Preparation of heterogeneous palladium catalysts supported on sporopollenin for heck coupling reactions

Article abstract of DOI:10.1080/15533174.2012.749895

The immobilized Schiff bases, S-[N-(2-aminoethyl)salicylal diimino] (1a), S-[N-(2-aminoethyl)cinnamaldiimino] (1b), S-[N-(2-aminoethyl)acetaldiimino] (1c), and their palladium(II) (2a-c) complexes, were synthesized onto a chemically modified sporopollenin with ethylenediamine. These complexes were investigated as catalysts in a Heck reaction of aryl halide with olefins. These immobilized palladium complexes is an efficient catalysts for Heck reaction of aryl halides with methyl and butyl acrylate. Copyright Taylor and Francis Group, LLC.

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Preparation of Heterogeneous Palladium Catalysts
Supported on Sporopollenin for Heck Coupling
Reactions
a
Mustafa Keleş
a
Osmaniye Korkut Ata University Faculty of Arts and Sciences Department of Chemistry ,
Osmaniye , Turkey
Accepted author version posted online: 13 Dec 2012.Published online: 07 Mar 2013.
To cite this article: Mustafa Keleş (2013) Preparation of Heterogeneous Palladium Catalysts Supported on Sporopollenin for
Heck Coupling Reactions, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:5, 575-579, DOI:
10.1080/15533174.2012.749895
To link to this article: http://dx.doi.org/10.1080/15533174.2012.749895
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:575–579, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.749895
Preparation of Heterogeneous Palladium Catalysts
Supported on Sporopollenin for Heck Coupling Reactions
Mustafa Keles¸
Osmaniye Korkut Ata University Faculty of Arts and Sciences Department of Chemistry, Osmaniye,
Turkey
Meanwhile, attachment the appropriate functional groups to
The immobilized Schiff bases, S-[N-(2-aminoethyl)salicylal metal center is the main goal in the design and synthesis solid
diimino] (1a), S-[N-(2-aminoethyl)cinnamaldiimino] (1b), S-[N- supported metal complexes. The solid supports have been chem-
(
2-aminoethyl)acetaldiimino] (1c), and their palladium(II) (2a–c)
ically altered into a ligand variety of coordination sites such as
complexes, were synthesized onto a chemically modified sporopol-
lenin with ethylenediamine. These complexes were investigated as
catalysts in a Heck reaction of aryl halide with olefins. These im-
ethylenediamine, diethylenetriamine, thionylchloride, cyanuric
chloride, and glycine.[
13–15]
Afterward, ligands bound to the
mobilized palladium complexes is an efficient catalysts for Heck solid support, amidation, esterification, or imine type reactions
reaction of aryl halides with methyl and butyl acrylate.
can be generated. Solid supported Schiff bases with a donor
atom were in general a certain metal ions are capable of complex
Keywords aryl halide, Heck reaction, immobilization, palladium, formation with metal. Transition metal Schiff base complexes
Schiff base, sporopollenin
can bound different types of solid support such as silica gel,
zeolite, and natural or synthetic organic polymers, have been
reported but very few reports are available on sporopollenin and
immobilized Schiff bases metal complexes. Sporopollenin is a
INTRODUCTION
Improving the productivity of organic processes in point of
preservation of energy, lowering the reaction time, generation of
waste is a major goal in synthetic chemistry.[ Heterogenized-
homogeneous catalysts and their use in fine chemical synthesis
has become major area of research, because the advantages of
these systems can have positive environmental consequences.
Heterogenized-homogeneous catalysts have been studied by
many researchers to compare transition metal complexes in ho-
natural polymer get from Lycopodium clavatum. Some advanta-
geous of sporopollenin as a solid support are as follows: (a) it is
chemically very stable, (b) it occurs naturally as a component of
the sports walls (it is not expensive), (c) it has a high capacity,
1–4]
and (d) it has a suitable functional group for further modifi-
cation.[
16,17]
In this study, we prepared multidentate Schiff base
ligands that covalently anchored onto sporopollenin and synthe-
sized their palladium(II) complexes for the Heck cross-coupling
reaction of aryl halides and alkenes. Furthermore, we indicate
that these heterogeneous palladium(II) catalysts can be readily
recovered and reused several times.
mogeneous systems and heterogeneous systems due to higher
catalytic activity under the same reaction parameters.[
5–9]
These
catalysts are readily separated from the product, can be eas-
ily removed from the reaction mixture by filtration, and can
be reused in subsequent reactions. In principle, the solid sup-
port attached to the palladium catalysts meets the previously
mentioned problems. Thus, partly to respond to this need for
practical applications, such as Heck reaction, heterogeneous
palladium catalysts can be synthesized. In this context, the solid
supported palladium catalysts performance for the Heck reac-
EXPERIMENTAL
General
All reactions were carried out in a Schlenk flask under
purified nitrogen atmosphere. All solvents were dried according
to standard procedures and then immediately distilled under ni-
trogen atmosphere prior to use. Support material: sporopollenin
was purchased from Fluka (Sigma-Aldrich Chemie, Germany)
[
10–12]
tion has been promising.
(
20 μm mesh) and used without further purification. Cin-
namaldehyde (93%), salicylaldehyde (99%), and acetaldehyde
99%) were used as purchased. Pd(cod)Cl2 were prepared as
Received 23 March 2012; accepted 10 November 2012.
The author would like to thank Dr. Serhan Uru s¸ and Dr. Tijen G u¨ rten
for technical support. The author is thankful to Osmaniye Korkut Ata
University for financial support.
Address correspondence to Mustafa Kele s¸ , Osmaniye Korkut Ata
University Faculty of Arts and Sciences Department of Chemistry,
(
[18]
described in the literature.
KBr pellets in a 4000–450 cm range using a Perkin-Elmer
RX1 FT-IR system (Osmaniye Korkut Ata University, Turkey).
FT-IR spectra were recorded as
−1
˙
8
0000, Osmaniye, Turkey. E-mail: mkeles@osmaniye.edu.tr
Jeol Neoscope Benchtop SEM (Kahramanmara s¸ S u¨ t c¸ u¨ Imam
575

576
M. KELES¸
FIG. 1. Syntheses of sporopollenin supported Schiff base ligands.
University, Turkey) was used for scanning electron microscope sporopollenin added previously prepared 0.066 mmol aldehyde
SEM) images. The catalytic products were analyzed by a (salicylaldehyde (7 mL) (1a), cinnamaldehyde (9 mL) (1b), and
(
Perkin-Elmer Clarus 500 series gas chromatograph equipped acetaldehyde (3.75 mL) (1c) solutions in ethanol. The mixtures
with a FID detector and a 30 m × 0.25 mm β-Dex capillary were stirred and refluxed further 12 h. The solid support Schiff
column. Thin layer chromatography was used for monitoring bases were filtered off under vacuum and washed completely
◦
the catalytic reactions.
with ethanol and dried in oven at 40 C for 4 h. (Figure 1)
Synthesis of Sporopollenin Immobilized Schiff bases
(1a–c)
Synthesis of Schiff Base Palladium(II) Complexes Onto
Sporopollenin immobilized Schiff bases were prepared as Solid Support
[
13]
described in the literature.
Palladium(II) complexes of sporopollenin immobilized
Sporopollenin immobilized Schiff bases; 5.000 g sporopol- Schiff base derivatives were prepared by mixing 1.00 g solid
lenin in 50 mL of toluene was heated, and after this, 15 mL supported Schiff base with 0.1 g (0.35 mmol) Pd(cod)Cl in
2
(0.2216 mol) ethylenediamine was added to the solution. The 50 mL ethanol, then refluxed for 6 h. The products were filtered
mixture was refluxed overnight, and allowed to cool to room off under vacuum, washed with ethanol, and dried in vacuum
◦
temperature. The product was filtered off under vacuum, washed at 50 C for 2 h. The synthetic route to the sporopollenin im-
◦
with ethanol and dried in a temperature at 40 C for 4 h. After- mobilized Schiff base palladium complexes is illustrated in
ward, 1.5 g (0.066 mmol of ethylenediamine) amine including Figure 2.
FIG. 2. Syntheses of sporopollenin immobilized palladium(II) Schiff base complexes.

SYNTHESIS PD(II) COMPLEXES, CATALYST BEHAVIOR
577
General Procedure for Heck Reactions
RESULTS AND DISCUSSION
Catalysts Preparation
An oven-dried Schlenk flask was charged with triethylamine
NEt3) (1.2 mmol) and 1-methyl-2-pyrrolidinone (NMP) (3 mL)
(
The sporopollenin-immobilized Schiff base ligands (1a–c)
and their palladium(II) complexes were characterized by
various analytical and spectroscopic methods and investigated
in Heck reaction as a catalyst. Although it is not known exactly
the chemical composition of sporopollenin it has unusual
chemical stability and resistance to biological and strong chem-
ical reagents. Analyses have revealed that the sporopollenin
is a biopolymer and contains long carbon chains (phenolic
and carboxylic groups) and does not contain nitrogen.[ The
ethylenediamine modified sporopollenin and Schiff bases 1a–c
were characterized by FT-IR analysis. According to Table 1,
it is understood that ethylenediamine is covalently bonded to
under nitrogen atmosphere followed by aryl halide (1 mmol),
olefin (1.2 mmol), and Pd(II) catalyst (30 mg, 1% mol of Pd(II)).
The flask was then sealed under N2 atmosphere and placed in
◦
an oil bath preheated at 100 C. The reaction mixture was stirred
and then allowed to cool to room temperature. After catalytic
reaction, the reaction mixture was filtered off under vacuum.
The mixture was poured into water (20 mL) and extracted with
ethyl acetate (3 × 20 mL). The extracts were washed with brine,
dried over MgSO4, and solvent was evaporated. The residue
was purified by flash column chromatography on a silica gel to
isolate the product.
19]
–
1
sporopollenin since band at 1744 cm corresponding to ν (C-O)
keto-enol tautomerism is disappearance.[ The FT-IR spectrum
of modified sporopollenin shows new bands at 1633–1658 cm–1
(1a–c) in the meantime these spectra are not present in the ab-
sorbance spectrum of sporopollenin. These bands are attributed
to -C-N bands, and show that ethylenediamine strongly bonding
to sporopollenin. In addition, after the reaction of ethylenedi-
amine with sporopollenin, the color of modified sporopollenin
turned to dark yellow, which is characteristic color for Schiff
bases. When aldehydes (salicylaldehyde, cinnamaldehyde,
and acetaldehyde) react with modified sporopollenin, the
13]
TABLE 1
FTIR bands of sporopollenin immobilized Schiff bases and
palladium complexes
Bonded phase
σ/cm–1
Band assignment
1a
1b
1c
2a
2b
2c
3363
ν(O—H)
ν(C-H) aliphatic
ν(C = N)
2934
1633
1277
-
NH2 band is disappeared in the FT-IR spectra. On the other
ν(C—N)
hand by reacting the Pd(cod)Cl2 with modified sporopollenin,
obtained spectrum showed that the band shifted to lower
wavenumber. The reason for shifted, Pd(cod)Cl2 anchored to
3404
ν(O—H)
2932
1635
1253
ν(C-H) aliphatic
ν(C = N)
ν(C—N)
3374
ν(O—H)
2927
1658
1279
ν(C-H) aliphatic
ν(C = N)
TABLE 2
a
Heck reaction of aryl halide with methyl acrylate
ν(C—N)
Conversion (%)b
3363
ν(O—H)
2936
1587
1204
ν(C-H) aliphatic
ν(C = N)
Entry Catalyst
Aryl halide
1.run 2. run 3.run
ν(C—N)
1
2
3
4
5
6
2a
2b
2c
2a
2b
2c
Iodobenzenene
Iodobenzenene
Iodobenzenene
Bromobenzene
Bromobenzene
Bromobenzene
98
94
99
89
95
99
86
86
99
88
91
80
71
70
63
69
79
74
3383
ν(O—H)
2947
1634
1223
ν(C-H) aliphatic
ν(C = N)
ν(C—N)
3403
ν(O—H)
2937
1642
1221
ν(C-H) aliphatic
ν(C = N)
aReaction conditions: aryl halide (1 mmol), methyl acrylate
(
1.2 mmol) triethylamine (1.2 mmol), and 0.01 mmol catalyst in 2 mL
ν(C—N)
◦
NMP, 120 C.
b
All reactions were determined by GC based on aryl halide.

578
M. KELES¸
FIG. 3. Scanning electron microscopy images of sporopollenin: (a) 1a and its palladium complex, (b) 1b and its palladium complex, and (c) 1c and its palladium
complex (accelerating voltage: 10 kV, vacuum high).
TABLE 3
a
Heck reaction of bromotoluene with methyl and butyl acylate
Conversion (%)b
Entry
Catalyst
Olefin
First run
Second run
Third run
7
8
9
0
1
2
2a
2b
2c
2a
2b
2c
Methyl acrylate
Methyl acrylate
Methyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
76
63
67
60
61
75
61
60
65
60
55
66
48
42
62
56
51
56
1
1
1
a
◦
Reaction conditions: bromotoluene (1 mmol), olefin (1.2 mmol) triethylamine (1.2 mmol), and 0.01 mmol catalyst in 2 mL NMP, 100 C.
All reactions were determined by GC based on aryl halide.
b

SYNTHESIS PD(II) COMPLEXES, CATALYST BEHAVIOR
579
modified sporopollenin and corresponding to formation of solid intermediates in pharmaceuticals.[20–22] All the three catalysts
supported palladium complexes (2a–c).
synthesized were very effective and the products were obtained
SEM images of 1a–c in Figure 3 show that aldehydes filled in good yield. Solid supported Pd(II) catalyst 2c was slightly
on sporopollenin. On the other hand, SEM images of the sample more active than 2a–b containing phenyl ring (Table 3).
(
2a–c) clearly shows, after the deposition of Pd(II) to modified
sporopollenin, the distribution of particles of palladium on the
support.
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