Styrene-hydroxyethyl methacrylate copolymer-supported porphyrinatomanganese(III) complexes: Synthesis and catalytic cyclohexane hydroxylation with molecular oxygen

Article abstract of DOI:10.1007/s11243-010-9373-y

Two new styrene-hydroxyethyl methacrylate copolymers containing immobilized porphyrinatomanganese(III) were prepared and characterized as microspheres by SEM, UV-Vis, FT-IR, and TG-DTG. Their catalytic activities have been investigated for the hydroxylati

Full text of DOI:10.1007/s11243-010-9373-y

Transition Met Chem (2010) 35:627–632
DOI 10.1007/s11243-010-9373-y
Styrene-hydroxyethyl methacrylate copolymer-supported
porphyrinatomanganese(III) complexes: synthesis and catalytic
cyclohexane hydroxylation with molecular oxygen
Yuan-Jian Ye
Han-Cheng Yu
Hong-Bin Ji Liang-Nian Ji
•
Jin-Wang Huang
•
Jin-Hua Cai
•
•
•
Wen-Hai Wu Xian-Tai Zhou
•
•
Received: 2 March 2010 / Accepted: 12 May 2010 / Published online: 29 May 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Two new styrene-hydroxyethyl methacrylate
copolymers containing immobilized porphyrinatomanga-
nese(III) were prepared and characterized as microspheres
by SEM, UV–Vis, FT-IR, and TG-DTG. Their catalytic
activities have been investigated for the hydroxylation of
cyclohexane in the presence of molecular oxygen under
mild conditions. The copolymer microspheres proved to be
more efficient catalysts than the corresponding non-
supported porphyrinatomanganese(III) complex. The alkyl-
ated polymer microspheres with porphyrinatomanga-
nese(III) had the highest catalytic activity, which may be
attributable to the hydrophobic microenvironment around
the porphyrinatomanganese(III) centers, resulting from the
alkyl groups.
metalloprophyrins and so increase their catalytic activities.
Among the supports that can be used to immobilize metal-
loporphyrins, polystyrene derivatives are often utilized,
because of their cheapness, ready availability, mechanical
robustness, chemical inertness, and facile functionalization
to provide a suitable microenvironment for the accommo-
dation of porphyrin catalytic centers [11–15]. We have
previously immobilized some metalloporphyrins on poly-
styrene-based supports, such as Merrifield’s resin, and
studied their catalytic activities in cyclohexane hydroxyl-
ation [16, 17]. Recently, we focused on a new method to
synthesize polystyrene-based supports for metalloporphy-
rins as catalysts for the hydroxylation of cyclohexane, and
styrene-methylacrylic acid copolymer microspheres were
prepared [18–20]. In this paper, we report another new
synthetic method for polystyrene-based supports to immo-
bilize metalloporphyrins. A new polystyrene-based support,
namely styrene-hydroxyethyl methacrylate copolymer
microspheres with hydroxy groups on the surface (P(St-
co-HEMA)), was synthesized. To immobilize porphyri-
natomanganese(III) on these copolymer microspheres,
two novel copolymer microsphere complexes, namely
P(St-co-HMEA)MnP and P(St-co-HMEA)MnP-C H ,
Introduction
Metalloporphyrins have been widely used as models for
cytochrome P450 in the epoxidation of alkenes and
hydroxylation of alkanes under mild conditions [1–5].
However, when they used in homogeneous catalysis, the lack
of a hydrophobic environment as found in the binding site of
cytochrome P450 may be one of the reasons why they have
limited capability as hydroxylation catalysts under mild
conditions. Immobilization of metalloporphyrins on solid
supports [6–10] can provide a microenvironment for such
1
7 35
were prepared and their catalytic activities with respect to
cyclohexane hydroxylation have been investigated and
compared with the non-supported metalloporphyrins.
Experimental
Y.-J. Ye ꢀ J.-W. Huang (&) ꢀ J.-H. Cai ꢀ H.-C. Yu ꢀ
W.-H. Wu ꢀ X.-T. Zhou ꢀ H.-B. Ji ꢀ L.-N. Ji
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry,
School of Chemistry and Chemical Engineering & State Key
Laboratory of Optoelectronic Material and Technologies,
Sun Yat-Sen University, 510275 Guangzhou,
People’s Republic of China
The precursor, 5-(4-(carboxymethoxy)phenyl)-10, 15, 20-tri
(
p-tolyl) porphyrin (CMPTTP), was synthesized previously
in our laboratory [25]. Styrene (St) was washed with 5%
NaOH several times to remove inhibitor and then distilled
under reduced pressure. 2-Hydroxyethyl methacrylate
e-mail: ceshjw@163.com
123

6
28
Transition Met Chem (2010) 35:627–632
(
HEMA) supplied from Alfa Aesar was purified by passing
Synthesis of styrene-hydroxyethyl methacrylate
0
through active alumina. 2, 2 -Azobisisobutyronitrile (AIBN)
was recrystallized from methanol. Other reagents were
commercially available and used without further
purification.
copolymer microspheres immobilized MnCMPTTP
(P(St-co-HEMA)MnP)
A mixture of MnCMPTTP (0.05 g, 0.061 mmol) and
thionyl chloride (20 mL) was refluxed for 7 h. After
reaction, the excess thionyl chloride was removed by dis-
tillation. The residue was dissolved in 1, 2-dichloroethane
(30 mL) and P(St-co-HEMA) (3 g) plus several drops of
pyridine were added in the solution. The crude product was
obtained by stirring the suspension at 80 °C for 12 h.
The polymer particles were filtered off and washed with 1,
2-dichloroethane, acetone, and ethanol successively. The
final product was dried for 24 h at 60 °C under vacuum.
Elemental analyses (C, H, and N) were obtained on a
Perkin-Elmer 240 Q elemental analyzer. ESI–MS spectra
were measured on a Thermo Finnigan LCQ DECA XP
spectrometer. UV–Vis and IR spectra were recorded on a
Shimadzu UV-3150 spectrophotometer and an Equinox 55
Fourier transformation infrared spectrometer, respectively.
The scanning electron microscopy (SEM) analyses were
performed with a JSM-6330F field emission scanning
electron microscope. An Iris (HR) inductively coupled
plasma (ICP)-atomic emission spectrometer was used to
determine the content of porphyrinatomanganese. Thermal
analyses were performed with a Netzsch TG-209 thermo-
gravimetric analyzer.
Synthesis of alkylated polymer particles
with porphyrinatomanganese(III)
(P(St-co-HEMA)MnP-C17H )
35
n-Octadecanoic acid (5.0 g, 17.6 mmol) was stirred at
0 °C. Then, thionyl chloride (7 mL) was added dropwise
and the mixture was refluxed for 5 h. The excess thionyl
chloride was removed by distillation. P(St-co-HEMA)MnP
Synthesis of 5-(4-(carboxymethoxy)phenyl)-10,
6
1
5, 20-tri(p-tolyl) porphyrin Mn(III) (MnCMPTTP)
A solution of Mn(OAc)2 (0.5 g, 2.0 mmol) and NaCl
1 g) in AcOH (40 mL) was mixed with a solution of
(3 g), 1, 2-dichloroethane (30 mL), and several drops of
(
pyridine were added, and the mixture was stirred at 80 °C
for 12 h. The polymer particles were filtered off and washed
with 1, 2-dichloroethane, acetone, and ethanol successively.
The final product was dried for 24 h at 60 °C under vacuum.
CMPTTP (0.2990 g, 0.41 mmol) in CHCl (20 mL). The
3
mixture was stirred at 65 °C for 8 h, then cooled and
washed with H O several times. After washing to neu-
2
trality with H O, drying over anhydrous Na SO , and
2
2
4
concentrating via rotary evaporation, the residue was
Catalytic experiments for cyclohexane hydroxylation
chromatographed on a silica gel column using CHCl as
3
eluent. Evaporation of solvent afforded MnCMPTTP as a
The catalytic aerobic hydroxylation of cyclohexane was
carried out at 30.0 ± 0.1 °C in a Schlenk flask [13, 17–24].
The catalytic system consisted of catalyst [copolymer-
supported porphyrinatomanganese(III), alkylated copolymer-
supported porphyrinatomanganese(III) or non-supported
porphyrinatomanganese(III)], cyclohexane (5.55 mmol), core-
green powder with 96% yield (0.3202 g). MS (ESI) m/z:
7
?
83 ([MnCMPTTP] ). Elemental analysis for C H
4
9
36
N O MnClꢀH O: Found: C, 70.2; H, 4.6; N, 6.7%; Calcd.:
4
3
2
C, 70.3; H, 4.6; N, 6.7%.
-2
Synthesis of styrene-hydroxyethyl methacrylate
copolymer microspheres (P(St-co-HEMA))
ductant (1.1 mmol ascorbate, 4.0 910 mmol thiosalicylic
acid), acetone/water (9:1, 10 mL), and pure oxygen
(101 kPa). p-Chlorotoluene (0.02 mmol) was used as an
The polymerization was performed in a 250-mL three-
necked flask equipped with an anchor-shaped stirrer and
condenser. Styrene (13.0 g), HEMA (2.0 g), divinylben-
zene (DVB) (0.46 g), polyvinylpyrrolidone (K-30) (PVP
K-30) (0.5 g), AIBN (0.12 g), C H OH (95 mL), and H O
internal standard. The products were monitored by GC
(GC-7890II). The immobilized metalloporphyrins were
recovered from the catalytic system by centrifugal separa-
tion after reaction for 3 h, washed with acetone, and reused
under identical conditions.
2
5
2
(
5 mL) were mixed together and stirred at 70 °C for 12 h
under a N atmosphere.
2
The mixture was then cooled to room temperature and
centrifuged at 4,000 r/min for removal of the dispersion
medium. The microspheres were washed several times with
ethanol to remove unconverted monomers and then
centrifuged under similar conditions. The final product was
dried for 24 h at 60 °C under vacuum.
Results and discussion
The strategy used to prepare styrene-hydroxyethyl
methacrylate copolymer microspheres with immobilized
porphyrinatomanganese(III) and alkylated polymer parti-
cles with porphyrinatomanganese(III) is shown in
1
23

Transition Met Chem (2010) 35:627–632
629
Scheme 1 Synthesis
scheme of P(St-co-HEMA)
MnP and P(St-co-HEMA)
OCH
HN
2
COOH
OCH
2
COOH
2
OCH COCl
MnP-C17H
35
Cl
N
Mn
Cl
N
Mn
N
Mn(OAc)2
CHCl , AcOH
N
N
SOCl2
N
N
NH
N
3
N
N
CMPTTP
MnCMPTTP
+
OH
OH
+
HEMA + DVB
P(St-co-HEMA)
OMnP
OH
OMnP
C17H35COCl
OOCC17H35
P(St-co-HEMA)MnP-C H
35
P(St-co-HEMA)MnP
17
Scheme 1. The porphyrinatomanganese(III) was immobi-
lized on the copolymer microspheres by a condensation
reaction between the carboxyl groups of the porphyrinato-
manganese(III) and hydroxyl groups of the styrene-
hydroxyethyl methacrylate copolymer microspheres, giving
P(St-co-HEMA)MnP. When only some of the hydroxyl
groups of the styrene-hydroxyethyl methacrylate copolymer
microspheres were reacted with the functionalized carboxyl
groups of the porphyrinatomanganese(III), reaction of the
remaining hydroxyl groups with n-octadecanoic acid
gave alkylated styrene-hydroxyethyl methacrylate copoly-
mer microspheres with immobilized porphyrinatomanga-
nese(III), P(St-co-HEMA)MnP-C H . The hydroxyl
The morphologies of these two copolymer catalysts and
the copolymer microspheres without porphyrinatomanga-
nese(III) P(St-co-HEMA) were obtained from scanning
electron micrographs (SEM). As shown in Fig. 1, the SEM
images of P(St-co-HEMA), P(St-co-HEMA)MnP, and
P(St-co-HEMA)MnP-C H present a smooth surface and
1
7 35
spherical morphology.
Solid-state UV–Vis spectra of these two catalysts
(Fig. 2) show typical Soret bands of MnCMPTTP at ca.
490 nm and Q bands in the region of 550 * 650 nm.
Compared to the non-supported MnCMPTTP (Fig. 2,
insert), these bands have redshifts about 15 nm, which can
be attributed to the distortion of the porphyrin rings usually
observed when metalloporphyrins are immobilized on solid
supports [27–30].
1
7 35
content of P(St-co-HEMA)MnP used to prepare P(St-co-
HEMA)MnP-C H , 1.081 mmol/g, was determined by
1
7 35
the method reported in the literature [25, 26]. After reacting
of 5.0 g of n-octadecanoic acid with 3 g of P(St-co-
HEMA)MnP, the hydroxyl content of the resulting P(St-co-
HEMA)MnP-C H , determined by the same method, was
The IR spectra of P(St-co-HEMA), P(St-co-HEMA)
MnP, and P(St-co-HEMA)MnP-C H are presented in
1
7 35
Fig. 3. The broad band in the region of 3,450 *
3,550 cm can be attributed to the hydroxyl group. The
-
1
1
7 35
-
1
two bands at 1,182 and 1,726 cm are assigned to the ester
0
.063 mmol/g. According to the difference of hydroxyl
-
1
content between the P(St-co-HEMA)MnP and the P(St-co-
HEMA)MnP-C H , the proportion of alkyl (–C H )
group. Four peaks at 1,600, 1,583, 1,493, and 1,452 cm
-
1
and two peaks at 758 and 700 cm are clearly observed in
all three spectra, which can be attributed to the benzene
rings of styrene. Comparing the three spectra, it can be seen
1
7
35
17 35
groups bonded to P(St-co-HEMA)MnP was calculated as
0
.779 mmol/g.
-
1
The porphyrinatomanganese(III) contents in these
that in the region of 3,450 * 3,550 cm , the band of P(St-
co-HEMA)MnP-C H is nearly absent. This indicates that
two polystyrene-supported complexes were determined
by analyzing the manganese content using ICP technol-
ogy and are as follows: P(St-co-HEMA)MnP, 0.39%
1
7 35
the n-octadecanoic acid is covalently immobilized on the
copolymer through an ester bond. The characteristic bands
of MnCMPTTP were not observed in the IR spectrum of
P(St-co-HEMA)MnP or P(St-co-HEMA)MnP-C H , no
-
3
(
4.73 9 10 mmol/g); P(St-co-HEMA)MnP-C H , 0.09%
17 35
-3
(
1.09 9 10 mmol/g).
1
7
35
123

6
30
Transition Met Chem (2010) 35:627–632
Fig. 1 SEM images of
P(St-co-HEMA) (a),
P(St-co-HEMA)MnP (b),
and P(St-co-HEMA)MnP-
17
C H35 (c)
0
0
0
0
.6
.4
.2
0.8
0.6
0.4
0.2
c
.0
4
50 500 550 600 650 700
Wavelength/nm
b
a
450
500
550
600
650
700
Wavelength/nm
Fig. 2 Solid-state UV–Vis absorption spectra of P(St-co-HEMA)
MnP (straight line), P(St-co-HEMA)MnP-C17 35 (dashed line).
Insert: absorption spectrum of MnCMPTTP in CH Cl
3500
3000
2500
2000
1500
1000
500
H
Wavenumbers/cm-1
2
2
Fig. 3 FT-IR spectra for P(St-co-HEMA) (a), P(St-co-HEMA)MnP
b), and P(St-co-HEMA)MnP-C17 35 (c)
(
H
doubt due to the low concentration of the complex in the
matrix [31].
Catalytic cyclohexane hydroxylation
Thermal stabilities of the copolymer catalysts have been
determined using thermogravimetric analysis (TGA). The
TG curves (Fig. 4) show that P(St-co-HEMA)MnP and
P(St-co-HEMA)MnP-C H degrade at 312 and 264 °C,
The results of cyclohexane hydroxylation catalyzed by
P(St-co-HEMA)MnP, P(St-co-HEMA)MnP-C H (fresh
1
7 35
1
7
35
and recovered), and MnCMPTTP are summarized in
Table 1. A control experiment using P(St-co-HEMA) alone
as catalyst did not lead to substantial product yields.
As shown in Table 1, the catalytic activity of P(St-co-
HEMA)MnP is much higher than that of MnCMPTTP.
respectively, which demonstrates that the catalysts are
thermally stable up to almost 260 °C. As the temperature
rises to 545 °C, the organic parts of P(St-co-HEMA)MnP
and P(St-co-HEMA)MnP-C H decompose completely.
1
7 35
1
23

Transition Met Chem (2010) 35:627–632
631
plays an important part in the catalytic process. As in our
previous report, the calculated length of the –C H alkyl
1
8 37
b
a
chain is 2,157 pm [17], which corresponds to the length of
C–C H linked on the surface of P(St-co-HEMA)MnP-
–
1
7 35
C H Because in our catalytic system, the solvent is a
17 35.
mixture of acetone and water, and the length of the alkyl
chain is greater than the size of the porphyrin ring, we
believe that the porphyrinatomanganese(III) may be
enclosed by these alkyl chains and the resulting hydro-
phobic microenvironment of porphyrinatomanganese(III)
is similar to that of the active center of natural cytochrome
P450. It is known that the key steps [4] in the catalytic
cycle of the cytochrome P450 catalyzed hydroxylation with
molecular oxygen, such as reduction of the high-spin ferric
complex to a ferrous complex, the binding of dioxygen to
the ferrous complex, the formation of the highly active
100
200
300
400
500
600
700
o
Temperature / C
[
[
Fe(IV)=O] species, and the oxygen transfer from the
Fe(IV)=O] species to substrate, are all promoted by the
Fig. 4 TG curves of P(St-co-HEMA)MnP (a) and P(St-co-HEMA)
MnP-C17 35 (b)
H
hydrophobic microenvironment provided by the protein.
This would explain why P(St-co-HEMA)MnP-C H has
1
7 35
The turnover number of P(St-co-HEMA)MnP is about 8
times greater than that of MnCMPTTP. Usually, the effi-
cient catalytic activities of supported porphyrins can be
explained by the nature of the active site environment, the
polymer providing a suitable hydrophobic microenviron-
ment for the substrate approach and oxygen binding to the
active site. Moreover, in supported porphyrins systems, the
formation of the unreactive l-oxo dimer is largely pre-
vented and the oxidative degradation of the porphyrins is
also significantly reduced [32], hence the catalytic activity
of P(St-co-HEMA)MnP is much higher than that of
MnCMPTTP.
higher catalytic activity than the other two catalysts.
It is notable that the copolymer-immobilized porphyri-
natomanganese(III) catalysts can be completely recovered
and effectively reused. As shown in Table 1, P(St-co-
HEMA)MnP and P(St-co-HEMA)MnP-C H retain their
1
7 35
high turnover numbers after being reused four times. All
reaction solutions, when analyzed after the catalytic reac-
tions, showed no sign of the characteristic Soret band of
MnCMPTTP, which demonstrates that no MnCMPTTP
was leaching into the reaction solution. These results reveal
the stable catalytic capabilities of these materials.
It is also worth noting that P(St-co-HEMA)MnP-C H
7 35
1
has a higher catalytic activity than P(St-co-HEMA)MnP.
The turnover number of P(St-co-HEMA)MnP-C H is
Conclusion
17 35
about 4 times greater than that of P(St-co-HEMA)MnP and
nearly 32 times greater than that of MnCMPTTP. This
demonstrates unambiguously that the microenvironment of
the porphyrinatomanganese(III) caused by the alkyl chains
By the synthesis of Mn(III) porphyrin with a functionalized
carboxyl and styrene-hydroxyethyl methacrylate copolymer
microspheres with a functionalised hydroxyl, we have pre-
paredtwonewcopolymermicrospheres,P(St-co-HEMA)MnP
Table 1 The catalytic activities
of P(St-co-HEMA)MnP,
a
b
c
Catalysts
Run
Product amount /lmol(turnover number )
P(St-co-HEMA)MnP-C17
and non-supported
porphyrinatomanganese(III)
H
35
,
Cyclohexanol
Cyclohexanone
Total
P(St-co-HEMA)MnP
P(St-co-HEMA)MnP-C17
MnCMPTTP
1
2
3
4
1
2
3
4
1
11.33 (21.78)
10.70 (20.58)
10.49 (20.17)
9.39 (18.05)
44.22 (88.27)
42.32 (84.46)
41.25 (82.33)
37.00 (73.86)
1.26 (2.51)
7.36 (14.15)
5.33 (10.25)
4.01 (7.72)
18.69 (35.93)
16.03 (30.83)
14.50 (27.89)
12.69 (24.40)
74.72 (149.14)
70.30 (140.31)
68.36 (136.46)
61.31 (122.38)
2.33 (4.65)
a
P(St-co-HEMA)MnP:
4
-
5
.2 9 10 mmol; P(St-co-
HEMA)MnP-C17
3.30 (6.35)
35
H :
-
4
H
35
30.50 (60.87)
27.98 (55.85)
27.12 (54.13)
24.31 (48.52)
1.07 (2.14)
5
.01 9 10 mmol;
MnCMPTTP:
-
.0 9 10 mmol
4
5
b
Reaction time: 4 h
c
Turnover number = product
mol)/catalyst (mol)
(
123

6
32
Transition Met Chem (2010) 35:627–632
and P(St-co-HEMA)MnP-C H . The turnover numbers
17 35
11. Leadbeater NE, Marco M (2002) Chem Rev 102:3217
1
2. Mirkhani V, Moghadam M, Tangestaninejad S, Kargar H (2006)
Appl Catal A Gen 303:221
3. Mansuy D (2007) C R Chim 10:392
of these two copolymer-supported catalysts to hydroxylate
cyclohexane are much greater than that of MnCMPTTP.
And P(St-co-HEMA)MnP-C H has the highest catalytic
1
1
7
35
14. Moghadam M, Tangestaninejad S, Mirkhani V, Mohammadpoor-
baltork I, Sirjanian N, Parand S (2009) Bioorgan Med Chem
activity, which may be attributable to the hydrophobic
microenvironment of porphyrinatomanganese(III) caused
by the enclosure of alkyl chains to porphyrinatomanga-
nese(III). It seems binding long alkyl to copolymer
microspheres is a good method to model the microenvi-
ronment of the active center of cytochrome P450.
1
7:3394
5. Gao BJ, Zhang GH, Li YB, Du RK (2009) Polym Advan Technol
0:1183
1
2
16. Liu ZL, Huang JW, Ji LN (1996) J Mol Catal A Chem 104:193
17. Huang JW, Mei WJ, Liu J, Ji LN (2001) J Mol Catal A Chem
1
70:261
8. Fu B, Yu HC, Huang JW, Zhao P, Ji LN (2008) Trans Met Chem
3:803
9. Fu B, Yu HC, Huang JW, Zhao P, Liu J, Ji LN (2009) J Mol Catal
A Chem 298:74
0. Fu B, Yu HC, Huang JW, Zhao P, Liu J, Ji LN (2009) Catal Lett
1
1
2
2
2
2
2
2
3
Acknowledgments We are grateful to the supports of Guangzhou
Municipality Science & Technology Bureau of China, the National
Natural Science Foundation of China, and National Key Foundation
Research Development Project (973) Item of China (No. 2007
CB815306).
1
27:411
1. Ren QZ, Huang JW, Liu ZL, Luo GT, Ji LN (1997) S Afr J Chem
0:181
5
2. Ren QZ, Huang JW, Peng XB, Ji LN (1999) J Mol Catal A Chem
148:9
3. Huang JW, Huang WZ, Mei WJ, Liu J, Hu SG, Ji LN (2000)
J Mol Catal A Chem 156:275
4. Ren QZ, Zhu ZA, Huang JW, Ji LN, Chen YT (2001) J Por-
phyrins Phthalocyan 5:449
5. Luo HY, Ma L, Mao WB, Huang JW, Ji LN (2002) Acta Sci Nat
Unvis Sun Yet-Sen 41:118
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