Rotation-restricted strategy to synthesize high molecular weight polyethylene using iminopyridyl nickel and palladium catalyst

Article abstract of DOI:10.1002/aoc.6140

Most of the iminopyridyl Ni (II) and Pd (II) catalysts are reported to oligomerize ethylene or yield very low molecular weight polyethylene. Moreover, the molecular weight of product is not sensitive to ligand sterics. In this contribution, we demonstrate that the bulky rotation-restricted substituents incorporated into iminopyridyl Ni (II) and Pd (II) catalysts that provide the right orientation are highly effective in retarding the chain transfer. Thus, (2,6-bis(10,11-dihydro-5H-dibenzo[a,d][7]annulen-5-yl)-4-methylphenyl)-1-(pyridin-2-yl)methanimine nickel (II) bromide (Ni3) and (2,6-bis(10,11-dihydro-5H-dibenzo[a,d][7]annulen-5-yl)-4-methylphenyl)-1-(pyridin-2-yl)methanimine palladium (II) methyl chloride (Pd3) with the phenyl substituents fixed in the diarylmethyl moiety produce polyethylene or functionalized polyethylene (ethylene-MA copolymer) with high M_n values up to 2.5 × 10⁴ g mol^?1, while allowing the high MA incorporation (3.2%–13.8%). In addition, the effects on the (co)polymerization behavior as a function of rotation-restricted substituent variations (free rotation, restricted rotation and fixation) were systemically studied. As a result, various molecular weight polyethylene and ethylene-MA copolymer with high MA incorporation ratio were also obtained in this system.

Full text of DOI:10.1002/aoc.6140

Received: 2 July 2020
DOI: 10.1002/aoc.6140
Revised: 21 July 2020
Accepted: 23 July 2020
F U L L P A P E R
Rotation-restricted strategy to synthesize high molecular
weight polyethylene using iminopyridyl nickel and
palladium catalyst
1
2
2
2
1
Hongwei Peng | Shuaikang Li | Gen Li | Shengyu Dai
| Mingjun Ji
|
1
1
Zhe Liu
| Lihua Guo
1
The Key Laboratory of Life-Organic
Analysis and Key Laboratory of
Pharmaceutical Intermediates and
Analysis of Natural Medicine, School of
Chemistry and Chemical Engineering,
Qufu Normal University, Qufu, 273165,
China
Most of the iminopyridyl Ni (II) and Pd (II) catalysts are reported to
oligomerize ethylene or yield very low molecular weight polyethylene.
Moreover, the molecular weight of product is not sensitive to ligand sterics. In
this contribution, we demonstrate that the bulky rotation-restricted
substituents incorporated into iminopyridyl Ni (II) and Pd (II) catalysts that
provide the right orientation are highly effective in retarding the chain
transfer. Thus, (2,6-bis(10,11-dihydro-5H-dibenzo[a,d][7]annulen-5-yl)-4-met-
hylphenyl)-1-(pyridin-2-yl)methanimine nickel (II) bromide (Ni3) and (2,6-bis
2
Institutes of Physical Science and
Information Technology, Anhui
University, Hefei, 230601, China
Correspondence
(10,11-dihydro-5H-dibenzo[a,d][7]annulen-5-yl)-4-methylphenyl)-1-(pyridin-2-yl)
Lihua Guo, The Key Laboratory of Life-
Organic Analysis and Key Laboratory of
Pharmaceutical Intermediates and
Analysis of Natural Medicine, School of
Chemistry and Chemical Engineering,
Qufu Normal University, Qufu, 273165,
China.
methanimine palladium (II) methyl chloride (Pd3) with the phenyl substituents
fixed in the diarylmethyl moiety produce polyethylene or functionalized
polyethylene (ethylene-MA copolymer) with high Mn values up to
4
−1
2.5 × 10 g mol , while allowing the high MA incorporation (3.2%–13.8%). In
addition, the effects on the (co)polymerization behavior as a function of rotation-
restricted substituent variations (free rotation, restricted rotation and fixation)
Email: guolihua@qfnu.edu.cn
Shengyu Dai, Institutes of Physical
Science and Information Technology,
Anhui University, Hefei 230,601, China.
Email: daiyu@ustc.edu.cn
were systemically studied. As
a
result, various molecular weight
polyethylene and ethylene-MA copolymer with high MA incorporation ratio
were also obtained in this system.
Funding information
K E Y W O R D S
National Natural Science Foundation of
China, Grant/Award Numbers: 21671118,
ethylene copolymerization, ethylene polymerization, iminopyridyl, Nickel, Palladium
51703215; Young Talents Invitation
Program of Shandong Provincial Colleges
and Universities; Natural Science
Foundation of Shandong Province, Grant/
Award Numbers: ZR2018MB023,
ZR2019BB078
1
| INTRODUCTION
The first two authors are equal first authors.
Correction added on 19 January 2021, after first online publication:
The note identifying the first authors had been mistakenly omitted.]
Late transition metal catalysts for olefin coordination-
insertion polymerization have received great attention
since the seminal discovery of Ni (II) and Pd (II)
[
Appl Organomet Chem. 2021;35:e6140.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.6140

2
of 11
PENG ET AL.
[
1]
α-diimine catalysts. The key to convert olefins to high
molecular weight polymers for these catalysts is the
incorporation of sterically bulky axial substituents on the
ligand since bulk can inhibit the chain transfer process.
Particularly, in contrast to early transition metal cata-
lysts, late transition metal catalysts not only could pro-
duce branched polyolefins by extensive chain walking
process but also generate the functional polyolefins by
the copolymerization of olefins with polar monomers due
structure is sterically incorporated compared to the sym-
metric α-diimine system.
Some strategies, including steric tuning of ortho sub-
[
16–23]
stituents on the N-aryl ring,
bulky substituents on the backbone
perturbation,
the introduction of
[
24–27]
and electronic
[
28–30]
have been used to increase the molec-
ular weight of polyolefins in the α-diimine catalysts sys-
tem. Among them, the modification of sterically bulky
ortho-aryl substituents is the most effective approach to
access high molecular weight polyolefins. For example,
α-diimine Ni (II) catalysts with ortho-H substituents on
both aryl rings oligomerize ethylene due to the incidental
[
2–7]
to their low oxophilicity.
In addition to the α-diimine catalysts, some interest-
ing results also have been revealed for [N, N] bidentate
iminopyridyl Ni (II) and Pd (II) catalysts.
ple, Laine discovered that the dimeric iminopyridyl Ni
II) catalysts generated low molecular weight polyethyl-
ene (Scheme 1, I, M < 3,500 at temperature above
By using bulkier dibenzhydryl group, more
active Ni (II) catalysts are obtained. However, the molec-
ular weight of polyethene in this system is still very low
[
8–10]
[2]
For exam-
β-H elimination (Scheme 1, IV). When the bulky sub-
stituent 2,6-diisopropyl is employed, high molecular
[1]
(
weight polyolefins can be produced (Scheme 1, V). Fur-
ther, using the bulkier dibenzhydryl or diarylmethyl
instead of diisopropyl, ultrahigh molecular weight poly-
n
ꢀ
[11,12]
2
0 C).
[26,31]
ethylene (UHMWPE) is obtained (Scheme 1, VI).
α-diimine Pd (II) catalysts also showed the similar trend
that the increase in steric bulk of ortho-aryl substituents
[
13]
(
Scheme 1, II, M < 1,000).
reported that iminopyridyl Pd (II) catalysts with the same
dibenzhydryl group produced highly branched oils
Gao and coworkers also
n
[32–34]
improved the molecular weight of the polyolefin.
Thus, the strategy to introduce substituents with bulky
steric hindrance in the α-diimine ligands has been
extremely studied in this field. However, as mentioned
above, this strategy most often showed no improvement
for iminopyridyl Ni (II) and Pd (II) catalysts. One excep-
tion example was the “half-sandwich” iminopyridyl Ni
(II) catalysts bearing the naphthyl moieties (Scheme 1,
[
14]
(
Scheme 1, II, M : 600–800).
Recently, our group
n
investigated the mono-ligated and bis-ligated effect of the
iminopyridyl Ni (II) catalysts with very bulky dia-
rylmethyl moieties on the catalytic activity and the struc-
ture (e.g., molecular weight and branching density) of
polyethylene. Similarly, the low molecular weight poly-
[
35,36]
ethylene is produced (Scheme 1, III, M < 8,300 at tem-
perature above 20 C).
showed high activity for ethylene polymerization while
produced oligomers or low-molecular-weight polyethyl-
ene since only a single ortho-disubstituted aryl imine
VII).
These catalysts provided effective axial
n
ꢀ
[15]
Basically, these catalysts
shielding and retarded chain transfer, thus affording
polyethylene with high molecular weight. This story told
us that the orientation of bulky substituent is very impor-
tant in iminopyridyl Ni (II) and Pd (II) system. On the
SCHEME 1 The reported iminopyridyl Ni
(
II) and Pd (II) catalysts (I–III, VII), steric tuning of
ortho substituents for α-diimine catalysts system
IV–VI) and our current work
(

PENG ET AL.
3 of 11
other hand, Guan and coworkers showed that their
cyclophane-based α-diimine Ni (II) and Pd (II) catalysts
could produce higher molecular weight polyethylene and
incorporate more methyl acrylate (MA) in ethylene-MA
presence of hydrochloric acid and zinc chloride
(Schemes S1 and S2 and Figures S4–S7). The
iminopyridine ligands L1–L3 were subsequently pro-
duced by the acid-catalyzed condensation reaction of
A1–A3 with picolinaldehyde (Scheme 2, Figures S8–S11,
S18, and S19). Compared to the reported the “half-sand-
[29,37,38]
copolymerization than the acyclic analogs.
Gao
and coworkers also displayed that increasing the steric
hindrance of the backbone structure for α-diimine cata-
lysts can decrease the associate chain transfer.
wich” iminopyridyl ligands bearing the naphthyl
[
24,39–43]
[35,36]
moieties,
these ligands can be more easily large-
The cyclophane design and the bulky backbone hinder
rotation of the catalyst's axial steric environment in these
α-diimine systems. In the system of iminopyridyl cata-
lysts with the dibenzhydryl group, the two phenyl substit-
uents in the dibenzhydryl moiety rotate freely around the
central C atom (Scheme 1, C*), which can influence the
orientation and the effective steric hindrance of this
bulky substituent. If this rotation is restricted, it is possi-
ble to retard chain transfer sufficiently and result in the
production of high molecular weight polyolefins. On the
basis of these considerations, we report here the rotation-
restricted strategy to increase the molecular weight of
polyolefins in iminopyridyl Ni (II) and Pd (II) systems. In
particular, the degree of restricted rotation (free rotation,
restricted rotation and fixation) on the catalytic proper-
ties toward ethylene polymerization and copolymeriza-
tion with MA was systemically studied. Most
surprisingly, the high molecular weight ethylene-MA
copolymer with high MA incorporation ratio was also
obtained using the iminopyridyl Pd (II) catalysts in this
system.
scale synthesized through simple reactions by the
reagents commercially available with no chromatography
involved. Treatment of the ligands with NiBr in ethanol
2
afforded
the
corresponding
mono-ligated
Ni
(II) complexes Ni1–Ni3. Ni1 already described in our
[
15]
recent work
was used for comparison with this series
of complexes. Identity and purity of Ni2 and Ni3 were
established by mass spectrometry (Figures S20 and S21)
and elemental analysis. Notably, we recently
reported that the reaction of L1 with (DME)NiBr2
(DME = ethylene glycol dimethyl ether) in CH Cl solu-
2
2
tion led to the bis-ligated Ni (II) complex (nickel center is
surrounded by two bidentate ligands). The production of
mono-ligated complex Ni1 and the corresponding bis-
ligated complex with the same ligand depended on the
[
15]
selection of solvents and metal precursors.
Herein, L2
and L3, which showed the higher steric hindrance than
L1 (ortho-substituted, ortho-bridged vs. para-substituted),
were also employed to react with (DME)NiBr in CH Cl
2
2
2
solution. However, according to the results of elemental
analysis and mass spectrometry, the obtained products
were still the mono-ligated Ni (II) complexes. This result
indicated that the introduction of ortho-substituent and
ortho-bridged substituent significantly increased the ste-
ric hindrance of the ligands and made it difficult to form
the bis-ligated complexes. Likewise, the palladium com-
plexes Pd1–Pd3 were also readily formed from the
reaction of the ligands L1–L3 with (COD)PdMeCl
(COD = 1,5-cycloocta diene) and fully identified by NMR
(Figures S12–S17), mass spectrometry (Figures S22–S24),
2
2
| RESULTS AND DISCUSSION
.1 | Synthesis and characterization of
the complexes
The anilines A1–A3 were synthesized by the dialkylation
of p-toluidine with the substituted benzhydrol in the
SCHEME 2 Synthesis of iminopyridine ligands and
the corresponding iminopyridyl Ni (II) and Pd
(
II) complexes

4
of 11
PENG ET AL.
1
3
and elemental analysis. All of these palladium complexes
showed the mono-ligated coordination mode, which are
similar with the previously reported iminopyridyl
Pd (II) complexes containing dibenzhydryl moiety
at δ 1.26 and 1.64 ppm in the C NMR, respectively,
while the corresponding peaks for Pd3 are δ 0.38 ppm in
13
the C NMR. Such a big change in the chemical shift
also can be attributed to the unique aryl orientation
in Pd3.
[14]
(
Scheme 1, II).
Single crystals of Ni3 and Pd3 were obtained by lay-
ering their CH Cl solution with hexane at ambient tem-
2
2
perature (Figure 1 and Table S1). In contrast to the
mono-ligated complex Ni1 with para-methyl substitu-
ents, which crystallized as a centrosymmetric dimer
2.2 | Ni (II)-catalyzed ethylene
polymerization
(
bridged-bromide) and adopted a distorted octahedral
Upon activation with AlEt Cl, all of the Ni (II) complexes
2
[15]
geometry,
Ni3 with more bulky ortho-bridged substit-
proved to be very high active toward ethylene polymeri-
7
−1 −1
uents showed the mononuclear structure with a distorted
tetrahedral geometry at the nickel center. The phenyl
substituents fixed in the diarylmethyl moiety for Ni3
lie nearly parallel to the five-member chelate ring
zation (up to 1.1 × 10 g mol h , Table 1, entry 1). The
polymerization results at the same temperature revealed
the following trend in their activities: Ni1 > Ni3 > Ni2.
The observed decreasing activity trend can be accounted
for by the increasing bulkiness of the substituents, going
from para-CH to ortho-CH or ortho-bridged CH . In
(
Ni1-N1-C5-C6-N2) with both of the dihedral angles
ꢀ
being 14.78 . Meanwhile, the dihedral angles between
the phenyl rings in the diarylmethyl moiety and the five-
member chelate ring for our reported Ni1 (CCDC num-
ber: 1816867) are 48.75 (below) and 16.85 (above),
respectively,
3
3
2
accord with the previous report, a less bulky group
allowed for a faster monomer trapping and consequently
ꢀ
ꢀ
[13]
higher activity.
However, Ni2 with ortho-CH is less
3
[15]
and much larger than those of Ni3. Thus,
active than Ni3 with ortho-bridged CH . Considering the
2
the fixation of the phenyl substituents in Ni3 provided
effective blockage and shielding of the axial positions of
the metal center and would be able to retard the associa-
tive chain transfer process. The palladium center for Pd3
showed a distorted square-planar geometry. Similarly,
the phenyl rings in the diarylmethyl moiety are also
nearly parallel to the five-member chelate ring
similar steric hindrance of ortho-CH and ortho-bridged
3
CH , the orientation of these bulky substituents, appar-
2
ently as a result of the degree of restricted rotation, also
plays a key role in determining the catalyst activity. The
striking feature of these results is increasing the degree of
restricted rotation from para-CH in Ni1 (free rotation)
3
to ortho-CH3 in Ni2 (restricted rotation), and ortho-
(
Pd1-N2-C2-C3-N1) for Pd3 with the dihedral angles
bridged CH in Ni3 (fixation) led to a dramatic increase
in molecular weight of the obtained polyethylene
2
ꢀ
ꢀ
being 14.36 (below) and 11.49 (above), respectively.
Further, the chemical shift of Pd-CH for Pd1 and Pd2 is
(Figures S50–S55). For example, M of the polyethylene
3
n
FIGURE 1 Solid-state molecular structures of nickel complex Ni3 (a) and palladium complex Pd3 (b) with 50% probability level, and H
atoms have been omitted for clarity

PENG ET AL.
5 of 11
[d]
TABLE 1 Ethylene polymerization
o
[a]
[b]
[b]
[c]
Entry
Catalyst
Ni1
T/ C
Yield/g
5.53
5.39
2.33
0.33
0.82
0.95
2.89
2.19
1.43
Act.
11.1
10.8
4.7
M
n
PDI
1.83
1.90
1.71
1.72
2.30
1.67
2.07
2.04
3.09
B
T
m
with Ni (II) catalysts
1
2
3
4
5
6
7
8
9
30
50
70
30
50
70
30
50
70
1,200
1,000
900
56
57
58
47
48
49
52
55
66
55
[
e]
Ni1
Wax
Wax
65
Ni1
Ni2
0.7
3,400
2,000
2,000
24,300
24,700
7,500
Ni2
1.6
58
Ni2
1.9
54
Ni3
5.8
74
Ni3
4.4
72
Ni3
2.9
63
Note: Conditions: Ni (II) catalyst (2 μmol), 200 eq. AlEt
2
Cl, 1 ml of CH
2
2
Cl , 29 ml toluene, 8 atm,
polymerization time (15 min).
a
Activity is in unit of 10 g mol h−1
6
−1
.
b
−1
ꢀ
M
n
is in unit of g mol , determined by GPC in trichlorobenzene at 150 C.
c
1
B = branches per 1,000 carbons, determined by H NMR spectroscopy, B = 1,000 × 2(ICH3)/3
CH2 + CH + ICH3). Branching numbers for low molecular weight samples (M < 10,000) were corrected for
(
I
n
end groups.
d
Determined by differential scanning calorimetry (DSC), broad peak.
e
Amorphous.
generated by Ni3 are nearly 1 order of magnitude higher
the polyethylene generated by Ni3 showed the highest
branching density at high temperature (70 C).
ꢀ
than that produced by Ni1 and Ni2 (M : 1,000–3,000
n
−
1
vs. 25,000 g mol ). Apparently, the molecular weight of
the obtained polyethylene in iminopyridyl system is
essentially governed by the orientation of the bulky
substituents, which is determined by the degree of the
restricted rotation and can provide effective axial
shielding for the metal center. It should be noted that late
transition metals such as nickel and palladium display a
very high propensity for β-hydride elimination, which
potentially leads to chain transfer in olefin polymeriza-
When the polymerization temperature increased from
ꢀ
ꢀ
ꢀ
30 C to 50 C and 70 C, the catalytic activity of Ni1 and
Ni3 decreased and the branching density increased,
[35]
which are consistent with previous observations.
How-
ever, the catalytic activity of Ni2 increased by increasing
the polymerization temperature. In addition, the molecu-
lar weight did not change significantly with increasing
temperature for Ni1. In the case of Ni2 and Ni3, the
molecular weight dropped considerably as the polymeri-
zation temperature increased. However, the molecular
[4]
tion. The initial work by Brookhart showed that the
key to obtain high molecular weight polymers using such
catalysts is the incorporation of ortho substituents on the
aryl imine groups which positions steric bulk at the two
axial sites above and below the square coordination
plane. Bulk at the two axial sites inhibits chain transfer
relative to chain propagation, and thus, the high polymer
ꢀ
weight of the polyethylene generated by Ni3 at 70 C was
still 7,500 g mol− and much higher than that obtained
by Ni1 and Ni2. This result indicated that the chain
transfer was also effectively retarded at high temperature
for Ni3.
1
[44]
molecular weight is achieved.
As aforementioned in
single crystal analysis, ortho-bridged CH in Ni3 inhibits
2.3 | Pd (II)-catalyzed ethylene (co)
2
the rotation of two phenyl substituents in the
dibenzhydryl moiety around the central C atom and
enforces a more “vertical” orientation and axial shielding
polymerization
Upon the activation of excess sodium tetrakis(3,5-bis
(trifluoromethyl)phenyl)borate (NaBArF), ethylene poly-
merization and copolymerization with MA were carried
out using these Pd (II) complexes. In ethylene polymeri-
zation, complexes Pd1–Pd3 showed moderate activities
under given conditions and generated highly branched
ethylene oligomers (Pd1 and Pd2) and polyethylene
(Pd3) (Table 2). No clear trend was observed for the
relationship between the catalytic activity and ligand
toward the metal center than para-CH in Ni1 and ortho-
3
CH in Ni2. In addition, the polyethylene generated by
3
Ni1 with less bulky para-CH showed higher branching
3
density than that by Ni2 with ortho-CH and Ni3 with
3
ꢀ
ꢀ
ortho-bridged CH at 30 C and 50 C (Figures S25–S33).
2
Accordingly, compared to the polyethylene generated by
Ni2 and Ni3, the polyethylene obtained by Ni1 showed
lower Tm or no Tm (wax) (Figures S44–S49). However,

6
of 11
PENG ET AL.
TABLE 2 Ethylene polymerization with Pd (II) catalysts
ꢀ
4 [a]
[b]
[c]
[c]
n
[d]
Entry
Cat.
Pd1
Pd1
Pd2
Pd2
Pd3
Pd3
T ( C)
30
yield (g)
1.62
Act.(10 )
M
n
M
n
M
w
/M
B
1
2
3
4
5
6
2.7
12.8
4.2
460
270
540
310
1.77
1.37
2.60
1.42
2.56
2.78
62
83
50
7.70
30
2.49
4,200
2,500
4,100
2,300
101
105
78
50
4.26
7.1
30
1.69
2.8
19,200
15,600
24,000
13,400
50
6.96
11.6
85
2 2
Note: Reaction conditions: Pd (II) catalyst (20 μmol), NaBArF (1.5 equiv.), CH Cl (40 mL), ethylene (4 atm), polymerization time (3 h).
a
4
−1 −1
Activity is in unit of 10 g mol
h .
b
−1
1
M
n
is in unit of g mol , determined by H NMR spectroscopy.
c
−1
ꢀ
M
n
is in unit of g mol , determined by GPC in THF at 40 C versus polystyrene standards.
d
1
B = branches per 1,000 carbons, determined by H NMR spectroscopy, B = 1,000 × 2(ICH3)/3(ICH2 + CH + ICH3). Branching numbers for low molecular weight
samples (M < 10,000) were corrected for end groups.
n
structure in Pd (II) system. In consistent with Ni
II) complexes, the restricted-rotation effect on the molec-
ular weight of the obtained product was also significant
for these Pd (II) complexes. The molecular weight of the
obtained polyethylene by Pd3 was approximately.
Generally, the incorporation of polar monomers will dra-
matically reduce copolymer molecular weight and the
catalytic activity. With this in mind, one can envision
that the iminopyridyl Pd (II) catalysts will produce lower
molecular weight functional cooligomers when the
behavior to catalyze ethylene homo-oligomerization has
been observed for most of these reported iminopyridyl Pd
(II) catalysts. However, compared to ethylene homo-
polymerization, the molecular weight of the generated
ethylene-MA cooligomer or copolymer was only slightly
changed except for Pd3, which afforded the decreased
molecular weight of the copolymer (Table 2, entries 2, 4,
6 vs. Table 3, entries 1, 2, and 3, respectively). Notably,
the ethylene-MA copolymer with high molecular weight
(approximately 1.0 × 10 g mol ) was obtained by Pd3
(Table 3, entry 3, Figures S62 and S63). Thus, the fixation
of the phenyl substituents in Pd3 also played a key role
in the generation of high molecular weight ethylene-MA
copolymers (Table 3 and Figure S3). Further, high MA
incorporation ratios of 3.2%–13.8% for Pd1–Pd3 were
observed (Figures S40–S43). Interestingly, Pd3 afforded
(
2
1
orders of magnitude higher than those by Pd1 and
order of magnitude higher than those by Pd2 (Table 2
and Figures S1, S2, and S56–S61), which further con-
firmed that the right orientation of aryl substituents is
crucial for iminopyridyl Ni (II) and Pd (II) catalysts. Nev-
ertheless, the polyethylene obtained by Pd3 are still
amorphous oils due to their high branching density
(
Figures S34–S39). On the other hand, an increase of the
ꢀ
ꢀ
temperature from 30 C to 50 C results in a higher activity
and branching density but a decreased molecular weight
of the products.
4
−1
A large number of α-diimine palladium catalysts
showed effective copolymerization of ethylene with polar
[
4]
monomers due to their functional group tolerance.
However, iminopyridyl Pd (II) catalysts for ethylene/
polar monomer copolymerization are rarely reported.
TABLE 3 Copolymerization of ethylene and MA with Pd (II) catalysts
4
[a]
[b]
[c]
[d]
[d]
[e]
Entry
Cat.
Pd1
Pd2
Pd3
Pd3
[MA] (M)
Yield (g)
1.38
Act.(10 )
X
M
M
n
M
n
M
w
/M
n
B
1
2
3
4
1
1
1
2
0.86
0.44
1.03
0.28
11.4
3.2
200
1,100
7,100
4,700
ꢀ
300
2,400
9,600
6,500
1.26
1.42
1.49
1.33
97
102
86
0.70
1.65
6.6
0.44
13.8
100
Note: Conditions: Pd catalyst (20 μmol), NaBArF (1.5 equiv.), total volume of CH
2
Cl
2
and MA: 20 ml, 8 h, 50 C, ethylene (4 atm).
a
4
−1 −1
Activity is in unit of 10 g mol
h .
b
M
X = monomer incorp. (mol %).
c
−1
1
n
M is in unit of g mol , determined by H NMR spectroscopy.
d
is in unit of g mol−1, determined by GPC in THF at 40 C versus polystyrene standards.
ꢀ
M
n
e
1
B = branches per 1,000 carbons, branching numbers were determined using H NMR spectroscopy, B = 1,000 × 2(ICH3)/3(ICH2 + CH + ICH3). The branches
ending with functional groups are added to the total branches.

PENG ET AL.
7 of 11
1
FIGURE 2
H NMR spectrum of ethylene-MA copolymer generated by Pd3 (Table 3, entry 4)
copolymer of up to 13.8% MA incorporation at
MA] = 2.0 M, which did not significantly decrease the
molecular weight (Mn approximately
.7 × 10 g mol ) of the obtained copolymer (Figure 2
diarylmethyl moiety showed that the rotation-restricted
strategy gave access to the proper orientation of bulky
substituents and provided effective blockage of the axial
positions of the metal center. As a result, Ni3 and Pd3
can produce polymers or copolymers with much higher
molecular weight than that obtained by other Ni (II) and
Pd (II) complexes in ethylene polymerization and copoly-
merization with MA. Meanwhile, Pd3 exhibited a high
MA incorporation up to 13.8% with only a slightly
decrease of the copolymer molecular weight. These
results suggested the potential for wide utility of rotation-
restricted strategy in developing new late transition metal
olefin polymerization catalysts.
[
=
4
−1
0
and Table 3, entry 4). The high efficiency in incorporat-
ing MA for these catalysts was most probably attributed
to the open coordination space around the pallidum cen-
ter, which originated from the less axially steric of the
pyridine moiety of the asymmetric iminopyridine ligand
relative to the symmetric α-diimine ligand. The unique
open microenvironment of the iminopyridine ligand
would favor MA coordination and subsequent insertion.
In addition, the MA units were incorporated predomi-
nately at the end of branches (Figure 2), which was
consistent
with
the
reported
α-diimine
Pd
[
2,3,45,46]
(II) catalysts.
Similarly, the functional highly
4 | EXPERIMENTAL SECTION
4.1 | General considerations
branched products obtained in this system are amor-
phous oils and may find a potential application in the
areas of interface active agents or viscosity modifiers.
[
47]
All manipulations were performed in a glovebox or using
standard Schlenk techniques. n-Hexane, ether, and tolu-
3
| CONCLUSIONS
ene were freshly distilled from sodium under N . Dic-
2
hloromethane was dried over P O5 overnight and
2
In summary, the strategy to increase the molecular
weight of polyolefins by introducing the bulky substitu-
ents in α-diimine Ni (II) and Pd (II) catalysts has been
extensively studied. However, this strategy most often
showed no improvement for iminopyridyl Ni (II) and Pd
distilled. Starting reagents for the synthesis of ligands
and complexes were purchased and used without purifi-
cation. The synthetic route for anilines A2 and A3 was
shown in supporting information. The ligand L1 and the
corresponding nickel complex Ni1 were synthesized
[15]
(II) catalysts. Herein, we report the rotation-restricted
according to the method we previously reported.
The
strategy to synthesize high molecular weight polyethyl-
ene or functionalized polyethylene using iminopyridyl Ni
palladium precursor (COD) PdMeCl was prepared by
[
48]
1
13
using a literature procedure.
H, C NMR spectra
(
II) and Pd (II) catalysts. The molecular structure of Ni3
were acquired by a Bruker DPX 500 spectrometer or a
JEOL JNM-ECZ600R 600 spectrometer at 25 C unless
ꢀ
and Pd3 with the phenyl substituents fixed in the

8
of 11
PENG ET AL.
+
otherwise stated. The chemical shifts were referenced to
585.3270. Found: 585.3252, [M + H] . Anal. Calcd for
C H N : C, 88.32; H, 6.89; N, 4.79. Found: C, 88.40; H,
6.90; N, 4.77.
the residual solvent resonance or SiMe signal (0 ppm).
4
43 40 2
1
H NMR spectra of polyethylene produced by Ni1–Ni3
were obtained on a JEOL JNM-ECZ600R 600 spectrome-
ter at 70 C using C D as solvent. Elemental analysis was
L3: The same procedure as above was employed. L3
was obtained as the yellow solid. Yield: 1.12 g, 77%. H
ꢀ
1
6
6
performed by the Analytical Center of the Anhui Univer-
sity. Mass spectra were determined using electro spray
ionization (ESI) LCMS-2010A or Atouflex Speed
MALDI-TOF MS. X-ray diffraction data were collected
NMR (500 MHz, CDCl ) δ 8.64 (d, J = 4.7 Hz, 1H,
3
N=C-H), 7.81–7.71 (m, 2H, Ar-H), 7.42–7.34 (m, 2H,
Ar-H), 7.00 (m, 8H, Ar-H), 6.91 (d, J = 7.5 Hz, 4H, Ar-H),
6.71 (m, 4H, Ar-H), 6.66 (s, 2H, Ar-H), 5.09 (s, 2H,
CHAr ), 3.42–3.30 (m, 4H, Ar-CH ), 2.68 (m, 4H,
at 298(2) K on a Bruker Smart CCD area detector with
2
2
α
13
graphite-monochromated
Mo
K
radiation
Ar-CH ), 2.10 (s, 3H, Ar-CH ). C NMR (126 MHz,
2 3
(
λ = 0.71073 Å). Molecular weight and molecular weight
CDCl ) δ 165.90 (N=C), 154.15, 149.15, 147.95, 140.62,
3
distribution of the products generated by Ni1–Ni3 were
139.68, 136.15, 132.26, 131.74, 130.91, 130.46, 129.44,
determined by gel permeation chromatography (GPC)
126.86, 125.75, 125.16, 122.61, 55.77 (CHAr ), 31.94
2
ꢀ
with a PL-220 at 150 C using trichlorobenzene as a
(Ar-CH ), 21.48 (Ar-CH ). ESI-MS (m/z): Calcd for
2
3
+
solvent, and the system was calibrated using polystyrene
standard. Molecular weight and molecular weight distri-
bution of the products obtained by Pd1–Pd3 were deter-
mined by GPC eluting with THF on a Tosh instrument
C H N : 581.2957. Found: 581.2947, [M + H] . Anal.
43 37 2
Calcd for C H N : C, 88.93; H, 6.25; N, 4.82.
43
36 2
Found: C, 88.79; H, 6.23; N, 4.78.
(
Tosh, Tokyo, Japan). The system was calibrated with
ꢀ
polystyrene standards and operated at 40 C with a flow
rate of 0.35 ml/min. Melting transition temperature
4.3 | Synthesis of Ni (II) complexes
(
Tm) of polymer samples was measured by differential
Ni2: A mixture of L2 (0.58 g,1.0 mmol) and anhydrous
scanning calorimetry (DSC) on an Auto Q20 from TA
Instrument. Samples were heated to 150 C under a
NiBr (0.22 g, 1.0 mmol) was added in dried ethanol
2
ꢀ
(10 ml) under N2. The reaction mixture was refluxed
under stirring for 24 h. The solution was allowed to cool
to room temperature, and the precipitate was formed.
The precipitate was washed with ether (3 × 5 ml) and
dried under vacuum to give Ni2 as orange powder
nitrogen flow (50 ml/min) and kept for 5 min to remove
ꢀ
ꢀ
thermal history, then cooled to 40 C at a rate of 10 C/
ꢀ
min, and finally reheated to 150 C at the same rate.
(
0.45 g, 56%). MALDI-TOF-MS (m/z): calcd. for
+
4.2 | Synthesis of ligands
C H BrN Ni: 721.1728. Found: 721.1379 [M-Br] . Anal.
43 40 2
Calcd for C H Br N Ni: C, 64.29; H, 5.02; N, 3.49.
43
40
2 2
L2: 2-Pyridylaldehyde (0.81 g, 7.5 mmol) and the aniline
A2 (1.28 g, 2.5 mmol) were dissolved in anhydrous
Found: C, 64.33; H, 5.05; N, 3.41.
Ni3: Using a procedure similar to that for the prepa-
ration of Ni2, Ni3 was obtained as orange powder
(0.68 g, 85%). MALDI-TOF-MS (m/z): calcd. for
toluene. Subsequently,
a
catalytic amount of
p-methylbenzenesulfonic acid (0.02 g) was added in the
solution, and the reaction mixture was refluxed under
stirring. After 12 h, the reaction mixture was concen-
trated and 200 ml methanol was added. The yellow solid
precipitated and was separated by filtration. The pure
product can be obtained by layering their CH Cl solu-
+
C H BrN Ni: 717.1415. Found: 717.1409 [M-Br] . Anal.
43
36
2
Calcd for C H Br N Ni: C, 64.62; H, 4.54; N, 3.50.
43
36
2 2
Found: C, 64.55; H, 4.57; N, 3.48.
2
2
tion with methanol at room temperature. Yield: 1.36 g,
4.4 | Synthesis of Pd (II) complexes
1
8
7%. H NMR (500 MHz, CDCl ) δ 8.52 (d, J = 4.7 Hz,
3
1
H, N=C-H), 7.64 (t, J = 6.9 Hz, 1H, Ar-H), 7.58
Pd1: To a solution of ligand L1 (0.58 g, 1.0 mmol) in
(
(
(
(
(
1
1
1
d, J = 7.8 Hz, 1H, Ar-H), 7.23 (m, 1H, Ar-H), 7.11–7.01
m, 8H, Ar-H), 7.01–6.94 (m, 4H, Ar-H), 6.86–6.81
m, 4H, Ar-H), 6.80 (s, 1H, Ar-H), 6.51 (s, 2H, Ar-H), 5.47
s, 2H, CHAr ), 2.11 (s, 3H, Ar-CH ), 1.94 (s, 12H, CH
dry CH Cl (10 ml) was added 0.26 g (COD)PdMeCl
2
2
(1.0 mmol). The reaction mixture was stirred for 24 h at
room temperature. The solvent was concentrated to
approximately 2 ml under reduced pressure, and 10 ml
n-hexane was added, resulting the formation of the
precipitate. The precipitate was washed with n-hexane
(3 × 5 ml) and dried under vacuum to give Pd1 as
2
3
13
PhMe)2). C NMR (126 MHz, CDCl ) δ 164.36 (N=C),
3
53.98, 149.48, 148.02, 141.78, 136.51, 136.05, 132.61,
32.14, 130.25, 129.74, 128.42, 126.31, 125.65, 124.95,
21.56, 45.87 (CHAr2), 21.55 (Ar-CH3), 19.27
1
yellow powder (0.56 g, 76%). H NMR (600 MHz,
(
CH (PhMe) ). ESI-MS (m/z): Calcd for C H N :
CDCl ) δ 9.10 (d, J = 4.5 Hz, 1H, N=C-H), 7.72
2
43 41
2
3

PENG ET AL.
9 of 11
(
7
td, J = 7.8, 1.5 Hz, 1H, Ar-H), 7.63–7.54 (m, 1H, Ar-H),
TOF-MS (m/z): calcd for C H N Pd: 686.1913. Found:
686.1448, [M-Me-Cl] . Anal. Calcd for C H ClN Pd: C,
44 39 2
43
36 2
+
.05 (d, J = 7.9 Hz, 4H, Ar-H), 6.93 (d, J = 8.0 Hz, 4H,
Ar-H), 6.81 (q, J = 8.1 Hz, 8H, Ar-H), 6.66 (s, 2H, Ar-
H), 6.32 (d, J = 7.6 Hz, 1H, Ar-H), 6.02 (s, 1H, Ar-H),
71.64 H, 5.33; N, 3.80. Found: C, 71.69; H, 5.37; N, 3.77.
5
.77 (s, 2H, CHAr ), 2.31 (s, 6H, CH (PhMe) ), 2.20
2 2
(
s, 6H, CH (PhMe) ), 2.18 (s, 3H, Ar-CH ), 0.99 (s, 3H,
4.5 | General procedure for Ni (II)-
catalyzed ethylene polymerization
2
3
13
Pd-CH3). C NMR (151 MHz, CDCl ) δ 171.09 (N=C),
3
1
1
1
51.25, 149.42, 142.14, 140.84, 139.36, 137.83, 136.53,
36.38, 136.17, 135.98, 129.67, 129.13, 128.99, 128.96,
28.28, 125.05, 51.34 (CHAr ), 21.70 (Ar-CH ), 21.17
A mechanically stirred 100 ml Parr reactor was heated to
120 C for 1 h under vacuum and then cooled to room
ꢀ
2
3
(
CH (PhMe) ), 21.08 (CH (PhMe) ), 1.26 (Pd-CH ).
temperature. The autoclave was pressurized to 1.1 atm of
ethylene and was then charged with 29 ml toluene and
2
2
3
MALDI-TOF-MS (m/z): calcd for C H N Pd: 690.2226.
Found: 690.0861, [M-Me-Cl] . Anal. Calcd for
C H ClN Pd: C, 71.25 H, 5.84; N, 3.78. Found: C,
43
40 2
+
0.4 ml solution of Et AlCl in toluene (1 M) at the desired
2
temperature. The system was maintained by continu-
ously stirring for 5 min, and then 1 ml solution of nickel
complex in CH Cl was injected and the ethylene pres-
44
43
2
7
1.19; H, 5.83; N, 3.72.
Pd2: Using the same procedure as for the synthesis of
2
2
Pd1, Pd2 was obtained as a yellow powder (0.53 g, 72%).
sure was increased to 8 atm to initiate polymerization
and stirred continuously at appropriate temperature for
the desired time. Polymerization was quenched by addi-
tion of acidified methanol (5% HCl in MeOH). The prod-
uct was precipitated in methanol, filtered, and dried
1
H NMR (600 MHz, CDCl ) δ 9.04 (d, J = 4.4 Hz, 1H,
3
N=C-H), 7.67 (td, J = 7.8, 1.5 Hz, 1H, Ar-H), 7.58–7.52
(m, 1H, Ar-H), 7.21 (d, J = 7.5 Hz, 2H, Ar-H), 7.17–7.14
(m, 2H, Ar-H), 7.05 (q, J = 6.8 Hz, 4H, Ar-H), 6.95
(t, J = 7.1 Hz, 2H, Ar-H), 6.78 (t, J = 7.2 Hz, 4H, Ar-H),
ꢀ
under vacuum at 45 C to a constant weight.
6
.59 (d, J = 7.5 Hz, 2H, Ar-H), 6.57 (s, 2H, Ar-H), 6.14
(
d, J = 7.6 Hz, 1H, Ar-H), 5.81 (s, 2H, CHAr ), 5.46
2
(
s, 1H, Ar-H), 2.39 (s, 6H, CH (PhMe) ), 2.14 (s, 3H,
4.6 | General procedure for Pd (II)-
catalyzed ethylene polymerization
2
Ar-CH ), 1.91 (s, 6H, CH (PhMe) ), 0.94 (s, 3H, Pd-CH ).
3
2
3
1
3
C NMR (151 MHz, CDCl ) δ 172.83 (N=C), 151.24,
3
1
1
1
48.76, 144.17, 143.16, 138.12, 137.88, 137.62, 136.89,
36.41, 136.30, 130.76, 130.58, 130.44, 130.37, 128.55,
28.18, 126.94, 126.61, 125.80, 125.77, 125.32, 45.74
A 350 ml stainless pressure reactor connected with a
high-pressure gas line was firstly dried at 90 C under vac-
ꢀ
uum for 1 h and then cooled to the desired polymeriza-
tion temperature. The reactor was charged with 38 ml of
CH Cl and the required amount NaBArF in a glovebox.
(
(
CHAr ), 21.68 (Ar-CH ), 20.96 (CH (PhMe) ), 19.48
2 3 2
CH (PhMe) ), 1.64 (Pd-CH ). MALDI-TOF-MS (m/z):
2
3
2
2
calcd for C H N Pd: 690.2226. Found: 690.0060,
After equilibration at the desired polymerization temper-
ature for 10 min, the required amount of catalyst in 2 ml
43
40 2
+
[
M-Me-Cl] . Anal. Calcd for C H ClN Pd: C, 71.25 H,
44 43 2
5
.84; N, 3.78. Found: C, 71.19; H, 5.83; N, 3.72.
of CH Cl2 was injected rapidly into the mixture via
2
Pd3: Using the same procedure as for the synthesis of
Pd1, Pd3 was obtained as a yellow powder (0.62 g, 84%).
syringe. With a rapid stirring, the reactor was pressurized
and maintained at 4 atm of ethylene. After 3 h, the pres-
sure reactor was vented and the polymer was dried under
vacuum to a constant weight.
1
H NMR (600 MHz, CDCl ) δ 9.22 (d, J = 4.7 Hz, 1H,
3
N=C-H), 7.77 (td, J = 7.7, 1.5 Hz, 1H, Ar-H), 7.69–7.64
(
(
(
(
(
(
m, 1H, Ar-H), 7.28 (d, J = 7.3 Hz, 2H, Ar-H), 7.18–7.12
m, 4H, Ar-H), 7.08 (dd, J = 13.1, 7.0 Hz, 4H, Ar-H), 6.93
d, J = 7.2 Hz, 2H, Ar-H), 6.78–6.73 (m, 4H, Ar-H), 6.50
d, J = 7.6 Hz, 1H, Ar-H), 6.20 (s, 1H, Ar-H), 6.15
4.7 | General procedure for Pd (II)-
catalyzed ethylene copolymerization
with MA
t, J = 7.3 Hz, 2H, Ar-H), 5.45 (s, 2H, CHAr ), 3.54
2
td, J = 13.9, 4.8 Hz, 2H, Ar-CH ), 3.32 (dt, J = 17.5,
2
3
.9 Hz, 2H, Ar-CH ), 2.94 (ddd, J = 18.1, 13.9, 4.9 Hz, 2H,
A 350 ml stainless pressure reactor connected with a
high-pressure gas line was firstly dried at 90 C under
2
ꢀ
Ar-CH ), 2.46 (dt, J = 14.0, 4.2 Hz, 2H, Ar-CH ), 2.12
2
2
13
(
(
s, 3H, Ar-CH ), 0.81 (s, 3H, Pd-CH ).
151 MHz, CDCl ) δ 172.80 (N=C), 152.12, 149.17, 143.35,
C NMR
vacuum for 1 h and then cooled to the desired polymeri-
zation temperature. The reactor was charged with the
required amount of CH Cl and NaBArF in a glovebox.
3
3
3
1
1
1
3
42.43, 140.30, 138.70, 137.73, 137.37, 134.99, 131.80,
31.73, 131.61, 130.11, 129.09, 128.09, 127.45, 127.17,
26.82, 126.79, 125.87, 55.77 (CHAr ), 33.37 (Ar-CH ),
2
2
After equilibration at the desired polymerization temper-
ature for 10 min, the required amount of freshly distilled
MA and the required amount of catalyst in 2 ml of
2
2
0.27 (Ar-CH ), 21.93 (Ar-CH ), 0.38 (Pd-CH ). MALDI-
2
3
3

10 of 11
PENG ET AL.
CH Cl were injected rapidly into the mixture via syringe.
[2] S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100,
2
2
1169.
With a rapid stirring, the reactor was pressurized and
maintained at 4 atm of ethylene. After 8 h, the pressure
reactor was vented and the copolymer was dried under
vacuum to a constant weight.
[
[
[
[
[
3] L. Guo, S. Dai, X. Sui, C. Chen, ACS Catal. 2016, 6, 428.
4] L. Guo, C. Chen, Sci. China Chem. 2015, 58, 1663.
5] A. Nakamura, S. Ito, K. Nozaki, Chem. Rev. 2009, 109, 5215.
6] L. Guo, W. Liu, C. Chen, Mater. Chem. Front 2017, 1, 2487.
7] S. Xiong, L. Guo, S. Zhang, Z. Liu, Chin. J. Chem. 2017, 35,
1209.
ASSOCIATED CONTENT
Supplementary Materials
[8] C. Bianchini, G. Giambastiani, L. Luconi, A. Meli, Coord.
Chem. Rev. 2010, 254, 431.
[9] G. Song, L. Guo, Q. Du, W. Kong, W. Li, Z. Liu, J. Organomet.
Chem. 2018, 858, 1.
[
[
10] S. Dai, S. Li, Polymer 2020, 200, 122607.
Full experimental details for the NMR and MS spectra
of compounds, NMR, GPC and DSC curves of polymer
samples. CCDC numbers of complexes Ni3 and Pd3 are
11] T. V. Laine, K. Lappalainen, J. Liimatta, E. Aitola, B. Löfgren,
M. Leskelä, Macromol. Rapid Commun. 1999, 20, 487.
12] T. V. Laine, U. Piironen, K. Lappalainen, M. Klinga, E. Aitola,
M. Leskelä, J. Organomet. Chem. 2000, 606, 112.
[
1
,985,218 and 1,985,217, respectively. These data can be
obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[13] W.-H. Sun, S. Song, B. Li, C. Redshaw, X. Hao, Y.-S. Li, F.
Wang, Dalton Trans. 2012, 41, 11999.
[
[
[
14] X.-L. Chen, J. Gao, H. Liao, H.-Y. Gao, Q. Wu, Chin. J. Polym.
Sci. 2018, 36, 176.
15] L. Guo, S. Li, M. Ji, W. Sun, W. Liu, G. Li, J. Zhang, Z. Liu, S.
Dai, Organometallics 2019, 38, 2800.
16] D. H. Camacho, E. V. Salo, J. W. Ziller, Z. Guan, Angew.
Chem. Int. Ed. 2004, 43, 1821.
ACKNOWLEDGEMENTS
We thank the Natural Science Foundation of Shandong
Province (ZR2018MB023 and ZR2019BB078), the Young
Talents Invitation Program of Shandong Provincial
Colleges and Universities, and the National Natural Sci-
ence Foundation of China (Grants 21671118 and
[17] D. Meinhard, M. Wegner, G. Kipiani, A. Hearley, P. Reuter,
S. Fischer, O. Marti, B. Rieger, J. Am. Chem. Soc. 2007, 129,
9
182.
18] J. L. Rhinehart, L. A. Brown, B. K. Long, J. Am. Chem. Soc.
013, 135, 16316.
19] Y. Liao, Y. Zhang, L. Cui, H. Mu, Z. Jian, Organometallics
019, 38, 2075.
[
[
[
5
1703215).
2
CONFLICT OF INTEREST
The authors declare no competing financial interests.
2
20] D. Zhang, E. T. Nadres, M. Brookhart, O. Daugulis, Organome-
tallics 2013, 32, 5136.
AUTHOR CONTRIBUTIONS
[21] L. Guo, W. Sun, S. Li, G. Xu, S. Dai, Polym. Chem. 2019, 10,
866.
22] S. Dai, S. Li, G. Xu, C. Wu, Y. Liao, L. Guo, Polym. Chem.
020, 11, 1393.
23] L. Guo, Y. Liu, W. Sun, Q. Du, Y. Yang, W. Kong, Z. Liu, D.
Chen, J. Organomet. Chem. 2018, 877, 12.
4
Hongwei
Peng:
Data
curation;
investigation.
[
[
[
Shuaikang Li: Data curation; investigation. Gen Li:
Investigation. Shengyu Dai: Conceptualization; formal
analysis; resources; supervision. Mingjun Ji: Data
curation; formal analysis; project administration. Zhe
Liu: Resources. Lihua Guo: Conceptualization; funding
acquisition; supervision.
2
24] L. Guo, H. Gao, Q. Guan, H. Hu, J. Deng, J. Liu, F. Liu, Q.
Wu, Organometallics 2012, 31, 6054.
[25] L. Zhong, G. Li, G. Liang, H. Gao, Q. Wu, Macromolecules
017, 50, 2675.
2
[
26] S. Zhong, Y. Tan, L. Zhong, J. Gao, H. Liao, L. Jiang, H. Gao,
Q. Wu, Macromolecules 2017, 50, 5661.
27] B. K. Long, J. M. Eagan, M. Mulzer, G. W. Coates, Angew.
Chem. Int. Ed. 2016, 55, 7106.
28] C. Popeney, Z. Guan, Organometallics 2005, 24, 1145.
29] C. S. Popeney, C. M. Levins, Z. Guan, Organometallics 2011,
30, 2432.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are
openly available in the supporting information of this
article.
[
[
[
ORCID
[
[
30] L. Guo, S. Dai, C. Chen, Polymer 2016, 8, 37.
31] L. Guo, K. Lian, W. Kong, S. Xu, G. Jiang, S. Dai, Organome-
tallics 2018, 37, 2442.
Shengyu Dai https://orcid.org/0000-0003-4110-7691
Zhe Liu https://orcid.org/0000-0001-5796-4335
Lihua Guo https://orcid.org/0000-0002-0842-9958
[32] S. Dai, X. Sui, C. Chen, Angew. Chem. Int. Ed. 2015, 54, 9948.
[33] L. Guo, C. Zou, S. Dai, C. Chen, Polymer 2017, 9, 122.
[34] S. Dai, S. Zhou, W. Zhang, C. Chen, Macromolecules 2016, 49,
8855.
REFERENCES
[
1] L. K. Johnson, C. M. Killian, M. Brookhart, J. Am. Chem. Soc.
995, 117, 6414.
1
[35] S. Dai, X. Sui, C. Chen, Chem. Commun. 2016, 52, 9113.

PENG ET AL.
11 of 11
[
[
[
[
[
[
36] Z. Chen, K. E. Allen, P. S. White, O. Daugulis, M. Brookhart,
Organometallics 2016, 35, 1756.
37] C. S. Popeney, D. H. Camacho, Z. Guan, J. Am. Chem. Soc.
[46] L. Guo, W. Liu, K. Li, M. Sun, W. Sun, L. Zhao, G. Jiang, H.
Peng, Z. Liu, S. Dai, Eur. Polym. J. 2019, 115, 185.
[47] S. Ray, P. V. C. Rao, N. V. Choudary, Lubr. Sci. 2012, 24, 23.
[48] E. V. Salo, Z. Guan, Organometallics 2003, 22, 5033.
2
007, 129, 10062.
38] C. S. Popeney, A. L. Rheingold, Z. Guan, Organometallics
009, 28, 4452.
2
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
39] L. Zhong, C. Du, G. Liao, H. Liao, H. Zheng, Q. Wu, H. Gao,
J. Catal. 2019, 375, 113.
40] L. Zhong, H. Zheng, C. Du, W. Du, G. Liao, C. S. Cheung, H.
Gao, J. Catal. 2020, 384, 208.
41] F.-S. Liu, H.-B. Hu, Y. Xu, L.-H. Guo, S.-B. Zai, K.-M. Song,
H.-Y. Gao, L. Zhang, F.-M. Zhu, Q. Wu, Macromolecules 2009,
4
2, 7789.
How to cite this article: Peng H, Li S, Li G, et al.
Rotation-restricted strategy to synthesize high
molecular weight polyethylene using iminopyridyl
nickel and palladium catalyst. Appl Organomet
Chem. 2021;35:e6140. https://doi.org/10.1002/aoc.
[
[
[
42] J. Liu, D. Chen, H. Wu, Z. Xiao, H. Gao, F. Zhu, Q. Wu,
Macromolecules 2014, 47, 3325.
43] C. Du, L. Zhong, J. Gao, S. Zhong, H. Liao, H. Gao, Q. Wu,
Polym. Chem. 2019, 10, 2029.
44] D. P. Gates, S. A. Svejda, E. Oñate, C. M. Killian, L. K.
Johnson, P. S. White, M. Brookhart, Macromolecules 2000, 33,
6140
2
320.
[
45] S. Mecking, L. K. Johnson, L. Wang, M. Brookhart, J. Am.
Chem. Soc. 1998, 120, 888.