Synthesis of conjugated Mn porphyrin polymers with p-phenylenediamine building blocks and efficient aerobic catalytic oxidation of alcohols

Article abstract of DOI:10.1016/j.apcata.2016.02.003

A series of conjugated metalloporphyrin polymers (MnP-AMPs) were synthesized based on Buchwald-Hartwig aromatic amination with p-phenylenediamine and manganese tetraphenylporphyrin as building blocks, and N-heterocyclic carbene-palladium complex as cataly

Full text of DOI:10.1016/j.apcata.2016.02.003

Applied Catalysis A: General 515 (2016) 164–169
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Synthesis of conjugated Mn porphyrin polymers with
p-phenylenediamine building blocks and efficient aerobic catalytic
oxidation of alcohols
Yongjin Li, Baoshuai Sun, Weijun Yang∗
Department of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082 Hunan, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of conjugated metalloporphyrin polymers (MnP-AMPs) were synthesized based on Buchwald-
Hartwig aromatic amination with p-phenylenediamine and manganese tetraphenylporphyrin as building
blocks, and N-heterocyclic carbene-palladium complex as catalyst. Brunauer–Emmett–Teller surface area
analysis, scanning electron microscopy and transmission electron microscopy showed that MnP-AMPs
had large surface areas and uniform pore sizes. The stable porous and superreticular conjugated structure
of MnP-AMP further activated manganese ions in the porphin ring compared with those in the original
monomanganeseporphyrin. Moreover, introducing C N bonds in MnP-AMP increased its polarity and
affinity to alcohols, so MnP-AMP exhibited high catalytic activity when applied to aerobic oxidation of
alcohols. For the catalysis of selective oxidation of benzyl alcohol to benzaldehyde with air, the conversion
and aldehyde selectivity both reached up to 100% under mild condition in acetonitrile at 40 ◦C. MnP-AMP
also remained stable in oxidation reaction system and still had high catalytic activity after several recycles.
© 2016 Elsevier B.V. All rights reserved.
Received 27 October 2015
Received in revised form 31 January 2016
Accepted 5 February 2016
Available online 8 February 2016
Keywords:
N-Heterocyclic carbene
Aromatic amination
Conjugated metalloporphyrin polymer
Alcohol oxidation
Catalysis
1. Introduction
Such polymers can form different kinds of covalent polymers
by changing the coupling groups [21,22]. Since para-covalent
Metalloporphyrins, as excellent biomimetic catalysts for C
H
polymerization hardly occurs in four para positions of metal-
loporphyrin, only phenylene- and alkynyl-coupling conjugated
polymers have been successfully synthesized till now [23,24].
Synthesis of phenylimine-coupling metalloporphyrin polymer and
application of it in the catalytic oxidation of alcohol have not been
reported yet. In this study, we designed a conjugated metallopor-
phyrin polymer coupled with phenylimine, which had a porous
network structure with hyperconjugation, further activating center
manganese ions compared with those in monometalloporphyrin. A
large number of C N bridging groups enhanced the polarity of the
polymer, so it showed high affinity to alcohols and superb catalytic
performance for the oxidation of alcohols into aldehydes.
The coupling reaction between phenylimine and metallo-
porphyrin polymer could not be catalyzed by common palla-
dium catalysts such as tetrakis(triphenylphosphine) palladium(0),
Pd(dba)2, and tetrakis (triphenylphosphine) palladium(0)/CuI. N-
Heterocyclic carbene palladium complex is a new coupling catalyst
for Buchwald-Hartwig aromatic amination [25,26]. N,N-(2,4,6)-
Methylimidazolium chloride, a N-heterocyclic carbene precursor,
was herein synthesized. It exhibited high catalytic activity when
combined with palladium acetate in four-directional coupling poly-
merization with p-phenylenediamine and T(p-Br)PPMnCl.
bond activation [1,2], can also be used in catalytic oxidation of
alcoholic hydroxyl group with high selectivity [3,4]. However, they
are generally responsible for catalysis in homogeneous systems
and prone to self-oxidation and degradation, rendering recycle
and reuse rather difficult [5]. The existing problems can mainly
be solved by utilizing metalloporphyrins in a multiphase pro-
cess, immobilization in most cases [6–8]. New bonds form in
metalloporphyrin immobilization, which are generally unstable
and easily breakable, so the performance in reuse is limited [9].
Self-oxidization, degradation, or difficulty in reuse cannot be cir-
cumvented by metalloporphyrin immobilization [10]. Aggregating
metalloporphyrin to special insoluble polymer is a new method for
the heterogeneous catalysis of metalloporphyrins [11–13].
Metalloporphyrin polymerization can be mainly divided into
four categories: hydrogen-bonding association [14,15], axial
polymerization [16], metal-organic frameworks [17,18], and para-
covalent polymerization [19,20]. Para-covalent polymerization
connects metalloporphyrin monomers through covalent bonds.
∗
Corresponding author.
E-mail address: wjyang@hnu.edu.cn (W. Yang).
http://dx.doi.org/10.1016/j.apcata.2016.02.003
0926-860X/© 2016 Elsevier B.V. All rights reserved.

Y. Li et al. / Applied Catalysis A: General 515 (2016) 164–169
165
2. Experimental
2.1. Reaction reagents
Palladium acetate (47.5% Pd) and potassium tert-butoxide (95%)
were obtained from J&K Chemicals. (p-Br)PPMnCl was synthesized
in our group according to documented procedures and character-
ized by IR, UV–vis, 1H NMR and MS spectroscopies [27] (Supporting
information). P-Phenylenediamine, chloromethyl ethyl ether and
other reagents were purchased from Alfa Aesar Corp. and Aldrich
Corp., and were all analytical grades without special treatment.
Fig. 1. Structure of (Pd(IMes)Cl2)2.
imidazolium chloride (IMes·HCl) on the basis of 1H NMR spectral
2.2. Synthesis of (Pd(IMes)Cl2)2 catalyst
data.
1H NMR (CDCl3): ␦ 2.08 [s, 12H, ortho-CH3], 2.27 [s, 6H, para-
CH3], 6.95 [s, 4H, meta-CH], 7.61 [s, 2H, im-H4.5], 10.06 [s, 1H, im-
H2].
2.2.1. Synthesis of glyoxal-bis (2,4,6-trimethylphenyl)-imine
Typical
procedures:
2,4,6-Trimethylaniline
(2.7042 g,
0.02 mmol) and n-propanol (12 mL) were added to a three-neck
flask, into which a mixture of 40% glyoxal (0.01 mol, 1.4510 g),
8 mL n-propanol and 4 mL water was then slowly added. After
4 h of reaction at 25 ◦C and another 2 h of reaction at 60 ◦C, the
reactants were removed into ice water to allow full evaporation.
The precipitate was collected by filtration, thoroughly washed
with n-propanol and then dried in vacuum with a yield of 71.2%
(2.0790 g). The products were identified on the basis of 1H NMR
and 13C NMR spectral data.
2.2.3. Synthesis of (Pd(IMes)Cl2)2 catalyst
Potassium tert-butoxide (33.6 mg, 0.30 mmol), potassium chlo-
ride (44.7 mg, 0.60 mmol), palladium acetate (27.0 mg, 0.12 mmol)
and IMes·HCl (102.0 mg, 0.30 mmol) were added to a three-neck
flask which had been purged thoroughly with argon. Deoxygenated,
anhydrous THF (12 mL) was added via a syringe under stirring,
and the solution was heated at reflux for 16 h after all the reac-
tion reagents dissolved. After reaction, the solution was evaporated
under argon at 30 ◦C, and the orange red solid complex was puri-
fied by silica gel chromatography (Et2O/hexanes, 1:1) with a yield
of 38%. The products were identified on the basis of 1H NMR, 13C
NMR and MS spectral data (Fig. 1).
1H NMR (CDCl3): ␦ 2.19 [s, 12H, ortho-CH3], 2.32 [s, 6H, para-
CH3], 6.93 [s, 4H, meta-CH], 8.13 [s, 2H, CH]. 13C NMR (CDCl3): ␦
18.2 [s, ortho-CH3], 20.7 [s, para-CH3], 126.5 [s, ortho-C], 128.9 [s,
meta-C], 134.1 [s, para-C], 147.4 [s, ipso-C], 163.0 [s, HC N].
(Pd(IMes)Cl2)2: MS: m/z 964; 1H NMR (CDCl3): ı 6.85 [s, 4H],
6.13 [s, 4H], 2.31 [s, 12H], 2.05 [s, 24H]; 13C NMR (CDCl3): ␦ 18.5
[ortho-CH3], 21.6 [para-CH3], 121.3 [C C], 127, 136.1, 136.9, 137.3
2.2.2. Synthesis of IMes·HCl
Typical procedures: The above obtained glyoxal-bis(2,4,6-
trimethylphenyl)-imine (0.4382 g, 1.50 mmol) was added to a
three-neck flask, degassed by three freeze-pump-thaw cycles, and
purged with argon. Afterwards, 5 mL THF was added to the flask
via a syringe until the solid completely dissolved at 45 ◦C. Then
chloromethyl ethyl ether and 1 mL THF were dropwise added to
the flask after the temperature was cooled to 15 ◦C. Finally, the
reactants were stirred at 20 ◦C for 1 h. After reaction, the pre-
cipitate was collected by filtration, thoroughly washed with THF
and then dried in vacuum with a yield of 62.0% (0.3169 g). The
obtained solid was characterized as N,N-(2,4,6-trimethylphenyl)
[aryl-C], 195.3 [N
C N]; Elemental analyses: C, H, Cl, N and Pd was
52.45, 4.98, 14.65, 5.88, and 22.04 wt% respectively.
2.3. Synthesis of MnP-AMP
A
mixture of (Pd(IMes)Cl2)2 (96.4 mg, 0.10 mmol), T(p-
Br)PPMnCl (100.2 mg, 0.10 mmol), p-phenylenediamine (27.0 mg,
0.25 mmol), potassium tert-butoxide (56.0 mg, 0.50 mmol) and
anhydrous m-xylene (8 mL) was added to a reaction flask, degassed
by three freeze-pump-thaw cycles, purged with argon, and stirred
Fig. 2. Schematic representation of the synthesis of MnP-AMP.

166
Y. Li et al. / Applied Catalysis A: General 515 (2016) 164–169
at 135 ◦C for 24 h. Finally, the mixture was allowed to cool at
room temperature, into which ethanol was added. The precipitate
was collected by filtration, thoroughly washed with water/ethanol,
trichloromethane respectively, and then dried in vacuum to give
MnP-AMP as a black solid in 86.1% isolated yield. (Fig. 2.).
2.4. Methods of polymer characterization
MnP-AMP was further purified by Soxhlet extraction for 24 h
with ethanol and trichloromethane before test.
FT-IR spectrum was measured by Fourier Transform Infrared
Spectrometer (IRrestige-21, Shimadzu). The sample was com-
pletely dried and diluted by potassium bromide as a pretreatment.
The specific surface areas and pore size distribution were
detected by Micromeritics TriStar II 3020 accelerated surface and
porosity analyzer with nitrogen as probing gas at 77 K. Before mea-
surement, samples were degassed and fully dried in vacuum at
120 ◦C for more than 12 h. The specific surface areas were calcu-
lated by the Brunauer–Emmett–Teller (BET) method, and the NFT
theory was utilized to estimate pore size, pore volume and pore
distribution.
Fig. 3. FT-IR spectra of MnP-AMP and T(p-Br)PPMnCl.
gassy carbon electrode. The electrodes were dried overnight at
room temperature for measurement. The electrochemical experi-
ments were conducted in 0.1 mol/L (CH3CH2)4NBr CH2Cl2 solution.
The experiments were cyclically scanned at a scan rate of 50 mV/s
at the room temperature after purging Ar gas for 10 min.
Field emission scanning electron microcopies (FE SEM) were
performed by a JEOL model JSM-6400F microscope. High resolu-
tion transmission electron microcopies (HR TEM) were performed
by a JEOL model JEM-3010 microscope.
The UV–vis diffuse reflectance spectra of MnP-AMP was
measured on an Agilent Technologies model Cary 100 UV–vis spec-
trophotometer equipped with integration sphere, and the samples
were diluted with BaSO4.
Elemental analyses of C, H, N were carried out on an German
Elementar corporation model vario ELIII. Elemental analyses of Pd
were carried out by atomic absorption spectrometry on America
Perkin Elmer model Aanalyst 700/800.
2.6. Catalytic oxidation of alcohols
Alcohols (3.0 mmol), MnP-AMP catalyst (3.0 × 10−3 mmol) and
acetonitrile (8 mL) were added to a three-neck flask, into which
isobutyraldehyde (9.0 mmol) was also dropped in three portions
(3.0 mmol each time) with stirring. The temperature and the air
flow rate were maintained at 40 ◦C and 150 mL/min respectively.
The reaction time was 2–6 h.
2.5. Cyclic voltammetry of the polymer
3. Results and discussion
Electrochemical measurements of cyclic voltammetry had been
investigated using a CHI66OB electrochemical workstation with
a three-electrode cell system, in which a glass carbon after load-
ing the MnP-AMP was used as the working electrode, a calomel
electrode as the reference electrode, and a Pt wire as the counter
electrode. As to electrode preparation, the sample MnP-AMP was
dispersed in 0.5 mL solvent mixture containing 11 ␮L of nafion
(5 wt%) and 0.49 mL of ethanol by sonication for more than 1 h to
obtain the stable suspension. And then 10 ␮L portion of the sample
solution was slightly dropped on the surface of the pre-polished
3.1. MnP-AMP characterization
As shown in Fig. 3, the IR spectrum of T(p-Br)PPMnCl exhibits a
characteristic Mn-N vibration band at 1010.9 cm−1, which is close
to that of MnP-AMP (1009.1 cm−1). The peaks at 1516 cm−1 and
1608 cm−1 correspond to C C stretches in phenyls respectively,
and that at 600 cm−1 represents C-Br in porphyrin. Different from
that of T(p-Br)PPMnCl, the characteristic peak of C-Br in MnP-AMP
at 600 cm−1 attenuates and even disappears due to consumption of
C-Br during the coupling reaction. MnP-AMP is a conjugated poly-
Fig. 4. (a) Nitrogen adsorption (᭹) and desorption (ꢀ) isotherm profiles of MnP-AMP at 77 K. (b) Pore size distribution (ꢀ) and cumulative pore volume (᭹) of MnP-AMP.

Y. Li et al. / Applied Catalysis A: General 515 (2016) 164–169
167
Fig. 6. (a) Cyclic voltammetry curves of MnP-AMP on the glass carbon electrodes
in 0.1 mol/L (CH3CH2)4NBr CH2Cl2 solution (black curve); (b) cyclic voltammetry
curves of T(p-Br)PPMnCl in CH2Cl2, 0.1 mol/L (CH3CH2)4NBr (red curve). Scan rate
is 50 mV/s. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)
Fig. 5. (a, b) FE SEM and (c and d) HR TEM images of MnP-AMP.
mer with metalloporphyrin and ursol building blocks, in which
the lone electron-pair of N atom conjugates with benzene ring,
making C N show double-bond properties. Given the new peak
at 1300 cm−1, the coupling reaction was successful. N H bond
exhibits a very weak absorption peak at 3300–3500 cm−1
.
The sorption curve of MnP-AMP at 77 K (Fig. 4a) is a typical
type-II sorption and a type-S sorption isotherm plot, exhibiting a
strong adsorption at low pressure (P/P0< 0.1). In addition, micro-
and mesopores coexisted in the framework. The BET surface area
was as high as 345 m2g−1, of which the micro-pore area (about
197 m2g−1) accounted for 57.1%. The main pore diameters were
about 1.27 nm (Fig. 4b), and these pores (about 0.226 cm3g−1) con-
tributed to 38.2% of the pore volume based on the cumulative pore
volume profile. Therefore, MnP-AMP was an excellent micro- and
mesoporous polymer.
FE SEM images (Fig. 5a and b) show that MnP-AMP has a
columnar structure accumulated by porphyrin layers among which
there is network interpenetration. Moreover, these layers were
diametered about 100–200 nm and irregularly sized, which led to
an unequal columnar distribution. As shown in HR TEM images
(Fig. 5c), these lamellar layers are diametered about 100 nm.
According to the high-magnification image (Fig. 5d), there are a
large number of about 1.0 nm nanoholes on the surface of MnP-
AMP, being consistent with the pore size analysis results.
The first reduction potential of MnP-AMP was significantly
reduced compared with the first reduction potential of T(p-
Br)PPMnCl (from −0.28 V right shift to −0.11 V), which indicated
that the structure of -NH-Ar- was introduced into the polymers
(Fig. 6). And the structure of -Ar-NH-Ar-NH-Ar- as conjugated
bridges between the porphyrin monomers was advantageous to the
electron flow to from lively valence ions, and made the reduction
of the metal more easily.
Fig. 7. The UV–vis diffuse reflectance spectra of MnP-AMP.
porphyrin units of MnP-AMP. Moreover, the UV–vis spectra of the
reaction supernatants after the oxidation reaction were also tested
and didn’t find the characteristic absorption bands of manganese
porphyrin moiety or related decomposition products, which also
proved no degradation was occurred in the oxidation reaction.
3.2. Analysis of polymerization process
3.2.1. Appropriate ratio of reactants
The proper theoretical molar ratios of porphyrin to p-
phenylenediamine should be 1:2 in porphyrin polymerization.
With different ratios tested, the polymer had yield of 89% and BET
surface area of 345 m2g−1 at 1:2.5. The yield was slightly higher
than that at 1:4 molar ratio, but its surface area was as low as
73 m2g−1 (Table 1).
The UV–vis diffuse reflectance spectra of the polymers before
and after the oxidation reaction were also measured (Fig. 7). The
UV–vis diffuse reflectance spectra have no evident changes before
and after the oxidation reaction even for more than three recy-
cle uses. In the curves, the absorption band at 464 nm is the Soret
band, and those at 583 and 622 nm are the Q-bands of the Mn-

168
Y. Li et al. / Applied Catalysis A: General 515 (2016) 164–169
Table 1
Table 2
Reactant ratios influenced the BET surface areas of the polymers.
Solvent, base and temperature screening for MnP-AMP synthesis.
Entry
Ratioa
Polymer Yield (%)
SBET (m2 g−1
)
Entry
Solvent
Base
Temp. (◦C)
Yield (%)
1
2
3
4
1:2
1:2.5
1:3
82
89
87
90
280
345
258
73
1
2
3
4
5
6
7
8
Dioxane
DMF
Toluene
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
KOt-Bu
Cs2CO3
CsF
110
110
110
110
110
110
135
135
135
135
135
23
19
53
51
49
50
89
67
43
36
– –a
1:4
m-Xylene
p-Xylene
o-Xylene
m-Xylene
m-Xylene
m-Xylene
m-Xylene
m-Xylene
a
Molar ratios of porphyrin to p-phenylenediamine.
9
10
11
K2CO3
KOH
3.2.2. Solvent, base and temperature screening for MnP-AMP
synthesis
a
No reaction product.
We initially focused on optimization of conditions for the cou-
pling reaction of MnP-AMP. Some preliminary studies revealed that
the best result was obtained with KOt-Bu as base and m-xylene as
solvent at 135 ◦C. Temperature, base and solvents affected the reac-
tion results evidently. Aromatic compounds containing benzene
ring were significantly superior to other solvents (Table 2, entries
1–7). For example, the yield of MnP-AMP, which was very low with
1, 4-dioxane and DMF as solvents (23%, 19%, Table 2, entries 1,
2), reached over 49% when toluene and xylene were used. On the
other hand, the yield of MnP-AMP was susceptible to temperature
changes. Increasing the temperature from 110 ◦C to 135 ◦C elevated
the yield from 51% to 89% (Table 2, entries 4, 7). Therefore, we chose
m-xylene with a higher boiling point as solvent in order to appro-
priately raise the reaction temperature. Besides, base was also an
important factor in reaction. Various bases affected the reaction
depending on the basic strength and solubility in related solvent.
KOt-Bu perfectly suited the reaction system due to suitable alka-
linity and solubility. Cs2CO3, CsF and K2CO3 led to low yields (67%,
43%, 36%, Table 2, entries 8, 9, 10), and even no reaction occurred
when KOH was used as base (Table 2, entry 11).
3.3. Catalytic oxidation of alcohol
In the presence of isobutyraldehyde, aerobic oxidation of alcohol
was well catalyzed with MnP-AMPs, producing the corresponding
aldehyde under mild condition in acetonitrile (Table 3) and the
mainly by-products of the oxidation reaction was the correspond-
ing carboxylic products by GC–MS detection.
The three polymers with different specific surface areas showed
markedly different catalytic performances (Table 3). When ben-
zyl alcohol was employed as the substrate, polymer S345 had the
best catalytic performance, achieving complete conversion within
2.0 h and aldehyde selectivity of 98%. The conversion and aldehyde
Table 4
S345 catalyzed oxidation of alcohols to aldehydes.a
Entry
1
Alcohol
Product
Time (h)
2.0
Conversion (%)
100
Aldehyde selectivity (%)
98
2
3
4
5
1.7
1.7
1.7
2.7
100
100
100
100
95
95
96
93
6
7
8
4.0
4.5
85
80
100
100
6.0
1.7
77
95
100
99
9
10
1.7
2.0
93
93
100
100
11
a
Reaction condition: 3.0 mmol of benzyl alcohol, catalyst: MnP-AMP (S345), Mn2+/benzyl alcohol = 1/130000 (molar ratio), 9.0 mmol of isobutyraldehyde, air flow:
150 mL/min, solvent: 6 mL of acetonitrile, temperature: 40 ◦C.

Y. Li et al. / Applied Catalysis A: General 515 (2016) 164–169
169
Table 3
mainly diametered 1.27 nm, and MnP-AMP had an obvious lamel-
lar structure, further composing a stereoscopic columnar structure.
In the catalytic oxidation experiment, the selectivity of benzalde-
hyde was up to 98% and the conversion of benzyl alcohol was 100%.
Besides exhibiting high catalytic oxidation activity against alcohols,
MnP-AMP was also easily recyclable and reusable. Hence, MnP-
AMP is an excellent heterogeneous catalyst for aerobic oxidation
of alcohol as an eligible substitute for corresponding metallopor-
phyrin.
Effect of different catalysts on catalytic oxidation of benzyl alcohol to benzaldehyde.a
Entry Catalyst
Time (h) Conversion (%) Aldehyde selectivity (%)
1
2
3
4
S345
S258
S73
2.0
2.7
4.0
100
100
87
98
95
92
73
T(p-Br)PPMnCl 1.7
100
a
Reaction condition: 3.0 mmol of benzyl alcohol, catalyst: Mn2+/benzyl alco-
hol = 1/130000 (molar ratio), 9.0 mmol of isobutyraldehyde, air flow: 150 mL/min,
solvent: 6 mL of acetonitrile, temperature: 40 ◦C.
Acknowledgement
selectivity of S73 were 87% and 92% respectively after 4.0 h. Also
exhibiting high catalytic activity as a homogeneous catalyst, T(p-
Br)PPMnCl completely converted benzyl alcohol into benzaldehyde
in 1.7 h, but the aldehyde selectivity was only 73%.
The authors thank the National Natural Science Foundation of
China (Grant No. 21576074) for financial support.
With surface area of 345 m2g−1, MnP-AMP S345 had excellent
catalytic performance for aromatic alcohol oxidation under mild
conditions, nearly completely converting most of them (Table 4,
entries 1–5) into corresponding aldehydes in 2.0 h. Furthermore,
MnP-AMP also well catalyzed the oxidation of 1-benzyl alcohol to
acetophenone, and cycloalkanol to cycloalkanone (Table 4, entries
6–8). Simple aliphatic primary alcohols such as methanol, ethanol
and propyl-alcohol can’t react in the oxidation reaction even the
reaction temperature was increased to the boiling points. When the
C number in the substrate was more than four, the aliphatic primary
alcohols began to react under mild condition (Table 4, entries 9–11).
The conversion rates were lower than that of benzyl alcohol com-
pounds but with a higher selectivity for the aldehyde. For example,
the conversion rate of n-butyl alcohol and the aldehyde selectiv-
ity were 95% and 99% after 1.7 h respectively (Table 4, entries 7).
Similar to that, with the C number in the substrate increased, the
conversion rate was a little reduced and the selectivity for the alde-
hyde always about 100%. C N bonds in MnP-AMP increased the
polarity of polymers and facilitated them to bind alcohol molecules.
MnP-AMP could be easily recycled after reaction by centrifu-
gation, filtration, desiccation, or other simple separation methods.
After 5 cycles, MnP-AMP had a recovery rate of more than 90%.
Meanwhile, the recovered catalyst remained highly active under
the optimized conditions. For example, the conversion rates of
benzyl alcohol remained 98%, 95% and 91% respectively in three
catalytic reactions, and the selectivity for the aldehyde has no obvi-
ous changed as 98%, 96% and 96% respectively in three catalytic
reactions.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.apcata.2016.02.
003.
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4. Conclusion
In conclusion,
a N-containing heterocyclic carbene palla-
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the N-arylation reaction in which metalloporphyrin and p-
phenylenediamine were used as substrates. We synthesized a
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