processes in-
volving photocatalysis1–3 and dye-sensitized solar cell sys-
tems.4,5 Among a number of metalloporphyrin complexes syn-
thesized so far, it is well known that high-valent metallo-
porphyrin complexes of GeIV, SnIV, PV, AsV, and SbV can
covalently connect to axial ligands through carbon, oxygen,
nitrogen, and sulfur atoms,6 which differs from the behavior
of transition-metal porphyrin complexes.7–10 We have paid
especially close attention to tetraphenylporphyrinatoantimo-
ny(V) complexes (Sb(tpp)) with functionalized moieties on
their axial ligands. We have already reported their photocata-
lytic properties11–13 and photoinduced intramolecular electron
and energy transfer between the porphyrin ring and the axial
ligands.13 Most studies on Sb(tpp) have been performed
using Sb(tpp) coordinated with an oxygen atom as an axial
ligand.14–21 However, there have been no systematic studies
on the electrochemistry or photochemistry of Sb(tpp) coordi-
nated with axial amino ligands, although the synthesis and
structural characterization of these complexes have been
reported previously.6,22
+
NH
Sb
+
Ph
Ph
N
N
N
N
N
N
Ph
Ph
Br-
Sb
Br-
Ph
Ph
N
N
Ph
Ph
OMe
R2
OMe
R1
X
NC
CF3
Cl
1a
1b
1c
1d
1e
1f
H
H
H
H
H
2a
2b
C6H5CH2-
HO(CH2)3-
CH3(CH2)3-
2c
2d
2e
H
iso-Pr-
Me
tert-Bu-
2f
MeO
-(CH2)4-
Scheme 1. Amino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) complexes 1 and 2.
Results
Synthesis of Sb(tpp) Complexes with an Amino Group as
an Axial Ligand. Introduction of axial ligands into high-val-
ent metalloporphyrin has usually been performed by exchang-
ing axial halogen ligands with nucleophiles.14,23–26 As a refer-
ence sample, dihydroxo(tetraphenylporphyrinato)antimony(V)
bromide (3) was prepared by the hydrolysis of dibromo(tetra-
Here we report the effect of axial amino ligands on the
spectroscopic and electrochemical properties of alkylamino-
(methoxo)(tetraphenylporphyrinato)antimony(V) bromide
and anilino(methoxo)(tetraphenylporphyrinato)antimony(V)
1
bromide 2 (Scheme 1).
Published on the web May 14, 2008; doi:10.1246/bcsj.81.583

584 Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
Amino(methoxo)(tetraphenylporphyrinato)antimony
Br
Br
+
+
Ph
Ph
Ph
Ph
R1R2NH
N
N
MeOH
N
N
Sb
N
Sb
N
N
N
1a-f
Ph
Ph
Br-
MeCN
reflux
90%
Ph
Ph
Br-
OMe
Br
4
5
MeCN-H2O (1:1)
reflux, quant.
X
NH2
OH
+
Ph
Ph
N
N
Sb
N
2a-x
N
Ph
Br-
Ph
OH
3
Scheme 2. Synthetic route of 1–3.
(A)
(B)
Potential / V vs. Ag/Ag+
Potential / V vs. Ag/Ag+
Figure 1. Cyclic voltammogram of 1d in (A) MeCN and in (B) MeCN in the presence of HClO4 (5:5 ꢂ 10ꢁ5 mol dmꢁ3).
phenylporphyrinato)antimony(V) bromide (4). The reaction of
4 with amines, however, gave free base tetraphenylporphyrin
(H2(tpp)) because the amines performed well as electron do-
nors to reduce 4 to the SbIII complex, which underwent deme-
tallation easily.20 As starting materials, therefore, we used bro-
mo(methoxo)(tetraphenylporphyrinato)antimony(V) bromide
(5), which has more negative reduction potential than 4;
red
E1=2 vs. SCE = ꢁ0:36 V for 5 and ꢁ0:23 V for 4.
The reaction of 5 with aliphatic amines successfully pro-
duced the corresponding alkylamino(methoxo)(tetraphenyl-
porphyrinato)antimony(V) 1a–1e in relatively good yield
(>70%), although 1f was only obtained in poor yield due to
decomposition during purification on silica gel (Scheme 2).
Similarly, 5 reacted with p-substituted anilines to produce
p-substituted anilino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) 2a–2e. However, the reaction of 5 with tertiary
amines such as Et3N and Bu3N produced H2(tpp), because
of the strong reducing abilities of these amines. In the case
of bifunctional amine 3-amino-1-propanol, coordination occur-
red selectively at the amino group, while no reaction occurred
at the hydroxy group. This was confirmed by X-ray crystallo-
graphic analysis of 1b in addition to assignment by NMR
spectra (Scheme 3).
Scheme 3. Crystal structure of 1b.
Electrochemical Properties. A typical example is the
cyclic voltammogram (CV) of 1d in MeCN, where reversible
first and second reduction peaks were observed at ꢁ0:52 and
ꢁ0:94 V, respectively, as shown in Figure 1A. The same CV
profiles were also observed in other complexes 1 and 2. The
first and second reduction peaks of 1 and 2 were reversible, be-
cause the ratio (ipc=ipa) of the peak current intensity during a
cathodic sweep (ipc) to that during an anodic sweep (ipa) was
measured to be 0.8–1.0, and the peak potential differences be-
tween the cathodic and anodic sweeps, which were predicted

S. Tsunami et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
585
Table 1. Spectroscopic and Electrochemical Data of Sb(tpp) Complexes 1–3 in MeCN
Absorption spectra
max/nm (log ")d)
Fluorescence spectra
max/nme) ꢀf ꢂ 102 f)
ox
1=2
c)
E
/Va)
E1re=d2/Vb)
pKa
ꢀG/eVg) Yield/%h)
ꢁ
ꢁ
1a
1b
1c
1d
1e
1f
1.33
1.40
1.41
1.33
1.33
1.42
ꢁ0:50, ꢁ0:90 4.30 422 (5.40), 556 (4.11), 596 (3.96)
ꢁ0:51, ꢁ0:90 5.02 419 (5.54), 553 (4.20), 594 (4.01)
ꢁ0:51, ꢁ0:91 5.03 421 (5.52), 556 (4.17), 596 (4.03)
ꢁ0:52, ꢁ0:94 4.41 421 (5.51), 556 (4.19), 596 (4.05)
ꢁ0:49, ꢁ0:94 4.84 419 (5.36), 553 (4.05), 593 (3.85)
ꢁ0:53, ꢁ0:95 5.02 419 (5.57), 553 (4.13), 594 (3.98)
594, 645
0.96
1.00
1.00
0.37
1.00
0.18
2.09
2.26
0.38
1.24
0.84
0.83
5.18
73
70
73
76
73
31
594, 645
594, 645
594, 645
594, 645
596, 646
594, 645
594, 645
594, 645
594, 654
594, 645
594, 645
596, 646
2a 1.23 (1.03)i) ꢁ0:48, ꢁ0:88
2b 1.23 (1.00)i) ꢁ0:42, ꢁ0:82
2c 1.12 (0.72)i) ꢁ0:54, ꢁ0:94
2d 1.03 (0.68)i) ꢁ0:55, ꢁ0:95
2e 0.78 (0.52)i) ꢁ0:56, ꢁ0:96
2f 0.76 (0.34)i) ꢁ0:57, ꢁ0:97
—
—
—
—
—
—
—
420 (5.40), 556 (4.08), 597 (3.92)
421 (5.27), 557 (3.85), 599 (3.70)
419 (5.61), 551 (4.22), 590 (3.95)
420 (5.44), 557 (4.11), 598 (3.98)
421 (5.27), 557 (3.85), 599 (3.70)
421 (5.51), 557 (4.00), 599 (3.82)
417 (5.62), 550 (4.49), 590 (4.30)
ꢁ0:37
ꢁ0:43
ꢁ0:42
ꢁ0:50
ꢁ0:74
ꢁ0:75
18
18
19
86
20
20
100
3
1.40
ꢁ0:51, ꢁ0:91
a) Half peak of oxidation potentials vs. SCE. b) Half peak of reduction potentials vs. SCE. c) Acid dissociation constants for con-
jugated acid of axial amino ligand. d) The absorption maximum of Sb(tpp) chromophore. e) The emission maxima in the fluorescence
spectra of Sb(tpp) chromophore under excitation at 420 nm. f) The fluorescence quantum yields of Sb(tpp) chromophore in MeCN
under excitation of Soret band at 420 nm. g) The free energy change for the electron transfer from axial ligands to Sb(tpp) at S1 state:
ox
1=2
ox
1=2
E0{0 ¼ 2:08 eV. h) Product yield from 5. i) The E of axial anilino ligands. The values in parenthesis are the E of the correspond-
ing substituted aniline.
theoretically, were between 40 and 80 mV. Furthermore, the
differences (ꢀE) between the first reduction peaks and the sec-
ond reduction peaks were 0.43–0.48 V. The half peaks of the
reduction potentials (E1=2red) and the oxidation potentials
2.5
2
Φ
red
(E1=2ox) of 1 and 2 are summarized in Table 1. The E1=2
of 1 was close to that of 3, independent of the axial ligands.
red
1.5
1
The E1=2 of 2 varied from ꢁ0:42 (X = CF3) to ꢁ0:57 V
(X = OMe), depending on the substituents (X) of the anilino
ligands. The reversible reduction process of 1 and 2 can be at-
tributed to the successive valence change from SbV to SbIII.21
ox
On the other hand, the E1=2 of 1 and 2 did not show a rever-
ox
0.5
0
sible peak. Although the E1=2 of 1a–1f were almost the same
ox
as that of 3, the E1=2 of 2a–2f varied from 1.23 (X = CF3)
to 0.76 V (X = OMe), depending on X, and lied between that
of the corresponding substituted anilines and that of 3. This
suggests that axial anilino ligands interacted with the porphy-
rin ring in HOMO levels in 2.
0.3
0.4
0.5
0.6
0.7
0.8
-∆G / eV
Figure 2. Plots of ꢀf vs. ꢀG.
Absorption and Fluorescence Properties.
Absorption
lino ligands to the excited singlet state of the Sb(tpp) group
would be negative for 2a–2e using E1=2red, E1=2ox, and the
excitation energy (E0{0 ¼ 2:08 V for S1 excitation) (Table 1).
The plots of ꢀf vs ꢀG showed a linear correlation (Figure 2).
Recently, the decay process from the S2 excited state of 2 un-
der excitation of the Soret band was investigated in detail.28
We elucidated that the charge-separation state between the
axial anilino ligand and the porphyrin ring participated in the
decay process from the S2 excited state.28 However, it was sug-
gested that the efficiency of the internal conversion from S2 to
S1 was the same as that of 3, since the ꢀf of 2d was constant
under excitation of the Soret band at 420 nm and the Q band at
557 nm. Therefore, the decrease in the ꢀf of 2 can be attribut-
ed to intramolecular charge transfer from the axial amino
ligand to the excited porphyrin ring in the S1 state.
and fluorescence spectral data of 1, 2, and 3 are summarized
in Table 1. Although the absorption maxima (ꢁmax) of 1 and
2 were observed at slightly longer wavelengths than that of
3, the axial coordination of nitrogen atoms to antimony atoms
caused no significant spectral changes for the Soret band or the
Q-band. The absorption spectra of 2 were essentially similar to
those of 3, except for the appearance of an extra band due to
the axial anilino ligand at wavelengths shorter than 300 nm.
Photoexcitation of 1 and 2 gave weak fluorescence, as
shown in Table 1. The fluorescence quantum yields (ꢀf) from
the Q bands of 1 and 2 were measured under excitation of the
Soret band at 420 nm. The ꢀf of 1 and 2 were much smaller
than that of 3 because of the effect of the axial amino ligand
(Table 1). As the electron-donating abilities of the substituents
of 2a–2f got stronger, ꢀf decreased remarkably except in the
case of 2c, which exhibited a heavy atom effect. The Rehm–
Weller equation (eq 1)27 was used to predict that the free en-
ergy change (ꢀG) for the electron transfer from the axial ani-
ox
red
ꢀG ¼ E1=2 ꢁ E1=2 ꢁ E0{0
Effect of Protons on Fluorescence Spectra and Reduc-
:
ð1Þ

586 Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
Amino(methoxo)(tetraphenylporphyrinato)antimony
H
NHR
+
NHR
Ph
+
Ph
H+
Ph
N
Ph
N
N
N
Sb
N
Sb
N
N
N
Ph
Ph
Br-
- H+
Br-
Ph
Ph
OMe
OMe
0.04
0.03
0.02
0.01
0
0.04
0.03
0.02
0.01
0
Φ
Φ
(A)
(B)
0
2
4
6
8
10
12
14
0
1
2
3
4
5
6
7
8
[HClO4]/10−5
M
[KOH]/10−6
M
Figure 3. Plots of ꢀf for 1a ( ) and 1c ( ) in MeCN solution with (A) the addition of HClO4 and (B) the subsequent addition of KOH.
(A)
(B)
0.05
0.04
0.05
0.04
Φ
Φ
0.03
0.02
0.01
0.03
0.02
0.01
0
10
20
30
40
0
20
60
100
140
[HClO4]/10–5
M
[KOH]/10–6
M
Figure 4. Plots ꢀf of 1a ( ) and 2d ( ) in MeCN solution with (A) the addition of conc. HClO4 and (B) the subsequent addition
of KOH.
tion Potentials. Figure 3A shows the dependence of ꢀf on
X
the concentration of HClO4 in MeCN solutions of 1a and 1c.
The addition of HClO4 induced a hysteretic enhancement of
ꢀf. Moreover, addition of an aqueous KOH solution to the
acidic MeCN solutions of 1a and 1c led to a sharp hysteretic
response of the concentration of OHꢁ to ꢀf, which nearly re-
turned to its original value (Figure 3B). In the case of 3, such
fluorescence response to acid or base addition was not ob-
served at all. It is suggested that a reversible protonation and
deprotonation occurs on the lone pair on the axial nitrogen
atom. Accordingly, we can easily estimate the acid dissocia-
tion constants (pKa) for the conjugate acid of the axial amino
ligand using Hþ titration curves. Thus, the pKa values 1a–1f
were determined to be 4.30–5.03 (Table 1). In the case of
2d, the addition of HClO4 enhanced ꢀf, but the addition of
KOH did not return to its original value (Figure 4). After titra-
tion, the formation of hydroxo(methoxo)(tetraphenylporphyri-
nato)antimony13 was confirmed by mass spectroscopy mea-
surement of the solution. Similar results were observed in all
2 with axial anilino ligands, suggesting that an acid-assisted
ligand-exchange reaction is induced quantitatively.
Ph
N
CF3CO2H
MeOH
2d +
2d +
V
Sb
N
N
∆
Ph
Ph
N
CF3CO2H
Br-
Et4N+X-
∆
Ph
OMe
X
Yield
6a
6b
5
MeO
Cl
90%
87%
22%
Br
Scheme 4.
Therefore, the axial ligand exchanges of 2d with nucleo-
philes were performed in the presence of acid (Scheme 4).
The reaction of 2d in MeCN–MeOH (3:1 v/v) for 2 h at
50 ꢃC in the presence of CF3CO2H (TFA) gave dimethoxo-
(tetraphenylporphyrinato)antimony(V) (6a)13 in 90% yield,
whereas no reaction occurred in the absence of TFA. The
use of HClO4 as a proton source gave the same products,

S. Tsunami et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
587
E1/2 red / V (vs.SCE)
X
X
-0.40
-0.42
2b
2a
(X= CF3)
(X= CN)
O
+
NH
Sb
+
Ph
N
Ph
N
N
N
Ph
-0.45
Ph
Sb
Br-
Br-
Ph
N
X=CN
X=F
X=H
Ph
N
N
N
-0.46
-0.48
Ph
OMe
Ph
OMe
8
-0.50
2
-0.54
-0.54
-0.55
2c
2d
2e
(X= Cl)
(X=H)
(X= Me)
X=OCH3
-0.55
-0.60
-0.56
-0.57
2f
(X= OMe)
LUMO of 8 (X=H)
LUMO of 2d
Figure 5. Comparison of the reduction potentials between 2 and 8.
but in lower yield than in the case of TFA. Also the reaction of
2d with Et4NþClꢁ and Et4NþBrꢁ in the presence of TFA in
MeCN gave chloro(methoxo)(tetraphenylporphyrinato)anti-
mony(V) (6b, 87%) and 5 (22%).13 respectively. These results
show that the protonated 2d induced the axial ligand exchange
reaction efficiently. On the other hand, the reaction of 2d
with P(OEt)3 in the presence of TFA gave H2(tpp). Moreover,
absorption spectra of the reaction solution showed absorption
at 465 nm due to tetraphenylporphyrinatoantimony(III) (7).20
Since P(OEt)3 is a good electron donor, the electron-transfer
reaction from P(OEt)3 to 2d occurred efficiently, generating
7, which gave H2(tpp) by demetalation.
(X = H) was delocalized over the porphyrin ring, whereas
the LUMO of 2d was delocalized over both the axial anilino
ligand and the porphyrin ring (Figure 5). Therefore, the energy
levels of the LUMO of 2, which are related to E1=2red, should
be strongly affected by the electronic characteristics of the
substituents on axial phenoxo ligands, but those of 8 should
not.
Interaction between the porphyrin ring and the axial anilino
ligands in a HOMO state will be the same as that in a LUMO
state, judging from the spectroscopic similarities between
Soret bands 1, 2, and 3. Thus, these results suggest that the
red
E1=2 of Sb(tpp) can be controlled by the electronic effect
of an axial anilino ligand.
Next, we investigated the additive effect of acid on the
red
E1=2 of 1. Figure 1B shows the CV of 1d in the presence
Conclusion
of HClO4 (5:5 ꢂ 10ꢁ5 mol dmꢁ3) in MeCN. Under acidic con-
ditions, two more reduction peaks appeared on the more posi-
tive side of 1d (ꢁ0:28 and ꢁ0:69 V vs. SCE) than in the case
of 1d under neutral conditions. The peak current of these new
reduction waves increased along with the increase in proton
concentration (0{5:5 ꢂ 10ꢁ5 mol dmꢁ3). The reduction peaks
observed were due to 1d protonated on the axial nitrogen atom.
The first and second reduction potentials of protonated 1d
appeared at ꢁ0:28 and ꢁ0:69 V, respectively, as irreversible
peaks. On the other hand, the reduction peak of 2 was not
observed under acidic conditions.
The Sb(tpp)s with axial amino ligands were characterized
red
from the viewpoint of being able to control E1=2 and ꢀf
by proton concentration and induce acid-assisted ligand ex-
change. It was found that the enhancement effect of ꢀf and
the shifts of reduction potentials over a wide range (ꢁ0:28–
ꢁ0:55 V; ꢀE ¼ 0:27 V) could be induced under acidic condi-
tions. The acid-assisted ligand exchange of 2d with nucleo-
philes will provide a novel method for synthesizing Sb(tpp)
complexes with various axial ligands.
Experimental
Instruments and Materials. UV–vis absorption spectra and
fluorescence spectra of solutions were measured on a Hitachi
U2001 spectrometer and on a Hitachi F4500 spectrometer, respec-
tively. 1H NMR spectra were taken in CDCl3 using Me4Si as
an internal standard on a Bruker AC 250P spectrometer at
250 MHz. SIMS spectra were obtained on a Hitachi M-2000AM
spectrophotometer. The PM3 calculation was performed on a
Silicon graphics O2 work station using the SPARTAN program.
All chemicals were of the best commercial grades available.
Synthesis of Amino(methoxo)(tetraphenylporphyrinato)-
antimony(V) Complexes 1–3. According to a reported meth-
od,29 3 and 5 were prepared by the reaction of 4 with H2O and
Discussion
We have previously reported the effect of an axial p-
red
substituted phenoxo ligand on E1=2 in methoxo(p-substitut-
ed-phenoxo)(tetraphenylporphyrinato)antimony(V) bromide
red
(8).21 In that report, the E1=2 were little affected by the p-
substituents on the phenoxo ligand. On the other hand, the
red
E1=2 of 2 depended strongly on the electron-donating or -ac-
cepting nature of the p-substituents (X) on the axial aniline
group. The PM3 calculations of 2d and the methoxo(phen-
oxo)(tetraphenylporphyrinato)antimony(V) complex (8; X =
H) predicted the LUMO orbitals (Figure 5). The LUMO of 8

588 Bull. Chem. Soc. Jpn. Vol. 81, No. 5 (2008)
Amino(methoxo)(tetraphenylporphyrinato)antimony
MeOH, respectively. An MeCN–pyridine solution (5:1 v/v
50 mL) containing 5 (1.1 mmol) and aliphatic amines or 4-substi-
tuted aniline derivatives was heated for 4 h at 80 ꢃC. The solvent
was evaporated and the residue was dissolved in CH2Cl2. The
CH2Cl2 solution was washed three times with 50 mL portions of
H2O. After evaporation, the crude product was chromatographed
on silica gel (Fuji Silysia BW-300) using CHCl3–MeOH (10:1
v/v) as an eluent to give 1 and 2. The spectral data of 1a–1f
are shown below. On 1H NMR measurements, peaks of NH proton
in 1 and 2 were not all observed due to extremely broad lines. The
spectral data of 2a–2e have been reported in recent literature.28
Benzylamino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) Bromide (1a): Yield 73% from 5; SIMS: m=z 869
(Mþ); 1H NMR (CDCl3) ꢂ ꢁ2:47 (3H, s, Sb-OCH3), ꢁ1:39
(2H, s, Sb–NH–CH2–), 4.27 (2H, d, J ¼ 7:2 Hz, axial Ph), 6.42
(1H, m, axial Ph), 6.65 (2H, t, J ¼ 7:3 Hz, axial Ph), 7.82–7.94
(12H, m, Ph), 8.24 (4H, d, J ¼ 6:9 Hz, Ph), 8.41 (4H, d, J ¼
6:4 Hz, Ph), 9.38 (8H, s, pyrrole).
3-Hydroxypropylamino(methoxo)(tetraphenylporphyri-
nato)antimony(V) Bromide (1b): Yield 70% from 5; SIMS:
m=z 837 (Mþ); 1H NMR (CDCl3) ꢂ ꢁ2:84 (2H, t, J ¼ 7:0 Hz,
Sb–NH–CH2–), ꢁ2:43 (3H, s, Sb–OCH3), ꢁ1:57 (2H, quint,
J ¼ 7:0 Hz, –CH2–), 1.28 (2H, t, J ¼ 7:4 Hz, –CH2–OH), 7.85–
7.91 (12H, m, Ph), 8.27 (4H, d, J ¼ 6:4 Hz, Ph), 8.55 (4H, d,
J ¼ 6:4 Hz, Ph), 9.41 (8H, s, pyrrole).
m, Ph), 8.35 (4H, d, J ¼ 6:4 Hz, Ph), 8.42 (4H, d, J ¼ 6:4 Hz,
Ph), 9.58 (8H, s, pyrrole).
Fluorescence Quantum Yields. The concentrations of 1 and
2 in MeCN solutions were adjusted for the absorbance to be less
than 0.1 at the excitation wavelength (420 nm). The fluorescence
quantum yields (ꢀf) were determined by using an MeCN solution
of 3 (ꢀf ¼ 0:0518) as an actinometer.13 The acid dissociation con-
stants (pKa) for the conjugated acid of axial amino ligand of 1
were estimated from a proton concentration at the half of the max-
imum fluorescence intensity.
Measurements of Redox Potentials. The oxidation and re-
duction potentials of a dried MeCN solution of 1–3 (1 ꢂ 10ꢁ2
mol dmꢁ3) in the presence of a supporting electrolyte (Et4NBF4;
0.1 mol dmꢁ3) were measured by cyclic voltammetry at a scan rate
of 300–500 mV sꢁ1 at 25 ꢃC on a BAS CV-50W cyclic voltamme-
ter using a carbon-disk working electrode, a Pt counter electrode,
and an Ag/AgNO3 reference electrode. The half-peaks of the
oxidation (E1=2ox) and reduction potentials (E1=2red) vs Ag/Agþ
were modified to those vs. SCE by the addition of +0.22 V.
X-ray Crystallographic Analysis. The structure of 1b was
determined unambiguously by X-ray crystallographic analysis
on an Enraf Nonius CAD-4 system using Mo Kꢃ irradiation
˚
(ꢁ ¼ 0:7107 A).
1b: C48H39N5O2SbBr, Mr ¼ 919, monoclinic, P21 (space
˚
˚
group number 4), a ¼ 12:7088 A, b ¼ 12:2072 A, c ¼ 15:4114
ꢃ
3
1:31 g cmꢁ3
,
˚
˚
Butylamino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) Bromide (1c): Yield 73% from 5; SIMS: m=z 836
(Mþ ꢁ 1); 1H NMR (CDCl3) ꢂ ꢁ3:09 (2H, t, J ¼ 7:0 Hz, Sb–
NH–CH2–), ꢁ2:43 (3H, s, Sb–O–CH3), ꢁ1:82 (2H, quint, J ¼
7:0 Hz, –CH2–), ꢁ1:08 (2H, hex, J ¼ 7:4 Hz, –CH2–), ꢁ0:41
(3H, t, J ¼ 7:4 Hz, –CH3), 7.82–7.94 (12H, m, Ph), 8.24 (4H,
d, J ¼ 6:4 Hz, Ph), 8.41 (4H, d, J ¼ 6:4 Hz, Ph), 9.38 (8H, s,
pyrrole).
A, ꢄ ¼ 106:7 , V ¼ 2290 A , Z ¼ 2, Dcalcd
¼
Dm ¼ 1:33 g cmꢁ3, R ¼ 0:0777, Rw ¼ 0:0863. The molecular
structure of 1b was drawn using Chem 3D based on X-ray
crystallographic data (Scheme 3). Crystallographic data reported
in this manuscript have been deposited with Cambridge Crystallo-
graphic Data Centre as supplementary publication No. CCDC-
677875. Copies of the data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK; fax: +44 1223 336033; or deposit@
ccdc.cam.ac.uk).
Isopropylamino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) Bromide (1d): Yield 76% from 5; SIMS: m=z 821
(Mþ ꢁ 1); 1H NMR (CDCl3) ꢂ ꢁ3:88 (1H, m, Sb–NH–CH–),
ꢁ2:42 (3H, s, Sb–OCH3), ꢁ1:99 (6H, d, J ¼ 6:2 Hz, –CH(CH3)2),
7.89–7.96 (12H, m, Ph), 8.29 (4H, d, J ¼ 6:4 Hz, Ph), 8.38 (4H, d,
J ¼ 6:4 Hz, Ph), 9.45 (8H, s, pyrrole).
This research was supported by a Grant-in-Aid for Scientific
Research (No. 19550068, No. 16550127, and No. 17029053
Scientific Research in Priority Areas 417) from the Ministry
of Education, Culture, Sports, Science and Technology. We
are grateful to Prof. H. Inoue (Tokyo Metropolitan University)
for additional financial support (SORST from Japan Science
and Technology Agency).
tert-Butylamino(methoxo)(tetraphenylporphyrinato)anti-
mony(V) Bromide (1e): Yield 73% from 5; SIMS: m=z 835
1
(Mþ ꢁ 1); H NMR (CDCl3) ꢂ ꢁ2:57 (3H, s, Sb–OCH3), ꢁ2:46
(9H, s, Sb–NH–C(CH3)3), 7.91–7.96 (12H, m, Ph), 8.30 (4H,
d, J ¼ 6:7 Hz, Ph), 8.39 (4H, d, J ¼ 6:8 Hz, Ph), 9.48 (8H, s,
pyrrole).
Pyperidino(methoxo)(tetraphenylporphyrinato)antimony(V)
Bromide (1f):
Yield 31% from 5; SIMS: m=z 846 (Mþ);
References
1H NMR (CDCl3) ꢂ ꢁ3:32 (4H, t, J ¼ 7:0 Hz, Sb–NH–(CH2)2–),
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–(CH2)2–), ꢁ0:52 (2H, quint, J ¼ 7:3 Hz, –CH2–), 7.89–7.96
(12H, m, Ph), 8.29 (4H, d, J ¼ 6:2 Hz, Ph), 8.38 (4H, d,
J ¼ 6:4 Hz, Ph), 9.48 (8H, s, pyrrole).
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