Transitional metals immobilized by coordination on aminophosphonate functionalized copolymers and their catalytic properties

Article abstract of DOI:10.1016/j.molcata.2015.07.035

Aminophosphonate functionalized copolymers were obtained as supports for transition metals immobilization in order to use them in catalytic applications. Styrene-divinylbenzene copolymer was functionalized with aminophosphonate groups by Kabachnik-Fields reaction. TG, FTIR, UV-vis-NIR and XPS confirmed the functionalization of the surface of polymer and evidenced the ligand effect of aminophosphonate groups on metal cation properties. Two effects of the supports were evidenced on interaction with cation metals respectively catalytic activity: ortho- or para- position of amino and phosphonate groups and nature of amine radicals. The fragile equilibrium between the two antagonistic effects could explain the formation of copolymer-3d metal ions assemblies and also the absence of interaction between manganese cation and supports with ortho position of amino and phosphonate groups. Catalytic properties of the obtained catalysts were evaluated in oxidation with hydrogen peroxide of organic compounds (anisole, cyclohexene, toluene, styrene, phenol). Turnover rate (TOF) values showed a higher activity, except oxidation of cyclohexene and phenol, for Cu catalysts with para isomer and ortho-Cl-C₆H₄ amine radical. Lower activity was obtained for Mn catalysts with similar supports. The recycled catalysts were still active after three times reusage, however, a high variation of the catalytic performance was evidenced for Mn catalysts.

Full text of DOI:10.1016/j.molcata.2015.07.035

Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Transitional metals immobilized by coordination on
aminophosphonate functionalized copolymers and their catalytic
properties
a
b
b
c
a
Adriana Popa , Ramona Ene , Diana Visinescu , Ecaterina Stela Dragan , Gheorghe Ilia ,
a
b,∗
Smaranda Iliescu , Viorica Parvulescu
Institute of Chemistry Timisoara of Romanian Academy, 24 Mihai Viteazul Blv., 300223 Timisoara, Romania
Ilie Murgulescu” Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania
Petru Poni” Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda 41 A, 700487 Iasi, Romania
a
b
c
“
“
a r t i c l e i n f o
a b s t r a c t
Article history:
Aminophosphonate functionalized copolymers were obtained as supports for transition metals immo-
bilization in order to use them in catalytic applications. Styrene-divinylbenzene copolymer was
functionalized with aminophosphonate groups by Kabachnik–Fields reaction. TG, FTIR, UV–vis-NIR
and XPS confirmed the functionalization of the surface of polymer and evidenced the ligand effect of
aminophosphonate groups on metal cation properties. Two effects of the supports were evidenced on
interaction with cation metals respectively catalytic activity: ortho- or para- position of amino and phos-
phonate groups and nature of amine radicals. The fragile equilibrium between the two antagonistic effects
could explain the formation of copolymer-3d metal ions assemblies and also the absence of interaction
between manganese cation and supports with ortho position of amino and phosphonate groups.
Catalytic properties of the obtained catalysts were evaluated in oxidation with hydrogen peroxide of
organic compounds (anisole, cyclohexene, toluene, styrene, phenol). Turnover rate (TOF) values showed
a higher activity, except oxidation of cyclohexene and phenol, for Cu catalysts with para isomer and
ortho-Cl-C6H4 amine radical. Lower activity was obtained for Mn catalysts with similar supports. The
recycled catalysts were still active after three times reusage, however, a high variation of the catalytic
performance was evidenced for Mn catalysts.
Received 19 September 2014
Received in revised form 29 July 2015
Accepted 30 July 2015
Available online 1 August 2015
Keywords:
Polymer supported catalysts
Aminophosphonate functionalized
copolymer
Cu(II) complexation
Mn(II) immobilization
Catalytic oxidation
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
-Aminophosphonates, due to their structural analogy to ␣-
groups [16] is often mentioned in literature. The first one-pot syn-
thesis of ␣-aminophosphonates has been achieved by the reaction
of OH-phosphonate in the presence of lanthanide triflate [17] as
the catalyst with imines generated in situ from aldehydes and
amines in organic solvent. Since Merrifield reported the method
of “solid-phase peptide synthesis” in 1963 [18], there has been an
increased interest in the application of polymers as participants
in catalysis [19–23], organic synthesis [24], environmental separa-
tion [25–30] and antibacterial agents [31–33]. Chloromethylated
polystyrene cross-linked with divinylbenzene is one of the most
widely employed macromolecular supports for heterogenization
of homogeneous catalysts [34]. The polymer-supported catalysts
have received wide attention because these materials offer advan-
tages to the new catalytic systems like selectivity, recyclability
and easy separation from reaction products leading to the oper-
ational flexibility [35]. The polymer-supported metal complexes
showed higher catalytic activity in various chemical reactions such
as oxidation [36,37], oxidative functionalization [38], hydrogena-
␣
amino acids, have been the subject of considerable interest [1].
Extensive investigations over the last twenty years have shown that
they are of particular importance in biological and medical research
[
2,3]. In this respect, the uses of ␣-aminophosphonates as enzyme
inhibitors, antibiotics and pharmacological agents, herbicides and
haptents of catalytic antibodies are well documented [4]. The mod-
ification of polymers has also received attention in the last years.
New materials were obtained by functionalization [5,6] or graft-
ing of polymers [7–9] and diversity of their applications increased.
The synthesis of modified polymers with phosphonic acid groups
[
10,11] phosphonate groups [12–15] and aminoalkylphosphonic
∗ Corresponding author.
E-mail address: vpirvulescu@icf.ro (V. Parvulescu).
http://dx.doi.org/10.1016/j.molcata.2015.07.035
381-1169/© 2015 Elsevier B.V. All rights reserved.
1

A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
263
tion [39] and acid catalysis processes [40]. For example, in oxidation
of phenol and epoxidation of cyclohexene the supported catalysts
showed low energy of activation than unsupported catalysts. This
clearly suggested that polymer supports played a significant role
in decreasing the energy of activation for these reactions in the
presence of metal complexes [41].
The aim of this work was to obtain new catalysts by immobi-
lization of Cu and Mn ions on funtionalyzed copolymer supports.
The surface of styrene-divinylbenzene copolymer was function-
alized with aminophosphonate groups in order to highlight their
effect on metals complexation and on catalytic properties of
the obtained materials. The impregnation of transition metals
on a chelating substrate like styrene-divinylbenzene copolymer
functionalized with aminophosphonate groups is similar with
an exchange or chromatographic processes [42,43]. Cu(II) and
Mn(II) cations were selected for the chelating effect on them
of aminomethylphosphonate groups [44] and influence of this
process on catalytic properties of the supported complexes. The
catalytic properties of Cu(II) and Mn(II) cations were evidenced
in oxidation with hydrogen peroxide of the organic compounds
cooling, the polymer beads were separated by filtration, washed
with methanol (3 × 20 mL), distilled water (3 × 20 mL), acetone
(3 × 20 mL) and finally with diethyl ether (3 × 20 mL) and dried at
◦
50 C for 24 h.
St-DVB copolymer functionalized with 2-hydroxybenzaldehyde
(2.79 mmoles CHO/gram of copolymer (B2)) or St-DVB copoly-
mer functionalized with 4-hydroxybenzaldehyde (2.94 mmoles
CHO/gram of copolymer (B3)) were obtained.
2.3. Synthesis of aminophosphonates grafted on macromolecular
substrates and immobilization of transtion metals
Four grams St-DVB copolymer (2.79 mmoles CHO /gram of
copolymer (B2) or 2.94 mmoles CHO /gram of copolymer (B3))
and tetrahydrofuran (THF 50 mL) were adeed to a 100 mL round
bottom flask fitted with reflux condensar, mechanical stirrer and
thermometer. The mixture was then maintained under stirring
for 2 h at room temperature to allow the copolymer beads to
swell. The molar ratio of CHO groups:diethylphosphite:amine
(propylamine, ortho-chloroaniline) was 1:1:1. The final mixture
◦
[
45–48]. Results obtained before [48] evidenced the influences
was maintained under stirring for 20 h at temperature of 60 C.
of styrene-divinylbenzene copolymer functionalyzed surface on
catalytic properties of the immobilized Cu(II) complexes. These
properties were evaluated in oxidation with hydrogen peroxide of
organic compounds (anisole, cyclohexene, toluene, styrene, phe-
nol). New catalysts were obtained in order to emphasize direct
effect of copolymer organic function as ligand of transitional metal
cations on catalytic activity, selectivity and stability.
After cooling, the polymer beads were separated by filtration,
washed with ethanol (3 × 20 mL), 1,2-dichloromethane (3 × 20 mL)
and diethyl ether (3 × 20 mL), and dried under a vacuum of 2 kPa at
◦
50 C for 24 h.
Immobilization of the metals was made by impregnation of dry
styrene-divinylbenzene support functionalized with aminophos-
phonate groups with CuCl2 and MnCl2 aqueous solutions in
conditions of maximum amount of metal obtained by adsorption
isotherms. After one washing step, the impregnated particles were
2
. Experimental
◦
dried 10 h at 80 C.
2.1. Materials
2.4. Characterization of the materials
Chloromethylated
chloromethylated St-6.7%DVB copolymer), supplied by Puro-
lite Victoria Romania, copolymer St-(6.7%)DVB grafted with
aldehyde groups synthesized in our laboratory [47], 2-hydroxy-
benzaldehyde (Sigma–Aldrich, 98%), 4-hydroxy-benzaldehyde
styrene–divinylbenzene
copolymer
The obtained materials were characterized by Fourier transform
(
infrared spectroscopy (Shimadzu FTIR), Ultraviolet-Visible-Near
Infrared spectroscopy (Jasco V-570-(UV–vis-NIR)), scanning elec-
tron microscopy (Philips XL-20, FEI Quanta 3D FEG) and atomic
absorption spectrophotometry (Spectra AA-220 Varian spec-
trophotometer). Thermal properties of the aminophosphonates
grafted on crosslinked macromolecular substrates were charac-
terized through thermogravimetric analysis (TGA) and differential
(
Merck, 98%), N,N-dimethylformamide (Sigma–Aldrich, 99%),
propylamine (Fluka, 99%), ortho-chloroaniline (Loba Chemie,
8%), tetrahydrofurane (Sigma–Aldrich, 99%), tetraethylammo-
nium iodide (Merck, 98%), potassium carbonate (Sigma–Aldrich,
9%), methanol, acetone ethanol, dichloromethane and diethyl
ether (Chimopar, 99%), CuCl ·2H O (Sigma–Aldrich, 99%), and
9
thermal analysis (DTA) using a TGA/SDTA 851-LF1100—Mettler
9
◦
apparatus at a heating rate of 10 C/min under N atmosphere and
2
2
2
◦
temperature in the range 20–600 C.
MnCl ·4H O (Sigma–Aldrich, 98%) were used as starting materials
2
2
The phosphorus content of the polymer-supported aminophos-
for the polymerics catalysts preparation.
phonates was obtained by adsorption in water of the P O5 from a
2
sample of the product precisely weighed and burnt out in an oxy-
gen atmosphere [13,32]. The obtained solution was titrated with
an aqueous solution of (NH ) Ce(NO ) 0.005 M in the presence of
2
2
.2. Reactions of chloromethylated St-DVB copolymer with
-hydroxy and 4-hydroxy-benzaldehyde
4
2
3 6
Eryochrome Black T as indicator.
The apparent density (ꢀap) was determined using a mercury
Chloromethylated St-DVB copolymer (14.22% Cl) was used
−
2
as the starting material in all syntheses. The synthesis of
St-DVB copolymers functionalized with 2-hydroxy and 4-hydroxy-
benzaldehyde under phase-transfer catalysis (PTC) conditions
in solid–liquid–liquid (chloromethylated St-DVB copolymer/N,N-
pycnometer at 1.333 × 10 Pa. The specific density (ꢀ ) was mea-
r
sured in n-heptane. The specific surface area (Ssp) was determined
by the nitrogen adsorption at the boiling temperature of liquid
nitrogen, by the Haul–Dümbgen method on a Ströhlein Area Meter
apparatus. The average pore radius was calculated using the fol-
lowing equation (cylindrical shape of pores being assumed):
dimethylformamide/aqueous potassium carbonate (K CO3 (30%))
2
was performed by previously described method [48]. Chloromethy-
lated St-DVB copolymer (10 g) was soaked 24 h in N,N-
dimethylformamide (DMF 40 mL) in a 250 mL round bottom flask.
After separation of DMF, the swollen copolymer was treated
with (9.8 g) 4-hydroxybenzaldehyde (or 2-hydroxybenzaldehyde),
2
Ssp
Vp
3
rp = (
) × 10 (nm)
(1)
where Vp = (1/ꢀap) − (1/ꢀr), pore total volume, mL/g.
(
(
0.2 mmol) of tetraethylammonium iodide and aqueous K CO3
The catalytic properties of polymer supported metals were
evaluated in oxidation with hydrogen peroxide of the organic
substrates (anisole, cyclohexene, toluene, styrene, phenol). The
reactions were carried out in the thermostated glass mini reactors
2
30%) (100 mL). The molar ratio of chloromethyl groups: 4-
hydroxybenzaldehyde (or 2-hydroxybenzaldehyde) was 1:2. The
◦
mixture was maintained under stirring for 18 h at 95 C. After

2
64
A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
CH2 CH
CH2 CH
CH2 CH
CH2 CH
CH2 CH
r
x-y
1-r-x
z
y-z
CH
CH Cl
CH2
O
2
CH2
O
CH2
O
CHO
CH P(OR`)2
HN
R
Fig. 1. Structure of the repetitive units of the final functionalized copolymer.
where: x–y—fraction of styrene units bearing pendant CH2Cl groups,
y–z—fraction of styrene units bearing CHO groups (Fi),
z—fraction of styrene units bearing aminophosphonate groups (Ff),
r—fraction of divinylbenzene (DVB) units.
Table 1
Table 2
Characteristics of aminophosphonates grafted on polymeric supports (B2 and B3).
Characteristics of 2-benzaldehyde (B2) and 4-benzaldehyde (B3) grafted on St-DVB
copolymers.
Code
B2
4B2
1B3
R-NH2
P (wt.%)
z
GF (mmols/g)
Code
Clf (%,w)
x
y
GF (mmol CHO/g of copolymer)
1
CH3CH2CH2-NH2
ortho-Cl-C6H4-NH2
CH3CH2CH2-NH2
ortho-Cl-C6H4-NH2
5.70
4.80
5.90
5.06
0.43
0.40
0.46
0.44
1.84
1.56
1.90
1.63
B2
B3
10.91
10.72
0.530
0.530
0.519
0.526
2.79
2.94
4B3
◦
22
20
18
(
5 mL) with magnetic stirring. All reactions were performed at 50 C
B2
4B2
temperature, time 8 h and 0.05 g amount of catalyst. The selected
molar ratio substrate/solvent (acetonitrile)/H O was 1/3.8/3 and
2
2
analysis of oxidation products was performed using a DANI GC 1000
gas chromatograph connected to a FID detector and mass spec-
trometer. The active compound leaching during the reaction was
verified by atomic absorption spectrophotometry (FAAS) measure-
ments and resubmission of filtrates under reaction conditions to
follow continuation of the reaction.
1
1
1
6
4
2
10
8
6
4
3
. Results and discussions
0
100
200
300
400
500
600
o
T C
3.1. Characterization of aminophosphates grafted on St-DVB
copolymer
Fig. 2. Thermograms for B2 and 4B2 samples.
The fraction (F) of the repetitive units of chloromethylated St-
DVB copolymer, functionalized with aminophosphonates groups,
was determined from the statistical structure (Fig. 1).
The main characteristics of the aminophosphonate groups
grafted on polymer support by one-pot polymer-analogous reac-
tions are given in Table 2.
Characterization of 2-benzaldehyde (B2) and 4-benzaldehyde
(
B3) grafted on St-DVB copolymer was obtained by the method
Cu/N and Mn/N atomic ratios were calculated reporting the
metal to minophosphonate concentration, determined by atomic
adsorption, respectively by one-pot polymer-analogues reactions.
The values of atomic ratio were ∼1 for Cu/N and ∼3, for Mn/N.
Thermograms of B2 and 4B2 are presented in Fig. 2. The ther-
mal behavior of the 4B2 sample shows characteristic “step weight”
previously described [49].
The polymer-analogous reactions are presented in Scheme 1.
The modified polymer sample showed FT-IR absorption peaks at
−
1
1
1
695 and 1150 cm corresponding to C O and C O stretching at
−
1
595 cm corresponding to the aromatic nucleus. The main char-
◦
acteristics of aldehydes grafted on polymer support are given in
Table 1.
The degree of functionalization with benzaldehyde groups was
around 3 mmol/gram copolymer.
The synthesis of copolymers functionalized with aminophos-
phonate groups occurs according to Scheme 2.
losses: in the first step 25–250 C, the constant weight loss (∼20%),
was attributed to evaporation of ortho-chloroaniline and other
◦
volatiles; in the second step 250–400 C, the weight loss (∼20%),
was attributed to the depolymerization of polystyrene chains,
degradation of styrene oligomers, the degradation of dialkylphos-
phite and degradation of P C bonds of the pendant groups; in the

A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
265
Scheme 1. The synthesis of 2- (4-) benzaldehyde grafted on St-DVB copolymer.
Scheme 2. The synthesis of aminophosphonate groups grafted on polymeric supports (B2, B3).
where: —copolymer St-6.7%DVB; R-NH2 = propylamine, ortho-chloroaniline,
ꢀ
HOP(OR )2 = diethylphosphite.
◦
third step 400–550 C, the weight loss (∼25%), was attributed to
The presence of the aminophosphonate groups grafted on the
polymer was confirmed by the FTIR spectra of the 1(4)B2 and
1(4)B3 supports (Fig. 5 and SI). The region between 2700 and
the depolymerization of polystyrene chains and the degradation of
styrene oligomers.
−
1
From the analysis of experimental data it was observed that the
stability of the copolymer was influenced by the nature of the pen-
dant groups of aminophosphonate type. The other compounds have
similar behavior. The morphological characteristics of all polymeric
materials are presented in Table 3.
3400 cm
contains absorption bands specific to the secondary
amine group. A large band, structured with sharp peaks cover the
−
1
2800–3000 cm
region and could be assigned to the symmet-
rical and antisymmetrical stretching vibrations of the secondary
ꢀ
ammine groups, ꢁsym(NH ) and ꢁas(NH ). Both P O and P
O R
2
2
The morphological characteristics of the chloromethylated St-
DVB copolymer used as substrate for the preparation of aldehyde
and aminophosphonate samples show a mesoporous material
because the average rp is under 50 nm. By the subsequent chem-
ical transformations, the morphology of the samples containing
aldehyde groups (B2 and B3 samples) was changed first, being
closer to a macroporous structure, with macropores larger than
bonds of the aminophosphonate group gave sharp and very intense
absorption bands in the FTIR spectra centered at ca. 1250 and
−
1
1050 cm , respectively. The aldehyde group and the aromatic
rings are responsible for the broad structured band located at
−
1
−1
ca. 1600 cm . The broadband centered at 3600 cm indicate the
presence of the surface water molecules for all types of support.
The analysis of the FTIR spectra of the Cu/Mn-(1,4)B2(3) samples
indicates strong modifications of the shapes and energies of the
absorption bands which may suggest an interaction between metal
cations and the aldehyde and/or aminophosphonate groups of the
support.
5
0 nm, and the corresponding decrease of the specific surface area.
However, the position of aldehyde group seems to have an influ-
ence on the morphological changes, the increase of pore volume
and of the average rp being more significant in the case of ortho-
benzaldehyde than in the case of para-benzaldehyde groups. The
same morphological differences can be observed after the introduc-
tion of aminophosphonate groups (samples 1B2 and 4B2 compared
with samples 1B3 and 4B3). The explanation could be found in the
differences in the polymer-solvent interactions, a poorer solvent for
the functionalized material resulted after the polymer analogous
reaction steps lead to larger pores than in the starting substrate
Both aminophosphonate and aldehyde groups contain poten-
tially donor atoms (oxygen and nitrogen atoms) able to coordinate
transition metal ions. The FTIR spectra of the Cu/Mn-(1,4)B2(3)
samples show that the absorption bands attributed to the symmet-
ric and asymmetric stretching vibration of the secondary amino
−
1
group (3500–2750 cm ), as well as those assigned to the P
O
ꢀ
−
1
and P
after the impregnation process. The carbonyl specific absorptions
O R groups (ca. 1050 and 1250 cm ) are blue-shifted
[
50,51].
In the SEM micrographs of samples B2 and 4B2 (Fig. 3), the
−
1
(1600–1640 cm ) are also broadened after the metal impregna-
tion. In order to get more information, NIR-UV–vis and XPS spectra
mesurements of the metal-containing products have been per-
formed and will be discussed below.
macropores are visible among the agglomerations of microspheres,
characterized by a dense structure. SEM micrographs of the support
containing aldehyde groups (B2) and aminophosphonate groups
(
4B2) show spherical morphology of the polymer microparticles.
The overlaid UV–vis spectra for the three types of supports:
chloromethylated styrene-6.7% DVB, non-functionalized and func-
tionalized with benzaldehyde group (in ortho- B2 and in para- B3)
are shown in Fig. 6.
All samples present intense, broad and structured absorptions
which cover the high-energy regions (200–350 nm). These bands
originate from the intra-aromatic ꢂ–ꢂ* transitions in copolymer.
For the functionalized support, the bands are red shifted as a
result of the insertion of an electron-withdrawing group ( CHO)
on the ꢂ-system of benzene ring. The weak band observed for
Therefore, the functionalized resin particles can be regarded as
macroporous materials, which consist in agglomerates of gel-
type microspheres between which a complex pore structure with
labyrinth of channels can be observed.
The functionalization of the support and immobilization of the
metals not alter the spherical morphology (Figs. 3 and 4A). The
effect of reaction on the polymer microparticles morphology was
insignificant (Fig. 4B). The effect of reactions in liquid phase was
the decrease of particles agglomeration and decrease of porosity.

2
66
A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
Table 3
Morphological characterization of the chloromethylated St-DVB copolymer, the aldehyde and aminophosphonate samples.
Sample/characteristics
Chloromet.St-DVB
B2
B3
17.4
0.6
1,0
1B2
1B3
4B2
4B3
2
Ssp, m /g
33.2
0.7
1.1
17.1
0.6
1.1
15.7
0.6
1.1
19.9
0.6
1.1
14.0
0.6
1.1
18.6
0.6
1.1
3
ꢀ
ap, g/cm
ꢀ
sp, g/cm3
Vp, mL/g
rp, nm
0.7
40.3
0.7
82.7
0.6
64.8
0.7
88.4
0.8
78.0
0.7
92.8
0.7
70.5
Fig. 3. SEM images of B2 polymer-supported benzaldehyde (A) and 4B2 aminophosphonates (B).
Fig. 4. SEM images of 4B2Cu sample before (A) and after (B) catalytic oxidation of cyclohexene.
1
B2Cu
B2Mn
1B3Cu
B3Mn
1
1
1B2
1
B3
3
500 3000 2500 2000 1500 1000 500
3
500 3000 2500 2000 1500 1000 500
-1
-1
Wavenumber (cm )
Wavenumber (cm )
Fig. 5. FTIR spectra of the polymeric supports 1B2 and 1B3 before and after impregnation with Cu (II) and Mn (II).
chloromethylated styrene-6.7% DVB, centered at approximately
and could be assigned to the n–ꢂ* transitions resulted from grafted
carbonyl groups on the support and also to chloride group [52].
The NIR-UV–vis spectra of the functionalized support with
aminophosphonate groups were recorded in the 200–1700 nm
region (Figs. 7 and 8). For the ortho-functionalized samples 1(4)B2
the very broad band located in the 200–450 nm region covers ꢂ–ꢂ*
3
70 nm is most likely arised from n–ꢂ* absorptions starting
from the lone pairs of the chloride moieties. For benzaldehyde-
functionalized copolymers (B2 and B3) an intense and broad (and
structured for B3) absorption is observed on 280–380 nm region

A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
267
and could be assigned to the allowed D–D transitions specific
to copper(II) ions in a six-coordinated surrounding with a dis-
torted octahedral geometry. A large band overlaps between 200
and 550 nm and covers most likely absorptions specific to copoly-
mer support and also the charge transfer bands from ligand to metal
B2
B3
II
ion (O → Cu ). The large shoulder at about 400 nm sustains also
the formation of the coordinative Cu(II) O bond, the oxygen donor
atoms belonging to the functionalized copolymer.
S-6.7%DVB
In order to identify which type of the functional group is effec-
tively employed in the interaction with the transition metal cations,
the characteristics of the aldehyde and aminophosfonate groups
were analyzed. On one hand, the aminophosphonates groups are
more basic than the carbonyl ones and have a higher potential to
coordinate transitional metal ions and form chelated complexes
200
300
400
500
600
700
800
with transitional metal cations [53,54]. On the other hand, two
Wavelength, nm
ꢀ
antagonistic effects of the high denticity P(O)(OR ) group were
2
Fig. 6. UV–vis spectra of chloromethylated St-6.7% DVB copolymer before and after
their functionalization with benzaldehyde group (orto-B2 and para B3).
expected to influence the stability of the copolymer-3d metal ions
assembly: (i) the formation of chelated complexes with copper(II)
metal ions which increases the overall stability of the system; (ii)
the electrostatic and steric hindrance effects from the substituted
aminophosphonate groups may strongly distort the geometry of 3d
metal cations and give more labile assemblies [55–58]. In our case,
it is very likely that the copper(II) cations interact with the support
through coordinative bonds established with the oxygen atoms of
the aminophosphonate groups. The XPS spectral data clearly indi-
transitions from aromatic rings and also n–ꢂ* absorptions of the
aminophosphonate and chloride group were evidenced. For para-
analogues, 1(4)B3, a broad absorption is observed in UV region
and is located at ca. 300 nm, being attributed to n–ꢂ* transitions
of the functionalized copolymer. The shoulder located at 260 nm
for 1B3 and 235 nm for 4B3 support are most likely a result from
the intra-benzene ꢂ–ꢂ* transitions [52].
The diffuse reflection spectra recorded for copper(II)-1(4)B2
samples suggest that the metal cations are anchored to support
through coordinative bonds. A large absorption band is observed
in the visible region, being centered at approximately 780 nm
cate the absence of any copper(II)-N bonds, the steric hindrance
of the Rꢀ alkyl radicals impeding the employment of the amine
nitrogen in the coordination of copper(II) cations.
For copper(II)-1(4)B3-samples the NIR-UV–vis spectra exhibit a
large and structured band which most likely cover the absorptions
originated from copolymer and/or charge transfer bands. The broad
absorption which is developed from visible toward low-energy
1
B2Cu
1B3Cu
1
B2Mn
1B3Mn
1
B2
1B3
200 400 600 800 1000 1200 1400 1600
200 400 600 800 1000 1200 1400 1600
Wavelength (nm)
Wavelength (nm)
Fig. 7. UV–vis spectra of the polymeric supports 1B2 and 1B3 before and after impregnation with Cu (II) and Mn (II).
4B3Cu
4B2Cu
4B2Cu a.r.
4B3Cu a.r.
4B2Mn
4B3Mn
4B2Mn a.r.
4B3Mn a.r.
4B2
4B3
200 400 600 800 1000 1200 1400 1600 1800
200 400 600 800 1000 1200 1400 1600
Wavelength (nm)
Wavelength (nm)
Fig. 8. UV–vis spectra of the polymeric supports 4B2 and 4B3 before, after impregnation with Cu (II) and Mn (II) and catalytic oxidation of cyclohexene (a.r.).

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A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
Table 4
Catalytic properties of Cu and Mn catalysts in oxidation reactions.
Sample
Cu/Mn mmol/g Cyclohexene
Anisole
Toluene
Styrene
Phenol
I
AR
TOF × 10−3(h−1
)
S (%)
TOF × 10−3(h−1
)
S (%)
TOF × 10−3(h−1
)
S (%)
TOF × 10−3(h−1
)
S (%)
TOF × 10−3(h−1
)
S (%)
1
1
1
1
4
4
4
4
B2Cu
B2Mn
B3Cu
B3Mn
B2Cu
B2Mn
B3Cu
B3Mn
1.84
4.70
1.92
5.24
1.56
4.91
1.63
5.12
1.64
1.42
1.76
2.71
1.42
1.86
1.58
2.53
38.83
15.61
41.21
35.64
30.62
15.26
33.72
11.92
63
46
72
51
68
45
78
56
29.22
15.11
32.16
11.20
34.16
13.53
40.24
10.29
89
64
72
52
91
64
79
55
27.93
13.17
31.42
9.86
22.53
17.11
32.67
11.91
78
32
84
52
79
48
86
71
42.41
15.02
36.55
11.68
38.85
10.09
46.13
12.34
76
42
87
56
84
62
76
68
54.56
18.29
41.22
14.62
65.52
19.96
54.39
16.88
68
36
72
41
64
54
72
67
regions suggest a similar coordination of copper(II) complexes as
in the cases of 1(4)B2 copolymers.
and copper(II)-1(4)B2 systems, but also the absence of interaction
between manganese(II) cation and 1(4)B2 supports as the elec-
tronic spectra suggested. This explains the higher decrease of Mn
content after first reaction cycle of 1B3Mn, 4B3Mn than 1B3Mn,
4B3Mn catalysts (Table 4).
For manganese(II) analogues, 1(4)B3Mn, the broadening
(
1B3Mn) of the high-energy absorption band (200–450 nm) with
a shoulder at ca. 450 nm (4B3Mn) could be a result of the forbidden
electron transition of manganese(II). This suggests the formation
of the coordinate bonds between the copolymer functional groups
3.2. Catalytic properties
(
most likely aminophoshonate group) and manganese(II) ions.
Although the electronic spectra could not provide more informa-
tion about the chemical surrounding of the Mn(II) ions, previous
reported examples containing similar Mn(II)-aminophoshonate
fragments sustain the involvement of the oxygen atoms of the
aminophoshonate group in coordinating of Mn(II) ions in six-
coordinate surrounding [59–61].
Catalytic properties of Cu and Mn cations immobilized
on styrene-divinylbenzene copolymer functionalized with
aminophosphate groups have been investigated in the oxida-
tion of anisole, cyclohexene, toluene, styrene and phenol with
hydrogen peroxide. Copper(II) and manganese(II) complexes sup-
ported on functionalized organic polymers are active catalysts for
efficient oxidation of olefins and aromatic compounds [48,62–64].
Turnover rate (TOF) values were calculated by reporting the moles
of the converted substrate, per hour, to the moles of metal in the
used catalyst. Table 4 evidence a higher activity of the catalysts
obtained by copper immobilization. The conversion values (Fig. 9)
are higher for samples with Mn as result of higher metal content of
the catalysts. The best activity was obtained in oxidation of phenol
for both cations, in case of the formation of complexes or not.
Comparing the catalytic activity of copper ion in similar oxidation
reactions [47] we can notify evident effects of organic functions
present on the support surface on the activity of the metal ion and
its complexes.
A
comparison of the UV–vis spectra of copolymer and
manganese(II)-1(4)B2 association reveal that the high-energy
absorptions preserve their patterns and decrease in intensities. In
these cases, the electronic spectra could not prove the association
of Mn(II) and 1(4)B2 support through coordinative bonds and sug-
gest rather the absence of any interaction between the transitional
metal cation and functional groups of the support.
The near-infrared region of the electronic spectra was also
analyzed. For all the samples, a low intensity and well-defined
absorption is distinguished at 1470 nm. Very weak absorptions are
observed at 1750 nm for copper(II). The shape, energy and intensity
of these bands suggest that absorption have a vibronic origin, due
to the water molecules deposed on the support surface.
A high variation of conversion was evidenced in oxidation of
anisole, cyclohexene, styrene and toluene, in case of Cu catalysts
with ortho- and para-isomers. These results can be considered the
effect of steric factor and microporous structure. The low effect of
microporosity on catalytic activity was evidenced comparing ortho-
and para-isomers. The higher surface area of para-isomers (Table 3)
can contribute to increased catalytic activity. A similar effect was
evidenced for the catalysts with Mn but, in this case, the effect of
low complexation was more evident. The higher activity, except
oxidation of cyclohexene and phenol, was obtained for Cu catalysts
The high-denticity and basicity of aminophosphonate groups
attached to copolymer favors the interaction of copper(II)
and manganese(II) cations with copolymer support through
coordinative bonds. The formation of chelated rings with metal-
aminophosphonate is opposite to the hindrance steric effect of the
P(O)(OR)2 groups and affect the overall stability of the complex
assemblies. The fragile equilibrium between the two antagonis-
tic effects could explain the formation of copolymer-3d metal
ions assemblies for copper(II) and manganese(II)-1(4)B3 samples
Fig. 9. Conversions of organic compounds in oxidation reactions on Cu and Mn catalysts.

A. Popa et al. / Journal of Molecular Catalysis A: Chemical 408 (2015) 262–270
269
Table 5
Reuse of Cu and Mn catalysts in oxidation reactions
Sample
Recycling time
Cu/Mnmmol/g
Cyclohexene
C (%)
Toluene
C (%)
Phenol
C (%)
S (%)
S (%)
S (%)
4
4
B3Cu
1
2
3
1.63
1.58
1.42
43.4
40.7
38.4
78
77
76
47
43
41
86
83
84
65.0
59.5
56.3
72
70
69
B3Mn
1
2
3
5.12
2.53
1.84
51.3
33.1
28.2
56
54
51
53.6
39.5
26.7
71
68
65
63.1
39.6
32.1
67
65
64
with para-isomer and ortho-Cl-C H4 amine radical. Lower activity
results reveal that the catalysts are still active after three times
reusage, however, the loss of the catalytic performance was evi-
denced for all the catalysts.
6
was obtained for Mn catalysts with similar supports. TOF values
of the reactions on Mn catalysts (Table 4) show the lowest activ-
ity for the samples with ortho-isomers (1B2 Mn and 4B2 Mn) and
ortho-Cl-C H amine radical. In the first two it was not evidenced
The main oxidation products of anisole were
2 or 4-
methoxyphenol, for cyclohexene oxidation were 2-cyclohexene-1-
ol, 2-cyclohexene-1-ones and cyclohexane-1,2-diol and for toluene
oxidation were o- and p-cresol, benzaldehyde and benzoic acid. In
oxidation of styrene the main product was benzaldehyde and in
case of phenol oxidation the main products are catechol and ortho-
or para-benzoquinone. In oxidation of C C bond from cyclohexene
and styrene the low selectivity was obtained for epoxides (∼2%).
The conversion to epoxide was higher for Mn-1(4)B2 samples
(∼4%). In Table 4 and 5 the selectivity (S) was evaluated in oxidation
of cyclohexene to 2-cyclohexene-1-ol, in oxidation of anisole to 4-
methoxyphenol, in oxidation of toluene to p-cresol, in oxidation
of styrene to benzaldehyde and in oxidation of phenol to cate-
chol. High selectivity was obtained for para hydroxylation products
in oxidation of anisole, toluene and phenol. Iresults presented in
Table 4 show higher selectivity values for 4-methoxyphenol in oxi-
dation of anisole and p-cresol in oxidation of toluene.
6
4
the formation of metal complexes by UV–vis spectra and atomic
absorption showed a pronounced leaching effect.
The low activity of the catalysts with CH CH CH amine radical
3
2
2
was evidenced for both kinds of catalysts in oxidation of cyclohex-
ene, toluene and styrene. It was considered effect of adsorption
as main step of reaction. Comparing functionalization degree of
polymer with metal content (Tables 2 and 4) three possible mech-
anisms of copper and manganese adsorption were considered:
complexation of the metal with aminonophosphate groups, chem-
ical interaction of the metal ion with active groups of the support
and physical adsorption of metal ions on the support. In case of Mn
immobilization on 1(4) B2 supports the last two possibilities were
considered. The high quantity of manganese immobilized on the
polymer support was evidenced atomic absorption measurements
and the leaching was significant.
They were carried out, in same conditions, the oxidation reac-
tions catalyzed by CuCl2 or MnCl2 in order of comparison the
catalytic performance for polymer supported catalysts and those
of unsupported metallic salts. The obtained results showed a good
activity of homogeneous catalysts. Unfortunately, it was evidenced
the secondary reactions such as complexation of Cu (II) with phenol,
anisole or alkyl substituted benzenes via donation of electrons [65],
the polymerization of styrene under conditions of acidic hydroly-
sis of the metallic salts and decomposition of hydrogen peroxide
by especially the manganese salt.
The main mechanism of Cu immobilization was complexation of
the metal with aminonophosphate groups of the supports. Consid-
ering the leaching as result of the interaction mechanism between
metal ion and functionalized support the low decrease of Cu con-
tent can be result of physical adsorption contribution. Variation of
the metal content before (I) and after catalytic reaction (AR) confirm
the high percent of copper complexation with aminonophosphate
groups and the stability of copper-ligand interaction (Table 4).
The stability of recycled 4B3Cu and 4B3Mn catalysts was tested
three times (fresh+ two reaction cycles) in cyclohexene, toluene
and phenol oxidation (Table 5). The amount of metal was quanti-
fied after each cycle of reaction. A decrease of about half of the initial
content of manganese in 4B3Mn sample after first cycle of reaction
was determined. The results were attributed to the high leaching of
Mn, thanks to its weak interaction with the support, and low stabil-
ity of Mn complex (Fig. 8). Conversion gets slightly decreased after
each recycle for 4B3Cu catalyst and selectivity remained nearly
the same in all the reactions in condition of stable Cu complex.
The variation of conversion was considered effect of the leaching.
A significant decrease in conversion, after first recycle, was evi-
denced for 4B3Mn sample and was attributed to the high variation
of the Mn content. A lower decrease of conversion was evidenced
for second and third cycles of reaction. The selectivity had no great
changes after third cycles of Cu and Mn catalysts. The obtained
4. Conclusions
Aminophosphonates grafted on styrene-divinylbenzene
copolymers by polymer-analogous reactions are efficient supports
in synthesis of new catalysts with Cu or Mn cations. Two effects
of the supports were evidenced on interaction with cation metals
respectively catalytic activity: ortho- or para- position of amino and
phosphonate groups and nature of amine radicals. The obtained
results suggest different interaction of Cu and Mn with amino,
phosphonate. These effects can be used to control the catalytic
process and their performances in oxidation of organic compounds.
The best catalytic activity and selectivity was obtained for copper
complexes immobilized on the functionalized copolymers.
Acknowledgements
V.P., R.E and A.P. authors are grateful to the Romanian Academy
(research programs 4.9.34 IPC/research program 2. project 2.4 ICT)
for financial support.
The authors would like to thanks to INFRANANOCHEM PROJECT
POS-CCE O 2.2.1, no. 19/01.03.2009.
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.molcata.2015.07.
0
35
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