Poster jin huang apme17 2nd

1. 4480 4520 4560 4600 m/z
Organocatalytic Copolymerization of CO2 and Oxetane: Step Forwards
Green Chemistry from C1 Synthon to Polymer
Jin HUANG1,Andrew P. Dove*2, Olivier Coulembier*1
Jin.huang@umons.ac.be
1 Laboratory of Polymeric and Composite Materials, Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons, Place du Parc 23, 7000 Mons, Belgium
2 Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, United Kingdom
Introduction
Plausible Mechanism
Catalytic activity is possiblely corresponding to the geometry of super
base instead of the pKa, since P4-tert-Bu features the strongest basicity
among investigated super base but worst performance. In addition,
copolymerization in presence of bicylic guanidine affords CO2-based
polymer with remarkable selectivity and molecular weight.
Results and Discussion
References
[1] Q. Liu, L. Wu, R. Jackstell, M. Beller, Nature Communications 2015, 6, 5993.
[2] O. Coulembier, S. Moins, V. Lemaur, R. Lazzaroni and P. Dubois, Journal of CO2
Utilization 2015, 10, 7-11.
[3] J.S. Jewell and W. A. Szarek, Carbonhydrate Research, 1971, 248-250.
[4] D. J. Heldebrant, P. G. Jessop, C. A. Thomas, C. A. Eckert, C. L. Liotta, The Journal of
Organic Chemistry 2005, 13, 5336-5338.
[5] D. Delcroix, B. M. Vaca, D. Bourissou, C. Navarro Macromolecules 2010, 43, 8828-
8835.
Carbon dioxide (CO2), a renewable C1 feedstock, has been researched in producing valuable chemicals for years [1]. The success of synthesizing useful compounds derived from CO2 not only affords alternative route
to mitigate the emission of green gas but also allows the utilization of fossil fuel in decreasing. Therefore, developing efficient catalytic system to transform CO2 into chemicals is still a great challenge for chemical
science. Base on our previous research of coupling CO2 and epoxide under very mild conditions [2], herein we report a novel synthetic approach to prepare CO2-based copolymer by coupling CO2 and oxetane using
iodine and co-catalysts under low pressure. CO2-based copolymer was obtained (Mn = 5.6 kDa, ĐM = 1.35) as attested by 1H-NMR and size exclusion chromatography (SEC).
Table 1. Copolymerization of oxetane and CO2 in presence of various dual
catalysts system. [a]
Entry
Co-
catalysts[e]
(pKa)[d]
Con.[b]
%
Selec. % [b]
Mn SEC
[c]
g·mol -1
ĐM SEC
[c]
TMC[f]
Carbonate
linkages
Ether
linkages
1 DBU (24.3) 82 8 72 20 1350 1.71
2 MTBD (25.5) 46 11 71 18 5640 1.35
3 TBD (26.0) 88 <1 82 18 4630 1.32
4
P4-tert-Bu
(42.7)
15 >99 0 0 NA NA
0 5 10 15 20 25
0
10
20
30
40
50
60
70
80
Selectivity%
Time /h
TMC
Carbonate linkages
Ether linkages
Scheme 1. First step of copolymerization
between oxetane and CO2 : generation of
TMC .
Figure 3. Selectivity plot with time consuming of copolymerization from
oxetane and CO2 in presence of iodine and TBD as catalysts.
Scheme 2. Second step of
copolymerization between oxetane and
CO2 : generation of copolymer.
To prove the second step of copolymerization from oxetane and CO2
catalyzed by iodine and bicyclic guanidine (Scheme 2), mimic reaction was
performed using oxetane/iodine 1:1 adduct as initiator to polymerize TMC
under similar conditions. Results show that polycarbonate (Mn = 5.0 kDa,
, ĐM = 1.35 ) with 6% ether linkages was obtained in agreement with
literature referring to ‘Active chain end’ (ACE) mechanism of
polymerization[5].
First step Second step
m/z=44
4482.5
4526.6
4584.6
m/z=58
Figure 1. MALDI-TOF spectrum of resultant CO2-based copolymer
(Table 1, entry 3) ranging from 4480 to 4650 Da doped with Na cation.
Conclusion
In conclusion, a means to the synthesis of novel CO2-based copolymer is
described, which enables to couple oxetane and carbon dioxide in
efficiency. The study reveals that the combination of iodine and bicyclic
guanidine provides excellent catalytic activity to the copolymerization.
Moreover, commercial available organocatalysts and mild reaction
conditions afford great opportunity to expand the scope of CO2
utilization. Future studies will focus on increasing molecular weight of
copolymer and obtaining poly (trimethylene carbonate) based on CO2
resource.
Acknowledgement
The authors thank the European Commission for their financial support
through the project SUSPOL-EJD 642671. O.C. is Research Associate for the
F.R.S. – FNRS of Belgium.
Figure 2. 1H-NMR spectrum of CO2-based copolymer after the purification (Table 1, entry 3).
1H-NMR AnalysisMass spectroscopy Analysis
Characterization of CO2-based copolymer after the purification was
carried out using 1H-NMR (Figure 1) and it evidently shows the typical
signal of carbonate linkages (4.23 ppm), ether linkage (3.49 ppm) and
end-group (3.74 ppm).
To confirm the structure of resultant copolymer from
CO2 and oxetane, mass spectroscopy was applied to the
analysis and it convincely shows CO2 (m/z = 44) and
oxetane (m/z = 58) in copolymer chain (Figure 1).
[a] Copolymerization conditions: 197 μmol of iodine (2.5mol%), 7.88 mmol of oxetane, [M]/[C] = 40/1, and
1 equivalent of super base, 10 bar of CO2, at 105 oC for 24 h. [b] Conversion and selectivity were
determined from 1H-NMR spectroscopy of crude mixture. [c] Determined by size-exclusion chromatography
(SEC) in tetrahydrofuran (THF) with polystyrene standard. [d] pKa value is referred from Croat. Chem. Acta
2014, 87, 385–395. [e] DBU = 1,8-Diazabicyclo(5.4.0)undec-7-ene. MTBD = 7-Methyl-1,5,7-
triazabicyclo[4.4.0]dec-5-ene. TBD = 1,5,7-Triazabicyclo[4.4.0]dec-5-ene. P4-tert-Bu = 1-tert-Butyl-4,4,4-
tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene)
[f] TMC = trimethylene carbonate.
We design a dual catalysts system combining iodine and super base,
since iodine features a region directly opposite the I-I sigma bond in
poorly shield nucleus by atoms’ electron cloud which enable iodine to
work as Lewis acid to activate oxetane [3] and super base traps free
CO2 molecule forming zwitterionic adduct [4] for the copolymerization.
Experiment Section
Although CO2 and oxetane clearly show up in mass
spectrum, the fine structure of copolymer still should be
figured out. Hence, NMR analysis was performed.
To interpret the copolymerization between CO2 and oxetane, a plausible
mechanism was proposed. It is possible in first step of
copolymerization, that TMC (capable for ring opening polymerization) is
obtained from the dual catalysts system (Scheme 1) and following
copolymerizaiton between TMC and oxetane to generate CO2-based
copolymer initiating by iodine [5] (Scheme 2).
We postulated the halogen
bonding between oxygen from
oxetane and iodine is formed
initially [3] and methylene group
of oxetane ring experience the
nucleophilic attack subsequently
from carboxylate group of
guanidine zwitterionic species [4]
to generate alkoxide ion. This
alkoxide intermediate is stabilized
via hydrogen bonding from
neither TBD hydrogen on 7-
position or MTBD hydrogen from
7- methyl group and TMC is
obtained by the back-biting
mechanism.
Kinetic study
To examine the first step of copolymerization, kinetic
study was carried out.
Results in figure 3 clearly show that TMC was obatined
with high selectivity at the very beginning and keeping
in low percentage constantly by time consuming which
enable to prove the first step of mechanism.
Regarding the second step
of copolymerization, after
required amount of TMC
is formed, the
polymerization
subsequently takes place
which is initiated by
iodine/oxetane adduct,
following zwitterionic
“Active Chain End (ACE)
mechanism” [5]. The
hydrolysis of chain end
leads to hydrogen group
as chain end which can be
confirmed from 1H-NMR
spectrum (Figure 2).
Mimic polymerization