C-H bond activation with Ge-oxyl complex generated by photoinduced- electron-transfer of di(hydroxo)porphyrin GeIV complex

Article abstract of DOI:10.1142/S1088424614500345

Visible-light irradiation of MeOH solution containing di(hydroxo) tetraphenylporphyrin atogermanium(IV) complex (tppGe(OH)₂; 1a), cumene, and Fe³⁺ ion (Fe(NO₃)₃) as an electron acceptor gave cumyl alcohol as an oxidative product along with Fe²⁺ ion as a reductive product. The quantum yield (Φ_ox) and turn over frequency (TOF) for the formation of cumyl alcohol was 0.033 and 111.1 h ^-1, respectively. The addition of KOH aqueous solution (1 mM) into reaction solution led to an increase of Φ_ox to 0.047. The free energy change (ΔG) with electron transfer from excited triplet state (³1a*) to Fe³⁺ was estimated as a large negative value (-1.37 eV). Furthermore, in 1a-photosensitized oxidation of MeOH in the presence of K₂PtCl₆ as an electron acceptor, formaldehyde (HCHO) was formed in Φ_ox = 0.034 and TOF = 120.0 h^-1. The isotope effect for the formation of HCHO (Φ_ox(H)/ Φ_ox(D) = 5.04) was observed when MeOH-d₄ was employed as an substrate. Both formation of cumyl alcohol and formaldehyde was not observed at all in the case of photosensitized reactions by tppGe(OMe) ₂ (1b) having two axial methoxo ligands. These findings indicate the photosensitized reaction was initiated by photoinduced electron transfer from ³1a* to Fe³⁺ or K₂PtCl₆ to generate porphyrin radical cation (1a^+?), which underwent a proton dissociation of hydroxo axial ligand to give tpp(OH)Ge-O^? (Ge-oxyl complex) as key intermediate. The Ge-oxyl complex oxidized substrates through a hydrogen-atom abstraction. It is strongly suggested that 1a can act as a good sensitizer for being able to activate C-H bond of organic compounds.

Full text of DOI:10.1142/S1088424614500345

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2014; 18: 529–534
DOI: 10.1142/S1088424614500345
Published at http://www.worldscinet.com/jpp/
C–H bond activation with Ge-oxyl complex generated
by photoinduced-electron-transfer of di(hydroxo)porphyrin
GeIV complex
Tsutomu Shiragami*, Ayano Kuroki, Jin Matsumoto and MasahideYasuda
Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki, Gakuen-Kibanadai, Miyazaki
889-2192, Japan
Received 29 January 2014
Accepted 3 July 2014
ABSTRACT: Visible-light irradiation of MeOH solution containing di(hydroxo)tetraphenylporphyrin
atogermanium(IV) complex (tppGe(OH)2; 1a), cumene, and Fe3+ ion (Fe(NO3)3) as an electron acceptor
gave cumyl alcohol as an oxidative product along with Fe2+ ion as a reductive product. The quantum
yield (Fox) and turn over frequency (TOF) for the formation of cumyl alcohol was 0.033 and 111.1 h-1,
respectively. The addition of KOH aqueous solution (1 mM) into reaction solution led to an increase of Fox
to 0.047. The free energy change (DG) with electron transfer from excited triplet state (31a*) to Fe3+ was
estimated as a large negative value (-1.37 eV). Furthermore, in 1a-photosensitized oxidation of MeOH in
the presence of K2PtCl6 as an electron acceptor, formaldehyde (HCHO) was formed in Fox = 0.034 and
TOF = 120.0 h-1. The isotope effect for the formation of HCHO (Fox(H)/Fox(D) = 5.04) was observed when
MeOH-d4 was employed as an substrate. Both formation of cumyl alcohol and formaldehyde was not
observed at all in the case of photosensitized reactions by tppGe(OMe)2 (1b) having two axial methoxo
ligands. These findings indicate the photosensitized reaction was initiated by photoinduced electron
3
transfer from 1a* to Fe3+ or K2PtCl6 to generate porphyrin radical cation (1a+ꢀ·), which underwent a
proton dissociation of hydroxo axial ligand to give tpp(OH)Ge-O· (Ge-oxyl complex) as key intermediate.
The Ge-oxyl complex oxidized substrates through a hydrogen-atom abstraction. It is strongly suggested
that 1a can act as a good sensitizer for being able to activate C–H bond of organic compounds.
KEYWORDS: carbon-hydrogen bond activation, germanium porphyrin, oxidation, photoinduced
electron transfer.
the photoepoxidation of cyclohexene sensitized by
INTRODUCTION
di(hydroxo)tetraphenylporphyrinatoantimony(V) complex
Metal-oxo porphyrin complexes are known as a key
(tppSb(OH)2+) efficiently occurred in the presence of
intermediate for various metabolic oxidation processes
K2PtCl6 as an electron acceptor in an aqueous acetonitrile
in P450 enzymatic model system [1, 2]. Therefore,
solution under visible light irradiation [8, 9]. In this
many oxidation processes using metal-oxo porphyrin
previous report, it was elucidated that Sb-oxo complex
complexes are also developed. For example, in thermal
(tpp(OH)Sb=O) generated by a proton dissociation of axial
process, some oxygen donors such as molecular oxygen
hydroxo ligand of porphyrin radical cation (tppSb(OH)2+ꢀ·),
[3], hydrogen peroxide [4, 5] or others [6, 7] are often
formed by photoinduced electron transfer from the excited
employed for the formation of metal-oxo porphyrin
triplet state of tppSb(OH)2+ to K2PtCl6, could be a key
complex. On the other hand, we previously found that
intermediate for the oxidation of cyclohexene, resulting
that the water molecule worked as an oxygen donor for
the formation of Sb-oxo complex. Furthermore, we
SPP full member in good standing
also reported that di(hydroxo)tetraphenylporphyrinato-
germanium(IV) complex (tppGe(OH)2; 1a) supported on
*Correspondence to: Tsutomu Shiragami, email: t0g109u@
cc.miyazaki-u.ac.jp, tel: +81 985-587313, fax: +81 985-587315
Copyright © 2014 World Scientific Publishing Company

530
T. SHIRAGAMI ET AL.
RO
Ph
N
N
Ph
Ge
N
Ph
N
Ph
OR
1a: R = H
1b: R = CH3
CH3
CH3
hν 1a
+ Fe3+
C
H
CH3
C
CH3
+ Fe2+
under Ar
OH
Fig. 1. Time-course plots for the formation of cumyl alcohol in
1a-sensitized oxidation of cumene
hν 1a
CH3OH + K2PtCl6
HCHO + K2PtCl4
under Ar
Scheme 1. 1a-sensitized oxidation of cumene and MeOH
SiO2 particle led to the photocatalytic oxidation of hydro-
carbons and MeOH to the corresponding alcohols and
HCHO under visible light irradiation, respectively [10]. In
this system, it was indicated that tpp(OH)Ge-O· (Ge-oxyl
complex) having O-radical character could be formed by
similar photochemical process with tppSb(OH)2 and could
participate in the oxidation process of organic substrates.
However, the mechanism is not clarified in detail due to
the heterogeneous reaction system.
Here, we will report on 1a-sensitized oxidation of
cumene and MeOH in homogeneous solution system
from viewpoint of mechanistic approach (Scheme 1).
This is the first example of an oxidation using Ge-oxyl
porphyrin complex generated by a photochemical process.
Therefore, this system can be regarded as a novel method
to generate Ge-oxyl porphyrin complexes.
Fig. 2. Time-course plots for the formation of formaldehyde in
1a-sensitized oxidation of MeOH
containing 1a (33 mM) and [PtCl6]2- (K2PtCl6, 0.5 mM) as
an electron acceptor, HCHO was formed lineally towards
an irradiation time (Fig. 2). Under irradiation in the
absence of [PtCl6]2-, HCHO was not obtained at all. The
Fox and TOF for the formation of HCHO were estimated
to be 0.034 and 120.0 h-1, respectively. These results
indicate that the photooxidations of cumene and MeOH
were sensitized by 1a even in homogeneous solution
system.
RESULTS AND DISCUSSION
Product analysis
The 1a-photosensitized reaction was performed by
the irradiation (550 nm) of MeOH solution containing 1a
(33 mM), cumene (1 mM), and Fe(NO3)3·9H2O (1 mM)
acting as an electron acceptor. Cumyl alcohol was formed
lineally toward the irradiation time without an induction
period (Fig. 1). The formation of Fe2+, which is one-
electron reduction product of Fe3+, was also detected in
the reaction solution after irradiation. No cumyl alcohol
was obtained under an irradiation in the absence of Fe3+.
The quantum yield (Fox) and turn over frequency (TOF)
for the formation of cumyl alcohol were estimated to be
0.033 and 111.1 h-1, respectively (Table 1). Therefore, 1a
works as a photocatalyst in this system.
Kinetic analysis
A reaction mechanism was elucidated by the
fluorescence quenching experiment of 1a and the kinetic
analysis for Fox. In the presence of Fe3+, the fluoresc
ence of 1a was not quenched at all. Similar result
was obtained even in the presence of [PtCl6]2-. These
results show that an initial step of photoreaction can
proceed from the excited triplet state of 1a (31a*),
not excited singlet state of 1a (11a*). It is suggested
that the initial step should be a photoinduced electron
3
transfer (PET) process from 1a* to Fe3+ or [PtCl6]2-,
In the case of 1a-photosensitized oxidation of MeOH
which was performed for a MeOH–H2O (9:1 v/v) solution
because both free energy changes (DG) calculated by
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 530–534

C–H BOND ACTIVATION WITH GE-OXYL COMPLEX GENERATED
531
OH
Φisc
Ge(tpp)3
OH
*
A
kd
OH
α kr [A]
1a
Ge(tpp)
OH
A-
kox [S]
OH
O
Product
Ge(tpp)+ or
OH
Ge(tpp)
OH
S
kx
Others
Scheme 2. Reaction scheme for 1a-sensitized oxidation
Fig. 3. Double reciprocal plot of the Fox against the
concentration of Fe3+ in the 1a-photosensitized oxidation of
cumene under neutral condition (·) and in the presence of
aqueous KOH solution ()
Rehm–Weller equation [11] using E0–0 (1a) = 1.63 eV,
E1/2ox(1a) = 1.24 V, E1/2red(Fe3+) = 0.98 V [6], and
E1/2red([PtCl6]2-) = 0.73 V vs. SCE [9] are much exoergic
(DG = -1.37 eV for Fe3+, DG = -1.12 eV for [PtCl6]2-).
Assuming the reaction route shown in Scheme 2, Fox
is expressed with an equation (Equation 1), where Fisc
is the quantum yield of intersystem crossing of 1a, a is
the efficiency of charge separation, b is the efficiency of
product formation from an intermediate, kd is the rate
constant for the deactivate process from 31a* to ground
state, kr is the rate constant for electron transfer from
31a* to the electron acceptor (A), kox is the rate constant
for oxidation process of substrate (S), and kx is the rate
constant for other reaction process.
kr[A]
kox [S]
(1)
. .
a
.
Fox = Fisc
kd + kr[A] kx + kox [S]
Fig. 4. Double reciprocal plot of Fox against the concentration
of cumene in the 1a-photosensitized oxidation of cumene under
neutral condition (·) and in the presence of aqueous KOH


 
 

kd
kx
1
1
.
.
(2)
=
1+
1+

 

.
Fox Fisc
a
k [A]
r
k [S]
ox

solution ()
kox [S]
kx + kox [S]
(3)
b =
plot also shows a straight line. On the other hand, even in
the double reciprocal plots of Fox against concentration
of [PtCl6]2- (0.1 mM–0.5 mM) in the MeOH oxidation
system, a straight line was obtained, as shown in Fig. 5.
Table 1 summarizes the kinetic parameters obtained from
both slope and intercept values in each plot. The results
of kinetic analysis well supported the proposal reaction
route shown in Scheme 2.
According to Equation 1, the reciprocal of Fox is
proportional to the reciprocal of concentration of A and
S, respectively (Equation 2). Indeed, Fig. 3 shows a
double reciprocal plot (Stern–Volmer type plot) of
Fox against concentration of Fe3+ in photosensitized
oxidation of cumene where Fox was measured at various
concentration of Fe3+ (0.5 mM–5 mM) and the fixed
concentration of cumene at 1 mM. The plots laid well
on a straight line. This result strongly indicates that the
single excited species of 1a should be responsible for
an electron transfer to Fe3+ (Scheme 2). Furthermore,
the reciprocal of Fox was plotted against the reciprocal
of concentration of cumene (Fig. 4), when Fox was
measured at various concentration of cumene (0.5 mM-1
mM) and the fixed concentration of Fe3+ at 5 mM. This
The limiting quantum yield (Flim) for the formation
of products is shown in Table 1. Since the values of Fisc
on metalloporphyrin complexes are generally estimated
to be around 0.9 [8], total efficiency (ab) of oxidative
process including PET became about 15% for cumene
oxidation system under basic condition and about 30%
for MeOH oxidation system, respectively.
In Scheme 2, two intermediates, porphyrin radical
cation (1a+ꢀ·) and Ge-oxyl complex, are assumed as the
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 531–534

532
T. SHIRAGAMI ET AL.
140
120
100
80
when the photoreaction of cumene and MeOH were
performed by using 1b having two axial methoxo ligands
and same redox potential with 1a, no oxidative product
was observed in both cases. These results show that the
proton dissociation process from an axial hydroxo ligand
is contributed to the formation of oxidative products,
strongly indicating that an active species should be
Ge-oxyl complex [10]. In general, it is known that an
oxygen atom on metal-oxo complex has either ionic
character or radical character. The isotope experiment
is often a convenient procedure to check the character
of oxygen atom on metal-oxo complex in a reaction.
60
Φ
40
20
0
0.0
2.0
4.0
[K2[PtCl6]]-1 / 103 M-1
6.0
8.0
12.0
10.0
Isotope effect for the formation of HCHO (Fox(H)/Fox(D)
=
5.04) was observed when MeOH-d4 was employed as
an substrate in 1a-photosensitized reaction. This value
indicates that hydrogen-atom abstraction from methyl
group should be involved in the oxidation process of
MeOH [13, 14]. This result also supports that Ge-oxyl
complex act as a key intermediate for the oxidation of
substrates.
Fig. 5. Double reciprocal plot of Fox against the concentration
of [PtCl6]2- in the 1a-photosensitized oxidation of MeOH
active spices for the oxidation of substrate. First of all, if
the oxidation process proceeds via 1a+ꢀ·, the hole transfer
mechanism from 1a+ꢀ· to substrate can be suggested as a
plausible reaction mechanism. However, the free energy
Reaction mechanism
change (DG) for hole transfer from 1a+ꢀ· to cumene
ox
calculatedfromtheoxidationpotentialsofcumene(E1/2
=
A plausible reaction mechanism was shown in
Scheme 3. Upon visible light irradiation, 1a+ꢀ· is formed
by an electron transfer process from the excited triplet
state of 1a to the electron acceptor, followed by Ge-oxyl
complex through a proton dissociation process from
1a+ꢀ·. A homolytic cleavage of C–H bond of substrates
are induced by the hydrogen-atom abstraction with an
oxygen radical on Ge-oxyl complex, resulting that a
carbon radical species (R·) is formed and 1a returns to an
original state. The existence of Ge-oxyl complex having
O-radical character was also reported in the photolysis
of tpp(OH)Ge(OOEt) to give acetaldehyde and ethanol
2.27Vvs.SCE)and1abecamealargepositivevalue(DG=
1.03 eV) [12]. Similarly, in the case of methanol
(E1/2ox = 1.65 V vs. SCE), the value of DG is also positive
(DG = 0.41 eV) [10]. These values show that a hole
transfer process scarcely occur thermodynamically in
this system. On the other hand, the formation of Ge-oxyl
complex needs a proton dissociation process of hydroxo
ligand on 1a+ꢀ·. Therefore, if Ge-oxyl complex works as
the active spices in the photoreaction, the increase of Fox
can be expected when the photoreaction was carried out
under the basic condition. In the oxidation of cumene,
the increase of Fox to 0.047 was observed by the addition
of aqueous KOH solution (1 mM) into reaction solution
as shown in Table 1. Both double reciprocal plots of
Fox against the concentration of Fe3+ and cumene gave
a straight line even under the basic condition (Figs 3
and 4). The value of kox/kx under basic conditions was
larger than that under neutral conditions. Furthermore,
18
[15]. The 18O-labelling experiment using H2 O in
cumene reaction system revealed that the oxygen source
for cumyl alcohol production should not be water since
18O atom was not incorporated into cumyl alcohol at all.
Accordingly, we speculated that the oxygen source can
be a small amount of molecular oxygen involved in argon
gas in cumene reaction system.
Table 1. Turn over frequency (TOF), quantum yield (Fox) and kinetic parameter in
1a-sensitized oxidation
b
Substrates TOF, h-1 Fox/10-2 kr/106, M-1.s-1a kox/kx/102 Flim
b
aFisc
Cumene
Cumenec
MeOH
111.1
157.8
120.0
3.3
4.7
3.4
5.1
1.4
0.8
4.5
5.1
—
0.05 0.28
0.15 0.33
0.18
0.46
—
0.27
—
b
a kd = 3.3 × 103 s-1. ꢀFlim = Fisc × a × b where F lim was a quantum yield of limiting
quantum yield at the fixed concentration of cumene at 1 mM. b Fisc was quantum yield of
c
intersystem crossing corresponding to the yield of excited triplet state. Aqueous KOH
solution (1 mM) was added.
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 532–534

C–H BOND ACTIVATION WITH GE-OXYL COMPLEX GENERATED
533
photoinduced
CDCl3; Me4Si): dH, ppm -2.56 (6H, s, –OCH3), 7.73–7.79
(12H, m, Ph), 8.25 (8H, d, J = 5.2 Hz, Ph), 9.02 (8H, s,
pyrrole). MS (MALDI-MS): m/z 717.16, (calcd. for
[M – OCH3]+ 717.25).
OH
electron transfer
hν
Ge(tpp)+ A-
OH
A
OH
1a
Ge(tpp)
OH
proton dissociation
Measurements
The quantitative analysis of cumyl alcohol as an
oxidative product of cumene was performed by using
GC-MS(ShimadzuQP-2000)withacapillarycolumn(DB-
1; 25 m × 0.25 mm × 0.25 mm). HCHO was quantitatively
analyzed by the absorption spectrophotometry using
4-amino-3-hydrazino-5-sulfonyl-1,2,4-triazole as color-
producing reagent [10]. The detection of Fe2+ cation was
carried out by the absorption spectrophotometry using
1,10-phenanthrorine as color-producing reagent.
O
hydrogen-atom
abstraction
Ge(tpp)
OH
R
RH
Scheme 3. A possible reaction mechanism for 1a-sensitized
oxidation
EXPERIMENTAL
Photoreactions
Instruments
MeOH solution (12 mL) containing 1a (0.39 mmol),
cumene (0.5–1.0 mM, usually 1 mM) and Fe(NO3)3·9H2O
(0.5–5.0 mM, usually 1 mM) was introduced into a
glass tube (20 mmf × 36 mm) and bubbled with argon
gas. MeOH was used without further purification.
Photooxidation were performed in a glass tube at room
temperature under argon atmosphere by an irradiation of
550 nm light obtained through the glass-filter with Xe
lamp (500 W). The photon number was measured to be
19.0 × 10-6 einstein/minute at 550 nm as a relative value for
the standard photoreaction [8]. Similarly photooxidation
of MeOH was performed for MeOH solution (9 mL,
22.2 M) containing 1a (0.33 mmol), K2PtCl6 (0.1–
0.5 mM, usually 0.5 mM) and H2O (1 mL) in a glass tube
under argon atmosphere.
1H NMR (400 MHz) spectrum was acquired with a
Bruker AV 400M spectrometer by using SiMe4 as an
internal standard. Matrix-assisted laser desorption/
ionization mass spectrum (MALDI-MS) was measured on
a Bruker Daltonics Autoflex III TOF/TOF in the positive
ion mode. Calibration of mass number was performed by
the internal standard method using polyethyleneglycol.
UV-vis absorption spectra and fluorescence spectra
of the reaction solution were obtained with a JASCO
V-550 spectrophotometer and a Shimadzu RF 5300PC
spectrophotometer, respectively.
Materials and preparation
2-Phenylpropane (cumene), 2-phenyl-2-propanol
(cumyl alcohol), HCHO, iron(III) nitrate hydrate
(Fe(NO3)3·9H2O), germanium tetrachloride (GeCl4) and
some organic solvents were purchased from Wako Pure
ChemicalIndustriesasaguaranteedreagentgrade(GR)and
used without further purification. Potassium hexachloro-
platinate(IV) (K2PtCl6) and tetraphenylporphyrin (H2tpp)
were purchased from Aldrich as a GR reagent. Also H218O
was taken from Aldrich.
The tppGe(OH)2 (1a) was synthesized according to the
literature [10]. The synthesis of di(methoxo)tetraphenyl-
porpyrinatogermanium(tppGe(OMe)2,1b)wasperformed
by the reaction of H2TPP (1.0 g) with GeCl4 (2.0 g) in
water-free quinolone (30 mL) at 150°C for 15 h under
N2 atmosphere. The reaction mixture was poured into
hexane to give the precipitate of crude complex having
two axial chloro ligands. The crude 1b was obtained by
refluxing MeOH solution of crude complex having two
axial chloro ligands in order to substitute two chloro
ligands to two methoxo ligands. After evaporation, 1b
was isolated by column chromatography on SiO2.
CONCLUSION
It was elucidated that the photochemical oxidation of
cumene and MeOH could be occurred by using Ge-oxyl
complex generated by photoinduced electron transfer
from 1a under visible light irradiation. The Ge-oxyl
complex can induce the C–H bond activation of organic
substrates due to acting as an O-radical intermediate. This
is the first example of a photocatalytic reaction using a
GeIV-porphyrin complex [16–18]. Among the studies on
C–H bond activation, either transition metal-complexes
(Mn, Fe and Cu) [19–21] or noble metal complexes (Pd,
Ru and Rh) [22–24] have been almost employed as a
catalyst. Therefore, this study, in which the C–H bond
activation was achieved by using non-transition metal
(typical element) complex, may be significant from
a viewpoint of “elemental strategy “in the region of
catalysis.
Acknowledgements
Di(methoxo)tetraphenylporpyrinatogermanium
(1b). Yield 85%. UV-vis (MeCN): lmax, nm (log e) 420
This work was partially supported by a Grant-in-Aid
for Scientific Research on Innovative Areas (Artificial
1
(5.88), 553 (4.97), 590 (4.34). H NMR (400 MHz;
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T. SHIRAGAMI ET AL.
photosynthesis (No. 2406)) from the Japan Society for
the Promotion of Science (JSPS).
11. Rehm D and Weller A. Isr. J. Chem. 1970; 8:
259–271.
12. Tajima T, Ishii H and Fuchigami T. Electrochem.
Commun. 2004; 4: 589–591.
13. Jung J, Ohkubo K, Prokop-Prigge KA, Neu HM,
Goldberg DP and Fukuzumi S. Inorg. Chem. 2013;
52: 13594–13604.
14. Lykakis IN, Vougioukalakis GC and Orfanopoulos
M. J. Org. Chem. 2006; 71: 8740–8742.
15. Balch AL, Cornman CR and Olmstead MM. J. Am.
Chem. Soc. 1990; 112: 2963–2967.
16. Kadish KM, Xu QY, Barbe J-M, Anderson JE,
Wang E and Guilard R. J. Am. Chem. Soc. 1987;
109: 7705–7707.
17. Ishii K, Abiko S and Kobayashi N. Inorg. Chem.
2000; 39: 468–472.
18. Ha J-H, Yoo SI, Jung GY, Paeng IR and Kim Y-R.
J. Mol. Struct. 2002; 606: 189–193.
19. Ryabov AD. Chem. Reviews 1990; 90: 403–424.
20. Shilov AE and Shul’pin GB. Chem. Reviews 1997;
97: 2879–2932.
21. Sun C-L, Li B-J and Shi Z-J. Chem. Reviews 2011;
111: 1293–1314.
REFERENCES
1. Groves T. In Cytochrome P450: Structure, Mecha-
nism and Biochemistry, 3th ed., Ortiz de Montel-
lano PR. Kluwer Academic/Plenum: New York,
2004; Chapter 1, pp. 1–44.
2. Meunier B, de Visser SP and Shaik S. Chem. Review
2004; 106: 3947–3980.
3. Ji L-N, Liu M, Hsieh A-K and Hor TSA. J. Mol.
Catal. 1991; 70: 247–257.
4. Battioni P, Renoud JP, Bartoil JF, Reina-Artilas M,
Fort M and Mansuy D. J. Am. Chem. Soc. 1988;
110: 8462–8470.
5. Nam W. Kim I, Lim MH, Choi HJ, Lee JS and Jang
HG. Chem. A-Eur. J. 2002; 8: 2067–2071.
6. Mirkhani V, Tangestaninejad S, Moghadam M
and Moghbel M. Bioorg. Med. Chem. 2004; 12:
4673–4677.
7. Groves JT and Nemo TE. J. Am. Chem. Soc. 1983;
105: 5786–5791.
22. Lyons TW and Sanford MS. Chem. Reviews 2010;
110: 1147–1169.
23. Colby DA, Bergman RG and Ellman JA. Chem.
Reviews 2010; 111: 624–655.
24. Arockiam PB, Bruneau C and Dixneuf PH. Chem.
Reviews 2012; 112: 5879–5918.
8. Shiragami T, Kubomura K, Ishibashi D and Inoue
H. J. Am. Chem. Soc. 1996; 118: 6311–6312.
9. Takagi S, Suzuki M, Shiragami T and Inoue H.
J. Am. Chem. Soc. 1997; 119: 8712–8713.
10. Shiragami T, Shiraki R, Makise R, Matsumoto J and
Yasuda M. Chem. Lett. 2010; 39: 874–875.
Copyright © 2014 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2014; 18: 534–534