26
X. Liu et al. / Journal of Organometallic Chemistry 768 (2014) 23e27
Table 3
obtained when 0.05 mol% Pd was used. Increasing the catalyst
loading did not have a significant beneficial effect on catalytic
performance during the reaction. Hence 0.05 mol% of catalyst was
used for further SuzukieMiyaura reactions. In summary, the
optimal condition was achieved using a combination of catalyst
(0.05 mol% Pd) and K2CO3 stirred in dioxane at reflux condition
(Table 1, entry 2).
Heck Reaction of Aryl Halides with terminal olefins catalyzed by catalyst 3b under
the optimal conditionsa.
Entry
R1
R2
X
Timeb/h
Yieldc/%
In an attempt to clarify the generality of the protocol, a range of
different aryl halides were reacted with substituted phenylboronic
acids under the optimal reaction conditions. A favorable effect of
electron-withdrawing substituents was normally observed in
palladium-catalyzed reactions. With our catalyst however,
electron-withdrawing groups in aryl bromides had relatively little
effect on the Suzuki coupling reaction. As shown in Table 2, aryl
iodides and bromides bearing electron-withdrawing and electron-
donating groups coupled efficiently with phenylboronic acid, and
generated the corresponding products in good to excellent yields
within 1 h (Table 2, entries 1e11). On the other hand, arylboronic
acids bearing electron-withdrawing and electron-donating groups
also coupled efficiently with 4-bromoanisole within 1 h and good
to excellent yields of the products were isolated (Table 2, entries
12e13). Although the homocoupling of arylboronic acids was
inevitable as a side reaction, it was noted that biphenyl come from
homocoupling of phenylboronic acid was no more than 1.5% of the
product mixture in all reactions. Moreover the homocoupling was
not observed to occur progressively throughout the reaction. In
palladium-catalyzed coupling reactions, oxidative addition to a Pd
(0) species was often the rate-determining step in the catalytic
cycle, and the relative reactivity typically decreases in the order of
I > OTf > Br [ Cl because of the different C-X dissociation energies.
For aryl chlorides, the electronic effect of substituents showed
different active. The electron-deficient substituted chlorobenzenes
such as 4-chloro-1-nitrobenzene could give 75% cross-coupling
products under the same conditions, while the electron-donating
substituents such as 4-amino-1-chlorobenzene only gave 35%
desired products (Table 2, entries 14e15). It was worthy
mentioning that arylboronic acids with an electron-withdrawing
substituent such as 2-(Trifluoromethoxy)phenylboronic acid
showed the lowest conversion, while active aryl chlorides with an
electron-donating substituent on the phenyl just like 4-Methox-
yphenylboronic acid gave better result (Table 2, entries 16e17).
Encouraged by the successful application of this novel polymer-
1
2
3
4
5
6
7
8
3-F
Ph(4-F)
Ph(4-F)
Ph(4-F)
Ph(4-F)
Ph(4-F)
Ph
Ph
Ph
Ph
Ph
I
I
I
I
I
I
I
I
I
I
Br
Br
Br
Br
2
2
2
2
2
2
2
2
2
2
5
5
5
5
93
92
89
90
91
90
94
95
4-CH3
4-OCH3
4-Cl
H
3-F
4-CH3
4-OCH3
4-Cl
H
H
H
9
91
90
10
11
12
13
14
COOMe
COOEt
COOMe
COOEt
68d
70d
73d
76d
4-NO2
4-NO2
a
Reaction condition: ArX (1.0 mmol), terminal olefins (2.0eq), Et3N (2.0eq),
catalyst 3b (0.05 mol%), dioxane (5 mL).
b
The reaction was monitored by GC.
GC Yield using n-decane as an internal standard.
Pd (0.5 mol%).
c
d
When the reaction was finished, Catalyst 3b were recovered by
simple filtration and washed with water, ethanol then acetone and
oven dried. As shown in Fig. 4, the catalysts could be reused for at
least five times without significant loss of activity.
Conclusion
In summary, a novel cross-linked polyallylamine polymer sup-
ported iminopyridylphosphine palladiumⅡ complexes has been
successfully prepared. This new heterogeneous palladium catalyst
presented good activity and high selectivity in SuzukieMiyaura and
Heck cross-coupling reaction without the need of addition of other
sources of ligands. In addition, the supported catalyst developed in
this study also has the advantage to be completely recoverable with
simple filtration. The catalyst could be reused, while keeping
similar catalytic activity for five successive reactions. All the ad-
vantages (high catalytic activity, stability, reusability) proved that
the new catalyst could be considered as a viable alternative in
cross-coupling reactions.
Ⅱ
supported iminopyridylphosphine palladium complex in Suzu-
kieMiyaura cross-coupling reaction and to extend its application
scope as catalyst, we carried out another classic palladium-
catalyzed CeC cross-coupling, namely, Heck reaction of aryl ha-
lides with terminal olefins. We explored the best coupling condi-
tions with iodobenzene and styrene using 3b as catalyst (Table 3,
entry 10). The results demonstrated that Et3N as the base in dioxane
was the best choice for cross-coupling reactions, which produced
90% desired product in 2 h at reflux temperature. Many aryl iodides
could react with terminal olefins and the yields of corresponding
coupling products were very satisfied. Poor yields of the coupling
products were obtained and longer reaction time and more amount
of catalyst were needed for completing the Heck reaction, which
were also the cases for the aryl bromides as substrates (Table 3,
entry 11e13).
Experimental section
All chemicals were of reagent grade. 2-(diphenylphosphino)
benzaldehyde was purchased from SigmaeAldrich. Cross-linked
The reusability of the catalyst was a very important theme,
especially for commercial application. The advantage of the novel
catalyst 3b (cross-linked polyallylamine polymer-supported imi-
Ⅱ
nopyridylphosphine palladium complex) lied in not only the high
catalytic activity attributed to the formation of CeC bond, but also
in the easy separation and recyclability. Recycling experiments
were carried out for the cross-coupling of bromobenzene and
benzeneboronic acid under the conditions descried in Table 1.
Fig. 4. Reusability test of the polymer supported iminopyridylphosphine palladium (Ⅱ)
complexes.
Liu, Xiang
