Exceptionally high turnover frequencies recorded for a new chitosan-based palladium(II) catalyst

Article abstract of DOI:10.1016/j.apcata.2016.05.012

To be industrially feasible, and applicable in synthesis of fine chemicals, a catalyst has to possess high turnover number (TON) and turnover frequency (TOF). In this study, a new cross-linked chitosan derivative was synthesized by using 2,2′-pyridil as a cross-linking agent. 2,2′-Pyridil cross-linked chitosan was used to as a support material for palladium catalyst. Chitosan-pyridil-based Pd(II) catalyst was tested in the microwave-assisted synthesis of biaryls via Suzuki coupling reactions. The catalyst yielded remarkable TONs of up to 20,000 and TOFs of up to 240,964 by using very low catalyst loading (5 × 10^-3% mol) in a short reaction time (5 min). The catalyst also showed a better recyclability.

Full text of DOI:10.1016/j.apcata.2016.05.012

Accepted Manuscript
Title: Exceptionally high turnover frequencies recorded for a
new chitosan-based palladium(II) catalyst
Author: Talat Baran Idris Sargin Ayfer Mente s¸ Murat Kaya
PII:
S0926-860X(16)30245-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2016.05.012
APCATA 15875
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
7-2-2016
5-5-2016
12-5-2016
Please cite this article as: Talat Baran, Idris Sargin, Ayfer Mente s¸ ,
Murat Kaya, Exceptionally high turnover frequencies recorded for
a
new chitosan-based palladium(II) catalyst, Applied Catalysis A, General
http://dx.doi.org/10.1016/j.apcata.2016.05.012
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Exceptionally high turnover frequencies recorded for a new
chitosan-based palladium(II) catalyst
1
*
2
1
2
Talat Baran , Idris Sargin , Ayfer Menteş , Murat Kaya
1Department of Chemistry, Faculty of Science and Letters, Aksaray University, Aksaray,
8100 Aksaray, Turkey.
6
2Department of Biotechnology and Molecular Biology, Faculty of Science and Letters,
Aksaray University, 68100 Aksaray, Turkey.
Corresponding author: Address: Department of Chemistry, Faculty of Science and Letters,
Aksaray University, Aksaray, Turkey, 68100
Tel.: +903822882142; Fax: +903822882142, E-mail address: talatbaran_66@hotmail.com
Email: talatbaran_66@hotmail.com
Email: idrissargin@hotmail.com
Email: ayfermentes@yahoo.com
Email: muratkaya3806@yahoo.com

Graphical Abstract
Highlights



A new cross-linked chitosan was obtained using 2,2′-Pyridil as a cross-linking agent
2,2′-Pyridil cross-linked chitosan was used as support for palladium catalyst
The catalyst yielded excellent TONs of up to 20000 and TOFs of up to 240964
Abstract
To be industrially feasible, and applicable in synthesis of fine chemicals, a catalyst has to
possess high turnover number (TON) and turnover frequency (TOF). In this study, a new
cross-linked chitosan derivative was synthesized by using 2,2′-Pyridil as a cross-linking agent.
2
,2′-Pyridil cross-linked chitosan was used to as a support material for palladium catalyst.
Chitosan-pyridil-based Pd(II) catalyst was tested in the microwave-assisted synthesis of
biaryls via Suzuki coupling reactions. The catalyst yielded remarkable TONs of up to 20000
and TOFs of up to 240964 by using very low catalyst loading (5x10−3 % mol) in a short
reaction time (5 min). The catalyst also showed a better recyclability.
Keywords: Suzuki coupling; pyridil; cross-linking; TON; TOF
1
. Introduction
The reactions of aryl halides with organo-boronic acids are known as Suzuki C−C coupling
reactions [1]. Chitosan has been widely used as a catalyst support material in the synthesis of
biaryls via Suzuki coupling reactions [2]. This versatile natural polymer has free hydroxyl and

amino groups. Especially through reactive amino groups, chitosan can be cross-linked easily
in order to enhance its metal ion affinity and mechanical strength. These unique properties
make chitosan a basic material for homogeneous and heterogeneous catalyst systems.
Numerous chitosan derivatives have been tested in different catalyst systems [1, 3-5].
Particularly chitosan-based ligands with imine groups are preferred for Suzuki coupling
reactions due to ease of production and high metal binding capacity. Cross-linking agents like
glyoxal, β-cyclodextrin polyaldehyde and glutaraldehyde have been used to form imine
groups within the polymer matrix [6]. Among them, glutaraldehyde is commonly preferred to
cross-link chitosan but its toxicity creates health issues. Hence, some researchers attempted to
design chitosan derivates using different cross-linking agents to make chitosan more selective
2
2
to platinum group metals [7]. Due to its high activity in C(sp )− C(sp ) coupling reactions,
palladium is the most widely preferred transition metal [8]. On the other hand, the activity of
any palladium catalyst is proportional to the number palladium ions coordinated to the ligand.
Ligands having more donor atoms (e.g., O, N, S) provide more coordination sites for the
metal ion to bind. In this respect, through the condensation of 2,2′-Pyridil, which has
diketone, with amino groups of chitosan, imine groups can be created. Therefore, 2,2′-Pyridil
can be used as a new cross-linking agent for chitosan. Due to the diimine groups that are
formed via the condensation, 2,2′-Pyridil cross-linked chitosan can function as a better ligand
for palladium ions to coordinate. Thus, a better selectivity, high turnover number (TON) and
turnover frequency (TOF) values can be achieved in Suzuki coupling reactions. Catalysts with
3
>
10 TONs are considered as high turnover catalyst (HTC). In a catalyst system, high
turnover numbers can be achieved with high product yields and low catalyst loading, and high
TOF values can be obtained with very short reaction time. Catalysts displaying high TONs
and TOFs are deemed as more economical and practical [9, 10]. Such catalyst systems can be
transferred from academic laboratories to the industrial applications. Especially high TOF
catalysts can be utilized in pharmaceutical and fine chemical applications [11].
This study aimed to synthesize a novel, 2,2′-Pyridil cross-linked chitosan derivative to be used
as a HTC support for palladium-catalysed Suzuki C−C coupling reactions. This new support
material was used for production of a palladium catalyst. 2,2′-Pyridil cross-linked chitosan
derivative and the Pd(II) catalyst (chitosan-pyridil-based Pd(II)) were characterized using FT-
IR, TGA, SEM-EDAX, ICP-OES and XRD. The catalytic activity of chitosan-pyridil-based
Pd(II) catalyst was tested in the microwave-assisted synthesis of biaryls without addition of
any solvent. In the tests experiments a very low catalyst loading (5x10−3 % mol) exhibited

better selectivity and gave exceptionally high TONs (2800−20000) and TOFs of up to
2
40964.
2
2
. Materials and methods
.1. Materials
Chitosan (448877-250G, deacetylation: 75-85%), 2,2′-Pyridil, acetic acid, palladium chloride,
sodium chloride, phenyl boronic acid, aryl halides, sodium hydroxide, potassium hydroxide,
sodium carbonate, acetonitrile, toluene and ethanol were obtained from Sigma-Aldrich and
used as supplied.
2
.2. Instrumentation
FT-IR spectra of 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-based Pd(II) catalyst
were recorded on a Perkin Elmer Spectrum 100 FTIR spectrophotometer. Thermal stability of
the products was studied on an EXSTAR S11 7300 (nitrogen atmosphere; heating range: 30-
6
50°C). The surface morphology of the samples was examined on a QUANTA-FEG 250
ESEM. The analyses of palladium and chloride ions on the catalyst were done using an
EDAX-Metek. X-ray diffractions of 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-
based Pd(II) catalyst were recorded on a Rigaku D max 2000 system (at 40 kV, 30 mA and
2
θ with a scan angle:5−50°). Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halendar
(
BJH) analyses were conducted on Gemini VII 2390 V1.03 (analysis adsorptive: N ;
2
equilibration time: 5 s; saturation pressure: 697.426 mmHg; evacuation rate: 100.0
mmHg/min; sample mass: 0.3590 g). Palladium ion content of the catalyst was analysed by
using Perkin Elmer Optima 2100 DV Inductively Coupled Plasma (ICP) Optical Emission
Spectrometer (OES). Synthesis of biaryl compounds was conducted using a domestic
microwave oven. Identification of the biaryls was done by using GC-MS Agilent GC-7890 A-
MS 5975.

2
.3. Synthesis of chitosan-pyridil-based Pd(II) catalyst
Preparation of 2,2′-Pyridil cross-linked chitosan
Chitosan solution (2% w:w) was prepared in 25 mL of acetic acid solution (2% v:v) and then
dropped into a coagulation solution containing methanol (60 mL), water (40 mL) and sodium
hydroxide (12 g) to obtain gelatinous chitosan beads. Then the chitosan beads were rinsed
extensively with distilled water to neutrality. Subsequently, gelatinous chitosan beads were
transferred into solution of 2,2′-Pyridil (0.2 g) and ethanol (50 mL), stirred under reflux for 24
h. Finally, yellow-orange product was removed by filtration, washed with ethanol to eliminate
unreacted 2,2′-Pyridil and dried at room temperature.
Preparation of chitosan-pyridil-based Pd(II) catalyst
First, 2,2′-Pyridil cross-linked chitosan (0.25 g) was suspended in water (25 mL). Then, water
solution of Na
2
PdCl (0.4 g, 15 mL) was added into the suspension, stirred for 6 h at 60°C.
4
Finally, the yellowish-green product was filtrated out and washed with water. As we
conducted synthesis of biaryl in solvent-free media under microwave heating, dried chitosan-
pyridil-based Pd(II) catalyst was powdered to increase the surface area on the catalyst prior to
use.
2
.4. Synthesis of biaryls
2
.4.1. Optimisation
In optimisation studies for the coupling reactions, we used a model reaction of 4-bromoanisol
with phenyl boronic acid under microwave irradiation. We tested optimum conditions for the
base system, catalyst loading and reaction time. In the model reaction, the highest yield was
achieved with K
2
CO
3
base system (NaOH: 65 %, KOH: 78 %, K
2
CO : >99%). Catalyst
3
loading is the key parameter to achieve high TON and TOF values. 5x10−3 % mol catalyst
loading gave the highest TONs and TOFs (Fig. 1).
To determine optimum reaction time, the model reaction was conducted at different reaction
times; 1-6 min. The highest product yield of 4-methoxybiphenyl was observed at 5 min (Fig.
2
).

2
.4.2. General procedure
The mixture of phenyl boronic acid (1.75 mmol), aryl halide (1.12 mmol), K
2
CO (3.75
3
mmol) and the catalyst (5x10−3 % mol) in a Schlenk tube was exposed to the microwave
irradiation (at 400 W) at 50°C for 5 min. The progress of the reactions was monitored by thin
layer chromatography (TLC). Then, reaction medium was extracted with toluene-water
mixture (2:1 v:v) and the organic phase was dried with addition of MgSO4. Finally, chemical
identification of the biaryls was done on a GC-MS.
2
.4.3. Recovery and reusability
At end of the each coupling reaction, the catalyst was recovered from the media by vacuum
filtration, washed with water and hot methanol to reactivate. In reusability tests, the
reactivated catalyst was used in the model reaction by following the general procedure.
2
.4.4. Chitosan-pyridil-based Pd(II) catalyst in conventional heating system
To draw a comparison between the microwave heating and conventional reflux-heating, the
catalytic activity of chitosan-pyridil-based Pd(II) catalyst in synthesis of 4-methoxy-biphenyl
was tested on the model reaction in conventional reflux-heating system. We followed the
general procedure as detailed in section 2.4.2, but here we used solvent i.e., toluene (6 mL)
and reaction media was refluxed on a heater at 100°C for 24 h under nitrogen atmosphere.
3
3
. Results and discussions
.1. Characterisation studies
FT-IR spectra analysis
FT-IR spectra of chitosan, 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-based Pd(II)
−
1
catalyst are presented in Fig. 3a, b and c, respectively. The peak appeared at 1647 cm in the
spectrum of 2,2′-Pyridil cross-linked chitosan corresponds to the imine group stretching (Fig.
3
b) [12]. Two bands observed at 1582 and 1562 cm−1 can be attributed aromatic ring C=C
stretching of 2,2′-Pyridil (Fig. 3b). In addition, we did not observe any bands for carbonyl
group stretching of 2,2′-Pyridil. These observations confirmed the condensation of 2,2′-Pyridil
with chitosan via amino groups.

In the spectrum of chitosan-pyridil-based Pd(II) catalyst, imine stretching vibration bands
−
1
were shifted to lower wave number (1628 cm ), indicating that involvement of imine groups
into coordination bonds (Fig. 3c) [12, 13].
TG/DTG analysis
Thermal stability of chitosan, 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-based
Pd(II) catalyst was investigated (Fig. 4). As seen in the thermograms, 2,2′-Pyridil cross-linked
chitosan (292°C) exhibited relatively lower thermal stability than unadulterated chitosan
(302°C). This lower thermal stability can be attributed to the decrease in the number amino
groups involving in hydrogen bond formation [14]. On the other hand, a further decrease was
recorded for chitosan-pyridil-based Pd(II) catalyst (218°C), which is the indication of lower
crystallinity of chitosan following the coordination of palladium ion. Additionally, it is highly
probable that the presence of palladium ions catalysed the thermal degradation of chitosan
chains [15].
SEM-EDAX analysis
Surface morphology of chitosan, 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-based
Pd(II) catalyst was displayed in Fig. 5. After the condensation of 2,2′-Pyridil with chitosan,
the surface features of unadulterated chitosan changed completely by giving a rougher coarse
irregular surface. However, the catalyst showed a regular surface morphology compared to its
ligand material. Also, in the EDAX spectrum of the catalyst (Fig. 6), the peaks for palladium
and chloride ions were observed, verifying the coordination of palladium ions to the 2,2′-
Pyridil cross-linked chitosan.
Palladium ion content of the catalyst was analysed on an ICP-OES. We determined 21.85 %
palladium content, which was very close the palladium content determined by EDAX (22.82
%).
X-ray diffractograms
X-ray diffractograms of chitosan, 2,2′-Pyridil cross-linked chitosan and chitosan-pyridil-based
Pd(II) catalyst are presented in Fig. 7a, b and c, respectively. As depicted in Fig.7a, two
characteristics peaks were observed at 10.4 and 19.8°. After cross-linking with 2,2′-Pyridil,

the peak at 10.4° disappeared and the peak at 19.8° widened (Fig. 7b). The diffractogram of
,2′-Pyridil cross-linked chitosan showed lower peak intensity and crystallinity than
2
unadulterated chitosan. This can be attributable to the decrease in the number of free amino
groups of chitosan following the condensation with 2,2′-Pyridil [16]. However, chitosan-
pyridil-based Pd(II) catalyst had the least peak intensity and crystallinity, demonstrating the
amorphous nature of the catalyst compared to its ligand and chitosan. Also, the peak at 40.8°
(
111 plane) is the indication of palladium ion [17]. This behaviour is in the line with previous
studies where the decrease in the crystallinity was ascribed to the metal ion coordination [12,
4].
1
BET analysis
BET and BJH analyses of chitosan-pyridil-based Pd(II) catalyst was performed. The results
demonstrated that the catalyst has porous nature (Table 1).
3
.2. Catalytic activity of chitosan-pyridil-based Pd(II) catalyst
The catalytic performance of chitosan-pyridil-based Pd(II) catalyst was tested in the
microwave-assisted coupling reactions of aryl halides with phenyl boronic acid under
optimum conditions in a solvent-free media (Scheme 2). The corresponding reaction yields,
TON and TOF values are listed in Table 2. The coupling reactions with aryl bromides gave
higher yields over the reactions with aryl iodides and aryl chlorides. This can be explained by
the bond dissociation energies and ionic radii of halides [1]. Due to their poor reactivity, aryl
chlorides produced the lowest reaction yields. This observation is consistent with the previous
literature reports [18]. As expected, for the all aryl halides the coupling reactions with
electron withdrawing groups yielded higher conversation than with electron donating groups.
In addition, the position of substituent group on aryl halides affected the reaction yields. As
seen from Table 2, aryl halides with para-substituents gave the highest yield, whereas ortho-
substituents produced the lowest product yield. Chemical identification of biaryl compounds
were conducted by using GC-MS (Please refer to Supplementary Data for the spectra of the
biaryls). The spectra demonstrated that cross-coupling reactions occurred with high selectivity
without producing any by-products.

TONs and TOFs of miscellaneous Pd catalysts reported in the literature are listed in Table 3.
As clearly seen from the table, chitosan-pyridil-based Pd(II) catalyst yielded moderately high
TON and remarkably high TOF. Here in this study, we attained high TONs and TOFs by
−
3
using a very small amount of catalyst load (5x10 % mol) with only 5 min microwave
irradiation. These findings demonstrate that 2,2′-Pyridil cross-linked chitosan can be a
suitable support material for palladium catalyst from a economical standpoint.
3
.3. Reusability and leaching tests
Recycle tests with the model reaction under optimised conditions revealed that chitosan-
pyridil-based Pd(II) catalyst possessed a better longevity. The reaction yields, TON and TOF
values corresponding to each run are listed in Table 4. We achieved high conversation rates
even after 7 runs. At the end of each cycle, negligible activity losses were observed. In the
−3
experiments, the catalyst load was relatively low; 5x10 % mol (3 mg), and the catalyst was
recovered by filtration from the reaction medium. It appears that some losses in the catalyst
amount during the separation are inevitable regarding such a low catalyst amount. Therefore,
the losses in catalytic activity can be attributed to the material loss. However, we also
conducted palladium leaching tests for the catalyst after seventh run. ICP-OES results
revealed ~2% leaching of palladium ions from the catalyst. This can be another contributor in
catalytic activity loss observed in reusability tests.
SEM images and EDAX spectrum of the catalyst after seven run are presented in Fig. 8.
Compared to the SEM images of the catalyst depicted in Fig. 5, it appears that surface
morphology of the catalyst remained smooth and no aggregation was observed. Also, the
EDAX spectrum of the catalyst confirmed the presence of palladium ion even after seven
runs.
Reaction conditions: 1.12 mmol 4-bromoanisole, 1.87 mmol phenyl boronic acid, 3.75 mmol
-3
base, 5x10 % mol chitosan-pyridil-based Pd(II), 50 °C, 5 min (~ 0.08 h) under MW
3
.4. Comparison of the catalytic activity of chitosan-pyridil-based Pd(II) catalyst
Under the optimised conditions, catalytic performance of two commercially available
palladium catalysts PdCl , Na PdCl and PdCl (CH CN) were investigated in the model
reaction. The commercial catalysts were less effective and their TON, TOF and reaction
2
2
4
2
3
2

yields are presented in Table 5. As seen, chitosan-pyridil-based Pd(II) catalyst showed higher
reaction yields, TON and TOF over the catalysts PdCl , Na PdCl and PdCl (CH CN)
Reaction conditions: 1.12 mmol 4-bromoanisole, 1.87 mmol phenyl boronic acid, 3.75 mmol
2
2
4
2
3
2
.
-3
base, 5x10 % mol catalyst, 50 °C, 5 min (~ 0.08 h) under MW
3
.5. Performance of chitosan-pyridil-based Pd(II) catalyst in conventional heating
system
In conventional reflux-heating system, we recorded low reaction yield and TON and TOF
values for chitosan-pyridil-based Pd(II) catalyst (Please refer to entry 18 Table 2). These
findings demonstrated that chitosan-pyridil-based Pd(II) catalyst is more suitable for
microwave irradiation technique.
4
. Conclusions
This study demonstrated that 2,2′-Pyridil cross-linked chitosan is an excellent polymeric
2
2
support for palladium catalysed Suzuki C(sp )−C(sp ) cross-coupling reactions. In
microwave-assisted synthesis of biaryls, chitosan-pyridil-based Pd(II) catalyst yielded
outstanding TONs and TOFs. These remarkable TONs and TOFs were attained with very low
catalyst loading (5x10−3 % mol) in a short span of time (5 min). This new high turnover
catalyst also exhibited better recyclability by retaining its activity up to 7 cycles. Catalysts
enjoying high TONs and TOFs are desired for applications in pharmacology and industrial
operations. In further studies, 2,2′-Pyridil cross-linked chitosan can used as support material
for other transition metals. The catalytic performance of chitosan-pyridil-based Pd(II) catalyst
should be tested in palladium catalysed Heck reactions.
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[
2
Figure and Scheme Captions
Fig.1 The effect of catalyst loading on Suzuki coupling reaction
Fig. 2 The effect of reaction time on Suzuki coupling reaction
Fig.3 FT-IR spectra of a) chitosan, b) 2,2′-Pyridil cross-linked chitosan, c) chitosan-pyridil-
based Pd(II) catalyst
Fig.4 TG/DTG diagrams a) chitosan, b) 2,2′-Pyridil cross-linked chitosan, c) chitosan-pyridil-
based Pd(II) catalyst
Fig. 5 SEM images of 2,2′-Pyridil cross-linked chitosan (a-c), chitosan-pyridil-based Pd(II)
catalyst (d-f)
Fig. 6 EDAX spectrum of chitosan-pyridil-based Pd(II) catalyst
Fig.7 XRD diagrams of a) chitosan, b) 2,2′-Pyridil cross-linked chitosan, c) chitosan-pyridil-
based Pd(II) catalyst
Fig. 8. SEM images and EDAX spectrum of chitosan-pyridil-based Pd(II) catalyst after seven
run
Scheme 1. Preparation of chitosan-pyridil-based Pd(II) catalyst
Scheme 2. Possible mechanism for Suzuki coupling reaction catalysed by chitosan-pyridil-
based Pd(II) catalyst.

.
.................................................................Figure 1...............................................
.
.................................................................Figure 2...............................................

.
.................................................................Figure 3...............................................
.
.................................................................Figure 4...............................................

.
.................................................................Figure 5...............................................
.
.................................................................Figure 6...............................................

.
.................................................................Figure 7...............................................

…
…………………………………………..Figure 8…………………………………..
…
………………………………………….Scheme 1……………………………………….

…
………………………………………….Scheme 2………………………………………..
Table 1. BET and BJH analyses of results of Chitosan-pyridil-based Pd(II) catalyst
Surface
Single point surface area
BET surface area
0.0688
0.0284
area
2
(
m /g)
BJH adsorption cumulative surface area of pores 0.001
7.000-3000.000 Å width
Single point adsorption total pore volume
1
Pore
0.000015
volume
BJH adsorption cumulative volumes of pores 17.000- 0.000024
3000.000 Å width
3
(cm /g)
Pore size
Å)
Adsorption average pore size (4V/A by BET)
BJH adsorption average pore width (4V/A)
20.6525
708.698
(

Table 2. Effect of chitosan-pyridil-based Pd(II) catalyst on Suzuki C-C reactions
Entry
X
Y
Yield (%)
TON
TOF
1
Br
2-OCH
3
3
3
91
18200
219277
2
3
4
5
6
7
8
9
Br
Br
Br
Br
Br
Br
Br
I
3-OCH
4-OCH
95
>99
85
88
79
82
84
33
19000
20000
17000
17600
15800
16400
16800
6600
228916
240964
204819
22000
3-NH
4-NH
3-NO
4-NO
4-CN
2
2
2
2
190361
205000
210000
82500
2-CH
3
1
1
1
1
1
1
0
1
2
3
4
5
I
I
I
I
CI
CI
3-CH
4-CH
4-OCH
3-NO
3-OCH
4-OCH
3
3
44
69
82
73
55
64
8800
106024
166265
197590
175904
137500
154217
13800
16400
14600
11000
12800
3
2
3
3
1
1
1
6
7
8*
CI
CI
Br
3-NO
4-CH
4-OCH
2
68
14
44
13600
2800
8800
163855
33735
367
3
3
Reaction conditions: 1.12 mmol aryl halide, 1.87 mmol phenyl boronic acid, 3.75 mmol
-3
K
2
CO
3
, 5x10 mol % chitosan-pyridil-based Pd(II) catalyst, 50 °C, 5 min (~ 0.08 h) under
MW.
TON: (turnover number, yield of product/ per mol of Pd).
TOF: (turn over frequency, TON/time of reaction (hour))
*
: Conventional heating method: 1.12 mmol aryl halide, 1.87 mmol phenyl boronic acid, 3.75
mmol K CO , 5x10-3 mol % catalyst, 100 °C, 24 h, 6 mL toluene
2
3

Table 3. TONs and TOFs of the Pd catalysts with miscellaneous supports for Suzuki C−C
cross-coupling reactions.
Support Material
Biopolymer–metal complex wool–Pd
Palladium Coordination Biopolymer
TON
188
243
TOF
38
49
References
[19]
[20]
Carboxymethyl chitosan supported palladium(II) 2450
catalysts
51
[5]
Nano Pd(0) supported on cellulose
320
980
1167
5000
220
58
[21]
[22]
[1]
[23]
[24]
[25]
[26]
Chitosan-supported Pd-nanoparticles
Pd nanosized particles supported on chitosan
Biomaterial supported Pd (II)catalyst
Chitosan as a support for heterogeneous Pd catalysts
Cellulose supported Pd(0) nanoparticles
Alginate/gellan-stabilized palladium nanoparticles
Palladium-supported sepiolite
196
292
417
1330
2256
188
193000 8042
65000
940000 39167 [28]
39000 [27]
Pd–sepiolite catalyst
Chitosan-pyridil-based Pd(II) catalyst
20000
240964 (present
Table 4. Reusability of chitosan-pyridil-based Pd(II) catalyst
Suzuki C-C reaction
The number of cycle
Reaction yield (%)
TON
TOF
st
1
2
3
4
5
6
>99
95
90
89
85
80
75
20000
19000
18000
17800
17000
16000
15000
240964
228916
216867
214458
204819
192771
180723
nd
rd
th
th
th
th
7
Table 5. Effect of different commercial Pd catalyst on C-C coupling reaction
Catalyst
PdCl
Na PdCl
PdCl
Reaction yield (%) TON
TOF
2
15
3000
36144
127711
139759
240964
2
4
53
58
>99
10600
11600
20000
2
(CH
3
CN)
2
chitosan-pyridil-based Pd(II) catalyst