A robust and recyclable polyurea-encapsulated copper(I) chloride for one-pot ring-opening/Huisgen cycloaddition/CO2 capture in water

Article abstract of DOI:10.1039/c6gc01956k

Multicomponent ring-opening/Huisgen cycloaddition reactions combined with CO₂ capture with a polyurea-encapsulated copper salt as a catalyst that in situ formed from simple CuCl and soluble polyurea during the reaction were carried out successf

Full text of DOI:10.1039/c6gc01956k

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Journal Name
ARTICLE
A Robust and Recyclable Polyurea-Encapsulated Copper(I)
Chloride for One-Pot Ring-Opening/Huisgen Cycloaddition/CO2
Capture in Water
Received 00th January 20xx,
Accepted 00th January 20xx
Yun Chena, Wei-Qiang Zhanga, Bin-Xun Yua, Yu-Ming Zhaoa, Zi-Wei Gao*a, Ya-Jun Jiana, Li-Wen
DOI: 10.1039/x0xx00000x
Xu*a,b
www.rsc.org/
The multicomponent ring-opening/Huisgen cycloaddition reactions combined with CO2 capture with polyurea-
encapsulated copper salt as catalyst that in-situ formed from simple CuCl and soluble polyurea during the reaction were
carried out successfully for the synthesis of -hydroxytriazoles under exceptionally mild conditions, in which the polyurea-
encapsulated copper(I) chloride was proved to be a robust and recyclable catalyst system with high yields as well as
excellent chemoselectivity in this reaction.
or polymeric materials. However, heterogeneous catalysts are
usually less reactive, necessitating harsher conditions, such as
higher temperature and pressure, and could be less selective
Introduction
In heterogeneous catalysis or heterogenization of
homogeneous catalytic systems that are robust and could be
readily separated from the reaction mixtures1, reactions at the
liquid-liquid or solid-liquid interface is a common phenomenon
and still hold a great potential for polymerization and synthetic
organic chemistry.2,3 For example, Bergbreiter and coworkers4
have recently reported that the enforced phase-selective
solubility of polyisobutylene (PIB)-bound Rh(II) catalysts in
biphasic liquid-liquid (heptane/acetonitrile mixtures) could be
used not only to recycle these rhodium catalysts but also to
suppress the formation of by-product in the cyclopropanation
and O-H insertion reactions of ethyl diazoacetate, which might
be due to increased phase segregation of the soluble polymer-
bound catalyst and the reactant (ethyl diazoacetate). Thus and
nowadays, reactions “in/on water”, “at the surface/interface”,
or by “phase-transfer” are important platforms for modern
catalysis and synthetic chemistry,2-5 especially as in most cases
solid or water can be used as the second phase, which would
be useful for the isolation of catalyst and products. In addition,
immiscible reaction partners react at the surface of solid or
interface of two liquids, which is also a convenient and
versatile route for the facile preparation of organic molecules
or substrate-selective in some cases.6 Of course, a general
drawback is that reactivity of immiscible metal catalysts that
generally immobilized on solid-state supports is often
decreased in comparison to that of the corresponding original
catalysts in homogeneous phase. Moreover, in many cases,
recovered metal catalysts have lower reactivity than that of
freshly used catalysts. Therefore, on the basis of basic
phenomenon with controllable reactions at the liquid-liquid or
solid-liquid interface, the development of more efficient
heterogeneous catalyst that has higher TON and TOF than that
of original catalyst in homogeneous system is highly desirable
from a viewpoint of Green Chemistry.7 It should be noted that,
considerable effort has been directed towards immobilizing
metal catalyst onto immiscible supports include amorphous
silica,8 porous ordered materials,9 and organic polymers.10
Notably, since the microencapsulation method was first
introduced in 1998,11 organic polymer support –based
microencapsulated technology has been worked as
privileged method for immobilizing metal catalysts onto
polymers in the past decades.12 As
new strategy,
a
a
microencapsulated catalysts (MC) were new type of
heterogeneous catalysts, in which the microcapsules are
backbones of immobilized catalysts, such as cross-linked
polymers and inorganic materials, including silica gel and
alumina, and thus are completely different from conventional
microcapsules that are used for coating and isolating
substances until their activity is needed.13 Thus with the MC
technique, the polymer incarcerate metal catalysts are
generally more robust against many solvents, including water.
Notably, among the polymers used in MC technique, polyureas
(PUA) have been attracted increasing attractions in the past
years.
a.Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education
(MOE) and School of Chemistry and Chemical Engineering, Shaanxi Normal
University, Xi’an 710062, P. R. China. E-mail: liwenxu@hznu.edu.cn (XLW);
zwgao@snnu.edu.cn (GZW)
b.Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry
of Education, Hangzhou Normal University, No 1378, Wenyi West Road, Science
Park of HZNU, Hangzhou 311121, P. R. China.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: Experimental details,
additional reaction data
DOI: 10.1039/x0xx00000x
, and NMR and HPLC spectra of products. See
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Polyureas (PUA) that are defined as ureylene containing effective group for the adsorption of metal salts in water, such
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DOI: 10.1039/C6GC01956K
functional –NHCONH- in the polymer backbones, are known as as various copper salts, including unstable CuCl, and other Cu(I)
an interesting and high performance polymer owing to the salts, in which the backbone of the polyurea would ligate and
high mechanical, thermal and chemical stability, good abrasion retain the metal species within the polymeric matrix. Although
resistance, high rate of healing, fast curing, and viscoelastic simple in concept of aggregation-induced encapsulation (AiEc),
properties.14 Especially, PUA has been well known to have encapsulation of copper is synthetically challenging since the
good flexibility and water repellency, which inspired chemists supported catalyst must be firmly trapped inside the
to expand the use of PUA as protective coating materials to immiscible supports (such as PUA) in order to avoid leaching of
new applications,15,16 such as heterogeneous support in metal ion into the liquid phase. Considered the facts that ureas
catalysis.16 In this context, Ley and co-workers have ever are geometric compatible with copper ion and the hydrogen-
reported the polyurea-encapsulated palladium for versatile bond acceptor,19 and known as excellent hydrogen-bond
cross-coupling reaction16a,16b,16f,16g, reduction of ketones16c
,
donors,20 we believed the aggregation-induced encapsulation
hydrogenolysis of epoxides16e, in which one of the most of copper catalyst could be recovered and reused in aqueous
promising features of palladium catalyst immobilization on organic transformations, which would also provide a facile
polyurea is microencapsulation. Ley and co-workers have also approach with new strategy to the green synthesis of useful
used microencapsulation technique to encapsulate osmium compounds, such as
tetroxide within a polyurea matrix that has been effectively
used in the dihydroxylation of olefins16d. Subsequently, these
commercially available polyurea-encapsulated palladium (also

-hydroxytriazoles reported in this work.
O
poly
+
poly
N
N
OCN
NCO
H
H
simplified as PdEnCat catalysts) with microencapsulation
technique have been used by other groups as an attractive
catalyst for tandem catalysis because of their high activity,
wide substrate scope, low leaching, and strong recycling
capability.16,17 Furthermore, the polyurea microcapsules are
proved to be completely insoluble in aqueous and most of
organic solvents, and it was found that polyurea is extremely
robust without any degradation under general reaction
conditions.16-18 Therefore, further efforts are directed in this
work toward the development of polyurea-encapsulated
copper catalyst with improved chemoselectivity and high
performance for environmentally benign transformations.
Herein we report a new reaction system for the one-pot
multicomponent ring-opening/Huisgen cycloaddition that can
be run with the need of green chemistry.
H N
NH
2
1a
2
Pyridine
RT, 0.5 h
2a
O
H
N
HN
O
HN
HN
N
O
O
N
H
NH
H
NH
Polyurea 3a
n
O
NH
NH
O
NH
N
O
N
H
HN
N
H
H
NH
O
NH
Results and discussion
Flexible PUA
NH
NH
NH
NH
O
Polyurea + Cu
Substrate 1 + Substrate 2 + -------------
Product
O
O
Polyurea 3a
Mn = 27757
Mw = 29145
Mz = 30974
Mz/Mw = 1.06
O
H2O
Strong
Hydrogen
Bonding
R
N
R
R
N
H
H
H2O
Cu
Aggregation-induced
H2O
H2O
Encapsulation (AiEc)
H2O
H2O
CuXn
R
N
NH
O
N
H
Aggregation
Mw/Mn = 1.05 (PDI)
H
H2O
H2O
M
H2O
Scheme 1. The synthesis of 1,2-diamine -derived polyurea (PUA)
featured with hydrogen bond network and possible folding backbone.
H2O
Recyclable Catalyst
(AiEc-M)
Hydrogen bonding
Hydrophilic
Folding
Hydrophobic
H
N
H
Cu(I)
Initially, on the basis of previous investigation on the use of
1,2-diamine that could be an important moiety for the
construction of stable copper complexes, such as salen- or
salan-Cu complex,21 we designed and prepared several 1,2-
diamine-derived polyureas with possible folding backbone for
encapsulated copper-catalyzed transformations reported in
this work (Scheme 1). Four different polyureas were achieved
in high yields. Interestingly, only the polyurea 3a was a soluble
polymer with high molecular weight (Mw = 29145 that
detected by GPC) and other 1,2-diamine -derived polyureas
N
H
NH
O
N
NH
O
Cu
O
N
N
H
O
Hydrophilic
Coordinated
N
n
H
n
AiEc-Cu
Figure
1
.
The development of aqueous copper-catalyzed
transformations and the illustration of polyurea-encapsulated copper(I)
catalyst on the basis of the hypothesis of aggregation-induced
encapsulation (AiEc).
As illustrated in Figure 1, we hypothesized that the 1,2-
diamine-linked urea functionality on polyurea could be
2 | J. Name., 2012, 00, 1-3
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3b-3d exhibited poor solubility in general solvents (Scheme 2), polyurea 3a and CuCl was proved to be an effective catalyst
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DOI: 10.1039/C6GC01956K
which hindered the determination of molecular weight by GPC system in this reaction. As shown in Table 1, the desired
and the structural analysis of 3b-3d. With four polyureas in product 7a was obtained in excellent yield (95%) and high
hand, we evaluated the catalytic application of these chemoselectivity (Entry 1, >99:1, only 7a was achieved without
structurally clear polyureas in the promotion of copper- isomer 6a). However, only moderate yield (50%) and inferior
catalyzed azide-alkyne cycloaddition reaction.
chemoselectivity was achieved in the absence of polyurea 3a
To our knowledge, one of the most powerful and widely (Entry 2), which supported the powerful role of polyurea in the
applied copper-mediated reactions of recent times is arguably stabilization and activation of copper catalyst for click
the azide-alkyne cycloaddition (Huisgen reaction).22,23 Notably, cycloaddition. In other words, the polyurea 3a also has a
this click-type transformation could be performed in water, strong ability to work as polymeric ligand because of its urea
which would be beneficial to numerous applications in green moiety.
chemistry and biological systems. Seeking a route that did not
Table 1. The effect of polyurea in the copper-catalyzed multicomponent azide-alkyne
require a preparation of organic azides that might be an
cycloaddition: Domino ring-opening and Huisgen cycloaddition of sodium azide,
epoxide 4a, and alkyne 5a.a
explosive reagent during the purification, we reasoned that
the direct use of sodium azide for multicomponent azide-
alkyne addition is ideal procedure in green chemistry.
Meanwhile, multicomponent cycloadditions are synthetically
important transformations, both in academic laboratory and in
OH
OH
NaN ( 1 eq.)
3
CuCl (x mol%)
Polyurea (10x mg)
O
+
N
+
N
N
N
Solvent, RT, 4-12 h
N
4a
5a
N
Ph
Ph
industry. Accordingly, the need for
a practical, atom-
7a
6a
economical, and environmentally benign version of
multicomponent azide-alkyne cycloaddition transformations
has received considerable interest in homogeneous catalytic
systems.24 However, previous methods are mostly restricted to
the use of complicated ligand, defectiveness in
chemoselectivity, and the difficulty in recyclability of catalyst
makes these strategies not ideal for green chemistry.
Therefore, the development of new catalyst system, polyurea -
encapsulated copper, that is devoid of these deficiencies in
multicomponent azide-alkyne cycloaddition would be of great
importance.
Entry
1
2
3
4
5
6
7
8
Cu
PUA
3a
-
Solvent
Yield (%)b
6a/7ac
<1/99
2:98
-
-
-
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl2
Cu2O
CuBr
CuBr2
CuCl
CuCl
CuCl
CuCl
H2O
H2O
CH2Cl2
CH3CN
THF
Toluene
H2O
H2O
H2O
H2O
H2O
H2O
95
50
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3b
3c
3d
3a
NR
NR
NR
NR
70d
75e
90f
60
55
85
73
70
-
2:98
2:98
<1/99
2:98
2:98
2:98
2:98
2:98
2:98
2:98
<1/99
9
10
11
12
13
14
15
16
17
O
H2O
H2O
H2O
H2O
N
O
O
N
NH
H
H
N
85
O
NH
N
NH
H
H
80
NH
H2O
96g
n
n
Poyurea 3b
Poyurea 3a
a Except the specified note, the reaction conditions as following: epoxide 4a (1
mmol), alkyne 5a (1 mmol), NaN3 (1 mmol), CuCl (1 mol%), and polyurea 3a (10
mg), in water/solvent (2 mL), at room temperature for 4-12 hours (entries 1, and
7-15, reaction time is 4-8 h; and for entries 2-6, reaction time is 12 h. b The
isolated yield of 7a. c It was determined by NMR, and confirmed by GC-MS. d The
use of 2.5 mol% of CuCl and 25 mg of polyurea 3a in this case. e The use of 5 mol%
of CuCl and 50 mg of polyurea 3a in this case. f The use of 0.5 mol% of CuCl and 5
mg of polyurea 3a in this case. g Under the CO2 atmosphere (balloon).
O
N
O
N
O
O
N
H
NH
N
NH
H
H
H
NH
NH
n
n
Poyurea 3d
Poyurea 3c
Solubity of polyurea in organic solvents
Polyurea
Toluene CHCl3
EtOAc
THF
MeOH
no
EtOH
no
DMSO
yes
Then the effect of solvent on the one-pot multicomponent
ring-opening/Huisgen cycloaddition reaction was evaluated at
room temperature. When the multicomponent reaction was
carried out in CH2Cl2, CH3CN, THF, or toluene, no desired
product was obtained (Entries 3-6). Therefore water (H2O) was
proved to be an integral part of such multicomponent addition
reaction. And interestingly, we found that the reaction with
larger amount of catalyst and polyurea (above 2.5 mol% CuCl)
gave decreased yield (Entries 7 and 8), thus the use of 1 mol%
CuCl was enough good in this reaction. It should be noted that
0.5 mol% CuCl and 5 mg of polyurea was enough good to
promote the one-pot multicomponent ring-opening/Huisgen
3a
3b
3c
3d
yes
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no no/swelling
no no/swelling
no no/swelling
no
Scheme 2. Various 1,2-diamine-deirved polyureas evaluated in this
work.
Therefore, the multicomponent click addition of sodium azide,
epoxide 4a, and alkyne 5a is carried out at room temperature
in water using polyurea 3a as a capsule in the copper catalysis.
Under the initial reaction conditions, the combinational use of
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cycloaddition reaction (Entry 9, 90% yield). Interestingly, other catalyst. And the basic aqueous solution was neutralized
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copper sources, such as CuCl2, Cu2O, CuBr, or CuBr2, only gave completely by CO2 capture, which is notDoOnI:ly10b.1e0n39e/fCic6iGaCl t0o19t5h6eK
moderate yield in this reaction (Entries 10-13, 55-85% yield). stability of polyurea-encapsulated copper catalyst but also
These experimental results showed that Cu(I)Cl catalyst would minimizes the waste-water discharges.
be better in the polyurea-encapsulated Huisgen cycloaddition, Notably, the reaction progress of polyurea 3a in the
which is different from our previous work on the encapsulation of copper catalyst in this aqueous
enantioselective Huisgen cycloaddition24. The matching of multicomponent ring-opening/Huisgen cycloaddition under
polyurea 3a and Cu(I)Cl could be supported by fluorescent the optimized reaction conditions is visually shown in Figure 2.
analysis (See Supporting Information, Figure S1), which The desired products assembled in or around the polyurea-
revealed the quenching of polyurea 3a with CuCl is the less encapsulated catalyst system in/on water, indicating the co-
pronounced of the tested metal ions (chloride anion) in precipitation of the polymer-supported copper catalyst and
solution. Although the physical and chemical properties of 3b- the water-insoluble triazoles during the one-pot ring opening
3d (Scheme 2, with different structure and solubility) were and Huisgen cycloaddition of sodium azide, epoxide 4a, and
different from that of polyurea 3a, the activity of these alkyne 5a. In fact, the click multicomponent reaction –initiated
insoluble polyureas 3b-3d was evaluated in this aqueous co-precipitation of the polymer-supported copper catalyst and
multicomponent transformation. As shown in Table 1 (Entries the water-insoluble triazoles was similarly to that of our
14-16), these polyurea material exhibited inferior ability to previously reported strategy on the reactive PMHS-SIPNs
promote this reaction because of its only moderate yields (70- (polymethylhydrosiloxane
(PMHS)-derived
semi-
85%) and slightly inferior chemoselectivity (98:2), which might interpenetrating networks)-involved hydrogenation reaction –
be arisen from comparably weaker encapsulated ability of initiated preparation of organosilicon-supported palladium or
these insoluble polyurea in water in comparison to that of TiO2/nanosilver catalyst.27 In this regard, recyclable polyurea-
polyurea 3a. Thus accordingly, polyurea 3a was suitable for the encapsulated copper catalyst (AiEc-Cu) was successfully
multicomponent ring-opening/Huisgen cycloaddition.
formed after the multicomponent ring-opening/Huisgen
cycloaddition was completed, which would be an ideal
heterogeneous isolation for green synthetic chemistry without
extraction by organic solvent.
OH
OH
O
NaN
3
+
Cu catalyst
N
N
+
N
N
N
H O
2
4a
5a
N
Ph
Ph
6a
7a
Harmful and basic waste water
This work
CO
2
NaOH
NaHCO
Na CO
3
2
3
H O
2
CO capture
2
Scheme 3. An overlooked product (NaOH) in the multicomponent ring-
opening/Huisgen cycloaddition of sodium azide, epoxide, and alkyne in
the previous reports: The environmentally benign process combined
with CO2 capture.
Interestingly, previous reports on the copper-catalyzed
multicomponent
ring-opening/Huisgen
cycloaddition25
(a)
(b)
(c)
(d)
(e)
neglected the formation of NaOH, which resulted into harmful
sodium hydroxide-containing basic waste water that opposed
to the exact demands of green chemistry. To the best of our
knowledge, there are no reports on the multicomponent
transformation combined with CO2 capture to date. Therefore,
we hypothesized that the sodium hydroxide could be
neutralized by CO2 in this reaction, which would be also an
environmentally benign process combined with CO2 capture
(Scheme 3). Notably, carbon dioxide (CO2) capture is
recognized as a necessary and important technology related to
energy security and environmental sustain ability, in which the
capture and separation of CO2 has been extensively
investigated for energy-saving process, conversion applications
of CO2, and meeting green-house gas emissions reduction
targets.26 As expected, the multicomponent ring-
opening/Huisgen cycloaddition under the CO2 atmosphere
gave slightly increased yield and good selectivity in term of the
ring-opening reaction with epoxide 4a (Table 1, entry 17). In
this case, the addition of CO2 balloon did not affect the
catalytic performance of polyurea-encapsulated copper
Figure 2. The image of desired polyurea-encapsulated copper catalyst (AiEc-
Cu) formed in the multicomponent ring-opening/Huisgen cycloaddition: (a)
initial stage (1 min); (a) initial stage (10 min); (c) when the reaction was
carried out for 2 h; (d) the last stage after reaction (4 h); (e) the recovered
polyurea-encapsulated copper catalyst mixed with product: The co-
precipitation of the polymer-supported copper catalyst and the water-
insoluble triazoles.
To further investigate the recyclability of the recovered
polyurea-encapsulated copper catalyst, the catalyst recycle
experiments were carried out to investigate the activity of the
AiEc-Cu catalyst in the catalytic multicomponent ring-
opening/Huisgen cycloaddition of sodium azide, epoxide 4a
,
and alkyne 5a. As a heterogeneous catalyst, the reusability of
polyurea-encapsulated copper catalyst was easily recovered
after filtration from the aqueous solution and washed with
EtOAc (The reaction product was soluble in EtOAc and the
polyurea-encapsulated copper catalyst was not soluble in this
solvent). The resulted solid was dried overnight and was used
without addition of CuCl and any further treatment. As shown
in Figure 3, a comparable catalytic activity with almost same
4 | J. Name., 2012, 00, 1-3
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good selectivity was observed when repeated use of 1 mol% of ligand or support resulted in fast and good conversion and the
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CuCl catalyst combined with small amount of polyurea 3a was reaction rate revealed the acceleratioDnOIe: f1f0e.1c0t39o/Cf6GpoCl0y1u9r5e6Ka
carried out under the optimized reaction conditions (Figure (Figure 4, run 1 with 3a). However, the multicomponent ring-
3).28 Thus the recovered AiEc-Cu catalyst could be reused at opening/Huisgen cycloaddition occurred slowly in the absence
least six runs and always yielded the desired product with of polyurea 3a (without polyurea 3a), which supported the
almost the same level of activity (>90% yield), which crucial role of polyurea in the initial step of ring-opening of
demonstrated the advantage of polyurea-encapsulated copper sodium azide to epoxide. In addition, the kinetics for a
catalyst
(AiEc-Cu)
in
this
multicomponent
ring- comparison of the first, 4th, and 6th run provided in Figure 4
showed the slight inactivation/loss of the catalyst was
occurring during reaction and/or the recovery process by
filtration.
opening/Huisgen cycloaddition reaction.
NaN3 ( 1 eq.)
CuCl (1 mol%)
Polyurea 3a (10 mg)
R1
R2
R2
R1
N
N
O
N
N
N
+
N
HO
HO
R3
+
R1
R2
H2O, RT, 4-8 h
with CO2 or without CO2
R3
R3
4
6
7
5
OH
OH
OH
OH
N
N
N
N
N
N
N
N
N
N
N
N
Ph
F
7a
95% yield
>99:1 (7a/6a)
7b
90% yield
>99:1 (7b/6b)
7c
85% yield
>99:1 (7c/6c)
7d
85% yield
>99:1 (7d/6d)
Cl
OH
OH
OH
OH
N
N
N
N
N
N
N
N
N
N
N
N
Figure 3. Recyclability of polyurea-encapsulated copper catalyst (AiEc-Cu) in
the catalytic multicomponent ring-opening/Huisgen cycloaddition of sodium
azide, epoxide 4a, and alkyne 5a: All reactions were performed with 5 mmol
of sodium azide, 5 mmol of epoxide 4a, 5 mmol of alkyne 5a, and water (5
mL), with the recovered polyurea-encapsulated copper catalyst (50 mg
7e
7f
7h
60% yield
80% yield
>99:1 (7e/6e)
87% yield
>99:1 (7f/6f)
7g
80% yield
F
polyurea 3a and 5 mg CuCl at the initial run)[28]
.
OH
N
HO
N
N
HO
N
N
N
N
N
N
N
N
HO
N
F
7j
85% yield
without CO2: 97:3 (7j/6j)
with CO2: 98:2 (7j/6j)
7k
85% yield
>99:1 (7k/6k)
7l
7i
Cl
85% yield
>99:1 (7l/6l)
87% yield
HO
HO
PhO
HO
N
N
HO
N
N
N
N
N
N
N
N
PhO
N
N
PhO
F
F
7n
73% yield
without CO2: 95:5 (7n/6n)
with CO2: 100:0 (7n/6n)
7m
80% yield
>99:1 (7m/6m)
7p
70% yield
100:0 (7p/6p)
7o
70% yield
100:0 (7o/6o)
Scheme 4. Substrate scope of polyurea-encapsulated copper-catalyzed
multicomponent azide-alkyne cycloaddition of sodium azide, epoxides, and
alkynes.
Figure 4. Plot of yield versus time (h) showing the different reaction
rate in the polyurea-activated multicomponent ring-opening/Huisgen
cycloaddition reaction of epoxide 4a with alkyne 5a in/on water.
Under the optimized reaction conditions, the reaction scope
for the evaluation of combinational use of polyurea 3a and
CuCl in the catalytic multicomponent azide-alkyne
cycloaddition of sodium azide, epoxides, and alkynes is then
investigated carefully. As shown in Scheme 4, this catalyst
system (AiEc-Cu) could efficiently promote sodium azide (NaN3)
to various epoxides, and subsequent Huisgen cycloaddition
and CO2 capture, affording the corresponding triazoles with
This reaction kinetics showed in Figure 4 also visually reflects
the recyclability of in-situ formed polyurea-encapsulated
copper catalyst (AiEc-Cu) from the aqueous phase. Notably,
the importance of polyurea 3a was supported by the kinetic
study, in which the use of polyurea 3a as macromolecular
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J. Name., 2013, 00, 1-3 | 5
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ARTICLE
Journal Name
alcoholic moiety in excellent isolated yields (16 examples, up multicomponent ring-opening/cycloaddition under the
View Article Online
to 95% yield). For example, both aromatic epoxides and alkyl optimized reaction conditions. In particuDlaOrI,:w10e.10p3e9r/fCo6rGmCe0d19t5h6eK
epoxides were suitable substrates for the one-pot multicomponent ring-opening/Huisgen cycloaddition reaction
multicomponent ring-opening/Huisgen cycloaddition, and of (R)-styrene oxide with various terminal alkynes examined to
aromatic or alkyl terminal alkynes bearing chloride, fluoride, reveal the enantioselective transformation. As reported in
ethyl, and other groups on aromatic rings were successfully Scheme 5, perfect enantioselectivities were detected by chiral
employed in this reaction, and almost all the multicomponent HPLC with all the multicomponent ring-opening/Huisgen
transformations were completed in good yields (Scheme 4). As cycloaddition reactions (100% ee for six examples in Scheme 5).
described above, the multicomponent ring-opening/Huisgen The absolute configuration was deduced by comparison with
cycloaddition combined with CO2 capture gave the same level previously reported method for the
of yield and chemoselectivity. Interestingly, different from that enantiopure
-hydroxytriazoles.25d It is reasonable to assume
the multicomponent ring-opening/Huisgen cycloaddition of that nucleophilic addition of basic azide to epoxide via SN2-
most of epoxides with alkynes, the addition of CO2 balloon was type pathway lead to the formation of -alcoholic azide that
beneficial to the enhancement of chemoselectivity for the quickly reacts with the terminal alkynes to give the desired
synthesis of 7j and 7n. For example, the inferior ratio of 97:3 alcohol-functionalized -hydroxytriazoles without involvement
preparation of



was achieved for the case of 7j without CO2, while better in the competitive racemization process.
chemoselectivity (98:2) was obtained in the presence of CO2
Table 2. Catalytic ring opening of styrene oxide with aniline: Additional evidence for the
atmosphere. Similarly, only 7n was obtained under the CO2
atmosphere, which is better than that without in-situ
neutralization by CO2. Therefore, the disadvantageous effect
of in-situ formed NaOH could be avoided by the process of CO2
capture. All these results showed the efficiency of the
polyurea-encapsulated copper catalyst in the multicomponent
ring-opening/Huisgen cycloaddition reaction was quite good
and suitable for the practical synthesis of primary or secondary
powerful potential of polyurea-encapsulated copper catalyst system in aqueous
transformations.a
OH
O
OH
NH2
Polyurea 3a (10 mg)
NH
Ph
+
+
NH
H2O, RT, 24 h
Ph
9a
4a
8a
10a
Entry
Catalyst
Yield (%)b
10a/9ac
80:20
90:10
90:10
98:2
alcohol-containing

-hydroxytriazoles.
1
2
3
4
5
none
Et3N
DABCO
60
70
75
75
85
OH
O
NaN3 ( 1 eq.)
Polyurea 3a
Cu@Polyurea
N
CuCl (1 mol%)
Polyurea 3a (10 mg)
N
N
+
>99:1
R
H2O, RT, 4-8 h
(R)-4a
5
a
7
R
Reaction conditions: cyclohexene oxide (1 mmol), aniline (1 mmol), Et3N or
DABCO (10 mol%, entry or entry 3) or polyurea (10 mg, entry 4) or
2
OH
OH
Cu@Polyurea (10 mg of polyurea 3a and 1 mg CuCl, containing 1 mo% of CuCl,
entry 5); b Yields refer to those of the isolated pure products. c The ratio of 10a/9a
is determined by NMR.
OH
N
N
N
N
N
N
N
N
N
Ph
Although ring-opening reaction of epoxides with amines has
been performed in water in the presence of trimethylamine
(Et3N), 1,4-diazabicycl-[2.2.2]octane (DABCO), and with or
without other catalysts,29 the chemoselectivity in these
aminolysis of 1,2-epoxies with arylamines is not satisfied. Thus
the starting point for our investigations was the above
observation that the polyurea-encapsulated copper catalyst
system is effective for the ring-opening reaction of 1,2-
epoxides. Preliminary experiments with the aniline as
nucleophilic reagent revealed that polyurea 3a and CuCl (1
mol%) in particular, is a highly active catalyst with excellent
(S)-7a
95% yield
100% ee
(S)-7b
90% yield
100% ee
(S)-7c
85% yield
100% ee
Cl
OH
N
OH
OH
N
N
N
N
N
N
N
N
F
(S)-7d
(S)-7e
80% yield
100% ee
F
(S)-7f
87% yield
100% ee
85% yield
100% ee
chemoselectivity (>99:1 10a
oxide. Notably, previous methods with Et3N or DABCO were
not good in regioselectivity (Entries 1-3, 10a 9a < 90:10),
which supported powerful potential of polyurea-encapsulated
copper catalyst in ring-opening reaction of epoxide with
arylamine in/on water.
Having achieved very good results with polyurea-encapsulated
copper catalyst under the eco-friendly solvent (water), the
scope of the catalyst has also been further extended for the
/9a) for the aminolysis of styrene
Scheme 5. Enantioselective multicomponent ring-opening/Huisgen
cycloaddition promoted by polyurea-encapsulated copper catalyst.
/
Moreover, the enantioselective multicomponent ring-
opening/Huisgen cycloaddition catalyzed by polyurea-
encapsulated copper catalyst was examined to demonstrate
the advantage of the catalyst system. As shown in Scheme 5,
excellent results with key SN2-type nucleophilic addition were
obtained by performing the stereoselective version of
6 | J. Name., 2012, 00, 1-3
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Page 7 of 10
Green Chemistry
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Journal Name
ARTICLE
ring-opening aminolysis reaction of various epoxides like 128.3, 127.1, 125.7, 120.3, 67.1, 65.1. HR-MS cVaielcwuAlratitceledOnflioner
+
DOI: 10.1039/C6GC01956K
styrene oxide, and 2-ethyloxirane. As shown in Scheme 6, in C16H15N3O[M+H] : 266.1288, found: 266.1287.
each case the polyurea-encapsulated copper catalyst showed
good to excellent results in terms of yields (80-90% isolated
yields) and regioselectivity (>99:1 for 1,2-epoxides).
Conclusions
In summary, we have successfully developed a sustainable and
efficient approach that focused on the development of
O
R1
R2
polyurea-encapsulated copper catalyst for multicomponent
ring-opening/Huisgen cycloaddition reactions and CO2 capture
in water. Especially, it was shown that the polyurea-
encapsulated CuCl was proved to be a robust and recyclable
catalyst system in this reaction, in which all the
multicomponent ring-opening/Huisgen cycloaddition reactions
R1
R2
OH
R2
R1
OH
Polyurea 3a (10 mg)
4
CuCl (1 mol%)
+
+
NH
Ar
NH
Ar
H2O, RT, 24 h
NH2
R
9
10
8
cr = Chemoselectivity (Ratio of 10/9)
resulted into
-hydroxytriazoles with high yields as well as
excellent chemoselectivity under exceptionally mild conditions.
Except the advantages of multicomponent transformation
carried out in environmentally friendly water, the
corresponding new reaction systems provide the following
merits: (i) Simple and high-yield method with high
OH
OH
OH
NH
OH
NH
Me
N
NH
9c
83% yield
9d
9a
85% yield
9b
90% yield
chemoselectivity for the synthesis of
-hydroxytriazoles in
80% yield
one-pot operation; (ii) Asymmetric synthesis of

-
cr <1:99
hydroxytriazoles from chiral epoxides with perfect
enantioselectivity (100% ee); (iii) The recyclability of polyurea-
encapsulated copper catalyst was determined to be carried
out by six runs; and (v) it is an good example for the
environmentally benign multicomponent transformation
combined with CO2 capture, which minimizes the waste-water
discharge in this work. In view of the established utility of
recovered copper catalyst encapsulated on polyurea with good
recyclability and high level of catalytic performance in this
work, we anticipate that the method by in-situ reaction-
initiated polymer-encapsulated transition metal catalyst will
find wide applicability and offer the possibility for the
development of green synthetic transformations, such as the
regioselective aminolysis of epoxides that described in this
work. Further investigations to encapsulate other catalytic
metal species, including new encapsulated- palladium or
osmium system are underway in our laboratory.
OH
NH
OH
NH
OH
Me
N
OMe
10b
80% yield
cr >99:1
10a
85% yield
cr >99:1
10c
80% yield
cr >99:1
Scheme 6. Ring-opening reaction of epoxide with aromatic amines
promoted by polyurea-encapsulated copper catalyst.
Experimental
General Procedure for the polyurea (3a)/CuCl -catalyzed one-
pot multicomponent ring-opening/Huisgen cycloaddition for
the synthesis of
-hydroxytriazoles combined CO2 capture:
NaN3 (65 mg, 1.0 mmol), the epoxide (1 mmol), and the alkyne
(1 mmol) were added to a suspension of CuCl (1 mg, 1 mol %
Cu) and Polyurea (10 mg) in H2O (2 mL) under
the carbon dioxide atmosphere (balloon). The reaction mixture
was stirred at room temperature and monitored by TLC until
total conversion of the starting materials. The solid was
obtained by filtration and washed by EtOAc (3 ×10 mL). The
extraction of aqueous phase with EtOAc was also performed
without loss of product, and collected organic phase were
dried with anhydrous Na2SO4, and concentrated in vacuo. The
product was isolated through a silica gel flash column as
Acknowledgements
This project was supported by the National Natural Science
Founder of China (No. 21173064, 21371112, 21446014, and
21472031), and Zhejiang Provincial Natural Science Foundation
of China (LR14B030001) is appreciated. This work is also
supported partially by the Program of “One Hundred Talented
People” of Shaanxi Province.
corresponding
-hydroxytriazoles. All the products are
confirmed by MS, and usual spectral methods (1H-NMR, 13C-
Notes and references
NMR) (see Supporting Information). For example, 2-phenyl-2-
‡ Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the
matter under discussion, limited experimental and spectral data,
and crystallographic data.
(4-phenyl-1H-1,2,3-triazol-1-yl)ethanol (7a): 95% yield; White
o
1
solid, melt Point:153-155 C. H NMR (400 MHz, CDCl3) δ 7.80
– 7.74 (m, 2H), 7.69 (s, 1H), 7.43 – 7.36 (m, 5H), 7.35 – 7.29 (m,
1H), 7.29 – 7.25 (m, 2H), 5.68 (dd, J = 8.2, 3.7 Hz, 1H), 4.63 (dd,
J = 12.4, 8.2 Hz, 1H), 4.23 (dd, J = 12.4, 3.8 Hz, 1H). 13C NMR
(101 MHz, CDCl3) δ 147.2, 135.7, 130.2, 129.2, 129.0, 128.8,
1
About heterogenization of homogeneous catalytic systems,
see: A. E. C. Collis and I. T. Horváth, Catal. Sci. Tech., 2011, 1,
912-919.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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for every run). In fact, the partial adsorption of copper with
View Article Online
polyurea 3a in water was confirmed by ICP-OES analysis, in
DOI: 10.1039/C6GC01956K
which the amount of copper was detected as 28.16 mg/g
before reaction (Run 1). Fortunately, the loss of small
amount of copper did not affect the catalytic performance of
polyurea-encapsulated copper catalyst before 6th run of
recyclability. And notably, and the catalytic turnover number
were up to 173000. The detailed investigation of such highly
active catalyst in click chemistry will be carried out and
reported elsewhere in the near future. To detect the
oxidation states of various reused polyurea-encapsulated
copper catalysts, X-ray photoelectron spectroscopy (XPS)
analysis was performed. Although the oxidation states of
reused polyuria-encapsulated copper catalysts was difficultly
confirmed by the XPS analysis (Figure S4, see Supporting
Information), these Cu species mainly existed in the same
form of Cu(II) or Cu(I). For the polyuria-encapsulated copper
catalyst, the Cu species mainly existed in the form of Cu(II).
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28 Inductively coupled plasma-optical emission spectroscopy
(ICP-OES) analysis of recycled polyurea-encapsulated copper
catalyst showed that the slight loss of the copper catalyst
was occurring during reaction and/or the recovery process
by filtration. The ICP analysis was done on the recovered
polymer after the first run, the third run, and after the fifth
run, and the corresponding results of copper amount were
3.89mg/g, 3.72 mg/g, and 3.35 mg/g (average 5% leaching
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DOI: 10.1039/C6GC01956K
Graphic Abstract
A Robust and Recyclable Polyurea-Encapsulated Copper(I) Chloride for One-Pot
Ring-Opening/Huisgen Cycloaddition/CO2 Capture in Water
Yun Chen, Wei-Qiang Zhang, Bin-Xun Yu, Yu-Ming Zhao, Zi-Wei Gao*, Ya-Jun Jian, Li-Wen Xu*
NaN3 ( 1 eq.)
CuCl (1 mol%)
Polyurea 3a (10 mg)
R1
R2
O
N
+
R3
N
N
HO
R1
H2O, RT, 4-8 h
with CO2 or without CO2
R2
R3
24 examples
up to 96% yield
Green
Click
Adsorption
Aggregation
CuCl
polyurea
Chemistry
OH
NaN3 ( 1 eq.)
O
CuCl (1 mol%)
Polyurea 3a (10 mg)
N
N
N
+
R
H2O, RT, 4-8 h
6 examples
100% ee
R
The one-pot ring-opening/Huisgen cycloaddition reactions combined with CO2 capture were
carried out successfully in the presence of polyurea-encapsulated CuCl.