Supported monocationic copper(II) complexes obtained by coordination with dialkylphosphonate groups on styrene-divinylbenzene copolymer as catalysts for oxidation of organic compounds

Article abstract of DOI:10.1016/j.molcata.2012.10.005

New catalysts were synthesized by immobilization of neutral and monocationic copper complexes Cu(hfac)₂ (hfac^- = hexafluoroacetylacetonato ligand) and [Cu(acac)(tmen)]NO₃ (acac ^- = acetylacetonato ligand, tmen = N,N,N′,N′-tetramethyl- ethylendiamine) on styrene-divinylbenzene copolymer functionalized with four different dialkyl phosphonate moieties typified by PPO(OR)₂ (with R = CH₃, C₂H₅, ⁱC₃H ₇, and ⁿC₄H₉). The formation of P(O)(OR)₂ phosphonates groups has been confirmed by the FT-IR spectra. Thermogravimetric analysis results reveal that the thermal stability of polymer support depend on the functional group attached. The complexes were anchored by coordination interaction between the copper(II) ion and the phosphonate oxygen atom on each of the four functionalized supports and the strength of the PO?Cuⁿ⁺ coordination interaction was influenced by the nature of the R group. The effect of functionalized supports on the structure and catalytic activity of Cu(hfac)₂ and [Cu(acac)(tmen)]⁺ mononuclear species was determined in oxidation of several organic compounds (anisole, cyclohexene, toluene, styrene, phenol) with hydrogen peroxide. The catalytic activity results show that the activity and selectivity of Cu(II) complexes depends on the equilibrium between steric factor and inductive electron-releasing effect. The best selectivity was obtained in oxidation of anisole, phenol and styrene for all the catalysts. The main products were for 2-methoxyphenol, catechol and benzaldehyde, respectively.

Full text of DOI:10.1016/j.molcata.2012.10.005

Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
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journal homepage: www.elsevier.com/locate/molcata
Supported monocationic copper(II) complexes obtained by coordination with
dialkylphosphonate groups on styrene–divinylbenzene copolymer as catalysts
for oxidation of organic compounds
Viorica Parvulescua,∗, Violeta Niculescua,b, Ramona Enea,∗, Adriana Popac, Mihaela Mureseanud,
Cristian D. Enee, Marius Andruhe
a “Ilie Murgulescu” Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest, Romania
b National Research and Development Institute for Cryogenics and Isotopes Technologies – ICIT, 4th Uzinei Street, 240050 Ramnicu Valcea, Romania
c Institute of Chemistry Timisoara of Romanian Academy, Romanian Academy, 24 Mihai Viteazul Blv., Timisoara, Romania
d University of Craiova, Faculty of Chemistry, Calea Bucuresti 107I, Craiova, Romania
e University of Bucharest, Faculty of Chemistry, Department of Inorganic Chemistry, 23 Dumbrava Rosie Street, Bucharest, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2012
Received in revised form 5 October 2012
Accepted 6 October 2012
Available online 13 October 2012
New catalysts were synthesized by immobilization of neutral and monocationic copper complexes
Cu(hfac)2 (hfac− = hexafluoroacetylacetonato ligand) and [Cu(acac)(tmen)]NO3 (acac− = acetylacetonato
ligand, tmen = N,N,Nꢀ,Nꢀ-tetramethyl-ethylendiamine) on styrene–divinylbenzene copolymer function-
alized with four different dialkyl phosphonate moieties typified by P PO(OR)2 (with R = CH3, C2H5,
iC3H7, and nC4H9). The formation of P(O)(OR)2 phosphonates groups has been confirmed by the FT-IR
spectra. Thermogravimetric analysis results reveal that the thermal stability of polymer support depend
on the functional group attached. The complexes were anchored by coordination interaction between
the copper(II) ion and the phosphonate oxygen atom on each of the four functionalized supports and
the strength of the P O· · ·Cun+ coordination interaction was influenced by the nature of the R group. The
effect of functionalized supports on the structure and catalytic activity of Cu(hfac)2 and [Cu(acac)(tmen)]+
mononuclear species was determined in oxidation of several organic compounds (anisole, cyclohexene,
toluene, styrene, phenol) with hydrogen peroxide. The catalytic activity results show that the activity and
selectivity of Cu(II) complexes depends on the equilibrium between steric factor and inductive electron-
releasing effect. The best selectivity was obtained in oxidation of anisole, phenol and styrene for all the
catalysts. The main products were for 2-methoxyphenol, catechol and benzaldehyde, respectively.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Supported catalysts
Polymer-supported Cu(II) complexes
Oxidation catalyst
Hydrogen peroxide
1. Introduction
and heterogeneous catalysts that sometimes might minimize the
drawbacks of both [8].
Investigation on metal–organic complexes represents one of the
most active areas of material science and chemical research. Major
advances have been made in the synthesis of these materials due to
their interesting properties and potential in various applications as
host–guest chemistry, ion exchange and catalysis [1–4]. The transi-
tional metal complexes have been supported on various materials,
but the microenvironment created by polymeric supports provided
a better control on the efficiency of the catalysts in organic com-
pounds reactions compared to inorganic oxides. Heterogenization
of catalysts has been the subject of many publications in this topic
[5–7] and has attracted a high interest due to its advantages, espe-
cially the possibility of combining the advantages of homogeneous
Special interest has been addressed to catalytic applications of
polystyrene-supported ligands and metal complexes [9–11,7]. The
immobilization of transition metals on polystyrene supports, which
is still one of the most popular polymeric materials used in synthe-
sis due to its low cost, ready availability, mechanical robustness,
chemical inertness, and facile functionalization [12], offers a num-
ber of advantages toward the traditional solution-phase chemistry.
Generally, the organic groups of the functionalized polymer are the
coordination sites that bind metal ions. Suitable bonds between
the support and the metallic ions are crucial for the effective per-
formance of the catalyst [13]. The polymer-anchored reagents can
react, by covalent bonds, with metal ion of the complex, with lig-
ands or precursors of the metals. The recovery of these catalysts is
effective and leaching is low comparatively with physically linked
supported catalysts.
The aim of this work is the evaluation of a new group
of neutral and monocationic metal complexes supported on
∗
Corresponding authors.
E-mail addresses: vpirvulescu@icf.ro (V. Parvulescu), ramona@icf.ro (R. Ene).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.10.005

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V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
styrene–divinylbenzene copolymer functionalized with phospho-
nate groups, from their synthesis to their application in the catalytic
oxidation of organic compounds (such as anisole, cyclohexene,
toluene, styrene and phenol) with hydrogen peroxide. In this
study, polymeric chelating resins containing phosphonate func-
tional groups [14–18] were synthesized by chemical modification
of the polymer support. Dialkylphosphonate moiety can bind metal
ions through the oxygen donor atom of the P O group. How-
ever, an organic phosphonate acts rather as a weak ligand and
highly Lewis acidic metal centers are needed for complex formation
[19,20]. Accordingly, we have chosen unsaturated mononuclear
copper(II) complexes with hexafluoroacetylacetonato anion that
have proved to possess an enhanced binding affinity for molecules
with a reduced donor ability such as radical-substituted ligands,
neutral organic or organometallic spacers [21–26]. An alternative
strategy involves the use of mixed-ligand copper(II) complexes
of [Cu(AA)(BB)]+ type (where AA stands for acetylacetonate or
salicylaldehydate, and BB for a chelating bidentate diamine, e.g.
1,10-phenanthroline or 2,2ꢀ-bipyridine), whose apical position at
the copper(II) ion has shown a remarkable availability for the
metal ion interaction with various ligands [27,28]. The equilibrium
between steric factor and inductive electron-releasing effect was
correlated with the oxidative catalytic activity of the new hetero-
geneous catalysts.
3008(w), 2974(w), 2922(w), 2895(w), 1589(m), 1553(m), 1516(m),
1385(vs), 1021(m), 953(m), 809(m).
The immobilization of Cu(hfac)2 and [Cu(acac)(tmen)]+
complex entities (where hfac− = hexafluoroacetylacetonate) on
phosphonate-containing copolymer supports was carried out
using the following general synthetic route: 350 mg of the chosen
phosphonate-modified styrene–divinylbenzene copolymer was
suspended into the solution of the appropriate complex (150 mg)
in 15–20 mL acetonitrile and refluxed for 6–7 h. The resulted mix-
ture was filtered while warm, and the solid product was washed
at room temperature with acetonitrile to colorless filtrate and
dried in air. In order to remove as much as possible the physically
adsorbed complex species, a Soxhlet extraction in acetonitrile was
performed for 6–8 h (2–3 cycles per hour). The solid products were
finally dried in a CaCl2 desiccator.
2.3. Characterization of the materials
Styrene–divinylbenzene copolymer functionalized with phos-
phonate groups were characterized by Fourier transformed
infrared spectroscopy with a Jasco FTIR spectrophotometer and
SEM microscopy (Zeiss EVO LZ 10 EP, FEI Quanta 3D FEG). The ther-
mal analysis of samples was performed with TG 209 (Netzsch) in
nitrogen atmosphere with a heating rate of 5 ◦C/min in the range
20–600 ◦C. The quantitative analysis of metal loadings of the cata-
lyst was carried out by atomic adsorption spectroscopy on Spectra
AA 110 Varian spectrometer equipped with Varian multi-element
hollow cathode lamps and air-acetylene burner. The phosphorus
content was determined according to modified Schoninger method
[16,33].
2. Experimental
2.1. Synthesis of the polymeric supports
The synthesis of the phosphonates grafted on a macroporous
styrene–7% divinylbenzene copolymer support was performed
by the method previously described [16,18]. The commercial
chloromethylated styrene–divinylbenzene copolymer (S–7%DVB,
13.84 mmol CH2Cl), macroporous type, was used as starting mate-
rial. All the other reagents were used without any purification. In
a 100 mL round bottom flask fitted with stirrer, reflux condenser
and thermometer, 3 g of PS and 50 mL N,N-dimethylformamide
were added. The mixture was then maintained under stirring
for 2 h at room temperature for copolymer beads swelling. Then,
dialkylphosphite and sodium carbonate were added, in order to
achieve a molar ratio chloromethyl groups:diphosphite:sodium
carbonate = 1:1.2:1 and 0.05% tetramethylammonium iodide cat-
alyst, respectively. The mixture was kept under stirring for
24 h at 100 ◦C. The polymer beads separated by filtration were
washed with 0.1 N HCl (3 × 20 mL), ethanol (3 × 20 mL), 1,2-
dichloromethane (3 × 20 mL) and ethyl ether (3 × 20 mL), and dried
under 2 kPa vacuum at 50 ◦C for 24 h.
The IR spectra of the metal complex-based materials (KBr pel-
lets) were collected on a Bruker Tensor 37 spectrophotometer in
the 4000–400 cm−1 range, and the UV–Vis–NIR diffuse reflectance
spectra were recorded on a JASCO V-570 spectrophotometer in the
190–1200 nm region, using MgO as a standard.
The obtained catalysts were tested in oxidation of the organic
compounds (anisole, cyclohexene, toluene, styrene, phenol). The
oxidation reactions were carried out in glass mini reactors (5 mL)
at 50 ◦C for 8 h, using 0.05 g catalysts and a 1/20/3 molar ratio
substrate/solvent (acetonitrile)/H2O2. The analysis of oxidation
products was performed using a DANI GC 1000 gas chromato-
graph connected to a FID detector. The active compound leaching
during the reaction was verified by resubmission of filtrates to reac-
tion conditions. Product identification was achieved by comparison
with GC peaks of the authentic compounds and GC–MS analysis that
was performed on a Thermo Scientific chromatograph equipped
with MS DSQ II Thermo and capillary column TR-5MS (30 m × 0.25
ID × 0.25 ␮m film thickness).
2.2. Synthesis and immobilization of the complexes
3. Results and discussion
Copper bis(hexafluoroacetylacetonate) complex (Cu(hfac)2)
was purchased from commercial sources and was used as received.
The [Cu(acac)(tmen)]NO3 complex (where acac− = acetylacetonato
anion, and tmen = N,N,Nꢀ,Nꢀ-tetramethyl-ethylendiamine) was syn-
thesized through a procedure previously reported for similar
derivatives [29–32] as follows: an ethanolic solution (15 mL)
of acetylacetone (400.4 mg, 4 mmol) deprotonated with triethyl-
amine (404 mg, 4 mmol) was mixed with 464.8 mg of N,N,Nꢀ,Nꢀ-
tetramethyl-ethylenediamine (4 mmol) dissolved in 15 mL ethanol.
The resulted solution was rapidly added to 25–30 mL water/ethanol
(1:1, v/v) solution of Cu(NO3)2·3H2O (966.4 mg, 4 mmol). The dark-
blue crystals obtained on slow evaporation of the solvents were
separated by filtration, washed with small amounts of ethanol and
water, and dried in air (yield: 75%). Selected IR data (KBr, cm−1):
3.1. Preparation and characterization of the functionalized
polymers and supported Cu(II) complexes
New polymeric supports functionalized with four different
dialkyl phosphonate moieties have been synthesized. The struc-
ture of the resins proposed in Fig. 1 is supported by FTIR spectra.
Some general remarks concerning the analysis of the FTIR spectra
(see Fig. 2) are as follows: (i) the formation of P(O)(OR)2 phos-
phonates groups on the styrene–7% divinylbenzene copolymer was
confirmed by the increase in the intensity of the absorption band at
around 1220 cm−1 associated with the vibration of the P O bond,
(ii) the characteristic P OH band appears at around 1000 cm−1
and (iii) a medium intensity band at 1600 cm−1 is assigned to the
P(O)OH group.

V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
277
Table 1
Characteristics of phosphonate groups grafted on styrene–divinylbenzene copolymers.
c
d
Code
Phosphite
P (%)a
yb
GF (mmol/g)
ꢀF (%)
PS PO(OCH3)2
PS PO(OC2H5)2
PS PO(OiC3H7)2
PS PO(OnC4H9)2
(CH3O)2POH
(C2H5O)2POH
(C3H7O)2POH
(C4H9O)2POH
6.46
6.21
5.13
6.12
0.34
0.34
0.29
0.39
2.10
1.98
1.66
1.96
53.13
53.13
45.31
60.94
Notations: x – fraction of styrene units bearing pendant CH2Cl groups (Fi); y – fraction of styrene units bearing pendant CH2P(O)(OR)2 groups (Ff) (R: CH3, C2H5, iC3H7,
nC4H9); Mmi – average molecular weight of the repetitive unit of the initial copolymer; Mmf – average molecular weight of the repetitive unit of the final copolymer; %P –
phosphorus percentage in the final copolymer; AP – atomic weight of phosphorus; MS – molecular weight of the repetitive unit of the styrene; MDVB – molecular weight of
the repetitive unit of the divinylbenzene; MSFi – molecular weight of the repetitive unit of the styrene functionalized unit Fi groups; MSFf – molecular weight of the repetitive
unit of the styrene functionalized with Ff groups; nP – number of phosphorus atoms in the pendant groups.
y·A ·n
P
a
P
P% =
y =
× 100.
M
+y(M −M
)
mi
SFf
SFi
%P·M
b
c
mi
.
100·n ·A −%P·(M −M
)
P
P
SFf
SFi
y
GF
=
=
.
M
y
mf
d
ꢀF
× 100, where Mmi = r · MDVB + x · MSFi + (1 − r − x) · MS, Mmf = r · MDVB + (x − y) · MSFi + y · MSFf + (1 − r − x) · MS.
x
O
to investigate the thermal stability. TG analysis indicated changes
in thermal stability of the polymers functionalized with pendant
phosphonate groups in comparison with the support of macro-
molecular chloromethylated styrene–divinylbenzene (Table 2).
The thermal stability is affected by the nature of the R radicals
of the phosphonate groups, the initial support having a better
thermal stability. It was showed that degradation of the polymer
support functionalized with different dialkyl phosphonate moieties
was gradual until 300 ◦C for all the supports and catalysts except
the samples with OC2H5 group. From the decomposition profile, it
appears a lower weight loss between 20 and 400 ◦C (Fig. 3). This is
a result of the polymer and Cu(II) complexes functions and ligands
decomposition. The sharp drop mass evidence at around 400 ◦C for
all the samples is a result of poly(styrene–divinyl benzene) co-
polymer degradation. The effect of alkyl chains of phosphonate
alcohol radicals is evidenced in Fig. 3 and also the insignificant Cu(II)
complex on thermal stability.
SEM images of the spherical particles of styrene–7% divinyl-
benzene copolymer support functionalized with PO(OC2H5)2 and
their morphology are presented in Fig. 4. The macropores are vis-
ible among the agglomerations of micro-particles, characterized
by a dense structure. The as-synthesized polymeric supports func-
tionalized with dialkyl phosphonate moieties were used thereafter
for the immobilization of Cu(hfac)2 and [Cu(acac)(tmen)]+ complex
entities.
CH2-Cl
P(OR) OH
CH2-P-(OR)2
/TMAI
100oC, 24 h, DMF
2
where: R = -OCH3, -OC2H5, -iC3H7, -nC4H9
Fig. 1. Preparation of the polymer-grafted phosphonates.
The main characteristics of the copolymer functionalized with
phosphonates groups are presented in Table 1. The calculated func-
tionalization degrees found by the analysis above can be explained
by the hypothesis that, in spite of extensive swelling of the starting
copolymer, some reactive chloromethyl groups are embedded into
the micropores of the copolymer “pearls” and could not be accessed
by the bulky functionalization agent [14]. The degrees of function-
alization with phosphonates groups are relatively high, ensuring
a sufficient concentration of active centers per unit mass of the
copolymer and being well-suited for application as polymer sup-
ported catalysts. The best functionalization was obtained for the
PS PO(OCH3)2 hybrid support (2.1 mmol/g).
The thermogravimetric analyses (TG) of the of polymeric sup-
ports and immobilized Cu(II) complexes were measured in order
A very good and homogeneous dispersion of Cu(II) complex par-
ticles on the copolymer support was evidenced by SEM microscopy
Fig. 3. TG of the immobilized [Cu(acac)(tmen)]NO3 complex on the polymer sup-
ports functionalized with four different dialkyl phosphonate moieties and TG of two
Cu(II) complexes on PS PO(OnC4H9)2 support.
Fig. 2. The infrared spectra of the phosphonates groups grafted on styrene–7%
divinylbenzene copolymer.

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V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
Table 2
TG data of polymeric supports and [Cu(acac)(tmen)]NO3 immobilized catalysts.
Sample
Weight loss (%)
T inflexion (◦C)
20–200 ◦
C
20–300 ◦
C
20–450 ◦
C
Styrene–7% divinylbenzene copolymer
PS PO(OCH3)2
3.25
4.57
4.70
5.20
4.10
7.80
8.70
14.25
11.20
12.99
14.60
50.20
12.60
15.40
23.72
94.72
39.57
65.50
78.80
64.50
65.80
427.7
367
405
375
200; 402
403
PS PO(OnC4H9)2
[Cu(acac)(tmen)]NO3 PS PO(OCH3)2
[Cu(acac)(tmen)]NO3 PS PO(OC2H5)2
[Cu(acac)(tmen)]NO3 PS PO(OiC3H7)2
[Cu(acac)(tmen)]NO3 PS PO(OnC4H9)2
400
(Fig. 5). We believe that this sustain the immobilization of the
complexes by coordination interaction between the copper(II) ion
and the phosphonate oxygen atom of the functionalized supports.
The SEM images (Fig. 5) show the change of Cu(II) complexes mor-
phology after immobilization. The new Cu(II) complexes on the
polymer surface are spherical formations with diameters around
500 nm.
The as-synthesized polymeric supports functionalized with
dialkyl phosphonate moieties were used thereafter for the immobi-
lization of Cu(hfac)2 and [Cu(acac)(tmen)]+ complex entities. As a
common feature of the infrared absorption spectra for the prod-
ucts based on isolated copper complex – copolymer, the strong
band due to the stretching vibration of the P O bond shifts to
lower frequencies (ꢁꢂ > 50 cm−1), indicating the involvement of
this group in the coordination of the metal ion. Nevertheless, the
These differences might be related to the ligand-field sym-
metry and strength that affect the metal ion–donor atom bond
stability and ultimately influence the abundance of the complex
entities immobilized on polymeric supports. In this regard, the
P
O· · ·Cu2+ coordination interaction appears to define a structural
feature whose relevance depends on the equilibrium established
between the following factors: (i) the steric hindrance generated
by the alkyl group of the phosphonate, which diminishes from
isopropyl and n-butyl to ethyl and methyl and (ii) the inductive
electron-releasing effect of R group that increases in the sequence
CH3 < C2H5 < nC4H9 < iC3H7.
On the basis of this information and knowing that the donor
atoms of the chelating ligands occupy the basal plane of the cop-
per(II) coordination sphere [34,35] it is legitimate to consider
a distorted octahedral geometry of the metal center, where the
P
O band characteristic to the initial supports is also present at
a relatively lower intensity pointing to the existence of a fraction
of free phosphonate groups. On the other hand, the band modi-
fications in the region 1660–1600 cm−1 arise from C O stretching
vibration of acetylacetonato-type ligand. In addition, FTIR spectra of
materials containing [Cu(acac)(tmen)]NO3 present a sharp band of
medium-to-strong intensity at around 1383 cm−1 that is associated
with the nitrate anion.
The diffuse reflectance spectra of the compounds resulted in the
reaction of copper(II) complexes with the functionalized copoly-
mers show a large asymmetric band in the region 600–1200 nm due
to d–d transitions. In the case of dimethyl and diisopropyl phospho-
nate derivatives, the above-mentioned band exhibits a significantly
reduced intensity compared to those occurring in the UV region,
being attributed to the transitions characteristic to the polymeric
organic substrate. As for diethyl and di-n-buthyl phosphonate-
based products, the maxima of the two categories of bands are
approximately equal in magnitude (Figs. 6 and 7).
Fig. 4. SEM images of styrene–7% divinylbenzene copolymer functionalized with
PO(OC2H5)2.
Fig. 5. SEM images of [Cu(acac)(tmen)]NO3 complex before (a) and after immobi-
lization on PS PO(OnC4H9)2 polymeric support (b).

V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
279
Fig. 8. Immobilization of coordinatively unsaturated metal centers of
[Cu(acac)(tmen)]+ and Cu(hfac)n complex species on polymer-supported
phosphonates (where R = CH3, C2H5, iC3H7, and nC4H9).
Fig. 6. The electronic spectra of [Cu(acac)(tmen)]NO3 containing polymer-
supported phosphonates: P PO(OCH3)2 (a), P PO(OC2H5)2 (b), P PO(OiC3H7)2 (c),
and P PO(OnC4H9)2 (d).
oxidation activities are the lowest. The highest conversions were
obtained in oxidation of cyclohexene and anisole, respectively, in
phenol oxidation on the copolymer supports functionalized with
PO(OC2H5) and PO(OCH3)2. These results confirm the significant
influence of the steric effect. An increased activity was obtained
in oxidation of cyclohexene and anisole on [Cu(acac)(tmen)]NO3
complex supported on styrene–divinylbenzene copolymer func-
tionalized with PO(OiC3H7). This sustains the involvement of the
equilibrium between steric and electronic effects on the oxidative
catalytic activity.
The same catalytic tests on Cu(hfac)2 complex supported on
styrene–divinylbenzene copolymer functionalized with phospho-
nate groups revealed, comparatively with the first complex, a lower
conversion of phenol and a higher one for toluene in their oxida-
tion reactions with hydrogen peroxide (Fig. 10). A very low activity
was obtained in oxidation of phenol, for all catalysts based on
Cu(hfac)2 and in oxidation of styrene on copolymer functionalized
with PO(OnC4H9)2.
axial positions belong to phosphonate oxygen atom and to a sol-
vent molecule or nitrate anion, respectively (Fig. 6). However, the
coexistence of five-coordinated complex species, namely Cu(hfac)2
moieties with the P O group occupying the apical site, is not
excluded (see Fig. 8).
3.2. Catalytic evaluation
The obtained supported metal complexes are active and selec-
tive in oxidation of organic compounds (anisole, cyclohexene,
toluene, styrene, phenol) with hydrogen peroxide. The differences
between the conversions of the organic substrates were related to
the strength of the P O· · ·Cu2+ coordination interaction depend-
ing mainly on the nature of the R group and on the ligands of
the Cu(II) complexes. Thus, [Cu(acac)(tmen)]NO3 complex sup-
ported on styrene–divinylbenzene copolymer functionalized with
PO(OnC4H9)2 group had lower activity in all the oxidation reactions
(Fig. 9). Furthermore, for all the phosphonate groups, the toluene
The comparative analysis of the catalytic results (Fig. 9) with
those of the electronic spectra (Fig. 6) evidences a positively effect
of strong P O· · ·Cu2+ interaction and negatively effect of steric
effect of PO(OnC4H9)2 group. Even if for the catalysts based on
Cu(hfac)2 complex the effect of P O· · ·Cu2+ interaction is lower,
Fig. 7. The electronic spectra of Cu(hfac)2 containing polymer-supported
phosphonates:
P
P
PO(OCH3)2 (a),
P
PO(OC2H5)2 (b),
P
PO(OiC3H7)2 (c), and
Fig. 9. Variation of the organic compounds conversion in their oxidation on
[Cu(acac)(tmen)]NO3 complex supported on various functionalized polymers.
PO(OnC4H9)2 (d).

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V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
Table 3
Variation of selectivity of Cu(II) complex catalysts in oxidation of phenol, anisole and styrene.
S (%)
Catalyst
P
PO(OCH3)2
P
PO(OC2H5)2
P
PO(OiC3H7)2
P
PO(OnC4H9)2
Cu(at)
Cu(hf)
Cu(at)
Cu(hf)
Cu(at)
Cu(hf)
Cu(at)
Cu(hf)
Sguaiacol
Scatechol
Sbenzaldehide
98
40
85
69
95
100
90
83
80
90
87
78
100
85
81
79
89
98
95
81
65
75
91
85
of the reaction the conversion of phenol was very low in oppo-
sition with the others compounds. The selectivity toward guaiacol
in the anisole oxidation reaction was high for all the tested catalysts
(Table 3).
For all the oxidation reaction of the aromatic compounds,
except styrene, the mechanism is typical for hydroxylation pro-
cesses [38]. Only in case of the styrene oxidation, the C
C
bond was activated and the highest activity was obtained for
[Cu(acac)(tmen)]NO3 complex immobilized on the copolymer
functionalized with PO(OiC3H7). In this reaction the electronic
effect was more important for the complex catalytic activity. The
analysis of the products resulted in oxidation of styrene evidence
the splitting of C C bond of the vinyl radical and formation of
benzaldehyde and benzoic acid as oxidation products. A very high
selectivity toward benzaldehyde was evidenced for all the tested
catalysts (Table 3). A low percent of the degradation products was
obtained in oxidation of styrene and phenol, respectively.
The catalytic properties of PS PO(OR)2CuL catalysts were con-
firmed by recycling the complex in three consecutive experiments
using anisole as model substrate. The catalyst was separated from
the reaction mixture after each experiment by filtration, washed
with solvent and dried carefully before using it in the subsequent
run. The results are shown a little reduction of anisole conversion
after first-reaction cycle. In the second and third-reaction cycle
any variation of conversion was evidenced. A small quantity of the
leached copper species was detected after first-cycle reaction.
Fig. 10. Variation of the organic compounds conversion in their oxidation on
Co(hfac)2 complex supported on various phosphonate-functionalized functional-
ized polymers phosphonates (where cyclohexene – Ch, styrene – St, toluene – T,
anisole – A, phenol – Ph).
the enhancement of the catalytic performances (see comparatively
Figs. 9 and 10) can be attributed to the favorable influence of hfac−
ligand on catalytic activity.
Comparatively catalytic tests of Cu(II) complexes and function-
alized polymers showed an insignificantly activity of l-Cu than
supports. In this case we consider that catalytic activity is a result
of phosphonate groups activity and their effect on copper ions.
The analysis of the reaction products shows, for all these
processes, the activation of C H bond with H2O2 like hydroxyl
radicals. The formation of OH radicals detected by ESR [36]
in reaction conditions can be explained by mechanism of per-
oxide decomposition in the presence of Cu(II) complexes [37].
Therefore, the catalytic processes are the result of competi-
tion between organic compounds adsorption and l-Cu2+ ⇔ l-Cu+
processes. The organic properties of the support increase adsorp-
tion properties and the Cu(II) complex promotes decomposition
of hydrogen peroxide to OH radicals. Thus, the products of
cyclohexene oxidation were 2-cyclohexene-1-ol, 2-cyclohexene-
1-one and cyclohexane-1,2-diol and of toluene oxidation were
o- and p-cresol, benzaldehyde and benzoic acid. For oxidation of
anisole the resulting products are 2- or 4-methoxyphenol and
for oxidation of phenol, the products are catechol and o- or
p-benzoquinone. In the oxidation of the above mentioned com-
pounds, the higher selectivity was for 2- methoxyphenol (guaiacol)
and catechol, respectively. The best selectivity toward catechol was
obtained for Cu(hfac)2 complex (Table 3). A very low selectivity to
catechol was obtained for the [Cu(acac)(tmen)]NO3 complex sup-
ported on styrene–divinylbenzene copolymer functionalized with
4. Conclusions
Cu(hfac)2 and [Cu(acac)(tmen)]+ mononuclear species were
anchored on polymer-supported dialkyl phosphonates, typified by
P
PO(OR)2 (with R = CH3, C2H5, iC3H7, and nC4H9). The FTIR
spectra of the complex-containing materials indicated the involve-
ment of the oxygen atom belonging to the phosphoryl group in
the coordination of the metal center. The differences observed in
the diffuse reflectance spectra of the catalysts containing the same
copper(II) complex were related to the strength of the P O· · ·Cun+
coordination interaction that is ultimately influenced by the nature
of the R group.
The significantly influences of the metal interactions with the
functionalized supports, the nature of the ligands in these new
catalysts based on copper complexes and the alcohol radical of
the phosphonate groups grafted onto the polymeric support were
evidenced on catalytic activity and selectivity. Such behavior was
considered as a result of the equilibrium between a steric factor and
an inductive electron-releasing effect. The analysis of the reactions
products of all the reactions, except styrene, reveals the activation
of C H bond.
P
PO(OnC4H9)2 groups. For this catalyst, the steric effect of n-butyl
radical on selectivity and conversion was similar (Fig. 7, Table 3).
The decrease of the phenol conversion and selectivity to catechol
were considered as a result of the steric and higher hydropho-
bic effects of (OnC4H9)2 groups. These alcoxide groups have the
limitative effect on the phenol adsorption. Thus, in the first 5 h
Acknowledgments
V.P., R.E and A.P. are grateful to the Romanian Academy
(research programs 4.9.34 IPC/research program 2, project 2.4 ICT)
for financial support.

V. Parvulescu et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 275–281
281
C.D.E. thanks for the financial support of postdoctoral program
grant POSDRU/89/1.5/S/60746 from the European Social Fund.
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