The clicked pyridyl-triazole ligand: From homogeneous to robust, recyclable heterogeneous mono- and polymetallic palladium catalysts for efficient Suzuki-Miyaura, Sonogashira, and Heck reactions

Article abstract of DOI:10.1002/adsc.201200619

Various mono- and polymetallic palladium complexes containing a 2-pyridyl-1,2,3-triazole (pyta) ligand or a nonabranch-derived (nonapyta) ligand have been synthesized by reaction of palladium acetate with these ligands according to a 1:1 metal-ligand stoi

Full text of DOI:10.1002/adsc.201200619

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DOI: 10.1002/adsc.201200619
The Clicked Pyridyl-Triazole Ligand: From Homogeneous to
Robust, Recyclable Heterogeneous Mono- and Polymetallic
Palladium Catalysts for Efficient Suzuki–Miyaura, Sonogashira,
and Heck Reactions
Dong Wang,a Dominique Denux,b Jaime Ruiz,a and Didier Astruca,*
a
ISM, UMR CNRS N8 5255, Univ. Bordeaux, 351 Cours de la Libꢀration, 33405 Talence Cedex, France
Fax : (+33)-5-4000-6994; e-mail: d.astruc@ism.u-bordeaux1.fr
ICMCB-CNRS, UPR9048, 87, Avenue du Docteur Schweitzer, 33608 Pessac Cedex, France
b
Received: July 13, 2012; Revised: October 12, 2012; Published online: January 4, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200619.
Abstract: Various mono- and polymetallic palladium methods and by thermogravimetry showing decom-
complexes containing a 2-pyridyl-1,2,3-triazole (pyta) position above 1108C. Both types of catalysts
ligand or a nonabranch-derived (nonapyta) ligand showed excellent activity for these cross carbon-
have been synthesized by reaction of palladium ace- carbon bond formations involving aryl halides in-
tate with these ligands according to a 1:1 metal- cluding activated aryl chlorides or acyl chloride. Be-
ligand stoichiometry and used as catalysts for sides the comparison between homogeneous and het-
carbon-carbon cross-coupling including the Suzuki– erogeneous catalysis, the key feature of these cata-
Miyaura, Sonogashira and Heck reactions. The un- lysts is their remarkable robustness that allowed re-
substituted monopalladium and nonapalladium com- cycling at least ten times in the example of the Heck
plexes were insoluble in all the reaction media, reaction with excellent yields and without significant
whereas tri- and tetranuclar palladium complexes reduction of the conversion.
were soluble, which allowed conducting catalysis
under either homogeneous or heterogeneous condi-
tions. The organopalladium complexes were charac- Keywords: catalysis; click chemistry; cross C C cou-
terized by standard analytical and spectroscopic pling; palladium; pyridine; recycling; triazoles
À
Introduction
Click chemistry has proven to be a powerful concept
allowing one to assemble molecular fragments under
green conditions,[1] the Cu-catalyzed alkyne–azide
(CuAAC) reaction being the most popular example
with the regioselective formation of 1,4-disubstituted
1,2,3-triazoles.[2,3] This click CuAAC reaction is all the
more useful as the 1,2,3-triazole heterocycle also is an
excellent ligand,[4] which brings about potential appli-
cations of 1,2,3-triazole complexes. Such applications
have already appeared in optics,[5] redox sensing[6] and
catalysis.[7] In the latter area, the clicked 1,2,3-triazole
ligand has proven useful for the mild stabilization of
catalytically very efficient nanoparticles.[6] On the
other hand, in molecular catalysis, examples using
1,2,3-triazole-derived ligands are scarce (Figure 1).[8–13]
Zhu and Yi[8] synthesized two efficient triazole ligands
Figure 1. 1,2,3-triazolyl ligands used in molecular catalysis
1 for the palladium-catalyzed Suzuki–Miyaura and (see text).[8–13]
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Dong Wang et al.
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Heck reactions. Fokin[4c,9] and Pericꢂs[10] designed pol- Results and Discussion
ytriazoles 2 that were powerful stabilizing ligands for
“click” reactions. A series of triazole-based N4 tet- Synthesis of the Monometallic Palladium 2-Pyridyl-
radenate ligands 3 was synthesized by Hao and 1,2,3-triazoles (Pd-pyta) Complexes
Wang,[11] and Mn(II) complexes containing these li-
gands showed efficient catalytic activities in the epoxi- Reactions between the known 2-pyridyl-1,2,3-triazoles
dation of various aliphatic terminal olefins with per- (pyta) 6a and 6b and palladium acetate, conducted in
acetic acid. Phosphino-1,2,3-triazoles 4[12] and phos- toluene under ambient conditions, lead to the 1:1
phinomethylene-1,2,3-triazoles 5[13] have been used by ligand-metal complexes 7a and 7b, respectively [Eq.
Zhang and Reekꢃs research groups, respectively, as re- (1)]. The five-membered chelate ring structures were
markable ligands for Suzuki–Miyaura, amination, and
allylic alkylation reactions. The 2-pyridyl-1,2,3-triazole
(pyta) complexes that compare to 2,2’-bipyridine have
already provided luminescent properties,[5] but cata-
lytic functions have so far been overlooked.
Here we report that the easily prepared pyta ligand
and a new, nona-branch analogue nonapyta coordi-
nate in 1:1 stoichiometry to PdACTHNUTRGNENUG(OAc)2, and that the
monomeric and three nonapyta Pd complexes corre-
sponding to the progressive loading of the nonapyta
ligand with Pd(II) provided efficient catalysts for
cross carbon-carbon coupling reactions. Examples of
the Suzuki–Miyaura,[14] Sonogashira[15] and Heck[16] re- confirmed by the NMR spectra of 7a and 7b in which
actions illustrate these catalytic applications. More- the ratio of pyta and palladium ion was 1 to 1, and by
over, the great robustness and various solubilities of elemental analysis. The proton signals of both pyri-
the pyta- and nonapyta-Pd catalysts allowed conduct- dine and 1,2,3-triazole were shifted, which indicated
ing both homogeneous and heterogeneous reactions that both of them were coordinated to the palladium
with recyclability of the heterogeneous catalysts. ion (Figure 2). The solubility of the palladium com-
Indeed, efficient catalysts are well known for these plex 7b, unlike that of 7a, was very low, which was
Pd-catalyzed cross-coupling reactions,[14–16] but the in- a message indicating that 7b has the potential of
terest for the pyta-Pd and nonapyta-Pd complexes re- being a heterogeneous catalyst.
sides in their robustness and recyclability and on the
comparison among the catalysts of various nucleari-
ties and solubilities.[17,18]
Synthesis of the Polymetallic Palladium-Nonapyta
Complexes
A new nona-branched ligand 10 was prepared, involv-
ing three tripods that resulted from the known
CpFe+-induced nona-allylation of mesitylene in
[FeCp(h6-mesitylene)]
ACHTUNGTRENNUNG
1
Figure 2. Magnified H NMR spectra of 6a (top) and 7a (bottom).
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The Clicked Pyridyl-Triazole Ligand: From Homogeneous to Robust
Scheme 1. Synthesis of the nona-branched ligand 10 and metallodendritic catalysts 11.
action with NaN3 yielding 9[6] (Scheme 1). Click than the first one. This and the fact that the fourth
CuAAC reactions in toluene between 9 and ethynyl- metallation step is slower than the three first ones
pyridine provided 10. Reactions of 10 with PdACTHNUGRTENUNG(OAc) strongly argues in favor of a fast monometallation of
under ambient conditions yielded various polymetallic each of the three tripods and slower second metalla-
palladium complexes 11x depending on the reaction tion of each tripod. The solubilities of the complexes
time. After 2 to 5 min of reaction, only the soluble tri- also drop after the third metallation, thus the syner-
metallic complex 113 was formed, then the tetrametal- gistic steric and solubility effects provide a rationaliza-
lic complex 114, somewhat less soluble, was synthe- tion for the fact that the second metallation of the tri-
sized after 20 to 30 min of reaction. Finally, the syn- pods is slower than the monometallation, and the lack
thesis of the insoluble nonametallic complex 119 re- of steric effect among the three tripods and the good
quired one to two days for completion under the solubility of 113 explain why the three tripods of 10
same reaction conditions (Figure 3). All the attempts are rapidly monometallated at comparable rates. The
to form a monometallic or bimetallic complex by low- structures of the complexes 113 and 114 were shown
1
ering the reaction time, the temperature or the by H NMR upon comparison of the relative intensi-
amount of PdACHTUNGTRENNUNG(OAc)2 resulted in the formation of mix- ties of the methyl peaks of the core SiMe2 and
À
tures of 113 together with unreacted ligand 10, indicat- Pd OAc groups, respectively, and the structures of
ing that the second and third metallations were faster the three polymetallic complexes were confirmed by
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Dong Wang et al.
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Figure 3. Metallodendritic catalysts 113, 114, and 119.
elemental analysis. Given the remarkable robustness the metallation reactions, the ligands 6a and 10
of the Pd-typa and Pd-nonatypa bonds at high tem- showed a distinct p-p* transition around 280 nm.
peratures, the catalytic activities of 7a, 7b, 113, 114 and After coordination, a slight red shift from 280 to
119 were then evaluated for the Suzuki–Miyaura, So- 293 nm was observed from the spectra of the mono-
nogashira, and Heck reactions.
ACHTUNGTRENpNUNG alladium complexes 6a and 7a, which was probably
assigned to the ligand-to-metal charge-transfer transi-
tion (LMCT).[19] Similar results were obtained for the
UV-Vis Spectroscopy of the Ligands and Palladium
Complexes
complexes of the nonaACTHNGUTRENlNUG iCAHTUNGTRENgNUNG and, the UV bands of the 113
and 114 are located at 286 and 287 nm through red
shifts, respectively. The corresponding l, A, and
Figure 4 shows the UV-vis spectra of the ligands 6a e values are listed in Table 1.
and 10 and palladium complexes 7a, 113, 114. Before
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The Clicked Pyridyl-Triazole Ligand: From Homogeneous to Robust
sis (Figure 5) coupled with mass spectrometry (see
the Supporting Information) has been carried out for
both samples under Ar. For the mono-Pd complex 7b,
a first weight loss corresponding successively to resid-
ual water and then solvent is observed. The slope
change for the fragment group of organic coum-
pounds formed from decomposition starts at 1308C
and are clearly visible without ambiguity after 1458C
(for coupling with mass spectrometry, see the Sup-
porting Information).
The nona-Pd complex 119 shows a slight weight loss
up to 1108C that corresponds to traces of residual
water, and decomposition begins above this tempera-
ture.
Figure 4. UV-vis spectra of the ligands and palladium com-
plexes.
Catalysis of the Suzuki–Miyaura Cross-Coupling
Reactions
The Suzuki–Miyaura reactions were carried out ho-
mogeneously in H2O/EtOH with the palladium com-
plexes 113, 114, and heterogeneously with the insolu-
ble palladium complexes 7b, 119 as catalysts. K2CO3
(3 equiv.) was used as base in all the reactions
(Table 2). We tested the influence of the EtOH/H2O
volume ratios for Suzuki–Miyaura reactions conduct-
ed at 508C. Using the catalyst 7b, the yields of cross
carbon-carbon coupling products were 82% and 88%
with EtOH/H2O ratios of 1:1 and 3:2, respectively
(Table 3, entries 2 and 3), showing the slight yield in-
crease upon increasing the EtOH content in this sol-
vent mixture. The heterogeneous catalysts 7b and 119
also provided excellent yields that compared to those
of the homogeneous catalyst catalysts 113 and 114.
The aryl chloride p-NO2-C6H4Cl also provided the
cross-coupling product in good yield upon reaction
Table 1. UV-vis characteristics of the ligands and palladium
complexes.
Compound
C [molLÀ1]
l [nm]
A
e [MÀ1 cmÀ1]
6a
7a
10
113
114
3.3ꢄ10À4
3.3ꢄ10À4
1.3ꢄ10À5
1.3ꢄ10À5
1.3ꢄ10À5
280
293
281
286
287
3.103
2.934
1.688
1.188
0.775
9.31ꢄ103
8.80ꢄ103
1.27ꢄ105
0.89ꢄ105
0.58ꢄ105
Thermogravimetric Analysis of the Palladium
Complexes 7b and 119
In order to determine the thermal stability of the with PhB(OH)2 using the heterogeneous catalyst 7b
mono- and nona-Pd complexes, thermogravitric analy- (entry 13).
Figure 5. Thermogravimetric analysis of 7b (left) and 119 (right).
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Table 2. Suzuki–Miyaura reactions of aryl halide with phenylboronic acid.[a]
Entry
X
R
Catalyst (mol%)
Temp. [oC]
Time [h]
C [%][b]
TON
1
2
3
4
5
6
7
8
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Cl
Cl
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
NO2
7b (0.5)
7b (0.5)
7b (0.5)
113 (0.5)
114 (0.5)
119 (0.5)
7b (0.5)
7b (0.5)
113 (0.5)
113 (0.5)
114 (0.5)
119 (0.5)
7b (2)
r.t.
50
50
50
50
50
80
50
50
80
50
50
120
120
48
48
48
48
48
48
48
96
48
48
48
48
120
120
77
82[c]
88
96
91
85
91
96
93
97
91
88
74
57
154
164
176
192
182
170
182
192
186
194
182
176
37
9
10
11
12
13
14
NO2
119 (2)
29
[a]
Reaction conditions: aryl halide (0.5 mmol), phenylboronic acid (0.75 mmol), K2CO3 (1.5 mmol, 207 mg), EtOH (7.5 mL),
H2O (5 mL).
C: conversion (yield of isolated product).
Solvent: EtOH (5 mL) and H2O (5 mL).
[b]
[c]
Catalysis of the Sonogashira Reactions
temperature. The reaction proceeded well with all
these catalysts. The catalyst 113 was soluble in Et3N
The complexes 7b, 113, 114, 119 catalyze the cross-cou- and showed better catalytic activities than the insolu-
pling reaction between benzoyl chloride and phenyl- ble catalysts 7b and 119. The catalyst 114 was partly
ACHTUNGTRENNUNGacetylene in a simple one-pot procedure without co- soluble and also provided a good result. A significant
catalyst and at low catalyst concentrations (Table 3). drop in the yield was detected upon lowering the cat-
All the reactions were carried out using two equiv. alyst content (entries 2–4).
triethylamine as both the base and solvent at room
Iodobenzene was also used as a substrate for Sono-
gashira reactions with phenylacetylene. When the re-
action was carried out at room temperature, a low
yield was obtained, and increasing the reaction tem-
perature to 508C improved the yield (Table 4, en-
Table 3. Sonogashira coupling of benzoyl chloride with phe-
nylacetylene.[a]
Table 4. Sonogashira coupling of iodobenzene with phenyl-
AHCTUNGTRENNUNG
acetylene.[a]
Entry
Catalyst (mol%)
Time [h]
C [%][b]
TON
1
2
3
4
5
6
7
8
7a (0.1)
7b (0.01)
7b (0.05)
7b (0.1)
113 (0.1)
114 (0.1)
119 (0.1)
119 (0.1)
48
48
48
24
12
12
24
48
90
44
76
86
95
93
87
89
900
4400
1620
860
950
930
870
890
Entry Catalyst Temp. [oC] Time [h] C [%][b] TON
1
2
3
4
5
6
7b
7b
113
114
119
119
r.t.
50
50
50
50
50
48
24
24
24
24
48
58
83
88
86
83
87
580
830
880
860
830
870
[a]
[a]
Reaction conditions: benzoyl chloride (1.2 mmol), phe-
nylacetylene (1 mmol), Et3N (2 mmol).
C: conversion (yield of isolated product).
Reaction conditions: iodobenzene (1.2 mmol), phenylace-
tylene (1 mmol), Et3N (2 mmol).
C: conversion (yield of isolated product).
[b]
[b]
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The Clicked Pyridyl-Triazole Ligand: From Homogeneous to Robust
Table 5. Mizoroki–Heck reaction of aryl halide substrates with styrene.[a]
Entry
X
Catalyst (mol%)
Temp. [oC]
Time
Conversion [%][b]
TON
1
2
3
4
5
6
7
8
I
I
I
I
I
I
Br
Br
7b (2)
7b (2)
7b (5)
113 (2)
114 (2)
119 (5)
7b (5)
119 (5)
100
100
100
100
100
100
120
120
24 h
48 h
48 h
48 h
48 h
48 h
7 d
79
86
96
93
92
94
64
55
40
43
19
47
46
19
13
11
7 d
[a]
Reaction conditions: aryl halide (0.5 mmol), styrene (1 mmol), K3PO4 (1.5 mmol, 318 mg), DMF (2 mL).
Yield of isolated product.
[b]
tries 1 and 2). Homogeneous catalysis with 113 Table 6. Recharging of the dendritic catalysts 7b and 119 for
the Heck reactions of iodobenzene with styrene.
smoothly catalyzed the reaction with somewhat better
yield than under heterogeneous conditions with 7b
and 119. The yield gap was not as large as in the reac-
tion with benzoyl chloride, however, possibly due to
partial solubilization of these heterogeneous catalysts
at high temperature. In addition, in general, benzoyl
chloride showed higher reactivity than iodobenzene.
Recharging run[a]
1
2
3
4
5
6
7
8
9
10
Catalyst 7b [conver- 96 93 93 92 92 93 91 91 91 91
sion (%)][b]
Catalyst 119 [conver- 94 93 91 91 92 91 89 87 84 78
sion (%)][b]
[a]
Recharging the catalysts for the reactions of entry 3 and
6 in Table 5.
Yield of isolated product.
[b]
Catalysis of the Heck Reaction
Mizoroki–Heck coupling reactions between halogeno-
benzenes and styrene using these palladium com-
plexes were successfull (Table 5). Both types, hetero- are listed in Table 6 (Figure 6), Table 7
ACHTUNGTRENNGNU (Figure 7) and
geneous (7b, 119) and homogeneous catalysts (113, Table 8 (Figure 8), which correspond to Suzuki–
AHCTUNGTRENNUNG
114), catalyzed the reaction between iodobenzene and Miyaura, Sonagashira, and Heck reactions, respective-
styrene in 92–96% yields. Meanwhile, either 2 mol% ly. From Table 7 , it appears that 7b showed good cat-
of homogeneous catalyst (113 or 114) or 5 mol% of alytic activity for the Suzuki reaction, but comparing
heterogeneous catalyst (7b or 119) provided excellent with the others, the advantage is not remarkable,
yields. The reaction between stilbene and the less re- even some catalytic systems are much better than
active bromobenzene gave a moderate yield, a longer ours. It is worth noting, however, that heterogeneous
reaction time and higher temperature than with iodo- 7b has the potential of recharge. Among the copper-
benze being required.
free systems for Sonogashira reactions, the ones con-
Taking the Heck reaction as example, the recovery taining phosphine or ionic liquid exhibited more sig-
and reuse of the heterogeneous catalysts 7b and 119 nificant activities. The TON of 7b is larger than those
were investigated. They could be recharged with iodo- of most phosphine- or ionic liquid-containing cata-
benzene and styrene at least ten times without signifi- lysts, which means that 7b is an outstanding catalyst
cant loss of their catalytic activity (Table 6), which for Sonogashira reactions. Although 7b does not show
showed the interest (easy catalyst recovery, high turn- a very good activity for the Heck reaction (Table 9),
over numbers) of these heterogeneous catalysts.
the high-temperature stable and heterogeneous prop-
erties render it rechargeable for ten times without sig-
nificant loss of catalytic activity. The possibility of
conversion between homogeneous and heterogeneous
catalysts upon change of substituent and palladium
nuclearity and the propery of recharge make this cat-
Comparison of the Catalytic Activities with
Literature Examples
We compared the catalytic activity of our catalyst 7b alyst family containing the pyridyl-triazole ligand
with literature examples that were published in 2011 original and useful.
or 2012. The reaction conditions and TON numbers
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Dong Wang et al.
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Figure 6. Catalysts and ligands from the literature for the Suzuki–Miyaura reaction.
Table 7. Comparison of catalytic activities with literature examples (Figure 6) for the Suzuki reaction between 4-methoxy-
ACHTUNGTRENNUNGhalobenzene and phenylboronic acid.
Entry
X
Catalyst (and
ligand) (mol%)
Solvent
Base
Other
additive
Time and
temperature
Yield
[%]
TON
1
2
Br
Cl
Br
Br
Br
Br
Br
Cl
Br
Br
Br
7b (0.5)
7b (0.5)
12 (1)
EtOH/H2O
EtOH/H2O
toluene
dioxane
EtOH/H2O
H2O
K2CO3
K2CO3
K3PO4
Cs2CO3
K2CO3
K2CO3
K3PO4
K3PO4·3H2O
KOH
Cs2CO3
Cs2CO3
no
no
no
no
no
TBAB
no
no
no
48 h, 508C
120 h, 1208C
2 h, 1008C
3 h, 808C
91
74
70
77
96
96
100
95
89
54
88
182
37
70
39
96
960
100
95
445
54
3[20]
4[21]
5[22]
6[23]
7[24]
8[25]
9[26]
10[27]
11[28]
Pd
N
PdCl2 (1)/L2 (1)
13 (0.1)
14 (1)
15 (1)
6 h, 608C
2 h, 1008C
4 h, 1308C
24 h, r.t.
24 h, 608C
10 h,1108C
18 h, 858C
MeOH
THF/H2O
MeOH/H2O
DMF/PhMe
DMSO
16 (0.2)
À
A
no
no
17 (0.5)
176
a L=P
ACHTUNGTRENNUNG(p-Tol)3}3.
Figure 7. Catalysts and ligands from literature for the Sonogashira reaction.
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The Clicked Pyridyl-Triazole Ligand: From Homogeneous to Robust
Table 8. Comparison of catalytic activities with literature examples (Figure 7) for the Sonogashira reaction between iodoben-
zene and phenylacetylene.
Entry Catalyst (and ligand) (mol%) Base
Solvent
Other additive Time and temperature Yield [%] TON
1
7b (0.1)
18 (0.1)
19 (2)
Et3N
K2CO3
Et3N
Et3N
Et3N
KOH
Et3N
H2O
AHCTUNGTERN[GNUN Bmim]PF6
CH3CN
H2O
EtOH
no
TBAB
no
no
no
no
no
no
24 h, 508C
2.5 h, 1008C
2 h, 808C
17 h,>818C
6 h, 408C
24 h, 708C
0.5 h, 1008C
5 h, r.t.
12 h, 808C
12 h, 608C
83
82
100
84
93
84
87
97
92
78
830
820
50
2[29]
3[30]
4[31]
5[32]
6[33]
7[34]
8[35]
A
N
42
20 (0.1)
930
210
174
323
1957
16
PdEnCatTM 30 (0.4)
21 (0.5)
Piperidine H2O
22 (0.3)
Et3N
Et3N
Et3N
Et3N
10[36] 23 (0.047)
11[37] 24 (5)
A
H2O
no
Figure 8. Catalysts and ligands from the literature for the Heck reaction.
Table 9. Comparison of catalytic activities with literature examples (Figure 8) for the Heck reaction between iodobenzene
and styrene.
Entry Catalyst (mol%)
Base
Solvent
Other additive Time and temperature
Yield [%] TON
1
7b (2)
14 (1)
21 (0.5)
24 (5)
25 (0.4)
26 (0.1)
27 (1)
K3PO4 DMF
K2CO3 MeOH
K2CO3 DMF
no
no
no
no
no
TBAB
no
no
TBAB
48 h, 1008C
24 h, 1108C
2 h, 1008C
6 h, 1008C
8 h, 1208C
6 h, 1008C
1 h, 1258C
12 h, 1008C
86
100
88
90
73
69
87
77
94
74
43
2[24]
3[38]
4[37]
5[39]
6[40]
7[41]
8[8]
100
176
18
182
690
87
77
47
74
15
DBU
H2O
K2CO3 DMAc
K2CO3 H2O
K2CO3 DMF
Pd
C
9[42]
Pd(l-proline)2 (2)
MW (200–300 W), 808C, 10 min
12 min, 1208C (10 W of MW)
20 min, 808C (ultrasound irradiation) 75
10[43] PdCl2 (1)
K2CO3 PEG-400 no
K2CO3 H2O PEG-200
11[44] Pd
A
Conclusions
whereby the two OAc ligands change their coordina-
tion type from chelate to monodentate, forming ex-
A new family of palladium complexes is shown to be tremely robust, yet catalytically efficient nonapyta
excellent as homogeneous or heterogeneous catalysts complexes.
for the Suzuki–Miyaura, Sonogashira and Heck reac-
tions of haloarenes. This family includes two mono-
The independence of the three tripods of the nona-
AHCNUTGERTGlNNUN iACTHNGUTREgNNUG and 10 induces large complexation rates that are
metallic 2-pyridyl-1,2,3-triazole (pyta) complexes, 7a, similar among the three tripods, with a complexation
that is soluble, and 7b that is almost insoluble in most rate that even increases from the first to the third
solvents, and three polymetallic nonapyta complexes, metallation. It is obviously the bulk introduced by the
the soluble trimetallic complex 113, the less soluble second metallation of each tripod that provokes the
tetrametallic complex 114 and the completely insolu- progressive insolubilization of the complexes contain-
ble nonametallic complex 119. Thus, the synthesis of ing more than three PdACHTUNTRGNEU(GN OAc)2 units, before further
the new nonabranched nonapyta ligand allowed us to metallation very slowly proceed heterogeneously up
delineate a strategy of progressive insolubilization of to the nonametallation. Altogether, this family of cat-
the catalysts upon progressive loading with PdACHTUNTRGNEU(GN OAc)2 alysts comprises mono- and polymetallic catalysts
Adv. Synth. Catal. 2013, 355, 129 – 142
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
137

Dong Wang et al.
FULL PAPERS
containing almost identical catalytic sites and share Synthesis of 1-Benzyl-4-phenyl-1H-[1,2,3]triazole
the property of robustness.
(6a)[47]
The monomeric complex 7b and the nonametallic
complex 119 are efficient heterogeneous catalysts that
can be recharged at least ten times without significant
loss of their catalytic activity, taking the Heck reac-
tion as example. Thus although these catalysts are not
as efficient with chloroarenes as some specific alkyl-
phosphine-containing catalysts such as the closely re-
lated 2-phosphino-1,2,3-triazolyl and 2-phosphinino-
methyl-1,2,3-triazolyl palladium catalysts that have
not been recycled, they are extremely robust, which
allowed their efficient recycling. In conclusion, in ad-
dition to the synthesis of a new remarkable family of
polynuclear complexes, this study brings about the
rare duality of catalyst efficiency and robustness for
cross carbon-carbon coupling reactions with recycling
applications.
2-Ethynylpyridine (0.5 mmol), benzyl azide (0.5 mmol) and
[CuACHTUNGTRENNG(U phen)ACHUTGNTNER(NUGN PPh3)2]NO3 (0.005 mmol, 4.27 mg) were added to
a test tube with a stir bar, and the mixture was stirred at
room temperature (25–288C) without exclusion of air under
solvent-free conditions. After 10 min, the mixture was dilut-
ed with ethyl acetate and filtered. The filtrate was evaporat-
ed under reduced pressure to obtain the crude product,
which was further purified by silica-gel chromatography (pe-
troleum ether/ethyl acetate as eluent) to afford 1-benzyl-4-
phenyl-1H-[1,2,3]triazole (6a); yield: (114 mg (97%).
1H NMR (300 MHz, DMSO-d6): d=8.70 (s, 1H, CH of tria-
zole), 8.60 (d, J=4.8 Hz, 1H, CH of pyridyl), 8.05 (d, J=
8.1 Hz, 1H, CH of pyridyl), 7.86–7.91 (m, 1H, CH of pyrid-
yl), 7.32–7.41 (m, 6H, CH of pyridyl and CH of phenyl),
5.69 (s, 2H, CH2-triazole).
Synthesis of Complex 7a
6a (70.5 mg, 0.3 mmol) and palladium acetate (67.4 mg,
0.3 mmol) were dissolved in anhydrous toluene (8.0 mL).
The mixture was stirred at room temperature for one day.
After the reaction, the solid was isolated by filtration and
washed successively with 20 mL toluene and 20 mL ether to
give 7a as a yellow solid; yield: 125 mg (91%). 1H NMR
(300 MHz, DMSO-d6): d=9.24 (s, 1H, CH of triazole),
8.21–8.27 (m, 1H, CH of pyridyl), 8.18 (d, J=6.9 Hz, 1H,
CH of pyridyl), 8.05 (d, J=5.7 Hz, 1H, CH of pyridyl),
7.59–7.64 (m, 1H, CH of pyridyl), 7.39–7.45 (m, 5H, CH of
phenyl), 5.83 (s, 2H, CH2-triazole), 1.93 (s, 3H, COCH3),
1.84 (s, 3H, COCH3); 13C NMR (100 MHz, CDCl3): d=
176.42 (C=O), 176.24 (C=O), 149.95, 148.47, 147.61, 141.88,
134.69, 129.73, 129.56, 129.12, 126.40, 126.34, 122.70 (C of
Ar), 55.83 (CH2-triazole), 24.05, 23.69 (COCH3); MS (ESI):
m/z=461.0619 [M+], calcd. For C18H18N4O4Pd: 460.7799;
anal. calcd. for C18H18N4O4Pd: C 46.92, H 3.94, N 12.16;
found: C 46.43, H 3.87, N, 11.86.
Experimental Section
General Data
Reagent-grade diethyl ether (used in hydrosilylation reac-
tions) was predried over sodium foil and distilled from
sodium-benzophenone anion under argon immediately prior
to use. Anhydrous toluene was dried from sodium. Triethyl-
amine was dried from calcium hydride. Other solvents and
chemicals were used as received.
Only hydrosilylation reactions were carried out using
Schlenk techniques or in a nitrogen-filled Vacuum Atmos-
phere drylab. Kartsted catalyst and PdACTHNURTGNENG(U OAc)2 (98% or
ꢀ99.9%) were purchased from Aldrich. Compounds 8, 9
were synthesized according to ref.[45]
Flash column chromatography was performed using silica
gel (300–400 mesh). 1H NMR spectra were recorded with
a 300 or 400 MHz spectrometer, 29Si NMR spectra were ob- Synthesis of 2-(1H-[1,2,3]triazol-4-yl)-pyridine (6b)[48]
tained at 59.6 MHz with a 300 MHz spectrometer, and
Trimethylsilyl azide (0.2 mL, 1.5 mmol) was added to
13C NMR spectra were recorded at 50, 75 or 100 MHz with
a DMF and MeOH solution (2 mL, 9:1) of CuI (9.6 mg,
200, 300 or 400 MHz spectrometers. Copies of H NMR, 29Si
1
0.05 mmol) and 2-ethynylpyridine (103 mg, 1 mmol) under
and 13C NMR spectra are provided (see Supporting Informa-
nitrogen. The reaction mixture was stirred at 1008C over-
tion). The soluble complex 1 was examined by cyclic voltam-
night. After consumption of 2-ethynylpyridine, the mixture
metry in CH2Cl2 at 208C with 0.1M [n-Bu4N]ACHTNUTRGENNG[U PF6] as sup-
was cooled to room temperature and filtered through
a short column of silica and concentrated. The residue was
purified with silica gel column chromatography (petroleum
ether/ethyl acetate, 10:1 to 1:1) to afford 2-(1H-[1,2,3]tria-
zol-4-yl)-pyridine 6b; yield: 95 mg (65%). 1H NMR
(300 MHz, DMSO-d6): d=15.27 (s, 1H, NH of triazole),
8.63 (d, J=3.6 Hz, 1H, CH of pyridyl), 8.38 (s, 1H, CH of
triazole), 8.00 (d, J=7.8 Hz, 1H, CH of pyridyl), 7.87–7.93
(m, 1H, CH of pyridyl), 7.35–7.39 (m, 1H, CH of pyridyl).
Caution: This reaction produces explosive and toxic hy-
drogen azide (HN3) in situ and must therfore be conducted
behind a safety shield in a hood.
porting electrolyte on a Pt electrode, and a chemically irre-
versible reduction wave was observed at 0.95 V vs. the inter-
nal reference decamethylferrocene[46] at a scan rate of
0.1 V.sÀ1 (see the Supporting Information). Elemental analy-
ses were performed by the Center of Microanalyses of the
CNRS at Lyon Villeurbanne, France.
For the thermogravimetric analysis, the samples have
been previously degased under primary vacuum during
45 min to reach 5·10À2 mbar, and the device has been filled
with pure argon with less than 2 ppm of O2. Experiments
have been performed under argon flux and with
a 2.58CminÀ1 ramp temperature (TGA Setaram TAG2400
device coupled with a Thermostar quadrupolar mass spec-
trometer from Balzer).
Caution: Sodium azide is potentially explosive. Great
care is needed when handling this compound.
138
asc.wiley-vch.de
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2013, 355, 129 – 142

The Clicked Pyridyl-Triazole Ligand: From Homogeneous to Robust
lated immediately by filtration and washed with successively
Synthesis of 7b
40 mL toluene and 40 mL ether to give 113 as a yellow solid.
The filtrate can continue to be stirred under the same condi-
tions, repeating above-mentioned operation, 113 was ob-
tained after drying under vacuum; yield: 20 mg (32%). The
product was kept under nitrogen. 1H NMR (300 MHz,
CDCl3): d=0.03 (s, 54H), 0.51 (s, 18H), 1.02 (s, 18H), 1.55
(s, 18H), 1.83 (s, 9H), 1.97 (s, 9H), 4.03–4.24 (m, 18H), 6.93
(s, 3H), 7.30–7.45 (m, 8H), 7.85–8.05 (m, 18H), 8.39 (s, 6H),
8.55–8.61 (m, 6H), 9.42 (s, 3H); 13C NMR (75 MHz,
CDCl3): d=176.49, 176.24, 172.88, 150.74, 150.25, 149.97,
148.94, 148.53, 147.95, 147.18, 141.00, 137.84, 127.25, 126.28,
124.77, 123.57, 122.53, 120.03, 37.16, 24.07, 23.67, 22.04, 0.03,
À0.24; 29Si NMR (CDCl3, 59.62 MHz): d=11.14, 2.89; MS
6b (73 mg, 0.5 mmol) and palladium acetate (112.3 mg,
0.5 mmol) were dissolved in anhydrous toluene (10.0 mL),
and the mixture was stirred at room temperature for one
day. After the reaction, the solid was isolated by filtration
and washed successively with 20 mL toluene and 20 mL
ether to give 7b as a yellow solid; yield: 165 mg (89%).
Anal. calcd. for C11H12N4O4Pd: C 35.64, H 3.26, N 15.12;
found: C 35.47, H 3.23, N 15.63.
Synthesis of the Dendritic Ligand 10
The azido dendrimer 9 (455.2 mg, 0.3 mmol) and 2-ethynyl-
pyridine (417 mg, 4.05 mmol) were dissolved in tetrahydro-
furan (THF), and water was added (20 mL:20 mL, THF/
(MALDI-TOF): m/z= 2764.8 [MÀ
ACHTUNGTRENNUNG
C138H192N36O12Pd3Si9: 3119.3; anal.
C138H192N36O12Pd3Si9: C 53.14, H 6.20, N 16.17; found: C
53.53, H 5.97, N 16.63.
·
water). At room temperature, CuSO4 5H2O was added
(1 equiv per branch, 1M aqueous solution), followed by the
dropwise addition of a freshly prepared solution of sodium
ascorbate (2 equiv per branch, 1M aqueous solution). The
solution was allowed to stir for 48 h at room temperature.
After removing THF under vacuum, dichloromethane and
an aqueous solution of ammonia were added. The mixture
[PdACHTNUTGRENUNG(OAc)2]4@dendrimer (114): Dendrimer 10 (48.9 mg,
0.02 mmol) and palladium acetate (18.0 mg, 0.08 mmol)
were dissolved in toluene (15 mL). The mixture was stirred
at less than 258C for 20–30 min, a bright yellow solid pre-
cipitated out from the solution. The solid was isolated im-
mediately by filtration and washed successively with 40 mL
toluene and 40 mL ether to give 114 as a light brown solid;
yield: 34 mg (51%). The product was kept under nitrogen.
1H NMR (300 MHz, CDCl3): d=9.48 (s, 4H), 8.55–8.62 (m,
5H), 8.40 (s, 5H), 7.87–8.09 (m, 20H), 7.29–7.44 (m, 8H),
6.96 (s, 3H), 4.05–4.24 (m, 18H), 1.97 (s, 12H), 1.85 (s,
12H), 1.59 (s, 18H), 1.05 (s, 18H), 0.59 (s, 18H), 0.02 (s,
54H); 13C NMR (75 MHz, CDCl3): d=176.46, 176.18,
172.97, 150.87, 150.75, 150.27, 150.14, 149.97, 148.49, 147.96,
147.60, 147.15, 137.84, 137.73, 124.78, 124.24, 123.57, 123.43,
120.04, 119.93, 44.19, 44.12, 37.15, 31.37, 24.07, 23.66, 22.20,
19.50, 17.80, 1.11, 0.96, À3.27, À3.30; 29Si NMR (CDCl3,
59.62 MHz): d=11.12, 6.65, 2.86, anal. calcd. for
C142H198N36O16Pd4Si9·2H2O: C 50.46, H 6.02, N 14.92; found:
C 50.71, H 5.87, N 14.60.
was allowed to stir for 10 min in order to remove all the
+
Cu(I) trapped inside the dendrimer as Cu
N
ganic phase was washed twice with water (20 mL), dried
with sodium sulfate, filtered on paper and the solvent was
removed under vacuum. The product was washed with pen-
tane (10 mL) in order to remove the excess of 2-ethynyl-pyr-
idine and precipitated using dichloromethane/pentane. The
dendrimer 10 was obtained as a brown solid; yield: 595 mg
1
(81%). H NMR (300 MHz, CDCl3): d=8.56 (d, J=4.5 Hz,
9H, CH of pyridyl), 8.16 (d, J=7.8 Hz, 9H, CH of pyridyl),
8.08 (s, 9H, CH of triazole), 7.76 (t, J=7.2 Hz, 9H, CH of
pyridyl), 6.98 (s, 3H, CH of Ar), 3.96 (s, 18H, SiCH2-tria-
zole), 1.64 (s, 18H, CH2CH2CH2Si), 1.11 (s, 18H,
CH2CH2CH2Si), 0.65 (t, J=7.5 Hz, 18H, CH2CH2CH2Si),
0.09 [s, 54H, SiACHTUNGTRENNUNG
(CH3)2]; 13C NMR (50 MHz, CDCl3): d=
150.64, 149.38, 148.07, 145.91, 137.00, 122.95, 122.79, 121.65,
120.22 (C of pyridyl, triazole, and phenyl), 44.04 (CH2-tria-
[PdACHTNUTGRENUNG(OAc)2]9@dendrimer (119): Dendrimer 10 (48.9 mg,
0.02 mmol) and palladium acetate (40.4 mg, 0.18 mmol)
were dissolved in anhydrous toluene (25 mL). The mixture
was allowed to stir for 48 h at room temperature. The solid
was isolated by filtration and washed successively with
20 mL toluene and 20 mL ether to give 119 as a brown solid;
zole), 41.85 and 41.38 (benzylic quaternary
CH2CH2CH2Si), 17.79 (CH2CH2CH2Si),
C
and
14.97
(CH2CH2CH2Si), À3.70 [Si
(CH3)2]; 29Si NMR (CDCl3,
ACHTUNGTRENNUNG
59.62 MHz): d=2.87; MS (MALDI-TOF): m/z=2467.8
[MNa+], calcd. for C126H174N36Si9: 2445.7; anal. calcd. for
yield:
80.4 mg
(90%);
anal.
calcd.
for
C
126H174N36Si9: C 61.88, H 7.17, N 20.62; found: C 61.67, H
C162H228N36O36Pd9·5H2O: C 42.70, H 5.26, N 11.07; found: C
42.69, H 5.18, N 10.87.
7.02, N 20.38.
Synthesis of the Metallodendritic Catalysts
[PdACHTUNGTRENNUNG(OAc)2]n@dendrimer (11)
General Procedure for the Sonogashira Reaction
The dendritic palladium complexes were prepared by using
Pd(OAc)2 and dendritic ligand 10 in freshly distilled toluene
T
A round-bottom flask (10 mL) containing monomeric or
dendritic catalyst (0.001 mmol) was subjected to the
Schlenk-line procedures of evacuation and purging of nitro-
gen for three cycles. Phenylacetylene (1 mmol), benzoyl
chloride or iodobenzene (1.2 mmol), and 2 equiv. Et3N
(2 mmol) were successively added, and the mixture was
stirred at room temperature or 508C. After the reaction was
finished, the mixture was diluted with dichloromethane and
filtered. The filtrate was removed under reduced pressure to
provide the crude product that was further purified by silica
gel chromatography (petroleum ether/ethyl acetate as
at the given concentrations for a period of time indicated in
the Supporting Information. Then, the solution was filtered,
the filter residues were washed with large amounts of tolu-
ene and ether to give the catalysts 113, 114, and 119 as yellow
or brown solids.
[PdACHTUNGTRENNUNG(OAc)2]3@dendrimer (113): Dendrimer 10 (48.9 mg,
0.02 mmol) and palladium acetate (40.4 mg, 0.18 mmol)
were dissolved in anhydrous toluene (15 mL). The mixture
was stirred at less than 258C for 2–5 min, a bright yellow
solid precipitated out from the solution. The solid was iso-
Adv. Synth. Catal. 2013, 355, 129 – 142
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
139

Dong Wang et al.
FULL PAPERS
eluent) to yield the corresponding Sonogashira coupling
products.
water, and the organic phase was dried using sodium sul-
phate, filtered on paper, and the solvent was removed under
vacuum. This provided the crude product that was further
purified by silica gel chromatography (petroleum ether as
eluent) to yield the corresponding Heck reaction products.
0.5 mmolK3PO4 was added to the flask containing the solid,
and the Schlenk-line procedures of evacuation and purging
of nitrogen for three cycles was conducted. Iodobenzene
(0.5 mmol), styrene (1 mmol), and DMF (3 mL) were suc-
cessively added using syringes, and the mixture was stirred
at 1008C for 48 h. The process can be repeated at least ten
times, and the yields indicated in table 6 were obtained.
1,3-Diphenyl-propynone: 1H NMR (300 MHz, CDCl3):
d=8.22–8.23 (m, 1H), 8.20 (t, J=1.8 Hz, 1H), 7.65–7.69 (m,
2H), 7.58–7.63 (m, 1H), 7.36–7.53 (m, 5H).
1,2-Diphenylethyne: 1H NMR (300 MHz, CDCl3): d=
7.51–7.56 (m, 4H), 7.30–7.38 (m, 6H).
General Procedure for the Suzuki Reaction
A round-bottom flask containing monomeric or dendritic
catalyst (0.0025 mmol), K2CO3 (1.5 mmol), and borophenylic
acid (0.75 mmol) was subjected to the Schlenk-line proce-
dures of evacuation and purging of nitrogen for three cycles.
Halobenzene (if halobenzene was liquid) (0.5 mmol), H2O
(5 mL), and ethanol (7.5 mL) were successively added using
syringes, and the mixture was stirred under controlled condi-
tions. After cooling to room temperature, the mixture was
diluted with dichloromethane and filtered. The filtrate was
washed with water and the organic phase was dried using
sodium sulfate, filtered on paper and the solvent was re-
moved under vacuum to provide the crude product that was
further purified by silica gel chromatography (petroleum
ether as eluent) to yield the corresponding Suzuki reaction
products.
Acknowledgements
Financial support from the China Scholarship Council (CSC)
from the Peopleꢀs Republic of China (Ph. D. grant to DW),
the Universitꢁ Bordeaux 1, and the Centre National de la Re-
cherche Scientifique (CNRS) is gratefully acknowledged.
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Procedure for Recycling the Catalysts
A
round-bottom flask containing catalyst 7b or 119
(0.025 mmol) and K3PO4 (1.5 mmol) was subjected to the
Schlenk-line procedures of evacuation and purging of nitro-
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(1 mmol), and DMF (3 mL) were successively added using
syringes, and the mixture was stirred at 1008C for 48 h.
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