Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous Catalysts and Dye Scavengers

Article abstract of DOI:10.1007/s10562-016-1884-5

Abstract: Six metalloporphyrin-based porous coordination polymers, Mn^II(TCP)-Mn^II(CP1), Fe^III(TCP)-Fe^III(CP2), Co^II(TCP)-Co^II(CP3), Ni^II(TCP)-Ni^II(CP4), Cu^II

Full text of DOI:10.1007/s10562-016-1884-5

Catal Lett
DOI 10.1007/s10562-016-1884-5
Metalloporphyrin-Based Porous Coordination Polymers:
Synthesis, Served as Heterogenous Catalysts and Dye Scavengers
Shu Sun1,2 · Qiong Yu1 · Wei Zhang1 · Xin Zhao1 · Jun Li1 · Fengxing Zhang1
Received: 23 August 2016 / Accepted: 4 October 2016
© Springer Science+Business Media New York 2016
Abstract Six metalloporphyrin-based porous coordi-
nation polymers, MnII(TCP)-MnII (CP1), FeIII(TCP)-
FeIII (CP2), CoII(TCP)-CoII (CP3), NiII(TCP)-NiII
(CP4), CuII(TCP)-CuII (CP5) and ZnII(TCP)-ZnII (CP6),
aggregation supported by SEM, TEM and powder XRD.
CP5 is a small particles aggregation with lower crystallin-
ity. These coordination polymers exhibit efective dye scav-
enging and catalytic activities toward the oxidation of alky-
lbenzene to ketones, and can be reused by iltration with
slight decreasing of catalytic activities.
(TCP=5,10,15,20-tetra(4-(phenoxy-4-yl)butanoic
acid)
porphyrin tetravalent anion) were prepared and charac-
terized. CP1, CP2, CP3, CP4 and CP6 are amorphous
Shu Sun and Qiong Yu have contributed equally to this work.
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1884-5) contains supplementary
material, which is available to authorized users.
* Jun Li
junli@nwu.edu.cn
1
Key Laboratory of Synthetic and Natural Functional
Molecule Chemistry of Ministry of Education, College
of Chemistry and Materials Science, Northwest University,
Xi’an, Shaanxi 710069, People’s Republic of China
2
Department of Chemical Engineering, Ordos Institute
of Technology, Ordos, Inner Mongolia 017000,
People’s Republic of China
1 3

S. Sun et al.
Graphical Abstract
MOF have been shown to be both catalytically competent
and porous with respect to chemical reactants [18, 20]. One
of the problems encountered in building robust and cata-
lytic MOF from porphyrins or metalloporphyrins, plagu-
ily, is that amorphous coordination polymers tend to be
generated, instead of crystalline frameworks. The metal-
loporphyrin-based coordination polymers (MpCP) is lower
crystallinity or even amorphous coordination polymers,
from which to distinguish crystalline frameworks. Similar
to the well-known MOF, the MpCP is constructed from
metalloporphyrins as metalloligand linkers and metal ions
or metal ions clusters as nodes by bonding these two com-
ponents with coordination bonds that is a type of chemical
bonds. The metalloligand linkers, metalloporphyrins, that’s
one of the key factors of MpCP. On one hand, the metal
ions situated in the centers of the metalloporphyrins can
be changed arbitrarily according to your will. On the other
hand, periphery substituent groups of the metalloporphy-
rins can be designed in accordance with the need to, such
as length, rigid or lexible, and the atoms coordinating to
nodes. Owning these two merits, metalloporphyrins render
the MpCP materials more accessible to functionalize and
structural design.
Keywords Metalloporphyrin · Alkylbenzene oxidation ·
Tert-butyl hydroperoxide · Heterogeneous catalytic · Dye
scavenger
1 Introduction
Metalloporphyrins have been extensively studied in the
past several decades for hydroxylation of alkanes and
epoxidation of alkenes [1–7]. When used as homogeneous
catalysts, unfortunately, they often sufer from quick deg-
radation such as ligand oxidation or µ-oxo dimer formation
[8]. Therefore, it would be advantageous to anchor and iso-
late catalytically active metalloporphyrins, prohibiting their
oxidative degradations and self-dimerizations [2, 9–12].
Initially, metalloporphyrins were immobilized onto organic
(e.g. polymers, ion-exchange resins) or inorganic supports
(e.g. zeolites, silica, clays) with the interaction of organic
covalent bonds [1, 3, 4, 13–15], electrovalent bonds or van
der Waals interactions (physical adsorption) [2]. Although
covalently bounded of polymers supported metalloporphy-
rin catalysts are much more stable than the inorganic sup-
ported entities, few suitable porphyrins or polymer supports
could be qualiied. Recently, crystalline metal–organic
coordination frameworks (MOF) based catalysts were pro-
posed and experimentally demonstrated [5, 6, 16–23], such
as the well known PIZA-3, a capable and robust oxidation
catalyst for the hydroxylation of a variety of linear and
cyclic alkanes and the epoxidation of cyclic alkenes [16].
Despite attractive approaches to the construction of cata-
lytic metalloporphyrins MOF developments, for instance
heterogenization of well-deined homogeneous catalysts
incorporated as MOF struts [17–19], MOF-encapsulation
of molecular catalysts, and post-synthesis incorporation
of catalytic metal sites [11], only few metalloporphyrins
Bearing all of the above in mind, and follow our
previous studies [24] we designed a new porphyrin,
5,10,15,20-tetra(4-(phenoxy-4-yl)butanoic acid)porphyrin
(H2TCP, see Scheme 1), given elongate and lexible periph-
ery substituents. Such porphyrin bears lexibility substitu-
ents, on one hand, would be formed the steady structures
of coordination polymers, in which the metalloporphyrins
could be preferred orientation for the variability of the sub-
stituents’ stretching direction. On the other hand, the poly-
mers could change their structures accordingly on diferent
substrate molecules in the processes of catalytic reactions,
in order to respond to the diferent substrates. The MpCPs,
1 3

Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous…
Scheme 1 Scheme of reaction for a synthesis of the methyl 4-(4-formylphenoxy)butanoate; b synthesis of metal-free porphyrins H2(TMEP) and
H2(TCP)
those are MnII(TCP)-MnII (CP1), FeIII(TCP)-FeIII (CP2),
CoII(TCP)-CoII (CP3), NiII(TCP)-NiII (CP4), CuII(TCP)-
CuII (CP5) and ZnII(TCP)-ZnII (CP6), were synthesized
from the custom designed porphyrin and excess metal ions,
of which the porphyrin cores can be in situ metalated read-
ily with metal ions. These MpCPs exhibit catalytic activi-
ties and selectivities toward the oxidation of alkylbenzene,
of which CP1 catalytic performance is the best relatively,
unfortunately, the yield declined slightly by reused. With-
out detectable catalysts leaching, fortunately, after three
times consecutively reused. Meanwhile, the dye adsorp-
tion properties of the MpCPs have been examined, the CP5
exhibits optimum performance relatively.
UV–Vis spectra were measured on a Shimadzu UV1800
spectrophotometer. The mass spectrometry analyses (MS)
were carried out using a MALDI-TOF MS (Shimadzu Bio-
tech). Infrared spectra were obtained on a BEQ UZNDX550-
FTIR spectrophotometer (Bruker) using KBr pellets. C, H, N
elemental analyses were performed on a Vario EL-III appa-
ratus (Bruker). 1H NMR spectra were measured on a Varian
INOVA-400 spectrometer (400 MHz, Varian, U.S.) by using
tetramethylsilane (TMS) as an internal standard, with the
chemical shifts relative to TMS. Scanning electron micro-
scope (SEM) images were recorded on a Quanta 400FEG
microscopes. Transmission electron microscopy (TEM)
images were obtained using JEOL JEM-3010 microscopes.
The powder X-ray difraction (PXRD) patterns were recorded
on a Bruker D8 difractometer using graphite monochromatic
copper radiation (Cu Kα) at 40 kV, 30 mA over the 2θ range
from 5° to 50°. Surface area experiments were performed at
77 K on a TriStar II 3020 apparatus (Micromeritics) using
nitrogen as the probing gas. Thermal gravimetric analysis
(TGA) were performed in lowing N2 with a heating rate of
10°C min−1 from 30 to 800°C on a Perkin-Elmer TGA-7
instrument. GC analyses were performed using a GC1100
chromatograph (PERSEE Beijing, China), N2 as the carrier
gas (35 cm3 min−1) and equipped with a fused silica capil-
lary 5% phenyl 95% dimethylpolysiloxane column (SE-54,
30m×0.32 mm).
2 Experimental
2.1 Chemicals and Instruments
All solvents and reagents were used as received without
further puriication, except for pyrrole and N,N-dimethyl
formamide (DMF) which were distilled before used. The
4-hydroxybenzaldehyde and methyl 4-bromobutyrate
were commercially available from Beijing chemical rea-
gents company. The alkylbenzene used as substrates were
commercially available from ChengDu Kelong Chemi-
cal Reagent Company. The oxidant tert-butyl hydroperox-
ide (TBHP) was commercially available from Sinopharm
Chemical Reagent Co., Ltd. The thin layer chromatog-
raphy (TLC) was performed on silica gel GF254 plates.
Chromatographic separations were carried out on silica gel
(100–200 mesh).
2.2 Synthesis
2.2.1 Synthesis of Methyl 4-(4-Formylphenoxy) Butanoate
In a 100 mL three-necked lask, a mixture of 4-hydroxy-
benzaldehyde (2.49 g, 20 mmol), methyl 4-bromobutanoate
1 3

S. Sun et al.
Table 1 Data of EDS, UV–Vis, FT-IR and GC-MS spectra of porphyrins and CP1–CP6
Compd
EDS
UV–Vis
IR
GC-MS
−
vsCOO
cm−1
νMn–N
ωN–H
Found
amu
Calcd
amu
λmax, nm
C
N
O
M
Mass (%)
Mass (%)
Mass (%)
Mass (%)
cm−1
cm−1
H2(TMEP)
H2(TCP)
CP1
421, 519, 554, 593, 650
419, 518, 555, 595, 651
389, 468, 542, 584
403, 469, 544, 594
423, 549, 593
966
978
1079.5a
1023.4a
1078.4
1022.4
55.32
56.26
57.70
52.88
53.67
53.79
9.05
8.30
7.65
7.28
7.19
7.16
14.05
13.43
15.65
14.53
14.38
14.78
21.63
22.01
21.65
25.31
24.76
24.27
1344
1337
1342
1343
1329
1337
995
991
995
997
988
991
CP2
CP3
CP4
420, 550, 592
CP5
435, 551, 590
CP6
420, 550, 590
a[M+H]+ charged
(3.67 mL, 20 mmol) and dried K2CO3 (2.78 g, 20 mmol)
was stirring in distilled DMF (30 mL) at 80°C under a
nitrogen atmosphere for 6 h. The reaction mixture was
decanted into cold water to remove the K2CO3. When
K2CO3 dissolved completely, the mixture extracted with
ethyl acetate. The organic layer was washed with NaCl sat-
urated aqueous solution, dried over MgSO4 and evaporated
to remove most of ethyl acetate. Amount of cold water was
added in the oily residual, the crude product, white pre-
cipitate was present. Finally, acicular crystal transparent
of desired product, methyl 4-(4-formylphenoxy) butanoate,
was obtained by recrystal with ethanol. Yield: 52%; Mp:
65°C; elemental analysis Calcd. for C12H14O4: C, 64.85; H,
6.35; found: C, 65.13; H, 6.32.
4.81, 4.78 (2H, –H2C–COO–), 2.74~2.70 (3H, CH3), 2.32,
2.28 (2H, –OCH2–), 1.61 (2H, –CH2–), −2.77 (2H, N–H).
H2(TCP) was obtained by alkaline hydrolysis of the
H2(TMEP). H2(TMEP) (0.20 g, 0.18 mmol) was dissolved
in tetrahydrofuran (15 mL), and KOH aqueous solution
(25 mL, 10%) was added, then heated to relux. The reac-
tion progress was monitored by TLC. After the reaction,
most of tetrahydrofuran was removed by vacuum distilla-
tion, and a lot of distilled water was added in residue, dis-
solved it. Finally, amount of H2(TCP) precipitated from
the solution which acidized with concentrated HCl to pH
3. The product was washed with distilled water and etha-
nol until the iltrate to colorless. Yield: 95%; Mp: >250°C;
Elemental analysis Calcd. for C60H54N4O12: C, 70.44;
H, 5.32; N, 5.48; Found: C, 70.91; H, 5.56; N, 4.95; MS
observed [M+H]+: 1023.4 amu, calculated M: 1022.4
amu; UV–Vis (nm, DMF) λmax: 423 (Soret band), 520,
558, 594, 651 (Q bands); FT-IR (cm−1): 3101, 2964, 1711,
1593, 1501, 1474, 1250, 1167, 1024, 978, 814.
2.2.2 Synthesis of H2(TMEP) and H2(TCP)
Methyl 4-(4-formylphenoxy) butanoate (6.67 g, 30 mmol)
was dissolved in propionic acid (120 mL), and was heated
to relux at 140°C. Then distilled pyrrole (2.70 mL,
40 mmol) was added dropwise and the mixture was
reluxed for 1 h. When cooling to room temperature, ~80%
of the solvent was evaporated and 40 mL ethanol was
added. Then the mixture was cooled overnight in refriger-
ator and collected the crude product by suction iltration.
The crude product was puriied by chromatography on a
silica-gel column with CH2Cl2 as the eluent solvent, and
collected the irst band, a desired purple solid of compound
H2(TMEP) was obtained. Yield: 15%; Mp: >250°C; ele-
mental analysis Calcd. for C64H62N4O12: C, 71.23; H, 5.79;
N, 5.19; found: C, 71.04; H, 6.03; N, 5.15; MS observed
[M+H]+: 1079.5 amu, calculated M: 1078.4 amu; UV–Vis
(nm, CH2Cl2) λmax: 421 (Soret band), 519, 554, 593, 650
(Q bands); FT-IR (cm−1): 2952, 1734, 1606, 1508, 1472,
2.2.3 Synthesis of M(TCP)-M (M=MnII, CP1; FeIII, CP2;
CoII, CP3; NiII, CP4; CuII, CP5; ZnII, CP6)
A
mixture of H2TCP (0.010 g, 0.01 mmol),
Mn(CH3COO)2·4H2O (0.015 g, 0.06 mmol) and DMF
(4 mL) was stirred, and then sealed in a 10 mL Telon-
lined stainless steel reactor, kept under autogenous pres-
sure at 90°C for 72 h. The dark-purple precipitate of reac-
tion was iltered and washed with water, DMF, CH2Cl2
and ethanol to remove any unreacted monomer. The target
product MnII(TCP)-MnII (CP1) was dried at 45°C under
vacuum for 12 h. CP2, CP3, CP4, CP5 and CP6 were pre-
pared following the procedure described for CP1 except
that Fe(NO3)3 (0.015 g, 0.06 mmol), Co(CH3COO)2·4H2O
(0.015 g, 0.06 mmol), Ni(CH3COO)2·4H2O (0.015 g,
0.06 mmol), Cu(CH3COO)2·H2O (0.012 g, 0.06 mmol)
1
1244, 1174, 1051, 966, 808. H NMR (400 MHz, CDCl3):
δ (ppm)=8.85 (8H, Pyrrole-H), 8.10~7.08 (16H, Ar–H),
1 3

Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous…
Fig. 2 Illustration of CP1–CP6, assembled from metalloligands and
metal ions nodes
Fig. 1 UV–Vis spectra of CP1–CP6 in solid
and Zn(CH3COO)2·2H2O(0.013 g, 0.06 mmol) were used
centrifugal, and the concentration of dye in solution was
instead of Mn(CH3COO)2·4H2O.
determined by UV–Vis.
2.3 Oxidation Procedure and Catalysts Reuse
3 Results and Discussion
All the oxidation reactions were carried out in a sealed vial.
A mixture of alkylbenzene (1.2 mmol), TBHP (3.6 mmol)
and the catalyst (CP1–CP6, 0.02 mmol, 5 mg) in water
(2.5 mL) was stirred at 80°C for 24 h. When time up, the
3.1 Synthesis and Characterization of H2(TMEP)
and H2(TCP)
1
In order to ensure that the designed porphyrin bears long
lexible substituents, as shown in Scheme 1, the alde-
hyde with the substituents, methyl 4-(4-formylphenoxy)
butanoate, was synthesized irstly. It is known that Adler
synthesis is a convenient strategy for preparing porphyrin
derivatives by the condensation of pyrrole and aldehyde
[25–29]. So that the metal-free tetr-methyl ester porphyrin,
H2(TMEP), was prepared by condensation of pyrrole with
methyl 4-(4-formylphenoxy)butanoate in hot propionic
acid. The metal-free tetr-carboxylic porphyrin, H2(TCP),
was obtained by hydrolysis of H2(TMEP) in KOH aqueous
solution.
results of reaction were examined by GC. H NMR and
MS spectral data conirmed the identities of the product.
The catalyst was recovered by centrifugation, washed with
water and ethanol successively, and dried in vacuum at
45°C to remove the solvent for several hours before new
utilization under similar reaction conditions.
After the use of catalyst for three consecutive times, the
ketone yield declined slightly and the selectivity remained
over 99%. The leaching experiments were made in the
same conditions described above, after 24 h of reaction the
catalyst was isolated by centrifugation and no characteristic
spectrum of the porphyrin or metalloporphyrin was detect-
able in the supernatant by UV–Vis.
UV–Vis spectroscopy is a convenient method, through
which can quickly determine the formation of the porphy-
rin ring. The UV–Vis spectra of H2(TMEP) and H2(TCP)
have Soret band at 421 and 419 nm, and Q bands located
at 519, 554, 593, 650 and 518, 555, 595, 651 nm, respec-
tively (see Table 1 and Fig. S1 in Supplementary Mate-
rial). These characteristic spectral data of porphyrin deriva-
tives are similar to Spellane [30], Kadish [31] reports
and our previous studies [24]. In the infrared spectra of
H2(TMEP) and H2(TCP), absorption bands of νBenzene ring in
the regions of 1606, 1508, 1472 cm−1, vC=O in 1734 cm−1,
2.4 Dye Adsorption Tests
Two typical dye molecules methylene blue (MB) and rho-
damine B (RB) were used to examine the adsorption prop-
erties of CP1–CP6 in further study. CP1–CP6 (5 mg)
was added to dye aqueous solution (10 mL, 50 mg L−1)
with continuously stirring at room temperature for 24 h,
respectively. The solution and adsorbent were separated by
1 3

S. Sun et al.
Fig. 3 SEM images of CP1 (a), CP2 (b), CP3 (c), CP4 (d), CP5 (e) and CP6 (f)
Fig. 4 TEM images of CP1 (a), CP2 (b), CP3 (c), CP4 (d), CP5 (e) and CP6 (f)
1 3

Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous…
420, 435 and 420 nm. All Q bands of CP1–CP6 were
reduced to two ones. It is suggested that the porphyrins
of CP1–CP6 are metalated, and MpCPs are mainly com-
posed of M(TCP) units. Although most of the absorption
bands observed in the infrared spectra of CP1–CP6 are
due to the porphyrins themselves, the subtle diferences
between the spectra of the custom-designed porphyrins
and CP1–CP6 suggest that the structure distinction of
them. An infrared spectral feature common to H2(TMEP)
and H2(TCP) is a wagging vibration absorption band
of ωN–H in the regions of 966 and 978 cm−1 (Table 1).
These bands are present in each spectrum of metal-free
porphyrin and absent from those of CP1–CP6. Mean-
while, a stretching vibration absorption band of νMn–N in
the region of 988–997 cm−1 is present in each spectrum
of CP1–CP6 and absent from that of the metal-free por-
phyrin (Table 1) [34]. These subtle diferences between
the infrared spectra of the porphyrins and CP1–CP6
indicate that metal cations are locating at the cores of
porphyrins and coordinating to four nitrogen atoms in
the MpCPs, which are consistent with the UV–Vis spec-
tra of CP1–CP6. In addition, it can be seen the vC=O
absorptions of H2(TMEP) and H2(TCP) in the region of
1734 and 1711 cm−1, as shown in Fig. S2 and Table S1,
those are absent from spectra of CP1–CP6. Meanwhile,
Fig. 5 Powder XRD pattern of CP1–CP6
−
νsCOO absorption bands of CP1–CP6 are present in the
Fig. 6 TGA of CP1–CP6
region of 1340 cm−1, which indicate that the peripheral
carboxyl of M(TCP) are ligating the nodes of metal ions
(MnII, FeIII, CoII, NiII, CuII and ZnII) in CP1–CP6. Con-
sequently, the recommended structure of CP1–CP6 is
shown in Fig. 2, metalloligands of M(TCP) combine with
nodes of metal ions (MnII, FeIII, CoII, NiII, CuII and ZnII)
forming the extension structure.
ωN–H in 966 cm−1 for H2(TMEP) and νBenzene ring in 1593,
1501, 1474 cm−1, vC=O in 1711 cm−1, ωN–H in 978 cm−1
for H2(TCP) accordingly (see Fig. S2 and Table S1). The
UV–Vis and infrared spectra provide limited informa-
tion as to the formation of diferent porphyrin derivatives,
but these are not the case for the mass spectral (MS) data
which are quite deinitive. The MS data in accordance with
the expected value of H2(TMEP) and H2(TCP), which are
Figures 3 and 4 show the SEM and TEM images of
CP1–CP6. The morphologies of CP1, CP2 and CP6 are
spherical particles, they are aggregations made up of dif-
ferent shape of smaller particles actually, which can be
seen from the TEM images (Fig. 4a, b, f). The morphol-
ogy of CP3 is willow leaf shape, and CP4 is long granu-
lar particles. The powder XRD patterns indicate that CP1,
CP2, CP3, CP4 and CP6 are amorphous aggregations (see
Fig. 5). CP5 is also an aggregation with uniform particle
size, and PXRD showed that it is a substance has a certain
degree of crystallinity.
1
also consistent with the elemental analysis and H NMR
of H2(TMEP) [31–33] (see Table 1, Scheme 1 and Fig.
S6). All the above, indicating the isolated porphyrins,
H2(TMEP) and H2(TCP), are consistent with the structures
illustrated in Scheme 1.
3.2 Synthesis and Characterization of M(TCP)-M
(M=MnII, CP1; FeIII, CP2; CoII, CP3; NiII, CP4;
CuII, CP5; ZnII, CP6)
BET speciic surface areas and most probable pore-
sizes of the CP1–CP6 based N2 adsorption data are sum-
marized in Table 2. CP1–CP6 have similar isotherm
proiles, and show type II ones with almost no hystere-
sis loops (Figs. S7, S8, S9, S10, S11, S12). In addition,
the wide ranges of pore-sizes of CP1–CP6 indicate that
the pores are primarily attributed to the accumulation
of particles, which can also be seen from the SEM and
TEM images. These suggest that the adsorption occurred
The MpCPs, CP1, CP2, CP3, CP4, CP5 and CP6, were
prepared from the custom designed porphyrin H2(TCP)
and excess metal ions in DMF under solvothermal. Mean-
while, the porphyrin cores were in situ metalated with the
metal ions. In Fig. 1, the UV–Vis spectra of CP1–CP6
show the characteristics of metalloporphyrins. The Soret
bands of CP1 and CP2 blue shift, respectively, to 389 and
403 nm, and those of CP3–CP6 red shift slightly to 423,
1 3

S. Sun et al.
Table 2 Oxygenation of alkylbenzene with TBHP catalyzed by CP1–CP6
Catalysts
Substrates
Products
Yielda, %
1st, 2nd, 3rd
Selectivitya, %
1st, 2nd, 3rd
Speciic surface
areab, m2 g−1
Most probable
pore sizeb, nm
O
CP1
82.1, 79.4, 78.1
56.0, 55.2, 54.0
85.0, 83.2, 80.0
75.2,74.2,72.3
48.0, 47.1, 46.2
56.0, 55.3, 54.0
68.1, 66.0, 65.0
37.5, 37.0, 36.0
20.3, 20.0, 19.8
5.0, 4.5, 4.3
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
>99, >99, >99
116.4
25
30
25
19
25
34
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
CP2
CP3
CP4
CP5
CP6
98.8
109.8
59.8
4.5, 4.0, 4.0
4.0,4.0,3.9
61.0, 60.0, 58.1
32.5, 30.2, 30.0
18.2,18.1,18.0
34.9, 34.0, 33.2
23.4, 23.0, 22.1
119.4
105.8
1 3

Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous…
Table 2 (continued)
Catalysts
Substrates
Products
Yielda, %
1st, 2nd, 3rd
Selectivitya, %
1st, 2nd, 3rd
Speciic surface
areab, m2 g−1
Most probable
pore sizeb, nm
O
22.5, 22.0, 22.0
Trace
>99, >99, >99
O
O
O
Blank
>99
>99
>99
Trace
Trace
Reaction conditions: alkylbenzene (1.2 mmol), TBHP (3.6 mmol), catalyst (5 mg), H2O (2.5 mL), temperature 80°C, time 24 h
aGC yield based on starting substrate
bBET speciic surface area of catalysts before the 1st cycle, N2 adsorption isotherm measurements at 77 K
Scheme 2 The probable free
radical mechanism for oxidation
of alkylbenzene with TBHP
over CP1–CP6 catalysts
mainly on the external of particles. So, presumably, cata-
lytic reactions likewise occur on the particles surface of
the MpCPs.
3.3 Alkylbenzene Oxidation with TBHP Catalyzed
by CP1–CP6
Thermogravimetric analysis was taken to examine the
thermal stability of CP1–CP6. As can be seen in Fig. 6,
CP1, CP3 and CP4 have similar mass loss processes, the
irst mass loss should be attributed to solvent molecules.
With the temperature increased there are plateaus, sub-
sequently, the second weight loss began in 240, 230 and
300°C for the CP1, CP3 and CP4, respectively, which
should correspond to decomposition of polymers struc-
tures. So that stable state can be maintained for the CP1,
CP3 and CP4 below 240, 230 and 300°C. CP2, CP5 and
CP6 underwent continuous processes of weight loss, there
is no plateau. However, the stable state of CP2, CP5 and
CP6 could be maintained below 360, 290 and 320°C, since
there are inlection points in the TGA curves of the MpCPs
in the temperatures.
To assess the catalytic properties of the new heteroge-
neous catalysts, the oxidation of alkylbenzene were car-
ried out using TBHP as the oxidant. In Table 2 are sum-
marized the results of ethylbenzene, propylbenzene and
diphenylmethane oxidation catalyzed by CP1–CP6,
respectively. It is show that all of CP1–CP6 exhibited
catalytic activities toward the oxidation of the three sub-
strates to ketones, and the selectivities were over 99 %
indicating the products were almost ketones. Among
them, the catalytic performance of CP1 was the best
to all of the three substrates, however, that of CP4 was
the worst. This result is consistent with our previous
researches, which is quite possibly because the CP1 is
based on manganese porphyrin, and the high catalytic
activities of manganese porphyrins have been conirmed
1 3

S. Sun et al.
Table 3 Oxygenation of
ethylbenzene with TBHP
catalyzed by CP1–CP6 and
other catalysts
Catalysts
Ethylbenzene Selectivity, %
conversion, %
Tempera- Time, h
ture, °C
Acetophenone Other products
CP1
82.1
75.2
68.1
5.0
>99
>99
>99
>99
>99
>99
>99
83a
–
80
80
24
24
24
24
24
24
12
16
12
120
24
CP2
–
CP3
–
80
CP4
–
80
CP5
61.0
34.9
82
–
80
CP6
MnIII(F10CPp)-NiII [24]
[(pymox-Me2)RuCl2]+BF4− [36] 95
–
80
–
65
–
12b
35e
2.7c, 4.3d
20
5 wt% Ag/SiO2 [37]
CeO2 nanorods [38]
38
88
67
88
120
105
80
65
Si/Al-pr-NH-et-N=methyl-
2-pyridylketone-Mn [39]
93
Pd-nanoparticles [40]
MnSBA-15 [41]
Mn-MCM-41 [42]
CNCr-2 [43]
92.3
25
93.5
37
0.5c, 6.0d
62d
10c, 50d
30d
130
80
24
8
60
39
80
24
8
45
69
70
Co/MCM-41 [44]
Zr-K-OMS-2 [45]
NMC [46]
26
85
9.1c, 5.9d
2.0d
80
24
10
24
20
48
12
62
98
65
88.3
83.1
>99
69.5
53.4
>99
>99
80.4
–
80
[Co(TCPp)]·2DMF [47]
ZJU-18 [48]
–
80
–
65
CoZnAl-MMO/Al2O3 [49]
12.1c, 7.5d
120
NMC nitrogen-doped mesoporous carbons
aIsolated product yields
b1-Phenylethanol
cBenzaldehyde
dOther products
e1-Phenyl-ethyl-tert-butyl-peroxide
by predecessors’ researches [1–7, 35]. Accordingly, we
tentatively speculate that the catalytic activities of the
CP1–CP6 could be attributed to the M(TCP) units which
are immobilized by ligating to nodes of metal ions (MnII,
FeIII, CoII, NiII, CuII and ZnII) in the MpCPs to prevent
their self-dimerization and oxidative degradation. In the
three substrates, the conversion rate of ethylbenzene is
relatively high for smaller molecule size. But the MpCPs
have no size selectivity, because all of them have cata-
lytic abilities for the substrates, which suggest that the
catalytic reactions occur on the surface of the MpCPs
particles.
In view of only ketones were formed as main prod-
ucts and no other product was found to be forming, as
shown in Scheme 2, alkylbenzene oxidation with TBHP
should follow a free radical mechanism in the pres-
ence of CP1–CP6 catalysts (see Fig. S16). Possibly, the
CP1–CP6 catalysts act as an initiator in the homolysis of
t-BuOOH (TBHP) into free alkoxy (t-BuO·) and alkylper-
oxy radicals (t-BuOO·) [37, 38]. Subsequently, oxidation
Fig. 7 Catalysts reuse of CP1–CP6
1 3

Metalloporphyrin-Based Porous Coordination Polymers: Synthesis, Served as Heterogenous…
Table 4 The adsorption
Dyes
CP1
Q (mg g−1
CP2
Q (mg g−1
CP3
Q (mg g−1
CP4
Q (mg g−1
CP5
Q (mg g−1
CP6
Q (mg g−1
)
capacities of CP1–CP6 for the
dyes of MB and RB
)
)
)
)
)
MB
RB
83
88
96
95
89
85
80
78
99
98
92
89
takes place at the α-carbon of the alkylbenzene [39]. For-
mation of the product ketones have been illustrated in
Scheme 2.
4 Conclusion
This work presents six heterogeneous catalytic MpCPs
of CP1–CP6 based on M(TCP) units, which were very
easily prepared from commercially available compounds,
able to selectively oxidize alkylbenzene exclusively
to ketones. The high catalytic eiciency observed for
CP1–CP6 may be attributed to M(TCP) units immobi-
lized in the MpCPs, owing to prohibit their self-dimer-
ization and oxidative degradation. Although, the ketone
yields were declining slightly for consecutively reused,
the selectivity remained over 99 % and without detect-
able catalysts leaching. The catalysts are robust toward
the oxidation reactions of alkylbenzene and easily recov-
ered by simple iltration. Furthermore, the dye adsorp-
tion properties of CP1–CP6 have been examined, show
that the MpCPs were capable of uptaking both of RB and
MB, among which the adsorption capability of CP5 is
optimum.
Considering the higher conversion rate of ethylbenzene
in the three substrates, in Table 3, the catalysts examined
in the present work and the other ones in previous litera-
tures used for oxidation of ethylbenzene with TBHP are
compared under diferent conditions. When the ethylben-
zene conversion (82.1%) and selectivity to acetophenone
(>99%) obtained in this work were compared with other
published data, it can be observed that the catalyst of CP1
employed here behaves in a comparable way, or even better,
in most cases with respect to other catalysts.
The stabilities of the heterogeneous catalysts CP1–CP6
were examined through repeated oxidations of the three
substrates using TBHP (see Fig. 7). The catalysts were
isolated, washed exhaustively with water, DMF and etha-
nol, successively, and dried before being used for the fresh
substrates and TBHP. There is a certain degree of decreas-
ing of catalytic activities, when the catalysts were consecu-
tively reused three times, however, without detectable cata-
lysts leaching.
Acknowledgments The authors gratefully acknowledge the
National Natural Science Foundation of China (Grant No. 21271148,
21671158) and the Natural Science Foundation of Inner Mongolia
Autonomous Region of China (Grant No. 2016MS0205) for inancial
support of this work.
3.4 Dye Adsorption Tests
Dyes are extensively used to produce attractive colours
in industries such as textile, paper-making, cosmetic and
leather. Furthermore, dyes form highly chronic toxicity
complexes by combining with various heavy metal oxides
in wastewater, which should be treated before discharged.
In addition, adsorption and separation of dyes in waste-
water is a potential application of MOF [50, 51]. So here,
we employed the most commonly used two dyes, methyl-
ene blue (MB) and rhodamine B (RB), to investigate dye
adsorption properties of the MpCPs. In aqueous solutions
of MB and RB (50 mg L−1), the MpCPs of CP1–CP6 were
added parallelly. For 24 h continuous stirring at room tem-
perature, the colours of the solutions turned lighter and
clearer compared to those of the original. Simultaneously,
the concentrations of MB and RhB were monitored by the
UV–Vis spectra as shown in Fig. S14 and S15. The results
show that CP1–CP6 were capable of uptaking organic dyes
including RB and MB, among which the adsorption capac-
ity of CP5 for both of MB and RhB is the highest (see
Table 4).
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