Green synthesis of palladium nanoparticles via branched polymers: A bio-based nanocomposite for C-C coupling reactions

Article abstract of DOI:10.1039/c6ra02242a

Catalytic process is the key process for many chemical industries. In this study, a novel heterogeneous Pd (CMH-Pd(0)) has been prepared by the deposition of palladium nanoparticles (Pd NPs) onto the surface of carboxymethyl functionalized hemicelluloses using ethanol as solvent and in situ reducing agent. The as prepared catalyst was characterized by TEM, HR-TEM, XRD, FT-IR, TGA and XPS. The loading level of Pd in the CMH-Pd(0) catalyst was 0.38 mmol g^-1. The catalyst showed high catalytic activity and versatility towards Heck coupling reactions under aerobic conditions and could be readily recovered and reused in at least five successive cycles without obvious loss in activity. The catalyst is promising for its renewability, environmental benefits, efficient catalytic activity, mild reaction conditions, simple product work-up and easy catalyst recovery.

Full text of DOI:10.1039/c6ra02242a

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Page 1 of 33
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Green Synthesis of Palladium Nanoparticles via Branched Polymers:
The Bio-Based Nanocomposite for C-C Coupling Reactions
a
*,a
*,a
b
c
Changyan Wu, Xinwen Peng, Linxin Zhong, Xuehui Li, Runcang Sun,
a
State Key Laboratory of Pulp and Paper Engineering, South China University of
Technology, 381 Wushan Road, Guangzhou 510640, China
b
School of Chemistry and Chemical Engineering, South China University of
Technology, 381 Wushan Road, Guangzhou 510640, China
c
Institute of Biomass Chemistry and Utilization, Beijing Forestry University, 35
Tsinghua East Road, Beijing 100083, China
*
Corresponding authors. Eꢀmail: fexwpeng@scut.edu.cn (Xinwen Peng) and
lxzhong0611@scut.edu.cn (Linxin Zhong)
Tel.: +86ꢀ020ꢀ87111735; Fax: +86ꢀ020ꢀ87111861.
1

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ABSTRACT
Catalytic process is the key of many chemical industries. In this study, a novel
heterogeneous Pd (CMHꢀPd (0)) has been prepared by deposition of palladium
nanoparticles (Pd NPs) onto the surface of carboxymethyl functionalized
hemicelluloses using ethanol as solvent and in situ reducing agent. The as prepared
catalyst was characterized by TEM, HRꢀTEM, XRD, FTꢀIR, TGA and XPS. The
ꢀ1
loading level of Pd in the CMHꢀPd (0) catalyst was 0.38 mmol g . The catalyst
showed high catalytic activity and versatility towards Heck coupling reactions under
aerobic conditions and could be readily recovered and reused in at least five
successive cycles without obvious loss in activity. The catalyst is promising for its
renewability, environment benefit, efficient catalytic activity, mild reaction conditions,
simple product workꢀup and easy catalyst recovery.
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Keywords: Heterogenenous Pd, Biomass, Hemicelluloses, Carboxymethyl
hemicelluloses, Heck reaction, Sustainable chemistry
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Introduction
The attribution of the Nobel prizes to the winners who developed crossꢀcoupling
catalysis reactions indicates the significance of these pioneering works as a landmark
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in organic chemistry and their great influence on material science. Since the
discovery of these reactions, they have been widely utilized in organic synthesis,
especially, palladium occupies a special position of crucial importance in the field of
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catalysis for different organic transformations. Recently, palladium nanoparticle
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catalysts have been used widely into various CꢀC coupling reactions. Especially,
palladiumꢀcatalyzed Heck crossꢀcoupling reaction of aryl halides with olefins is found
to be one of the most powerful synthetic methods for the formation of CꢀC bonds
between alkenes and aryl or alkyl halides. These coupling products find good
applications as intermediates in the preparation of materials, natural products, and
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bioactive compounds. Among the crossꢀcoupling processes, Heck reaction is
especially widely used, because of its attractive attributes such as commercial
availability, air and water stability and functionalꢀgroup compatibility, and thus has
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been widely used in many industrial processes, especially in pharmaceuticals, fine
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chemicals, natural product synthesis, material science, bioorganic chemistry and
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conducting polymers.
Traditionally, homogeneous catalyst system such as Pd(OAc) or PdCl was used for
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Heck reaction. Although, conventional catalytic systems have a series of advantages,
the utilization of green, efficient chemistry approaches and reusable catalysts are of
great importance in the light of contemporary design of synthetic processes. During
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Heck reaction, Pd (0) acts as active site to initiate the catalytic cycle, and the catalytic
activity depends on the capacity of Pd (0) species to activate the carbonꢀhalogen bond
by oxidative addition, which can be further adjusted by the steric and electronic
properties of the ligands attached to the nanoparticles. In this regard, phosphine
ligands have been extensively utilized because of its effectiveness in stabilizing the Pd
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(0). However, despite general utility of the phosphine ligands, they are susceptible to
oxidation during the reaction, which results in phosphine oxides and “palladium
black”, and thus decreasing the catalytic activity. In addition, several other
shortcomings such as the pollution of products, tedious workꢀup, high cost, and
difficulty in separation and recovery of the catalyst from the reaction mixture always
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puzzled researchers.
In order to overcome these drawbacks, many researchers have made great efforts to
develop environmentally benign Pd heterogeneous catalysts. Most of the reported
supports for catalytic applications are based on various inorganic and organic
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materials, such as metal oxides, porous silicate, silica materials, clay, zeolites,
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ionic liquid, carbon materials and synthetic polymers. However, the synthesis of
these supports involves either high temperature calcinations or polymerization of
petrochemical and expensive feed stocks. Taking into consideration of all these issues
as well as the increasing environmental emphasis on materials and processes,
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tremendous efforts have been made to develop natural polymers supported catalysts.
Biopolymers are the most important environmentꢀfriendly resources with several
interesting features, for example, renewability, high sorption capacity, stability of
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metal anions, and facile functionalization. Recently, Marzieh et al. reported cellulose
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supported palladium (0) for Heck coupling reactions. Nicola and coꢀworkers utilized
lignin as support for Heck, Suzuki and Sonogashira crossꢀcoupling reactions in water
with satisfactory product yields and selectivity. In addition, the
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nanopalladiumꢀentrapped several other biopolymers, such as chitosan, alginate,
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gelatin, starch, cyclodextrin and DNA were fabricated as first successful
achievements of such strategy and were further evaluated as the ideal supports for
various catalytic applications.
Among various biopolymers, hemicelluloses are heteropolysaccharides with various
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branches. The units of main chain include xylose, glucose, uronic acid, etc.
Hemicelluloses possess many hydroxyl groups, and therefore hemicelluloses can bind
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and stabilize heavy metal ions. In addition, as compared to cellulose, chitosan and
other high crystalline biopolymers, hemicelluloses show unique features, for example,
controlled surface chemistry, solubility in various solvents. Thus hemicelluloses have
great potential to be modified and utilized. Our interest focuses on developing
hemicelluloses based functional materials and especially, developing hemicelluloses
or their derivatives as the natural ligands for palladium nanoparticle preparation to
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respond to the current call for environment friendly and sustainable green chemistry.
Carboxymethyl hemicelluloses (CMH) which have both carboxyl groups and
hydroxyl groups are synthesized by hemicelluloses with monochloroacetic acid
(MCA), and the reaction scheme is shown in Figure 1. It has been reported that
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chelating ligands containing O atom result in more stable and efficient Pd catalysts.
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Thus, CMH can be used as excellent natural ligands for catalysts preparation. In this
study, we focused on the preparation of hemicellulosesꢀbased heterogeneous catalyst
by the anchoring of palladium on the surface of CMH with O–O ligand interaction,
where the oxygen on both hydroxyl groups and carboxy groups acted as ligand and
stabilizer for Pd NPs, and its application in Heck crossꢀcoupling reaction. The
superiority of physical and chemical structure, convenience for preparation, natural
polydentate ligand and minimization of catalysts cost made our ideal catalytic
CMHꢀbased nanocomposite exhibit relatively high catalytic efficiency, selectivity and
stability in the CꢀC coupling reactions.
Experimental Section
Chemicals
All of reagents used including halides, olefins, palladium acetate, MCA and
pꢀtoluenesulfonic acid were purchased from Aladdin Reagent Co., Ltd., and were used
without further purification. N, Nꢀdimethylformamide (DMF), dimethyl sulfoxide
(DMSO), ethanol (EtOH), acetonitrile, triethylamine and sodium hydroxide were
purchased from National Medicine Group Chemical Reagent Co., Ltd. Hemicelluloses
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were prepared according to literature. The sugar analysis showed the proportion of
sugar composition (relative weight percent): 89.4% xylose, 5.80% arabinose, 1.90%
glucose, 0.70% galactose, 1.80% glucuronic acid, and 0.60% galactose acid.
Preparation of CMH
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The carboxymethylation of hemicelluloses was shown in Figure 1. The typical
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procedure for the preparation of CMH was according to the literature, with slight
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modifications. The details were shown in supporting information. And six samples
were prepared by changing the reaction conditions. (Table S1 in ESI†)
Preparation of CMH-Pd (0)
CMH powder (1.0 g) and palladium acetate (0.1 g) were suspended in 50 mL EtOH,
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and then Pd (Ⅱ) in the slurry was reduced by EtOH at 60 C for 12 h. After the
reaction, the black slurry was filtered and washed for several times with ethanol and
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finally with diethyl ether and dried at 50 C under vacuum to give the catalyst
CMHꢀPd (0) with a Pd loading of 0.38 mmol/g calculated by inductively coupled
plasma atomic emission spectroscopy (ICPꢀMS).
Characterizations
Fourier transform infrared spectra (FTꢀIR) were measured through a Bruker Tensor 27
FTꢀIR spectrometer. The thermal stabilities of CMH and CMHꢀPd (0) catalyst were
determined by TA Q500 thermo gravimetric analyzer (TGA). The morphologies of the
samples were recorded by a JEMꢀ2100 (HR) transmission electron microscopy (TEM)
working at 200 kV. The content of palladium in catalyst was determined by
TEMꢀenergy dispersive spectrometer (EDS) and ICPꢀMS using Agilent 7700
equipment. Xꢀray powder diffraction (XRD) patterns were collected using a
BrukerꢀD8 Advance diffractometer with Cu Kα radiation (λ=0.154 nm). Xꢀray
photoelectron spectroscopy/ESCA (XPS) was recorded on Axis Ultra DLD instrument
using Al Kα radiation (hν=1486.6 eV) with contaminated C as an internal standard
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(C1s=284.6 eV). HꢀNMR (600 Hz) and CꢀNMR (150 Hz) spectra were accumulated
on a Bruker AVANCE III HD 600 spectrophotometer system.
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General procedure for Heck coupling reaction
A mixture of aryl halide (1.0 mmol), olefin (1.2 mmol), triethylamine (2.0 mmol) and
CMHꢀPd (0) catalyst (50 mg, 1.9 mol% Pd) were added into a 35 mL pressure tube, 3
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mL DMF was then added. The mixture was heated and stirred at 120 C for 6 h. After
the reaction was completed, the catalyst was filtrated and washed with ethyl actate for
several times. Before extraction by ethyl actate for three times, the filtrate was diluted
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with water and the organic phase was dried over anhydrous Na SO and then
evaporated under vacuum to obtain crude product. The isolated product was collected,
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purified by flash column chromatography and characterized by HꢀNMR and
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CꢀNMR.
General procedure for catalyst recovery
The catalytic activity of CMHꢀPd (0) catalyst was examined after reaction. In a
reaction vessel, iodobenzene (1.0 mmol), ethyl acrylate (1.2 mmol), triethylamine (2.0
mmol) and CMHꢀPd (0) catalyst (50 mg, 1.9 mol% Pd) were mixed in DMF. The
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mixture was heated and stirred at 120 C for 6 h. The heterogeneous catalyst was
separated by filtration and washed with ethyl actate for three times, which followed
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by drying at 70 C. The catalyst was directly used for the second run, and the same
process was repeated for the next run.
Heterogeneity test
A mixture of iodobenzene (1.0 mmol), ethyl acrylate (1.2 mmol), triethylamine (2.0
mmol) and CMHꢀPd (0) catalyst (50 mg, 1.9 mol% Pd) were added into a 35 mL
pressure tube, 3 mL DMF was then added. The mixture was heated and stirred at 120
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C. After 2 h of reaction progress, the catalysts were separated by hot filtration. The
filtrate was further reacted under the same conditions for another 4 h. The following
process after the Heck reaction was performed by the same procedure mentioned in
the general procedure for Heck coupling reaction.
Results and Discussion
Characterization of CMH-Pd (0) catalyst
Figure S1a shows the typical absorption frequencies of hemicelluloses at 3431, 2920,
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1629, 1465, 1250, 1169, 986, and 897 cm . Compared to the spectra of
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hemicelluloses, the peak at 1735 cm in Figure S1b is ascribed to the carbonyl
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vibration absorption, and the new bond at 1605 cm is attributed to ꢀCOO stretching
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vibration. The band at around 1419 cm is assigned to ꢀCH scissoring vibration.
Appearance of these bands suggests that the reaction between hemicelluloses and
MCA occurs successfully. Interestingly, the FTꢀIR spectra of CMHꢀPd (0) is similar to
that of CMH scaffold in terms of the characteristic peaks, which indicates that the
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physical bonding exists between Pd NPs and CMH.
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The HꢀNMR spectrums of hemicelluloses and CMH are shown in Figure S2 in ESI†.
The major signals at 4.39, 4.00, 3.71, 3.47, 3.29, and 3.21 ppm in Figure S2a are
corresponded to the Hꢀ1, Hꢀ5eq, Hꢀ4, Hꢀ3, Hꢀ5ax, Hꢀ2 of nonꢀsubstituted βꢀDXyl,
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respectively. In Figure S2b, the new band at 4.52 ppm is ascribed to the substituted
carboxymethyl ꢀCH ꢀ. These observations confirm the occurrence of
carboxymethylation of hemicelluloses with MCA. Figure S2c and Figure S2d show
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Acetyl ꢀCH in xylan gives a signal at 23.28 ppm. The CꢀNMR spectrum of CMH
shows the new signal at 176.12 ppm, which is assigned to the carboxyl groups. The
signal at 69.94 ppm is ascribed to the methylene carbon atoms of carboxymethyl
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groups.
In conclusion, the results further indicated the reaction between
hemicelluloses and MCA occurred.
The structure of CMHꢀPd (0) was further studied by means of powder Xꢀray
diffraction (XRD), as shown in Figure 2. The broad peaks of CMHꢀPd (0) were
observed at 2θ=40.0
°, 46.1° and 67.5°, corresponding to (111), (200) and (220)
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crystalline planes of the faceꢀcentered cubic (fcc) lattice (PDFꢀ# 46ꢀ1043).
Figure 3 displays the XPS spectra of CMH and CMHꢀPd (0). Besides O and C
elements in CMH, CMHꢀPd (0) contains Pd element. The Pd 3d spectrum shows two
typical peaks at 334.3 eV and 339.6 eV for 3d5/2 and 3d , respectively, which
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correspond to Pd (0). These results well agree with XRD results.
Figure 4 showed the TEM images of CMHꢀPd (0) before and after catalysis. A typical
TEM image of CMHꢀPd (0) was shown in Figure 4a, which clearly showed the
formation of metallic Pd nanoparticles with size range of 11ꢀ19 nm and the average
particle size was about 15 and 16 nm. The freshly prepared CMHꢀPd (0) particles
were homogeneous on the CMH surface. High resolution transmission electron
microscopy (HRꢀTEM) image of an individual Pd nanopaticle showed clear lattice
fringes with an interplanar distance of approximately 0.22 nm, corresponding to (111)
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planes of Pd (Figure 4d). There were clearly numerous crystal forms on the surface of
the asꢀprepared CMHꢀPd (0), as indicated by the corresponding electron diffraction
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pattern form (Figure 4c). The element Pd presented in the product was shown in
Figure 4e. All of these results clearly confirmed that the palladium complex was
immobilized onto xylan molecular chains.
Generally, heating is necessary in the Heck crossꢀcoupling reaction. Hence, the
thermal stability of CMHꢀPd (0) catalyst was studied by TGA. As illustrated in Figure
5, compared to CMH, the catalyst exhibited relatively good thermal stability up to 210
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C. Weight loss along with exothermic peak occurred when temperature was higher
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than 210 C. With the increase of temperature, the decrease of catalyst weight was
more obvious. The decomposition of CMH was complete when temperature was
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raised to 360 C and the oxide of palladium was remained.
CMH-Pd (0) catalyzed Heck reaction
The Heck coupling reaction of iodobenzene with ethyl acrylate or styrene was utilized
as a model reaction to investigate the catalysis performance of CMHꢀPd (0), and the
results were listed in Table 1 and Table 2. The results indicated that solvent, catalyst
loading, reaction temperature, time and DS of CMH were the key factors that
significantly affected the catalytic efficiency of Pd NPs for the formation of CꢀC
bonds. Subsequently, the influence of solvent on the reaction was investigated (Table
1, entries 1ꢀ5). Solvent screening gave a maximum yield of 74% in DMF (Table 1,
entry 1). A relatively high yield of 84% for the crossꢀcoupled direct arylation product
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could be obtained within 6 h (Entry 16 in Table 1).However, H O and CH CN
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resulted in trace amount of product (Entries 4 and 5). The moderate yields (53% and
48%) (Entries 2 and 3) indicate that reactions of iodobenzene with ethyl acrylate in
EtOH and DMSO were also not effective compared to DMF. The reasons may be
explained as follows. On the one hand, CMH could dissolve in H O and DMSO, so
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the structure of CMHꢀPd (0) was not stable when the reaction was carried out in H
or DMSO. On the other hand, without reflux system, 120 °C was over the boiling
points of CH CN, EtOH and H O, which may not facilitate the reaction. Therefore,
DMF was the optimum solvent.
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In addition, the effect of the catalyst loading on product yield was examined (Table 1,
entries 6ꢀ10 and 1). When the amount of catalyst was reduced to 12.5 mg (0.48 mol%),
a good yield 60% (Table 1, entry 7) was retained, indicating that CMHꢀPd (0) was a
relatively active catalyst for the direct coupling reactions of aryl halides with olefins.
Controlling experiment demonstrated that no reaction could occur in the absence of
the CMHꢀPd (0) (Entry 6 in Table 1), suggesting that the asꢀprepared CMHꢀPd (0)
catalyst actually acted as the real catalyst. The results showed that the optimal catalyst
dosage was 1.9 mol%.
The optimal reaction temperature was established by monitoring the coupling reaction
o
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of iodobenzene with ethyl acrylate as a function of temperature from 60 C to 140 C
(Table 1, entries 11ꢀ14 and 1). The reaction processed successfully and the yield
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exceeded 60% even at low temperature (80 C, Table 1, entry 12). The yield of
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product increased when the reaction temperature was increased from 60 to 120 C.
Due to the side reactions the yield of product decreased slightly when the temperature
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was raised to 140 C, for further exploration, 120 C was selected as the optimum
temperature.
w
As shown in Table 2, the DS and M of CMH had significant influence on the
catalytic activity of the palladium nanocomposites. Hemicelluloses was a kind of ideal
support with the yield up to 84%, however, a good yield 90% was obtained when the
DS of CMH was up to 0.24. With the increase of DS of CMH, the product yield of
Heck reaction was increased, which indicated that carboxy groups have better ability
for Pd NPs coordination and stabilization. However, the increase of DS of CMH
resulted in the decrease of Mw which might further have great influence on the service
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life of the CMHꢀPd (0). Because of the decrease of Mw, the molecular chain and
side chains of CMH were broken and shortened, the twisting capacity of CMH
molecular chains for Pd NPs stabilization was impaired. Therefore, for further study,
DS=0.24 was chose as the typical DS.
The reaction scope was also investigated using a range of functionalized aryl halides
and olefins under the optimized reaction condition, and the results were summarized
in Table 3. In general, all the aryl iodides afforded the corresponding products in good
to excellent yields ranging from 90% to 99%. As for different vinyl substrates, such as
styrene, acrylic acid, methyl acrylate, ethyl acylate and nꢀbutyl acrylate resulted in
high yields (Table 3, entries 4ꢀ8). For aryl bromides, the catalyst showed lower
activity (Table 3, entries 3, 9, 11, 13, 15). Meanwhile, aryl bromides with
electronꢀwithdrawing groups afforded the corresponding products in better yield up to
87% and 94% (Table 3, entries 13 and 15). The coupling reactions of aryl chlorides
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with ethyl acrylate required extended reaction time and the yields of corresponding
coupling products were unsatisfactory, because the oxidativeꢀaddition of CꢀCl bond to
catalyst species was usually difficult. Functional groups including methoxyl, methyl,
1
13
carbonyl and nitryl are also tolerated. HꢀNMR and CꢀNMR spectra of all products
were confirmed. The results indicated that CMHꢀPd (0) as a novel catalyst was a
relatively good choice for Heck coupling reactions.
Reusability of CMH-Pd (0) catalyst
The recyclability of the asꢀprepared CMHꢀPd (0) catalyst was studied by using the
reaction between iodobenzene and ethyl acrylate as a model reaction. The catalyst
could be recovered by simple filtration. After being washed adequately by EtOH and
dried in air, the catalyst could be reused for the next reaction, and the results are listed
in Table 4. The yield of the product was decreased from 97% to 89% in the fifth run,
and retained nearly 92% of its original reactivity, indicating that CMH stabilized Pd
NPs catalyst was highly stable and recyclable. The decreasing activity of the catalyst
upon recurrent usage can be explained by the fact that the aggregation of the Pd NPs
(Figure 6b). As we all known, Pd NPs are not stable and prone to aggregate because
of their large surface cohesion energy. The formation of Pd NPs by reduction of Pd (II)
40
is composed of two steps, that is, the nucleation and the growth of nuclei. When the
initial Pd nuclei is formed, the hydroxylꢀgroups and carboxyl of CMH participate in
controlling growth of Pd nuclei. The strong bonding interaction between CMH and Pd
atom prevents individual particle from aggregation, and thus giving well dispersed Pd
NPs with small size. After five reaction cycles, the stability of CMH is decreased, thus
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the interaction between Pd NPs and CMH reduced. In this work, excellent activity and
recyclability overcame the reused and environmental problems for homogeneous
catalyst. Therefore, the wildly available and renewable raw materials, good catalytic
properties and reuse performance can significantly decrease the overall cost, and
improve the efficiency of the synthetic process for practical applications.
Heterogeneity of the CMH-Pd (0) during the Heck coupling reaction
In order to prove the heterogeneous nature of the CMHꢀPd (0) and the absence of Pd
leaching, the following reaction conditions were conducted. First, the standard
o
reaction was processed at 120 C for 2 h (the product yield was 75% checked by
column purification of the product), and then CMHꢀPd (0) was hot filtrated, the
o
reaction mixture was left stirring at 120 C for another 4 h. The product yield was
only 80%. In another test, after full conversion (6 h, 97% yield), the filtrate was
analyzed by ICPꢀMS, the results showed that the amount of palladium was 0.2 ppm.
This indicated that the leakage of Pd NPs during catalytic experiments was negligible
and the nature of reaction was heterogeneous.
Taking iodobenzene reacting with styrene as an example, we compared the results
achieved in this work with other biopolymerꢀbased catalysts supported catalysts for
the Heck coupling reaction, and the results are listed in Table 5. As shown in Table 5,
CMHꢀPd (0) catalyst showed some extensive improvement in reaction conditions,
such as reaction time, catalyst dosage and yield. For example, CELLꢀPd (0),
PdNPs@XH afforded a much longer reaction time and higher dosage of palladium
catalysts, although high yield was obtained. In addition, the procedure for the
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preparation of PNPꢀSSS is complex and not green, in which thionyl chloride and
chloroform were employed during the synthesis reaction, despite the yield was higher
than CMHꢀPd (0) achieved. Catalysis for the Heck reaction by utilizing renewable
CMHꢀPd (0) catalyst based on biomass presents an ideal chemical process. The
CMHꢀPd (0) catalyst is promising for its renewability, environment benefit, efficiently
catalytic activity, thus has great potential to be applied into the industry processes.
Conclusion
In summary, CMHꢀPd (0) catalyst is a very active and stable bioꢀbased
nanocompostite catalyst for the Heck coupling reaction. Furthermore, the catalyst
could be easily recovered and reused by simple filtration, which was perfect in terms
of cost and environmental sustainability. The catalyst could be reused at least five
times without considerable deactivation. Driven by all these advantages, CMHꢀPd (0)
catalyst will have great potential to be applied in pharmaceutical industry and other
environment benign chemical industries.
Associated Content
1
Details for CMH preparation, FTꢀIR and H NMR spectra of CMH, spectral data and
1
13
copies of H and CꢀNMR spectra for the synthesized compounds are shown in
supporting information.
Author Information
Corresponding authors. Eꢀmail: fexwpeng@scut.edu.cn (Xinwen Peng) and
lxzhong0611@scut.edu.cn (Linxin Zhong).
Tel.: +86ꢀ010ꢀ62336972;
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Fax: +86ꢀ010ꢀ62336972.
Notes
The authors declare no competing financial interest.
Acknowledgments
The project is supported by the National Natural Science Foundation of China
(21404043, 31430092 and 21336002), Pearl River S&T Nova Program of Guangzhou
(2014J2200063), Science and Technology Project of Guangdong Province
(2015A010105005), Research Fund for the Doctoral Program of Higher Education
(201301721200240), Fundamental Research Funds for the Central Universities.
Abbreviations
CMH, carboxymethyl hemicelluloses; Pd NPs, palladium nanoparticles; MCA,
monochloroacetic acid; DMF, N,Nꢀdimethylformamide; DMSO, dimethyl sulfoxide;
EtOH, ethanol; CMHꢀPd (0), carboxymethyl hemicelluloses with Pd (0) catalyst;
FTꢀIR, fourier transform infrared spectra; TGA, thermal gravimetric analysis; TEM,
transmission electron microscopy; HRꢀTEM, high resolution transmission electron
microscopy; XRD, Xꢀray powder diffraction; EDS, TEMꢀenergy dispersive
spectrometer; FTꢀIR, fourier transform infrared spectra; TGA, thermo gravimetric
analyzer; XPS, Xꢀray photoelectron spectroscopy/ESCA; ICPꢀMS, inductively
coupled plasma mass spectrometry.
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a
Table 1. Optimization of the Heck reaction conditions .
o
b
Entry
1
Catalyst (mg)/DS=1.77
50
Solvent
DMF
Temp ( C)
Time (h) Yield (%)
120
8
8
74
53
48
8
2
3
4
5
6
7
8
9
50
50
20
50
0
EtOH
120
120
120
120
120
120
120
120
120
60
DMSO
8
3
CH CN
8
H
2
O
8
4
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
8
trace
60
67
73
74
16
65
67
64
83
84
75
71
12.5
25
75
100
50
50
50
50
50
50
50
50
8
8
8
1
0
1
8
1
8
1
1
1
1
1
1
1
2
3
4
5
6
7
8
80
8
100
140
120
120
120
120
8
8
4
6
10
12
a
Reaction conditions: 1.0 mmol iodobenzene, 1.2 mmol ethyl acrylate, 2.0 mmol
b
triethylamine, 3 mL Solvent. Isolated yield was based on the iodobenzene.
4
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a
Table 2. Optimization of the DS of CMH for Heck reaction .
o
b
Entry
1
DS
0
Mw
Temp ( C)
Time (h) Yield (%)
283410
120
84
56
59
54
62
77
90
6
6
6
0
.055
.082
177080
148100
183250
113650
82727
120
120
120
120
120
120
2
3
4
5
6
7
0
0
.0534
6
6
0
.109
.177
0
6
6
0
.24
51383
a
Reaction conditions: 1.0 mmol iodobenzene, 1.2 mmol styene, 2.0 mmol
b
triethylamine, 3 mL DMF. Isolated yield was based on the iodobenzene.
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a
Table 3. Heck reactions of aryl halides with olefins .
b
Entry
R
1
X
I
R
2
Yield/%
97
Product
O
1
2
3
4
5
6
7
8
9
H
H
H
3a
3b
3a
3c
3d
3e
3f
3g
3c
3h
3h
3i
O
I
90
O
Br
I
32
O
pꢀCH O
91
3
OH
pꢀCH
3
O
I
95
O
O
pꢀCH O
I
96
3
O
O
pꢀCH
pꢀCH
3
3
O
O
I
96
O
O
I
92
O
O
O
O
O
O
O
O
O
O
O
pꢀCH O
Br
I
34
3
O
O
O
O
O
O
O
O
O
O
1
0
1
pꢀCH
3
96
1
pꢀCH3
Br
I
31
12
13
14
15
pꢀCH
pꢀCH
3
CO
CO
94
3
Br
I
87
3i
pꢀNO2
pꢀNO
pꢀNO2
99
3j
2
Br
94
3j
c
1
6
7
8
Cl
Cl
63
3i
c
c
1
1
pꢀCH
3
CO
55
3j
Cl
pꢀCH
3
O
12
3c
2
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b
Entry
R1
X
R2
Yield/%
trace
Product
3h
O
O
c
1
9
pꢀCH
3
Cl
a
Reaction conditions: 1.0 mmol aryl halide, 1.2 mmol olefin, 2.0 mmol triethylamine,
o
b
c
5
0 mg CMHꢀPd (0) (1.9 mol% Pd), 3 mL DMF, 120 C, 6 h. Isolated yield. At 120
o
C for 24 h.
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Table 4. Successive Heck reaction using recovered catalysts .
o
b
Entry
1
Catalyst
Solvent
DMF
Temp ( C)
Yield (%)
HꢀPd (50 mg)
120
97
95
95
90
87
97
96
96
94
89
2
3
4
5
6
7
8
9
HꢀPd 1st reuse
HꢀPd 2nd reuse
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
120
120
120
120
120
120
120
120
120
HꢀPd 3rd reuse
HꢀPd 4th reuse
CMHꢀPd (50mg)
CMHꢀPd 1st reuse
CMHꢀPd 2nd reuse
CMHꢀPd 3rd reuse
CMHꢀPd 4th reuse
1
0
a
Reaction conditions: 1.0 mmol iodobenzene, 1.2 mmol ethyl acrylate, 2.0
o
b
mmol triethylamine, 3 mL DMF at 120 C for 6 h. Isolated yield was based
on the iodobenzene.
4
4
4
4
4
4
4
24
25
26
27
28
29
30
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6

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Table 5. Catalytic performance of different Pd-based catalysts in the Heck reaction.
Entry
1
Catalyst
Solvent
T (°C)
110
t (h)
24
Catalyst Dosage (mol%)
1
Yield (%)
80
Ref.
2
a
HPCD/Pd/CaCO
3
H
2
O/DMF
b
2
CELLꢀPd(0)
DMF
120
12
2.3
100
23
c
H
2
O
reflux
90
1.5
8
1.2
2
28
35
3
4
5
6
7
PNPꢀSSS
95
92
d
PdNPs@XH
3
CH CN
e
Pd/BC
DMF
DMF
DMF
DMF
120
120
120
120
8
0.1
0.9
1.7
37
87
69
CMCꢀPd (Ⅱ)
HꢀPd (0)
6
This work
This work
6
84
90
CMHꢀPd (0)
6
1.9
This work
8
a
b
c
Palladium on calcium carbonate combined to 2ꢀhydroxypropyla/bꢀcyclodextrins. Cellulose supported Pd(0). Pd
d
e
nanoparticles supported on silicaꢀstarch substrate. Xylanꢀtype hemicellulose supported Pd (0). Bacteria cellulose
nanofibers supported Pd (0).
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Figure 1. Schematic illustration for the preparation of CMH.
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(
111)
(
b)
(
200)
(
220)
(
a)
2
0
40
60
ο
2
θ
4
4
44
45
Figure 2. XRD diffraction patterns of (a) CMH and (b) CMHꢀPd (0) catalyst.
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
2
9