Enhancement on Alternating Copolymerization of Carbon Monoxide and Styrene by Dibenzobarrelene-Based α-Diimine Palladium Catalysts

Article abstract of DOI:10.1021/acs.macromol.8b01786

CO/styrene copolymerization by α-diimine palladium catalysts is a promising method for direct synthesis of polyketones. The effect of the catalyst backbone structure on CO/styrene copolymerization has been studied with the aim of developing robust α-diimine palladium catalysts able to improve the polymerization productivity and controllability. Dibenzobarrelene derived α-diimine palladium catalysts without o-aryl substituents were designed and synthesized for CO/styrene alternating copolymerization. Introduction of the rigid and bulky dibenzobarrelene backbone enhanced the thermal stability and the productivity of palladium catalyst. The dibenzobarrelene ligand backbone also improved the polymerization controllability, and living CO/styrene copolymerizations were achieved at 15 °C using α-diimine palladium catalysts in CH₂Cl₂. The steric hindrance of backbone and the π- π stacking between the dibenzobarrelene backbone and the aniline played crucial roles in stereocontrol and productivity.

Full text of DOI:10.1021/acs.macromol.8b01786

Article
pubs.acs.org/Macromolecules
Cite This: Macromolecules XXXX, XXX, XXX−XXX
Enhancement on Alternating Copolymerization of Carbon Monoxide
and Styrene by Dibenzobarrelene-Based α‑Diimine Palladium
Catalysts
Zefan Xiao, Handou Zheng, Cheng Du, Liu Zhong, Heng Liao, Jie Gao, Haiyang Gao,* and Qing Wu
School of Materials Science and Engineering, PCFM Lab, GD HPPC Lab, Sun Yat-sen University, Guangzhou 510275, China
S
* Supporting Information
ABSTRACT: CO/styrene copolymerization by α-diimine palladium catalysts
is a promising method for direct synthesis of polyketones. The effect of the
catalyst backbone structure on CO/styrene copolymerization has been studied
with the aim of developing robust α-diimine palladium catalysts able to improve
the polymerization productivity and controllability. Dibenzobarrelene derived
α-diimine palladium catalysts without o-aryl substituents were designed and
synthesized for CO/styrene alternating copolymerization. Introduction of the
rigid and bulky dibenzobarrelene backbone enhanced the thermal stability and
the productivity of palladium catalyst. The dibenzobarrelene ligand backbone
also improved the polymerization controllability, and living CO/styrene
copolymerizations were achieved at 15 °C using α-diimine palladium catalysts
in CH2Cl2. The steric hindrance of backbone and the π−π stacking between the
dibenzobarrelene backbone and the aniline played crucial roles in stereocontrol
and productivity.
resting state is the palladium−acyl−carbonyl species, and the
rate-limiting step is the coordination of vinyl arene
monomer.19,41 Therefore, bulky o-aryl substituents of α-
diimine ligand usually lead to a decrease in productivity and
molecular weight of polyketone because of the steric repulsion
between vinyl arene monomer and o-aryl substituents of the
ligand,37−39 which is contrast to the steric effect on olefin
polymerization using α-diimine nickel and palladium cata-
lyst.42−48 On the other hand, less bulky o-aryl substituents
generally lead to a short lifetime of palladium catalysts because
of their poor stability although introduction of electron-
donating groups on the meta-/para-position of the aniline
moieties can improve the stability of palladium catalysts.35,43
Less bulky o-aryl substituents also hardly suppress the chain
transfer reaction (β-hydrogen elimination or monomer-assisted
β-hydrogen abstraction) and the access of counterion to metal
center,19,37 thereby lowing molecular weight and broadening
polydispersity of copolymer.39,49 The design of the α-diimine
palladium catalyst with the subtle steric bulk of o-aryl for CO/
vinyl arene copolymerizations thus remains a great challenge.
In comparison with modification on the aniline moiety, a
few modifications of backbone in the α-diimine palladium
catalyst for CO/styrene copolymerization were studied.
Although the hydrogen derived α-diimine palladium catalyst
(ArNC(R)−(R)CNAr, R = H) was more highly active
than the methyl- and acenaphthene-based α-diimine palladium
INTRODUCTION
■
Polyketones generated by olefin/carbon monoxide (CO)
alternating copolymerization have been of great interest over
the past decades due to their unusual properties, the wide
range of application as engineering material, and the cheap and
available stocks.1,2 Moreover, the postfunctionalization of the
polyketone macromolecules is possible with no degradation of
the polymeric chain yielding new polymeric materials because
of the presence of the carbonyl group.3−7 The late transition
metal catalysts, especially palladium-based catalysts, are
capable for catalyzing olefin/CO copolymerization effi-
ciently.8−10 The diphosphine palladium catalysts are highly
efficient for alkene/CO copolymerization,8 and a CO/
ethylene/propylene terpolymer called “Carilon” has been
successfully commercialized by Shell Company.11 However,
diphosphine palladium catalysts are not suited for vinyl arene/
CO copolymerization.12 Instead, palladium catalysts bearing
bidentate nitrogen ligands can efficiently catalyze styrene/CO
copolymerization.12−33 Two noteworthy examples are the 2,2′-
bipyridine palladium catalysts and the 1,10-phenanthroline
palladium catalysts, which are excellent catalysts for the
copolymerizations of styrene or 4-tert-butylstyrene with CO,
yielding the perfectly alternating polyketones.12−20
α-Diimine palladium catalysts for vinyl arene/CO copoly-
merization have recently attracted considerable interest
because of easy modifications on steric and electronic
effects.34,35 Previous documents have mainly addressed the
steric effect of o-aryl substituents on the productivity and the
stereocontrol on vinyl arene/CO copolymerization.36−40
Additionally, mechanistic studies have demonstrated that the
Received: August 18, 2018
Revised: October 23, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Scheme 1. Synthetic Route of α-Diimine Palladium Complexes
catalysts (R = Me, acenaphthene),37 the steric effect of the
backbone substituent should be ruled out because of the
square-planar conformation of palladium complexes. Herein,
we proposed a promising approach to enhancement on
palladium-catalyzed CO/styrene copolymerization by increas-
ing the steric bulk of the α-diimine ligand backbone while this
approach is highly efficient for enhancing stability and living
fashion of α-diimine nickel and palladium catalysts for
(co)polymerization of ethylene and polar monomer.43−45,50,51
A series of dibenzobarrelene-based α-diimine palladium
catalysts without o-aryl substituents have been synthesized
for living alternating CO/styrene copolymerization by moving
steric bulk from the o-aryl to the ligand backbone. We
envisioned that the bulk of the rigid dibenzobarrelene
backbone showed a steric effect on the palladium center and
expectedly inhibited the chain transfer reaction as well as the
access of counterion to metal center, and no substituents on
the ortho-position of aryl provided an open space for
coordination of styrene monomer. The unprecedented
influence of π−π stacking between the dibenzobarrelene
backbone and the aniline on the productivity and the
stereocontrol in CO/styrene copolymerization was also
discovered.
CH2Cl2. Normally, the chloromethylpalladium complexes
N1−N4 displayed a distorted square-planar coordination
around the palladium center (Figures 1−4). The bulky and
Figure 1. Crystal structure of α-diimine palladium complex N1 (front
and side views). The hydrogen atoms and two CH2Cl2 molecules are
omitted for clarity.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Palladium Com-
plexes. Dibenzobarrelene derived α-diimine palladium com-
plexes with m-/p-methoxy groups but without o-aryl
substituents were designed based on previously reported steric
and electronic effects of the aniline moiety.34,52 The
chloromethylpalladium complexes (N1−N3) were prepared
according to similar synthetic route (Scheme 1).50,53 These
neutral palladium complexes were further treated with sodium
tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (NaBArF) and
acetonitrile to yield the cationic palladium complexes [(α-
diimine)Pd(CH3CN)Me]+BArF− (1−3).42,50 All of the
reported α-diimine palladium complexes were fully charac-
terized by 1H and 13C NMR and elemental analysis.
Acenaphthene (N4 and 4) and methyl (N5 and 5) derived
α-diimine palladium complexes were also prepared and used
for copolymerization comparison (Scheme 1).
Figure 2. Crystal structure of α-diimine palladium complex N2 (front
and side views). The hydrogen atoms are omitted for clarity.
Single crystals of neutral palladium complexes N1−N4
suitable for X-ray diffraction analysis were obtained by slow
diffusion of hexane into the palladium complex solution in
Figure 3. Crystal structure of α-diimine palladium complex N3 (front
and side views). The hydrogen atoms and a CH2Cl2 molecule are
omitted for clarity.
B
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
exist in both the solution and the solid.60,61 Therefore, the
unique dibenzobarrelene backbone provides the steric effect
and the π−π stacking interaction, which is anticipated to have
a great influence on CO/styrene copolymerization.
CO/Styrene Copolymerization. Cationic palladium com-
plexes were active for CO/styrene copolymerization. In the
reported literature, 1,4-benzoquinone (BQ) was added into
catalytic systems as an oxidant promoter to inhibit the
decomposition of the active species (Pd2+) to inactive
palladium metal (Pd0) and improve the lifetime of palladium
catalyst and as a radical scavenger to prohibit the radical
polymerization of styrene.1 Herein, effects of solvent and of
1,4-benzoquinone were first studied using catalyst 3. Polymer-
ization results in Table 2 showed that catalyst 3 exhibited a
higher productivity and produced a lower molecular weight
copolymer in 2,2,2-trifluoroethanol (CF3CH2OH) than that in
dichloromethane. In 2,2,2-trifluoroethanol, the presence of 1,4-
benzoquinone led to a drop in molecular weight of the
copolymer because of rapid chain transfer. These observations
were in agreement with previous reports.14,62,63 However, the
addition of 1,4-benzoquinone led to an increase in molecular
weight of the copolymer with decreased polydispersity index
(PDI) in CH2Cl2. These results strongly indicated that 1,4-
benzoquinone remarkably promoted copolymerization in
CH2Cl2 and could not play a role of chain transfer agent in
the absence of alcoholic environment.
Figure 4. Crystal structure of α-diimine palladium complex N4 (front
and side views). The hydrogen atoms and a CH2Cl2 molecule are
omitted for clarity.
rigid dibenzobarrelene backbone of palladium complexes can
effectively shield the back space of palladium metal and show
moderate axial steric effect. For the dibenzobarrelene derived
α-diimine palladium complex with bulky o-diisopropyl groups
for ethylene polymerization, it has been reported that aniline
moieties are nearly perpendicular to the five-membered Pd−
diimine ring plane.50 However, it is noteworthy that aniline
moieties of palladium complexes N1−N3 without o-aryl
substituents are nearly parallel to the aryl rings of the
dibenzobarrelene backbone. Crystal parameters in Table 1
Table 1. Crystal Parameters with Regard to the π−π
Stacking Effect of Complexes N1−N4
CO/styrene copolymerizations were further studied using
cationic palladium catalysts 1−3 under various temperatures
(Table 3) in the presence of 1,4-benzoquinone in CH2Cl2.
Generally, palladium catalysts were highly sensitive to reaction
temperature toward CO/styrene copolymerizations. A slight
temperature variation of 5 °C led to a significant change in
productivity and copolymer molecular weight. When the
reaction temperature was increased from 10 to 25 °C, the
productivity of three palladium catalysts 1−3 greatly increased.
When the temperature was further increased to 30 °C, catalysts
1 and 2 showed decreased productivity while catalyst 3
exhibited increased productivity. Palladium catalyst 3 showed
the highest productivity under same conditions, which was
consistent with previously reported electron-donating effect on
CO/styrene copolymerizations.34,35,37 Besides, the molecular
weight of copolymers increased and then decreased while the
polydispersity index (PDI) became broad consistently with
increased reaction temperature. The highest molecular weight
and narrow PDI values (PDI < 1.20) were observed at 15 °C.
On the basis of narrow polydispersity, the theoretical
molecular weights of the obtained copolymers could be
calculated by the ratios of the weight of the produced polymer
to the amount of palladium catalyst used. The theoretical
values were larger than the actual measured values at 20 °C
(entries 8 and 13 in Table 3), indicating that occurrence of
chain transfer reaction. The calculation results in Table 3 and
Pd
dihedral angles between dibenzobarrelene
and aniline (deg)
vertical distance of
two aryl (Å)
complex
N1
N2
N3
N4
6.4241, 15.687
2.943, 5.857
14.154, 23.978
66.229, 88.778
2.5435, 2.6093
2.1735, 2.2580
2.3502, 2.8922
show that dihedral angles between the aniline moieties and the
aryl ring of dibenzobarrelene are below 20° and vertical
distances of two aryl rings are within 3 Å for palladium
complexes N1 and N2. These crystal data strongly indicate the
existence of the offset or slipped π−π stacking interaction,
which has different conformations to face-to-face and edge-to-
face stacking interactions.54−57 According to the definitions of
the pitch and roll angles presented by Curtis for the parallel-
displaced description of the offset π−π stacking, palladium
complexes N1 and N2 have a “roll” π−π stacking.58 The
reducing π−π stacking effect is observed for palladium complex
N3 with increased methoxy groups. The unconcerned π−π
stacking interactions are also present on a dibenzobarrelene-
based α-diimine nickel complex with 2-substituents and a
palladium complex with 4-substituents.53,59 For acenaphthyl α-
diimine palladium analogue N4, no π−π stacking interaction is
observed although the acenaphthene ring is aromatic (Figure
4). Besides, the π−π stacking interaction has been proved to
a
Table 2. Effects of BQ and of Solvent on CO/Styrene Copolymerization Using 3
b
b
entry
[BQ]/[Pd]
solvent
CH2Cl2
CH2Cl2
CF3CH2OH
CF3CH2OH
yield (g)
productivity (g CP/g Pd)
Mn (kg/mol)
PDI
1
2
3
4
5
0
5
0
1.7812
0.3320
2.4212
1.3423
1318
250
1790
990
63.1
29.7
3.7
1.27
1.39
1.27
1.31
5.2
a
Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd] = 6800, 1.0 atm of CO (absolute pressure), T = 30 °C, t = 24 h, 20 mL of
b
solvent. Molecular weight and PDI were determined by GPC using tetrahydrofuran as eluent.
C
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
a
Table 3. CO/Styrene Copolymerization Results by Palladium Catalysts 1−5
b
c
entry
catalyst
temp (°C)
yield (g)
productivity (g CP/g Pd)
Mn‑GPC (kg/mol)
PDI
Mn‑theor (kg/mol)
1
2
3
4
5
6
7
8
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
30
25
20
15
10
30
25
20
15
10
30
25
20
15
10
30
25
20
15
10
30
25
20
15
10
0.9682
1.1909
0.7940
0.7122
0.4385
1.4111
1.4913
1.3939
1.0007
0.6510
1.7812
1.6378
1.5330
1.1852
0.6762
1.3284
1.4994
1.3458
1.0067
0.6565
0.1741
0.2239
0.2257
0.2147
0.1951
716
881
587
527
324
1044
1103
1031
740
40.4
76.8
80.1
85.6
55.6
53.1
57.8
87.3
91.4
67.0
63.1
65.4
86.9
96.0
63.4
5.8
1.49
1.27
1.19
1.04
1.02
1.50
1.34
1.19
1.12
1.04
1.27
1.26
1.23
1.18
1.10
1.69
1.68
1.62
1.39
1.34
1.38
1.47
1.49
1.49
1.38
62.5
56.1
34.5
109.8
78.8
51.2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
482
1318
1212
1134
877
500
983
1109
996
745
486
129
120.7
93.3
53.2
9.4
16.3
27.2
30.9
4.2
5.9
8.2
166
167
159
144
11.2
16.1
a
Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd] = 6800, [1,4-benzoquinone]/[Pd] = 5, 1.0 atm of CO (absolute pressure),
b
t = 24 h, 20 mL of CH2Cl2. Molecular weight and PDI were determined by GPC using chloroform (entries 1−5) or tetrahydrofuran (entries
c
6−25) as eluent. Theoretical molecular weights were calculated by the ratios of the weight of the produced polymer to the amount of palladium
catalyst used.
Table S1 showed that the theoretical molecular weights of
copolymers produced by palladium catalyst 3 with 3,4,5-
trimethoxyanilines were well consistent with the determined
molecular weight by GPC, while the determined molecular
weights of copolymers produced by palladium catalysts 1 and 2
were larger than the theoretical molecular weights by factors of
∼1.5 and ∼1.1, respectively. This could be attributed to
different initiation efficiencies of living palladium catalysts, and
introduction of methoxy groups enhanced the initiation
efficiency of palladium catalysts for CO/styrene copolymeriza-
tion.
Encouraged by the enhancement of 3,4,5-trimethoxyanilines,
we further synthesized acenaphthene (4) and methyl (5)
derived α-diimine palladium catalysts with 3,4,5-trimethoxy-
anilines and investigated backbone effect of palladium catalysts
on CO/styrene copolymerization. Comparisons of copoly-
merization results using catalysts 3 versus 4 versus 5 at same
reaction conditions (entries 11−25 in Table 3) clearly
demonstrated ligand backbone effects. As initially envisioned,
the introduction of the bulky backbone remarkably enhanced
the thermal stability of the α-diimine palladium catalysts and
polymerization controllability. The methyl-based α-diimine
palladium catalyst 5 showed the lowest productivity and
produced the lowest molecular weight copolymer. When
acenaphthene was used instead of methyl on the backbone,
enhanced productivity and increased molecular weight were
observed. At elevated temperature of 30 °C, acenaphthene
derived α-diimine palladium catalyst 4 also showed reduced
productivity, but dibenzobarrelene derived palladium catalyst 3
showed the highest productivity. More notably, molecular
weight distributions of copolymers became narrow when the
dibenzobarrelene was installed on the backbone, and narrowly
dispersed copolymers (PDI < 1.20) were produced in a living
fashion below 15 °C.
To reliably calculate productivity and probe the thermal
stability of catalyst 3, CO/styrene copolymerizations using
catalyst 3 were performed above 30 °C using chlorobenzene as
reaction solvent instead of low-boiling-point CH2Cl2 (Table
4). Catalyst 3 was slightly less active in chlorobenzene than the
system in CH2Cl2 at the same conditions (30 °C) and
produced lower molecular weight polymers with broad
distributions (entry 11 in Table 3 versus entry 8 in Table 4)
Table 4. CO/Styrene Copolymerization Results Using 3 at
a
High Temperatures
b
temp
(°C)
time
(h)
yield
(g)
productivity
(g CP/g Pd)
Mn
b
entry
(kg/mol) PDI
1
2
3
4
5
6
7
8
60
50
40
40
40
40
35
30
24
24
8
16
24
32
24
24
0.9287
1.6700
0.6579
1.3357
1.9367
2.6012
1.7364
1.5070
687
1236
487
4.1
6.7
1.34
1.56
1.68
1.81
1.88
1.89
1.69
1.63
20.4
21.2
22.4
23.5
43.1
56.9
988
1433
1925
1285
1115
a
Polymerization conditions: 12.7 μmol of Pd catalyst, [styrene]/[Pd]
= 6800, [1,4-benzoquinone]/[Pd] = 5, 1.0 atm of CO (absolute
b
pressure), 20 mL of chlorobenzene. Molecular weight and
polydispersity index were determined by GPC using THF as eluent.
D
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
because of the difference in solvent polarity. With increased
temperature from 30 to 60 °C in chlorobenzene, the
productivity of catalyst 3 increased and then decreased, and
the highest productivity was achieved at 40 °C. Slightly
reduced productivity and drop in polymer molecular weight
were observed at 50 °C, suggesting that catalyst 3 was stable
whereas chain transfer reaction greatly accelerated. The activity
of catalyst 3 (productivity/h) at different time periods ranging
from 8 to 32 h was used to test the catalyst lifetime at 40 °C in
chlorobenzene. Figure 5 clearly shows that activity values
Scheme 2. Palladium-Catalyzed CO/Styrene
Copolymerization and the π−π Stacking Assisted
Coordination of Styrene for the Dibenzobarrelene-Based α-
Diimine Palladium
anthracene ring of aromatic aniline and styrene monomer
was presumed.39
The living feature of copolymerization was further
investigated using 1−3 at 15 °C (Table S1). Figure 6 shows
Figure 5. Plots of activity versus reaction time in CO/styrene
copolymerization using 3 at 40 °C in chlorobenzene and the image of
system solutions of 3 and 5.
remained relatively constant while polymer molecular weight
slightly increased with prolonging time (Table 4). The
palladium black generated from the decomposition of the
catalyst in the polymerizing mixture was not observed for
catalyst 3, whereas it appeared for the palladium catalyst 5 with
dimethyl backbone at 30 °C (Figure 5). These results strongly
indicated that bulky dibenzobarrelene backbone enhanced the
thermal stability, the productivity of α-diimine palladium
catalysts, and the polymerization controllability.
◆
◇
△
,
●
▲
○
Figure 6. Plots of Mn ( ,
,
) and PDI ( ,
) as a function of
styrene conversion using catalysts 1−3 at 15 °C and GPC curves of
copolymers obtained by catalyst 3.
symmetric GPC traces of the copolymers obtained by 3 at
different conversions of styrene monomer without tail peaks,
which shift to the higher molecular weight region with the
increased monomer conversion. Plots of number-average
molecular weights (Mn) as a function of styrene conversion
also illustrate that Mn grows linearly with the styrene
conversion, and PDI (Mw/Mn) values are below 1.20 within
30 h, proving living copolymerizations with long lifetime using
three catalysts 1−3. The copolymer with high molecular
weight (Mn = 1.1 × 105 g mol−1) was formed after 30 h using
3, and its PDI was still precisely controlled (PDI = 1.18). To
the best of our knowledge, this represents one of few samples
on living copolymerization of CO and styrene using palladium
catalysts.14
Alternating CO/styrene copolymerization mechanism has
been previously investigated, and the end groups of polyketone
chain have been also analyzed by MALDI-TOF-MS to
elucidate the polymerization reaction cycles involving the
initiation and chain transfer/termination.14,62 Herein, we
characterized the chain end groups of low-molecular-weight
polyketones by NMR analysis. Figure 7 shows 1H NMR of the
polyketone produced in the trifluoroethanol CF3CH2OH (Mn
= 3700, entry 3 in Table 2). The characteristic signals of CC
double bond were observed at 5.75 and 5.23 ppm, indicating
the form of chain terminal b (−CHCHPh) by β-hydrogen
The enhancement of the dibenzobarrelene backbone on
CO/styrene copolymerization can be attributed to the unique
nature of the bulky dibenzobarrelene backbone. The rigid
dibenzobarrelene backbone kinetically improve the stability of
palladium complexes because of a similar well-known Thorpe−
Ingold effect between nitrogen donor atoms. The steric
demand of the dibenzobarrelene backbone not only is expected
to suppress the chain transfer reaction and enhance the
controllability but also shields the back space of palladium
center,50 thereby prohibiting the access of counterion to metal
center and improving productivity.37 On the other hand, the
resting state is the palladium−acyl−carbonyl species and the
rate-limiting step is the coordination of styrene monomer for
palladium-catalyzed CO/styrene copolymerization.19,41 The
offset π−π stacking between the aniline and the dibenzobarre-
lene backbone may affect the enantioselective coordination of
the styrene monomer.39 The formation of the offset π−π
stacking among three aryl rings promotes the coordination of
styrene monomer, thus improving the productivity (Scheme
2). Carfagna previously proposed a hypothesis on π−π
stacking to explain enhanced productivity in aryl α-diimine
palladium-catalyzed CO/styrene copolymerization, whereas no
any evidence on π−π stacking was provided. A stabilizing effect
deriving from a π−π stacking interaction between the
E
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
realized perfectly alternating CO/styrene copolymeriza-
tion.34,64,65
The stereochemistry of the CO/styrene copolymers was
further characterized by 13C NMR spectroscopy recording the
spectra in a mixture solution of 1,1,1,3,3,3-hexafluoro-
isopropanol (HFIP) and CDCl3. Figure 9 showed the ipso-
1
Figure 7. H NMR spectrum of the copolymer obtained by 3 in
CF3CH2OH.
elimination. 19F NMR of the polyketone produced in the
trifluoroethanol further showed two resonances at −62.44 and
−73.57 ppm (Figure 8), which were assigned to the chain
Figure 9. The ipso-carbon atom region on 13C NMR spectra of CO/
styrene copolymers by catalysts 1−5.
carbon region (137−135 ppm) on 13C NMR spectra of the
CO/styrene copolymers, and the microtacticity was deter-
mined by integration of the signals assigned to the ipso-carbon
atom. The calculated triads in Table 5 showed that
Table 5. Stereoregularity of CO/Styrene Copolymers
Produced by Catalysts 1−5
b
stereoregularity (triads %)
Figure 8. 19F NMR spectrum of the copolymer obtained by 3 in
CF3CH2OH.
a
entry
catalyst
T (°C)
ll
lu + ul
uu
Tg (°C)
1
3
5
6
11
16
21
1
1
1
2
3
4
5
30
20
10
30
30
30
1
1
1
3
5
29
26
26
35
51
57
61
70
73
73
62
44
14
14
111
113
112
112
111
103
100
beginning groups CF3CH2OOC− (g) and the chain terminal
CF3CH2OCH(Ph)− (h), respectively. The chain beginning
group CF3CH2OOC− (g) was derived from the oxidation of
the Pd−H intermediate by the 1,4-benzoquinone, while the
terminal CF3CH2OCH(Ph)− (d) was originated from chain
transfer to trifluoroethanol (Scheme S4 in the Supporting
29
25
30
b
a
All entries are in Table 3. Calculated from the intensities of the 13
NMR ipso-carbon atom resonances.
C
1
Information). The integral of H NMR further showed that
chain transfer by β-hydrogen or monomer-assisted β-hydrogen
abstraction (red route in Scheme S4) was predominant, and a
small amount of chain transfer to trifluoroethanol was also
proved by 19F NMR.19
polymerization temperature had almost no influence on the
stereoregularity, but the dibenzobarrelene backbone signifi-
cantly affected the stereoregularity of the CO/styrene
copolymers. Methyl and acenaphthene derived α-diimine
palladium catalysts 4 and 5 afforded random copolymers
with nearly same triads (ll = 25−29%, uu = 14%). However,
catalysts 1−3 with dibenzobarrelene backbone produced
syndiotacticity-rich copolymers with uu triads of 44−70%
and the almost absence of ll triads.
Previously, Carfagna reported that the steric effect of o-aryl
substituents on the stereoregularity of the CO/styrene
copolymers and presented a ligand-assisted chain-end stereo-
control mechanism.38 Herein, the influence of dibenzobarre-
lene backbone on stereocontrol was also reasonably
interpreted by a π−π stacking-assisted chain-end stereocontrol
mechanism. Besides, the π−π stacking between aniline and the
dibenzobarrelene backbone might affect the enantioselective
coordination of the styrene monomer to forming the π−π
stacking among three aryl rings (Scheme 2),38 which might be
responsible for syndioselectivity. This speculation was further
supported by the effect of the methoxy on syndioselectivity.
The syndiotacticity (uu trials) of CO/styrene copolymers was
However, the polyketone produced in CH2Cl2 in a living
fashion did not show CC double bond resonances in the 1H
NMR spectrum (Figure S36), indicating no occurrence of
chain transfer/termination (Scheme S4). In chlorobenzene, the
low-molecular-weight polyketone produced at 60 °C showed
CC double bond signals (entry 1 in Table 4), and the
beginning methyl a was also observed (Figure S37). The
molecular weight of the copolymer calculated by 1H NMR (Mn
= 4200) was consistent with the value determined by GPC
(Mn = 4100). Therefore, the chain transfer took place by β-
hydrogen elimination or monomer-assisted β-hydrogen
abstraction,19 and 1,4-benzoquinone did not play a role of
chain transfer agent in the absence of alcoholic environment,
which was well consistent with experimental results in Table 2.
The copolymerization products are real polyketone poly-
mers without homopolystyrene. 1H NMR spectroscopies
(Figure 7 and Figure S38) of copolymerization products
showed that no characteristic signals of the methylene on
consecutive styrene unit were observed at 1.8−1.2 ppm,
indicating that all these α-diimine palladium catalysts 1−5
F
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
decreased by increasing numbers of methoxy group on the
meta-position of aniline. As shown in crystal parameters with
regard to the π−π stacking effect of palladium complexes in
Table 1, catalysts 1 and 2 have stronger π−π stacking between
the dibenzobarrelene backbone and aniline moieties than
catalyst 3 with three methoxy groups, thereby having a higher
syndioselectivity. In addition to previously reported steric and
electronic effects on stereocontrol in palladium-catalyzed CO/
styrene copolymerization,32,36,39 the π−π stacking that we
describe here provides a new access to tuning the stereo-
regularity of the CO/styrene copolymers.
With increased the syndiotacticity of CO/styrene copoly-
mers, the solubility of the copolymer became poor. The
products obtained by catalysts 2−5 were easily dissolved
tetrahydrofuran (THF) and CHCl3, while the polymers
obtained by catalyst 1 have poor solubility in THF. Differential
scanning calorimetry (DSC) in Figure 10 showed that only one
Future work is focused on copolymerizations of CO with
various vinyl arene monomers and stereocontrol.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations involving air- and
moisture-sensitive compounds were performed under an atmosphere
of dried and purified nitrogen using standard vacuum-line, Schlenk, or
glovebox techniques.
Materials. Anhydrous dichloromethane, chlorobenzene, diethyl
ether, and hexane were dried and purified by standard methods and
freshly distilled under nitrogen. ZnCl2 was stored in the oven at 110
°C overnight prior to use. Anthracene, vinylene carbonate, and
trifluoroacetic acid were purchased from Energy Chemical and used as
received. Substituted anilines were purchased from Tokyo Chemical
Industry and used as received. Carbon monoxide (CP grade 99.99%)
was supplied by Air Liquid. Styrene monomer was also purchased
from Energy Chemical, dried over CaH2, and then freshly distilled
under vacuum prior to use in polymerization. Other commercially
available reagents were purchased and used without purification.
Measurements. Elemental analyses (C, H, and N) were
performed on a Vario EL microanalyzer. NMR spectra of ligands,
palladium complexes, and polymers were performed on Bruker 400
MHz instruments in CDCl3 or CD3OD using TMS as a reference. 13
C
NMR spectra of polyketones were recorded in 1,1,1,3,3,3-hexafluoro-
isopropanol with addition of CDCl3 for locking purposes. GPC
analyses of the molecular weights and molecular weight distributions
(PDI = Mw/Mn) of the polymers were performed on a Waters Breeze
2 GPC chromatograph equipped with a differential refractive-index
detector. Tetrahydrofuran (THF) or chloroform was used as the
eluent at a flow rate of 1.0 mL/min. DSC analyses were conducted
with a PerkinElmer DSC-4000 system. The DSC curves were
recorded as second heating curves from 30 to 300 °C at a heating
rate of 10 °C/min and a cooling rate of 10 °C/min.
Crystal Structure Determination. The crystals of palladium
complexes were mounted on a glass fiber and transferred to a Bruker
CCD platform diffractometer. Data obtained with the ω−2θ scan
mode were collected on a Bruker SMART 1000 CCD diffractometer
with graphite-monochromated Cu Kα radiation (λ = 1.54184 Å) or
Mo Kα radiation (λ = 0.71073 Å). The structures were solved using
direct methods, while further refinement with full-matrix least-squares
on F2 was obtained with the SHELXTL program package. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
introduced in calculated positions with the displacement factors of the
host carbon atoms.
Figure 10. DSC curves of CO/styrene copolymers obtained by
catalysts 1−5 at 30 °C.
glass transition was observed for all of samples, and no melting
peak appeared on the secondary heating curves of DSC
analysis. Dibenzobarrelene-based palladium catalysts 1−3
afforded CO/styrene copolymers with higher glass-transition
temperature (Tg) than 4 and 5, which was attributed to the
increased syndiotacticity of the copolymer.
Copolymerization of CO/Styrene. In a typical copolymeriza-
tion, a round-bottom Schlenk flask with a stirring bar was heated for 3
h at 150 °C under vacuum and then cooled to room temperature. The
solution of palladium catalyst (1.27 × 10−5 mol) and 1,4-
benzoquinone ([BQ]/[Pd] = 5) in dichloromethane were added
into the glass reactor equipped with a CO gas line. After
establishment of the reaction temperature, the system was
continuously stirred for 5 min, and then 10 mL of styrene was
added by syringe to the well-stirred solution. The reaction
temperatures were controlled with an external water bath or a cooler
in polymerization experiments. The solution was allowed to react for
the desired time at 1 atm CO (absolute pressure). Polymerization was
terminated by pouring the reaction mixture into 100 mL of acidic
methanol (95:5 methanol/HCl) and stirred for 0.5 h at room
temperature. To remove metallic palladium, the polymer was
dissolved in CHCl3, filtered through Celite, and precipitated with
methanol. The solid was washed thoroughly with methanol and dried
under vacuum to constant weight.
CONCLUSIONS
■
In summary, we have reported α-diimine palladium catalysts
with the dibenzobarrelene backbone that catalyze living
alternating CO/styrene copolymerization. Introduction of the
rigid and bulky dibenzobarrelene backbone and electron-
donating m-/p-methoxy groups on aniline moieties enhanced
the thermostability and productivity of the α-diimine
palladium catalyst. The dibenzobarrelene ligand backbone
also improved the controllability in molecular weight and
stereoselectivity of CO/styrene copolymer, and living CO/
styrene copolymerizations were successfully achieved using
three α-diimine palladium catalysts 1−3. The obtained CO/
styrene products obtained by catalysts 1−3 were syndiotactic-
ity-rich alternating copolymers with glass-transition temper-
atures of ∼112 °C. The π−π stacking among three aromatic
rings of the aniline, the dibenzobarrelene, and the styrene
played crucial roles in productivity and stereocontrol. In
addition to previously reported steric and electronic effect of
the aryl substituents, a novel approach was provided for
enhancement on alternating CO/styrene copolymerization by
the steric effect and the π−π stacking of the ligand backbone.
Synthesis of α-Diimine Ligands. 9,10-Dihydro-9,10-ethanoan-
thracene-11,12-dione compounds were prepared according to the
literature.66,67 The condensation reaction of the α-dione compound
with the corresponding aniline facilely produced the α-diimine ligands
L1 and L5 in high purity,52,68 and L2−L4 were prepared by a
transamination reaction (Schemes S1−S3).34
G
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
5.50 (s, 2H, CH), 3.93 (s, 6H, p-OCH3), 3.87 (s, 12H, m-OCH3). 13
C
NMR (100 MHz, CDCl3), δ (ppm): 161.12 (CN), 153.68 (Ar−
C−m-OCH3), 146.16 (Ar−C in backbone), 138.75 (Ar−C−N),
134.55 (Ar−C−p-OCH3), 127.93, 124.86 (Ar−C in backbone), 97.18
(Ar−C), 61.10 (p-OCH3), 56.15 (m-OCH3), 50.31 (CH). Anal.
Calcd for C34H32N2O6: C, 72.32; H, 5.71; N, 4.96. Found: C, 72.29;
H, 5.71; N, 4.93.
L1 (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar
= 4-methoxyaniline): 9,10-Dihydro-9,10-ethanoanthracene-11,12-
dione (2.34 g, 10.0 mmol), dry zinc chloride (4.09 g, 30.0 mmol),
and 4-methoxyaniline (2.71 g, 22.0 mmol) were suspended in acetic
acid (10 mL) under a nitrogen atmosphere. The mixture was reflux
heated for 45 min and then filtered. The solid was washed with diethyl
ether (3 × 2 mL) and dried. In a separating funnel, the obtained solid
was dissolved in dichloromethane, and a saturated solution of
potassium oxalate was added. After shaking for 5 min, the organic
layer was separated, washed with water (3 × 50 mL), dried with
sodium sulfate, filtered, and evaporated to dryness. The residual solids
were further purified by recrystallization from ethanol to give L1 as
yellow crystals in 90% yield. 1H NMR (400 MHz, CD3OD), δ (ppm):
7.36−7.21 (m, 8H, Ar−H), 7.03 (s, 4H, Ar−H), 6.91 (d, 4H, Ar−H),
5.52 (s, 2H, CH), 3.91 (s, 6H, p−OCH3). 13C NMR (100 MHz,
CDCl3), δ (ppm): 160.91 (CN), 156.75 (Ar−C−p-OCH3), 143.18
(Ar−C−N), 138.67 (Ar−C in backbone), 127.78 (Ar−C in
backbone), 124.58 (Ar−C in backbone), 121.51 (Ar−C), 114.42
(Ar−C), 55.19 (p-OCH3), 50.01 (CH). Anal. Calcd for C30H24N2O2:
C, 81.06; H, 5.44; N, 6.30. Found: C, 81.01; H, 5.46; N, 6.27.
L4, Ar−NC(An)−(An)CN−Ar (An = acenaphthene, Ar =
3,4,5-trimethoxyphenyl). L4 was synthesized similarly to L2 using
acenaphthequinone and 3,4,5-trimethoxyaniline. L4 was collected as
orange crystals in 92% yield. 1H NMR (400 MHz, CDCl3), δ (ppm):
7.94 (d, 2H, Ar−H), 7.45 (t, 2H, Ar−H), 7.09 (d, 2H, Ar−H), 6.38
(s, 4H, Ar−H), 5.50 (s, 2H, CH), 3.95 (s, 6H, p-OCH3), 3.83 (s,
12H, m-OCH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 161.70
(CN), 154.18 (Ar−C−m-OCH3), 147.85 (Ar−C−N), 141.75
(Ar−C in backbone), 134.68 (Ar−C−p-OCH3), 131.29, 129.20,
128.16, 127.79, 124.19 (Ar−C in backbone), 95.38 (Ar−C), 61.20 (p-
OCH3), 56.11 (m-OCH3). Anal. Calcd for C30H28N2O6: C, 70.30; H,
5.51; N, 5.47. Found: C, 70.32; H, 5.51; N, 5.46.
L5, Ar−NC(Me)−(Me)CN−Ar (Ar = 3,4,5-trimethoxyphen-
yl). 2,3-Butanedione (0.87 mL, 10.0 mmol) was added to methanol
(40 mL), and several drops of formic acid were also added. When the
solution was stirring, 3,4,5-trimethoxyaniline (3.84 g, 21.0 mmol) was
added. The mixture was stirred at room temperature overnight,
cooled, filtered, and washed with cool methanol (3 × 2 mL). The
residual solids were further purified by recrystallization from ethanol
to give L5 as yellow crystals in 93% yield. 1H NMR (400 MHz,
CDCl3), δ (ppm): 6.02 (s, 4H, Ar−H), 3.85 (s, 18H, OCH3), 2.20 (s,
6H, CH3). 13C NMR (400 MHz, CDCl3), δ (ppm): 168.70 (CN),
153.04 (Ar−C−m-OCH3), 147.02 (Ar−C−p-OCH3), 134.44 (Ar−
C−N), 96.03 (Ar−C), 61.02 (p-OCH3), 56.08 (m-OCH3), 15.61
(CH3). Anal. Calcd for C22H28N2O6: C, 63.45; H, 6.78; N, 6.73.
Found: C, 63.40; H, 6.83; N, 6.69.
Synthesis of Neutral α-Diimine Palladium Complexes. All
neutral α-diimine palladium complexes were prepared by the reaction
of Pd(COD)MeCl with the corresponding α-diimine ligand. A typical
synthetic procedure for N1 was described as follows: 1.1 mmol of
ligand L1 and 1.0 mmol of (COD)PdMeCl were added to a Schlenk
tube together with 20 mL of dichloromethane, and the reaction
mixture was then stirred for 24 h at room temperature. The solution
was evaporated under vacuum to 3 mL, and then 50 mL hexane was
added. After being filtered and washed with hexane (3 × 5 mL), the
complex was precipitated as an orange solid.
L2 (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar
= 3,5-dimethoxyaniline). 9,10-Dihydro-9,10-ethanoanthracene-11,12-
dione (2.34 g, 10.0 mmol) and dry zinc chloride (4.09 g, 30.0 mmol)
were suspended in 10 mL of acetic acid under a nitrogen atmosphere.
The mixture was heated to 50−60 °C, and 3,5-bis(trifluoromethyl)-
aniline (3.44 mL, 22.0 mmol) was added. The solution was reflux
heated for 45 min and then filtered. The solid was washed with diethyl
ether (3 × 2 mL) and dried. The obtained solid and 3,5-
dimethoxyaniline (4.60 g, 30.0 mmol) were dispersed in methanol
(30 mL), and stirred at room temperature overnight. The suspension
was filtered, and the solid was washed with n-hexane (3 × 2 mL) and
dried. In a separating funnel, the obtained solid was dissolved in
dichloromethane, and a saturated solution of potassium oxalate was
added. After shaking for 5 min, the organic layer was separated,
washed with water (3 × 50 mL), dried with sodium sulfate, filtered,
and evaporated to dryness. The residual solids were further purified
by recrystallization from ethanol to give L2 as yellow crystals in 88%
1
yield. H NMR (400 MHz, CDCl3), δ (ppm): 7.38−7.23 (m, 8H,
Ar−H), 6.34 (s, 2H, Ar−H), 6.11 (s, 4H, Ar−H), 5.48 (s, 2H, CH),
3.85 (s, 12H, m-OCH3). 13C NMR (100 MHz, CDCl3), δ (ppm):
161.32 (Ar−C−m-OCH3), 160.96 (CN), 152.13 (Ar−C−N),
138.61 (Ar−C in backbone), 127.93 (Ar−C in backbone), 124.96
(Ar−C in backbone), 98.01 (Ar−C), 96.58 (Ar−C), 55.63 (m-
OCH3), 50.20 (CH). Anal. Calcd for C32H28N2O4: C, 76.17; H, 5.59;
N, 5.55. Found: C, 76.18; H, 5.60; N, 5.51.
N1, [(Ar−NC(An)−(An)CN−Ar)]PdCH3Cl (An = diben-
zobarrelene, Ar = 4-methoxyaniline). The palladium complex N1 as
an orange powder was obtained in 89% yield. H NMR (400 MHz,
CDCl3), δ (ppm): 7.40−7.23 (m, 8H, Ar−H), 7.18−7.11 (d, 2H, Ar−
H), 7.11−7.00 (m, 4H, Ar−H), 6.94−6.88 (d, 2H, Ar−H), 5.47 (s, H,
CH), 5.30 (s, H, CH), 3.92 (s, 3H, p-OCH3) 3.89 (s, 3H, p-OCH3),
L3, (Ar−NC(An)−(An)CN−Ar) (An = dibenzobarrelene, Ar
= 3,4,5-trimethoxyaniline). L3 was synthesized similarly to L2 using
3,4,5-trimethoxyaniline instead of 3,5-dimethoxyaniline. L3 was
collected as yellow crystals in 86% yield. 1H NMR (400 MHz,
CDCl3), δ (ppm): 7.38−7.21 (m, 8H, Ar−H), 6.15 (s, 4H, Ar−H),
1
H
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
0.68 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm):
173.73, 166.26 (CN), 158.91, 158.52 (Ar−C−p-OCH3), 138.28,
137.58 (Ar−C−N), 137.04, 136.67, 128.95, 125.38, 124.56, 123.07
(Ar−C in backbone), 114.61, 114.08 (Ar−C), 55.50, 53.51 (p-
OCH3), 51.00, 49.44 (CH), 3.32 (Pd−CH3). Anal. Calcd for
C31H27ClN2O2Pd: C, 61.91; H, 4.53; N, 4.66. Found: C, 61.88; H,
4.55; N, 4.62.
N5, [Ar−NC(Me)−(Me)CN−Ar]PdCH3Cl (Ar = 3,4,5-
trimethoxyphenyl). The palladium complex N5 as an orange powder
was obtained in 84% yield. H NMR (400 MHz, CDCl3), δ (ppm):
1
6.28 (s, 2H, Ar−H), 6.14 (s, 2H, Ar−H), 3.98 (d, 6H, p-OCH3), 3.87
(s, 6H, m-OCH3), 3.85 (s, 6H, m-OCH3), 2.26 (s, 3H, CH3), 2.15
(s,3H, CH3), 0.77 (s, 3H, Pd−CH3). 13C NMR (400 MHz, CDCl3), δ
(ppm): 175.31, 168.95 (CN), 153.84, 153.12 (Ar−C−m-OCH3),
142.75, 141.10 (Ar−C−N), 136.57, 136.24 (Ar−C−p-OCH3), 99.85,
98.59 (Ar−C), 61.02 (p-OCH3), 56.34 (m-OCH3), 21.01, 19.92
(CH3), 3.55 (Pd−CH3). Anal. Calcd for C23H31ClN2O6Pd: C, 48.18;
H, 5.45; N, 4.89. Found: C, 48.22; H, 5.48; N, 4.84.
Synthesis of Cationic α-Diimine Palladium Complexes. All
cationic α-diimine palladium complexes were prepared by the reaction
of NaBArF and acetonitrile with the corresponding neutral α-diimine
complex. A typical synthetic procedure for 1 was described as follows:
0.5 mmol of palladium complex N1, 0.55 mmol of NaBArF, and 0.5
mL of acetonitrile were added to a Schlenk tube together with 30 mL
of diethyl ether, and the reaction mixture was then stirred for 24 h at
room temperature. The solution was filtered by Celite and then
evaporated under vacuum to 5 mL, and 50 mL of hexane was added.
After being filtered and washed with hexane (3 × 5 mL), the complex
was collected as a yellow solid.
N2, [(Ar−NC(An)-(An)CN−Ar)]PdCH3Cl (An = dibenzo-
barrelene, Ar = 3,5-dimethoxyaniline). The palladium complex N2 as
an orange powder was obtained in 86% yield. H NMR (100 MHz,
1
CDCl3), δ (ppm): 7.41−7.27 (m, 8H, Ar−H), 6.48 (t, 1H, Ar−H),
6.46 (t, 1H, Ar−H), 6.30 (d, 2H, Ar−H), 6.13 (d, 2H, Ar−H), 5.49
(s, H, CH), 5.17 (s, H, CH), 3.84 (s, 12H, m-OCH3), 0.78 (s, 3H,
Pd−CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 173.15, 166.87
(CN), 161.58, 160.86 (Ar−C−m-OCH3), 146.94, 145.68 (Ar−C−
N), 137.35, 136.49, 129.13, 128.99, 125.51, 125.36 (Ar−C in
backbone), 100.95, 100.08 (Ar−C), 99.97, 99.26 (Ar−C), 55.71,
55.65 (m-OCH3), 50.99, 49.54 (CH), 3.24 (Pd−CH3). Anal. Calcd
for C33H31ClN2O4Pd: C, 59.92; H, 4.72; N, 4.23. Found: C, 59.89; H,
4.76; N, 4.20.
1, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF]
N3, [(Ar−NC(An)−(An)CN−Ar)]PdCH3Cl (An = diben-
(An = dibenzobarrelene, Ar = 4-methoxyaniline). The palladium
zobarrelene, Ar = 3,4,5-trimethoxyaniline). The palladium complex
1
1
complex 1 as a yellow powder was obtained in 72% yield. H NMR
N3 as an orange powder was obtained in 85% yield. H NMR (400
(400 MHz, CDCl3), δ (ppm): 7.70 (s, 8H, Ar−H in BArF−), 7.51 (s,
4H, Ar−H in BArF−), 7.44−7.31 (m, 8H, Ar−H in backbone), 7.09
(d, 2H, Ar−H), 7.07−6.97 (m, 4H, Ar−H), 6.86 (d, 2H, Ar−H), 5.41
(s, H, CH), 5.11 (s, H, CH), 3.91 (s, 3H, p-OCH3), 3.84 (s, 3H, p-
OCH3), 1.97 (s, 3H, CH3CN), 0.61 (s, 3H, Pd−CH3). 13C NMR
(100 MHz, CDCl3), δ (ppm): 177.74, 167.96 (CN), 162.58,
162.08, 161.59, 161.09 (Ar−C−B in BArF−), 159.96, 159.51 (Ar−C−
p-OCH3), 136.78 (Ar−C−N), 136.70 (Ar−C in backbone), 136.50
(Ar−C−N), 135.90 ((Ar−C in backbone), 134.95 (Ar−C−CF3 in
BArF−), 129.91, 129.81 (Ar−C in backbone), 129.48, 129.17, 128.86,
128.76, 128.54 (CF3 in BArF−), 126.05, 125.74, 125.75 (Ar−C in
backbone), 123.34, 123.27 (Ar−C in BArF−), 122.91 (Ar−C),
121.41, 120.63 (Ar−C in BArF−), 117.62 (CH3CN), 115.21, 114.96
(Ar−C), 55.74, 55.68 (p-OCH3), 50.98, 49.29 (CH), 7.54 (CH3CN),
2.74 (Pd−CH3). Anal. Calcd for C65H42N3O2BF24Pd: C, 54.58; H,
2.79; N, 2.77. Found: C, 54.53; H, 2.82; N, 2.75.
MHz, CDCl3), δ (ppm): 7.42−7.28 (m, 8H, Ar−H), 6.41 (s, 2H, Ar−
H), 6.21 (s, 2H, Ar−H), 5.56 (s, H, CH), 5.28 (s, H, CH), 3.97 (s,
3H, p-OCH3), 3.96 (s, 3H, p-OCH3), 3.95 (s, 6H, m-OCH3), 3.90 (s,
6H, m-OCH3), 0.79 (s, 3H, Pd−CH3). 13C NMR (100 MHz,
CDCl3), δ (ppm): 173.55, 166.69 (CN), 153.94, 153.27 (Ar−C−
m-OCH3), 141.08, 139.59 (Ar−C−N), 137.49, 137.06 (Ar−C−p-
OCH3), 136.60, (Ar−C in backbone), 129.16, 129.05, 125.35, 125.25
(Ar−C in backbone), 100.65, 99.04 (Ar−C), 61.04 (p-OCH3), 56.41
(m-OCH3), 53.48 (CH2Cl2), 51.03, 49.58 (CH), 3.42 (Pd−CH3).
Anal. Calcd for C35H35ClN2O6Pd: C, 58.26; H, 4.89; N, 3.88. Found:
C, 58.29; H, 4.86; N, 3.84.
N4, Ar−NC(An)−(An)CN−Ar (An = acenaphthene, Ar =
3,4,5-trimethoxyphenyl). The palladium complex N4 as a red powder
1
was obtained in 90% yield. H NMR (400 MHz, CDCl3), δ (ppm):
8.09 (q, 2H, Ar−H), 7.54 (m, 2H, Ar−H), 7.42 (d, 1H, Ar−H), 6.78
(d, 1H, Ar−H), 6.48 (s, 2H, Ar−H), 6.44 (s, 2H, Ar−H), 3.96 (d,
6H, p-OCH3), 3.87 (d, 12H, m-OCH3), 1.03 (s, 3H, Pd−CH3). 13C
NMR (400 MHz, CDCl3), δ (ppm): 176.22, 166.45 (CN), 154.42,
153.59 (Ar−C−m-OCH3), 143.34, 142.32 (Ar−C−N), 141.12 (Ar−
C in backbone), 137.17, 136.80 (Ar−C−p-OCH3), 134.41, 131.30,
130.85, 128.81, 128.62, 126.59, 125.96, 125.33, 125.12 (Ar−C in
backbone), 99.46, 98.40 (Ar−C), 61.51, 6.49 (p-OCH3), 56.34, 56.32
(m-OCH3), 4.12 (Pd−CH3). Anal. Calcd for C31H31ClN2O6Pd: C,
55.62; H, 4.67; N, 4.18. Found: C, 55.64; H, 4.62; N, 4.14.
2, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF]
(An = dibenzobarrelene, Ar = 3,5-dimethoxyaniline). The palladium
1
complex 2 as a yellow powder was obtained in 75% yield. H NMR
(400 MHz, CDCl3), δ (ppm): 7.70 (s, 8H, Ar−H in BArF−), 7.52 (s,
4H, Ar−H in BArF−), 7.46−7.25 (m, 8H, Ar−H), 6.53 (s, 1H, Ar−
H), 6.48 (s, 1H, Ar−H), 6.14 (d, 1H, Ar−H), 6.06 (d, 3H, Ar−H),
5.42 (s, H, CH), 5.18 (s, H, CH), 3.84 (s, 6H, m-OCH3), 3.80 (s, 6H,
m-OCH3), 1.99 (s, 3H, CH3CN), 0.72 (s, 3H, Pd−CH3). 13C NMR
I
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(100 MHz, CDCl3), δ (ppm): 180.10, 168.59 (CN), 162.57 (Ar−
C−B in BArF−), 162.12 (Ar−C−m-OCH3), 162.09 (Ar−C−B in
BArF−), 162.06 (Ar−C−m-OCH3), 161.60, 161.10 (Ar−C−B in
BArF−), 145.48, 145.24 (Ar−C−N), 136.48, 135.76 (Ar−C in
backbone), 134.95 (Ar−C−CF3), 130.05, 129.96 (Ar−C), 129.31,
129.20, 128.91, 128.63, 128.57 (CF3 in BArF−), 126.06, 125.93,
125.81 (Ar−C in backbone), 123.35, 121.57, 120.64 (Ar−C in
backbone), 123.35, 121.57, 120.64 (Ar−C in BArF−), 117.63
(CH3CN), 100.04, 99.97, 99.62, 98.96 (Ar−C), 55.79, 55.69 (m-
OCH3), 51.11, 49.51 (CH), 7.32 (CH3CN), 2.53 (Pd−CH3). Anal.
Calcd for C67H46N3O4BF24Pd: C, 52.59; H, 3.03; N, 2.75. Found: C,
52.62; H, 3.04; N, 2.73.
5, [Ar−NC(Me)−(Me)CN−Ar]Pd(CH3CN)CH3[BArF]
(Ar = 3,4,5-trimethoxyphenyl). The palladium complex 5 as a yellow
powder was obtained in 81% yield. H NMR (400 MHz, CDCl3), δ
1
(ppm): 7.68 (s, 8H, Ar−H in BArF−), 7.52 (s, 4H, Ar−H in BArF−),
6.13 (s, 2H, Ar−H), 6.03 (s, 2H, Ar−H), 3.88 (d, 6H, p-OCH3), 3.81
(d, 12H, m-OCH3), 2.19 (s, 3H, CH3), 2.17 (s, 3H, CH3), 2.02 (s,3H,
CH3CN), 0.67 (s, 3H, Pd−CH3). 13C NMR (100 MHz, CDCl3), δ
(ppm): 180.38, 171.52 (CN), 162.55, 162.04, 161.57, 161.08 (Ar−
C−B in BArF−), 154.35 (Ar−C−m-OCH3), 141.22, 140.92 (Ar−C−
N), 137.36 (Ar−C−p-OCH3), 134.93 (Ar−C−CF3 in BArF−),
129.76, 129.48, 129.19, 128.85 (CF3 in BArF−), 126.02, 123.32,
120.60 (Ar−C in BArF−), 117.62 (CH3CN), 98.09, 97.71 (Ar−C),
61.21 (p-OCH3), 56.41 (m-OCH3), 21.24, 19.42 (CH3), 7.34
(CH3CN), 2.53 (Pd−CH3). Anal. Calcd for C57H46N3O6BF24Pd: C,
47.47; H, 3.22; N, 2.91. Found: C, 47.45; H, 3.23; N, 2.86.
3, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF]
(An = dibenzobarrelene, Ar = 3,4,5-trimethoxyaniline). The palladium
ASSOCIATED CONTENT
* Supporting Information
■
1
complex 3 as a yellow powder was obtained in 70% yield. H NMR
S
(400 MHz, CDCl3), δ (ppm): 7.68 (s, 8H, Ar−H in BArF−), 7.50 (s,
4H, Ar−H in BArF−), 7.44−7.30 (m, 8H, Ar−H), 6.23 (s, 2H, Ar−
H), 6.14 (s, 2H, Ar−H), 5.44 (s, H, CH), 5.18 (s, H, CH), 3.96 (s,
3H, p-OCH3), 3.94 (s, 3H, p-OCH3), 3.85 (s, 12H, m-OCH3), 1.99
(s, 3H, CH3CN), 0.71 (s, 3H, Pd−CH3). 13C NMR (100 MHz,
CDCl3), δ (ppm): 177.48, 168.52 (CN), 162.54, 162.04, 161.55,
161.06 (Ar−C−B in BArF−), 154.34, 154.30 (Ar−C−m-OCH3),
139.67, 139.49 (Ar−C−N), 137.96, 137.47 (Ar−C−p-OCH3),
136.51, 135.76 (Ar−C in backbone), 134.90 (Ar−C−CF3 in
BArF−), 130.14, 130.05 (Ar−C in backbone), 129.50,
129.18,128.84, 128.72, 128.56 (CF3 in BArF−), 126.01, 125.76,
125.62 (Ar−C in backbone), 123.30, 121.41, 120.60 (Ar−C in
BArF−), 117.60 (CH3CN), 98.83 (Ar−C), 61.34, 61.30 (p-OCH3),
56.54, 56.52 (m-OCH3), 51.16, 49.51 (CH), 7.62 (CH3CN), 2.62
(Pd−CH3). Anal. Calcd for C69H50N3O6BF24Pd: C, 52.11; H, 3.17;
N, 2.64. Found: C, 52.12; H, 3.13; N, 2.61.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.8b01786.
1
NMR spectra of ligands and palladium complexes, H
and 13C NMR of polymers, crystallographic data, CO/
styrene living copolymerization data (DOCX)
X-ray crystallographic data of N1 (CIF)
X-ray crystallographic data of N2 (CIF)
X-ray crystallographic data of N3 (CIF)
X-ray crystallographic data of N4 (CIF)
AUTHOR INFORMATION
Corresponding Author
*(H.G.) Fax +86-20-84114033; Tel +86-20-84113250; e-mail
gaohy@mail.sysu.edu.cn.
■
ORCID
Haiyang Gao: 0000-0002-7865-3787
Notes
The authors declare no competing financial interest.
4, [(Ar−NC(An)−(An)CN−Ar)]Pd(CH3CN)CH3[BArF]
(An = acenaphthene, Ar = 3,4,5-trimethoxyaniline). The palladium
complex 4 as a red powder was obtained in 90% yield. 1H NMR (400
MHz, CDCl3), δ (ppm): 8.11 (m, 2H, Ar−H in backbone), 7.66 (s,
8H, Ar−H in BArF−), 7.55 (m, 2H, Ar−H in backbone), 7.48 (s, 4H,
Ar−H in BArF−), 7.42 (d, 1H, Ar−H in backbone), 6.80 (d, 1H, Ar−
H in backbone), 6.51 (s, 2H, Ar−H), 6.47 (s, 2H, Ar−H), 3.98 (s,
3H, p-OCH3), 3.97 (s, 3H, p-OCH3), 3.83 (s, 6H, m-OCH3), 3.82 (s,
6H, m-OCH3), 2.08 (s, 3H, CH3CN), 0.92 (s, 3H, Pd−CH3). 13C
NMR (100 MHz, CDCl3), δ (ppm): 176.73, 168.34 (CN), 162.51,
162.01, 161.52, 161.02 (Ar−C−B in BArF−), 154.75, 154.50 (Ar−C−
m-OCH3), 146.15 (Ar−C−N), 140.97 (Ar−C in backbone), 137.97,
137.60 (Ar−C−p-OCH3), 134.86 (Ar−C−CF3 in BArF−), 133.26,
132.59, 131.53 (Ar−C in backbone), 129.44, 129.15, 128.99, 128.84,
128.68, 128.53 (CF3 in BArF−), 126.62, 125.98, 125.69, 125.28,
124.53 (Ar−C in backbone), 123.27, 121.44, 120.56 (Ar−C in
BArF−), 117.56 (CH3CN), 98.22, 97.88 (Ar−C), 61.46, 61.44 (p-
OCH3), 56.49, 56.46 (m-OCH3), 8.10 (CH3CN), 2.62 (Pd−CH3).
Anal. Calcd for C65H46N3O6BF24Pd: C, 50.75; H, 3.01; N, 2.73.
Found: C, 50.71; H, 3.03; N, 2.70.
ACKNOWLEDGMENTS
■
This work was supported by grants from National Natural
Science Foundation of China (NSFC) (Project 21674130,
51873234), Natural Science Foundation of Guangdong
Province (2017A030310349), the Fundamental Research
Funds for the Central Universities (17lgjc02), and PetroChina
Innovation Foundation (2017D-5007-0505).
REFERENCES
■
(1) Drent, E.; Budzelaar, P. H. M. Palladium-Catalyzed Alternating
Copolymerization of Alkenes and Carbon Monoxide. Chem. Rev.
1996, 96, 663−682.
(2) Sommazzi, A.; Garbassi, F. Olefin-Carbon Monoxide Copoly-
mers. Prog. Polym. Sci. 1997, 22, 1547−1605.
(3) Sen, A.; Jiang, Z.; Chen, J. T. Novel Nitrogen-Containing
Heterocyclic Polymers Derived from the Alternating Ethylene-Carbon
Monoxide Copolymer. Macromolecules 1989, 22, 2012−2014.
(4) Kosaka, N.; Hiyama, T.; Nozaki, K. Baeyer−Villiger Oxidation of
an Optically Active 1,4-Polyketone. Macromolecules 2004, 37, 4484−
4487.
J
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(5) Milani, B.; Crotti, C.; Farnetti, E. Hydrogen Transfer Reduction
of Polyketones Catalyzed by Iridium Complexes: A Novel Route
towards More Biocompatible Materials. Dalton Trans 2008, 4659−
4663.
(6) Zhang, Y.; Broekhuis, A. A.; Picchioni, F. Thermally Self-Healing
Polymeric Materials: The Next Step to Recycling Thermoset
Polymers? Macromolecules 2009, 42, 1906−1912.
(7) Cheng, C.; Guironnet, D.; Barborak, J.; Brookhart, M.
Preparation and Characterization of Conjugated Polymers Made by
Postpolymerization Reactions of Alternating Polyketones. J. Am.
Chem. Soc. 2011, 133, 9658−9661.
(8) Sen, A.; Lai, T. W. Novel Palladium(II)-Catalyzed Copoly-
merization of Carbon Monoxide with Olefins. J. Am. Chem. Soc. 1982,
104, 3520−3522.
(9) Lai, T. W.; Sen, A. Palladium(II)-Catalyzed Copolymerization of
Carbon Monoxide with Ethylene. Direct Evidence for a Single Mode
of Chain Growth. Organometallics 1984, 3, 866−870.
(10) Bianchini, C.; Meli, A. Alternating Copolymerization of Carbon
Monoxide and Olefins by Single-Site Metal Catalysis. Coord. Chem.
Rev. 2002, 225, 35−66.
(11) Alperowicz, N. Shell to Produce New Engineering Plastic in the
U.K. Chem. Week 1995, 156, 22.
(12) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U.
W. Syndiotactic Poly(1-oxo-2-phenyltrimethylene): On the Mode of
the Chain Growth under Palladium Catalysis. Angew. Chem., Int. Ed.
Engl. 1991, 30, 989−991.
(13) Brookhart, M.; Rix, F. C.; DeSimone, J. M.; Barborak, J. C.
Palladium(II) Catalysts for Living Alternating Copolymerization of
Olefins and Carbon Monoxide. J. Am. Chem. Soc. 1992, 114, 5894−
5895.
(14) Milani, B.; Corso, G.; Mestroni, G.; Carfagna, C.; Formica, M.;
Seraglia, R. Highly Efficient Catalytic System for the CO/Styrene
Copolymerization: Toward the Stabilization of the Active Species.
Organometallics 2000, 19, 3435−3441.
(15) Soro, B.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Zucca, A.;
Bastero, A.; Claver, C. Effect of 5-Me Substituent(s) on the Catalytic
Activity of Palladium(II) 2,2′-Bipyridine Complexes in CO/4-tert-
Butylstyrene Copolymerization. J. Organomet. Chem. 2004, 689,
1521−1529.
(16) Scarel, A.; Milani, B.; Zangrando, E.; Stener, M.; Furlan, S.;
Fronzoni, G.; Mestroni, G.; Gladiali, S.; Carfagna, C.; Mosca, L.
Palladium Complexes with 3-Alkyl-Substituted-1,10-Phenanthrolines:
Effect of the Remote Alkyl Substituent on the CO/Olefin
Copolymerization Reactions. Organometallics 2004, 23, 5593−5605.
(17) Durand, J.; Zangrando, E.; Stener, M.; Fronzoni, G.; Carfagna,
Carbon Monoxide Catalyzed by a Cationic Bioxazoline Pd(II)
Complex. Macromol. Rapid Commun. 1995, 16, 9−14.
(23) Brookhart, M.; Wagner, M. I. Synthesis of a Stereoblock
Polyketone through Ancillary Ligand Exchange. J. Am. Chem. Soc.
1996, 118, 7219−7220.
(24) Milani, B.; Anzilutti, A.; Vicentini, L.; Sessanta o Santi, A.;
Zangrando, E.; Geremia, S.; Mestroni, G. Bis-Chelated Palladium(II)
Complexes with Nitrogen-Donor Chelating Ligands Are Efficient
Catalyst Precursors for the CO/Styrene Copolymerization Reaction.
Organometallics 1997, 16, 5064−5075.
(25) Reetz, M. T.; Haderlein, G.; Angermund, K. Chiral Diketimines
as Ligands in Pd-Catalyzed Reactions: Prediction of Catalyst Activity
by the AMS Model. J. Am. Chem. Soc. 2000, 122, 996−997.
(26) Binotti, B.; Carfagna, C.; Gatti, G.; Martini, D.; Mosca, L.;
Pettinari, C. Mechanistic Aspects of Isotactic CO/Styrene Copoly-
merization Catalyzed by Oxazoline Palladium(II) Complexes.
Organometallics 2003, 22, 1115−1123.
(27) Milani, B.; Scarel, A.; Zangrando, E.; Mestroni, G.; Carfagna,
C.; Binotti, B. Cationic Palladium Complexes with Mono- and
Bidentate Nitrogen-Donor Ligands: Synthesis, Characterization and
Reactivity in CO/Styrene Copolymerization Reaction. Inorg. Chim.
Acta 2003, 350, 592−602.
́
(28) Bastero, A.; Claver, C.; Ruiz, A.; Castillon, S.; Daura, E.; Bo, C.;
Zangrando, E. Insights into CO/Styrene Copolymerization by Using
PdII Catalysts Containing Modular Pyridine−Imidazoline Ligands.
Chem. - Eur. J. 2004, 10, 3747−3760.
̈
(29) Schatz, A.; Scarel, A.; Zangrando, E.; Mosca, L.; Carfagna, C.;
Gissibl, A.; Milani, B.; Reiser, O. High Stereocontrol and Efficiency in
CO/Styrene Polyketone Synthesis Promoted by Azabis(oxazoline)−
Palladium Complexes. Organometallics 2006, 25, 4065−4068.
(30) Bergman, S. D.; Goldberg, I.; Carfagna, C.; Mosca, L.; Kol, M.;
Milani, B. Palladium Complexes Containing Large Fused Aromatic
N−N Ligands as Efficient Catalysts for the CO/Styrene Copoly-
merization. Organometallics 2006, 25, 6014−6018.
́
́
(31) Bella, A. F.; Ruiz, A.; Claver, C.; Sepulveda, F.; Jalon, F. A.;
Manzano, B. R. Pyrazolyl-Pyrimidine Based Ligands in Palladium
Catalyzed Copolymerization and Terpolymerization of CO/Olefins. J.
Organomet. Chem. 2008, 693, 1269−1275.
(32) Canil, G.; Rosar, V.; Dalla Marta, S.; Bronco, S.; Fini, F.;
Carfagna, C.; Durand, J.; Milani, B. Unprecedented Comonomer
Dependence of the Stereochemistry Control in Pd-Catalyzed CO/
Vinyl Arene Polyketone Synthesis. ChemCatChem 2015, 7, 2255−
2264.
(33) Rosar, V.; Dedeic, D.; Nobile, T.; Fini, F.; Balducci, G.; Alessio,
E.; Carfagna, C.; Milani, B. Palladium Complexes with Simple
Iminopyridines as Catalysts for Polyketone Synthesis. Dalton Trans
2016, 45, 14609−146019.
(34) Scarel, A.; Axet, M. R.; Amoroso, F.; Ragaini, F.; Elsevier, C. J.;
Holuigue, A.; Carfagna, C.; Mosca, L.; Milani, B. Subtle Balance of
Steric and Electronic Effects for the Synthesis of Atactic Polyketones
Catalyzed by Pd Complexes with Meta-Substituted Aryl-BIAN
Ligands. Organometallics 2008, 27, 1486−1494.
(35) Amoroso, F.; Zangrando, E.; Carfagna, C.; Muller, C.; Vogt, D.;
Hagar, M.; Ragaini, F.; Milani, B. Catalyst Activity or Stability: the
Dilemma in Pd-Catalyzed Polyketone Synthesis. Dalton Trans 2013,
42, 14583−14602.
(36) Binotti, B.; Carfagna, C.; Zuccaccia, C.; Macchioni, A. From
Atactic to Isotactic CO/p-Methylstyrene Copolymer by Proper
Modification of Pd(II) Catalysts Bearing Achiral α-Diimines. Chem.
Commun. 2005, 92−94.
(37) Binotti, B.; Bellachioma, G.; Cardaci, G.; Carfagna, C.;
Zuccaccia, C.; Macchioni, A. The Effect of Counterion/Ligand
Interplay on the Activity and Stereoselectivity of Palladium(II)−
Diimine Catalysts for CO/p-Methylstyrene Copolymerization. Chem.
- Eur. J. 2007, 13, 1570−1582.
(38) Carfagna, C.; Gatti, G.; Mosca, L.; Passeri, A.; Paoli, P.; Guerri,
A. Stereocontrol Mechanism in CO/p-Methylstyrene Copolymerisa-
tion Catalysed by Aryl-α-Diimine Pd(II) Complexes. Chem. Commun.
2007, 4540−4542.
C.; Binotti, B.; Kamer, P. C. J.; Muller, C.; Caporali, M.; van Leeuwen,
̈
P. W. N. M.; Vogt, D.; Milani, B. Long-Lived Palladium Catalysts for
CO/Vinyl Arene Polyketones Synthesis: A Solution to Deactivation
Problems. Chem. - Eur. J. 2006, 12, 7639−7651.
(18) Durand, J.; Zangrando, E.; Carfagna, C.; Milani, B. New
Atropisomeric N-N Ligands for CO/Vinyl Arene Copolymerization
Reaction. Dalton Trans 2008, 2171−2182.
(19) Rix, F. C.; Rachita, M. J.; Wagner, M. I.; Brookhart, M.; Milani,
B.; Barborak, J. C. Palladium(II)-Catalyzed Copolymerization of
Styrenes with Carbon Monoxide: Mechanism of Chain Propagation
and Chain Transfer. Dalton Trans 2009, 8977−8992.
(20) Campos-Carrasco, A.; Estorach, C. T.; Bastero, A.; Reguero,
́
̀
M.; Masdeu-Bulto, A. M.; Francio, G.; Leitner, W.; D’Amora, A.;
Milani, B. Cationic Palladium(II) Complexes for CO/Vinyl Arene
Copolymerization in the Presence of Carbon Dioxide. Organometallics
2011, 30, 6572−6586.
(21) Brookhart, M.; Wagner, M. I.; Balavoine, G. G. A.; Haddou, H.
A. Polymers with Main-Chain Chirality. Synthesis of Highly Isotactic,
Optically Active Poly(4-tert-butylstyrene-alt-CO) Using Pd(II)
Catalysts Based on C2-Symmetric Bisoxazoline Ligands. J. Am.
Chem. Soc. 1994, 116, 3641−3642.
(22) Bartolini, S.; Carfagna, C.; Musco, A. Enantioselective Isotactic
Alternating Copolymerization of Styrene and 4-Methylstyrene with
K
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(39) Carfagna, C.; Gatti, G.; Paoli, P.; Binotti, B.; Fini, F.; Passeri,
A.; Rossi, P.; Gabriele, B. New Aryl α-Diimine Palladium(II) Catalysts
in Stereocontrolled CO/Vinyl Arene Copolymerization. Organo-
metallics 2014, 33, 129−144.
(40) Carfagna, C.; Gatti, G.; Paoli, P.; Rossi, P. Mechanism for
Stereoblock Isotactic CO/Styrene Copolymerization Promoted by
Aryl α-Diimine Pd(II) Catalysts: A DFT Study. Organometallics 2009,
28, 3212−3217.
(41) Carfagna, C.; Gatti, G.; Martini, D.; Pettinari, C. Syndiotactic
CO/Styrene Copolymerization Catalyzed by α-Diimine Pd(II)
Complexes: Regio- and Stereochemical Control. Organometallics
2001, 20, 2175−2182.
(42) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and
Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins.
J. Am. Chem. Soc. 1995, 117, 6414−6415.
(43) Guo, L.; Gao, H.; Guan, Q.; Hu, H.; Deng, J.; Liu, J.; Liu, F.;
Wu, Q. Substituent Effects of the Backbone in α-Diimine Palladium
Catalysts on Homo- and Copolymerization of Ethylene with Methyl
Acrylate. Organometallics 2012, 31, 6054−6062.
(44) Liu, F.-S.; Hu, H.-B.; Xu, Y.; Guo, L.-H.; Zai, S.-B.; Song, K.-
M.; Gao, H.-Y.; Zhang, L.; Zhu, F.-M.; Wu, Q. Thermostable α-
Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of
the Substituted Backbone Structure on Catalytic Properties and
Branching Structure of Polyethylene. Macromolecules 2009, 42, 7789−
7796.
(45) Zhong, L.; Li, G.; Liang, G.; Gao, H.; Wu, Q. Enhancing
Thermal Stability and Living Fashion in α-Diimine−Nickel-Catalyzed
(Co)polymerization of Ethylene and Polar Monomer by Increasing
the Steric Bulk of Ligand Backbone. Macromolecules 2017, 50, 2675−
2682.
(46) Dai, S.; Sui, X.; Chen, C. Highly Robust Palladium(II) α-
Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethyl-
ene and Copolymerization with Methyl Acrylate. Angew. Chem., Int.
Ed. 2015, 54, 9948−9953.
Interactions in Designed Hemoproteins. J. Am. Chem. Soc. 1999, 121,
11798−11812.
(56) Sinnokrot, M. O.; Valeev, E. F.; Sherrill, C. D. Estimates of the
Ab Initio Limit for π−π Interactions: The Benzene Dimer. J. Am.
Chem. Soc. 2002, 124, 10887−10893.
(57) Rashkin, M. J.; Waters, M. L. Unexpected Substituent Effects in
Offset π−π Stacked Interactions in Water. J. Am. Chem. Soc. 2002,
124, 1860−1861.
(58) Curtis, M. D.; Cao, J.; Kampf, J. W. Solid-State Packing of
Conjugated Oligomers: From π-Stacks to the Herringbone Structure.
J. Am. Chem. Soc. 2004, 126, 4318−4328.
(59) Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. Semi-
Crystalline Polar Polyethylene: Ester-Functionalized Linear Poly-
olefins Enabled by a Functional-Group-Tolerant, Cationic Nickel
Catalyst. Angew. Chem., Int. Ed. 2016, 55, 7106−7110.
(60) Hunter, C. A.; Sanders, J. K. M. The Nature of π−π
Interactions. J. Am. Chem. Soc. 1990, 112, 5525−5534.
(61) Lu, W.; Chan, M. C. W.; Zhu, N.; Che, C.-M.; Li, C.; Hui, Z.
Structural and Spectroscopic Studies on Pt···Pt and π−π Interactions
in Luminescent Multinuclear Cyclometalated Platinum(II) Homo-
logues Tethered by Oligophosphine Auxiliaries. J. Am. Chem. Soc.
2004, 126, 7639−7651.
(62) Scarel, A.; Durand, J.; Franchi, D.; Zangrando, E.; Mestroni, G.;
Carfagna, C.; Mosca, L.; Seraglia, R.; Consiglio, G.; Milani, B. Mono-
and Dinuclear Bioxazoline-Palladium Complexes for the Stereo-
controlled Synthesis of CO/Styrene Polyketones. Chem. - Eur. J. 2005,
11, 6014−6023.
(63) Scarel, A.; Durand, J.; Franchi, D.; Zangrando, E.; Mestroni, G.;
Milani, B.; Gladiali, S.; Carfagna, C.; Binotti, B.; Bronco, S.; Gragnoli,
T. Trifluoroethanol: Key Solvent for Palladium-Catalyzed Polymer-
ization Reactions. J. Organomet. Chem. 2005, 690, 2106−2120.
(64) Mu, J.; Fan, W.; Shan, S.; Su, H.; Wu, S.; Jia, Q. Thermal
Degradation Kinetics of Polyketone Based on Styrene and Carbon
Monoxide. Thermochim. Acta 2014, 579, 74−79.
(65) Gall, B. T.; Pelascini, F.; Ebeling, H.; Beckerle, K.; Okuda, J.;
(47) Zai, S.; Gao, H.; Huang, Z.; Hu, H.; Wu, H.; Wu, Q.
Substituent Effects of Pyridine-Amine Nickel Catalyst Precursors on
Ethylene Polymerization. ACS Catal. 2012, 2, 433−440.
(48) Pei, L.; Liu, F.; Liao, H.; Gao, J.; Zhong, L.; Gao, H.; Wu, Q.
Synthesis of Polyethylenes with Controlled Branching with α-Diimine
Nickel Catalysts and Revisiting Formation of Long-Chain Branching.
ACS Catal. 2018, 8, 1104−1113.
(49) Rosar, V.; Meduri, A.; Montini, T.; Fini, F.; Carfagna, C.;
Fornasiero, P.; Balducci, G.; Zangrando, E.; Milani, B. Analogies and
Differences in Palladium-Catalyzed CO/Styrene and Ethylene/
Methyl Acrylate Copolymerization Reactions. ChemCatChem 2014,
6, 2403−2418.
Mulhaupt, R. Molecular Weight and End Group Control of Isotactic
̈
Polystyrene Using Olefins and Nonconjugated Diolefins as Chain
Transfer Agents. Macromolecules 2008, 41, 1627−1633.
(66) Amon, C. M.; Banwell, M. G.; Gravatt, G. L. Oxidation of
Vicinal Diols to α-Dicarbonyl Compounds by Trifluoroacetic
Anhydride-Activated Dimethyl Sulfoxide. J. Org. Chem. 1987, 52,
4851.
(67) Mondal, R.; Shah, B. K.; Neckers, D. C. Photogeneration of
Heptacene in a Polymer Matrix. J. Am. Chem. Soc. 2006, 128, 9612−
9613.
(68) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. C−H Bond
Activation by Cationic Platinum(II) Complexes: Ligand Electronic
and Steric Effects. J. Am. Chem. Soc. 2002, 124, 1378−1399.
(50) Zhong, S.; Tan, Y.; Zhong, L.; Gao, J.; Liao, H.; Jiang, L.; Gao,
H.; Wu, Q. Precision Synthesis of Ethylene and Polar Monomer
Copolymers by Palladium-Catalyzed Living Coordination Copoly-
merization. Macromolecules 2017, 50, 5661−5669.
(51) Liu, J.; Chen, D.; Wu, H.; Xiao, Z.; Gao, H.; Zhu, F.; Wu, Q.
Polymerization of α-Olefins Using a Camphyl α-Diimine Nickel
Catalyst at Elevated Temperature. Macromolecules 2014, 47, 3325−
3331.
(52) Gasperini, M.; Ragaini, F.; Cenini, S. Synthesis of Ar-BIAN
Ligands (Ar-BIAN = Bis(aryl)acenaphthenequinonediimine) Having
Strong Electron-Withdrawing Substituents on the Aryl Rings and
Their Relative Coordination Strength toward Palladium(0) and -(II)
Complexes. Organometallics 2002, 21, 2950−2957.
(53) Huo, P.; Liu, W.; He, X.; Wei, Z.; Chen, Y. Substituent Effects
and Activation Mechanism of Norbornene Polymerization Catalyzed
by Three-Dimensional Geometry α-Diimine Palladium Complexes.
Polym. Chem. 2014, 5, 1210−1218.
(54) Janiak, C. A. Critical Account on π−π Stacking in Metal
Complexes with Aromatic Nitrogen-Containing Ligands. J. Chem. Soc.,
Dalton Trans. 2000, 3885−3896.
(55) Liu, D.; Williamson, D. A.; Kennedy, M. L.; Williams, T. D.;
Morton, M. M.; Benson, D. R. Aromatic Side Chain−Porphyrin
L
DOI: 10.1021/acs.macromol.8b01786
Macromolecules XXXX, XXX, XXX−XXX