Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by Ga(III) porphyrin clay minerals system with high durability and usability

Article abstract of DOI:10.1246/bcsj.20140378

Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) porphyrinclay hybrid compound was investigated. Gallium(III) porphyrin did not aggregate on the clay surface, and thus, maintained photoactivity for the photochemical reaction. Gallium(III) porphyrin without clay decomposed immediately in the photochemical reaction. On the other hand, gallium(III) porphyrin adsorbed on clay was more stable than that without clay during the photochemical reaction and the altered porphyrin on clay still had photocatalytic ability along with original porphyrin. It was suggested that gallium(III) porphyrin was protected by clay surface during the photochemical reaction. In addition, the efficiency for the photochemical chlorination and oxygenation reaction was kept even at high porphyrin adsorption densities on clay. These findings are beneficial to construct efficient and durable photochemical reaction systems.

Full text of DOI:10.1246/bcsj.20140378

Photochemical Chlorination and Oxygenation Reaction
of Cyclohexene Sensitized by Ga(III) Porphyrin-Clay Minerals System
with High Durability and Usability
Takamasa Tsukamoto,1,2 Tetsuya Shimada,1,3 Tsutomu Shiragami,4 and Shinsuke Takagi*1,3
1Department of Applied Chemistry, Graduate Course of Urban Environmental Sciences, Tokyo Metropolitan University,
1-1 Minami-ohsawa, Hachiohji, Tokyo 192-0397
2JSPS (Japan Society for the Promotion of Science), Chiyoda-ku, Tokyo 102-0083
3Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo 192-0397
4Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki,
1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192
E-mail: takagi-shinsuke@tmu.ac.jp
Received: December 4, 2014; Accepted: January 9, 2015; Web Released: January 19, 2015
Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) porphyrin-clay
hybrid compound was investigated. Gallium(III) porphyrin did not aggregate on the clay surface, and thus, maintained
photoactivity for the photochemical reaction. Gallium(III) porphyrin without clay decomposed immediately in the
photochemical reaction. On the other hand, gallium(III) porphyrin adsorbed on clay was more stable than that without
clay during the photochemical reaction and the altered porphyrin on clay still had photocatalytic ability along with
original porphyrin. It was suggested that gallium(III) porphyrin was protected by clay surface during the photochemical
reaction. In addition, the efficiency for the photochemical chlorination and oxygenation reaction was kept even at high
porphyrin adsorption densities on clay. These findings are beneficial to construct efficient and durable photochemical
reaction systems.
Organic-inorganic hybrid compounds,1-13 especially dye-
clay complexes,1-8 have been investigated by many researchers
with a view to constructing photofunctional materials. Clay
minerals used as host materials are multilayered compounds
consisting of stacked aluminosilicate nanosheets. Among them,
swellable clays such as saponite can disperse completely as
single nanosheets in aqueous solution. Saponite has negatively
reported that photoactivities of dye molecules such as fluo-
rescence quantum yield or excited lifetime are maintained or
enhanced by the complex formation with clay.17,18 These find-
ings are beneficial to construct photofunctional materials.
On the other hand, photochemical chlorination and oxygen-
ation reactions of alkenes sensitized by metalloporphyrins
with water as both electron and oxygen atom donor in homo-
geneous water-acetonitrile solution have been reported by
several groups including us.19-22 The proposed mechanism of
this photochemical reaction is as follows. First, one-electron
oxidation of excited triplet state metalloporphyrin takes place
by an electron acceptor in aqueous acetonitrile. Subsequently,
oxo-complex of metalloporphyrin produced from hydroxo or
aquo coordinated porphyrin cation radical is attacked by an
alkene. Then, epoxide or alcohol species are produced via
carbocationic intermediates of metalloporphyrin. Chlorination
of the alkenes is also catalyzed in the presence of chloride
anion. The reaction formula using hexachloroplatinate(IV)
anion ([PtIVCl6]2¹) as an electron acceptor and cyclohexene
(C6H10) as a substrate is shown below. The detailed reaction
mechanism is shown in Figure 1. And the proposed chlorina-
tion reaction of cyclohexene is shown in Figure S2.
charged structures and the cation-exchange capacity (CEC)
¹1 8
is ca. 1.0 © 10¹3 equiv g
. Its structure and stoichiometric
formula are shown in Figure S1 (Supporting Information). The
aqueous dispersion of saponite whose particle size is small
(<ca. 100 nm) is substantially transparent in the UV-visible
range.
Cationic dye molecules can adsorb on anionic clay sur-
face and can be intercalated between anionic clay sheets by
Coulomb’s interaction and form organic-inorganic hybrid
compounds.1-8 However, dye molecules on or in such inorganic
host materials are generally likely to lose their photoactivities
because of undesirable aggregation behaviors of them.12
Recently, we have found that tetracationic porphyrin molecules
can adsorb on the saponite nanosheet surfaces without aggrega-
tion even at high adsorption density. This behavior is observed
when the distance of intramolecular cationic points in porphy-
rin and the average distance of anion points on the clay sur-
face coincide well with each other (size-matching effect or
intercharge distance matching effect).8,14-16 We also have
C6H10 þ ½PtIVCl6ꢀ2ꢁ þ H2O
hꢀ
ꢁꢁꢁꢁꢁꢁꢁꢁ! C6H10O þ ½PtIICl4ꢀ2ꢁ þ 2HCl
ð1Þ
Metalloporphyrin
578 | Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan

Acceptor
Acceptor
+
OH
III
Ga
OH
O
- H+
III
Ga
IV
Ga
Cl−
O
+
II
decomposition
Ga
OH
hν
+
OH
Cl
Cl
Cl
O
O
OH
III
Ga
OH
Cl
Cl
Cl
II
Ga
Acceptor
H2O
H+
Acceptor
= porphyrin
Figure 1. Proposed reaction for the photochemical chlorination and oxygenation of alkene sensitized by GaIII porphyrin.
catalyst. It should be noted that this reaction system is quasi-
homogeneous, because the complex can be well swelled in the
N
N
N
solution and optically transparent in visible region. [GaIII(TPP)-
(OH)] is used as a reference photocatalyst without clay, because
[GaIII(TMPyP)(OH)]4+ forms insoluble salt with an anionic
electron acceptor and cannot work as reference photocatalyst
in the absence of clay. The photochemical reactions using these
photocatalysts with and without clay were examined.
N
N
HO
HO
III
III
N
N Ga
N
N Ga
N
N
N
[GaIII(TPP)(OH)]
[GaIII(TMPyP)(OH)]4+
Experimental
Materials and Measurements. Clay minerals (saponite):
Sumecton SA was received from Kunimine Industries Co.,
Ltd. Hydroxo(5,10,15,20-tetraphenylporphyrinato)gallium(III)
([GaIII(TPP)(OH)], denoted as GaIIITPP) was synthesized
according to A. Coutsolelos and K. M. Kadish’s methods26,27
and characterized by 1H NMR. Hydroxo[5,10,15,20-tetrakis-
Figure 2. Structures of gallium(III) porphyrins.
To extend the utilization and enhance the operability and
durability of this photooxygenation reaction, the combination
with heterogeneous reaction fields would be beneficial. For
example, homogeneous photocatalysts such as metal com-
plexes have been combined with inorganic host materials such
as nano scrolls or mesoporous solids.23-25 However, in such
heterogeneous system, photoactivities of catalysts tend to be
lowered compared to homogeneous system because the photo-
catalyst aggregates on the solid surface and loses photoactiv-
ity due to the shortened excited lifetime. In addition, typical
inorganic materials providing heterogeneous reaction fields
are often scattering bodies, and thus, the efficiency of photo-
chemical reaction is lowered. In this sense, clay minerals are
beneficial as host material for photochemical reactions, because
i) dye molecules adsorb on the clay surface without aggregation
and do not lose photoactivity even at high density by choosing
appropriate combination of dye and clay and ii) clay nanosheet
can disperse into a single nanosheet in solution and can be
transparent in the UV-visible range.
In this study, we have investigated photochemical chlorina-
tion and oxygenation reaction of cyclohexene sensitized by
tetracationic metalloporphyrin-clay complex as a heterogene-
ous chemical reaction system. Gallium(III) porphyrins are
chosen as a metalloporphyrin for the photochemical reaction.
Gallium(III) porphyrins are nonionic 5,10,15,20-tetraphenyl-
porphyrinato hydroxo gallium(III) and tetracationic 5,10,15,20-
tetrakis(N-methyl-4-pyridyl)porphyrinato hydroxo gallium(III)
tetrachloride, denoted as [GaIII(TPP)(OH)] and [GaIII(TMPyP)-
(OH)]Cl4, respectively (Figure 2). [GaIII(TMPyP)(OH)]Cl4
adsorbed on clay nanosheet is used as a heterogeneous photo-
(N-methyl-4-pyridyl)porphyrinato]gallium(III)
tetrachloride
([GaIII(TMPyP)(OH)]Cl4, denoted as GaIIITMPyP) was pur-
chased from Mid-Century Chemicals (Chicago, IL). Hexa-
chloroplatinate(IV) disodium salt (denoted as Na2[PtIVCl6])
was purchased from Aldrich. Cyclohexene was purchased from
Nacalai Tesque and purified by short alumina column just
before use.
UV-visible absorption spectra were obtained on Shimadzu
UV-3150 spectrophotometer. Monochromatic light through
filters (Edmund Optics Inc.) from a 500W Xe arc lamp
(USHIO 500-DKO) was used for photochemical reactions.
Interference filters were used for ca. 10 mW monochromatic
lights (-max = 550 and 610 nm). Long pass filters of 630 nm
and IR short path filters were used for monochromatic light
(-max = 640 nm). Irradiation photon intensity was measured
with an ADCMT 8230 optical power meter (ADC Corpora-
tion). The reaction products were analyzed by Shimadzu QP-
2010 GC-MS spectrometer.
Photochemical Reaction Using GaIIITPP without Clay.
The concentrations of GaIIITPP as a sensitizer, cyclohexene as
a substrate and Na2[PtIVCl6] as an electron acceptor were 1.0 ©
10¹5, 1.0 © 10¹1, and 5.0 © 10¹4 M (M = mol L¹1), respec-
tively. The solvent was 5 mL water-acetonitrile (30/70 (v/v)).
The sample solution was added to a 1 © 1 © 4 cm quartz cell
sealed with a septum cap. The oxygen in sample solution was
removed by nitrogen bubbling for 30 min in the dark at room
Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan | 579

3.5
3
temperature. Monochromatic light (-max = 550 nm) was irra-
diated to the stirred sample through a 4 cm light path. The
photochemical reaction was monitored with a UV-visible
spectrometer through a 1 cm light path. The reaction mixture
after the photochemical reaction was vacuum-distilled, and
the products were analyzed by GC-MS spectrometer. Mono-
chromatic light (-max = 640 nm) was used for the subsequent
photochemical reaction sensitized by altered GaIIITPP.
GaIIITPP
excited at 550 nm
416
[PtIVCl6]2-
0
B-band
2.5
2
Q-band
551
× 10
1.5
1
638
2 min
437
0.5
0
Preparation and Identification of GaIIITMPyP/Clay
Complex.
GaIIITMPyP/clay complex was prepared by
250
350
450
550
650
mixing porphyrin and clay in solution. Adsorption of porphyrin
on clay was identified judging from an absorption spectral shift
of porphyrin on the clay.28 The concentration of porphyrin was
1.0 © 10¹5 M. The adsorption densities of porphyrin on the
clay surface were controlled by the clay concentrations. The
loading levels of porphyrin were 20, 40, and 60% vs. CEC of
Wavelength / nm
Figure 3. The absorption spectral change of the photoreac-
tion mixture sensitized by GaIIITPP. [GaIIITPP] = 1.0 ©
10¹5 M. [cyclohexene] = 1.0 © 10¹1 M. [Na2PtIVCl6] =
5.0 © 10¹4 M. The solvent was water-acetonitrile (30/70
(v/v)). Irradiation time (-max = 550 nm) was 0, 0.33, 0.67,
1, 1.33, 1.67, 2, 3, 4, 5, 7, 10, 15, and 20 min.
¹1
clay in 2.0 © 10¹4, 1.0 © 10¹4, and 6.7 © 10¹5 equiv L clay
dispersion, respectively. At all loading levels, GaIIITMPyP was
adsorbed on the clay without aggregation according to absorp-
tion spectra.
H
H
H
Cl
Cl
Cl
Cl
- e−
Cl−
Cl−
H
H
Photochemical Reaction Using GaIIITMPyP/Clay Com-
plex. The concentrations of porphyrin, substrate, and electron
acceptor, the volumes of solvent and optical cell, and the
methods of optical measurement and product analysis were
same as those in the investigation without clay. Monochromatic
light (-max = 550 nm) was irradiated to the sample. Mono-
chromatic light (-max = 610 nm) was used for the subsequent
photochemical reaction sensitized by altered GaIIITMPyP.
[PtIVCl6]2-
H
Ar
Ar
Ar
HO
N III
N Ga
N
H
H
Without clay
N
Cl
H
- e−
Cl−
Ar
- H+
H
H
[PtIVCl6]2-
With clay
Figure 4. Proposed decomposition reaction for porphyrin
cation radical with and without clay.
Results and Discussion
Photocatalytic Reaction Sensitized by GaIIITPP without
Clay. Photochemical chlorination and oxygenation reaction of
cyclohexene sensitized by GaIIITPP without clay was examined
by irradiating visible light (-max = 550 nm). As a result, the
photochemical reaction proceeded according to the change of
absorption spectra of GaIIITPP and [PtIVCl6]2¹. The electron-
transfer reaction to [PtIVCl6]2¹ would be from not excited
singlet state GaIIITPP but excited triplet state judging from the
fact that porphyrin could react with a small amount of electron
acceptor. During the photoirradiation, B-band at 416 nm and Q-
band at 551 nm of GaIIITPP decreased and disappeared after
2 min irradiation (Figure 3). And, the quantum yield (ΦeT) for
the electron transfer from excited GaIIITPP to [PtIVCl6]2¹ was
clay is shown in Figure 4. On the other hand, [PtIVCl6]2¹
was consumed slightly with the decomposition of GaIIITPP
(shown as dotted arrow in Figure 3). The oxidative products
of cyclohexene in the photoreaction mixture were almost not
observed by GC-MS; the total concentration of photoproduct
was 0.5 © 10¹5 M at 7 min irradiation (Table 1). The product
was not formed by a catalytic process with GaIIITPP because
the turnover number (TON), that is molar number of oxidative
products of cyclohexene until 1 mol photocatalyst is decom-
posed, was about 0.6. These results suggest that most porphyrin
cation radical [GaIIITPP]•+ produced by photoinduced electron-
transfer reaction was decomposed without participating in a
catalytic cycle.
¹2
estimated to be 4 © 10 from the irradiation photon intensity
The further photochemical reaction sensitized by the chlorin-
like photolyte of GaIIITPP was also examined by irradi-
ating visible light (-max = 640 nm). [PtIVCl6]2¹ was slightly
consumed and chlorin-like porphyrin decomposed gradually
by 180 minutes irradiation as shown in Figure 5. And, the
quantum yield (Φ¤eT) for the electron transfer from the excited
photolyte of GaIIITPP to [PtIVCl6]2¹ judging from the decrease
and the decreased amount of [PtIVCl6]2¹ absorption at 2 min
irradiation. The ΦeT value is rough and it is difficult to esti-
mate an exact value because the absorption spectra of photo-
lyte of porphyrin were superimposed some what on those of
[PtIVCl6]2¹. The absorption spectra of reaction mixture did
not change by air exposure after irradiation. Judging from its
absorption spectra (-max = 437 and 638 nm), the photolyte of
GaIIITPP was supposed to be chlorin derivative in which one
β-pyrrole position of porphine macrocycle becomes a single
bond.29-32 The decomposition of porphyrin would be due to an
¹2
of [PtIVCl6]2¹ absorption was estimated to be 1 © 10 at 10
min irradiation. The additional total photochemical oxygenated
product in subsequent irradiation was 0.7 © 10¹5 M (= (1.2 ¹
0.5) © 10¹5 M) (Table 1). The TON value was about 3. These
results indicate that the chlorin-like porphyrin also acts as a
sensitizer for the photochemical chlorination and oxygenation.
¹
addition of chloride anion (Cl ) to a β-pyrrole position of its
cation radical ([GaIIITPP]•+). This speculation is supported by
the fact that the decomposition of GaIIITPP was suppressed
Photocatalytic Reaction Sensitized by GaIIITMPyP4+
/
¹
by the addition of AgNO3 as quencher of Cl (not shown). The
Clay Complex. Photochemical chlorination and oxygenation
reaction of cyclohexene sensitized by GaIIITMPyP-clay com-
proposed producing scheme of Cl-adducts of porphyrin without
580 | Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan

Table 1. Products of Photochemical Chlorination and Oxygenation Reaction of Cyclohexene Sensitized by GaIIITPP and [GaIIITMPyP]-
Clay Complexa)
Products/10¹5 M
Irradiation
OH
Cl
OH
O
O
Sensitizer
Cl
Cl
Total
yield
Power/mW
(-max/nm)
Time
/min
trans
trans
cis
GaIIITPP
0
0
0.1
0.5
0
0
0.1
0.3
0
0
0.5
1.5
0.2
0.1
0.2
1.2
0.1
0.1
0.4
3.2
0.2
1.0
2.7
0.5
1.2
4.0
8.3 (550)
4.1 (640)
8.1 (550)
8.5 (610)
7
+180
40
GaIIITPP (photolyte)
[GaIIITMPyP]-clay
[GaIIITMPyP]-clay (photolyte)
27.0
33.7
+220
¹1
a) [GaIII porphyrin] = 1.0 © 10¹5 M, [Na2PtIVCl6] = 5.0 © 10¹4 M, [cyclohexene] = 1.0 © 10¹1 M, [clay] = 2.0 © 10¹4 equiv L
.
Visible light for porphyrins (550 nm) was irradiated first. Subsequently, other visible lights for the photolytes of GaIIITPP and
GaIIITMPyP were irradiated at 640 and 610 nm, respectively. The solvent was 5 mL water-acetonitrile (30/70 (v/v)). The product
values of porphyrin photolyte are the sum of products obtained in first and subsequent irradiation.
3.5
3
3.5
3
[GaIIITMPyP]-clay (20% vs. CEC)
Photolyte of GaIIITPP
excited at 640 nm
425
[PtIVCl6]2-
[PtIVCl6]2-
excited at 550
0
553
615
2.5
2
2.5
2
428
40 min
B-band
Q-band
× 10
1.5
1
1.5
1
638
B-band
Q-band
× 10
437
0.5
0
0.5
0
250
350
450
Wavelength / nm
550
650
250
350
450
550
650
Wavelength / nm
Figure 6. The absorption spectral change of the photo-
reaction mixture sensitized by GaIIITMPyP-clay com-
plex. The loading level was 20% vs. CEC of clay.
Figure 5. The absorption spectral change of the photo-
reaction mixture sensitized by the photolyte of GaIIITPP
that would be Cl-adducts of porphyrin. [GaIIITPP] = 1.0 ©
10¹5 M. [cyclohexene] = 1.0 © 10¹1 M. [Na2PtIVCl6] =
5.0 © 10¹4 M. The solvent was water-acetonitrile (30/70
(v/v)). Irradiation time (-max = 640 nm) was 0, 1, 10, 30,
90, and 180 min.
[GaIIITMPyP] = 1.0 © 10¹5 M.
[cyclohexene] = 1.0 ©
10¹1 M. [Na2PtIVCl6] = 5.0 © 10¹4 M. [clay] = 2.0 ©
10¹4 equiv L¹1. The solvent was water-acetonitrile (30/
70 (v/v)). Irradiation time (-max = 550 nm) was 0, 1, 2, 5,
10, 15, 20, 25, 30, 35, and 40 min.
plex was examined by irradiating visible light (-max = 550 nm).
Although the photochemical reaction proceeded along with
GaIIITPP, some differences from GaIIITPP were observed. Under
the condition of 20% dye loading versus CEC of clay, during
the photoirradiation, the absorption of GaIIITMPyP decreased
more slowly than that of GaIIITPP as shown in Figure 6. And,
most of the B-band of GaIIITMPyP was preserved even after
40 min irradiation in contrast to complete decomposition of
GaIIITPP after 2 min irradiation. The quantum yield (ΦeT) for
the electron transfer from the excited GaIIITMPyP to [PtIVCl6]2¹
derivatives but Cl-substitutions of porphyrin.33,34 This result
suggests the attack of Cl to porphyrin cation radical should
¹
be suppressed or controlled by anionic clay surface sterically
and electrically and the proton dissociation from porphyrin
cation radical might proceed, leading to Cl-substitutes of por-
phyrin (Figure 4). On the other hand, [PtIVCl6]2¹ was consumed
somewhat on its absorption. And the total concentration of
photochemical oxygenated product was 4.0 © 10¹5 M at 40 min
irradiation (Table 1). The TON value was about 30. These
results indicate that the GaIIITMPyP-clay complex has a higher
catalytic ability compared to GaIIITPP.
¹2
was estimated to be 3 © 10 at 2 min irradiation. From these
results, it was suggested that GaIIITMPyP-clay complex was
more stable in the photochemical reaction than GaIIITPP without
clay. During the 40 min photoirradiation, the B-band at 425 nm
and Q-band at 553 nm of GaIIITMPyP decreased and new B-
band at 428 nm and Q-band at 615 nm were superimposed on
the spectra (Figure 6). The absorption wavelength and spectral
shape of the new species were different from those of the
photolyte of GaIIITPP. These results indicate that the observed
species maintained most of its own porphyrin π-conjugated
system. Judging from absorption wavelength and spectral
shape, the species on clay was expected to be not chlorin
Next, the photoreaction sensitized by the photolyte of
GaIIITMPyP on clay was also examined irradiating visible
light (-max = 610 nm). Interestingly, [PtIVCl6]2¹ was complete-
ly consumed by 220 min irradiation on the absorption spectra
(Figure 7). And, the quantum yield (Φ¤eT) for the electron trans-
fer from the excited photolyte of GaIIITMPyP to [PtIVCl6]2¹ was
¹2
estimated to be 1 © 10 at 10 min irradiation. The additional
total photochemical oxygenated product in subsequent irradi-
ation was 29.7 © 10¹5 M (= (33.7 ¹ 4.0) © 10¹5 M) (Table 1).
Considering both the first and subsequent irradiations, total
products by GaIIITMPyP-clay complex were 28 times those by
Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan | 581

3.5
3
GaIII Porphyrin-clay Hybrid Photocatalyst
Photolyte of [GaIIITMPyP]-clay (20% vs. CEC)
excited at 610 nm
[PtIVCl6]2-
Stirring
Static
2.5
2
B-band
428
615
Q-band
1 min
0
× 10
Quasi-
homogeneous
photocatalyst
Separating of
photocatalyst
1.5
1
220 min
0.5
0
Reaction
mixture
Photocatalyst
250
350
450
Wavelength / nm
550
650
Figure 8. The appearance of photoreaction mixture sensi-
tized by the altered GaIIITMPyP-clay complex with and
without stirring.
Figure 7. The absorption spectral change of the photo-
reaction mixture sensitized by the photlyte of GaIIITMPyP
that would be Cl-substitutes of porphyrin. The loading
level was 20% vs. CEC of clay. [GaIIITMPyP] = 1.0 ©
10¹5 M. [cyclohexene] = 1.0 © 10¹1 M. [Na2PtIVCl6] =
5.0 © 10¹4 M. [clay] = 2.0 © 10¹4 equiv L¹1. The solvent
was water-acetonitrile (30/70 (v/v)). Irradiation time
(-max = 610 nm) was 0, 10, 20, 40, 60, 80, 100, 120,
120, 140, 160, 180, 200, and 220 min.
GaIIITPP without clay. This mixture of dye-clay complex is
useful for photoreaction because the clay dispersion is trans-
parent in UV-visible range. And, they behaved as heterogene-
ous and the product mixture and precipitated catalyst could be
separated when the reaction mixture was stored without stirring
(Figure 8). The separation of product mixture and photocatalyst
is useful for systemization of the photoreaction because it is
possible to extract products and add reactants over again.
GaIIITPP. The TON value reached about 80. Moreover, the
photolyte of GaIIITMPyP was stable and not completely
decomposed by subsequent irradiation as shown in Figure 7.
These results indicate that the photolyte of GaIIITMPyP-clay
complex also has a higher catalytic ability than that of GaIIITPP.
It is suggested that there are some types of Cl-substitutions
of GaIIITMPyP and that the substitution of Cl into porphyrin
macrocycle occurred continuously with proceeding of photo-
reaction because some changes of the absorption spectra of
Q-band were observed (Figures 6 and 7).
Conclusion
Photochemical chlorination and oxygenation reactions of
cyclohexene sensitized by gallium(III) porphyrin without clay
and cationic gallium(III) porphyrin-anionic clay complex were
investigated. In a homogeneous system without clay, porphyrin
as photocatalyst decomposed immediately in the photoreac-
tion and the altered porphyrin did not have photocatalytic
ability. On the other hand, porphyrin molecule complexed with
clay was more stable than that without clay. Additionally, the
altered porphyrin with clay maintained its own π-conjugation
system and also had catalytic ability along with original
porphyrin. These results were expected to be due to steric and
electric protection of porphyrin cation radical from chloride
anion by clay surface. Moreover, the protection of porphyrin
and photochemical reaction efficiency did not change even
under high porphyrin adsorption conditions on clay. These
results were expected to be due to adsorption behavior of
porphyrin molecules on the clay surface without aggregation.
The porphyrin-clay complex could catalyze the photochemical
reaction well like homogeneous photocatalyst in stirred reac-
tion mixture and could be separated from product mixture like
heterogeneous one without stirring. This behavior allows both
efficient photoreaction and convenient extraction of product.
These findings are beneficial to construct and develop artificial
photochemical systems using the porphyrin-clay hybrid com-
pounds as quasi-homogeneous photocatalysts.
As a result, it is accomplished to improve the efficiency of
the photochemical reaction due to steric and electric protection
effect of photocatalyst by clay nanosheet surface.
Photocatalytic Reaction Using GaIIITMPyP4+/Clay
Complex at Various Loading Levels.
Additionally, the
photocatalytic reactions using GaIIITMPyP-clay complex at
various loading levels of GaIIITMPyP were investigated by
controlling concentrations of clay. Even in increasing adsorp-
tion densities of GaIIITMPyP on the clay surface, their behavior
for the photoreaction were not different. Both of the amounts of
products and the behaviors of decomposition of GaIIITMPyP
were almost the same at 20, 40, and 60% vs. CEC loadings
(Figures S3, S4, S5, and S6). As a result, the quantum yields
for electron transfer from excited GaIIITMPyP (ΦeT) and its
excited photolyte (Φ¤eT) to [PtIVCl6]2¹ were almost constant
¹2
at all dye loadings. The ΦeT and Φ¤eT values were 3 © 10 at
¹2
2 min irradiation and 1 © 10 at 10 min irradiation, respec-
tively. The amounts of the oxidative products of cyclohexene
were also the same regardless of dye loadings (Table S1).
These results indicated that its catalytic ability can be main-
tained and the protection effect of photocatalyst by clay can
be working uneventfully even under high density adsorption
conditions due to nonaggregate array of dye molecules on the
clay surface (Size-matching Effect).8,14-16
This work has been partly supported by a Grant-in-Aid for
Scientific Research (B), a Grant-in-Aid for Scientific Research
on Innovative Areas (2406) and a Grant-in-Aid for JSPS
Research Fellows (No. 263441).
Reusability
of
GaIIITMPyP4+/Clay
Complex.
Supporting Information
GaIIITMPyP-clay complex works like homogeneous photo-
catalyst in stirred reaction mixture due to dispersion of clay
nanosheet and the photoreaction could proceed well along with
The structure of synthetic saponite (Figure S1), the proposed
reaction scheme for the chlorination reactions of cyclohexene
582 | Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan

16 S. Takagi, T. Shimada, Y. Ishida, T. Fujimura, D. Masui, H.
Tachibana, M. Eguchi, H. Inoue, Langmuir 2013, 29, 2108.
17 T. Tsukamoto, T. Shimada, S. Takagi, J. Phys. Chem. A
2013, 117, 7823.
18 T. Tsukamoto, T. Shimada, S. Takagi, J. Phys. Chem. C
2013, 117, 2774.
(Figure S2), the absorption spectral change of the photoreac-
tion mixture sensitized by GaIIITMPyP-clay and its photolyte-
clay complexes at 40 and 60% vs. CEC (Figures S3, S4, S5,
and S6), and the products of photochemical oxygenation reac-
tion of cyclohexene sensitized by GaIIITMPyP and its photolyte
on the clay surface at various dye loadings (Table S1) are
available electronically on J-STAGE.
19 H. Inoue, S. Funyu, Y. Shimada, S. Takagi, Pure Appl.
Chem. 2005, 77, 1019.
20 S. Funyu, T. Isobe, S. Takagi, D. A. Tryk, H. Inoue, J. Am.
Chem. Soc. 2003, 125, 5734.
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Bull. Chem. Soc. Jpn. 2015, 88, 578–583 | doi:10.1246/bcsj.20140378
© 2015 The Chemical Society of Japan | 583