T. Baran, A. Mente s¸ / Journal of Organometallic Chemistry 803 (2016) 30e38
37
Table 2
and 10); this can be accounted for the poor activity of the aryl
chlorides in Suzuki coupling reactions [33]. The activity tests were
also conducted in the presence of electron withdrawing groups
The data of ICP-OES and elemental analysis.
Compound
Element (%)
(please refer to the entries 6 and 7) and still, high conservation
Cu
Pd
C
H
N
C/N
values were achieved. The turnover numbers (TON) and turn over
frequency (TOF) values [34] of all the products were observed to be
consistent with the literature reports (Table 4).
CS
-
-
-
-
-
43.14
49.35
6.78
6.10
8.34
5.86
5.17
8.42
[
[
OCMCS-2a]
OCMCS-2a-PdCl
2
]
26.1
3.9. Mercury poisoning experiments
Table 3
Effect of Pd complexes on CeC coupling reaction.
The mercury poisoning tests are generally conducted to reveal
the nature of the catalyst in question; homogeneous or heteroge-
neous. It is already known that a catalyst with a homogeneous
nature is not affected by the presence of mercury, while a hetero-
geneous catalyst is poisoned and loses its activity [35,36]. The
mercury poisoning tests showed that the catalyst lost its activity
upon addition of mercury; indicating that the catalyst had a het-
erogeneous nature [23].
Catalyst Yield (%)
PdCl
2
16
33
Na PdCl
OCMCS-2a-PdCl
2
4
[
2
]
>99
Reaction conditions: 1.12 mmol 4-bromoanisole, 1.87 mmol
phenyl boronic acid, 3.75 mmol K
mL toluene, 100 C, 12 h.
2
CO
3
, 0.02 mol % catalyst,
ꢀ
6
3
.10. Reusability test of catalyst
[
31] given below:
DS ¼ [(aC/N) e (C/N)
where (C/N) is the C/N of the modified chitosan ([OCMCS-2a]) (C/
Reusability tests of the catalyst were investigated and the results
m
o
]/ n
are presented in Table 5. Prior to the reusability tests, the catalyst
was activated by rinsing with water and hot methanol. Under op-
timum conditions, the activated catalyst was used in the model
reactions. The catalyst did not lose its activity even after six runs.
m
N) is the C/N of the CS, and a and n are the number of nitrogen and
carbon introduced after CS modification, respectively.
o
3.11. Leaching test
3.8. Catalysis of the Suzuki reaction
Subsequent to each reusability run, the products were removed
Under the optimum conditions the catalytic efficiencies of the
catalyst, the commercial PdCl and Na PdCl compounds were
2 2 4
from the reaction media and the filtrate was assayed with an ICP-
OES to detect the presence of any leached Pd(II) ions in the
organic phase. The assay showed the absence of Pd(II) ions in the
filtrate; this is the consistent with the heterogeneous nature of the
catalyst [23].
tested in the model Suzuki coupling reaction (Table 3). It was
revealed that the catalytic activity of the catalyst was significantly
higher than the commercial palladium compounds. To determine
the activity of the catalyst on the different substrates, the reaction
of phenyl boronic acid with different aryl halides were studied and
the results are listed in Table 4. The high conversion values (with
the exception of the entry 3) demonstrated that the reactions with
aryl bromides occurred with high efficiencies (the entries 1 to 7).
The comparison of aryl iodides with aryl chlorides revealed that the
reactions with aryl iodides were achieved with higher yields (entry
4. Conclusions
In this study a new chitosan based water soluble Schiff base was
produced through carboxymethylation of chitosan. Also, a novel
Pd(II) complex of the Schiff base was synthesized and used as a
catalyst in Suzuki coupling reactions. The identification of the
1
13
8
). These discrepancies observed in the conversion values can be
products were performed with FTIR, H NMR, C CP-MAS NMR, TG/
DTG, SEM/EDAX, XRD, ICP-OES, UVeVis, magnetic moment mea-
surements, molar conductivity measurements, mercury poisoning
and leaching tests. The catalytic activity of the synthesized Pd(II)
complex was tested in the synthesis of 10 biarlys compounds
explained with referring to the ionic radii of the halogens and the
bond dissociation energies [23,32]. These findings are consistent
with the reports in the literature [23,32]. The lowest conversion
values were recorded in the presence of aryl chlorides (the entries 9
Table 4
Effect of complexes on Suzuki cross-coupling reaction.
Entry
X
Y
Yield (%)
TON
TOF
[OCMCS-2a-PdCl
2
]
[OCMCS-2a-PdCl
2
]
2
[OCMCS-2a-PdCl ]
1
2
3
4
5
6
7
8
9
Br
Br
Br
Br
Br
Br
Br
I
3-OCH
4-OCH
3
3
95
4750
5000
1850
4950
4900
4600
4650
3050
400
396
417
154
412
408
383
387
254
33
>99
37
99
98
92
93
61
8
3-CH
3
3-NH
4-NH
2
2
4-NO
4-CN
2
4-CH
3-OCH
4-CH
3
Cl
Cl
3
10
3
12
600
50
ꢀ
2 3
CO , 0.02 mol % catalyst, 6 mL toluene, 100 C, 12 h.
Reaction conditions: 1.12 mmol aryl halide, 1.87 mmol phenyl boronic acid, 3.75 mmol K
TON: (turnover number, yield of product/per mol of Pd).
TOF: (turn over frequency, TON/time of reaction).