Glycol metalloporphyrin derivatives in solution or immobilized on LDH and silica: Synthesis, characterization and catalytic features in oxidation reactions

Article abstract of DOI:10.1039/c3cy00472d

We reacted [meso-tetrakis(pentafluorophenyl)porphyrin] with ethylene glycol to obtain porphyrins substituted with one to four hydroxyalkyloxy groups at position 4 of the meso-aryl groups. We then inserted iron(iii) or manganese(iii) into the mono- and tet

Full text of DOI:10.1039/c3cy00472d

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Glycol metalloporphyrin derivatives in solution or
immobilized on LDH and silica: synthesis,
characterization and catalytic features in oxidation
reactions†
Cite this: Catal. Sci. Technol., 2014,
4, 129
b
b
Kelly A. D. F. Castro,ab Mário M. Q. Simões, M. Graça P. M. S. Neves,
*
b
a
a
*
José A. S. Cavaleiro, Fernando Wypych and Shirley Nakagaki
We reacted [meso-tetrakis(pentafluorophenyl)porphyrin] with ethylene glycol to obtain porphyrins
substituted with one to four hydroxyalkyloxy groups at position 4 of the meso-aryl groups. We then inserted
iron(III) or manganese(III) into the mono- and tetra-substituted free-base derivatives, which afforded the
corresponding metalloporphyrin complexes. Next, we immobilized the iron(III) and manganese(III) porphyrins
on two supports: layered double hydroxide (LDH) and silica (synthesized by the sol–gel process). We char-
acterized the resulting solids using powder X-ray diffraction (PXRD), UV–vis electronic spectroscopy, and
electron paramagnetic resonance (EPR), and we investigated the catalytic activity of the materials in both
homogeneous and heterogeneous media. The metalloporphyrins provided good catalytic conversions in
(Z)-cyclooctene oxidation. As for cyclohexane oxidation, the catalysts were selective for the alcohol
instead of the ketone. In the case of heterogeneous catalysis, the immobilized metalloporphyrins
furnished slightly lower yields as compared with homogeneous catalysis. However, these solids presented
a major advantage: reusability. Indeed, these solid catalysts retained their activity for at least three cycles
in the case of (Z)-cyclooctene oxidation.
Received 4th July 2013,
Accepted 17th October 2013
DOI: 10.1039/c3cy00472d
www.rsc.org/catalysis
effect that substituents exert on the metalloporphyrin
macrocycle: (1) they increase the lifetime and reactivity of
Introduction
In recent years, various scientists have developed a large
number of systems based on synthetic metallomacrocycles
to model cytochrome P-450.1–8 Within this class of com-
pounds, porphyrins and analogues have deserved special
attention. These versatile derivatives find application in dif-
ferent areas such as catalysis,1–13 medicine,14,15 electronics,16
solar cells,17,18 and sensors,19,20 among others.21 In the field
of catalysis, metalloporphyrins have proven to be able to
effectively oxidize hydrocarbons and other organic com-
pounds under mild conditions.3,22–36
the active catalytic species in solution, and (2) they inhibit
the formation of dimeric species and the oxidative self-
destruction process that inactivates the catalyst.5
Extensive investigations have shown that halogenated
metalloporphyrins are more resistant to degradation via free-
radical attack than those containing electron-donating sub-
stituents. Metalloporphyrins containing electron-withdrawing
substituents also efficiently catalyze the oxygenation of hydro-
carbons and a wide variety of other organic compounds.3,5,12,38,39
In this context, the free-base ligand [5,10,15,20-
tetrakis(pentafluorophenyl) porphyrin], [H2(TPFPP)], consti-
tutes a surprisingly versatile compound, mainly for catalytic
purposes.40–44 It consists of an important platform to prepare
new porphyrin ligands because it can undergo many types of
structural modification via nucleophilic substitution of the
p-fluorine atoms.43,44 Chemically modifying [H2(TPFPP)] or
the corresponding metal complexes45 with appropriate nucle-
ophiles allows for their functionalization with substituents
that will make them potentially applicable in the photody-
namic therapy (PDT) of several diseases.44,46,47 In addition,
by choosing the right substituents, one can immobilize the
Many studies have shown that structurally modifying
metalloporphyrins3,5,37 improves catalytic performance in homo-
geneous medium. This is a consequence of the stereo-electronic
a Laboratório de Química Bioinorgânica e Catálise; Universidade Federal do
Paraná (UFPR), CP 19081, CEP 81531-990, Curitiba, Paraná, Brazil.
E-mail: shirleyn@ufpr.br
b Department of Chemistry and QOPNA, University of Aveiro, 3810-193 Aveiro,
Portugal. E-mail: gneves@ua.pt
† Electronic supplementary information (ESI) available: NMR 1H and 19F, FTIR,
HRMS and UV–vis of the free-base porphyrins P2–P6. UV–vis, MALDI (TOF/
TOF) and HRMS of the metalloporphyrins. See DOI: 10.1039/c3cy00472d
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metalloporphyrin on different supports, creating new mate-
rials for heterogeneous catalysis.11–13,21–25
Iodosylbenzene (PhIO) was synthesized through the hydroly-
sis of iodosylbenzene diacetate.58 The resulting solid was care-
fully dried under reduced pressure and kept at 5 °C. Mg/Al
LDH at a molar ratio of 3 : 1 and intercalated with nitrate
anions was prepared as described previously.26,59 Porphyrin
P1, used as platform for further functionalization, was pre-
pared according to the literature.60
In general, metalloporphyrins containing bulky or electro-
negative substituents at any position of the meso-aryl groups
present high catalytic efficiency, resulting in good product
yields during the oxidation of many substrates.12,13,25,26,48–51
However, the use of these catalysts in homogeneous medium
is limited because it is not possible to recover or reuse the
catalyst, not to mention that parallel reactions sometimes
deactivate the catalytic species.3,5
Synthesis of the free-base porphyrins P2–P6 from the reaction
of ethylene glycol with porphyrin P1 (see Fig. 1 for abbreviations)
Therefore, researchers have searched for strategies to immo-
bilize metalloporphyrins on different inorganic supports, so as
to enable catalyst recovery and reuse and to prevent catalytic
species deactivation.11–13,24–26,34,35,48,52 The immobilization pro-
cedure and the support may also lead to a more selective cataly-
sis: the combination of the porphyrin complex and the support
may create structures with cavities and pores, culminating in
unusual selectivity, such as size- and shape-selectivity.53,54
Studies have shown that metalloporphyrin immobiliza-
tion on rigid supports, such as silica gel, inhibits dimer for-
mation because it suppresses the interactions between the
metalloporphyrin complexes fixed on the support surface.24
In the last decade, silica preparation by sol–gel process
emerged as a very useful technique to immobilize different
compounds, including catalytically active metalloporphyrins.
The sol–gel method produces high-purity solids under mild
conditions and at low cost. One possible sol–gel route is the
hydrolytic route: polymerization of silicon alkoxides [e.g.,
tetraethyl orthosilicate (TEOS) (Si(OC2H5)4] affords an inorganic
solid bearing siloxane (Si–O–Si) and silanol groups (Si–OH).
This process is conducted in the presence of a solvent, usually
an alcohol, and an acid or base catalyst.55
Porphyrin P1. P1 was prepared using the nitrobenzene
methodology.60 The resulting solid was purified by column
chromatography (silica gel) using a chloroform–petroleum
ether (1 : 1) mixture as the eluent. After solvent evaporation, P1
was recrystallized in dichloromethane–petroleum ether in 11%
yield. Molecular formula: C44H10F20N4; 1H NMR δH, ppm
(CDCl3): −2.92 (broad s, 2H, NH) and 8.12 (s, 8H, H-β); 19F NMR
δF, ppm (CDCl3): −160.00 (8F, dd, J = 25.4 and 8.5 Hz, Ar o-F),
−174.7 (4F, t, J = 21.2 Hz, Ar p-F), and −184.79 to −184.97 (8F, m,
Ar m-F); UV–vis λmax, nm (CH2Cl2): 410, 504, 539, 582, and 648;
MS (m/z): 975 [M]+.
Porphyrin P2. Ethylene glycol (12.5 mmol) was dissolved
in 15 mL of dry THF; then, NaH (0.66 mmol) was added to
Layered double hydroxides (LDH) are another example of
inorganic supports; they consist of synthetic lamellar compounds
with a structure derived from natural brucite. In the LDH struc-
ture, magnesium ions are octahedrally coordinated to hydroxyl
groups.56 These octahedra are interconnected, resulting in “two-
dimensional” layers that interact via van der Waals forces.
Because LDH have divalent and trivalent ions, they contain
positively charged layers of metal hydroxides stacked along
the basal direction. Intercalation of hydrated anions ensures
total neutralization, so the general formula of an LDH can be
represented as [M1−xIIIMxII(OH)2]x+[Ax/nn−·yH2O]x−.26,56,57
In this paper, we report on the synthesis of metallo-
porphyrins bearing appended ethylene glycol units. We aimed
to obtain complexes displaying the appropriate structure to
interact with solid supports such as LDH and silica (obtained by
the sol–gel process). We evaluated the catalytic activity of the
synthesized complexes in (Z)-cyclooctene and cyclohexane oxida-
tion in both homogeneous and heterogeneous media. We also
describe the recovery and reuse of the heterogeneous catalysts.
Experimental
All the chemicals used in this study were purchased from
Aldrich, Sigma, or Merck and were of analytical grade.
Fig. 1 Schematic representation of the reactions of porphyrin P1 with
ethylene glycol in order to obtain derivatives P2–P6.
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the solution. The reaction mixture was kept under magnetic
stirring and nitrogen atmosphere for 30 min. Next, a solution
of P1 (0.076 mmol in 15 mL of THF) was introduced into the
reaction mixture, and the resulting solution was heated at
reflux until consumption of the starting (as confirmed by
TLC, ca. 1 h). After cooling to room temperature, the mixture
was diluted with chloroform and washed three times with
10 mL of water. The organic solvent was evaporated under
reduced pressure. Preparative TLC was used to purify the
crude solid, using chloroform–methanol (9 : 1 v/v) as the
mobile phase. The first fraction was identified as porphyrin
P2 (61% yield): m.p. >300 °C; 1H NMR δH, ppm (CD3OD):
9.10 (broad s, 8H, H-β), 4.10 (t, J = 4.5 Hz, 2H, CH2), and 4.70
(t, J = 4.5 Hz, 2H, CH2) (the signal relative to the NH protons
was not observed due to their replacement by deuterium
from deuterated methanol); 19F NMR δF, ppm (CD3OD):
−190.13 (dt, J = 7.5 and 21.4, 6F, F-meta), −184.33 (dd, J = 7.7
and 21.4, 2F, F-meta), −180.54 (t, J = 21.4, 3F, F-para), −167.34
(dd, J = 7.7 and 21.5, 2F, F-ortho), and −165.30 (m, 6F, F-ortho);
UV–vis (CH2Cl2) λmax, nm (log ε): 412 (5.20), 506 (4.08), 582
(3.90), and 656 (2.95); HRMS (FAB+) m/z: calculated for
C46H16F19N4O2 (M + H)+: 1017.096, found: 1017.0964 (Fig. S1,
S6, and S11 – ESI†).
2F, F-para), −165.77 (dd, J = 7.7 and 21.5, 4F, F-ortho), and
−163.75 (dd, J = 7.6 and 21.7, 4F, F-ortho); UV–vis (CH2Cl2)
λmax, nm (log ε): 412 (5.42), 506 (4.08), 582 (3.60), and 654
(2.92); HRMS (FAB+) m/z: calculated for C48H20F18N4O4 (M + H)+:
1059.1231, found: 1059.12498 (Fig. S3, S8, and S11 – ESI†).
The fourth fraction was identified as porphyrin P5
(40% yield), which had the following features: m.p. >300 °C;
1H NMR δH, ppm (CD3OD): 9.10 (broad s, 8H, H-β), 4.11
(t, J = 4.4, 2H, CH2), and 4.70 (t, J = 4.4, 2H, CH2); 19F NMR δF,
ppm (CD3OD): −188.63 (dt, J = 7.3 and 21.3, 2F, F-meta),
−182.84 (dd, J = 7.3 and 21.3, 6F, F-meta), −179.13 (t, J = 21.3,
1F, F-para), −165.75 (dd, J = 7.3 and 21.3, 6F, F-ortho), and
−163.73 (dd, J = 7.4 and 21.3, 2F, F-ortho); UV–vis (CH2Cl2)
λmax, nm (logε): 412 (5.30), 510 (4.19), 582 (3.65), and 654 (2.69).
HRMS (FAB+) m/z: calculated for C50H25F17N4O6 (M + H)+:
1101.1536, found: 1101.1559 (Fig. S4, S9, and S11 – ESI†).
Finally, the fifth fraction was identified as porphyrin P6
(25% yield): m.p. >300 °C; 1H NMR δH, ppm (CD3OD): 9.10
(broad s, 8H, H-β), 4.11 (t, J = 4.4, 2H, CH2) , and 4.70 (t, J =
4.4, 2H, CH2); 19F NMR δF, ppm (CD3OD): −182.86 (dd, J = 7.5
and 21.5, 8F, F-meta) and −165.73 (dd, J = 7.4 and 21.5, 8F,
F-ortho); UV–vis (CH2Cl2) λmax, nm (log ε): 412 (4.90), 508
(4.20), 582 (3.69), and 654 (2.73); HRMS (FAB+) m/z: calculated
for C52H31F16N4O8 (M + H)+: 1143.1842, found: 1143.1864
(Fig. S5, S10, and S11 – ESI†).
Porphyrin derivatives P3, P4, P5, and P6. The general
procedure used to obtain P3, P4, P5, and P6 was similar to
that described for the preparation of P2; the only difference
was that in the present case, a higher amount of NaH
(5 mmol) was employed. The reaction mixture was kept
under magnetic stirring and nitrogen atmosphere for 30 min.
Next, a solution of P1 (0.151 mmol in 15 mL of THF) was
added, and the reaction mixture was heated at reflux until
consumption of the starting P1, as confirmed by TLC (24 h).
After cooling to room temperature, the mixture was diluted
with chloroform and washed three times with 10 mL of
water. The organic solvent was evaporated under reduced
pressure. Preparative TLC was used to purify the crude solid,
and chloroform–methanol (9 : 1 v/v) was the mobile phase.
P2, P3, P4, P5, and P6 were crystallized in methanol. The first
fraction was identified as porphyrin P2 (31.5 mg, 6% yield).
The second fraction was identified as porphyrin P3 (8% yield)
The above reaction yields were achieved after 24 h; when
the reaction was performed for 8 h, the reaction yields were
as follows: (7%), P2 (22%), P3 (11%), P4 (12%), P5 (40%),
and P6 (3%).
The preparation of P6 was also optimized to 96% yield.
For this purpose, the reaction was performed by reacting P5
(0.02 mmol) with an excess of ethylene glycol (12.5 mmol)
and 0.21 mmol of NaH for 3 h at 80 °C (Fig. 1).
Synthesis of manganese and iron porphyrins (MPx)
The free-base porphyrins P2 and P6 were metallated with
FeCl2 or Mn(CH3COO)2, by modifying the conventional
methodology reported by Kobayashi, using 0.02 mmol of
porphyrin dissolved in 15 mL of DMF and an excess of
5 times of the metal salt.61 For the metallation with man-
ganese, two drops of pyridine were added to aid ligand
deprotonation. This reaction was allowed to proceed under
reflux conditions for 8 h (compounds MP9 and MP10).
Concerning the metallation with iron, DMF was also used
as the solvent with an excess of 5 times of the metal salt,
and the reaction was carried out under reflux conditions
for 24 h. To help with ligand deprotonation, sodium ace-
tate (0.06 mmol) was also added to the reaction medium
(compounds MP7 and MP8).
1
with the following characteristics: m.p. >300 °C; H NMR δH,
ppm (CD3OD): 9.10 (broad s, 8H, H-β), 4.10 (t, J = 4.5, 2H,
CH2), and 4.70 (t, J = 4.5, 2H, CH2); 19F NMR δF, ppm
(CD3OD): −188.64 (dt, J = 7.3 and 21.3, 4F, F-meta), −182.81
(dd, J = 7.9 and 22.1, 4F, F-meta), −179.08 (t, J = 21.3, 2F,
F-para), −165.79 (dd, J = 7.5 and 22.1, 4F, F-ortho), and −163.74
(dd, J = 7.7 and 21.3, 4F, F-ortho); UV–vis (CH2Cl2) λmax, nm
(log ε): 412 (5.45), 506 (4.10), 582 (3.61), and 654 (2.94). HRMS
(FAB+) m/z: calculated for C48H20F18N4O4 (M + H)+: 1059.1231,
found: 1059.12507 (Fig. S2, S7, and S11 – ESI†).
The third fraction was identified as porphyrin P4
(14% yield) and presented the following characteristics: m.p.
>300 °C; 1H NMR δH, ppm: 9.10 (broad s, 8H, H-β), 4.10
(t, J = 4.4, 2H, CH2), and 4.70 (t, J = 4.4, 2H, CH2); 19F NMR δF,
ppm (CD3OD): −188.62 (dt, J = 7.6 and 21.7, 4F, F-meta),
−182.82 (dd, J = 7.7 and 21.5, 4F, F-meta), −179.06 (t, J = 21.7,
After the metallation process, the solvents were removed
under vacuum. The resulting solids were washed thoroughly
with water to remove excess metal salts. The complexes were
also purified by column chromatography using methanol as
the eluent and silica as the stationary phase, the yields rang-
ing from ca. 94 to 98%.
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The resulting metalloporphyrins were designated MPx
flask. Then, THF (15 mL), TEOS (3 mL) and 1 mL of water
with a drop of HCl (6 mol L−1) were added, in this sequence.
The reaction mixture was stirred for 1 h at room temperature
and kept at about 50 °C until completely dry. The final com-
pounds were obtained after 72 h. FePx–SGA and MnPx–SGA
were beige and dark brown, respectively. The resulting solids
were powdered in a mortar and washed several times with
methanol. UV–vis analysis of the methanol used in the wash-
ing process did not detect any characteristic MPx bands in the
solvent. A control silica sample was also prepared in the
absence of MPx under the same conditions described above.
(where M = Fe3+ or Mn3+ and x = 7, 8, 9, or 10) (Fig. 2) and
presented the following characteristics: FeP7 (C46H13F19FeN4O2)
UV–vis (methanol) λmax, nm (log ε): 406 (4.30), 502 (3.21),
and 579 (3.10); MALDI (TOF/TOF) (m/z): 1070.01 [M + H]+,
corresponding to the calculated formula C46H13F19FeN4O2.
FeP8 (C52H28F16FeN4O8) UV–vis (CH2Cl2) λmax, nm (logε):
390 (4.56), 506 (3.55), and 572 (3.11); HRMS (FAB+) (m/z):
1196.09968 [M + H]+, corresponding to the calculated for-
mula C52H18F16FeN4O8. MnP9 (C46H13F19MnN4O2) UV–vis
(CH2Cl2) λmax, nm (log ε): 456 (4.47), 500 (3.12), and 552
(3.36); HRMS (FAB+) (m/z): 1069.01101 [M + H]+, correspond-
ing to the calculated formula C46H13F19MnN4O2. Anal.
calc. for C48H16F19MnN4O4·2H2O: C, 49.5; H, 1.73; N, 4.81.
Found: C, 49.5; H, 2.46; N, 5.17%. MnP10 (C52H28F16MnN4O8)
UV–vis (CH2Cl2) λmax, nm (logε): 456 (4.38), 500 (3.09),
and 552 (3.35); HRMS (FAB+) (m/z): 1195.10267 [M + H]+,
corresponding to the calculated formula C52H18F16MnN4O8
(Fig. S13–S20 – ESI).
Catalytic oxidation reactions
Catalytic oxidation reactions were carried out in a 2 mL ther-
mostatic glass reactor equipped with a magnetic stirrer
placed inside a dark chamber. (Z)-Cyclooctene (previously
purified on an alumina column) or cyclohexane oxidation by
PhIO was accomplished in the presence of the tested catalyst.
In a standard heterogeneous catalysis experiment, the differ-
ent MPx-support catalysts and the oxidant (MPx/PhIO molar
ratio = 1 : 50) were suspended in 400 μL of acetonitrile and
degassed with argon for 15 min. The reaction started after
the substrate was added to the reaction medium (MPx/sub-
strate molar ratio = 1 : 5000); oxidation was carried out under
magnetic stirring for 1 h. At the end of the reaction, sodium
sulfite was introduced in the reaction mixture to eliminate
excess PhIO. The reaction solution, along with the reaction
products, was transferred to a 2 mL volumetric flask. The
solid catalyst was washed several times with methanol and
acetonitrile to extract any reaction product that might have
remained adsorbed on it. The washing solutions were added
to the previously separated reaction supernatant, and the con-
tent of these combined solutions was analyzed by gas chroma-
tography, using high-purity (99.9%) undecane or 1-octanol
(acetonitrile solution, 1.0 × 10−2 mol L−1) as the internal stan-
dard. Product yields were based on the amount of PhIO added
to each reaction. Control reactions were also performed in the
absence of MPx using the same methodology described
above. A similar experimental procedure was followed for the
homogeneous catalysis assays, but the solid catalyst washing
process was unnecessary.
Immobilization of porphyrin derivatives MP2 and MP6
on different supports
Layered double hydroxide (LDH). Mg/Al LDH (Mg/Al molar
ratio = 3 : 1) intercalated with nitrate anions was prepared
using the co-precipitation methodology as described previ-
ously.26,59 MPx–LDH (where M = Fe3+ or Mn3+ and x = 7, 8, 9,
or 10) were prepared by dispersing around 500 mg of the sup-
port LDH in 10 mL of methanol and MPx (2.6 μmol (3.2 mg)
of MnP9 and about 7.1 μmol (8.0 mg) of the other
metalloporphyrins).26 This suspension was stirred for 5 h,
and the resulting solid was filtered and exhaustively washed
with methanol. The supernatant and the methanol from the
washing process were analyzed by using UV–vis spectros-
copy to quantify the MPx that was removed from the matrix
by leaching during the washing process; the MPx loading
was calculated for each solid. The final light brown solids
MPx–LDH were dried at 55 °C for 48 h.
Silica. The solids resulting from MPx immobilization on
silica (MPx–SGA) were achieved by simultaneous preparation
of the silica by the sol–gel process and impregnation of the
metallocomplex. The silica gel was synthesized through TEOS
hydrolysis, employing HCl as the catalyst and THF as the
solvent. Briefly, MPx (4.0 μmol; 5.0 mg) was added to a glass
The solids that displayed better catalytic activity in the
first use were recovered; washed with water, methanol, aceto-
nitrile, and dichloromethane; dried; and reused in other cata-
lytic cycles using (Z)-cyclooctene as substrate. The resulting
washing solutions of all the recovered catalysts were analyzed
by using UV–vis spectroscopy to evaluate whether MPx was
leached from the support.
Characterization techniques
1H and 19F NMR spectra were recorded on a Bruker Avance
300 spectrometer at 300.13 and 282.38 MHz, respectively.
Deuterated chloroform or methanol was used as the solvent;
TMS (δ = 0 ppm) was the internal standard. Chemical shifts
are reported in ppm (δ); coupling constants (J) are given in
Fig. 2 Schematic representation of iron(III) and manganese(III) porphyrins,
where L represents the counter-ion (chloride or acetate).
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Hz. Mass spectra were acquired using a 4800 Proteomics
Analyzer mass spectrometer (MALDI TOF/TOF); HRMS spec-
tra were recorded on VG AutoSpec Q and M mass spectrome-
ters (Vigo University).
Increasing the reaction time to 24 h and using a 33 : 1 NaH/
porphyrin ratio favored the formation of tri- and tetra-
substituted porphyrins (P5, 40%; P6, 25%). After 8 h, we also
isolated the tri-substituted porphyrin P5 in 40% yield, as well
as porphyrins P2–P4 in yields ranging from ca. 11 to 22%; we
obtained porphyrin P6 as a minor fraction (3%). As stated in
the experimental part, we obtained the tetra-substituted por-
phyrin P6 in excellent yield (96%) when we conducted the
last substitution on the tri-substituted porphyrin P5 in the
presence of a large molar excess of ethylene glycol.
We identified the first isolated fraction as the mono-
substituted porphyrin P2 using 1H and 19F NMR; this com-
pound bore a single group derived from ethylene glycol, with
an Rf (retention index) very close to that of the unsubstituted
porphyrin P1. Fractions 2 and 3 corresponded to the di-
substituted porphyrins P3 and P4; their Rf values were close.
The fourth fraction corresponded to the tri-substituted por-
phyrin P5, whereas the fifth fraction, the most polar,
consisted of the tetra-substituted porphyrin P6.
Electronic spectra (UV–vis) were obtained using a Cary–
Varian or a Shimadzu UV-2501PC spectrophotometer in the
300–800 nm range. To characterize the solids by diffuse
reflectance, a UV–vis Jasco V560 spectrophotometer was used.
Transmission Fourier Transform Infrared (FTIR) spectra
were registered on a FT Mattson 7000 Galaxy spectrophotom-
eter in the 400–4000 cm−1 range using KBr pellets. KBr
was ground together with a small amount of the solid to be
analyzed, and the spectra were collected with a resolution of
4 cm−1 and an accumulation of 64 scans.
For X-ray diffraction (XRD) measurements, self-oriented
films were placed on neutral glass sample holders. The
measurements were performed in the reflection mode using
a Shimadzu XRD-6000 diffractometer operating at 40 kV
and 40 mA (Cu-Kα radiation λ= 1.5444 Å) with a dwell time
of 1° min−1.
Electron paramagnetic resonance (EPR) measurements of
the powder materials were conducted on an EPR Bruker EMX
microX spectrometer (frequency X, band 9.5 GHz) at room
temperature and at 77 K (using liquid N2), using the perpen-
dicular microwave polarization (perpendicular polarization
CW-EPR).
The products from the catalytic oxidation reactions were
quantified using the gas chromatographs Varian 3900 and
Agilent 6850 (FID detector) equipped with a DB-5 type capil-
lary column (J&W Scientific) or a DB-WAX type capillary col-
umn (J&W Scientific). Quantitative analysis was carried out
by internal standard methodology.
We numbered each of the porphyrins in accordance
with their polarity; P1 was the least polar. We character-
ized porphyrins P2 to P6 (Fig. 1) by using UV–vis and
FTIR spectroscopies, 1H and 19F NMR, and HRMS (FAB+)
(Fig. S1–S12 – ESI†).
The UV–vis spectra of porphyrins P2–P6 did not signifi-
cantly differ from the spectrum of the starting porphyrin P147
(Fig. S11 – ESI†). Therefore, substitution of the fluorine atom
did not cause major changes in the free-base porphyrins. In
other words, the different peripheral substituents did not
alter the transition mode of the porphyrin molecules.63
P2 to P6 exhibited the typical FTIR bands of free-base
porphyrins at 3342, 3122, and 2937 cm−1, due to NH, CH
(phenyl), and CH (pyrrole) stretching, respectively; 1575 cm−1
,
related to symmetric angular deformation in the plane of
the pyrrole ring NH; 1482 cm−1, corresponding to CH–R′–R′′
axial deformation; and 1372 cm−1, related to C–N axial defor-
mation, among others. In addition, we also detected other
bands characteristic of ethylene glycol binding to the porphy-
rin, namely at 1078 cm−1 (C–O–C symmetric axial deforma-
tion), 1152 cm−1 (C–O–C asymmetric axial deformation),
1457 cm−1 (CH deformation), and 3434 cm−1 (OH stretching)64
(Fig. S12 – ESI†).
Results and discussion
Synthesis of the free-base porphyrins P2–P6
Porphyrin P1 [H2(TPFPP)] is a suitable platform to obtain dif-
ferent porphyrin and metalloporphyrin derivatives. Nucleo-
philes can easily replace the fluorine atom in the p-position,
affording the desired products in good yields.43
The fluorine atoms' reactivity depends on the nucleophile.
Sulfur-containing derivatives are more reactive than amines
and alcohols (HS–CH2R > H2N–CH2R ~ HO–CH2R), so they
require less drastic conditions.44
We adapted the reaction conditions used to prepare the
free-base porphyrins P2–P6 (Fig. 1) from literature proce-
dures.44,62 First, to improve ethylene glycol nucleophilicity,
we generated the corresponding sodium salt by reacting this
compound with sodium hydride in THF at room tempera-
ture. Then, we added porphyrin P1 to the resulting mixture
and stirred it at 80 °C for 1, 8, or 24 h.
Synthesis of manganese and iron porphyrins (MPx)
We metallated porphyrins P2 and P6 using the appropriate
iron(III) and manganese(III) salts (Fig. 2). We employed
UV–vis and FTIR spectroscopies, as well as HRMS (FAB+)
and MALDI (TOF/TOF), to confirm the metallation process
(Fig. S13–S16 – ESI†); we verified the MPx oxidation state
using EPR (Fig. 3).
The yields of mono- (P2), di- (P3 and P4), tri- (P5), and
tetra- (P6) substituted porphyrins (Fig. 1) depended on reac-
tion time and NaH amount. Using the reaction time of 1 h
and 8 : 1 NaH/porphyrin ratio, we were able to preferentially
isolate the mono-substituted porphyrin P2 (61% yield).
The combination of five unpaired electrons in high-spin
Fe3+ will result in three doublets, 1/2, 3/2, and 5/2
(Kramer doublets). The extent to which these energy levels
are filled depends on the separation field and the tempera-
ture.65 In a stronger symmetry tetragonal crystal field, the
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ion has four unpaired electrons and a d4 configuration with
S = 2, typically featuring a pronounced Jahn–Teller distortion
that results in a substantial spin-orbit coupling. As a result,
mononuclear Mn(III) centers typically present no signals
(EPR silent) in the X-band EPR technique under perpendicu-
lar microwave polarization.68
Immobilization of FeP7, FeP8, MnP9, and MnP10 on
different supports
Layered double hydroxides (LDH). On the basis of our
recent studies on the intercalation/functionalization of solid
LDH with different organic molecules, e.g., triethanolamine,26
(3-aminopropyl)triethoxysilane,11 and iron porphyrins,12 we
chose LDH as support to immobilize the prepared MPx. We
obtained the LDH (Mg/Al molar ratio of 3 : 1, containing nitrate
as intercalated anion) through co-precipitation and used it
without any further functionalization. We characterized the
solids using powder X-ray diffraction and infrared spectros-
copy; the results agreed with literature data.11–13,25,26,35,59 We
immobilized MPx (MP7 to MP10) on the prepared LDH to
obtain MPx–LDH. The way these neutral MPx anchor on the
LDH support still requires elucidation, but one cannot exclude
the interactions between the π-conjugated electron cloud of the
macrocycle rings and the structure of highly hydroxylated
layers11–13,25,26 (Fig. 4). Table 1 lists the percentages of MPx
immobilized on the LDH.
Powder X-ray diffraction is a powerful tool to monitor the
intercalation of compounds into different layered com-
pounds.11,12,69 The basal distances obtained before and after
the immobilization process provide clues about the immobi-
lization mode.12,25,26 For example, when the intercalation of
the complex occurs in the LDH interlayer space, the basal
spacing increases.12
Fig. 3 EPR spectra at room temperature: (a) FeP8, (b) FeP7, (c) MnP9,
and (d) MnP10.
parameter field deployment is large; hence, one can detect
the transitions only at 1/2 (g⊥ = 6.0 and g∥ = 2.0). When the
local symmetry changes from tetragonal to orthorhombic
(less symmetric), the resulting distortion in the porphyrin
plane distorts the associated levels, generating other signals.
Systems with maximum distortion contain only one signal
(g = 4.3). Two parameters can describe the separation field:
D (axial separation) and E (rhombic separation); the ratio
between D and E can range from 0 to 0.33 (maximum rhom-
bohedral character), and the respective g values arise.66 Thus,
in solution or in the solid state, at room temperature or at
lower temperature, iron porphyrins generally present signals
in the region of g⊥= 6.0 and g∥ = 2.0, which can be attributed
to high-spin Fe(III) in axial symmetry and S = 5/2.66
The EPR spectra of complexes FeP7 and FeP8 (Fig. 3a and b)
displayed the characteristic signal of high-spin Fe(III) in axial
symmetry. Besides that, FeP8 presented low-intensity signals
due to high-spin Fe(III) at g = 4.26 (Fig. 3a), which corresponds
to high-spin Fe(III) in orthorhombic symmetry.67 FeP8 also
displayed other signals in the region of g = 2.0.
The solids resulting from MPx immobilization on the
LDH displayed an X-ray diffraction pattern similar to those
We estimated the D/E ratio using a rhombogram for Fe
(S = 5/2)66 to verify whether all the signals appeared in the
spectrum. We estimated the ratio to be 0.16; therefore, the
signals should be detected at transition states 1/2 and 3/2,
with the values of g = 8.3, g = 6.0, g = 2.9, and g = 2.0. Such
ratio indicated that FeP8 had a rhombic distortion as com-
pared with FeP7.
The influence of axial ligands and the presence of extra
groups either in the macrocycle structure or in the axial
ligand should be considered when analyzing macrocycle
distortion. In our case, the chloride axial ligand in the iron
porphyrin cannot distort the macrocycle and presents con-
comitant EPR signals, so the four OCH2CH2OH groups in
FeP8 might explain the macrocycle distortion (orthorhombic
symmetry) and the EPR signals.
The manganese porphyrin perpendicular microwave polar-
ization X-band EPR spectra at room temperature and 77 K
were similar, with no EPR signals (Fig. 3c and d), attesting
that MnP9 and MnP10 are Mn(III) porphyrinates. The Mn(III)
Fig. 4 Proposed modes for MPx immobilization on LDH; mono-
substituted MPx (MP7 and MP9) and tetra-substituted MPx (MP8
and MP10).
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Table 1 Immobilization of iron and manganese porphyrins on LDH and silica (obtained by the sol–gel process)
Loading (complex per mass of prepared solid)
(mol g−1 b % (m/m)c
Percentage of
Solid
immobilizationa
)
FeP7–SGA
FeP7–LDH
FeP8–SGA
FeP8–LDH
MnP9–SGA
MnP9–LDH
MnP10–SGA
MnP10–LDH
100
97
100
88
100
100
100
90
3.2 × 10−6
1.2 × 10−5
3.1 × 10−6
1.3 × 10−5
2.8 × 10−6
1.4 × 10−5
2.8 × 10−6
5.1 × 10−6
0.36
1.38
0.38
1.59
0.34
1.57
0.35
0.64
a
b
Immobilization percentage based on the mass of MPx used during MPx immobilization on LDH and on silica. Mol of MPx per mass (g) of
solid support. c Mass (g) of MPx per mass (g) of solid support.
obtained from the pure support (LDH) (Fig. 5). Diffraction
peaks appeared at 10.90, 21.94, and 34.69 (in 2*θ), which cor-
respond to the basal (00l) diffraction peaks. The basal dis-
tance of 8.9 Å, obtained from the higher order basal peak, is
characteristic of hydrated nitrate anions intercalated between
the LDH layers.70 This clearly shows that MPx did not inter-
calate between the layers, but they were adsorbed at the outer
layered crystal surface or even became trapped in the voids of
the agglomerated crystals (Fig. 4).
We confirmed the presence of FePx and MnPx in the LDH
by UV–vis analyses. We detected the typical Soret band of
each MPx in the spectra of the solid samples (432, 418, 472,
and 476 nm for FeP7–LDH, FeP8–LDH, MnP9–LDH, and
MnP10–LDH, respectively, Fig. 6).
Fig. 6 UV–vis spectra of (a) FeP7–LDH, (b) FeP8–LDH, (c) MnP9–LDH,
The spectrum of the raw LDH did not present bands in the
(d) MnP10–LDH, (e) FeP7–SGA, (f) FeP8–SGA, (g) MnP9–SGA, and
(h) MnP10–SGA.
region of 400 nm, so the bands in this region of the spectra of
MPx–LDH can only be due to immobilized MPx. The struc-
tural distortion of the porphyrin ring upon metalloporphyrin
immobilization on the rigid support tends to shift the elec-
tronic spectrum bands to higher wavelength. This behavior
stems from the steric hindrance posed by the medium, which
can substantially change the metalloporphyrin structure.34
When we compared the UV–vis spectra of the immobilized
MPx–LDH (Fig. 6) with the spectra of the solid free MPx
samples (Soret band at 418, 402, 460, and 460 nm for FeP7,
FeP8, MnP9, and MnP10, respectively, figures not shown), we
noted approximately 20 nm bathochromic shifts of the Soret
band, depending on MPx. This indicated that immobilization
significantly distorted the metalloporphyrin ring. These shifts
can denote destabilization of the frontier orbital HOMO in
relation to the LUMO in distorted systems, which could result
from the physical and chemical interactions between MPx
and the support surface.71 Metalloporphyrins can interact
with the hydroxyl groups present on the LDH surfaces without
significantly distorting the complex; on the other hand,
metalloporphyrins can undergo distortion to maximize inter-
action with the support (Fig. 4). In fact, immobilization can
greatly distort the porphyrin ring so that the a2u porphyrin
orbital (HOMO orbital) approaches the eg orbital (LUMO),
thereby reducing the total energy and shifting the band
toward the red region of the spectrum.72
Compared with Fe, Mn perfectly fits the cavity of the por-
phyrin ring, so FePx tends to be more distorted. The metal
size and its fitting into the porphyrin ring can influence the
ring conformation and the stability of the complex.73
The interaction between MPx and the solid support
may account for the shift and broadening of the bands in
Fig.
5 Powder X-ray diffraction patterns: (a) LDH, (b) FeP7–LDH,
(c) FeP8–LDH, (d) MnP9–LDH, and (e) MnP10–LDH.
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the spectra of MPx–LDH; indeed, this interaction may
pose steric limitations on immobilized MPx.74 Interestingly,
the immobilized tetra-substituted MPx (FeP8–LDH and
MnP10–LDH) displayed a more red-shifted Soret band than
FeP7 and MnP9, an effect that can be attributed to the MPx
structure: FeP8 and MnP10 contain four extra substituents at
the meso-phenyl groups, whereas and MnP9 have only one.
As discussed before, these groups exert a larger steric effect
on the porphyrin ring. To adjust the macrocycle structure to
the LDH layers and to promote MPx immobilization, it is
possible that the ring experiences some distortion, which
shifts the Soret band. The larger the number of substituents
bound to the porphyrin, the more red-shifted the Soret band
becomes (Fig. 6).
Studies on the electronic spectroscopy and surface photo-
chemistry of organic molecules adsorbed on silica gel have
shown that the adsorption of organic molecules on silica gen-
erally results in red-shifted bands, a consequence of the inter-
action of π electrons (porphyrin) with the surface hydroxyls.75
In addition to the intense band in the region of 400 nm,
characteristic metalloporphyrin bands appeared in the visible
region of the MPx–LDH spectra (named Q bands).
The EPR technique also attested to the presence of the iron
porphyrins in FeP7–LDH and FeP8–LDH: these solids displayed
the characteristic Fe(III) EPR signals (figures not shown).
Silica obtained by the sol–gel process. Because silica is an
inert support under oxidation reaction conditions, it is
suitable for achieving immobilization of different complexes
including metalloporphyrins.24,34,52,76–79 Table 1 presents the
immobilization percentage of each MPx and the loading that
resulted from the immobilization process.
When one accomplishes metalloporphyrin immobilization
on silica obtained by the sol–gel process, it is possible that
the metallocomplex inserts into the three-dimensional struc-
ture voids or between the particles. The complex might also
bind to the hydroxylated silica surface. The exact immobiliza-
tion mode is difficult to determine, but different techniques
can detect silica formation and the presence of each complex.
We analyzed the solids MPx–SGA (silica obtained by the
sol–gel process under acid catalyzed conditions), as well as
the control silica SGA (without MPx) using PXRD (figures not
shown). All PXRD patterns exhibited the same profile: a typi-
cal halo in the region of 20 and 30° (in 2θ), corresponding to
an amorphous structure.34,80
460, and 468 nm for FeP7–SGA, FeP8–SGA, MnP9–SGA, and
MnP10–SGA) (Fig. 6).
When we compared the UV–vis spectra of immobilized
FePx–SGA with the spectra of the solid samples of free FePx,
once again we noted that the Soret band shifted toward red.
Hence, the FePx ring experiences some kind of distortion
due to its confinement in the support. The shift verified that
MnP10–SGA was smaller, suggesting that FePx underwent
greater distortion in the silica network. As for MnP9–SGA, we
did not notice any significant shifts, suggesting that it immobi-
lizes on the support in a different fashion. In fact, Iamamoto
and co-workers reported that such shift to wavelengths of lower
energy upon metalloporphyrin immobilization is probably due
to the putative distortion of the porphyrin ring; interaction of
the macrocycle with the silica surface favors this distortion.81
The change in the UV–vis spectrum of metalloporphyrins
immobilized on silica seems to depend on both the structure
of the complex and the support. Vidoto et al.74 and Castro
et al.34 observed
a red-shifted Soret band when they
immobilized β-halogenated73 and meso-substituted34 iron
porphyrins on a silica matrix using the sol–gel process.
Poltowicz et al. also observed that the UV–vis spectra of
supported metalloporphyrins did not change with respect
to the spectra of the corresponding metalloporphyrins in
homogenous solution only when the ring did not undergo
extensive distortion during the immobilization process.82
The EPR technique also helped us characterize FePx–SGA,
namely the iron oxidation and spin state, and the possible
distortions in the porphyrin ring due to immobilization. We
obtained spectra similar to those observed for free FePx and
FePx–LDH, suggesting that FePx immobilization on silica did
not distort the ring considerably (figures not shown).
Catalytic oxidation reactions
We investigated the catalytic activities of non-immobilized
MPx (homogeneous catalysis) and MPx supported on LDH or
silica (MPx–LDH or MPx–SGA, heterogeneous catalysis) in
(Z)-cyclooctene epoxidation (Tables 2 and 3, respectively).
We also conducted recycling studies on the solids that
performed better during heterogeneous catalysis (Table 4).
Furthermore, we tested these catalysts in cyclohexane oxida-
tion (Tables 5 and 6); cyclohexane is a more inert substrate,
and metalloporphyrins catalyze its oxidation to two major
products: cyclohexanol and cyclohexanone. For comparison
purposes, we evaluated the homogeneous and heteroge-
neous catalysts under similar reaction conditions. We con-
firmed that the catalytic results achieved with MPx–LDH
and MPx–SGA were really due to the immobilized MPx: con-
trol reactions carried out with the pure matrices of LDH
and SGA (containing no MPx) did not give any oxidation
products (in the case of cyclohexane) or furnished oxidation
products in very low yields (for (Z)-cyclooctene).
We also characterized MPx–SGA using FTIR (figures not
shown). We detected the characteristic bands of the support
in the region of 3420 cm−1, due to typical axial deformation of
the surface Si–OH groups; at 1630 cm−1, assigned to the bend-
ing of physisorbed water molecules; and at 1100 cm−1, typical
of the stretching of the 180-degree angle of the Si–O–Si groups
of the four tetrahedral SiO2. We did not observe the FTIR
bands related to MPx, probably because MPx concentration
was low as compared with the amount of support (Table 1).
We confirmed the presence of FePx and MnPx in SGA
by UV–vis spectroscopy (Fig. 6, spectra e–h); we detected
the typical Soret band of each MPx in the spectra (424, 418,
(Z)-Cyclooctene. It is easy to oxidize (Z)-cyclooctene in the
presence of metalloporphyrins—this reaction leads to a
single product, cyclooctene oxide. The low stability of the
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Table
2
(Z)-Cyclooctene oxidation by PhIO catalyzed by MPx in
Table
5
Cyclohexane oxidation by PhIO catalyzed by MPx in
homogeneous mediuma
homogeneous mediuma
Catalyst
Run
Epoxide yieldb (%)
Catalyst
Run
Alcohol yielda (%)
Ketone yielda (%)
[Fe(TPFPP)]Cl
FeP7
FeP8
[Mn(TPFPP)]Cl
MnP9
1
2
3
4
5
6
7
100
71
94
98
88
96
12
[Fe(TPFPP)]Cl
FeP7
FeP8
[Mn(TPFPP)]Cl
MnP9
1
2
3
4
5
6
7
85
62
72
34
52
64
Trace
2.0
Trace
Trace
6.0
Trace
Trace
Trace
MnP10
MnP10
PhIOc
PhIOb
a
a
The cyclooctene oxide yield was calculated on the basis of the
amount of PhIO used in each reaction. The catalytic results represent
an average of at least duplicate reactions. MP/PhIO/(Z)-cyclooctene
The yield of cyclohexanol and cyclohexanone were calculated on the
basis of the amount of PhIO used in the reaction. The results represent
an average of at least duplicate reactions. MP/PhIO/cyclohexane molar
b
b
molar ratio = 1 : 50 : 5000. Reaction time: 1 h. Cyclooctene oxide.
ratio = 1 : 50 : 5000. Reaction time: 1 h. Control reaction, without
catalyst.
c
Control reaction with no catalyst addition.
Table
6 Cyclohexane oxidation by PhIO catalyzed by MPx in
heterogeneous mediuma
Table
3 (Z)-Cyclooctene oxidation by PhIO catalyzed by MPx in
heterogeneous mediuma
Yield (%)a
Alcohol
1 hb
Epoxide yielda (%)
Ketone
24 hc
Catalyst
Run
Catalyst
Run
24 hb
FeP7–LDHb
1
2
3
4
5
6
7
8
9
58
29
69
42
84
20
30
71
15
32
12
10
FeP7–SGAb
FeP7–LDH
FeP8–LDH
MnP9–LDH
MnP10–LDH
PhIO + LDHd
1
2
3
4
5
1
24
5
1
—
15
41
16
8
Trace
Trace
3.8
Trace
—
FeP8–LDHb
FeP8–SGAb
MnP9–LDHb
MnP9–SGAb
MnP9–SGAc
MnP10–LDH
MnP10–SGAb
MnP10–SGAc
PhIO + SGAd
PhIO + LDHe
—
a
The yields were calculated on the basis of the amount of PhIO used
in the reaction. The results represent an average of at least duplicate
b
reactions. MP/PhIO/cyclohexane molar ratio = 1 : 50 : 5000. Reaction
10
11
12
time. c No ketone was observed after 1 h of reaction. d Control reaction,
without catalyst.
a
The yield of cyclooctene oxide was calculated on the basis of the
amount of PhIO used in the reaction. The results represent an
average of at least duplicate reactions. MP/PhIO/(Z)-cyclooctene
b
c
molar ratio = 1 : 50 : 5000. Reaction time of 1 h. Reaction time of
3 h. Control reaction: the solid obtained by the sol–gel process in
allyl species formed from this substrate as compared with
the allyl species generated from other alkenes (for example,
cyclohexene) favors epoxide production.83,84 Scientists fre-
quently employ this substrate as a diagnostic compound in
catalytic systems involving metalloporphyrins. The catalytic
oxidation of this cycloalkene by PhIO under the catalytic
action of a certain metalloporphyrin demonstrates the effi-
ciency and the stability of that particular catalytic complex
and evidences how catalysts, in solution or immobilized on
different supports, differ in terms of reactivity. This reaction
also provides information on the accessibility of the iron(III)
and manganese(III) sites in the immobilized metalloporphyrin
to the substrate and the oxidant. Table 2 presents the results
obtained in (Z)-cyclooctene epoxidation catalyzed by MPx in
homogeneous medium.
Usually, metalloporphyrins containing bulky or electroneg-
ative groups in the ortho-positions of the meso-substituents
of the porphyrin ring give good results in the catalyzed oxida-
tion reactions.5,6 This performance stems from the steric and
electronic effects that the substituents exert on the porphyrin
ring—the more electronegative the substituent, the longer
the active catalytic species lifetime.5 Additionally, these bulky
substituents may prevent the formation of inactive species
(e.g., dimeric species) and the porphyrin ring auto-oxidative
d
the absence of MPx was grounded, and the resulting powder was
used as catalyst. Control reaction: the reaction was performed
with LDH without MPx using the same mass as in the case of the
catalytic reaction using MPx–LDH.
e
Table 4 Reusability studies on the (Z)-cyclooctene oxidation by PhIO
catalyzed by MPx–LDH under heterogeneous conditions
Catalyst
Run
Epoxide yielda (%)
FeP7–LDH first reuse
FeP7–LDH second reuse
FeP7–LDH third reuse
FeP8–LDH first reuse
FeP8–LDH second reuse
FeP8–LDH third reuse
MnP9–LDH first reuse
MnP9–LDH second reuse
MnP9–LDH third reuse
MnP10–LDH first reuse
MnP10–LDH second reuse
MnP10–LDH third reuse
1
2
3
4
5
6
7
8
9
55
57
54
65
70
68
74
70
68
75
74
67
10
11
12
a
The yield of cyclooctene oxide was calculated on the basis of the
amount of PhIO used in the reaction. The results represent an
average of at least duplicate reactions. MP/PhIO/(Z)-cyclooctene
molar ratio = 1 : 50 : 5000. Reaction time: 1 h.
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destruction. Together, these factors may explain the different
MPx performances in (Z)-cyclooctene epoxidation (Table 2).
As expected, [Fe(TFPP)Cl] and [Mn(TFPP)Cl] (runs 1 and 4,
respectively) furnished product yields as high as 98%.85,86 As
for FeP7 and MnP9 (in which one fluorine atom is replaced
with ethylene glycol, runs 2 and 5, respectively) and FeP8 and
MnP10 (in which four fluorine atoms are substituted with
ethylene glycol, runs 3 and 6, respectively), the epoxide yields
decreased. Bearing in mind that electronegative groups
increase the catalytically active metal-oxo species lifetime, the
absence of these groups should reduce the catalytic activity.3
However, the epoxide yield decreased more markedly for the
mono-substituted complexes as compared with the tetra-
substituted ones. Therefore, the four ethylene glycol substitu-
ents in FeP8 and somehow inhibited the dimeric species for-
mation and porphyrin ring auto-oxidative destruction. Moreover,
the presence of bulkier substituents can affect ring symmetry,
causing some distortion. Hence, substitution at the four
p-positions of the phenyl rings distorted the porphyrin ring in
FeP8 and to a larger extent than substitution at one p-position
of the phenyl rings in FeP7 and MnP9. This fact may have
influenced the formation and stabilization of the active cata-
lytic oxo-species, resulting in lower epoxide yields for the
mono-substituted complexes (FeP7 and MnP9).
When we used MPx–LDH (Table 3, runs 1, 3, 5, and 8)
under the same reaction conditions (same reaction time), we
achieved epoxide yields lower than or similar to those
observed for homogeneous catalysis (Table 2, runs 2, 3, 5,
and 6). The epoxide yields decreased by 13% for FeP7–LDH
and 25% for FeP8–LDH and MnP10–LDH. Interestingly,
MnP9–LDH was as effective as its homogeneous counterpart
(84% vs. 88%, Table 3, run 5, and Table 2, run 5, respectively).
In general, bulky substituents seem to sterically hinder
the approach between reactants and catalyst, thereby making
the access of the oxidant and the substrate to the macrocycle
metal center difficult and preventing the formation of the
active catalytic oxo-species and the oxidation reaction prod-
ucts. The steric effect exerted by the substituents was even
more evident in the case of immobilized MPx, as the catalytic
results suggest. Furthermore, the mono- and tetra-substituted
MPx behaved differently, suggesting distinct MPx immobili-
zation modes on LDH; thus, the way MPx were immobilized
on the matrix influenced their reactivity. The presence of four
–OR groups probably favored the interaction of MnPx with
the LDH support. Consequently, access of the substrate and
oxidant to the catalytic center was more hindered in FeP8
and MnP10 (Table 4, runs 3 and 8) as compared with the
mono-substituted FeP7 and MnP9 (Table 4, runs 1 and 5),
leading to greater decline in product yields in the case of the
tetra-substituted catalysts.
(Table 3, runs 7 and 10). This strongly suggests that the MnPx
may have been trapped in the silica network, making the
access of the oxidant to the metal center to form the active
catalytic oxo-species difficult. In this sense, a longer reaction
time should allow the reagents more time to interact.
Although the yields decreased for all the tested MPx–LDH
and MPx–SGA as compared with MPx in homogeneous
medium, immobilization offered a major advantage: it enabled
catalyst recyclability. Indeed, UV–vis analyses did not detect
any MPx leaching from the support after the first use or after
the washing and drying processes. To investigate the recyclabil-
ity of MPx–LDH, we reused them in a second (Z)-cyclooctene
epoxidation reaction (Table 4). In general, all the reused
MPx–LDH led to similar yields as compared with the corre-
sponding fresh catalyst. Hence, MPx did not leach from the
support LDH and enabled us to reuse MPx–LDH without loss
of catalytic activity. The results obtained in the recycling reac-
tions also indicated that MPx were resistant to the reaction
conditions and interacted strongly with the support. We
recovered MPx–LDH after the first reaction by simple filtra-
tion, washing, and drying. In fact, analysis of all the reaction
mixtures after the catalytic reactions and the recovery proce-
dure failed to display the characteristic MPx Soret band. After
reuse, we recovered the MPx–LDH again and reused them in a
third reaction; we did not detect any alterations in their activ-
ity. The reusability and stability of MPx–LDH point to a prom-
ising and economically viable process.
Cyclohexane. We also evaluated the catalytic activity and
selectivity of the prepared materials in cyclohexane oxidation.
Metalloporphyrin-catalyzed oxidation of this cycloalkane usu-
ally furnishes cyclohexanol and cyclohexanone;83 alcohol is
usually the preferential product.
In accordance with the literature,3,5,7,84,85,87–93 [Fe(TPFPP)]Cl
and [Mn(TPFPP)]Cl (homogeneous catalysis) catalyzed cyclo-
hexane oxidation efficiently and selectively (runs 1 and 4;
alcohol yield = 85 and 34%; ketone yield = 2.0 and 6.0%,
respectively). Table 5 shows that the reaction yields for the
modified iron porphyrins FeP7 and FeP8 were lower than
the yields obtained for [Fe(TPFPP)]Cl. As discussed above in
the case of (Z)-cyclooctene epoxidation, substitution of fluo-
rine atoms by the –OR groups from the ethylene glycol moie-
ties justifies this decrease.
For manganese porphyrins, we observed a reverse trend:
the modified manganese porphyrins MnP9 and MnP10 afforded
higher product yields than [Mn(TPFPP)]Cl. The solvent used in
the catalytic studies—acetonitrile (ACN)—may have contributed
to this result. We have verified that the best reaction medium
for catalytic reactions using metalloporphyrins similar to
[M(TPFPP)]Cl (M = Fe or Mn) is a mixture of solvents such as
dichloromethane and acetonitrile 1 : 1 (v/v);12,13,26,35,93 this
mixture solubilizes both the substrate and PhIO, while the
catalyst is not always completely soluble in this medium.
Some years ago, Iamamoto and co-workers92 reported that
when they used dichloromethane (DCM) as the solvent, they
achieved the best [Mn(TPFPP)]Cl catalytic performance in
cyclohexane oxidation. However, when these authors used the
We also investigated the catalytic activity of MPx–SGA in
(Z)-cyclooctene epoxidation (Table 3, runs 2, 4, 6, 7, 9, and
10). All the MPx–SGA afforded lower yields as compared with
the parent MPx–LDH and MPx in homogeneous medium. We
decided to carry out the epoxidation reactions for longer
periods (3 h), and we verified that the product yield increased
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same solvent for [Fe(TFPP)Cl], they verified competitive oxida-
tion reactions between DCM and cyclohexane, which dimin-
ished the product yield. ACN can minimize competitive
reactions between solvent and substrate, although in some
cases it can also compete with cyclohexane for the catalytic
active center, as it can be oxidized to HCN and formalde-
hyde.92 In the present work, we chose to use only ACN as sol-
vent because it is more appropriate from an environmental
standpoint and seems to affect the catalytic activity of the
tested MPx to a lesser extent.
site, thus favoring catalysis.26,36,42,98,99 On the basis of our
previous experience, we conducted the MPx–LDH-catalyzed
cyclohexane oxidation reactions for 24 h (Table 6). The
results show that all the MPx–LDH afforded better results
after 24 h of reaction as compared with reaction time of 1 h.
Once again, FeP8–LDH performed the best.
We did not detect any significant ketone formation. The
exception was MnP9–LDH. Although a longer reaction time led
to better yields, the reaction became less selective in this case.
Over oxidation of alcohol might underlie ketone production.23,89
Table 5 also reveals that MPx bearing four –OR groups at
the para-positions of the meso-phenyls of the macrocycle
(more symmetric) furnished higher product yields as com-
pared with MPx containing only one –OR group, a behavior
we had already verified during (Z)-cyclooctene epoxidation.
FePx provided better yields than MnPx,93 because recombina-
tion between the active catalytic species originated from FePx
and cyclohexane was faster as compared with MnPx.93–95
Indeed, it is known that the intermediate species formed
after the abstraction of a proton from the substrate by man-
ganese porphyrin, (Mn(IV)(OH)Por)+, is more stable as com-
pared with the intermediate species originated from the iron
porphyrin, (Fe(IV)(OH)Por)+.95 In the generally accepted reac-
tion pathway,96,97 the active catalytic species abstracts a
hydrogen atom from the substrate, generating an alkyl radi-
cal and a hydroxo-metalloporphyrin in a cage solvent. Oxygen
rebound preferably occurs within the cage, forming the alco-
hol. A more kinetically stable intermediate, as in the case of
manganese porphyrins, results in recombination of the cata-
lyst with the alkyl radical (radical species escapes from the
vicinity of the intermediate species–solvent cage).94 In the
case of the iron porphyrin, oxygen rebound is rapid.95
MPx immobilization on LDH elicited a drastic drop in the
cyclohexanol yield as previously noted by some of us when
we immobilized [Fe(TPFPP)]Cl on this same support.26 In the
particular cases of FeP7–LDH, MnP9–LDH, and MnP10–LDH,
the yields were less than 10% after 1 h of reaction (Table 6).
FeP8–LDH gave the best result after 1 h of reaction
(Table 6, run 6, 24% alcohol yield). Although this yield was
lower than that achieved with FeP8 in homogeneous catalysis
(Table 5, run 1), this solid has the advantage of recyclability.
Furthermore, FeP8–LDH catalyzed cyclohexane oxidation
more effectively than Fe(TFPP)–LDH (alcohol yield = 7.0%),26
justifying the modification of P1 with ethylene glycol.
Conclusions
We successfully accomplished the chemical modification of
the porphyrin [H2(TPFPP)] using ethylene glycol. We obtained
five derivatives as a result of the substitution of the p-fluorine
atoms on the meso-phenyl rings by an alkoxide from ethylene
glycol. We characterized the obtained porphyrins using
UV–vis and FTIR spectroscopies, and 1H and 19F NMR. We
metallated the mono- and tetra-substituted derivatives with
Fe(III) and Mn(III), which furnished stable metalloporphyrin
complexes. We immobilized the resulting metalloporphyrins
on two different supports: LDH and silica (obtained by the
sol–gel methodology). Preliminary results demonstrated
that these materials are catalytically active in the oxidation of
(Z)-cyclooctene and cyclohexane by PhIO. Furthermore, we
were able to reuse the LDH-immobilized metalloporphyrins in
at least three additional cycles of (Z)-cyclooctene oxidation.
Acknowledgements
The authors are grateful to Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq), Coordenação
de Aperfeiçoamento de Pessoal de Nível Superior (CAPES),
Fundação Araucária, Fundação da Universidade Federal do
Paraná (FUNPAR), and Universidade Federal do Paraná
(UFPR) for the financial support. Thanks are also due to
Fundação para a Ciência e a Tecnologia (FCT, Portugal),
European Union, QREN, FEDER and COMPETE for funding
the QOPNA research unit (project PEst-C/QUI/UI0062/2011)
and the Portuguese National NMR Network, also supported
with funds from FCT. Kelly A. D. F. Castro also thanks CAPES
for the PhD sandwich scholarship (process 6883-10-9).
In general, under ideal reaction conditions, better yields
are not expected upon increasing the reaction times when
reactions are conducted in a homogeneous medium. We had
previously optimized the reaction time used in all the cata-
lytic experiments;12,24,26,34 in most cases, one hour of reac-
tion was enough to obtain the best catalytic results. However,
for heterogenized metalloporphyrins, increasing the reaction
time can lead to better yields, mainly if the heterogenization
process somehow blocks the access of the reactants to the
metal center of the immobilized catalyst. The longer contact
time between the solid catalyst, the substrate, and the oxi-
dant can facilitate the access of both reactants to the active
Notes and references
1 P. Battioni, J. F. Bartoli, D. Mansuy, Y. S. Byun and
T. G. Traylor, J. Chem. Soc., Chem. Commun., 1992, 1051.
2 A. Agarwala and D. Bandyopadhway, Chem. Commun.,
2006, 4823.
3 J. T. Groves, J. Inorg. Biochem., 2006, 100, 434.
4 R. Davydov, T. M. Makris, V. Kofman, D. E. Werst,
S. G. Sligar and B. M. Hoffman, J. Am. Chem. Soc., 2001,
123, 1403.
5 D. Dolphin, T. G. Traylor and L. Y. Xie, Acc. Chem. Res.,
1997, 30, 251.
This journal is © The Royal Society of Chemistry 2014
Catal. Sci. Technol., 2014, 4, 129–141 | 139

View Article Online
Paper
Catalysis Science & Technology
6 K. S. Suslick, ed. K. Kadish, K. Smith and R. Guilard,
The Porphyrin Handbook, Academic Press, New York, 1999.
7 A. J. Appleton, S. Evans and J. R. L. Smith, J. Chem. Soc.,
Perkin Trans. 2, 1995, 281.
8 M. E. Kosal and K. Suslick, J. Solid State Chem., 2000, 152, 87.
9 N. G. Giri and S. M. S. Chauhan, Catal. Commun., 2009, 10, 383.
10 J. H. Han, S.-K. Yoo, J. S. Seo, S. J. Hong, S. K. Kimb and
C. Kim, Dalton Trans., 2005, 402.
11 F. Wypych, A. Bail, M. Halma and S. Nakagaki, J. Catal.,
2005, 234, 431.
12 M. Halma, K. A. D. F. Castro, C. Taviot-Gueho, V. Prévot,
C. Forano, F. Wypych and S. Nakagaki, J. Catal., 2008, 257, 233.
13 S. Nakagaki, F. L. Benedito and F. Wpych, J. Mol. Catal. A:
Chem., 2004, 217, 121.
14 S. Hirohara, M. Nishida, K. Sharyo, M. Obata, T. Ando and
M. Tanihara, Bioorg. Med. Chem., 2010, 18, 1526.
15 N. M. M. Moura, F. Giuntini, M. A. F. Faustino,
M. G. P. M. S. Neves, A. C. Tomé, A. M. S. Silva, E. M. Rakib,
A. Hannioui, S. Abouricha, B. Röder and J. A. S. Cavaleiro,
ARKIVOC, 2010, 24.
16 L. Grill, M. Dyer, L. Lafferentz, M. Persson, M. V. Peters and
S. Hecht, Nat. Nanotechnol., 2007, 2, 687.
17 W. M. Campbell, A. K. Burrell, D. L. Officer and K. W. Jolley,
Coord. Chem. Rev., 2004, 248, 136.
33 R. Paula, M. M. Q. Simões, M. G. P. M. S. Neves and
J. A. S. Cavaleiro, J. Mol. Catal. A: Chem., 2011, 345, 1.
34 K. A. D. F. Castro, M. Halma, G. S. Machado, G. P. Ricci,
G. M. Ucoski, K. J. Ciuffi and S. Nakagaki, J. Braz. Chem.
Soc., 2010, 21, 1329.
35 S. Nakagaki, M. Halma, A. Bail, G. G. C. Arízaga and
F. Wypych, J. Colloid Interface Sci., 2005, 281, 417.
36 M. Halma, A. Bail, F. Wypych and S. Nakagaki, J. Mol. Catal.
A: Chem., 2006, 243, 44.
37 R. J. Abraham and I. Marsden, Tetrahedron, 1992, 48, 7489.
38 N. A. Stephenson and A. T. Bell, J. Am. Chem. Soc., 2005, 127,
8635.
39 E. H. Schaab, A. E. M. Crotti, Y. Iamamoto, M. J. Kato,
L. V. C. Lotufo and N. P. Lopes, Biol. Pharm. Bull., 2010,
33, 912.
40 F. R. Longo, M. G. Finarelli and J. B. Kim, J. Heterocycl.
Chem., 1969, 6, 927.
41 C. K. Chang and F. Ebina, J. Chem. Soc., Chem. Commun.,
1981, 778.
42 W. Nam, H. J. Lee, S.-Y. Oha, C. Kimb and H. G. Jang,
J. Inorg. Biochem., 2000, 80, 219.
43 J. I. T. Costa, A. C. Tomé, M. G. P. M. S. Neves and
J. Cavaleiro, J. Porphyrins Phthalocyanines, 2011, 15, 1116.
44 J. Králova, T. Bríza, I. Moserova, B. Dolensky, P. Vasek,
P. Pouckova, Z. Kejik, R. Klaplánek, P. Martázek, M. Dvorak
and V. Král, J. Med. Chem., 2008, 51, 5964.
18 D. K. Panda, F. S. Goodson, S. Ray, R. Lowell and S. Saha,
Chem. Commun., 2012, 48, 8775.
19 T. Malinski and Z. Taha, Nature, 1992, 358, 676.
20 D. Vlascici, E. Fagadar-Cosma, I. Popa, V. Chiriac and
M. Gil-Agusti, Sensors, 2012, 12, 8193.
45 P. Battioni, E. Cardin, M. Louloudi, B. Schollhorn,
G. A. Spyroulias, D. Mansuy and T. G. Traylor, Chem.
Commun., 1996, 2037.
21 J. L. Sessler and D. Seidel, Angew. Chem., Int. Ed., 2003,
42, 5134.
22 B. Meunier, Chem. Rev., 1992, 92, 1411.
23 J. R. Lindsay Smith, Y. Iamamoto and F. S. Vinhado, J. Mol.
Catal. A: Chem., 2006, 252, 23.
24 G. M. Ucoski, K. A. D. F. Castro, K. J. Ciuffi, G. P. Ricci,
J. A. Marques, F. S. Nunes and S. Nakagaki, Appl. Catal., A,
2011, 404, 120.
25 M. Halma, A. Bail, F. Wypych and S. Nakagaki, J. Mol. Catal.
A: Chem., 2006, 243, 44.
26 K. A. D. F. Castro, A. Bail, P. B. Groszewicz, G. S. Machado,
W. Schreiner and F. Wypych, Appl. Catal., A, 2010, 386, 51.
27 D. Mansuy, C. R. Chim., 2007, 10, 392.
46 L. F. Pedrosa, M. C. Souza, M. A. F. Faustino,
M. G. P. M. S. Neves, A. M. Silva, A. C. Tomé, V. F. Ferreira
and J. A. S. Cavaleiro, Aust. J. Chem., 2011, 64, 939.
47 S. Silva, P. M. R. Pereira, P. Silva, F. A. A. Paz,
M. A. F. Faustino, J. A. S. Cavaleiro and J. Tomé, Chem.
Commun., 2012, 48, 3608.
48 K. J. Ciuffi, H. C. Sacco, J. C. Biazzotto, E. A. Vidoto,
O. R. Nascimento, C. A. P. Leite, O. A. Serra and Y. Iamamoto,
J. Non-Cryst. Solids, 2000, 273, 100.
49 J. R. Lindsay Smith and Y. Iamamoto, J. Mol. Catal. A:
Chem., 2006, 252, 23.
50 F. G. Doro, J. R. Lindsay Smith, A. G. Ferreira and
M. D. Assis, J. Mol. Catal. A: Chem., 2000, 164, 97.
51 A. L. Faria, T. C. O. Mac Leod and M. D. Assis, Catal. Today,
2008, 863, 133.
28 B. Meunier, S. P. Visser and S. Shaik, Chem. Rev., 2004,
104, 3947.
29 M. M. Q. Simões, R. De Paula, M. G. P. M. S. Neves and
J. A. S. Cavaleiro, J. Porphyrins Phthalocyanines, 2009, 13, 589.
30 S. M. G. Pires, M. M. Q. Simões, I. C. M. S. Santos,
S. L. H. Rebelo, M. M. Pereira, M. G. P. M. S. Neves and
J. A. S. Cavaleiro, Appl. Catal., A, 2012, 439, 51.
31 C. M. B. Neves, M. M. Q. Simões, I. C. M. S. Santos,
F. M. J. Domingues, M. G. P. M. S. Neves, F. A. A. Paz,
A. M. S. Silva and J. A. S. Cavaleiro, Tetrahedron Lett., 2011,
52, 2898.
52 A. T. Papacídero, L. A. Rocha, B. L. Caetano, E. Molina,
H. C. Sacco, E. J. Nassar, Y. Martinelli, C. Mello, S. Nakagaki
and K. J. Ciuffi, Colloids Surf., A, 2005, 275, 27.
53 G. S. Machado, G. G. C. Arízaga, F. Wypych and S. Nakagaki,
J. Mol. Catal., 2010, 274, 130.
54 G. S. Machado, F. Wypych and S. Nakagaki, J. Colloid
Interface Sci., 2012, 377, 379.
55 W. Stober and A. Fink, J. Colloid Interface Sci., 1968, 26, 62.
56 E. L. Crepaldi and J. B. Valim, Quim. Nova, 1998, 21, 300.
57 V. Rives and M. A. Ullibarri, Coord. Chem. Rev., 1999,
181, 61.
32 S. L. H. Rebelo, A. R. Gonçalves, M. M. Pereira,
M. M. Q. Simões, M. G. P. M. S. Neves and J. A. S. Cavaleiro,
J. Mol. Catal. A: Chem., 2006, 256, 321.
58 J. C. Sharefkin and H. Saltzmann, Org. Synth., 1963, 43, 60.
140 | Catal. Sci. Technol., 2014, 4, 129–141
This journal is © The Royal Society of Chemistry 2014

View Article Online
Catalysis Science & Technology
Paper
59 J. Inacio, C. Taviot-Guého, C. Forano and J. P. Besse, Appl.
Clay Sci., 2001, 18, 255.
60 A. M. R. Gonsalves, J. M. T. B. Varejão and M. M. Pereira,
J. Heterocycl. Chem., 1991, 28, 635.
81 L. B. Bolzon, H. R. Airoldi, F. B. Zanardi, J. C. Granado and
Y. Iamamoto, Microporous Mesoporous Mater., 2013, 168, 37.
82 J. Poltowicz and J. Haber, J. Mol. Catal. A: Chem., 2004,
220, 43.
61 H. Kobayashi, T. Higuchi, Y. Kaizu, H. Osada and M. Aoki,
Bull. Chem. Soc. Jpn., 1975, 48, 3137.
83 D. R. Leanord and J. R. Lindsay-Smith, J. Chem. Soc., Perkin
Trans. 2, 1991, 25.
62 D. Samaroo, M. Vinodu, X. Chen and C. M. Drain, J. Comb.
Chem., 2007, 9, 998.
84 P. Inchley, J. R. Lindsay-Smith and R. J. Lower, New J. Chem.,
1989, 13, 669.
63 W. Zheng, N. Shan, L. Yu and X. Wang, Dyes Pigm., 2008,
77, 153.
85 E. C. Zampronio, M. C. A. F. Gotardo, M. D. Assis and
H. P. Oliveira, Catal. Lett., 2005, 104, 53.
64 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds parts A and B, Wiley Interscience
Publication, 5th edn, 1997.
86 O. J. Lima, D. P. Aguirre, D. C. Oliveira, M. A. Silva, C. Mello,
C. A. P. Leite, H. C. Sacco and K. J. Ciuffi, J. Mater. Chem.,
2011, 11, 2476.
65 M. Nakamura, Coord. Chem. Rev., 2006, 250, 2271.
66 R. Cammack and C. E. Cooper, Methods Enzymol., 1993,
227, 353.
67 R. Cheng, P. Chen, P. Gau, C. Cheu and S. Peng, J. Am.
Chem. Soc., 1997, 119, 2563.
68 M. T. Caudle, C. K. Mobley, L. M. Bafaro, R. Lobrutto,
G. T. Yee and T. L. Groy, Inorg. Chem., 2004, 43, 506.
69 S. Nakagaki and F. Wypych, J. Colloid Interface Sci., 2007,
315, 142.
70 F. Cavani, F. Trifirb and A. Vaccari, Catal. Today, 1991,
11, 173.
87 G. R. Friedermann, M. Halma, K. A. D. F. Castro,
F. L. Benedito, F. G. Doro, S. M. Drechsel, A. S. Mangrich,
M. D. Assis and S. Nakagaki, Appl. Catal., A, 2006, 308, 172.
88 Y. Iamamoto, C. M. C. Prado, H. C. Sacco, K. J. Ciuffi,
M. D. Assis, A. P. J. Maestrin, A. J. B. Melo, O. Baffa and
O. R. Nascimento, J. Mol. Catal. A: Chem., 1997, 117, 259.
89 Y. Iamamoto, M. D. Assis, K. J. Ciuffi, H. C. Sacco,
L. Iwamoto, A. J. B. Melo, O. R. Nascimento and
C. M. C. Prado, J. Mol. Catal. A: Chem., 1996, 109, 189.
90 J. T. Groves and T. E. Nemo, J. Am. Chem. Soc., 1983,
105, 6243.
71 H. Kameyama, H. Suzuki and A. Amano, Chem. Lett., 1988,
1117.
91 T. G. Traylor and W. P. F. D. Bandyopadhhyay, J. Am. Chem.
Soc., 1989, 111, 8009.
72 M. Gouterman, J. Mol. Spectrosc., 1961, 6, 138.
73 M. J. Nappa and R. J. McKinney, Inorg. Chem., 1988,
27, 3740.
92 Y. Iamamoto, M. D. Assis, K. J. Ciuffi, C. M. C. Prado,
B. Z. Prellwitz, M. Moraes, O. R. Nascimento and H. C. Sacco,
J. Mol. Catal. A: Chem., 1997, 116, 365.
74 E. A. Vidoto, M. S. M. Moreira, F. S. Vinhado, K. J. Ciuffi,
O. R. Nascimento and Y. Iamamoto, J. Non-Cryst. Solids,
2002, 304, 151.
93 G. S. Machado, P. B. Groszewicz, K. A. D. F. Castro,
F. Wypych and S. Nakagaki, J. Colloid Interface Sci., 2012,
374, 278.
75 M. Espinosa, S. Pacheco and R. Rodriguez, J. Non-Cryst.
Solids, 2007, 353, 2573.
94 J. A. Smegal and C. L. Hill, J. Am. Chem. Soc., 1983, 105, 3515.
95 J. T. Groves and D. V. Adhyam, J. Am. Chem. Soc., 1984,
106, 2177.
96 J. T. Groves, R. C. Haushalter, M. Nakamura, T. E. Nemo
and B. J. Evans, J. Am. Chem. Soc., 1981, 103, 2884.
97 J. T. Groves, T. E. Nemo and R. S. Meyers, J. Am. Chem. Soc.,
1979, 101, 1032.
76 H. C. Sacco, K. J. Ciuffi, J. C. Biazzotto, C. Mello,
D. C. Oliveira, E. A. Vidoto, O. R. Nascimento, O. A. Serra
and Y. Iamamoto, J. Non-Cryst. Solids, 2001, 284, 174.
77 M. A. G. Sánchez, S. R. Tello, R. Sosa and A. Campero,
J. Sol-Gel Sci. Technol., 2006, 37, 93.
78 M. Trytek, M. Madjan, A. Lipke and J. Fiedurek, J. Catal.,
2012, 286, 193.
79 F. Figueira, J. A. S. Cavaleiro and J. P. C. Tomé, J. Porphyrins
Phthalocyanines, 2011, 15, 517.
80 H. Tanaka, T. Yamada, S. Sugiyama, H. Shiradoti and
R. Hino, J. Colloid Interface Sci., 2005, 286, 812.
98 M. Halma, K. A. D. F. Castro, V. Prévot, C. Forano,
F. Wypych and S. Nakagaki, J. Mol. Catal. A: Chem., 2009,
310, 42.
99 S. Nakagaki, K. A. D. F. Castro, M. Halma, G. S. Machado,
S. M. Drechsel and F. Wypych, J. Braz. Chem. Soc., 2006, 17,
1672.
This journal is © The Royal Society of Chemistry 2014
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