Scandium-Catalyzed Regio- And Stereoselective Cyclopolymerization of Functionalized α,ω-Dienes and Copolymerization with Ethylene

Article abstract of DOI:10.1021/jacs.9b04275

The precise control of regio- and stereochemistry in the cyclopolymerization of heteroatom-functionalized α,ω-dienes is of much interest and importance, but has remained a challenge to date. We report herein the regio-, diastereoselective and stereoregula

Full text of DOI:10.1021/jacs.9b04275

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Article
Scandium-Catalyzed Regio- and Stereoselective Cyclopolymerization
of Functionalized #,#-Dienes and Copolymerization with Ethylene
Haobing Wang, Yanan Zhao, Masayoshi Nishiura, YANG YANG, Gen Luo, Yi Luo, and Zhaomin Hou
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b04275 • Publication Date (Web): 25 Jul 2019
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Journal of the American Chemical Society
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Scandium-Catalyzed Regio- and Stereoselective Cyclopolymerization
of Functionalized ,-Dienes and Copolymerization with Ethylene
Haobing Wang,†,II Yanan Zhao,§,II Masayoshi Nishiura,†,‡ Yang Yang,† Gen Luo,§ Yi Luo,*§ Zhaomin
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Hou*†,‡,§
†Advanced Catalysis Research Group, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako, Saitama 351-
0198, Japan
‡Organometallic Chemistry Laboratory, RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198,
Japan
§State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024,
P. R. China
Supporting Information Placeholder
ABSTRACT: The precise control of regio- and stereochemistry in the cyclopolymerization of heteroatom-functionalized α,ω-dienes
is of much interest and importance, but has remained a challenge to date. We report herein the regio-, diastereoselective and stere-
oregular cyclopolymerization of ether- and thioether-functionalized 1,6-heptadienes by a half-sandwich scandium catalyst. The
polymerization of 4-benzyloxy-1,6-heptadiene selectively afforded the corresponding benzyloxy-functionalized cyclic polymer com-
posed of 1,2,4-cis-substituted-ethylenecyclopentane (ECP) microstructures in a isospecific fashion (95% mmm). In contrast, the
polymerization of 4-phenylthio-1,6-heptadiene exclusively yielded 1,2-trans-1,4-cis-ECP units with high isotacticity (95% rrr). The
DFT calculations revealed that an interaction between the scandium atom in the catalyst and the heteroatom in a diene monomer
played an important role in controlling the regio- and stereochemistry of the diene cyclopolymerization. The copolymerization of
functionalized 1,6-heptadienes with ethylene has also been achieved in a controlled fashion.
INTRODUCTION
oselectivity at either the 1,3-dimethylene skeleton or the 5-
siloxy substituent (Scheme 1a, top).4 The cyclopolymerization
of 4-tert-butyldimethylsiloxy-1,6-heptadiene by Fe and Co
catalysts has been reported to yield polymers containing the
five-membered ring 1,2- ethylene-4-siloxycyclopentane (ECP)
Organic polymers with cyclic repeating units in the polymer
backbone are of much interest and importance in both aca-
demic research and industrial applications.1 Cyclic polyolefins
bearing heteroatom functional groups are of special interest, as
they may show improved beneficial properties compared to
the heteroatom-free polymers. The cyclopolymerization of
α,ω-dienes such as 1,5-hexadiene and 1,6-heptadiene by transi-
tion metal catalysts has demonstrated particular utility for the
preparation of cyclopolyolefins.2-5 In this transformation, the
precise control of the regio- and stereochemistry is highly im-
portant to obtain high-performance polymers. However, com-
pared to the polymerization of unsubstituted α,ω-dienes, it is
usually difficult to control the regio- and stereoselectivity of
the cyclopolymerization of heteroatom-functionalized α,ω-
dienes, because of the lack of suitable catalysts that can not
only show good compatibility with the heteroatom functional
group but can also govern the stereochemistry of the heteroa-
tom-substituent in addition to the regio- and stereoselectivity
control of the common cyclization process. It has been previ-
ously reported that zirconocence catalysts could show compat-
ibility with some sterically demanding siloxy-substituted α,ω-
dienes, such as 4-tert-butyldimethylsiloxy-1,6-heptadiene.
However, the resulting siloxy-functionalized polymer products
Scheme 1. Transition-Metal-Catalyzed Cyclopolymerization of
Heteroatom-Functionalized 1,6-Heptadienes
consisted of
a mixture of trans- and cis-fused 1,3-
methylenecyclohexane (MCH) units without showing stere-
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units (Scheme 1a, bottom).5b Although 1,2-cis- or 1,2-trans
Homopolymerization of Heteroatom-Functionalized 1,6-
1
2
3
4
5
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7
8
diastereoselectivity could be achieved by choosing a Fe or Co
catalyst, respectively, a control of the stereoselectivity on the
4-siloxy substituent was not achieved and no stereoregulary
(tacticity) of the repeating ECP units was observed. Despite
continued interest and recent advances in this area, the precise
control of the regio- and stereochemistry in the cyclopolymeri-
zation of heteroatom-functionalized α,ω-dienes has remained a
challenge to date.6
Heptadienes by Half-Sandwich Scandium Catalysts. At first, we
examined the polymerization of 4-benzyloxy-1,6-heptadiene
(O-1) by using a combination of the C5H5-ligated scandium
complex Sc-1 and [Ph3C][B(C6F5)4] as a catalyst.9 With the
monomer to catalyst feed ratio [O-1]/[Sc-1] = 100/1, the
polymerization slowly took place at room temperature, reach-
ing 35% conversion in 24 h (Table 1, run 1). The resulting
polymer contained a mixture of cyclized and uncyclized units,
as shown by the NMR analyses. When the larger C5Me4H-
ligated scandium complex Sc-2 was employed, rapid polymeri-
zation was observed under the same conditions, selectively
affording the cyclic polymer product with Mn = 28.8 ×103 g
We have recently found that organo rare-earth metal cata-
lysts can show unique activity and selectivity in various trans-
formations of heteroatom-containing organic substrates,7,8
including the regio-, stereospecific polymerization of heteroa-
tom-functionalized -olefins,8q,r because of the unique heteroa-
tom-affinity of the rare-earth metal ions. These findings have
promoted us to examine the cyclopolymerization of heteroa-
tom-functionalized α,ω-dienes by rare-earth metal catalysts.
We report herein the regio-, diastereoselective and stereoregu-
lar cyclopolymerization of heteroatom-functionalized 1,6-
heptadienes by a half-sandwich scandium catalyst, in which the
regio- and stereoselectivity is uniquely controlled through the
interaction between the catalyst metal center and the heteroa-
tom. This protocol has efficiently afforded a new family of
functionalized cyclic polyolefins with unprecedentedly high
regio- and diastereoselectivity at all of the three chiral carbon
centers together with highly stereoregular orientation of the
cyclic ECP units (Scheme 1b). The cyclocopolymerization of
the heteroatom-functionalized 1,6-heptadienes with ethylene
is also described.
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mol and Mw/Mn = 2.50 (Table 1, run 2). When the [O-
1
1]/[Sc-2] feed ratio was raised to 500/1, the monomer was
quantitatively converted within 3 h, but an insoluble polymer
product (1,2-dichlorobenzene at 145 °C) was yielded probably
due to cross-linking (Table 1, run 3). The use of a further ste-
rically demanding C5Me4SiMe3-ligated scandium complex Sc-3
with [O-1]/[Sc-1] = 100/1 yielded the cyclic polymer product
with a narrower molecular distribution (Mn = 18.7 kg/mol and
Mw/Mn = 1.50) (Table 1, run 4). As the [O-1]/[Sc-3] feed
ratio was raised to 500/1, the number average molecular
weight (Mn) of the resulting polymer showed a pronounced

1
increase to 86.5 ×103 g mol , and no cross-linked insoluble
product was observed (Table 1, run 5). The polymerization of
O-1 by Sc-3 proceeded even at -20 °C, affording the cyclic pol-
ymer product with higher stereoselectivity (Table 1, run 6). At
50 °C, the polymerization took place more rapidly but with
slightly lower stereoselectivity (Table 1, run 7).
RESULTS AND DISSCUSION
Table 1. Sc-Catalyzed Cyclopolymerization of Heteroatom-Functionalized 1,6-Heptadienesa
Mnc (×103 g
e
e
time
(h)
conv.
(%)b
1,2-trans-1,4-cis/
1,2,4-cisd
Tg
Tm
c
run
diene (D)
[Sc]
D/[Sc]
temp.
Mw/Mn
tacticityd
mol
)
1
(°C)
n.d.f
10
(°C)
n.d.f
122
n.d.f
122
125
124
116
n.o.h
122
n.o.h
160
162
1
2
O-1
O-1
O-1
O-1
O-1
O-1
O-1
O-2
O-2
S-1
Sc-1
Sc-2
Sc-2
Sc-3
Sc-3
Sc-3
Sc-3
Sc-3
Sc-2
Sc-3
Sc-3
Sc-3
100/1
100/1
500/1g
100/1
500/1g
100/1
100/1
100/1
100/1
100/1
100/1
500/1g
20
20
20
20
20
-20
50
20
20
20
20
20
24
0.5
3
35
100
100
100
70
n.d.f
28.8
n.d.f
18.7
86.5
17.1
19.8
12.8
6.7
n.d f
2.50
n.d f
1.50
2.20
2.89
1.90
1.86
1.98
2.05
2.13
2.73
n.d.f
6/94
n.d.f
n.d.f
95% mmm
n.d.f
3
n.d.f
4
1
6/94
6/94
2/98
12/88
9/91
11/89
75/25
94/6
94/6
95% mmm
95% mmm
98% mmm
90% mmm
atactic
11
5
48
12
0.5
24
96
48
3
11
6
84
11
7
99
13
8
64
50
9
30
80% mmm
n.d.f
47
10
11
12
57
17.9
7.1
13
S-2
100
98
95% rrr
95% rrr
28
S-2
3
10.1
31
a Conditions: [Sc] (0.02 mmol), [Ph3C][B(C6F5)4] (0.02 mmol), diene (0.5 M), 20 °C. b Weight of polymer obtained/weight of monomer used. c Determined by gel permeation chromatography
d
e
f
(GPC) in tetrahydrofuran at room temperature against polystyrene standard. Determined by 13C NMR analysis. Determined by differential scanning calorimetry (DSC). n.d. = not deter-
mined. g diene (1.0 M). h n.o. = not observed.
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The H and 13C NMR analyses revealed that the cyclopol-
ymer products (poly(O-1)) were exclusively composed of
1,2,4-cis-substituted ECP units (94%) (Figure 1a; see also
Figures S9-S16). In the 13C{1H} NMR spectrum, the signal of
the C1 atom in the ECP ring was identical to that of the C2
atom (δ 41.2), and the C3 signal was identical to that of the C5
atom (δ 37.5), suggesting that the C6 and C7 methylene sub-
stituents on the C1 and C2 atoms in the ECP ring should be cis
to each other (Figure 1a). The benzyloxy-substituted carbon
atom C4 showed a sharp signal at δ 80.0, indicating that the
configuration of the benzyloxy substituent was also well fixed.
A well-expanded NOESY spectrum showed distinct correlation
between the C4H proton (3.98 ppm) and the C1H as well as
C2H proton (1.78 ppm) (Figure S16), suggesting that the
benzyloxy group on C4 should be stereoselectively oriented cis
to the CH2 substituents on the C1 and C2 atoms in the ECP
ring. These results are indicative of a highly regulated 1,2,4-cis
diastereoselective ECP configuration. More remarkably, the
13C{1H} NMR signals of all the carbon atoms in the ECP units
appeared as well-resolved singlets, suggesting that the ECP
units were oriented with high stereoregularity (mmm = 95%,
isotactic).10 The DSC analysis of the polymer products re-
vealed melting temperatures (Tm) at 122-125 °C (Table 1, runs
2-7; Figures S18, S20, S22), in agreement with the high stere-
oregularity of the ECP units.
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Figure 1. 13C{1H} NMR spectra (125 MHz, 1,1,2,2-C2D2Cl4,
26.8 °C). (a) Poly(O-1) (Table 1, run 4), (b) Poly(S-2) (Table 1,
run 11).
spectrum of poly(S-2), the chemical shifts of the C1 (δ 44.9)
and C2 (δ 46.5) carbon atoms in the ECP ring were signifi-
cantly different, and so were those of the C3 (δ 39.9) and C5
(δ 40.7) atoms, suggesting that the C6 and C7 methylene sub-
stituents on the C1 and C2 atoms should be trans to each other
(Figure 1b). In the HETCOR spectrum, the difference in
chemical shift between the two protons on the C5 atom (δ
40.7, 1.2 and δ 40.7, 2.4) was much bigger that on the C3 atom
(δ 39.9, 1.7 and δ 39.9, 1.9) (Figure S53), probaly because of
the influence of the PhS substituent on the C4 atom. This sug-
gests that the PhS substituent on the C4 should be diastereose-
lectively oriented cis to the C1 and trans to the C2 substituents
on the ECP ring (i.e., 1,2-trans, 1,4-cis configuration). The
13C{1H} NMR signals of all the carbon atoms in the ECP units
appeared as well-resolved singlets, suggesting that the ECP
units should be oriented in a highly stereospecific fashion (rrr
= 95%, isotactic). In agreement with the high stereoregularity,
ploy(S-2) showed high melting temperatures (Tm) at 160-
162 °C and apparent crystallization temperature at 83-86 °C
(Table 1, runs 11 and 12; Figures S59, S61). The selective
formation of the 1,2-trans, 1,4-cis-ECP units in the polymeriza-
tion of S-2 stands in sharp contrast with the exclusive for-
mation of the 1,2,4-cis ECP configurations in the case of O-1
and O-2, again demonstrating the significant influence of the
heteroatom in the present polymerization.
The cyclopolymerization of 4-phenoxy-1,6-heptadiene (O-
2) by Sc-3 also took place in a regio- and diastereoselective
fashion, selectively affording the corresponding phenoxy-
substituted poly(ECP) in a 1,2,4-cis fashion (91%), but the
reaction was much slower than that of the benzyloxy analog O-
1 under the same conditions (Table 1, run 8). In contrast with
the high tacticity of poly(O-1), poly(O-2) synthesized by Sc-3
showed poor stereoregularity (atactic) (Figure S32). These
results suggest that the substituent on the oxygen atom in a
ether-substituted 1,6-heptadiene could show significant influ-
ences on the activity and stereoregularity of the cyclopolymer-
ization of the diene unit.8q The use of the smaller C5Me4H-
ligated Sc-2 catalyst improved the tacticity (80% mmm), but
the reaction remained sluggish (30% conversion in 96 h) (Ta-
ble 1, run 9, Figure S38). It is also worth noting that the cyclo-
polymerization of the oxygen-free 1,6-heptadiene by Sc-3
yielded the six-membered ring MCH units (91%) with no ste-
reoselectivity,3f standing in sharp contrast with the exclusive
formation of the five-membered ring ECP units in the
polymerization of the ether-functionalized 1,6-heptadienes O-
1 and O-2. These results suggest that the ether group may
show critical influences not only on the stereoselectivty but
also on the regioselectivity of the diene cyclopolymerization.
DFT Calculations of the Cyclopolymerization of S-2 and O-1.
To acquire insights into the high regio- and stereoselectivity
observed above, we preformed the DFT calculations of the
cyclopolymerization of S-2 and O-1 catalyzed by the cationic
species (Cat) generated by the reaction of Sc-3 with 1 equiva-
lent of [Ph3C][B(C6F5)4]. In the case of S-2, once the sulfur
atom and a vinyl group in the diene are coordinated to the Sc
center, the S-bonded prochiral C4 atom in S-2 becomes chiral
because of desymmetrization. Two coordination configura-
tions (i.e., AS(4R) and AS(4S)) of C4 were therefore considered
for the insertion/cyclization reactions, respectively (Figure 2).
In both pathways, the si-coordination insertion mode was cal-
culated to be more kinetically favorable than the re-fashion
(19.8 and 21.6 vs 29.1 and 28.9 kcal/mol, Figure 2), which is
consistent with the previous DFT analyses of the Sc-catalyzed
polymerization of 4-phenylthio-1-butene.8q It has also been
found that si-AS(4R) is more stable than si-AS(4S) by 2.8
To further probe the heteroatom effects, we then examined
sulfur-functionalized 1,6-heptadienes by using catalyst Sc-3.
Compared to O-1, the sulfur analog 4-benzylthio- 1,6-
heptadiene S-1 was much less active and less selective under
the same conditions, which afforded ploy(S-1) composed of a
75:25 mixture of the 1,2-trans- and 1,2-cis- ECP units with 57%
conversion in 48 h (Table 1, run 10; Figures S45-S46). By
contrast, 4-phenylthio-1,6-heptadiene (S-2) showed much-
higher activity and higher stereoselectivity than S-1, selectively
yielding the thioether-functionalized cyclic polymer consisting
of isotactic 1,2-trans, 1,4-cis-ECP units with rrr = 95% (Table
1, runs 11 and 12; Figure 1b).10,11 In the 13C{1H} NMR
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kcal/mol and the formation of si-BS(1S,4R) is more favored CS(1S,2S,4R) (ΔG‡ = 12.6 kcal/mol) to give si-DS(1S,2S,4R)
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both kinetically and thermodynamically in comparison with si-
BS(1S,4S) (barriers of 19.8 vs 21.6 kcal/mol and reaction ener-
gies of −0.3 vs 2.8 kcal/mol, Figure 2). Once the more stable
si-BS(1S,4R) was generated, different coordination/insertion
fashions (re- or si-) of the remaining C=C bond could yield
two diastereo-cyclic products with different configurations.
The intramolecular coordination of the remaining C=C bond
to the Sc atom in si-BS(1S,4R) could yield si-CS(1S,4R) or re-
CS(1S,4R). Although si-CS(1S,4R) is 0.8 kcal/mol higher in
energy than re-CS(1S,4R), the subsequent insertion of the C=C
double into the Sc−alkyl bond in si-CS(1S,4R) via si-TS-
(si-insertion, 1,2-trans-1,4-cis product) is more favorable than
the pathway of re-CS(1S, 4R)  re-TS-CS(1S,2R,4R)  re-
DS(1S,2R,4R) (re-insertion, energy barrier of 26.8 kcal/mol,
1,2-cis-1,4-trans product). A further calculation of the reaction
of the second S-2 monomer with si-DS(1S,2S,4R) also indicated
more favorable si-insertion and subsequent si-cyclization pro-
cess to give a second 1,2-trans-1,4-cis ECP unit (Figure S118).
Repetition of these si-insertion and si-cyclization modes would
therefore afford the isotactic polymer product, being in agree-
ment with the experimental observation.
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Figure 2. Computational analysis of the insertion/cyclization of first molecule of S-2 by the cationic species (Cat) generated by the reaction of Sc-3
with [Ph3C][B(C6F5)4]. (A) DFT-calculated energy profile. (B) Structures of the stationary points shown in the energy profile. The less fa-
vored pathway is pale-colored. R = CH2C6H4NMe2-o, TS: transition state, Gsol: Relative Gibbs free energy in solution.
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Figure 3. Computational analysis of the insertion/cyclization of first molecule of O-1 by the cationic species (Cat) generated by the reaction of Sc-3
with [Ph3C][B(C6F5)4]. (A) DFT calculated energy profile. (B) Structures of the stationary points shown in the energy profile. The less fa-
vored pathway is pale-colored. R = CH2C6H4NMe2-o, TS: transition state, Gsol: Relative Gibbs free energy in solution.
In the case of O-1 (Figure 3), the si-coordination insertion
mode of the first C=C bond is also more kinetically favorable
than the re-fashion. In contrast to S-2, however, in the two si-
coordination insertion modes, the pathway of si-AO(4S)si-
TS-AO(1S,4S)si-BO(1S,4S) is more energetically favored than
that of si-AO(4R)si-TS-AO(1S,4R)si-BO(1S,4R) (Figure 3).
This indicates that the S configuration on the C4 atom of O-1
becomes more favorable during the si-coordination insertion
of the first C=C bond. In the cyclization step, the re-
CO(1S,4S)-involved intramolecular insertion of the remaining
C=C bond into the Sc‒alkyl bond is significantly more favora-
ble than that of si-CO(1S,4S) (barriers of 9.7 + 5.8 = 15.5 vs
22.9 + 5.8 = 28.7 kcal/mol, Figure 3). The incorporation of
the second O-1 monomer was also calculated to favor the simi-
lar way as the first monomer adopted (Figure S119). Repeti-
tion of these si-insertion and re-cyclization modes could there-
fore afford the isotactic polymer product, being in line with the
experimentally observed selectivity.
Mechanism of the Sc-Catalyzed Cyclopolymerization of S-2 and O-1.
On the basis of the DFT calculations described above, the pos-
sible scenarios of the regio- and stereospecific cyclopolymeri-
zation of S-2 and O-1 by Sc-3 are shown in Schemes 2a and 2b,
respectively. The chelation of the Sc atom by S-2 with the S
atom and a C=C bond occurs in a si-coordination fashion to
give the most favorable si-AS(4R) configuration (Scheme 2a).
The subsequent 2,1-insertion of the Sc-coordinated C=C bond
into the Sc−CH2C6H4NMe2-o bond would generate the si-
BS(1S,4R) intermediate. The intramolecular si-coordination of
the remaining C=C bond to the Sc atom followed by 1,2-
sinsertion into the Sc−C σ bond via si-CS(1S,4R) may then take
place to give the thermodynamically and kinetically favored
1,2-trans cyclopentane species si-DS(1S,2S,4R). Similarly, the
si-coordination of the second monomer S-2 to the Sc atom (to
give si-ES(4R)) and the subsequent si-2,1-insertion would yield
si-FS(1S,4R). The intramolecular si-1,2-insertion (cyclization)
of the remaining C=C bond via si-GS(1S,4R) should generate
another ECP unit (see si-HS(1S,2S,4R)) with a configuration
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Scheme 2. Possible Mechanisms of Regio- and Stereoselective Cyclopolymerization of S-2 (a) and O-1 (b) by Sc-3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
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30
31
32
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34
35
36
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39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
identical to that in si-DS(1S,2S,4R). The incorporation of the
third S-2 monomer into si-HS(1S,2S,4R) in the same manner
should then afford the 1,2-trans, 1,4-cis-fused ECP microstruc-
tures with isotactic stereoregularity (rrr-IS).
the si-BO(1S,4S) intermediate. The intramolecular re-
coordination of the remaining C=C bond to the Sc atom fol-
lowed by 1,2-sinsertion into the Sc−C σ bond via re-CO(1S,4S)
could give the thermodynamically and kinetically favored
1,2,4-cis-subsititued ECP species re-DO(1S,2R,4S). Similarly,
the successive incorporation of the second and third O-1 mon-
omers in a si-2,1-/re-1,2-insertion/cyclization manner would
afford the isospecific 1,2,4-cis-fused ECP units mmm-IO.
In the case of monomer O-1 (Scheme 2b), the chelation of
the Sc atom with the O atom and a C=C bond would prefera-
bly give the si-AO(4S) configuration, as shown by the DFT
analysis. The subsequent 2,1-insertion of the Sc-coordinated
C=C bond into the Sc−CH2C6H4NMe2-o bond should yield
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Journal of the American Chemical Society
Table 2. Copolymerization of Heteroatom-Functionalized 1,6-Heptadienes with Ethylene by Sc-3a
1
2
3
4
5
6
7
8
b
Mn (×103 g
e
e
diene
(D)
time
(min)
i.r.c
(%)
Tg
Tm
yield
(g)
diene
conv. (%)
activity (g mol-
1,2-trans-1,4-cis/
1,2,4-cisd
b
run
D/[Sc-3]
Mw/Mn
Sc1 h1 atm
)
mol
14.1
55.9
)
1
1
(°C)
10
-19
-17
-9
(°C)
1
2
3
4
5
6
7
8
O-1
O-2
O-2
O-2
S-1
100/1
100/1
500/1
1000/1
100/1
100/1
200/1
500/1
10
5
0.30
0.47
2.16
3.56
0.40
0.40
0.79
2.00
74
50
62
65
88
62
77
94
-
1.53
2.05
2.20
1.74
1.88
1.45
2.35
3.89
100
9
6/94
7/93
7/93
7/93
75/25
94/6
94/6
94/6
116
282
126
9
30
45
90
0.5
1.5
3
216
100.8
147.9
24.4
29.6
18.5
14.7
15
25
74
19
35
77
127
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
153
n.o.f
13.3
8
n.o.f
S-2
2400
1580
2000
14
21
29
120
S-2
113/139
n.o.f
S-2
a Conditions: [Sc-3] (0.02 mmol), [Ph3C][B(C6F5)4] (0.02 mmol), ethylene (1 atm), toluene (50 mL) at 20 °C. b Determined by GPC in 1,2-dichlorobenzene at 145 °C against polystyrene
standard. c Incorporation ratio of D, determined by 1H NMR analysis. d Determined by 13C NMR analysis. e Determined by DSC. f n.o. = not observed.
Copolymerization of Heteroatom-Functionalized 1,6-
Heptadienes with Ethylene. With the establishment of the regio-
and stereoselective cyclopolymerization of the heteroatom-
functionalized 1,6-heptadienes, their copolymerization with
ethylene was also examined (Table 2). Under the coexistence
of O-1 and ethylene (1 atm) with [O-1]/[Sc-3] = 100/1, only
the homopolymer of O-1 was formed (Table 2, run 1). This is
probably due to the strongly coordinating ability of the ben-
zyloxy group in O-1, which may hamper the coordina-
tion/insertion of ethylene at the catalyst metal center. By con-
trast, the copolymerization of the phenoxy-substituted mono-
mer O-2 with ethylene occurred rapidly under the same condi-
tions, although the homopolymerization of O-2 was less effi-
cient. With [O-2]/[Sc-3] = 100/1 under 1 atm of ethylene at
room temperature, a copolymer product with Mn = 55.9 ×103 g
poly(OSiEt3) (Scheme 3). Poly(OSiEt3) exhibited a much low-
er Tg (–10 °C) than that of poly(O-1) (Tg = 11 °C) without
showing a Tm or Tc in the DSC profile (Figure S111). The pro-
tonolysis of poly(OSiEt3) by aqueous HCl in THF gave the
corresponding HO-functionalized polymer poly(OH).
Poly(OH) demonstrated excellent thermal stability (Tg
=
105 °C, Tm = 261 °C, Td (decomposition temperature) =
400 °C; Figures S114 and S115) and excellent solvent re-
sistance (insoluble in dichlorobenzene at 145 ºC).
Scheme 3. Transformations of Poly(O-1)
mol and O-2 incorporation of 9 mol% was obtained in 5 min
(Table 2, run 2). As the [O-2]/[Sc-3] ratio was raised to 500/1
and 1000/1, the molecular weight (Mn) of the resulting copol-
ymers significantly increased to 100.8 × 103 g mol and 147.9
×103 g mol , and the O-2 incorporation ratio increased to 15
mol% and 25 mol%, respectively (Table 2, runs 3 and 4). The
13C{1H} NMR analyses revealed that the copolymers con-
tained predominantly isolated 1,2,4-cis ECP units (Figures
S74-S81). Uncyclized pendency vinyl group was not observed,
suggesting that the cyclization step competed well against eth-
ylene insertion in the present copolymerization.
1
CONCLUSION
In summary, we have achieved for the first time the regio-,
diastereoselective and highly stereoregular cyclopolymeriza-
tion of ether- and thioether-functionalized 1,6-heptadienes
and their copolymerization with ethylene by using a half-
sandwich scandium catalyst such as Sc-3. The unprecedented
diastereoselectivty and stereoregularity could be ascribed to
the unique interaction between the catalyst metal center and
the heteroatom in a diene monomer, as shown by DFT calcula-
tions. This protocol has afforded a new family of heteroatom-
functionalized cyclic polyolefins which were difficult to pre-
pare previously. Our findings may also help design and synthe-
size new catalysts for efficient and regio-, stereoselective cy-
clopolymerization and related transformations of various func-
tional dienes.

1

1
The copolymerization of S-1 and ethylene (1 atm) with [S-
1]/[Sc-3]
= 100/1 afforded the corresponding sulfur-
functionalized copolymer with 74 mol% incorporation of the S-
1 monomer and a 75/25 mixture of the 1,2-trans-1,4-cis- and
1,2,4-cis-ECP units (Table 2, run 5). The copolymerization of
S-2 and ethylene with [S-2]/[Sc-3] = 100/1, 200/1, and 500/1
gave the copolymers with the S-2 incorporation ratio = 19, 35,
and 77 mol%, respectively (Table 2, runs 6-8). The copoly-
mers possessed predominantly the 1,2-trans, 1,4-cis-ECP units,
similar to the homopolymerization of S-2.
EXPERIMENTAL SECTION
Materials and methods. All manipulations of air and moisture-
sensitive compounds were performed under a dry nitrogen atmos-
phere by use of standard Schlenk techniques or a nitrogen-filled
Mbraun glovebox. Nitrogen was purified by being passed through
a Dryclean column DC-A4 (4 Å molecular sieves, Nikka Seiko
Co.) and a Gasclean GC-XR column (Nikka Seiko Co.). Solvents
were purified by an Mbraun SPS-800 Solvent Purification System
and dried over fresh Na chips in the glovebox. [Ph3C][B(C6F5)4]
(97%) was purchased from Strem Chemical Corporation and used
without purification. Rare-earth catalysts Cp′Sc(CH2C6H4NMe2-
Transformations of a Cyclic Polymer. Replacement of the

benzyl groups in poly(O-1) (Mn = 86.5 ×103 g mol , Table 1,
run 4) with the triethylsilyl group could be achieved by reac-
tion with Et3SiH in the presence of a catalytic amount of
B(C6F5)3, quantitatively affording the Et3SiO-substituted
1
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Journal of the American Chemical Society
Page 8 of 11
o)2 (Sc-1: Cp′
=
C5H5, Sc-2: Cp′
=
C5Me4H, and Sc-3:
0.02 mmol) was then added through a syringe under vigorous
stirring. The polymerization was quenched after 5 minutes by
1
2
3
4
5
6
7
8
C5Me4SiMe3), were synthesized according to the literatures.9,12 4-
Functionalized-1,6-heptadienes (O-1, O-2, S-1 and S-2) were syn-
thesized from 4-hydroxy-1,6-heptadien (purchased from Aldrich)
according to the literatures.8q,13 4-Functionalized-1,6-heptadienes
(O-1, O-2, S-1, and S-2) were purified by distillation from
Al(octyl)3 (25 wt.% in hexanes) before use.
adding methanol (50 mL). The polymer product was collected by
filtration, washed with methanol, and then dried in vacuum at
100 °C to a constant weight (0.47 g). The resulting polymer was
soluble in hot toluene, dichlorobenzene and 1,1,2,2-
tetrachloroethane. Solvent fractionation experiments suggest that
no homopolyethylene was formed. The phenoxy substituted cyclic
unit content in the copolymer was calculated from the 1H NMR
analysis.
The deuterated solvents benzene-d6 (99.6 atom % D), CDCl3
(99.8 atom % D), and 1,1,2,2-tetrachloroethane-d2 (99.6 atom %
D) were obtained from Kanto Chemical Co. Inc. and Cambridge
Isotope. The NMR data of the polymers were obtained on a
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Bruker AVANCE III HD 500 NMR (FT, 500 MHz for H; 125
ASSOCIATED CONTENT
Supporting Information
MHz for 13C) spectrometer with CDCl3 (at 26.8 °C) or 1,1,2,2-
1
C2D2Cl4 (at 120 °C) as a solvent. The chemical shifts for H NMR
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/jacs.xxxxxx.
Experimental and computational details, NMR spectra and other
characterization data, including Figures S1-S119 (PDF).
were recorded in ppm downfield from tetramethylsilane (TMS)
with the solvent resonance as the internal standard (7.16 ppm for
C6D6, 7.26 ppm for CDCl3, 6.0 ppm for 1,1,2,2-C2D2Cl4). The
chemical shifts for 13C{1H} NMR were recorded in ppm downfield
using the central peak of C6D6 (128.06 ppm), CDCl3 (77.16 ppm),
1,1,2,2-C2D2Cl4 (73.78 ppm) as the internal standard. Coupling
constants (J) are reported in Hz and refer to apparent peak multi-
plications. The abbreviations s, d, t, q and m stand for singlet,
doublet, triplet, quartet and multiplet in that order.
The molecular weights and the molecular weight distributions
of homopolymers were determined at 40 °C by gel permeation
chromatography (GPC) on a HLC-8320 GPC apparatus (Tosoh
Corporation). THF was employed as an eluent at a flow rate of
0.35 mL/min. The molecular weights and the molecular weight
distributions of all the copolymers were determined at 145 °C by
high temperature gel permeation chromatography (HT-GPC) on
AUTHOR INFORMATION
Corresponding Author
luoyi@dlut.edu.cn
houz@riken.jp
Author Contributions
II H.W and Y.Z contributed equally to this work.
ORCID
Haobing Wang: 0000-0002-9104-1726
Yanan Zhao: 0000-0002-3928-3429
Masayoshi Nishiura: 0000-0003-2748-9814
Yang Yang: 0000-0002-3041-8593
Gen Luo: 0000-0002-5297-6756
Yi Luo: 0000-0001-6390-8639
Zhaomin Hou: 0000-0003-2841-5120
a
HLC-8321GPC/HT apparatus (Tosoh Corporation). 1,2-
Dichlorobenzene (DCB) was employed as an eluent at a flow rate
of 1.0 mL/min. The calibration was made by use of polystyrene
standard (Tosoh Corporation). The DSC measurements were
performed on a DSC 7000X (HITACHI) at a rate of 10 °C/min.
Any thermal history difference in the polymers was eliminated by
first heating the specimen to 180 °C (or 300 °C), cooling at
10 °C/min to −100 °C (or −30 °C) and then recording the second
DSC scan. TGA was recorded on TGA-50 thermogravimetric
analyzer (Shimadzu). The temperature range is 30 to 500 °C at
the heating rate of 10 °C min-1.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
General procedure for the homopolymerization of functionalized
dienes. Polymerization of O-1 (Table 1, run 3): In a THF-free
glovebox, a toluene solution (2 mL) of [Ph3C][B(C6F5)4] (18.4
mg, 0.02 mmol) was slowly added to a toluene solution (2 mL) of
(C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 (Sc-3, 10.1 mg, 0.02 mmol)
under magnetic stirring in a 10 mL glass tube with cap. After the
mixture was stirred for 5 min, O-1 (404.0 mg, 2.0 mmol) was add-
ed into the reaction solution. The tube was sealed and kept stir-
ring in the glovebox at room temperature for 1 hour. The
polymerization was quenched by addition of methanol (10 mL).
Then the mixture was poured into methanol (50 mL) to precipi-
tate the polymer product. The precipitated polymer was dried
under vacuum at 60 °C to a constant weight (404 mg, 100% yield).
General procedure for the copolymerization of functionalized dienes
with ethylene (Table 2, run 2). In a THF-free glovebox, a toluene
solution (45 mL) of O-2 (376 mg, 2 mmol) was charged into a
three-necked flask with a magnetic stir bar. The flask was taken
outside, set in a water bath (20 °C), and connected to a well-
purged Schlenk ethylene line and a paraffin oil-sealed stopper by
use of a three-way cock. Ethylene (1 atm) was introduced into the
system and was saturated in the solution by stirring for 2 min. A
toluene solution (5 mL) of (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2
(Sc-3) (10.1 mg, 0.02 mmol) and [Ph3C][B(C6F5)4] (18.4 mg,
This work was supported in part by A Grant-in-Aid for Scientific
Research (A) (JP19H00897), a Grant-in-Aid for Scientific Re-
search (S) (26220802), a Grant-in-Aid for Scientific Research (C)
(No. 17K05824) a Grant-in-Aid for Scientific Research on Inno-
vative Areas (17H06451) from JSPS and by the ImPACT Pro-
gram of Council for Science, Technology and Innovation, the
Cabinet Office, Government of Japan and the National Natural
Science Foundation of China (nos. U1862115, 21674014). The
authors also thank the RICC (RIKEN Integrated Cluster of Clus-
ters) and the Network and Information Center of Dalian Universi-
ty of Technology for computational resources.
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