Cationic manganese(III) porphyrins bound to a novel bis-functionalised silica as catalysts for hydrocarbons oxygenation by iodosylbenzene and hydrogen peroxide

Article abstract of DOI:10.1016/S1381-1169(01)00200-X

The cationic manganese porphyrins, manganese(III) 5,10,15-tris(2,6-dichlorophenyl)-20-(4-N-methylpyridyl)porphy rin ([Mn{M(4-N-MePy)TDCPP}]²⁺), 5,10,15,20-tetra(2,3,5,6-tetrafluoro-4-trimethylammoniumpheny l)porphyrin ([Mn(TF4TMAPP)]⁵⁺) and 5,10,15-20-tetra(4-N-methylpyridyl)porphyrin ([Mn{T(4-N-MePy)P}]⁵⁺) supported on silica modified with propylimidazole (IPG), sulfonatophenyl (SiSO₃^-) and both propylimidazole and sulfonatophenyl (SiSO₃^-(IPG)) were studied as catalysts in the epoxidation of (Z)-cyclooctene and oxidation of cyclohexane. High product yields were obtained using PhIO as oxidant without leaching, except for IPG, of the catalyst from the support surface. The catalysts were also used with H₂O₂ in the epoxidation of (Z)-cyclooctene with and without a co-catalyst (imidazole or ammonium acetate). The best catalyst [Mn{T(F4TMAPP}]-SiSO₃(IPG) achieved nearly 200 turnovers of the product cis-epoxycyclooctane using ammonium acetate as co-catalyst. The analogous homogeneous catalyst systems did not exhibit the same efficiency. These results confirmed the two-fold role of imidazole in oxygenations of hydrocarbons by H₂O₂ and Mn(III) porphyrins.

Full text of DOI:10.1016/S1381-1169(01)00200-X

Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
Cationic manganese(III) porphyrins bound to a novel
bis-functionalised silica as catalysts for hydrocarbons
oxygenation by iodosylbenzene and hydrogen peroxide
Fábio S. Vinhado, Cynthia M.C. Prado-Manso, Hérica C. Sacco, Yassuko Iamamoto∗
Departamento de Qu´ımica, FFCLRP, Universidade de São Paulo, Av. Bandeirantes 3900, CEP 14040-901, Ribeirão Preto, SP, Brazil
Received 22 January 2001; accepted 24 April 2001
Abstract
The cationic manganese porphyrins: manganese(III) 5,10,15-tris(2,6-dichlorophenyl)-20-(4-N-methylpyridyl)porphyrin
([Mn{M(4-N-MePy)TDCPP}]2+), 5,10,15,20-tetra(2,3,5,6-tetrafluoro-4-trimethylammoniumphenyl)porphyrin ([Mn(TF4T-
MAPP)]5+) and 5,10,15,20-tetra(4-N-methylpyridyl)porphyrin ([Mn{T(4-N-MePy)P}]5+) supported on silica modified with
propylimidazole (IPG), sulfonatophenyl (SiSO3−) and both propylimidazole and sulfonatophenyl (SiSO3−(IPG)) have been
studied as catalysts in the epoxidation of (Z)-cyclooctene and oxidation of cyclohexane. High yields of products were ob-
tained using PhIO as oxidant without leaching, except for the IPG, of the catalyst from the surface of the support. The
catalysts also have been used with H2O2 in the epoxidation of (Z)-cyclooctene with and without a co-catalyst (imidazole
or ammonium acetate). The best catalyst [Mn{T(F4TMAPP)}]-SiSO3(IPG) achieved almost 200 turnovers of the product
cis-epoxycyclooctane using ammonium acetate as co-catalyst. The analogous homogeneous systems have been studied for
comparison, but they did not reach the same efficiency. With these studies the two-fold role of imidazole in oxygenations
of hydrocarbons by H2O2 and Mn(III) porphyrins was confirmed. The characterisation of supported metalloporphyrins by
UV–VIS spectroscopy is reported too. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Manganese(III) porphyrin; Hydrocarbons oxygenation; Role of co-catalyst; Bis-functional support; Hydrogen peroxide
1. Introduction
can be easily destroyed during the reaction and (ii)
it is not easy to recover the catalyst at the end of the
reaction for re-use [1–3].
In the search of versatile catalytic systems that
mimic the action of cytochrome P-450-dependent
monooxygenases, some synthetic metalloporphyrins
have been found to be highly efficient homogeneous
catalysts for alkene epoxidation and alkane hydrox-
ylation, using oxygen a−tom donors such as iodosyl-
benzene (PhIO), HSO5 or H2O2. However, these
homogeneous catalysts have some drawbacks: (i) they
In recent publications it has been argued that these
limitations might be avoided by binding the metallo-
porphyrins to solid materials [4]. The support can also
provide steric and electronic effects, which, in some
respects, are analogous to the influence of the protein
matrix of hemoproteins [5,6]. There are reports using
metalloporphyrins, bound to silica [7], ion exchange
resins [8] and clays [9] as catalysts in reactions of
hydrocarbons oxygenation by PhIO with some sys-
tems reaching high yields of products and improved
regioselectivity [9]. Within this context it would be
∗ Corresponding author. Tel.: +55-16-602-3782;
fax: +55-16-633-8151.
E-mail address: iamamoto@usp.br (Y. Iamamoto).
1381-1169/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(01)00200-X

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F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
interesting to extend the applications of these sup-
ported catalysts to include the use of the cheap and
clean oxidant H2O2 [10–12]. In this respect it is im-
portant to promote the heterolytic cleavage of the
O–O bond of H2O2 at the expense of its homolysis.
In solution this can be achieved with a co-catalyst
(commonly a heterocyclic nitrogen base [13] or an
ammonium salt, such as ammonium acetate [14] or a
combination of a carboxylic acid and a heterocyclic
base [15]) added to the reaction. The role of the
co-catalyst in such systems is to facilitate the forma-
iments, to supports with only propylimidazole (IPG)
or only sulfonatophenyl groups (SiSO3−). These cat-
alysts were used for (Z)-cyclooctene epoxidation and
the hydroxylation of cyclohexane using PhIO and for
the epoxidation of (Z)-cyclooctene with H2O2 as the
oxygen donor.
2. Experimental
2.1. Materials
=
tion of the active oxygen species Mn(V) O from the
reaction of Mn(III) porphyrin with H2O2 [13].
[Mn{T(4-N-MePy)P}]Cl5 was obtained from Mid-
century. All solvents and reagents were of commercial
grade unless otherwise stated and were purchased
from Merck, Fluka and Aldrich. Dichloromethane
(DCM), dichloroethane (DCE), methanol (MeOH)
and acetonitrile (ACN) HPLC grade were used as
received. Cyclohexane and (Z)-cyclooctene were pu-
rified by column chromatography on basic alumina
prior to use and their purities were checked by gas
chromatographic analysis. Hydrogen peroxide (H2O2
30% in H2O, Fluka) was stored at 5◦C and checked
This paper describes the development of catalytic
systems based on a silica support modified with two
functional groups; propylimidazole, to act as a ligand
to the Mn(III) and an acid/base co-catalyst, and sul-
fonatophenyl groups, to anchor cationic metallopor-
phyrins to the support by electrostatic interactions. The
catalysts used were [Mn{M(4-N-MePy)TDCPP}]2+
,
[Mn{T(F4TMAPP)}]5+ and [Mn{T(4-N-MePy)P}]5+
(Fig. 1). These were bound to supports modified with
the two groups described above and, for control exper-
Fig. 1. Synthetic metalloporphyrins.

F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
281
−
by titration every 3 months [16]. Iodosylbenzene was
prepared as described previously [17]. Samples were
stored in a freezer and analysed every 6 months by
iodometric assay.
of propylimidazole/g of IPG. SiSO3 was pre-
pared by refluxing a suspension of silica gel with
2-(4-chlorosulfonylphenyl)ethyltrichlorosilane
in
toluene, according to the method of Leal et al. [23].
After hydrolysis and neutralisation with NaHCO3, the
excess of salt was eliminated after washing with H2O,
the material was dried under vacuum at 100◦C for 8 h.
Elemental analysis: C = 4.40%, H = 1.37% and S =
1.74% indicates that the material had 5.0 × 10−4 mol
of sulfonatophenyl per gram of SiSO3−. SiSO3−(IPG)
2.1.1. Manganese(III) porphyrins
2.1.1.1. [Mn{M(4-N-MePy)TDCPP}]2+
.
The syn-
thesis of the M(4-N-Py)TDCPPH2 was carried out
according to previously reported procedure [18].
This compound was characterised by UV–VIS spec-
troscopy, thin layer chromatography (TLC) on silica
gel, FAB MS and 1H NMR spectroscopy confirm-
ing the structure and the purity of the porphyrin.
Manganese insertion into M(4-N-Py)TDCPPH2 was
achieved by heating the free-base porphyrin and
MnCl2·4H2O at reflux in N,N-dimethylformamide
(DMF) [19]. At the end of the reaction, the solvent
was removed under vacuum and the Mn porphyrin
obtained was separated from the free-base by col-
umn chromatography on alumina. The separation was
monitored by UV–VIS spectroscopy and by TLC on
alumina. The Mn porphyrin obtained (80% yield)
gave a single spot by TLC (3%, v/v MeOH/DCM).
[Mn{M(4-N-Py)TDCPP]+ was methylated by reac-
tion with a large excess of CH3I in DMF at room tem-
perature, under argon [20]. The unreacted CH3I and
DMF were removed under vacuum. The iodide an-
ion was exchanged quantitatively for chloride using a
Dowex 1 × 2-200 1-chloride ion exchange resin with
1%, v/v H2O/MeOH as eluent. The product gave one
spot by TLC on alumina (5%, v/v MeOH/DCM).
−
was prepared by refluxing a suspension of SiSO3
with 3-chloropropyltrimethoxysilane and imidazole in
toluene for 45 min. The solid obtained was dried under
vacuum at 100◦C. Elemental analysis: C = 6.73%,
H = 1.40%, S = 1.60% and N = 0.82% shows
that the material had 2.9 × 10−4 mol of propylimida-
zole/g of SiSO3−(IPG). A scheme representing the
functionalisation of the silica is shown in the Fig. 2.
2.1.3. Preparation of supported manganese(III)
porphyrins
Mn(III) porphyrin ligation to the solid supports
was achieved by stirring a solution of Mn(III)
porphyrin,
DCM, [Mn{T(F4TMAPP)}](PF6)5 in ACN or
[Mn{T(4-N-MePy)P}]Cl5 in H2O with sus-
[Mn{M(4-N-MePy)TDCPP}]Cl2
in
a
pension of support for 10–20 min. The result-
ing catalysts [Mn{T(F4TMAPP)}]-support and
[Mn{T(4-N-MePy)P}]-support were washed with
MeOH and the [Mn{M(4-N-MePy)TDCPP}]-support
was washed with DCE in a Soxhlet extractor overnight
to remove unbound and weakly bound Mn(III) por-
phyrin. The solids were dried for 3 h at 100◦C.
UV–VIS : (DCM) λmax, nm (ε, mol−1 l cm−1) 368,
480 (4.3 × 104), 580
2.2. UV–VIS spectra
ESI MS: (m/z 924 [M − Cl−]+, calc. av. m/z 925),
(m/z 889 [M − 2Cl−]+, calc. av. m/z 889), (m/z 445
[M − 2Cl−]2+, calc. av. m/z 444).
The UV–VIS spectra were recorded on a Hewlett-
Packard 8453 Diode Array UV–VIS spectropho-
tometer. In the case of supported Mn(III) porphyrins,
spectra were recorded in a 2 mm path length quartz
cell, using a mixture of the supported catalyst and the
support in a suspension in CCl4.
2.1.1.2. [Mn{T(F4TMAPP)}]5+
.
[Mn{T(F4TMA-
PP)}]5+ was obtained by a modification of the method
of La et al. [21] as reported recently [22].
2.3. ESI MS spectra and FAB MS
2.1.2. Solid supports
IPG was obtained previously [18] and had el-
emental analysis: C = 4.00%, H = 1.37% and
N = 0.20%, which corresponds to 7.1 × 10−5 mol
ESI and FAB MS spectra were recorded on a
VG Analytical Autospec mass (University of York)
spectrometer and ESI mass spectra were run by the

282
F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
Fig. 2. Functionalisation of surface silica with sulfonatophenyl and propylimidazole groups.
EPRSC Mass Spectrometry Service Centre (Univer-
sity of Wales, Swansea).
dard (cyclohexanone for (Z)-cyclooctene epoxidation,
octan-1-ol for cyclohexane oxidation) were dissolved
in DCE (DCE/ACN 1:1 for reactions with H2O2) and
the oxidant was added. Yields based on the oxidant
added, were determined by removing aliquots of the
reaction mixture and analysing them by gas chro-
matography. No reaction occurred in control reactions
in the absence of the Mn(III) porphyrin.
2.4. Product analysis by gas chromatography
Gas chromatographic analyses were performed on a
Hewlett Packard HP 6890 Series GC System, coupled
to a flame ionisation detector, using a capillary column
(HP-INNOWAX, cross-linked poly(ethylene glycol),
length 30 m; i.d. 0.25 mm, film thickness 0.25 ␮m) and
nitrogen as the carrier gas.
3. Results and discussion
3.1. Characterisation of supported manganese(III)
porphyrins by UV–VIS spectroscopy
2.5. Procedure for catalytic oxygenations
All substrates were checked prior to use, by gas
chromatography, to ensure that they were free from
oxidation products. Reactions were carried out in a
2 ml vial sealed with a teflon-coated silicone septum
and stirred at room temperature. Catalyst, co-catalyst
(for reactions with H2O2), substrate and internal stan-
The presence of the Mn(III) porphyrin was con-
firmed by UV–VIS spectroscopy for all the Mn(III)
porphyrin-supported catalysts studied. A typical spec-
trum is shown in the Fig. 3. This study shows that
no detectable demetallation or exchange of the metal
ion occurred during the preparation procedure, since

F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
283
Fig. 3. UV–VIS spectra of dash: solution of [Mn{M(4-N-MePy)TDCPP}]Cl2 and solid: suspension of [Mn{M(4-N-MePy)TDC-
PP}]-SiSO3(IPG) in CCl4.
all bands observed for the supported manganese por-
phyrins are characteristic of a Mn(III) porphyrin [24].
The loadings were quantified by measuring the
amount of unloaded Mn(III) porphyrin, in the com-
bined reaction solvent and washings, by UV–VIS
spectroscopy (Table 1).
used in this study can also be bound directly to
unmodified silica, as has been noted before for
metallo-tetra(N-methylpyridyl)porphyrins [9]. How-
ever, this binding is weaker than that to SiSO3 and
the catalysts obtained are less efficient. The results
from these systems are not included in this paper.
−
The data reveal that the Mn(III) porphyrins
−
linked to ionic supports SiSO3 and SiSO3−(IPG)
3.2. Catalytic oxygenations with PhIO
have the highest loadings. With IPG the coordina-
tive bond to the Mn(III) porphyrins is reversible
[25], allowing competitive coordination solvents
such as acetonitrile and methanol to displace the
Mn(III) porphyrin. The cationic Mn(III) porphyrins
3.2.1. Epoxidation of (Z)-cyclooctene
The epoxidation of (Z)-cyclooctene with PhIO
catalysed by the manganese porphyrins which is
an easy oxidation that gives only one product
Table 1
Amounts of cationic Mn(III) porphyrins bound to the supports
Support
Metalloporphyrin
Solvent used in Soxhlet extraction
Loading (%)
IPG
IPG
IPG
[Mn{M(4-N-MePy)TDCPP}]2+
[Mn{TF4TMAPP}]5+
DCM
ACN/MeOH
MeOH
DCM
ACN/MeOH
MeOH
DCM
ACN/MeOH
MeOH
74
85
95
94
97
98
95
100
99
[Mn{T(4-N-MePy)P}]5+
−
SiSO3−
[Mn{M(4-N-MePy)TDCPP}]2+
a
SiSO3−
[Mn{TF4TMAPP}]5+
SiSO3
[Mn{T(4-N-MePy)P}]5+
[Mn{M(4-N-MePy)TDCPP}]2+
[Mn{TF4TMAPP}]5+
SiSO3−(IPG)
SiSO3−(IPG)
SiSO3−(IPG)
[Mn{T(4-N-MePy)P}]5+
a From [22].

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F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
Table 2
Oxidation of (Z)-cyclooctene by PhIO catalysed by cationic Mn(III) porphyrins
Catalyst
Cis-epoxycyclooctane (%)a
Leaching (%)
[Mn{M(4-N-MePy)TDCPP}]Cl2
80
92
78
100
97
94
92
94
44
77
53
63
–
15
0
0
–
20
0
0
–
0
[Mn{M(4-N-MePy)TDCPP}]-IPG
[Mn{M(4-N-MePy)TDCPP}]-SiSO3
[Mn{M(4-N-MePy)TDCPP}]-SiSO3(IPG)
b,c
[Mn{TF4TMAPP}](PF6)5
[Mn{TF4TMAPP}]-IPGb
b,c
[Mn{TF4TMAPP}]-SiSO3
[Mn{TF4TMAPP}]-SiSO3(IPG)b
d,e
[Mn{T(4-N-MePy)P}]Cl5
[Mn{T(4-N-MePy)P}]-IPGf
[Mn{T(4-N-MePy)P}]-SiSO3
0
0
[Mn{T(4-N-MePy)P}]-SiSO3(IPG)
a Yields based on starting PhIO after 24 h in DCE, magnetic stirring and room temperature. Amounts: Mn(III)P, 2.3 × 10−7 mol or
equivalent of supported catalyst; alkene, 200 ␮l; PhIO, 5.5 mg; DCE, 800 ␮l.
b In CAN.
c From [22].
d From [28].
e In ACN/DCM/MeOH 6:3:1.
f From [25].
cis-epoxycyclooctane, was first studied to obtain in-
formation about the accessibility of the Mn(III) cen-
tres of the supported catalysts towards substrates and
oxidants. All the reactions were carried out in DCE,
since this is a good solvent for several oxygenation
reactions catalysed by metalloporphyrins [26,27].
The results obtained with the cationic Mn(III) por-
phyrins in homogeneous and supported systems reveal
that the catalysts bearing halogen substituents on the
meso-aryl positions are more efficient than the others
in the oxygenations (Table 2).
3.2.2. Oxidation of cyclohexane
To obtain further information about the effective-
ness of the supported catalysts, they were compared
using the hydroxylation of alkanes, which are less
reactive than alkenes. The substrate chosen was the
cyclohexane and the selectivities of the reactions for
cyclohexanol and cyclohexanone formation were de-
termined. The best yields, as above, were obtained
with the catalysts bearing the electron-withdrawing
–Cl and –F substituents (Table 3). The presence
of these substituents, make the active intermedi-
=
Catalyst filtration after reactions with man-
ganese porphyrins ligated to IPG, followed by
UV–VIS spectroscopy of the filtrates, showed that
∼15% of [Mn{M(4-N-MePy)TDCPP}]2+, 20% of
[Mn{T(F4TMAPP)}]5+ and 0% of [Mn{T(4-N-
MePy)P}]5+ was leached from the support. In
contrast, no leaching was detected with the cationic
catalysts electrostatically bound to the anionic sup-
ports. The latter observation was confirmed by filtering
the catalyst before the end of the reaction; the filtrate,
with fresh oxidant, showed no catalytic activity [29].
It is noteworthy that control reactions, using the sup-
ports under identical conditions but without Mn(III)
porphyrins, gave low epoxidation yields ∼ 5%.
ate Mn(V) O more electrophilic and hence more
reactive toward hydrocarbons. Although leaching
was observed for [Mn{M(4-N-MePy)TDCPP}]2+
and [Mn{T(F4TMAPP)}]5+ on IPG (10 and 5%,
respectively), it is clear by comparison of the re-
activity of [Mn{M(4-N-MePy)TDCPP}]2+ and
[Mn{M(4-N-MePy)TDCPP}]-IPG that the imidazole
groups of the support improve the catalyst’s effi-
ciency presumably by coordination to the Mn(III)
porphyrin. They also increase the alcohol/ketone se-
lectivity. Imidazole groups are known to favour the
=
formation of the active oxidant Mn(V) O [13,30]
relative to Mn(IV)–O in these systems. The former
active intermediate Mn-oxo transfer oxygen to the

F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
285
Table 3
Oxidation of cyclohexane by PhIO catalysed by cationic Mn(III) porphyrins
Catalyst
Cyclohexanol (%)a
Cyclohexanone (%)a
Leaching (%)
[Mn{M(4-N-MePy)TDCPP}]Cl2
[Mn{M(4-N-MePy)TDCPP}]-IPG
[Mn{M(4-N-MePy)TDCPP}]-SiSO3
[Mn{M(4-N-MePy)TDCPP}]-SiSO3(IPG)
[Mn{T(F4TMAPP)}](PF6)5
22
70
38
69
70
74
48
79
4
6
<1
<1
<1
15
9
23
13
2
–
10
0
0
–
5
0
0
–
[Mn{TF4TMAPP}]-IPG
b
[Mn{TF4TMAPP}]-SiSO3
[Mn{TF4TMAPP}]-SiSO3(IPG)c
d,e
[Mn{T(4-N-MePy)P}]Cl5
[Mn{T(4-N-MePy)P}]-IPG
40
44
43
5
7
6
0
0
0
[Mn{T(4-N-MePy)P}]-SiSO3
[Mn{T(4-N-MePy)P}]-SiSO3(IPG)
a Yields based on starting PhIO after 24 h in DCE, magnetic stirring and room temperature. Amounts: Mn(III)P, 2.3 × 10−7 mol or
equivalent of supported catalyst; alkane, 200 ␮l; PhIO, 1.1 mg; DCE, 800 ␮l.
b In ACN, from [22].
c In CAN.
d In ACN/DCM/MeOH 6:3:1.
e From [9].
substrates faster and more selective than the latter
[31–33].
carbons without catalysis. However, its expense, low
oxygen content (7.3% w/w) and polymeric nature are
significant disadvantages that limit its use [25]. By
contrast hydrogen peroxide is an important oxidant
since it is inexpensive, has high oxygen content and
is clean. For these reasons H2O2 was examined as an
oxidant with the supported Mn(III) porphyrins cata-
lysts in this study. The results from the epoxidation
3.3. Catalytic oxygenations with H2O2
Iodosylbenzene is a convenient source of oxygen
for use in small scale epoxidations since it gives good
conversions and does not normally react with hydro-
Table 4
Oxidation of (Z)-cyclooctene by H2O2 catalysed by cationic Mn(III) porphyrins in the presence or absence of added imidazole (Im)a
Catalyst
Cis-epoxycyclooctane (%)∗
Leaching (%)
Without Im
With Im
[Mn{M(4-N-MePy)TDCPP}]Cl2
[Mn{M(4-N-MePy)TDCPP}]-IPG
[Mn{M(4-N-MePy)TDCPP}]-SiSO3
6
11
5
11
4
13
6
7
3
7
3
4
51
45
38
45
25
37
28
38
10
13
10
17
–
25
0
0
–
−
[Mn{M(4-N-MePy)TDCPP}]-SiSO3(IPG)
[Mn{T(F4TMAPP)}](PF6)5
[Mn{TF4TMAPP}]-IPG
[Mn{TF4TMAPP}]-SiSO3
[Mn{TF4TMAPP}]-SiSO3(IPG)
[Mn{T(4-N-MePy)P}](PF6)5
[Mn{T(4-N-MePy)P}]-IPG
–
−
[Mn{T(4-N-MePy)P}-SiSO3
[Mn{T(4-N-MePy)P}]-SiSO3(IPG)
∗ Yields based on starting H2O2 after 24 h in DCE/ACN (1:1), magnetic stirring and room temperature.
a Amounts: Mn(III)P, 2.3 × 10−7 mol or equivalent of supported catalyst; alkene, 200 ␮l; H2O2, 2.4 ␮l; imidazole, 4.6 × 10−6 mol;
DCE/ACN 1:1, 800 ␮l.

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of (Z)-cyclooctene catalysed by supported cationic
Mn(III) porphyrins are presented in the Table 4 and
show that moderate yields of epoxide were obtained
in the presence of imidazole co-catalyst.
porphyrins-SiSO3(IPG) indicate that the imidazole
bound to the support is unable to exert the two-fold
role of co-catalyst in oxygenations of hydrocar-
bons by H2O2 catalysed by Mn(III) porphyrins.
In the supported system, the co-catalyst may act
as a Mn ligand in trans-position of the OOH lig-
and, but it is unable to act as acid/base catalyst,
which is necessary for formation of intermediate
Mn(III)–OOH [13]. This two-fold role of imida-
zole was evidenced previously for homogeneous
systems [34,35].
The data in the Table 4 show two main trends:
1. [Mn{M(4-N-MePy)TDCPP}]2+ and [Mn{T(F4T-
MAPP)}]5+ in homogeneous and heterogeneous
systems give the highest yields of cis-epoxycyclo-
octane, due to the electron-withdrawing halogen
substituents on the meso-aryl positions, which in-
=
crease the electrophilicity of the Mn(V) O active
oxidant.
We also observed that most efficient catalysts are
bound to the bis-functional support SiSO3−(IPG). Pre-
sumably these have the benefit of both the sulfonate
and imidazole groups. The former ensures the metal-
loporphyrin is securely anchored to the support and
the latter by axial ligation to the manganese act as
proximal ligand, facilitating the formation of active
species, as occurs in natural peroxidases. Furthermore,
the co-catalyst imidazole attached on the silica surface
is protected and is unable to undergo the competitive
oxidation with the substrate as reported by Collman
et al. [36].
2. The best yields of cis-epoxycyclooctane occur
on addition of free imidazole. It has been re-
ported previously that Mn(III) porphyrin-catalysed
oxidations of hydrocarbons by H2O2 in homo-
geneous solution are dramatically improved by
the addition of a co-catalyst (e.g. heterocyclic ni-
trogen bases or ammonium acetate), which, by
acting as an acid/base catalyst and as an axial
ligand for the manganese, favours the forma-
=
tion of Mn(V) O through the heterolytic cleav-
age of peroxide bond O–O [13]. The higher
yields of cis-epoxycyclooctane when imidazole
was added to reactions catalysed by Mn(III)
In another experiment with a large excess of the
H2O2, the more efficient catalysts [Mn{M(4-N-MePy)-
Fig. 4. Epoxidation of (Z)-cyclooctene upon successive addition of H2O2 to a CH3COONH4/catalyst mixture. Conditions: successive addition
of H2O2 (50 eq. relative to the catalyst every 45 min) to a (Z)-cyclooctene: CH3COONH4: catalyst (3500:100:1) mixture in ACN/DCE (5:4).

F.S. Vinhado et al. / Journal of Molecular Catalysis A: Chemical 174 (2001) 279–288
287
TDCPP}]-SiSO3(IPG) and [Mn{T(F4TMAPP)}]-
SiSO3(IPG) gave 155 and 190 catalyst turnovers,
respectively, in the epoxidation of (Z)-cyclooc-
tene (Fig. 4).
2. The best catalysts in this study have halogenated
meso-aryl groups.
3. The cationic Mn(III) porphyrins studied, mainly
the halogenated [Mn{M(4-N-MePy)TDCPP}]2+
However, when the [Mn{M(4-N-MePy)TDCPP}]-
SiSO3(IPG) catalyst was recycled in another oxidation
of (Z)-cyclooctene with H2O2 (molar ratio cata-
lyst:oxdant 1:100) a low yield of cis-epoxycyclooctane
(∼7%) was obtained due, probably, to the oxidative
destruction of the catalyst. This conclusion was sup-
ported by a UV–VIS study of the homogeneous reac-
tion using [Mn{M(4-N-MePy)TDCPP}]Cl2 and H2O2
which showed the bleaching of the Mn porphyrin.
Product analysis showed that only 30 turnovers of
cis-epoxycyclooctane were obtained with the homo-
geneous catalyst (Fig. 4).
In the recycling studies using a large excess of
H2O2, the co-catalyst added was the CH3COONH4. In
this condition high amount of co-catalyst is required,
if imidazole were used could result in an oxidative
competition between co-catalyst and substrate [36].
It is important to emphasise that the supported sys-
tems reported in this paper are moderately efficient cat-
alysts for the epoxidation of (Z)-cyclooctene by H2O2
(Table 4), reaching yields of cis-epoxycyclooctane
comparable to those reported for manganese(III)
5,10,15,20-tetra(2,6-dichloro-3-acetylaminophenyl)
porphyrin, linked by a covalent bond to silica [10].
The catalysts used in the present study are, however,
easier to anchor to the support since the attachment
is achieved mainly by electrostatic binding and does
not involve the formation of a covalent linkage.
and [Mn{T(F4TMAPP)}]5+
,
linked to the
bis-functional support SiSO3−(IPG) are efficient
catalysts for (Z)-cyclooctene epoxidation by PhIO
and H2O2 and cyclohexane oxygenation by PhIO.
This support provides two important benefits: the
sulfonatophenyl groups ensure the metallopor-
phyrin is securely anchored to the support and
the propilimidazole groups by axial ligation to the
Mn(III) act as proximal ligand, reflecting the role
of histidine in some enzymes. Moreover, there
is the advantage that the method to anchor the
Mn(III) porphyrin on the support is very simple
since it is by electrostatic and coordinative binding.
Acknowledgements
This work was supported by CAPES, CNPq and
FAPESP. We are grateful to Professors Osvaldo Anto-
nio Serra, Marilda Dores Assis and John R. Lindsay
Smith for helpful discussions.
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