Fast Living Polymerization and Helix-Sense-Selective Polymerization of Diazoacetates Using Air-Stable Palladium(II) Catalysts

Article abstract of DOI:10.1021/jacs.8b11628

In this work, air-stable palladium(II) catalysts bearing bidentate phosphine ligands were designed and prepared, which could initiate fast and living polymerizations of various diazoacetate monomers under mild conditions. The polymerization afforded the desired polymers in high yields with controlled molecular weights (M_ns) and narrow molecular weight distributions (M_w/M_ns). The M_ns of the isolated polymers were linearly correlated to the initial feed ratios of monomer to catalyst, confirming the living/controlled manner of the polymerizations. The M_n also increased linearly with the monomer conversion, and all of the isolated polymers showed narrow M_w/M_ns. The polymerization was relatively fast and could be accomplished within several minutes. Such fast living polymerization method can be applied to a wide range of diazoacetate monomers in various organic solvents at room temperature in air. Taking advantage of the living nature, we facilely prepared a series of block copolymers through chain extension reactions. The amphiphilic block copolymers synthesized by this method exhibited interesting self-assembly properties. Moreover, polymerization of achiral bulky diazoacetate by Pd(II) catalysts bearing a chiral bidentate phosphine ligand leads to the formation of polymers with high optical activity due to the formation of the predominantly one-handed helix of the main chain. The helix sense of the polymers was determined by the chirality of the Pd(II) catalysts.

Full text of DOI:10.1021/jacs.8b11628

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Article
Fast Living Polymerization and Helix-Sense-Selective Polymerization
of Diazoacetates Using Air-Stable Palladium(II) Catalysts
Jia-Hong Chu, Xun-Hui Xu, Shu-Ming Kang, Na Liu, and Zong-Quan Wu
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b11628 • Publication Date (Web): 29 Nov 2018
Downloaded from http://pubs.acs.org on November 29, 2018
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Fast Living Polymerization and Helix-Sense-
Selective Polymerization of Diazoacetates Using Air-
Stable Palladium(II) Catalysts
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Jia-Hong Chu, Xun-Hui Xu, Shu-Ming Kang, Na Liu, and Zong-Quan Wu*
Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering,
and Anhui Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, Hefei
University of Technology, 193 Tunxi Road, Hefei 230009 Anhui Province, China
ABSTRACT. In this work, air-stable palladium(II) catalysts bearing bidentate phosphine ligands
were designed and prepared, which could initiate fast and living polymerizations of various
diazoacetate monomers under mild conditions. The polymerization afforded desired polymers in
high yields with controlled molecular weights (M s) and narrow molecular weight distributions
n
(
M /M s). The M s of the isolated polymers were linearly correlated to the initial feed ratios of
w n n
monomer to catalyst, confirming living/controlled manner of the polymerizations. The M also
n
increased linearly to the monomer conversion, and all the isolated polymers showed narrow
M /M s. The polymerization was relatively fast, and can be accomplished within several minutes.
w
n
Such fast living polymerization method can be applied to a wide range of diazoacetates monomers
in various organic solvents at room temperature under air. Taking advantage of the living nature,
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a series of block copolymers were facilely prepared through chain extension reactions. The
amphiphilic block copolymers synthesized by this method exhibited interesting self-assembly
properties. Moreover, polymerization of achiral bulky diazoacetate by Pd(II) catalysts bearing
chiral bidentate phosphine ligand lead to the formation of polymers with high optical activity due
to the formation of predominated one-handed helix of the main chain. The helix-sense of the
polymers was determined by the chirality of the Pd(II) catalysts.
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Introduction
It is well-known that the C-C main chain polymers are one of the most important classes of
synthetic polymers and have been widely used in our modern life. These polymers are generally
prepared via the polymerization of vinyl monomers. An alternating method is the polymerization
of one carbon (C1) units such as isocyanide, dimethylsulfoxonium methylide and diazocarbonyl
compounds.1-5 The latter one is of particular interest because it can afford well-defined C-C main
chain polymers bearing polar substituents at every main chain carbons, which cannot be accessed
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,7
by Ziegler-Natta catalysts. Thus, the diazoacetates polymerization seems an attractive route to
prepare C-C main chain functional polymers. It can be argued that the radical polymerization of
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dialkyl fumarates or maleates can also produce polymers with similar structures. However, the
living/controlled polymerizations of these monomers have never been attained so far.
Recently, some organometallic compounds such as copper, palladium, and rhodium complexes
have been reported to promote the polymerization of diazoacetates. Nevertheless, the Cu-mediated
polymerizations can only generate low molecular weight oligomers.10 The Rh-mediated
polymerization of ethyl and benzyl diazoacetates yield syndiotactic polycarbenes with high
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11-14
molecular weights (M s).
While it is difficult to control the M and usually afford polymers
n
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with broad molecular weight distribution. Ihara and coworkers have reported a series of excellent
π-allylPdCl based complexes that can promote the polymerization of various diazoacetates
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monomers, which made great contributions in this interesting research field.15-17 In those
pioneering works, they have proposed a possible mechanism for the Pd(II)-mediated diazoacetates
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polymerizations via detailed analyses of polymer chain end structures. Moreover, high molecular
weight polymers with moderate stereoregularity can also been obtained by using the Pd(II)
catalyst.19 However, living/control polymerization using the Pd(II) catalysts is still a great
challenge. There is only one example on controlled polymerization of diazoacetate, in which a
very specific diazoacetate monomer bearing a sterically bulky phosphazenes was employed.20
Beside those disadvantages, most of the reported catalysts for the diazoacetate polymerization are
sensitive to air, and the polymerizations have to be performed under an inert atmosphere except
for some Rh-catalysts.13,14 Additionally, the reported diazoacetates polymerizations usually
require a quite long time because of the low activity of the catalysts. Therefore, developing air-
stable catalysts for fast living polymerization of common diazoacetate monomers is of great
desired.
The polymerization of diazoacetates afford polycarbenes comprised of C-C single bonds and
carrying substituents on each main chain carbon. Introducing appropriate substituents on
polycarbenes pendants may endow the polymer with a stable helical conformation due to the steric
hindrance between the adjacent pendants.21,22 De Bruin and coworkers have revealed that
poly(ethylidene acetate) can adopt a flexible helical structure due to the steric repulsion between
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their ethyl side groups through computational molecular modeling. As we know, helix is the
central structure motif in biomacromolecules and plays important roles in living system including
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catalysis, recognition, replication, etc. Partially stimulated by the elegant helices in Mother Nature,
fully synthetic helical polymers with controlled helix sense has attracted considerable research
efforts in the past few decades.24-27 Such research is not only just for mimicking the helices and
functions in nature but also for developing new materials with novel functions and applications in
asymmetric catalysis, chiral resolution, self-assembled nanomaterials, and electronic devices and
so on.28-32 Although great efforts have been devoted, the number and type of artificial helical
polymers are still very limited, which strongly restricts the exploration on their structures and
functions. Thus exploring novel helical polymers is of continuous and great interesting. Although
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the structure of polycarbenes is similar to helical polyisocyanide, its helical conformation and
the related chiroptical properties have rarely been explored to date.23 Helix-sense-selective
polymerization of achiral monomers can afford a helical polymers with controlled helicity, in
which, a small amount of chiral catalyst, initiator or additives can produce a large amount of chiral
materials.33-41 The chirality of the afforded polymers is only come from the helicity of the main
chain without containing any chiral pendants.
In this contribution, we report a family of air-stable Pd(II) complexes bearing a bulky bidentate
phosphine ligand which can efficiently initiate fast living polymerizations of various diazoacetate
monomers at room temperature under an air atmosphere. The polymerizations are relatively fast,
and can be accomplished within several minutes. The living polymerizations lead to the formation
of well-defined polycarbenes in high yields with controlled M s and narrow molecular weight
n
distributions (M /M s) (Scheme 1). Taking advantage of this method, well-defined block
w
n
copolymers can be facilely prepared. Moreover, the synthetic polycarbenes bearing bulky pendants
was revealed to possess a stable helical conformation in solution. Helix-sense-selective
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polymerization of achiral diazoacetate monomers using a chiral Pd(II) catalyst afforded helical
polycarbenes with high optical activity owing to the predominant of one-handed helix.
Results and Discussion
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Scheme 1. Polymerization of Diazoacetates Using Air-Stable Pd(II) Catalysts
N2
H
-allylPdCl/Ligand
C
mPd/L
OR
OR
H
Solvent, r.t.
O
O
Monomer
Polycarbenes
OR = OBn
OC H
O(CH2CH2O)3CH3
6
13
1
2
3
CH O
O
O
2
4
5
6
Ligand:
Ph P
Ph P
Ph P
2
2
2
O
S
O
S
O
S
But
But
But
N
N
N
H
H
H
PPh2
PPh2
PPh2
LA
LR
LS
Fast Living Polymerizations. As shown in Scheme 1, benzyl diazoacetate (1) was first
prepared and employed as a model monomer. It was polymerized by various Pd(II) catalysts to
disclose the polymerization activity of the synthesized Pd(II) complexes. The Pd(II) catalysts
bearing different ligands were simply prepared through the reaction of commercial available π-
allylPdCl with the corresponding phosphine ligands in THF at room temperature. Initially, the
ratio of phosphine atom to palladium was fixed at 2/1 ([P] /[Pd] = 2/1). The resulting solution of
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Pd(II) catalyst was directly used for the diazoacetate polymerization without isolation and
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purification steps to minimize the decomposition of the complexes during the handling process.
All the polymerizations of monomer 1 using the Pd(II) complexes were conducted in THF at room
temperature under nitrogen atmosphere ([1] = 0.3 M, [1] /[Pd] = 50). After 24 h, the
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polymerization solution was precipitated into a large amount of n-hexane. It was found that the
ligand on the Pd(II) catalyst played important effect on the polymerization behaviors, although
other experimental conditions were identical. White polymeric solid can only precipitated from
t
the polymerization solutions using the Pd(II) catalysts bearing tri-tert-butylphosphane ( Bu P) and
3
bis(diphenylphosphino)-1,1'-binaphthalen (BINAP) ligands (run 1 and 4, Table 1). No polymeric
materials could be isolated from the polymerizations using triphenylphosphine (PPh ) and 1,3-
3
bis(diphenylphosphino)propane (dppp) ligands on the Pd(II) catalysts (run 2-3, Table 1). The
isolated polymers were first analyzed by size exclusion chromatography (SEC). The M and M /M
n
n
w
determined by SEC with equivalent to polystyrene standards were summarized in Table 1. All the
isolated polymers exhibited molecular weight around 6~7 kDa, while the M /M values are much
w
n
different and depending on the ligand. It seems that increasing the steric hindrance of the alkyl
phosphine ligand on the Pd(II) catalyst will decrease the M /M value. Thus, we further
w
n
synthesized
a
bulky bidentate phosphine ligand (N-[2-(diphenylphosphino)-1-[2-
A
(
diphenylphosphino)phenyl]ethyl]-2-methyl) (L ) followed the reported procedure, and used as
4
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ligand in the Pd(II)-mediated diazoacetate polymerization. The large size and relative rigid
A
structure of L might promote the polymerization of diazoacetate under a living/controlled manner.
A
To verify this hypothesis, the Pd(II)/L catalyst was prepared through the reaction of π-allylPdCl
A
A
with the L in THF at 25 C. The polymerization of 1 with Pd(II)/L was performed in THF at 25
C ([1] = 0.3 M, [1] /[Pd] = 50) followed the same experimental condition described above. To
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our delight, SEC trace of the isolated polymer showed a symmetrical and unimodal elution peak
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(
Figure 1a). The M of the isolated poly-1 (the footnote indicates the initial feed ratio of monomer
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to catalyst) was determined to be 7.0 kDa, very close to the theoretical value (7.4 kDa). Most
importantly, it showed a very narrow molecular weight distribution, and the M /M is only 1.16.
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This result suggested that the Pd(II)/L is a good catalyst for the polymerization of 1 and gives a
polymer with expected M and narrow M /M .
n
w
n
Table 1. The Results for Polymerization of 1 Using Pd(II) Catalystsa
b
c
d
d
e
run ligand [M] /[Pd]
[L] /[Pd]
M (kDa) M /M
yield (%)
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n
w
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1
1
1
1
tBuP 50
PPh3 50
dppp 50
Binap 50
2
6.8
-f
1.47
-f
62
-f
2
1
-f
-f
-f
1
5.8
7.0
8.3
10.1
11.9
13.7
14.8
16.9
6.8
6.9
1.57
1.16
1.17
1.17
1.16
1.18
1.19
1.19
1.34
1.29
64
81
80
83
85
81
82
82
76
78
LA
LA
LA
LA
LA
LA
LA
LA
LA
50
1
75
1
100
125
150
175
200
50
1
1
1
0
1
2
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1
1
0.5
2
50
a
b
The polymerizations were carried in THF at 25 C for 24 h according to Scheme 1. The initial
c
d
feed ratio of monomer to catalyst. The feed ratio of phosphine ligand to π-allylPdCl. The M and
M /M values were determined by SEC with equivalent to polystyrene standards. The isolated
yields. No polymer could be isolated.
n
e
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living/controlled chain-growth manner. To verify this hypothesis, a series polymerizations of
A
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experimental condition but in different initial feed ratios of monomer to catalyst. It was found that
all the polymerizations were proceeded smoothly and yielded the expected polymers in high yields
(yield > 80%, Table 1). As shown in Figure 1a, the SEC curves of the isolated polymers exhibited
unimodal and symmetrical elution peaks, and continually shifted to higher M -region with the
n
increased ratio of monomer to catalyst. The M and M /M values of the isolated polymers
n
w
n
determined by SEC were summarized in Table 1. The M of the isolated polymers increased
n
linearly and in proportion to the initial feed ratio of monomer 1 to the Pd(II) catalyst (Figure 1b).
Moreover, all the isolated polymers showed narrow molecular weight distributions with M /M <
w
n
A
1
.20. This result confirmed that the polymerization of 1 using Pd(II)/L as catalyst did proceed in
a living/controlled manner. Taking advantage of this method, a variety of poly-1 s with controlled
m
M and narrow M /M were facilely obtained in high yields (>80%) just through the variation on
n
w
n
the initial feed ratio of monomer to catalyst (Table 1). It is worthy to note that variation on the feed
A
ratio of L to the π-allylPdCl has strong influence on the results of the polymerization. The best
A
A
ratio of the L to π-allylPdCl was determined to be 1 to 1 ([L ] /[π-allylPdCl] = 1/1). Further
0
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A
increase or decrease the ratio of L to π-allylPdCl in the catalysts, the M /M of the generated
w
n
polymers became broad (run 12 and 13 in Table 1, and Figure S1 in Supporting Information). Thus
A
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the catalyst Pd(II)/L with [Pd] /[L ] = 1/1 was used in the following studies.
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1
2
3
4
5
6
7
8
9
0
1
18
19
20
21
22
23
24
50
100
[1] /[Pd]0
150
200
Retention time (min)
0
A
Figure 1. (a) Size exclusion chromatograms of poly-1 s prepared using the Pd(II)/L -mediated
m
polymerization of 1 with different initial feed ratio of monomer to catalyst. (b) Plots of the M and
n
A
M /M values of poly-1 s as a function of the initial feed ratios of 1 to the Pd(II)/L . The
w
n
m
polymerizations were carried out in THF at 25 C for 24 h. M and M /M were determined by
n
w
n
SEC with polystyrene standards (SEC conditions: eluent = THF; temperature = 40 C).
A
To get more details, the polymerization of 1 with Pd(II)/L was carried in THF at 25 C with
presence of dimethyl terephthalate as internal standard ([1] = 0.3 M, [1] /[Pd] = 100). The
0
0
0
polymerization was followed by high performance liquid chromatography (HPLC) to estimate the
monomer conversion as well as SEC to estimate the M and M /M values of the generated
n
w
n
polymers at different polymerization stages. As outlined in Figure 2a, poly-1 s isolated at different
m
stages showed unimodal and symmetric SEC traces, and continually shifted to shorter retention
time region with the progress of the polymerization. Plots of the monomer conversion with M and
n
M /M values of the isolated polymers were displayed in Figure 2b. The M of the generated
w
n
n
polymer increased linearly and in proportion to the conversion of monomer 1, while all the isolated
polymers showed narrow molecular weight distribution with M /M < 1.18. This result further
w
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1
1
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1
1
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2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
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3
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4
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4
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5
6
supports the living/controlled nature of the Pd(II)-mediated benzyl diazoacetate polymerization.
Moreover, it was found that the polymerization was relatively fast, more than 90% of monomer
was consumed within 10 min, suggesting the high activity of the Pd(II) catalyst (Figure 2c). Kinetic
study revealed that the polymerization obey the first-order reaction rate law (Figure 2d). The
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
‒
1
appearance rate constant was estimated to be 0.41 s , further confirms the fast living nature of the
polymerization. It is worthy to note that the previously reported catalysts or initiators for the
polymerization of diazoacetate monomers may require a long time, usually take more than ten
hours and sometimes several days to accomplish the polymerizations.13-18 The fast polymerization
rate of this new catalyst suggests the presence of appropriate phosphine ligand on the Pd(II)
catalyst not only endow the polymerization with excellent controllability but also enhance the
activity of the catalyst, making the polymerization with fast living characters. The previously
reported catalysts for the diazoacetates polymerizations usually require to be performed under inert
A
atmosphere. In sharp contrast, the fast living polymerizations initiated by the Pd(II)/L here can
be facilely performed under an air atmosphere, and yielded the desired polymers with expected Mn
and narrow M /M (Table S1, Supporting Information). The influence of air on the polymerization
w
n
A
A
using the Pd(II)/L catalyst is negligible. Probably the bulky and rigid ligand of L protected the
living center of the Pd(II) units on the chain growth terminal, and suppressed the chain transfer
and chain termination during the polymerization process. The accurate mechanism for this ligand
promoted fast living polymerization is not very clear at the current stage. Ihara and coworkers have
proposed an initiation and termination mechanism for the Pd(II)-mediated diazoacetates
18
polymerization. Since the polymerizations used the same π-allylPdCl as catalyst precursor, the
A
Pd(II)/L catalyst may follow a similar mechanism. While other possible mechanisms cannot be
completely excluded because the polymerization behaviors are different.
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(
a)
(b)10
6
90 s
1
1
2
0 s
2.5
.0
20 s
80 s
40 s
9
8
7
6
2
1.5
1.0
0.5
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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0
1
2
3
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5
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9
0
1
2
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9
0
1
2
3
4
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6
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8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
19
20
21
22
23
24
60
70
80
90
100
Retention time (min)
Conversion (%)
4
3
2
1
(
c)100
(d)
80
60
40
20
0
0
50
100 150 200 250
Time (s)
50
100
150
Time (s)
200
250
A
Figure 2. (a) Time-dependent SEC chromatograms for Pd(II)/L initiated living polymerization
of 1. (b) Plots of M and M /M values as a function of the conversion of monomer 1. (c) Plot of
n
w
n
the conversion of monomer 1 with polymerization time. (d) First-order kinetic plot for the
A
A
polymerization of 1 initiated by Pd(II)/L . The polymerization of 1 using Pd(II)/L catalyst was
performed in THF at 25 C with [1] = 0.3 M, and [1] /[Pd] = 100.
0
0
0
A
The fast living polymerization of 1 using the Pd(II)/L as catalyst was then attempted be
performed in various organic solvents with different polarity (Table S2, Supporting Information).
It was found that the polymerization could be facilely performed in toluene, chloroform,
dichloromethane, and chlorobenzene at room temperature. All the polymerizations led to the
formation of well-defined poly-1 s in high yields. Although the M /M became broad when the
m
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2
2
2
2
2
2
2
3
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3
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3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
polymerizations were performed in dichloromethane and chlorobenzene. The broad polydispersity
is likely due to the presence of ethanol stabilizer in the solvents that acted as a chain-transfer
4
3
agent. The polymerizations performed in n-hexane and methanol were failed because of the poor
solubility of the generated polymers in these solvents. These results indicated the polymerization
can be carried out in various organic solvents, while the THF is the best.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(a)
Hc
CHCl3
a
C m
b
O
O
a
b
c
Hc
Hd
(b)
C m
C n
b
a
O
O O
O
f (1.5H)
a
e
f
C H
4
9
c,d,e
b (2H)
Hd
(c)
f
C n
e
O
O
e
f
d
C H
4
9
8
7
6
5
4
3
2
1

(ppm)
1
Figure 3. H NMR (600 MHz) spectra of poly-1 , poly(1 -b-2 ), and poly-2 recorded in
5
0
100
75
100
CDCl at 25 C.
3
In addition to SEC, the formation of the well-defined polymers were further characterized by
1
13
31
1
H, C, and P NMR, and FT-IR analyses (Figure S2-S5, Supporting Information). The H NMR
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spectrum of poly-1 showed intense resonance at 7.48‒6.69 and 5.21‒4.28 ppm, which were
5
0
attributed to the protons of phenyl ring and benzyl methylene, respectively (Figure 3a). The
resonance of the main chain CH proton was located at 3.86‒3.21 ppm and splitted into doublet.
13C NMR spectrum also confirmed the chemical structure of the isolated polycarbene (Figure S2,
Supporting Information). The resonance of the main chain carbon of poly-1 was splitted into two
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
5
0
1
16
peaks located at 45.0 and 46.5 ppm, consist to the H NMR analysis. Note that the main chain
1
3
carbon of a fully atactic polycarbene usually showed multiple resonances from 43-48 ppm on C
1
6,17
13
NMR, suggesting the yielded poly-1 may possess some content of stereoregularity.
The C
5
0
resonances of the carbonyl carbon of poly-1 showed a major signal at 170.0 ppm accompanied
50
with minor signal at 171.1 ppm. On the basis of the pioneering works of Ihara and de Bruin, the
resonance at 171.1 ppm can be ascribed to the syndiotactic polycarbene.12,13,16,19 Thus, the isolated
3
1
poly-1 may contains a rather enhanced isotactic sequence. Interestingly, P NMR spectrum of
5
0
poly-1 showed two broad signals at 15.89 and 16.82 ppm, indicating the Pd(II) unit was quite
5
0
stable and was maintained at the living chain-end after the post polymerization treatments (Figure
S3, Supporting Information). FT-IR spectrum of the poly-1 showed characteristic vibration of
5
0
−
1
C=O at 1730 cm , corresponding to the ester pendants (Figure S4, Supporting Information).
Collectively, these studies confirmed the formation of expected polycarbenes.
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1
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1
2
2
2
2
2
2
2
2
2
2
3
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3
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3
3
4
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6
16
(
a)
(b)
50
2.5
7
1
1
5
00
25
14
2.0
1.5
1.0
1
2
0
8
6
150
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
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1
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.5
18
19
20
21
22
23
24
50
75
100
125
150
Retention time (min)
[2] /[Pd]
0
0
(d)100
2.5
2.0
1.5
1.0
0.5
0.0
(c)
2
.5
.0
.5
.0
80
60
40
6
2
1
1
5
4
3
20
0
0.5
30
40 50 60 70 80 90
Conversion (%)
0
100 200 300 400 500
Time (s)
A
Figure 4. (a) Size exclusion chromatograms of poly-2 s prepared from the Pd(II)/L -catalyzed
m
polymerization of 2 in THF at 25 C with different initial feed ratio of monomer to catalyst. (b)
A
Plotted of M and M /M values of poly-2 s as a function of the initial feed ratio of 2 to Pd(II) /L
n
w
n
m
catalyst. (c) Plots of M and M /M values as a function of the conversion of monomer 2 catalyzed
n
w
n
A
by Pd(II)/L in THF at 25 C. (d) Plot of monomer conversion as a function of the polymerization
time and first-order kinetic plot for the polymerization of 2 initiated by Pd(II)/LA.
A
The established fast living polymerization method using Pd(II)/L catalyst was then applied to
various diazoacetates monomers with different substituents to disclose the monomer scope. As
shown in Scheme 1, monomer 2 bearing less steric n-hexyl ester was polymerized in THF at 25
A
C by using Pd(II)/L catalyst ([2] = 0.3 M, [2] /[Pd] = 50), followed the procedure described
0
0
0
above. SEC analyses revealed the polymerization was succeeded, the isolated poly-2 showed
5
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unimodal and symmetrical elution peak on SEC curve (Figure 4a). The M and M /M were
n
w
n
determined to be 6.9 kDa and 1.17, respectively. Further studies suggested the polymerization was
also proceeded in a living/controlled manner because the M of the produced poly-2 s increased
n
m
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
linearly to the initial feed ratio of monomer to catalyst (Figure 4b). All the isolated poly-2ms
showed narrow molecular weight distribution with M /M < 1.20. To get more details, the
w
n
A
polymerization of 2 with the Pd(II)/L catalyst was followed by SEC and HPLC to disclose the
relationship between monomer conversion with reaction time, M and M /M values of the
n
w
n
produced polymers. As shown in Figure 4c, the M of the poly-2 s isolated at different
n
m
polymerization stages was linearly correlated to the conversion of monomer 2, while the M /M
w
n
kept narrow (M /M < 1.20). It was found that the polymerization was relatively fast, more than
w
n
8
0% of monomer 2 was consumed within 10 min (Figure 4d). These studies further revealed the
A
polymerization of less steric alkyl diazoacate monomer using the Pd(II)/L as catalyst was also
proceeded in a fast living fashion, efficiently afforded the desired polycarbenes in high yields with
1
controlled M and narrow M /M . The chemical structure of poly-2 was further confirmed by H,
n
w
n
m
1
3
1
C NMR and FT-IR (Figure 3c, and Figure S6-S7 in Supporting Information). H NMR spectrum
of poly-2100 showed characteristic resonances at 4.22‒3.81 and 3.61‒2.85 ppm, respectively
corresponding to the OCH of pendants and CH of the main chain (Figure 3c).
2
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
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5
5
5
5
5
5
5
6
A
a
Table 2. Polymerizations of Various Diazoacetates by Pd(II)/L in THF at 25 C
run monomer [M] /[Pd]0b time (h) M (kDa) M /M
c
c
yield (%)
d
0
n
w
n
1
2
3
4
5
6
7
8
9
2
2
2
3
3
4
4
4
5
5
5
6
6
6
50
0.5
0.5
0.5
12
12
8
6.9
1.17
1.20
1.20
1.20
1.19
1.18
1.19
1.20
1.17
1.20
1.18
1.13
1.15
1.14
79
84
76
55
60
78
81
82
75
76
81
43
34
35
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
100
150
50
11.3
14.9
6.2
8.5
6.1
9.9
12.2
6.2
7.4
8.7
3.1
3.5
4.1
100
50
100
150
50
8
8
12
12
12
24
24
24
1
0
1
100
150
50
1
12
1
1
3
4
100
150
a
c
b
The polymers were prepared according to Scheme 1. The initial feed ratio of monomer to catalyst.
The M and M /M values were determined by SEC with equivalent to polystyrene standards.
n
w
n
d
The isolated yields.
A
The fast living polymerization method using Pd(II)/L catalyst was then applied to other
diazoacetate monomers including 2-(2-(2-methoxyethoxy)ethoxy)ethyl 2-diazoacetate (3), 1-
naphthalenylmethyl ester diazoacetate (4), phenyl ester diazoacetate(5), and diphenylmethyl ester
diazoacetate (6) (Scheme 1). The polymerizations were performed in THF at room temperature,
followed the same procedure to that of monomer 1 and 2. As expected, all the polymerizations
afforded desired polymers with controlled M and narrow M /M (Table 2, and Figure S8-S18 in
n
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Supporting Information). Thus, it can be concluded that the established fast living polymerization
A
method using Pd(II)/L as catalyst can be applied to a variety of diazoacetate monomers.
Chain Extension Reactions. To further confirm the living nature of the polymerization and
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
also to reveal the activity of the Pd(II) complex on the chain end, chain extension reaction of the
isolated poly-1 with a new feed of diazoacetate monomer was then performed. By this method,
m
well-defined block copolymers may be facilely obtained. The Rh-catalyst also showed living
character and has been used in the synthesis of block polycarbenes although some random
segments may contained.44-46 While well-defined block polycarbenes have rarely been reported.20
As shown in Scheme 2, the isolated poly-1100 (M = 10.1 kDa, M /M = 1.18) was treated with
n
w
n
monomer 2 in THF at 25 C ([2] = 0.3 M, [2] /[Pd] = 75). SEC analysis indicated the block
0
0
0
copolymerization did take place because the elution peak of the resulting polymer shifted to the
high-M region, while it still remained symmetric and unimodal (Figure 5a). The M of the isolated
n
n
block copolymer poly(1 -b-2 ) was estimated to be 18.6 kDa, remarkably larger than that of the
1
00
75
precursor poly-1100 (M = 10.1 kDa, M /M = 1.18), while the distribution kept narrow with M /M
n
n
w
n
w
1
=
1.20 (Table 3). H NMR spectra also supported the formation of the expected block copolymer
1
poly(1 -b-2 ). As displayed in Figure 3b, H NMR spectrum of poly(1 -b-2 ) recorded in
1
00
75
100
75
CDCl at 25 C is almost the superposition of the respective two homopolymers of poly-1 and
3
m
poly-2 . The resonances come from the two blocks could be clearly observed. Moreover, the block
n
ratio deduced from the integral analyses of the resonances at 5.21‒4.23 ppm of poly-1100 segment
and at 1.82‒1.58 ppm of the poly-2 segment is ca. 4:3, which agree with the initial feed ratio of
7
5
the two monomers used in the block copolymerization. Note that the random copolymerization of
the two diazocarbonyl monomers usually showed the shifted resonances of the two repeating
units.20,44 Combined with FT-IR and differential scanning calorimetry (DSC) analyses (Figure
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
S19 and S20, Supporting Information), these studies confirmed the formation of expected block
copolymer, and further supported the living nature of the polymerization of diazoacate monomers
A
using Pd(II)/L as catalyst. It is worthy to point out that the living chain end of the polymers can
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
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5
6
7
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9
0
1
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5
6
7
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9
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1
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6
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9
0
maintained for quite a long time even in solution, because the solution of poly-1100 in THF stored
at room temperature for one week can still chain extended with a new feed of monomer. Taking
advantage of this method, a variety of block copolymers with tunable compositions, controlled Mn
and narrow M /M was facilely prepared just through the variation on the initial feed ratios of the
w
n
two monomers to the Pd(II) catalyst (Table 3).
Scheme 2. Chain Extension Reaction of Poly-1 with Monomer 2 and 3
m
H
H
H
H
C
H
C
C
C
mPd/L
O
C
m
n
m
n
2
, THF, r.t
3, THF, r.t
O
O
O
OC H
O
O
O
O
O(CH CH O) CH
2 2 3 3
6
13
poly(1 -b-2 )
poly-1m
poly(1m-b-3n)
m
n
(
a)
(b)
(c)
H O
poly-1100
2
THF
poly(1100-b-3100
)
poly(1100-b-275
)
18
19
20
21
22
23
1
10
100
1000
Retention time (min)
Diameter (nm)
Figure 5. (a) SEC curves of chain extension reactions. (b) DLS of amphiphilic block copolymer
poly(1 -b-3 ) measured in THF and water. (c) TEM image of the self-assembled structure
1
00
100
formed from poly(1 -b-3 ) in water.
1
00
100
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After the block copolymerization was established, amphiphilic block copolymer was facilely
prepared through the copolymerization of poly-1100 with monomer 3 which bearing a triethylene
glycol monomethyl ether chain to provide the block copolymer with amphiphilic character (Table
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
3
). The structure of poly(1 -b-3 ) block copolymer was confirmed by SEC (Figure 5a), H
1
00
100
NMR, and FT-IR (Figure S21 and S22, Supporting Information). Because of the amphiphilic
feature, the block copolymer has good solubility in most common organic solvents including THF,
chloroform, dichloromethane, and in water as well. To further support the formation of
amphiphilic block copolymer, the self-assembly property of poly(1 -b-3 ) in selective solvents
1
00
100
was investigated. Dynamic light scattering (DLS) study revealed the hydrodynamic diameter of
poly(1 -b-3 ) in THF was smaller than 10 nm, indicating it was molecularly dissolved (Figure
1
00
100
5
b). However, when the solvent was changed from THF to water, a good solvent for poly-3100 but
a poor solvent for poly-1100 segment, the diameter of poly(1 -b-3 ) increased to ca. 95 nm. The
100
100
increased size was probably due to the self-assembly of the amphiphilic block copolymer into
supramolecular micelles in water. The critical aggregation concentration of poly(1 -b-3 ) block
1
00
100
copolymer was determined to be 0.087 mg/mL (Figure S23, Supporting Information). The
morphology of the self-assembled supramolecular structure was further investigated by
transmission electron microscopy (TEM). As shown in Figure 5c, spherical nanoparticles with ca.
8
5 nm diameter were clearly observed on the TEM images of poly(1 -b-3 ) casted from the
100 100
water solution. All these studies confirmed the formation of amphiphilic block copolymer, and
further supported the living nature of the polymerization of diazoacetate monomers using the
Pd(II) catalyst.
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a
Table 3. Results for the Block Copolymerization Using Poly-1 as the Macroinitiator
m
homopolymer
block copolymer
b
b
b
b
c
run polymer
M (kDa) M /M
M (kDa) M /M
Yield (%)
n
w
n
n
w
n
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
poly(1 -b-2 )
7.0
1.15
1.18
1.16
1.18
14.2
18.6
14.0
21.5
1.19
1.20
1.20
1.21
80
84
68
67
5
0
50
poly(1 -b-2 ) 10.1
1
00
75
poly(1 -b-3 )
7.1
5
0
50
poly(1 -b-3 ) 10.3
1
00
100
aThe block copolymerizations were performed in THF at 25 C for 8 h according to Scheme 1.
The M and M /M values were determined by SEC with equivalent to polystyrene standards.
b
c
n
w
n
The isolated yields.
Helix-Sense Selective Polymerization. The backbone of polycarbenes was constituted by C-C
single bonds and carrying pendant on each main chain carbon. Thus it may form a helical
conformation if the pendants are bulky enough, similar to that of the helical polyisocyanide.21-23
However, to the best of our knowledge, the helical conformation and the related chiroptical
properties of polycarbenes have rarely been disclosed to date. To address this challenge, two chiral
R
S
A
catalysts Pd(II)/L and Pd(II)/L bearing R- or S-ligand, analogue to Pd(II)/L were prepared and
4
2
employed in the polymerization of monomer 1 (Scheme 1). Firstly, monomer 1 was polymerized
R
by chiral Pd(II)/L catalyst in THF at 25 C under the same experimental conditions described
above, afforded the expected R-poly-1 in high yield (>80%) with expected M and narrow M /M
m
n
w
n
1
(Figure S24, Supporting Information). The H NMR, FT-IR and UV-vis spectrum of R-poly-1
5
0
A
were almost the same to that of poly-1 prepared using the achiral catalyst Pd(II)/L , indicating
5
0
the same chemical structure of the two polymers (Figure S25-S27, Supporting Information). The
optical activity of R-poly-1100 was investigated by CD and UV-vis spectra recorded in THF at 25
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C. To out delight, intense positive CD was observed at the absorption region around 205‒230 nm,
corresponding to the absorption of the R-poly-1100 backbone (Figure 6a). Since there are no chiral
substituents on the polymer backbone or on the pendants, the optical activity was reasonably
ascribed to the predominated one-handed helical conformation of the polymer backbone induced
by the chiral catalyst during the process of the helix-sense-selective polymerization. However, the
CD intensity of R-poly-1100 was not stable, it gradually decreased in solution even at low
temperature (‒10 C), and almost no CD could be discerned after 5 h (Figure 6b, and Figure S28
in Supporting Information). In contrast, almost no changes could be observed on the absorption
spectrum of R-poly-1100 during the course of CD decrease. Thus, it can be speculated that the
polycarbene bearing benzyl benzoate did form a helical conformation in solution, while it is
unstable and quickly transferred to random coil. It is worthy to note that the helix of the polymer
is come from the twist of the C-C main chain. The arrangement of the pendants, the tacticity may
has significant influence on the helix formation. The partial stereoregular segments of the
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
generated R-poly-1 synthesized by using this new method may play important roles on the helix
m
formation.
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
a) 6
3
0 h
(b)6
0
1
.5 h
.5 h
2
1
1
0
.0
.5
.0
.5
2 h
4
3
5
h
h

0

2
0

0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-3
-6
0.0
2
10
220
230
240
0
1
2
3
4
5
Wavelength (nm)
Time (h)
10
(
c)
(d)8
3
00
00
5
0
2
2
1
0
4
0
100
0
R-poly-430
R-poly-450
R-poly-480
R-poly-4100
R-poly-4125
S-poly-4125
-5

-
10
15
20
-100
-200
-300

-4

-
-
-8
220
240
260
0
2
4
6
8
10
12
Wavelength (nm)
M (kDa)
n
Figure 6. (a) Time-dependent CD and UV-vis spectra of R-poly-1100 in THF at 25 C. (b) plotted
of CD intensity at 205 nm of R-poly-1100 with time. (c) CD and UV-vis spectra of R-poly-4 and
m
S-poly-4 with different M . (d) Plots of CD and optical rotation values of R-poly-4 and S-poly-
m
n
m
4m with Mn.
It has been reported that introducing of bulky substituents onto a polymer pendants can
stabilized the helical conformation of a synthetic polymer due to steric hindrance between the
adjacent repeating units.21-24 Thus, to make polycarbenes with more stable helical conformation, a
series of R-poly-4 s with different M s and narrow M /M s were facilely prepared just by varying
m
n
w
n
R
the initial feed ratio of monomer to the Pd(II)/L catalyst (Table 4, and Figure S29-S31 in
Supporting Information), followed the procedure described above. Because of more bulky of the
pendants, they may possess stable helical conformation in solution. As expected, all the isolated
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R-poly-4 s polymers with different M s showed intense positive CD at the absorption region of
m
n
the polymer backbone, indicating the formation of predominated one-handed helix. To our delight,
the helical conformation of the main chain was quite stable, no discernable change could be
observed on the CD and UV-vis spectra in THF solution at the temperature range from ‒10 to 55
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0

C for 24 h (Figure S32, Supporting Information). The helical conformation could be maintained
in various solvents with different polarity at 25 C, including THF, chloroform and
dichloromethane, suggesting the solvents have no significant influence on the helical structure
(Figure S33, Supporting Information). Moreover, the optical activity of R-poly-4100 showed a
linear correlation with its concentration at the range of 0.05‒0.30 mg/mL in THF at 25 C (Figure
S34 and S35, Supporting Information), confirming the optical activity was come from its helical
backbone, not the supramolecular aggregation. To disclose the CD was come from the polymer
R
R
backbone other than the residual L ligand, the CD and UV-vis spectra of Pd(II)/L were recorded
in THF at 25 C. As anticipated, it showed intense CD at 205‒220 nm, while the CD and UV-vis
patterns were completely different to those of the R-poly-4100 (Figure S36, Supporting
R
Information). Moreover, no CD could detected on Pd(II)/L at the same concentration as that on
R
the chain end of R-poly-4 . When the optically active L ligand was completely removed by
1
00
treated R-poly-4100 with NaBH , the isolated polymer showed almost the same CD and UV-vis
4
patterns (∆ε221 = 8.32, Figure S37 in Supporting Information), and the optical rotation was also
maintained ([α]25 = 216.54). Thus it can be safely concluded that the optical activity of R-poly-
D
R
4100
was not come from the Pd(II)/L group of the chain end, but the R-poly-4 backbone itself.
m
Since the repeating units of the R-poly-4 were achiral, the CD was ascribed to the helical
m
conformation of the main chain with predominated one-handed helix.
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 4. Polymerizations of 4 in THF at Room Temperature Using Chiral Catalystsa
Mnc
yieldd
(%)
78
b
c
∆ε221e [α]25
f
run polymer
[M] /[Pd]
M /M
D
0
0
w
n
(
kDa)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
1
1
1
S-poly-420 20
S-poly-430 30
4.0
5.1
6.2
7.2
8.6
1.16
1.17
1.17
1.19
1.20
‒4.03 ‒108.12
‒5.47 ‒144.54
‒5.91 ‒165.54
‒6.96 ‒184.50
‒7.58 ‒207.58
‒8.33 ‒218.54
‒8.33 ‒220.14
5.96 168.66
6.91 188.54
7.59 205.12
8.27 215.68
83
S-poly-440 40
S-poly-450 50
S-poly-460 60
S-poly-480 80
S-poly-4100 100
R-poly-440 40
R-poly-450 50
R-poly-460 60
R-poly-480 80
R-poly-4100 100
75
72
74
10.1 1.19
12.1 1.20
73
75
6.1
7.3
8.8
9.9
1.18
1.20
1.20
1.18
82
78
0
1
2
73
71
11.9 1.18
72
8.27 217.45
a
R
S
The polymers were prepared in THF at 25 C for 8 h using Pd(II)/L and Pd(II)/L as the catalyst.
b
c
The initial feed ratio of monomer to catalyst. The M and M /M values were determined by SEC
using polystyrene standards. Isolated yields. The optical rotations were recorded in THF at 25
C. The molar circular dichroisms at 221 nm were measured in THF at 25 C.
n
w
n
d
e
f

Further studies revealed the CD intensity of R-poly-4 s was dependent on the M (Figure 6c).
m
n
Increasing the M lead to the increase of the ellipticity (θ) until it became constant when the M
n
n
reached to 10.1 kDa (Figure 6d). The optical rotation of R-poly-4 showed similar relationship
m
with M (Figure 6d). This study indicated that the optical activity was indeed resulted from the
n
helical polycarbene backbone and became stable when the degree of the polymerization reached
S
to ca. 80. To get more details, monomer 4 was then polymerized by Pd(II)/L catalyst, the
R
enantiomeric antipode of Pd(II)/L , under the same experimental conditions. As anticipated, the
isolated S-poly-4125 showed an intense negative CD at the absorption region of the backbone, and
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was almost the mirror image to that of the R-poly-4 . While the UV-vis spectra of the two
1
25
polymers were almost the same (Figure 6c). The CD intensity and optical rotations of S-poly-4m
also increased with the increase of the M until the value of M reached to 9.9 kDa, similar to that
n
n
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
of R-poly-4 (Figure 6d). Collectively, these studies revealed that the polycarbenes bearing bulky
m
pendants can possessing a stable helical conformation in solution. This is the first study that
disclosed the helicity and the chiroptical properties of polycarbene backbone.
Conclusions
In summary, we have developed a family of novel Pd(II)-based catalysts, which could promote
a fast living polymerization of various diazoacetates under mild conditions under air. The
polymerization was very fast, and can be accomplished within several minutes, afforded
polycarbenes in high yields with controlled M and narrow M /M . Taking advantage of this
n
w
n
method, a variety of block copolymers were facilely prepared through chain extension reaction.
Moreover, fast living polymerization of diazoacetates bearing bulky substituents by chiral Pd(II)
catalysts afforded well-defined polycarbenes with high optical activity due to the formation of
predominated one-handed helix. The present study provides not only a novel method for fast living
polymerization of various diazoacetates under mild conditions, but also for the first time revealed
the helical conformation of polycarbene, which may have great potentials in many fields including
chiral recognition, enantiomer separation and asymmetric catalyst, and so on.
ASSOCIATED CONTENT
Supporting Information. This material is available free of charge via the Internet at
http://pubs.acs.org.
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1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Experimental procedure, and additional spectra of the polymers, monomers and the related
mediates.
AUTHOR INFORMATION
0
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1
2
3
4
5
6
7
8
9
0
Corresponding Author
*
E-mail: zqwu@hfut.edu.cn (Z.-Q. Wu)
Notes
The authors declare no completing financial interest.
ACKNOWLEDGMENT
This work is supported by the Natural Scientific Foundation of China (21622402, 51673057, and
21574036) and the Fundamental Research Funds for the Central Universities of China. Z.-Q. Wu
thanks the 1000plan Program for Young Talents of China. N. Liu thanks Anhui Provincial Natural
Science Foundation (1608085MB41).
REFERENCES
(
(
(
1) Jellema, E.; Jongerius, A. L.; Reek, J. N. H.; de Bruin, B. C1 Polymerisation and Related C–
C Bond Forming ‘Carbene Insertion’ Reactions. Chem. Soc. Rev. 2010, 39, 1706−1723.
2) Cahoon, C. R.; Bielawski, C. W. Metal-promoted C1 polymerizations. Coord. Chem. Rev.
2
018, 374, 261−278.
3) Luo, J.; Shea, K. J. Polyhomologation. A Living C1 Polymerization. Acc. Chem. Res. 2010,
3, 1420–1433.
4
(4) Ehara, E. Poly(substituted Methylene) Synthesis: Construction of C–C Main Chain from One
Carbon Unit. Adv. Polym. Sci. 2010, 231, 191–232.
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(
5) Suarez, A. I. O.; del Río, M. P.; Remerie, K.; Reek, J. N. H.; de Bruin, B. Rh-Mediated C1-
Polymerization: Copolymers from Diazoesters and Sulfoxonium Ylides. ACS Catal. 2012, 2,
2046–2059.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
5
5
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0
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4
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