Nanopalladium on polyethylenimine–grafted starch: An efficient and ecofriendly heterogeneous catalyst for Suzuki–Miyaura coupling and transfer hydrogenation reactions

Article abstract of DOI:10.1002/aoc.3853

Functionalized natural polysaccharides are attractive supports for colloidal metal nanocatalysts due to their abundance, cheapness, biocompatibility and biodegradability. In this study, isocyanate–functionalized starch was prepared by treating with diisocyanate. Polyethylenimine grafted onto starch via the formation of urea linker. The palladium nanoparticles deposited starch PEIS@Pd(0) was obtained through a chelating–in situ reduction procedure. Characterization of these materials was done using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X–ray diffraction, and inductive coupled plasma atomic emission spectrometry. The catalytic activity of PEIS@Pd(0) was then tested in two series of model reactions: Suzuki–Miyaura coupling and transfer hydrogenation. The catalyst could be recovered by simple filtration and was reused for five times without significant loss of catalytic activity, which confirmed the good stability of the catalyst.

Full text of DOI:10.1002/aoc.3853

Received: 17 January 2017
DOI: 10.1002/aoc.3853
Revised: 23 February 2017
Accepted: 24 March 2017
F U L L PA P E R
Nanopalladium on polyethylenimine–grafted starch: An efficient
and ecofriendly heterogeneous catalyst for Suzuki–Miyaura
coupling and transfer hydrogenation reactions
Lixia Fu | Wenxiu Deng | Lujie Liu | Yanqing Peng
Shanghai Key Laboratory of Chemical
Functionalized natural polysaccharides are attractive supports for colloidal metal
nanocatalysts due to their abundance, cheapness, biocompatibility and biodegrad-
ability. In this study, isocyanate–functionalized starch was prepared by treating with
diisocyanate. Polyethylenimine grafted onto starch via the formation of urea linker.
The palladium nanoparticles deposited starch PEIS@Pd(0) was obtained through a
chelating–in situ reduction procedure. Characterization of these materials was done
using Fourier transform infrared spectroscopy, scanning electron microscopy,
transmission electron microscopy, X–ray diffraction, and inductive coupled plasma
atomic emission spectrometry. The catalytic activity of PEIS@Pd(0) was then tested
in two series of model reactions: Suzuki–Miyaura coupling and transfer hydrogena-
tion. The catalyst could be recovered by simple filtration and was reused for five
times without significant loss of catalytic activity, which confirmed the good
stability of the catalyst.
Biology, School of Pharmacy, East China
University of Science and Technology,
Shanghai 200237, People's Republic of
China
Correspondence
Yanqing Peng, Shanghai Key Laboratory of
Chemical Biology, School of Pharmacy, East
China University of Science and Technology,
Shanghai 200237, People's Republic of
China.
Email: yqpeng@ecust.edu.cn
Funding information
Shanghai Commission of Science and Tech-
nology, Grant/Award Number: 08431901800
KEYWORDS
catalyst, palladium nanoparticles, polyethylenimine, Suzuki–Miyaura coupling, transfer hydrogenation
1
| INTRODUCTION
solid substrates can stabilize the catalysts and allow their
recycled uses.
[
3]
Despite the excellent activity and selectivity of homogeneous
catalysts, they have inherent drawbacks in catalyst separation
and recycling. In contrast, heterogeneous catalysts are much
The application of solid–supported noble metal
nanocatalysts, particularly Pd(0) clusters, has increased
dramatically in recent years. Among various solid supports
[1]
[4]
[5]
[6]
affordable for industrial application.
Nanometer–sized
such as functionalized oxide, charcoal, zeolite, poly-
[
7]
[8]
colloidal metal catalysts, sometimes termed semi–heteroge-
neous or quasi–homogeneous catalysts, have received
increasing attention because they often offer higher catalytic
efficiency than larger size materials, because of their large
mer, and metal–organic framework, ecofriendly natural
polysaccharides (e.g. starch and cellulose) are attractive ones
due to their abundance, biocompatibility and biodegradabil-
[
9]
ity.
For example, carboxymethylcellulose–supported
[2]
surface–to–volume ratio. However, two technical issues
restrict their wide applications. First, the separation and
recovery of such catalytic nanoparticles in their isolated form
is very challenging due to their small sizes. Residual
nanocatalysts are generally considered very undesirable
because of their potential harmful impact on the environ-
ment. Immobilization of nano–sized metal catalysts onto
palladium nanoparticles generated in situ from palladium(II)
carboxymethylcellulose was found to be an efficient and
reusable catalyst for Heck–Matsuda and Suzuki–Miyaura
[
10]
couplings.
Palladium and Fe O nanoparticles could be
3 4
deposited onto N–(2–aminoethyl)acetamide functionalized
cellulose afforded a reusable catalyst in the oxidation reaction
[
11]
of ethylbenzene.
Appl Organometal Chem. 2017;e3853.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 9
https://doi.org/10.1002/aoc.3853

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FU ET AL.
Functional polymers provide stabilization for metal nano-
particles through the framework or by binding weakly to the
nanoparticle surface through heteroatoms. Polyethylenimine
(PEI) is a branched, water‐soluble polymer used for a wide
variety of applications. As a chelating agent, PEI plays the
[
12]
role of efficient stabilizer during the preparation
assembly
or
[
13]
of noble metal nanoparticles. PEI modified
solids are satisfactory supports of noble metal nanocatalysts.
Gold nanoparticles immobilized on PEI modified polyacrylo-
nitrile fiber is a highly efficient and recyclable heterogeneous
[
14]
catalyst for the reduction of 4‐nitrophenol by NaBH4.
PEI can also be grafted onto natural polysaccharides
[
15]
through chemical modification. PEI–grafted starch,
[
16]
[17]
cellulose
and chitosan
were applied for the removal
of heavy metal ions from aqueous solutions. The biocompat-
ible backbone of polysaccharides is favorable in biological
research. Recently, polysaccharides grafted with PEI were
[18]
introduced as gene delivery platform and vehicles for drug
[
19]
delivery.
To the best of our knowledge, however, the
PEI–grafted polysaccharide as functional support of noble
metal nanocatalysts has not yet been investigated.
Herein, we report the design and preparation of PEI–
grafted starch supported palladium nanoparticles with the
aim to develop an efficient catalytic system that promotes
various reactions. The functional support was obtained by
grafting polyethylenimine onto isocyanate–functionalized
starch. In comparison with traditional epoxide ring opening
amination route, this activation method was demonstrated to
be much efficient. The catalyst was synthesized through a
chelating–in situ reduction method to form monodispersed
Pd NPs with an average diameter of ~8 nm on the surface of
the PEI grafted starch. The catalytic activity of as–synthesized
PEIS@Pd(0) was evaluated in two model reactions: (1)
Suzuki–Miyaura coupling reaction between substituted
bromobenzenes and arylboronic acids, and (2) transfer hydro-
genation of carbonyl compounds and chalcones with
SCHEME 1 Preparation of polyethylenimine–grafted starch and
depositon of palladium nanoparticles
nanoparticles. Starch has great number of hydroxyl groups
on the surface capable of chemical modification. Initially, the
starch granules were activated by treating with p–phenylene
diisocyanate (1 equiv. per glucose unit) in anhydrous
acetonitrile for 12 hours at room temperature. Symmetric
diisocyanate was anchored on the surface of starch by forming
carbamate linkage, with another isocyanate group remained as
a reaction site for further decoration. The reactive support thus
obtained was grafted with polyethyleneimine (Mw ≈ 600,
Aldrich) to afford PEI grafted starch (denoted as PEIS).
Routinely, polyethylenimine–grafted polysaccharides
were prepared by treating PEI with epoxy–functionalized
polysaccharides (epoxide ring opening amination route).
The epoxide moiety is a strained but apparently stable three
membered ring. Epoxide ring opening amination often
needs catalysts, elevated temperatures or long reaction times
HCOONH as hydrogen donor. The catalyst can be recovered
4
and recycled for at least five times without significant loss of
catalytic activity.
[
21]
(
e.g. 60°C, 12h ). Hence, microwave irradiation has
2
| RESULTS AND DISCUSSION
.1 | Surface activation and grafting
recently been reported to accelerate the grafting of PEI on
[
22]
epoxy–functionalized cellulose fiber.
In the present work,
2
isocyanate–functionalized starch was employed as a much
efficient reactive support in comparison with epoxy–function-
alized one. In our investigation, a short reaction time and mild
condition (room temperature, 3h) were chosen for grafting
procedure. This success depends on the excellent reactivity
of isocyanate group with amino groups on PEI.
The processes of surface activation, polyethylenimine–
grafting, and depositon of palladium nanoparticles were
illustrated in Scheme 1. Polyethyleneimine (PEI) is a polymer
without uniform repeat units. It contains linear regions and
branched regions with primary amino functions as terminal
units and secondary amino functions as linear units. The
Surface modification was confirmed by Fourier transform
infrared spectroscopy. The appearance of absorption band at
2280 cm− is attributed to the isocyanate groups stretching
[
20]
dendritic units consist of tertiary amines (Scheme 1A).
1
This fact made it an efficient polymeric ligand for the
chelation of metal cations as well as stabilization of metal
‐
1
vibration, while the absorption peaks at 1639 and 1561 cm

FU ET AL.
3 of 9
is related to C=O stretching vibration and N–H bending vibra-
tion, respectively (Figure 1, b). These facts proved that the
starch was funtionalized by diisocyanate through
a
carbamate linkage. The characteristic peak of isocyanate
disappeared after the isocyanate–functionalized starch was
treated with PEI (Figure 1, b and c), indicating the complete
consumption of isocyanate groups during grafting. The load-
ing of amino groups on PEIS was determined as 7.5 mmol/g
by acid–base titration analysis. According to the result of
nitrogen content determined by elemental analysis, amine
group loading was calculated as 8.3 mmol/g. This difference
might be partly attributed to the existence of nitrogen in the
linkages.
The surface morphology of unmodified starch and PEI
grafted starch were observed through SEM images as shown
in Figure 2. It shows that the starch granules present regular
surface morphology. The grafting of PEI had no significant
effect on the surface morphology, indicating the structure of
starch granules had not been destroyed during the chemical
modification.
2
.2 | Depositon of palladium nanoparticles
Pd(0) loaded PEIS was obtained through a chelating–in situ
reduction procedure. As‐prepared PEIS was then tested as a
chelating support of palladium catalyst since Pd(II) could
be bound readily by coordination to the amine groups. Pd(II)
loaded PEIS was firstly prepared by exposing PEIS to PdCl2
solution, followed by washing with ethanol to remove
unbinding Pd(II) ions. In a one–pot in situ reduction
procedure, above–mentioned suspension of Pd(II) loaded
PEIS could be transformed to PEIS@Pd(0) through in situ
reduction with sodium boronhydride. Upon reduction the
color of catalyst changed rapidly from yellow–gray to black
due to the formation of black Pd(0) nanoparticles.
FIGURE 2 SEM images of (a) unmodified starch (b) PEIS
X‐ray diffraction (XRD) patterns of blank PEIS support,
Pd(II) loaded PEIS and PEIS@Pd(0) were shown in Figure 3.
A broad reflection (2θ=10–40°) is observed in the XRD
FIGURE 3 XRD patterns of (a) blank PEIS support, (b) Pd(II)
loaded PEIS and (c) PEIS@Pd(0). Inserts illustrate the digital
photographs of corresponding samples
patterns of blank PEIS support and Pd(II) loaded PEIS
(Figure 3, a and b, respectively), which is attributed to the
reflection of amorphous matrix. The pattern of PEIS@Pd
recycled after hydrogenation reaction exhibited characteristic
diffused peaks around 40°, 46°, and 68°, which could be
FIGURE 1 FTIR spectra of (a) unmodified starch (b) isocyanate–
functionalized starch and (c) PEI grafted starch

4
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FU ET AL.
assigned to (111), (200) and (220) reflections of the face
centered cubic (fcc) structure corresponding to metallic
reaction media than pure ethanol. The ratio of EtOH/H O
2
also influenced the efficiency and EtOH:H O=1:1(v/v) was
2
[
23]
palladium,
indicating that the Pd was deposited on the
the best choice (Table 1, Entries 3–5). The advantage of the
mixed solvent might to be attributed to the good solubility
of the organic reactants and the inorganic base.
support as nanocrystals. It should be mentioned that certain
reflection peaks in low‐intensity could be identified at 2θ
=
40° and 46°, implying that small amount of metallic Pd
After fixing a suitable solvent, the reaction was repeated
using different bases (Table 1, Entries 6–10). Among the
bases, K CO was proved to be the best one. K PO and
exists in the sample of Pd(II) loaded PEIS (Figure 3, b). This
observation might to be ascribed to the weak reductive
activity of starch.
2
3
3
4
[
24]
Na CO were also effective. Unfortunately, NaHCO and an
2 3 3
Furthermore, the formation of Pd nanoparticles was
confirmed by transmission electron microscopy (TEM) as
presented in Figure 4. No clearly visible nanoparticles could
be observed on Pd(II) loaded PEIS (Figure 4, A). In contrast,
TEM image of PEIS@Pd(0) recovered after hydrogenation
displayed the well dispersed nature of the Pd NPs situated
on the external surface of the support (Figure 4, B). The
marked rectangle is magnified in Figure 4C, shows that the
well monodispersed Pd NPs on PEI grafted starch were of
nearly spherical shape, with an average diameter of 4.3 nm
as can be seen in the embedded histogram. The average
particle size of the Pd NPs was further estimated by the
peak width of the (111) Bragg reflection using Scherrer's
equation: D=Kλ/βcosθ, where β is the half–peak width of
the corresponding peak, θ is the diffraction angle, λ is the
organic base, triethylamine, did not give ideal reactivity
under the same reaction conditions (Table 1, Entries 9 and
10). The influence of the amounts of catalyst was also
investigated. Catalytic amount (2mol%) of Pd was sufficient
for a satisfactory result, while an increase in the proportion
to 3mol% produced comparable yields. Smaller amounts
of Pd (1mol%) resulted in an inferior yield (Table 1,
Entries 11 and 12).
With the optimized reaction conditions in hand, the sub-
strate scope of PEIS@Pd(0) in Suzuki–Miyaura coupling
reaction was investigated, for which a range of phenyl
bromides and aryl iodides were coupled with various
phenylboronic acids (Scheme 2). In general, good to
excellent yields (87–92%) of corresponding biphenyl com-
pounds were obtained after 2–4 h with 2 mol% palladium
loading (Table 2). Arylboronic acid bearing strong elec-
tron–donating groups need a relatively longer time to pro-
duce a good yield, and the steric hindrance effect might
have a certain impact on the reaction rate (Table 2, Entry 12).
The recyclability of PEIS@Pd(0) catalyst was further
investigated because the good recyclability of the heteroge-
neous catalyst is an important issue for practical applications.
The recyclability was assessed in model reaction under opti-
mized reaction conditions. On completion of the reaction, the
catalyst was recovered from the reaction mixture by filtration,
washed several times with water and ethanol, and dried in air.
The catalyst could be reused for at least five cycles without a
significant loss of yield and catalytic activity (Table 2,
Entries 1–6). The recyclability of the catalyst can be
attributed to the efficient stabilization of the Pd nanoparti-
cles. The TEM image of PEIS@Pd(0) after consecutive six
runs of Suzuki–Miyaura coupling reaction shows that there
is no agglomeration of Pd nanoparticles (Figure 4D).
Furthermore, the filtrate was subjected to ICP–AES to check
the possible leaching of palladium from PEIS@Pd(0) with
the satisfactory result indicating the absence of leaching from
the catalyst. Namely, the catalyst was very stable under the
reaction condition.
wavelength of the Cu K radiation (0.154178 nm), and K is
α
a constant of value 0.89. The average diameter was calculated
to be 5.5 nm, which was consistent with the results from the
TEM image. The percentage of palladium content in the
PEIS@Pd(0) catalysts was determined by chemical analysis
using inductive coupled plasma atomic emission spectrome-
try (ICP–AES). The accurate content of Pd on PEIS@Pd(0)
was determined to be 9.6%wt, which is equal to 0.90 mmol/g.
2
.3 | Suzuki–Miyaura coupling reaction
The palladium–catalyzed Suzuki–Miyaura cross–coupling
reaction of aryl halides with arylboronic acids is one of the
most powerful and versatile methods for the synthesis of
[25]
symmetric and asymmetric biaryls. Over the past decades,
this reaction has achieved great progress and been applied
extensively in material science and fine chemicals and phar-
[26]
maceutical industries.
On the other hand, the catalytic
activities of palladium catalysts are commonly tested using
Suzuki–Miyaura coupling reaction.
The coupling of bromobenzene and phenylboronic acid
was chosen as a model for studying the effects of different
solvents and bases. Only ethanol, water and their mixture
were chosen as solvents due to environmental concerns.
The amount of PEIS@Pd(0) was initially fixed as 2mol%
Finally, we compared the results achieved in this work
with those reported elsewhere over many supported catalysts.
Taking phenyl bromide reaction with phenylboronic acid as
an example, the results are listed in Table 3. The turnover
number (TON=mol of product/mol of catalyst) and turnover
frequency (TOF =TON/time (h)) were calculated on the basis
(
calculated based on palladium content) with K CO as a
2 3
base (Table 1, Entries 1–5). The screening experiment reveals
that the reaction was performed in water the yield was very
low (38% after 4 h). The mixtures of EtOH/H O are better
2

FU ET AL.
5 of 9
FIGURE 4 TEM images of (a) Pd(II) loaded PEIS, and (b) PEIS@Pd(0). Magnified area (c) was marked as a rectangle in B. Embedded was the
corresponding particle size distribution histograms based on statistical analyzes of 100 particles from TEM image. (d) TEM image of the recovered
catalyst after six runs
of the amount of diphenyl product. As can be seen from the
Table 3, PEIS@Pd(0) was comparable with many of others
in terms of the TON and TOF. Some catalysts showed much
higher TON and TOF values due to very low Pd dosages
2.4 | Transfer hydrogenation of carbonyl
compounds and chalcones
Chemoselective hydrogenation is an important class of reac-
tions that is extensively employed in the academic and
(Table 3, Entries 1 and 2).

6
of 9
FU ET AL.
a
TABLE 1 Condition optimization in model reactions
b
Entry
Pd (mol%)
Bases
Solvents
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
2
2
2
2
2
2
2
2
2
2
1
3
K
K
K
K
K
K
K
2
2
2
2
2
3
2
CO
CO
CO
CO
CO
3
3
3
3
3
EtOH
2
4
2
2
2
2
2
2
2
2
2
2
64
38
87
83
76
85
87
81
48
34
79
89
2
H O
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
EtOH/H
2
O (1:1, v/v)
2
O (2:1, v/v)
2
O (1:2, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
2
O (1:1, v/v)
PO
4
CO
3
Na
CO
2 3
NaHCO
3
1
1
1
0
1
2
Et
3
N
K
K
2
CO
3
3
2
CO
a
Conditions: bromobenzene (2 mmol), phenylboronic acid (3 mmol), base (3 mmol), 6ml of solvent, 75°C.
b
Isolated yields
Suzuki reaction, we wanted to test the catalytic activity of
PEIS@Pd(0) in transfer hydrogenation of carbonyl com-
pounds with ammonium formate as an eco–friendly hydrogen
donor (Scheme 3, Route A).
SCHEME
reactions
2
PEIS@Pd(0)–catalyzed Suzuki–Miyaura coupling
The scope of the reaction was firstly studied using
typical carbonyl compounds as substrates. The transfer
hydrogenation of structurally diverse aromatic aldehydes
and ketones proceeded efficiently to give the corresponding
alcohols in good to excellent yields (Table 3). The reaction
rates of ketones were relatively slower than those of
aldehydes perhaps due to the steric hindrance. However,
even the hindered benzophenone also gave high isolated
yield of product (90%) after prolonged reaction time
TABLE 2 Suzuki–Miyaura coupling reaction catalyzed by
PEIS@Pd(0)
a
Entry
R1
R2
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
H
H
2 (Run 1)
87
89
88
86
86
85
89
90
92
87
88
2 (Run 2)
(Table 4, Entry 9). No significant and regular electronic
2 (Run 3)
effects of electron–donating and electron–withdrawing
substituents could be observed. Dehalogenation is a possible
side reaction occurs under reductive conditions. In the case
of 4–bromobenzaldehyde (Table 4, Entry 4), no
dehalogenation byproduct was detected. It is worth to
mention that 4‐nitrobenzaldehyde gave a more complicated
result. No predictable products could be detected after the
consumption of starting aldehyde, instead of several uniden-
tified byproducts.
The recyclability of the PEIS@Pd was examined in the
reduction of 4‐bromobenzaldehyde. The catalyst was
separated from the reaction mixture by simply centrifugation
after each cycle and the clear supernatant liquid was decanted
slowly. The residual catalyst was washed thoroughly with
ethyl acetate, followed by drying at 60°C for 2 h. Then, the
catalyst was reused with a fresh charge of reactants for subse-
quent recycle runs under the same conditions. Desired prod-
ucts were obtained in 87, 90, 89, 88 and 86% yield, indicating
2 (Run 4)
2 (Run 5)
2 (Run 6)
H
4‐Cl
H
3
3
3
3
4
4‐Me
4‐Br
H
H
1
0
2
3‐NO
2
1
4‐Me
2‐OMe
a
Conditions: bromoarenes (2 mmol), arylboronic acid (3 mmol), PEIS@Pd(0)
(2mol% Pd), K
2
CO
3
(3 mmol), EtOH (3 ml) and water (3 ml), 75°C.
b
Isolated yields.
industrial researches. In catalytic transfer hydrogenations,
palladium–based catalysts are considered to be the most
[
36]
effective.
Encouraged by the impressive results for the

FU ET AL.
7 of 9
TABLE 3 A comparison of the efficiency of PEIS@Pd(0) with several supported nano Pd catalyst in Suzuki–Miyaura coupling reaction
‐
1
Entry
Catalyst
Pd–Ni(20)/RGO
Pd/3–ampy–rGO
Pd–CoFe NPs
Time (min)
Yield (%)
TON
TOF (h )
Ref.
[
[
[
[
[
[
[
[
[
27]
1
2
3
4
5
6
7
8
9
15
20
59
95
9687
23750
49
38750
71250
4
28]
29]
30]
31]
32]
33]
34]
35]
2
O
4
720
360
360
240
60
79
Pd on aminopropyl polymethylsiloxane
Pd on magnetic mesoporous support
Pd on magnetic hollow carbon
100
77
50
8
77
13
97
97
24
Pd–CS@SiO
2
90
90
90
Pd on biguanide SBA–15
Pd on hollow mesoporous spheres
PEIS@Pd(0)
55
99
99
119
12
480
120
98
98
1
0
87
44
22
This work
the reused catalyst was efficient for all the six runs (Table 4,
Entries 4–9).
As bifunctional ketenes with both carbonyl group and
double bond, chalcones were selected to probe the
chemoselectivity of PEIS@Pd in transfer hydrogenation
(Scheme 3, Route B). It was found that the double bonds of
chalcones were hydrogenized in 100% conversion, whereas
the carbonyl groups remained untouched (Table 5). It is in
accord with the previously reported results about transfer
hydrogenation (HCOONH or HCOOH as hydrogen donor)
4
SCHEME
hydrogenation of carbonyl compounds
3
PEIS@Pd(0)–catalyzed chemoselective transfer
in the presence of homogeneous Pd–heterocyclic carbene
[
37]
[38]
catalyst, polymer–stabilized Pd Nps or HAP–supported
[39]
Pd(0) catalyst.
The effect of stoichiometry on chemoselectivity was thus
explored as follow. After the double bonds were completely
hydrogenized, more ammonium formate (equimolar to that
in the first stage) was charged in the reaction mixture. After
stirring for another 12 hours, the carbonyl groups still
remained untouched. This fact further confirmed the
chemoselectivity of this catalyst.
TABLE 4 The transfer hydrogenation of carbonyl compounds with
HCOONH catalyzed by PEIS@Pd(0)
4
a
Entry
R1
R2
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
H
H
H
H
H
4
86
90
91
89
87
90
89
88
86
88
87
86
89
90
4‐Me
4‐Cl
4‐Br
4
6
6 (Run 1)
6 (Run 2)
6 (Run 3)
6 (Run 4)
6 (Run 5)
6 (Run 6)
7
TABLE 5 Chemoselective transfer hydrogenation of chalcones with
a
4
HCOONH catalyzed by PEIS@Pd(0)
Entry
R3
R4
Time (h)
Yield (%)b
1
2
3
4
5
H
H
12
10
10
15
15
15
88
86
89
83
89
90
10
11
12
13
14
4‐OMe
H
H
H
H
4‐Cl
Me
Me
Me
Ph
8
2,4‐Cl
2
4‐Me
4‐OMe
H
10
H
2‐OH
4‐OMe
H
10
H
18
6
4‐OMe
a
a
Reaction conditions: substrates (5 mmol), HCOONH
10% mol), CH CN (4 ml), H O (4 mL), 60°C.
4
(20 mmol), PEIS@Pd(0)
Reaction conditions: chalcones (5 mmol), HCOONH
4
(20 mmol), PEIS@Pd(0)
(
3
2
3 2
(10% mol), CH CN (4 ml), H O (4 ml), 60°C.
b
b
Isolated yields.
Isolated yields.

8
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FU ET AL.
3
| CONCLUSIONS
(20 ml×3) to remove unreacted isocyanate, and dried under
vacuum at 40°C for 2h. Desired isocyanate–functionalized
starch was obtained as a white powder (26.80 g).
In conclusion, we report our investigation results on the use of
polyethylenimine–grafted polysaccharide as functional sup-
port of noble metal nanocatalysts. Isocyanate–functionalized
starch was attached with PEI and was loaded with Pd
nanoparticles by treating the functional surface with PdCl2,
followed by reduction. TEM images revealed that the support
was fully loaded with well‐dispersed Pd nanoparticles. The
catalyst PEIS@Pd(0) was then evaluated for the Suzuki
coupling and transfer hydrogenation reactions to afford good
to excellent yields. It is important to note that the supported
catalyst could be recovered by simple filtration and reused at
least five times without significant loss of its catalytic activity,
which confirmed the good stability of the catalyst.
4
.3 | Preparation of polyethyleneimine grafted
starch (PEIS)
14.00 g of isocyanate–functionalized starch was suspended in
a solution of 14.00 g polyethyleneimine in 50 mL anhydrous
acetonitrile. The mixture was stirred at room temperature for
3 h. The grafted starch was collected by filtration and washed
with acetonitrile (10 ml×4). After being dried under vacuum,
19.92 g of PEIS was obtained as free–flowing white powders.
4.4 | Preparation of PEIS@Pd(0)
To a suspension of PEIS (1.00 g) in 5 ml of acetonitrile was
added 0.18 g (1 mmol) of palladium chloride. The mixture
was stirred at 40°C for 12 h. Then 20 ml of ethanol contain-
ing 76 mg (2 mmol) of sodium boronhydride was slowly
dropped into the suspension under vigorous stirring. After 2
h of reduction, the products were obtained by filtration,
washed thoroughly with deionized water (10 mL×3) and
ethanol (10 ml×3). Following the product was dried under
vacuum to obtain PEIS@Pd(0) as a black powder (1.10 g).
4
| EXPERIMENTAL
.1 | General
4
All chemicals and solvents were purchased from commercial
sources and used as received. Maize starch used in this work
was purchased from RONGS Co. Ltd. (food grade; catalogue
number: 69023738; 20–25% amylose, ash ≤ 0.15%, lipids 0%).
The PEI was purchased from Aldrich with an average molecu-
lar weight of 600. Melting points were recorded on a Buchi
B–540 apparatus. FT–IR spectra were taken on a Thermo
Nicolet 6700 FTIR spectrophotometer using KBr pellets.
XRD patterns were recorded on a Rigaku D/MAX 2550 VB/PC
4.5 | General procedure for the Suzuki–
Miyaura coupling catalyzed by PEIS@Pd(0)
Arylboronic acid (3 mmol), substituted bromobenzene
diffractometer with monochromatized Cu K radiation at a
setting of 40 kV and 100 mA. H and C NMR spectra were
measured on a Bruker AC 400 instrument in CDCl using
α
(
2 mmol), K CO (0.41 g, 3 mmol) and 44 mg (2% mol) of
1
13
2 3
PEIS@Pd(0) were added to a 20 mL reaction vial containing
EtOH (3 mL) and water (3 ml). The mixture was stirred at
3
TMS as an internal standard (see Supporting Information).
Mass spectra were recorded on a Shimadzu QP 1100 EX mass
spectrometer (ionization potential 70 eV). The morphology
of the samples was observed using JEOL JSM–6360 LV
scanning electron microscope and JEOL JEM–1400 trans-
mission electron microscope. The loading of palladium
was determined on an Agilent 725 ES inductively coupled
plasma atomic emission spectrophotometer (ICP–AES).
7
(
5°C for a specified period as monitored by TLC or GC
Table 2). On completion of the reaction, the mixture was
filtered and the catalyst was washed successively with water
1 mL) and EtOH (1 ml). The combined filtrate was then
(
extracted by ethyl acetate (3 ml×3). Combined organic layer
was then dried over anhydrous Na SO and concentrated
2
4
under reduced pressure. The residue was purified by column
chromatography on silica gel with a mixture of EtOAc: PE
(
v/v = 1: 10) to give pure product.
4
.2 | Preparation of isocyanate–functionalized
starch
4.6 | General procedure for the transfer
hydrogenation catalyzed by PEIS@Pd(0)
In a 250 ml round–bottomed flask equipped with a drying
tube, 16.01 g (100 mmol) of p–phenylene diisocyanate was
dissolved in a mixture of anhydrous acetonitrile (20 ml) and
DMF (50 ml). Then 16.20 g (100 mmol glucose unit) of
pre–dried maize starch was added in one portion. The
resulting suspension was stirred at room temperature for
To a solution of HCOONH (1.26 g, 20 mmol) in CH CN
4
3
(4 ml) and water (4 ml) was added 0.55 g (10% mol) of Pd(II)
loaded PEIS. The mixture was stirred at 60°C for 30 min (the
color of catalyst changed from yellow–gray to black rapidly).
Afterwards 5 mmol of carbonyl compounds (aldehydes,
ketones or chalcones) was then introduced into the reaction
vessel. The stirring continued to the appropriate time as
12 h. The solid was filtered, washed successively with
anhydrous DMF (20 ml×3) and anhydrous ethyl acetate

FU ET AL.
9 of 9
monitored by TLC or GC (Table 2 and 3). On completion of
the reaction, the mixture was filtered and the catalyst was
washed with ethyl acetate (3 ml×3). The aqueous filtrate
was then extracted by ethyl acetate (3 ml×3). Combined
EA extracts was dried over anhydrous Na SO and concen-
trated under reduced pressure. The residue was purified by
column chromatography on silica gel with a mixture of
EtOAc: PE (v/v = 1: 10) to give pure product.
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How to cite this article: Fu L, Deng W, Liu L, Peng
Y. Nanopalladium on polyethylenimine–grafted starch:
an efficient and ecofriendly heterogeneous catalyst for
Suzuki–Miyaura coupling and transfer hydrogenation
reactions. Appl Organometal Chem. 2017;e3853.
https://doi.org/10.1002/aoc.3853
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