Preparation of copper complexes coordinated by N21,N22-etheno bridged porphyrin and the application to photooxidation of phenol derivatives

Article abstract of DOI:10.1142/S1088424615500583

Copper(I) complexes coordinated with a N²¹,N²²-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N²¹,N²²-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.

Full text of DOI:10.1142/S1088424615500583

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2015; 19: 1–8
DOI: 10.1142/S1088424615500583
Published at http://www.worldscinet.com/jpp/
Preparation of copper complexes coordinated
by N21,N22-etheno bridged porphyrin and the application
to photooxidation of phenol derivatives
Yuko Takao*a◊, Fukashi Matsumotoa, Kazuyuki Moriwakia, Takumi Mizunoa,
Toshinobu Ohnoa and Jun-Ichiro Setsune*b
a Osaka Municipal Technical Research Institute, Joto-ku, Osaka 536-8553, Japan
b Department of Chemistry, Graduate School of Science, Kobe University, Nada-ku, Kobe 657-8501, Japan
Received 2 May 2014
Accepted 19 March 2015
ABSTRACT: Copper(I) complexes coordinated with a N21,N22-etheno bridged porphyrin ligand
were synthesized as a unique coordination structure. The copper porphyrin complexes promoted
photooxidations of a phenol derivative in organic solution under aerobic condition with visible
photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper
porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a
phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the
reaction. The structural study found that the active species contributing to the photooxidation reaction
was the di(m-hydroxo)dicopper(II) complex of N21,N22-etheno bridged porphyrin generated by oxidation
of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous
condition.
KEYWORDS: bridged porphyrin, copper complex, photooxidation, phenol derivative, heterogeneous
reaction.
derivatives, photooxidation method using a singlet
INTRODUCTION
oxygen photosensitizer is regarded as a friendly process
Oxidation of phenol derivatives is of special interest
for environment compared with other chemical oxidation.
because the oxidized products of phenol derivatives
It uses minimum harmful chemicals, and utilizes oxygen
have various industrial applications. For example,
from air and visible light having the largest energy
benzoquinone derivatives are known to be precursors of
density in solar radiation as unlimited natural resources
Vitamin E and other medicines, and they are important
[1, 5, 6c]. Further, immobilizations of photosensitizers on
specialty chemicals in the pharmaceutical and dye
solid supports have been attempted to increase utility of
industries [1, 2]. On the other hand, some phenol deriva-
the photosensitizers [2]. Heterogeneous reaction allows
tives such as chlorinated or p-alkylated phenols are
for easy separation of products and sensitizers, which is
known to resist from biodegradation and accumulate in
an advantage from the viewpoint of easier isolation of
the environment, so sustainable methods of oxidative
the products in the case of photochemical synthesis. In
decomposition for the wastewater treatment are needed
the situation of the wastewater treatment, immobilization
[3, 4]. Among several methods for oxidation of phenol
means that insoluble photosensitizers provide the reaction
sites in aqueous solution, and the recovery and re-use of
photocatalysts become more convenient. Immobilization
◊ SPP full member in good standing
also has an advantage to decrease quenching of
photosensitizers by singlet oxygen.Although a number of
examples about the photooxidations have been reported
*Correspondence to:Yuko Takao, email: yuktakao@omtri.or.jp,
fax: +81 6-6963-8049; Jun-ichiro Setsune, email: setsunej@
kobe-u.ac.jp, fax: +81 78-803-5770
Copyright © 2015 World Scientific Publishing Company

2
Y. TAKAO ET AL.
in which the photosensitizers are classic dyes such as
Methylene Blue and Rose Bengal, it is a problem for the
sensitizers to be photodegraded upon long irradiation.
Thus it is important to develop efficient and stable
photosensitizers.
probably because the OH ligand of the Pd2(OH)2 core of
the bidentate porphyrin complex acted as a base.
This time, we prepared copper complexes coordinated
by the N21,N22-etheno bridged porphyrins as unique
bidentate ligands. Copper is not so expensive metal, and
its complexes have been known as practical catalysts for
hydrolysis or a variety of carbon–carbon bond forming
reactions [12]. While copper complexes of porphyrins
have been studied variously from structural, and
physicochemicalpointsofview[13],recentlyapplications
of the complexes have been reported as photocatalysts
[14]. Then here we describe the preparation and structure
of the copper complexes with the N21,N22-etheno
bridged porphyrin ligands, application of the complex
as a photosensitizer in oxidation of phenol derivatives,
and further the behavior and effect of the complex as a
photocatalyst in heterogeneous reaction.
Porphyrin derivatives are candidates of excellent
photosensitizer for the photooxidation of various
substrates, while several catalytic oxidations using
porphyrinoid complexes have been studied also
including usage of strong oxidants [3, 5, 7]. Burrows
and co-workers have investigated photooxidations
of phenolic derivatives and reported that porphyrin
derivatives well photosensitized such reactions leading
to formation of the corresponding quinones [1a, 6].
They proposed the reaction process involving formation
of singlet oxygen as one of the dominant mechanisms
and suggested the contribution of also photostability of
the photosensitizers. Then much effort has been made
to develop effective photooxidations of phenols using
photochemical characteristics of porphyrins [4, 5, 8].
We have investigated the coordination chemistry and
organometallic chemistry of palladium complexes of
N21,N22-etheno bridged porphyrin [9], which played
a role of bidentate ligand, strongly coordinated to
metal, and influenced the dynamic behavior of the
coexisting ligand [10]. Then, we have already reported
the properties and application of unique m-(dihydroxo)
dipalladium(II) complex with N21,N22-etheno porphyrin
ligand that can be used as a photosensitizer in oxidation
of phenol derivatives [11]. The reaction proceeded under
mild conditions in neutral solution at room temperature,
RESULTS AND DISCUSSION
Copper complexes with N21,N22-etheno bridged
porphyrin ligand were prepared by reactions of N21,N22-
etheno bridged porphyrin monoprotonated form with
excess amount of Cu(I) reagent at room temperature
(Scheme 1). Monoprotonated N21,N22-(diphenyletheno)
octaethylporphyrin (2) was allowed to react with [Cu(I)
(CH3CN)4]PF6 (5 equiv.) in CH2Cl2 at room temperature
underargonforonedaytoaffordN21,N22-(PhC=CPh)(OEP)
Cu(I)PF6 (3a). N21,N22-(PhC=CPh)(OEP)Cu(I)ClO4 (3b)
was prepared by the reaction of 2 with [Cu(I)(CH3CN)4]
N
Ph
N
N
N
HN
N
N
Ph
N
N
ii)
iii)
Ph
N
Ph
Cu
NH
HN
-
ClO4
X-
OEP
i)
2
3a: X = PF6
3b: X = ClO4
Ph
Ph
N
N
N
N
Ph
N
N
N
Ph
N
N
Cu(MeCN)4PF6
Ph
Ph
Ph
Ph
Cu
Ph
HN
Ph
N
Cu
Ph
N
-
-
ClO4
PF6
Ph
1
3c
2c
Reagent: i) Cu(OAc)2, ii) Co(OAc)2, FeCl3, Ph
Ph, HClO4, iii) Cu(MeCN)4X
Scheme 1. Preparation of copper(I) complexes with porphyrin or N21,N22-(diphenyletheno) bridged porphyrin derivatives
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 2–8

PREPARATION OF COPPER COMPLEXES COORDINATED BY N21,N22-ETHENO BRIDGED PORPHYRIN
3
and co-workers [16]. This elongation suggests p–back
donation from a d-orbital of Cu to the anti-bonding
molecular orbital of the ethylene moiety. On the other
hand, recrystallization of 3b in a mixture of CH2Cl2 and
MeOH at ambient temperature promoted air-oxidation
to generate crystals of di(m-hydroxo)dicopper(II)
diporphyrin 4b in 64% yield. The X-ray crystallography
of 4b revealed a Cu2(OH)2 diamond core where Cu(II) is
ligated by two pyrrolenine nitrogens and two hydroxyl
oxygens with the Cu–N distances of 1.974(2) and
1.988(2) Å and the Cu–O distances of 1.927(2) and
1.916(3) Å (Fig. 2b) [15].
Fig. 1. UV-vis spectra of 2 and 3a in acetonitrile
The efficiencies of the Cu(I) complexes of N21,N22-
etheno bridged porphyrins (3) as photosensitizers were
evaluated in the photooxidation of 2,6-di-tert-butylphenol
(DBP). When the acetonitrile solution of DBP (3 mM)
containing 3a (0.3 mM) was irradiated with visible
light by a xenon lamp (350 nm < l < 800 nm) under
air, only 2,6-di-tert-butyl-1,4-benzoquinone (DBQ) was
formed selectively as an initial oxidized product, which
1
has been proven by H NMR chemical shifts of the
product in comparison with those of the authentic sample
[11b]. Table 1 shows the activity of photosensitizers as
1
estimated by the DBQ yields, determined by H NMR
spectra. Then 80% conversion from DBP to DBQ was
observed after 90 min photoirradiation with addition
of 3a. The photooxidation never proceeded in the
absence of porphyrins, and addition of 3a to deaerated
solution resulted in no conversion of DBP after 90 min
photoirradiation. And 50 min photoirradiation in the
presence of 3b afforded 64% conversion of DBP, while
only 7% of DBP changed without photoirradiation.
While the efficiency of TPP derivative (3c) was not very
Fig. 2. Ortep drawings with 50% level thermal ellipsoids of 3b
(a) and 4b (b). Counter ions (ClO4-), solvent molecules, and all
hydrogen atoms are omitted for clarity
ClO4. A TPP analog, N21,N22-(PhC=CPh)(TPP)Cu(I)PF6
(3c) was prepared similarly. Figure 1 shows the UV-vis
spectra of 2 and 3a in acetonitrile. The intense Soret band
in the UV-vis spectrum of 3a showed bathochromic shift
from 401 nm for 2 to 412 nm, and three weak absorptions
at 535, 569 and 615 nm in the Q-band region for 2 were
split into four absorptions at 536, 569, 578 and 612 nm for
3a. The MALDI TOF-MS spectrometry of 3a showed a
peak at 773.3584 that is in good agreement with the theory
(773.3644 for [M-PF6]+).
Table 1. Efficiency in photooxidation of DBP with
photosensitizers under visible light irradiationa
Dye
[DBP], mM
Time, min
Conv., %
—
3a
3a
3a
3b
3b
4b
3c
3
40
90
90
50
50
50
50
50
50
50
50
0
80
0b
3
3
Recrystallization of Cu(I) complex of N21,N22-etheno
bridged porphyrin 3b from a mixture of Et2O and CH2Cl2
with a small amount of MeOH in a refrigerator gave flaky
single crystals. X-ray crystallography of 3b showed that
a copper atom was placed out of the porphyrin plane
and existed between the double bond of the N21,N22-
(PhC=CPh) bridge moiety and two imine nitrogen
atoms, N23 and N24, with the Cu–C(bridge) distance of
1.934(3) and 1.937(3) Å, and the Cu–N(imine) distance
of 1.858(3) and 1.859(3) Å (Fig. 2a) [15]. The length of
the double bond of the etheno bridge was 1.409(5) Å
and longer than that of N21,N22-diphenyletheno bridged
tetraphenylporphyrin monoprotonated form [N21,N22-
(PhC=CPh)(TPP)HClO4] (1.333 Å) reported by Callot
2
58
7c
2
2
64
61
55
86
52
22
2
2
2
2
OEP
1
2 d
2 e
a Photoirradiation (350 nm < l < 800 nm) of DBP
in acetonitrile in the presence of 10 mol% of dye.
b O2 was removed by Ar bubbling. c Not irradiated.
d Solvent contains 10% CH2Cl2. e In CH2Cl2.
Copyright © 2015 World Scientific Publishing Company
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Y. TAKAO ET AL.
Ph
Ph
N
N
N
N
-
2ClO4
N
Ph
N
N
Cu
HO
O2
OH
Ph
N
Cu
Cu
-
ClO4
N
N
N
N
3b
Ph
Ph
N
N
N
N
OEP
4b
Fig. 3. Change in visible spectrum at Q-band of 3a (2.2 × 10-4 M)
in acetonitrile with time through the visible light irradiation with
a 500-W xenon lamp
Scheme 2. Generation of active species from bidentate
porphyrin Cu complex in photooxidation system
bridged porphyrin in 5 mol% catalyzes photooxidation
of DBP to DBQ in 96% yield when irradiated for 60 min
[11b]. This Pd complex shows the higher photocatalytic
activity than 3a.
different from those of OEP derivatives under the same
condition, N21,N22-etheno bridged porphyrin structure
seemed to afford higher conversion than ordinary
tetradentate Cu(II) porphyrin (1) and free base OEP.
This would be partly because of the photostability, since
it was confirmed that Pd complex of N21,N22-etheno
bridged porphyrin was more photostable than the free
base porphyrin and Pd complex of normal porphyrin
[11]. In this reaction N21,N22-etheno bridged porphyrin
monocation (2) afforded higher conversion than Cu(I)
complex of the bridged porphyrin. Although the
oxidation activity of 2 and OEP may be ascribed to the
photosensitized formation of singlet oxygen, the Cu(I)
complexes seem to act in a different manner.
To elucidate the mechanism of these photooxidation
catalyzed by the Cu(I) complex of N21,N22-etheno bridged
porphyrin, the UV-vis spectral change of 3a through
photoirradiation in the absence of phenol derivatives
was monitored in acetonitrile under the standard reaction
condition. Four peaks at 536, 566, 577 and 610 nm in
the Q-band region of 3a were red-shifted to 543, 568,
585 and 614 nm with time (Fig. 3). The resulting spectral
pattern with the second lowest energy band in the Q-band
region specifically decreased is in accord with the UV-vis
spectral pattern of 4b. So it is considered that Cu(I)
porphyrin complex of N21,N22-bridged porphyrin was
photooxidized to di(m-hydroxo)dicopper(II) complex in
acetonitrile solution under aerobic condition (Scheme 2).
Then in this case, it is presumed that the photooxidation
of phenol derivative using 3b was promoted by di(m-
hydroxo)dicopper(II) complex of N21,N22-bridged por-
phyrin as an active species formed in the photoreaction
system. In fact, 4b showed very similar reactivity for the
photooxidation of DBP (61%) to that of 3b under the
same reaction conditions. The catalytic activity of some
di(m-hydroxo)dicopper(II) complexes in the oxidation of
phenols and catechols has been reported in the literature
[17], and also we have previously reported that the di(m-
hydroxo)dipalladium(II) complex of N21,N22-etheno
The photocatalytic activity of the Cu complexes in
heterogeneous reaction was also studied in photooxidation
of p-n-propylphenol (PNPP) in aqueous solution for
the purpose of application to wastewater treatment. The
photosensitizers were simply adsorbed on silica gel as
support to make composite photocatalysts employed in
aqueous solution. It is expected that the composite gives
active sites for photooxidation of the phenol substrate and
then allows easy recovery. In this way, 0.1 g of a support
was merely immersed in a chloroform solution of a
regular amount of photosensitizer (4 × 10-6 mol), and after
adsorption the solution was evaporated and subjected
directly to the heterogeneous photooxidation in water. So
the composite may include also some amount of free solid
photosensitizer unadsorbed on support depending on their
adsorptive ability. The amount of immobilized sensitizers
on support without desorption is estimated as shown in
Table 2. The adsorptive abilities (4 × 10-5 mol.g-1) of 3a
and 3c on support were higher than those of OEP, (S-Pc)Cu
and the monoprotonated porphyrin 2c. The most part of the
added copper complex of N21,N22-bridged porphyrin was
immobilized on support without desorption in the above-
mentioned protocol for the preparation of photocatalyst
from 3a and 3c. Their adsorptive ability was also higher
than that of di(m-hydroxo)dipalladium(II) bisporphyrin
(2 × 10-5 mol.g-1) evaluated similarly. It was confirmed
that the photosensitizers were not desorbed with water
from the composite by absorption-spectral measurement
of that water.
The aqueous solution of PNPP (1.5 mM) containing
the composite of 3a was irradiated with visible light,
and the photodegradation of PNPP was monitored by
1H NMR spectra. Under the condition the concentration
of PNPP was decreased fast, and the most part was
degraded in 60 min photoirradiation. Figure 4 shows
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PREPARATION OF COPPER COMPLEXES COORDINATED BY N21,N22-ETHENO BRIDGED PORPHYRIN
Table 2. Evaluation of amount of immobilized sensitizers on supporta by UV-vis spectrophotometry
5
Photo-sensitizer Added amount, mol
l
maxb, nm
Absorbance in filtratec Immobilized amount, mol.g-1
3a
3c
4.07 × 10-6
4.01 × 10-6
4.04 × 10-6
4.01 × 10-6
4.07 × 10-6
414
440
433
401
630d
0.235
0.356
0.550
0.651
0.142
4.0 × 10-5
4.0 × 10-5
1.2 × 10-5
2.3 × 10-6
3.3 × 10-5
2c
OEP
(S-Pc)Cu
a 0.04 g of silica gel. b In CHCl3. c CHCl3 solution diluted to 1 L. dAqueous solution.
It is considered that 3a is immediately oxidized to
di(m-hydroxo)dicopper(II) complex of N21,N22-etheno
bridged porphyrin when immobilizing on support and
it played a role of active species from the beginning in
the heterogeneous photoreaction process. The plausible
mechanism in the heterogeneous photooxidation is
shown in Scheme 3. It is considered that the oxidized
Cu(II) complex 4a forms a strong coordination bond with
deprotonatedsilanolgroupofsilicagelinonesiteofCu(II)
with disaggregating. The silica-supported complex (A)
can afford the reaction site for phenol by ligand exchange
to form the phenolate Cu(II) complex (B). The attack of
dioxygen to the aromatic ring of (B) may generate the
alkylperoxide complex (C) by the process of one-step
two-electron transfer to dioxygen or that of two-step
one-electron transfer to dioxygen. Then radical cleavage
of this active intermediate (C) liberates p-benzoquinone
as a main oxidation product with forming the alkoxide
complex (D), from which silica-supported Cu(II) complex
of N21,N22-etheno bridged porphyrin (A) is regenerated
Fig. 4. Heterogeneous photodegradation of PNPP in aqueous
solution with porphyrin complexes on silica gel under visible
light irradiation with a 500-W xenon lamp
the heterogeneous photodegradation of PNPP in
aqueous solution containing the composite made from
various photosensitizers. The results might reflect
the photocatalytic activity of the sensitizers well.
Ph
Ph
N
N
N
N
HO
2PF6
Cu
n-Pr
Ph
OH
Cu
H2O
Ph
HO
Silica gel
N
N
N
N
Ph
O2
Ph
N
N
N
N
Cu
N
N
N
N
OH
Ph
Ph
O
Cu
Si
O
N
Ph
N
N
(A)
(4a)
Ph
N
O
Si
Cu
n-PrOH
(B)
n-Pr
PF6
Ph
Ph
(3a)
O2
H2O
N
N
N
N
Ph
Ph
hn
N
N
N
N
N
N
Cu
N
N
OEP
OPr
O
O
Si
Cu
(D)
O
O
O
Si
n-Pr
(C)
O
O
Scheme 3. Plausible mechanism for the heterogeneous photooxidation reaction
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J. Porphyrins Phthalocyanines 2015; 19: 5–8

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Y. TAKAO ET AL.
by hydrolysis and also the phenolate complex (B) can be
formed by ligand exchange. Besides the catalytic process,
singlet oxygen formed by the sensitizing effect of the
bidentate porphyrin ligand coordinating to the copper
may also contribute to the photooxidation, since there
have been studies on the generation of singlet oxygen
by sensitizers adsorbed on silicagel [2c–2f]. But it is
considered that this heterogeneous reaction depends on
the catalytic mechanism mainly and the adsorptive ability
is an important factor to influence the result. Thus, in
contrast to the homogeneous reaction, the photooxidation
of PNPP with 3a proceeded faster than that with 2 in
the heterogeneous one. Moreover, the photostability
of N21,N22-etheno bridged porphyrin structure seems to
contribute to the efficiency of the photooxidation.
In this system the used photocatalyst can be recovered
through filtration and re-used after washing and drying.
The composite of 3a was little inactivated after three
recycles in the photooxidation of PNPP under the same
condition. So it is important that the copper complex of
N21,N22-etheno bridged porphyrin can be applied in the
heterogeneous photoreaction system with high adsorptive
ability from a viewpoint of practical utilization, and
is therefore significant that the complex can be easily
activated in the preparation process of composite
photocatalyst.
and then the solution was evaporated. Flush column
chromatography of the residue on silica gel with
CH2Cl2-acetone (20:1), followed by recrystallization of
the main fraction from CH2Cl2 with n-hexane gave 3a
1
(4.2 mg) in 37% yield. H NMR (300 MHz, CDCl3): d,
ppm 11.07, 10.34, (s × 2, 1H × 2, meso-H); 10.47 (s,
2H, meso-H); 6.19 (t, 2H, bridge Ph-p-H); 5.86 (t, 4H,
bridge Ph-m-H); 3.33 (br, 4H, bridge Ph-o-H); 4.41–3.99
(m, 16H, CH2CH3); 1.94, 1.79, 1.72, 1.48 (t × 4, 6H × 4,
CH2CH3). HRMS (MALDI-TOF): m/z 773.3584 (calcd.
for [C50H54N4Cu]+ 773.3644). MS (MALDI-TOF): m/z
144.81 (calcd. for [PF6]- 144.96). UV-vis (MeCN): lmax
,
nm (log e) 612 (3.82), 578 (4.01), 569 (3.99), 536 (3.95),
412 (5.06).
Preparation of copper(I) N21,N22-(diphenyletheno)
octaethylporphyrin perchlorate (3b). Monoprotonated
form 2 (25 mg, 0.031 mmol) was allowed to react with
[Cu(I)(CH3CN)4]ClO4 (98 mg, 0.31 mmol) in CH2Cl2
(10 mL), and the reaction mixture was worked up in a
similar manner as the case of 3a. Recrystallization from
CH2Cl2 with diethyl ether gave 3b (25 mg) in 94% yield.
1H NMR (300 MHz, CDCl3): d, ppm 11.17, 10.34, (s
× 2, 1H × 2, meso-H); 10.47 (s, 2H, meso-H); 6.19 (t,
2H, bridge Ph-p-H); 5.86 (t, 4H, bridge Ph-m-H); 3.31
(br, 4H, bridge Ph-o-H); 4.47–3.94 (m, 16H, CH2CH3);
1.93, 1.78, 1.73, 1.47 (t × 4, 6H × 4, CH2CH3). HRMS
(MALDI-TOF): m/z 773.3666 (calcd. for [C50H54N4Cu]+
773.3644). MS (MALDI-TOF): m/z 98.93 (calcd. for
[ClO4] - 98.95). UV-vis (CH2Cl2): lmax, nm (log e) 612
(3.87), 577 (4.07), 567 (4.06), 537 (4.01), 413 (5.18).
Preparation of copper(I) N21,N22-(diphenyletheno)
tetraphenylporphyrin hexafluorophosphate (3c).
Monoprotonated N21,N22-(diphenyletheno)tetraphenyl-
porphyrin 2c (10 mg, 0.011 mmol) was allowed to react
with [Cu(I)(CH3CN)4]PF6 (14 mg, 0.04 mmol) in CH2Cl2
(10 mL), and reaction mixture was treated in a manner
analogous to that described above. Recrystallization from
CH2Cl2 with n-hexane gave 3c (3.0 mg) in 27% yield.
1H NMR (300 MHz; CDCl3): d, ppm 9.04, 9.00, 8.70,
8.54 (d × 2, 2H × 4, pyrrole-b-H); 8.79–7.62 (m, 20H,
meso-Ph-H); 6.38 (t, 2H, bridge Ph-p-H); 6.05 (t, 4H,
bridge Ph-m-H); 3.42 (br, 4H, bridge Ph-o-H). HRMS
(MALDI-TOF): m/z 853.2441 (calcd. for [C58H38N4Cu]+
853.2392). MS (MALDI-TOF): m/z 144.81 (calcd. for
[PF6]- 144.96). UV-vis (CH2Cl2): lmax, nm (log e) 635
(3.71), 596 (4.13), 556 (4.03), 441 (5.14).
EXPERIMENTAL
General
(Octaethylpophyrinato)Cu(II) (1) and N21,N22-etheno
bridged porphyrin (2) were prepared by the modified
literature methods [18, 19]. [Cu(I)(CH3CN)4]ClO4 was
prepared in the usual way [20]. Solvents were purified
prior to use by conventional methods. Deuterated
solvents, [Cu(I)(CH3CN)4]PF6, copper(II) phthalocyanine-
3,4′,4′′,4′′′-tetrasulfonic acid tetrasodium salt [(S-Pc)
Cu(II)] and other chemicals were of reagent grade.
1H-NMR spectra were recorded using a JEOL AL-300
spectrometer (300 MHz) at room temperature. Chemical
shifts were reported in ppm with respect to the reference
frequency of TMS (in CDCl3 and CD3CN) and TSP (in
D2O). MALDI-TOF-MS measurements were performed
on a Shimadzu AXIMA Confidence mass spectrometer.
The UV-visible spectra were measured on a Shimadzu
UV-3100B instrument.
Oxidation of 3b to di(m–hydroxo)dicopper(II)
bis[N21,N22-(diphenyletheno)octaethylporphyrin]
bis(perchlorate) (4b).Copper(I) N21,N22-(diphenyletheno)
octaethylporphyrin perchlorate 3b (9.8 mg, 0.011 mmol)
was recrystallized from CH2Cl2 and MeOH overnight to
give the CuII complex 4b (6.0 mg) in 60% yield. 1H NMR
(300 MHz; CDCl3): d, ppm 11.43, (br, 2H, meso-H); 7.83
(br, 6H, meso-H); 6.38, 5.61 (br × 2, 4H × 2, Ph-m-H);
5.72 (t, 4H, Ph-p-H); 5.17, 4.87 (br × 2, 4H × 2); 5.02 (s,
2H); 4.34, 3.66 (br × 2, 8H × 2); 4.13, 3.10 (br × 2, 4H ×
2); 2.03, 1.53, 1.26, 0.71 (br × 4, 12H × 4, CH2CH3). MS
Synthesis
Preparation of copper(I) N21,N22-(diphenyletheno)
octaethylporphyrin hexafluorophosphate (3a). Mono-
protonated N21,N22-etheno bridged octaethylporphyrin 2
(10 mg, 0.012 mmol) was allowed to react with [Cu(I)
(CH3CN)4]PF6 (18 mg, 0.05 mmol) in CH2Cl2 (5 mL) at
room temperature under argon in the dark for one day,
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J. Porphyrins Phthalocyanines 2015; 19: 6–8

PREPARATION OF COPPER COMPLEXES COORDINATED BY N21,N22-ETHENO BRIDGED PORPHYRIN
7
(MALDI-TOF): m/z 790.06 (calcd. for [C50H55N4OCu]+
790.37). UV-vis (CH2Cl2): lmax, nm (log e) 618 (3.96), 588
(4.15), 573 (4.17), 547 (4.15), 419 (5.19).
CONCLUSION
N21,N22-etheno bridged porphyrins were metallated by
Cu(I) reagent owing to the formation of the Cu(I)-alkene
p-bonding in addition to the ligation of two pyrrole
nitrogens. X-ray crystallography of the Cu(I) porphyrin
demonstrated unusually short Cu–C and Cu–N distances
and very long C–C double bond. Aerial oxidation of the
Cu(I) porphyrin was promoted in MeOH to give di(m-
hydroxo)dicopper(II) complex. The copper porphyrin
complexespromotedphotooxidationofaphenolderivative
inacetonitrilesolutionunderaerobicconditionwithvisible
light irradiation. It is considered that the active species
in the photooxidations were di(m-hydroxo)dicopper(II)
porphyrin complexes produced by oxidation of Cu(I)
complexes of N21,N22-etheno bridged porphyrins, though
di(m-hydroxo)dipalladium(II) complex of N21,N22-etheno
bridged porphyrin has shown the higher photocatalytic
activity than the copper complexes. In the homogeneous
photoreaction system, it seems a merit that the active di(m-
hydroxo)dicopper(II) porphyrin complex is generated
spontaneously in aerated solution. Further, the copper
porphyrin complexes were utilized to heterogeneous
photoreaction in aqueous solution by immobilization
on support. It seems that on immobilization the di(m-
hydroxo)dicopper(II) porphyrin complex is effectively
formed from Cu(I) complex resulting in composite
photocatalyst. The copper complex with N21,N22-etheno
bridged porphyrin has a high adsorptive ability and the
composite contains much amount of immobilized active
sensitizer for the photooxidation of target compounds. The
high photostability of the complex with N21,N22-etheno
bridged porphyrin is also considered to contribute the
efficiency as the photocatalyst. It seems that the activity
of homogeneous reaction is due to the formation of singlet
oxygen more and the efficiency in the heterogeneous
one is predominated by the catalytic pathway. Thus the
photooxidation of phenol derivative with the composite
photocatalyst of the copper complex with N21,N22-etheno
bridged porphyrin proceeded faster than that of the
monoprotonated derivative in spite of the higher efficiency
of the latter than the former in the homogeneous reaction.
Another advantage in heterogeneous system is that the
composite photocatalyst can be easily recovered and
re-used by filtration, washing and drying. Thus the copper
complexes described here contributed to photooxidation
of phenol derivative under aerobic condition with visible
irradiation as photosensitizer in both of homogeneous
and heterogeneous system in which the (hydroxo)Cu(II)
complexes to be formed from the Cu(I) complexes with
N21,N22-etheno bridged porphyrin played a role of the key
species.
Homogeneous photooxidation
DBP (2 mM) and a sensitizer (0.2 mM) were dissolved
in an aerated acetonitrile-d3 solution and irradiated with
visible light (350 nm<l<800 nm) by a 500 W xenon
lamp passed through cut filters with stirring in a flask
at room temperature. A 0.5 mL of sample solution was
withdrawn and analyzed by 1H NMR spectroscopy
before and after photoirradiation. The conversions were
evaluated from a ratio of the integral values of a doublet
signal at 7.16 ppm for DBP before the photoreaction and a
singlet signal at 6.48 ppm for photooxidatively produced
DBQ assigned to m-phenyl protons using a singlet signal
at 7.37 ppm for p-dichlorobenzene as an internal standard.
Heterogeneous photooxidation
0.1 g of silica gel was suspended in a 2 mL of
chloroform solution containing a porphyrin derivative
(4 × 10-6 mol) or aqueous solution of (S-Pc)Cu. The
suspension was stirred for 10 min, evaporated and dried
under vacuum. Thus prepared composite (10 mg) was
added to an aerated deuterium oxide solution (2.2 mL)
containing PNPP (1.5 mM) and the mixture was
photoirradiated in a similar manner as above. The content
1
of PNPP was monitored by the H NMR measurement
after centrifugation and filtration of the sample solution.
The integral values of two doublet signals at 7.17 and
6.85 ppm for PNPP assigned to o- and m-phenyl protons
were used in comparison with a TSP signal at 0 ppm as
an internal standard.
Evaluation of amount of immobilized sensitizer
0.04 g of silica gel was suspended in a 2 mL chloroform
solution of a porphyrin derivative (ca. 4 × 10-6 mol)
or aqueous solution of (S-Pc)Cu. The suspension was
evaporated, washed with a 4 mL of solvent and then
filtered. The volume of the washing filtrate was made
exactly to 50 mL. This filtrate was further diluted 5
times for 3a, 12.5 times for 3c, and 10 times for OEP.
The concentration of the desorbed sensitizer in washing
filtrate was calculated on the basis of the UV-vis
absorbance. Then the amount of immobilized sensitizer
was evaluated.
UV-vis monitoring of photooxidation of Cu(I)
porphyrin (3a)
A 0.3 mL of acetonitrile solution containing 3a
(0.2 mM) was placed in 1 mm optical cell. The cell was
set in a holder with external water-cooling, and irradiated
with visible light in a similar manner as the photocatalysis
study. In the course of photoreaction process in 120 min
UV-vis spectrum was recorded.
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