Cobalt-Mediated Switchable Catalysis for the One-Pot Synthesis of Cyclic Polymers

Article abstract of DOI:10.1002/anie.202106285

A cobalt salen pentenoate complex [salen=(R,R)-N,N′-bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediamine] is rationally designed as the catalyst for the ring-opening copolymerization (ROCOP) of epoxides/anhydrides/CO₂. Via migratory insertion of carbon monoxide (CO) into the Co?O bonds, the ROCOP-active species α-alkene-ω-O-Co^III(salen) can be rapidly and quantitatively transformed into α-alkene-ω-O₂C-Co^III(salen) telechelic linear precursors. Upon dilution of reaction mixtures, the homolytic cleavage of Co?C bonds induced by visible light generates α-alkene acyl radicals that spontaneously undergo intramolecular radical addition to afford organocobalt-functionalized cyclic polyesters and CO₂-based polycarbonates with excellent regioselectivity. The cyclic products can either react with radical scavengers to generate metal-free cyclic polymers or serve as photo-initiators for organometallic-mediated radical polymerization (OMRP) to produce tadpole-shaped copolymers.

Full text of DOI:10.1002/anie.202106285

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
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Accepted Article
Title: Cobalt-Mediated Switchable Catalysis for One-Pot Synthesis of
Cyclic Polymers
Authors: Yong Wang, Yajun Zhao, Shuaishuai Zhu, Can Liao, Jacky
W. Y. Lam, Xingping Zhou, Xianhong Wang, Xiaolin Xie, and
Ben Zhong Tang
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202106285
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10.1002/anie.202106285
Angewandte Chemie International Edition
COMMUNICATION
Cobalt-Mediated Switchable Catalysis for One-Pot Synthesis of
Cyclic Polymers
Yajun Zhao,[a] Shuaishuai Zhu,[a] Can Liao,[a] Yong Wang,*, [a], [b] Jacky W. Y. Lam,[b] Xingping Zhou,[a]
Xianhong Wang,[c] Xiaolin Xie[a] and Ben Zhong Tang[b]
[a]
Y.J. Zhao, S.S. Zhu, Dr. Y. Wang, Prof. Dr. X. P. Zhou, Prof. Dr. X. L. Xie.
School of Chemistry and Chemical Engineering
Huazhong University of Science and Technology
Wuhan 430074, P. R. China
E-mail: tcwy@mail.hust.edu.cn
[b]
[c]
Dr. Y. Wang, Dr. Jacky W. Y. Lam, Prof. Dr. B. Z. Tang.
Department of Chemistry
The Hong Kong University of Science and Technology
Clear Water Bay, Kowloon, Hong Kong, P. R. China
Prof. Dr. X. H. Wang.
Key Laboratory of Polymer Ecomaterials
Changchun Institute of Applied Chemistry, CAS
Changchun 130022, P. R. China
Supporting information for this article is given via a link at the end of the document.
Abstract: Owing to the temporal/spatial control over reactions,
switchable catalysis is emerging as a powerful tool to regulate
polymer sequence and architecture directly from monomer mixtures.
Herein, a cobalt salen pentenoate complex [salen = (R,R)-N,N′-
bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediamine] is rationally
designed as the catalyst for the ring-opening copolymerization
(ROCOP) of epoxides/anhydrides/CO2. Via the migratory insertion of
carbon monoxide (CO) into the Co-O bonds, the ROCOP active
species α-alkene-ω-O-CoIII(salen) can be rapidly and quantitatively
transformed into α-alkene-ω-O2C-CoIII(salen) telechelic linear
precursors. Upon dilution of reaction mixtures, the homolytic cleavage
of Co-C bonds induced by visible light generates α-alkene acyl
radicals that spontaneously undergo intramolecular radical addition to
afford organocobalt functionalized cyclic polyesters and CO2-based
polycarbonates with excellent regioselectivity. The cyclic products can
either react with radical scavengers to generate metal-free cyclic
polymers or serve as the photo initiators for organometallic mediated
radical polymerization (OMRP) to produce tadpole-shaped
copolymers. This work opens a new avenue for the direct synthesis of
cyclic polymers from monomer mixtures via switchable catalysis.
modification of the metal coordination sphere, or via a metal
oxidation state change, and therefore successfully synthesized
well defined block copolymers in a one-pot process.[3] Williams
reported the switchable polymerization between ring-opening
copolymerization (ROCOP) of CO2/anhydrides/epoxides and
ROP of cyclic esters by controlling the chemistry of the metal
chain end group.[4] Yet, the majority of current achievements are
limited to the regulation of the block sequence from monomer
mixtures via the switching between mechanistically similar
polymerization techniques.[5] Inherited from their endless
molecular topology, cyclic polymers exhibit intriguing properties
such as higher thermostability, slower degradation rate, lower
viscosity and smaller hydrodynamic volume in comparison to their
linear counterparts.[6] Typically, the synthetic methodology of
cyclic polymers can be classified into two main families, namely
the ring-expansion (RE) and ring-closure (RC) techniques.[7]
Among them, the RC ones are most widely exploited due to their
straightforward design principles, ideal control over molecular
weights and numerous structural diversities.[8] Generally, at least
three steps are involved in, for example, unimolecular
heterodifunctional ring-closure including 1) synthesis of parent
polymer; 2) chain-end functionalization; 3) cyclization reaction
Owing to the inspirational correlation between the elegantly
programmed structures and the highly specialized functions of
biopolymers, a central focus in modern polymer chemistry is to
precisely regulate polymer sequence and architecture for the
development of advanced materials.[1] Switchable catalysis is an
intriguing catalytic strategy inspired by biological activities,
whereby a well-designed catalyst exhibits different activities in
response to external stimuli.[2] Due to this temporal/spatial control,
catalytic transformations can occur without interference from each
other in a one-pot/one-step manner. Therefore, it is envisaged
that switchable catalysis will permit an exceptional efficiency for
the synthesis of polymeric materials with ever-increasing
structural sophistication directly from mixtures of monomers. In
this vision, Diaconescu and Byers discriminated between different
monomers in ring-opening polymerization (ROP) via in situ
9]
(Figure 1A).[7c, As each of these steps requires a laborious
purification process and a distinct catalyst, RC approach is often
time-consuming and costly.
Figure 1. Overview of the synthetic processes for cyclic polymers via
unimolecular heterodifunctional RC.
1
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Cobalt complexes with nucleophilic ancillary groups (LCoIII-X, X =
halogen, carboxylate) have been widely used as catalysts for
ROCOP of epoxides/anhydrides/CO2 to provide facile access to
biodegradable polyesters and CO2-based polycarbonates.[10] It is
well-accepted that alternative chain propagation process is
allowed in cobalt-catalyzed ROCOP by the reversible formation
and dissociation of Co-O bonds.[11] On the other hand,
organocobalt complexes (LCoIII-R) featuring Co-C bonds undergo
homolytic cleavage to generate carbon-centered radicals under
mild conditions, which is key to various biological activities
mediated by Vitamin B12.[12] Due to the “persistent radical effect”
of LCoIII-R resulted from the reversible deactivation of LCoII, the
carbon-centered radicals selectively react with a third substrate
rather than self-coupling, making LCoIII-R mediated radical
the obtained alkyl cobalt complexes were highly sensitive to light
and/or air as we failed to obtain any satisfactory characterization
data. In this regard, propanethiol was added as a radical
scavenger to remove the cobalt salen moiety after the radical
cyclization process.[15] As revealed by gas chromatography/mass
spectrometry of the concentrated reaction mixture, neither δ-
valerolactone nor α-methylene-γ-butyrolactone were formed in
the reaction. Instead, α-methyl-γ-butyrolactone was detected as
the predominant product (Figure 2B). After precipitation of the
concentrated reaction mixture into cold methanol to remove
(salen)CoII complex, α-methyl-γ-butyrolactone with high purity
was obtained (95% yield, Figures S5, S6). Therefore, it is
tentatively assumed that the acyl radicals show high tendency to
add to a more substituted carbon, which obeys Markovnikov’s rule
to endow the radical cyclization process with excellent
regioselectivity.[16] Also, the absence of unsaturated cyclic ester
products suggests that (salen)CoIII-R is unable to undergo β-H
abstraction (1,2-elimination) like their (porphyrin)CoIII-R and
(salophan)CoIII-R analogues.[17] This interesting phenomenon
may be attributed to the electron-donating effect of the
cyclohexene N-backbone, which weakens the Lewis acidity of
Co.[18]
reaction an attractive synthetic tool in both organic and polymer
13]
chemistry.[5b,
Recently, our group reported the fast and
quantitative transformation of Co-O bonds into Co-C bonds via
migratory insertion of carbon monoxide (CO), whereby the
catalytic activity of (salen)CoIIICl could be switched from ROCOP
to organometallic-mediated radical polymerization (OMRP).[14]
Herein, we successfully tackle the challenge of synthesizing cyclic
polymers directly from monomer mixtures via CO triggered switch
from ROCOP of epoxides/anhydrides/CO2 to photo-induced
intramolecular radical cyclization reaction (Scheme 1). Central to
this protocol is the rational design and judicious choice of a cobalt
salen pentenoate complex [(salen)CoIII-OPe, compound 1] as the
ROCOP catalyst, where CO triggers the transformation of
ROCOP active species α-alkene-ω-O-CoIII(salen) into α-alkene-
ω-O2C-CoIII(salen) linear precursors that are capable of
undergoing photo-induced radical cyclization reaction with
excellent regioselectivity.
Scheme 1. Cobalt-mediated switchable catalysis for one-pot synthesis of cyclic
polymers from ROCOP to photo-induced radical cyclization (For simplification,
only ROCOP of epoxides/anhydrides were presented here).
To elucidate the design principle, 3-buten-1-yloxycarbonyl cobalt
salen (compound 2) was first synthesized as a modal compound
(Figure 2A). The structure was well-confirmed by NMR
spectroscopy and electrospray mass spectrometry (ESI-MS,
Figures S1-S3). Then, the photo-induced radical cyclization of 2
was conducted at room temperature in degassed CH2Cl2 (2 × 10-
Figure 2. Model reaction of photo-induced intramolecular radical cyclization
process. A) Photo-induced cyclization of 2 and post modification via reacting
with propanethiol (10 eq., white LED, 10 mW·cm-2, 25 °C). B) Gas
chromatography of the concentrated reaction mixture (bottom) and that of
commercially available δ-valerolactone, α-methylene-γ-butyrolactone and α-
methyl-γ-butyrolactone as standards (up). C) Synthesis of 3 via 1 catalyzed ring-
opening of EO and the subsequent CO insertion reaction.
3
M). Results showed that unlike the alkoxycarbonyl analogues,
2
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10.1002/anie.202106285
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COMMUNICATION
Furthermore, (salen)CoIII-OPe (compound 1) was facilely
polymerization rates but poor control on the polymerization, which
could be attributed to the low solubility of PA in PO (Table 1,
entries 3-4). Then the ROCOP of PO and PA was carried out
under optimized reaction conditions ([PO]/[PA]/[1]=1000/100/1)
for 8 h before the reaction mixture was allowed to stir under 1 atm
CO for 2 h in the dark. According to the 1H NMR spectra, the PA
conversion remained unchanged after the CO migratory insertion
process, verifying that ROCOP was completely impeded upon
addition of CO (Figure S18). This phenomenon, together with the
dark green color of the resulting product strongly suggest the
incorporation of the cobalt salen moiety into the polymer.
Moreover, characteristic signals assigned to salen ligand as well
as alkoxycarbonyl cobalt moiety (Co-CO2) could be observed on
the 13C NMR spectrum of the product (Figures S19-S20). A solid
evidence for the quantitative transformation from (salen)CoIII-OR
to (salen)CoIII-CO2R came from the MALDI-TOF-MS spectrum,
which revealed one population of signals in accordance with
[(salen)CoIIIO2CC4H7 + (PO + PA)n + PO + CO]Na+ (Figure 3C).
synthesized
from
(salen)CoII
and
4-pentenoic
acid
(C4H7CO2H).[19] As revealed by NMR and ESI-MS spectroscopy,
an alkoxycarbonyl cobalt complex (compound 3) was successfully
synthesized with a 99% yield via 1 catalyzed ring-opening of
ethylene oxide (EO) and the subsequent CO insertion reaction
(Figures 2C, S11-S13), verifying that the transformation of Co-O
bond to Co-C bond via migratory insertion of CO is quantitative.
Next, we investigated the ROCOP of propylene oxide (PO) and
phthalic anhydride (PA) at room temperature. To ensure that all
the propagating chains are initiated by the ancillary axial
pentanoate group (C4H7CO2-), no cocatalysts were added in all
the experiments. (salen)CoIII-OPe showed a low catalytic activity
at a [PO]/[PA]/[1] ratio of 1000/50/1 to give a PA conversion of
only 9% and a turnover frequency (TF) of only 0.2 h-1 in 24 h
(Table 1, entry 1). When the amount of PA was enhanced to give
a [PO]/[PA]/[1] ratio of 1000/100/1, the TF value was significantly
increased to 1.3 h-1. As revealed by 1H NMR spectrum, the
resulting poly(propylene phthalate) (PPE)
Table 1. ROCOP of PO and PA via sole catalysis of (salen)CoIII-OPe[a]
displayed a completely alternating structure
(Figure S14). The SEC curve exhibited
monomodal distribution with a low dispersity (Ð
1.08). Moreover, the number-average
a
[d]
[e]
[PO]0/[PA]0
Time
(h)
Conv.[b]
(PA,%)
Conv.[b]
(PO,%)
Mn,th
Mn,SEC
Entry
TF[c]
Ð[e]
=
/[1]
(kDa)
(kDa )
molecular weight (Mn = 2.9 kDa) was close to the
theoretical value (Mn,th = 3.2 kDa) as well as that
calculated from 1H NMR spectrum (Mn,NMR = 3.4
kDa) (Figure S15). Notably, the MALDI-TOF-MS
spectrum of the product (Table 1, entry 1)
exhibited only one series of signals assigned to
[C4H7CO2 + (PO + PA)n + PO + H]Na+, verifying
that all the products were end-capped with
alkene moieties (Figure S17). At 60 °C, the
polymerization rate significantly increased to a
TF of 7.0 h-1. Further increment of the PA
loading resulted in steadily enhancement of the
1
2
1000/50/1
1000/100/1
1000/100/1
1000/200/1
1000/500/1
24
12
4
9
0.9
1.7
0.2
1.3
7.0
4.1
5.4
1.0
-
-
16
28
62
13
3.2
2.9
1.08
1.14
1.21
1.31
3[f]
4
2.9
5.8
5.1
30
12
12.3
6.6
25.5
13.4
22.7
30.1
5
[a] Reaction conditions: room temperature, 1 (70 mg, 0.1 mmol), PO (7.0 mL, 100 mmol). [b]
Conversion of PA determined by 1H NMR spectroscopy. [c] Turnover frequency (TF) = moles of
product per mole of catalyst per hour. [d] Mn,th = [MW(PA) + MW(PO)] × [PA]0/[1] × Conv. (PA).
[e] Determined by SEC analysis in THF. [f] Conducted at 60 °C.
Figure 3. Cobalt-mediated switchable catalysis for synthesis of cyclic polymers via stepwise method, [PO]/[PA]/[1] = 1000/100/1 for 8 h at room temperature,
followed by stirring under 1 atm CO for 2 h in the dark, and photo-induced radical cyclization under white LED (10 mW·cm-2) for 12 h at 0.3 g/L. A) 1H NMR spectrum
of l-PPE-CoIII(salen). B) 1H NMR spectrum of c-PPE-CoIII(salen). C) MALDI-TOF-MS spectrum of l-PPE-CoIII(salen). D) MALDI-TOF-MS spectrum of c-PPE-
CoIII(salen). E) SEC curves of c-PPE-CoIII(salen) and l-PPE-CoIII(salen).
3
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COMMUNICATION
After successful synthesis of the targeted linear α-alkene-ω-CO2-
CoIII(salen) precursor [l-PPE-CoIII(salen)], the photo-induced
radical cyclization reaction was then exploited in dilute solution
(0.3 g/L) at room temperature for 12 h. Notably, the
charactorization of the resulting macro alkyl cobalt complex could
be smoonthly conducted, suggeting that c-PPE-CoIII(salen) was
relatively stable in comparison to the cyclization product of 2,
possibly ascribed to the shielding effect of the tangled polymer
chains that protect the alkyl cobalt moiety from O2. According to
the 1H NMR spectrum, the signals at 5.33 ppm assigned to alkene
moiety disappeared (Figures 3A-3B). Also, the charatoristic
Due to these encouraging experimental results, the ROCOP
process, CO migratory insertion and photo-induced radical
cyclization were further integrated within a one-pot, efficient
process (Table 2). The whole procedure comprised three stages:
1) ROCOP of epoxides/CO2/anhydrides; 2) migratory insertion of
CO to afford α-alkene-ω-O2C-CoIII(salen) precursor; 3) photo-
induced intramolecular radical cyclization upon in-situ dilution of
reaction mixture. The ROCOP was conducted in a pear-shaped
bottle with a [PO]/[PA]/[1] ratio of 1000/100/1, and the reaction
was kept in the dark (wrapped by aluminum foil) during steps 1)
and 2). Taking entry 1 in Table 2 as an example, a PA conversion
of 24% was obtained within 20 h, giving a linear α-alkene-ω-OH
telichelic PPE (l-PPE) during the first stage. After stirring under 1
atm CO for 2 h, the linear precursor α-alkene-ω-CoIII(salen)
telichelic PPE [l-PPE-CoIII(salen), Mn = 4.3 kDa, Ð = 1.09] was
obtained during the second stage. Then, the reaction entered the
third stage in a dilute condition (0.3 g/L) to afford target cyclic
product c-PPE-CoIII(salen) (Mn = 3.9 kDa, Ð = 1.11, Figures S27-
S28).
signals of Co-CO2 at 162.7 ppm could not be observed on the 13
C
NMR and the HSQC spectrum (Figures S21-S22). Note that
correlations on the HMBC spectrum further confirmed the
occurence of radcial coupling reaction between acyl radical and
alkene moiety (Figure S23). The MALDI-TOF-MS spectra
remained the same and the cyclic product exhibited a longer size
exclusion retention time than the parent linear analogue due to
the contracted conformation and the reduced free volumes
(Figures 3C-3E).[20] It is worth mentioning that the cyclic product
c-PPE-CoIII(salen) can serve as a macroinitiator for photo-
regulated OMRP of methyl acrylate (MA) in CH2Cl2 at room
temperature, allowing the facile synthesis of tadpole-shaped
cyclic copolymer with PPE ring and poly(methyl acrylate) tail (c-
1
PPE-b-PMA) (Scheme 4). According to H NMR spetrum of the
reaction mixture, MA conversion reached 30% in 6 h. The product
displayed a monomodal and narrow distribution and the Mn was
in good agreement with the theoretical value, which indicated a
100% initiation efficiency and well-controlled manner of the
polymerization (Figures S24-26).
Scheme 4. Synthesis of tadpole-shaped c-PPE-b-PMA copolymers via chain
extension of MA with c-PPE-CoIII(salen) as the macroinitiator (see SI for detail).
Table 2. Synthesis of cyclic polymers via switchable catalysis of cobalt involving ROCOP and photo-induced radical cyclization. [a]
ROCOP and CO insertion
Photo-cyclization
Time
(h)
Entry
Monomer
c
d
d
Conv.b
(epoxide, %)
Conv.b
Mn,th
Mn1,SEC
Mn2,SEC
d
d
Ð1
Ð2
(anhydride, %)
(kDa)
(kDa)
(kDa)
1
2
[PO]/[PA]
[PO]/[PA]
20
42
12
24
30
3
2.4
6.5
24
65
25
28
36
-
4.9
13.4
4.8
4.3
12.6
3.6
1.09
1.12
1.12
1.11
1.09
1.10
1.18
3.9
11.8
3.2
1.11
1.14
1.14
1.15
1.13
1.15
1.23
3
[EO]/[PA]
2.5
4
[PO]/[NBA]
[PO]/[THPA]
[PO]/[CO2]
[PO]/[CO2]
2.8
5.2
4.3
3.8
5
3.6
7.6
6.6
6.1
6e
7e
20.0
10.2
10.0
8.8
-
5
21.0
21.4
18.6
16.2
a Reaction conditions: ROCOP processes run at room temperature, epoxide (100 mmol), [epoxide]/[anhydride]/[1] = 1000/100/1; CO migratory
insertion processes run under 1 atm CO for 2 h in the dark; photo-induced radical cyclization processes run white LED (10 mW·cm-2) in dilute solution
(0.3 g/L for entries 1, 3-5 and 0.1 g/L for etries 2, 6 and 7) for 12 h, . b Determined by the 1H NMR spectrum. c Mn,th = [MW(epoxide) + MW (anhydride
or CO2)] × 1000 × Conv.(epoxide). d Determined by SEC analysis in THF. e [epoxide]/[1] = 1000/1, CO2 800 psi.
1
Through H NMR analysis of aliquots taken at regular intervals,
conversion of PA reached 65 % in 42 h. Before the CO insertion
process, a few droplets of the reaction mixture were taken and
precipitated into cold methanol to afford a linear polymer l-PPE
(Mn = 12.0 kDa, Ð =1.10). In this case, propanethiol was added
as the radical scavenger into the cyclization reaction mixture after
the third stage to obtain a cobalt-free cyclic polymer (c-PPE). The
SEC trace of the product obtained by cyclization reaction at a l-
PPE-CoIII(salen) concentration of 0.3 g/L displayed a bimodal
distribution with a main component at 12.0 kDa and a minor
4
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10.1002/anie.202106285
Angewandte Chemie International Edition
COMMUNICATION
component at 25.2 kDa, which indicated the occurrence of both
intermolecular and intramolecular radical addition reaction under
the experimental condition. To our delight, the product, with a
monomodal and narrow distribution, was successfully obtained
when the concentration of l-PPE-CoIII(salen) was further diluted to
0.1 g/L (Figure 4A). The resulting c-PPE-CoIII(salen) could also
serve as a efficient photoinitiator for OMRP of MA to synthesize
c-PPE-b-PMA with higher content of PPE (Figures S31-S33). By
post modification with propanethiol after the third stage of the
reaction, organocobalt moiety could be effectively removed to
give a metal-free c-PPE. According to the thermogravimetric
analysis (TGA), c-PPE and l-PPE displayed 5 wt % weight loss at
257 °C and 240 °C, respectively. The better thermal stability of
cyclic polyesters as compared to their linear counterpart could be
attributed to the lack of chain end group that hinder the backbiting
depolymerization mechanism, instead of the cyclic topology
(Figures S35-S36).[21] Owing to the contracted conformation and
the reduced free volume, the glass transition temperature of c-
PPE (54.5 °C) is 13.3 °C higher than its linear counterpart (Figure
4B). Furthermore, we embarked on expanding the scope of
monomers. Due to its less steric hindrance, EO displayed higher
activity during the ROCOP. On the other hand, cis-5-norbornene-
In summary, the first example of switchable catalytic system that
involves ROCOP of epoxides/anhydrides/CO2 and photo-induced
intramolecular radical addition reaction has been demonstrated,
which enabled the direct synthesis of well-defined cyclic
polyesters and cyclic CO2-based polycarbonates from mixtures of
monomers in an efficient process. The key to this protocol is the
rational design of a cobalt salen pentenoate catalyst [(salen)CoIII-
OPe], whereby the ROCOP active species α-alkene-ω-O-
CoIII(salen) can be quantitatively and quickly transformed into α-
alkene-ω-O2C-CoIII(salen) linear precursors via migratory
insertion of CO into Co-O bonds. Upon dilution of the reaction
mixture, the homo-cleavage of Co-C bonds induced by visible
light generates α-alkene acryl radicals that spontaneously
undergo radical cyclization reaction. The resulting organocobalt
incorporated cyclic polymers can serve as macroinitiator for
OMRP of vinyl monomer to give facile access to tadpole-shaped
polymers. Alternatively, it can react with radical scavengers such
as thiol compounds to afford metal-free cyclic polymers. Notably,
the modal reaction of 3-buten-1-yloxycarbonyl cobalt salen
complex is suggestive of excellent regioselectivity and
chemoselectivity of the radical addition reaction. This work
demonstrates the possibility to synthesize cyclic polyesters with
diverse functionality directly from monomer mixtures via a RC
approach.
endo-2,3-dicarboxylic
tetrahydrophthalic anhydride could be used to synthesize
unsaturated cyclic polymers for postpolymerization
anhydride
and
cis-1,2,3,6-
modification.[22] Notably, cyclic poly(propylene carbonate) (PPC)
were also successfully synthesized via the switchable catalysis,
except that the ROCOP of PO and CO2 was conducted in
autoclave an airtight transparent window (Figures S43-S46).
Acknowledgements
YW, YJZ and XPZ thank the Financial support from National Key
R&D Plan (No.2016YFB0302400), NSFC (No.21604027) of
China, the Fundamental Research Funds for the Central
Universities (HUST:2019JYCXJJ015) as well as the analytical
and testing assistance from the Analysis and Testing Center of
HUST.
Keywords: Switchable catalysis • photo-induced radical closure
• cyclic polymer• ROCOP •biodegradable polymer
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The Table of Contents
Yajun Zhao,[a] Shuaishuai Zhu,[a] Chan
Liao,[a] Yong Wang,*, [a], [b] Jacky W. Y.
Lam,[b] Xingping Zhou,[a] Xianhong
Wang,[c] Xiaolin Xie[a] and Ben Zhong
Tang [b]
Page No. – Page No.
Cobalt-Mediated Switchable Catalysis
for One-Pot Synthesis of Cyclic
Polymers
The first example of switchable catalytic system that involves ROCOP of
epoxides/anhydrides/CO2 and photo-induced intramolecular radical addition reaction
has been demonstrated, which enabled the direct synthesis of well-defined cyclic
polyesters and cyclic CO2-based polycarbonates from mixtures of monomers in an
efficient process.
7
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