Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization

Article abstract of DOI:10.1002/chem.202101521

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (F_n; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (M_w=8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (M_w=20-50 kDa).

Full text of DOI:10.1002/chem.202101521

Accepted Article
Accepted Article
Title: Fluorinated α-Diimine Nickel Mediated Ethylene
(Co)Polymerization
Authors: Xiaoqiang Hu, Yixin Zhang, Baixiang Li, and Zhongbao Jian
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202101521
Link to VoR: https://doi.org/10.1002/chem.202101521
01/2020

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
Fluorinated -Diimine Nickel Mediated Ethylene (Co)Polymerization
Xiaoqiang Hu,[a,b] Yixin Zhang,[a] Baixiang Li,[a] Zhongbao Jian*[a,b]
Abstract: Fluorine substituents in transition metal catalysts are of significantly great importance in olefin polymerization catalysis; however, the
comprehensive effect of fluorine substituents is elusive in seminal late transition metal -diimine catalytic system. In this contribution, fluorine
substituents at various positions (ortho-, meta-, and para-F) and with different numbers (Fn; n = 0, 1, 2, 3, 5) were installed into the well-defined
N-terphenyl amine and thus were studied for the first time in the nickel -diimine promoted ethylene polymerization and copolymerization with
polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity,
polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a
notable result, the ortho-F substituted -diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight
(Mw = 8,703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted -diimine nickel
catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (Mw = 20-50 kDa).
studied in ethylene polymerization (Scheme 1B).[67-74] The effect
of fluorine substituents on thermal stability and activity of catalyst,
and molecular weight and branching density of polymer is
observed. In contrast, study on the influence of fluorine
Introduction
substituents in the classic Brookhart -diimine nickel catalyst is
particularly rare, although it is definitely important to enrich the
The role of fluorine substituents is of great importance in organic
products, homogeneous catalysis, and olefin polymerization
milestone -diimine species.[75] A notable example is that
catalysis as well. An event of β-H elimination that leads to chain
installing ortho-F substituents into a cyclophane-based -diimine
transfer reaction is necessarily suppressed for obtaining high
molecular weight polymers in olefin polymerization.[1-3] For this
purpose, advanced techniques[4] including steric and electronic
regulation of ligands,[5-9] redox strategy,[10-13] secondary
interaction,[14,15] and bimetallic synergistic effect[16-20] have been
extensively utilized in the design of early- and late-transition-metal
catalysts. Notably, fluorine substituents mainly the ortho-F
substitution in olefin polymerization catalysts are also a powerful
tool for inhibiting chain transfer reaction because of the weakly
donating nature.[21] The prominent case is that phenoxy-imine or
enolatoimine titanium catalysts bearing fluorine substituents
feature a living nature for polymerization of ethylene and
propylene (Scheme 1A).[22-27] A C-H···F-C interaction between the
ortho-F substitution with the -H atoms of the growing chain is
proposed to suppress chain transfer process (Scheme 1).
nickel catalyst leads to substantial differences in catalytic
behavior and polymer property in ethylene polymerization.[76]
A
unique M···F interaction between the ortho-F substitution with the
active metal center is elucidated to stabilize the highly reactive
14e− alkyl intermediate (Scheme 1), thereby suppressing the -H
elimination reaction. The result is indicative of the important effect
of fluorine substituents; however, comprehensive study on the
fluorinated effect is inhibited by unavailable catalysts based on
this special cyclophane -diimine framework, and thus is elusive
thus far.
Strikingly, late-transition nickel catalysts more easily suffer from
a more pronounced -H elimination reaction, resulting in chain
transfer and also the seminal chain walking in ethylene
polymerization.[28-66] Fluorine substituents in these catalysts is
also effective in tuning elementary reaction pathways, likewise.
Phenoxy-imine nickel catalysts bearing fluorine (F) substituents
or fluorocarbon (CnF2n+1) substituents have been thoroughly
[a]
X. Q. Hu, Dr. Y. X. Zhang, B. X. Li, Prof. Dr. Z. B. Jian
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences
Scheme 1. Proposed roles of fluorine substituents in catalytic olefin
polymerization (Top) and the related catalysts applied (Bottom).
Renmin Street 5625,Changchun 130022, China
E-mail: zbjian@ciac.ac.cn
X. Q. Hu, Prof. Dr. Z. B. Jian
University of Science and Technology of China
Hefei 230026, China.
We are interested in terphenyl-based -diimine nickel catalysts
for olefin (co)polymerizations.[65] In this contribution, we now show
that, using a feasible N-terphenyl framework, fluorine substituents
at various positions and with different numbers are installed into
-diimine nickel catalysts for ethylene polymerization and
copolymerization with polar monomers (Scheme 1C). This for the
first time enables an investigation on the effect of ortho-, meta-,
and para-F substituents in the -diimine system with regard to
[b]
Supporting information for this article is given via a link at the end of
the document. General procedures, and characterization and
analysis data (NMR, GPC, DSC, and IR) for anilines, ligands,
complexes (CCDC Nos.: 2017269 (Ni-1F), 2017273 (Ni-2F), and
2017274 (Ni-5F); These data are provided free of charge by
Cambridge Crystallographic Data Centre), polyethylenes, and
copolymers (108 pages).
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
catalytic activity, polymer molecular weight and branching density, without ortho-fluorine atoms could be easily synthesized through
and incorporation of polar monomer.
the classic Suzuki coupling reaction of 2,6-dibromo-4-
methylaniline with the corresponding arylboronic acids. However,
for N-terphenylamines (NH2-3F' and NH2-5F) containing ortho-
fluorine atoms, it is essential to first borylation of 2,6-dibromo-4-
methylaniline and then Suzuki coupling with the corresponding
aryl bromide compounds. Subsequently, a series of fluorinated -
diimine ligands could be prepared in excellent yields by p-
toluenesulfonic acid catalyzed condensation reaction of
acenaphthoquinone with 2.05 equiv. of the N-terphenylamine in
toluene for several days at 120 oC. All of these -diimine ligands
were characterized by elemental analysis and 1H/13C NMR
spectroscopy (for details, see Supporting Information).
Results and Discussion
Nickel catalysts design. To access the fluorinated -diimine
ligands and the corresponding -diimine nickel catalysts, two
completely different methods were utilized to synthesize a series
of fluorine-containing anilines, due to the low nucleophilicity of the
aryl groups that contain ortho-fluorine atoms (Scheme 2).[77] Rigid
N-terphenylamines (NH2-0F, NH2-1F, NH2-2F, and NH2-3F)
Scheme 2. Synthetic routes of the fluorinated -diimine ligands and the related Ni(II) catalysts.
Figure 1. Molecular structures of the cation part of Ni-1F, Ni-2F and Ni-5F drawn with 30% probability ellipsoids. Hydrogen atoms and borate anion are omitted for
clarity. Ni-1F: selected bond lengths (Å): Ni1-O1 1.812(2), Ni1-O2 1.817(2), Ni1-N1 1.915(2), Ni1-N2 1.921(2); selected bond angles (°): O2-Ni1-N1 175.97(8), O2-
Ni1-N2 91.23(8), O1-Ni1-O2 96.16(7), O1-Ni1-N1 87.87(8), O1-Ni1-N2 172.28(8), N1-Ni1-N2 84.76(8). Ni-2F: selected bond lengths (Å): Ni1-O1 1.812(4), Ni1-O2
1.797(5), Ni1-N1 1.896(5), Ni1-N2 1.883(5); selected bond angles (°): O2-Ni1-O1 95.4(2), O2-Ni1-N2 89.2(2), O1-Ni1-N2 175.3(2), O2-Ni1-N1 175.1(2), O1-Ni1-N1
89.3(2), N2-Ni1-N1 86.1(2). Ni-5F: selected bond lengths (Å): Ni1-O1 1.809(2), Ni1-O2 1.807(2), Ni1-N1 1.915(2), Ni1-N2 1.925(2); selected bond angles (°): O2-
Ni1-O1 96.64(9), O2-Ni1-N2 89.53(9), O2-Ni1-N1 173.13(9), O1-Ni1-N2 173.33(10), O1-Ni1-N1 89.40(9), N1-Ni1-N2 84.59(9).
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
The corresponding -diimine nickel complexes Ni-0F, Ni-1F,
Ni-2F, Ni-3F, Ni-3F', and Ni-5F could be synthesized by a typical
reaction of -diimine ligand with 1 equiv. of Ni(acac)2 and 1 equiv.
of [Ph3C][B(C6F5)4]. The pure nickel precatalysts could be
separated from the mixture by simply washing with diethyl ether
and n-hexane, which were fully identified by elemental analysis
and 1H/13C/19F NMR spectroscopy (for details, see SI). Note that
the usual dibromo nickel complexes were unavailable when
reacting ligands L2~L5 with NiBr2(DME). In particular, single
crystals of Ni-1F, Ni-2F, and Ni-5F that are suitable for X-ray
of Supporting Information), all six -diimine Ni(II) catalysts Ni-
0F~Ni-5F showed high activities (106~107 g mol-1 h-1) in ethylene
polymerization (Table 1). Overall, catalytic activities dropped
o
o
rationally with the increase of temperature from 30 C to 90 C;
however, at the harsh temperature of 120 oC, catalytic activity still
maintained on a high level of 3.3  106 g mol-1 h-1 (Table 1, entry
19). Furthermore, as anticipated, the molecular weight of the
generated polyethylenes decreased with elevating temperature,
which is attributed to a faster chain transfer rate with increasing
temperature. In addition, branching densities of these
polyethylenes obtained could be varied in a wide range
(1.2~80.2/1000C). The results revealed that branching density is
related to not only the structure of catalysts but also the
polymerization temperature. The elevated temperature resulted in
increasing of branching density obviously, indicating that
diffraction analysis were obtained by
a solvent diffusion
(dichloromethane/n-hexane) method and their molecular
structures were verified in Figure 1. The acac-based Ni(II) centers
in Ni-1F, Ni-2F, and Ni-5F sited in a square planar coordination
sphere defined by N1, N2, O1, and O2, which is in contrast to the
typical tetrahedral geometry of dibromo Ni(II) complexes. In Ni-5F, branching density can be tuned by varying temperature. Also, the
the closest distance between the ortho-F atom and the Ni(II)
center was 3.238 Å, which is shorter than the sum of the van der
Waals radii of the Ni and F atoms (3.31 Å). This potential
intramolecular interaction (Ni···F interaction) might compete with
ethylene coordination and -H elimination, thus affecting catalytic
properties. Note that there is no correlation between the number
of fluorine atoms on the ligand and the Ni-N bond lengths.
Effect of fluorine substituents on ethylene polymerization. In
situ activated with 500 equiv. of AlEt2Cl (screening of alkyl
aluminum reagents including MAO, MMAO, AlEt2Cl, TiBA, TMA,
and EASC in ethylene polymerization could be found in Table S1
polymer melting point fell dramatically with the increase of
branching density.
The effect of fluorine substituents at different positions with
various numbers in -diimine Ni(II) catalysts was studied in detail
in ethylene polymerization (Figure 2). In comparison with the non-
fluorinated catalyst Ni-0F, the catalyst Ni-1F containing four para-
F atoms produced polyethylenes with slightly higher activities.
Branching densities were higher, but polymer molecular weights
(Mw) dropped (Table 1, entries 1-3 vs. 4-6). In terms of the catalyst
Ni-2F that contains eight meta-F atoms, the polymerization
reaction not only exhibited slightly lower activities but also lower
Table 1. Ethylene polymerization with fluorinated nickel catalysts.[a]
[c]
Entry
1
Cat.
T (oC)
30
60
90
30
60
90
30
60
90
30
60
90
0
t (min)
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
20
40
10
10
20
30
60
120
30
60
10
10
10
Yield (g)
5.74
4.61
3.05
6.01
5.58
3.17
5.32
4.01
2.55
5.20
1.82
1.66
1.76
1.30
0.92
1.58
3.04
0.81
0.55
3.61
5.15
10.12
24.45
7.33
14.87
0.56
0.54
0.30
Act. (107)[b]
3.44
2.77
1.83
3.61
3.35
1.90
3.19
2.41
1.53
3.12
1.09
1.00
1.06
0.78
0.55
0.47
0.46
0.49
0.33
1.08
1.03
1.01
1.22
1.47
1.49
0.34
0.32
0.18
Mw (104)[c]
15.0
5.5
Mw/Mn
2.57
2.11
1.84
2.14
1.82
1.95
2.00
1.95
1.85
1.87
1.88
1.95
1.49
1.40
1.44
1.32
1.39
1.46
1.61
1.58
1.46
1.63
brs[d]
26.7
36.5
45.0
44.3
58.7
63.4
68.2
76.1
80.2
66.6
76.5
80.1
2.6
Tm[e] (oC)
112.3
95.1
Ni-0F
Ni-0F
Ni-0F
Ni-1F
Ni-1F
Ni-1F
Ni-2F
Ni-2F
Ni-2F
Ni-3F
Ni-3F
Ni-3F
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-3F'
Ni-5F
Ni-5F
Ni-5F
2
3
3.2
72.0
4
3.7
97.6
5
2.7
71.4
6
2.0
53.9
7
4.7
62.8
8
3.5
37.8
9
2.5
-
10
11
12
13
14
15
16
17
18
19
20
21
22[f]
23[f]
24[g]
25[g]
26
27
28
5.0
68.7
4.0
42.6
2.8
-
254.2
66.4
48.3
121.9
172.9
34.4
26.9
446.9
620.7
821.6
130.1
120.1
114.0
112.3
111.0
105.3
99.3
30
60
60
60
90
120
0
6.3
10.7
12.0
11.7
14.7
17.1
2.8
128.2
126.4
125.4
124.5
132.1
131.5
115.5
111.0
102.6
0
4.0
0
4.2
[h]
[h]
0
-
-
5.2
0
732.2
870.3
28.0
1.31
1.41
1.45
1.47
1.82
1.2
0
1.4
30
60
90
10.8
12.8
17.0
27.0
16.3
[a] Reaction conditions: Ni catalyst (1 μmol), AlEt2Cl (500 equiv.), toluene/CH2Cl2 (98 mL/2 mL), polymerization pressure (8 bar), all entries are based on at least
two runs, unless noted otherwise. [b] Activity is in unit of g mol-1 h-1. [c] Determined by gel permeation chromatography (GPC) in 1,2,4-trichlorobenzene at 150 °C
or 160 °C if necessary. [d] brs = Number of branches per 1000C, as determined by 1H NMR spectroscopy. [e]Determined by DSC (second heating). [f] toluene/CH2Cl2
(148 mL/2 mL). [g] polymerization pressure (20 bar). [h] The molecular weight is beyond the GPC detector limit (1000  104 g mol-1).
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
molecular weights compared to Ni-0F, although branching
densities further raised to 80.2/1000 C. When installing four para-
F atoms and eight meta-F atoms into Ni-0F, the catalyst Ni-3F
likewise featured lower activities and lower molecular weights but
higher branching densities. These results indicated that the para-
F substituents and/or the meta-F substituents in -diimine Ni(II)
catalysts were slightly unfavorable for ethylene polymerization in
terms of polymer molecular weights and sometimes catalytic
activities; however, both could enhance branching densities of
polyethylenes. We speculate that the remote electron-
withdrawing fluorine substituents namely the meta-F substitution
will reduce electron density of the -diimine ligands, which feature
a reduced coordination/stabilization towards the cationic nickel
center to accelerate a deactivation, thus declining activity; even
though on the other hand more electron-withdrawing ligands
increase activity because ethylene insertion barriers are lower.[78]
Notably, both the para- and/or meta-F substituents in -diimine
Ni(II) catalysts fail to effectively suppress the -H elimination
reaction. This should be ascribed to the absence of a C-H···F-C
interaction or a Ni···F interaction (see Scheme 1).
coordination/insertion, polymer molecular weight is determined by
the rate of ethylene coordination/insertion relative to the rate of
chain transfer, and branching density is dependent on the rate of
chain
walking
relative
to
the
rate
of
ethylene
coordination/insertion. Based on the Guan’s conclusion,[76]
a
proposed Ni···F interaction between the ortho-F substitution with
the active nickel center (Scheme 1) retards the ethylene
coordination/insertion, leading to the decreased activity.
Decrease on activity using Ni-3F' probably rules out the C-H···F-
C interaction that will not affect ethylene coordination. Notably,
this Ni···F interaction is more pronounced to suppress the -H
elimination pathway induced by a Ni···H interaction, thus
inhibiting not only chain transfer but also chain walking. As a result,
polymer molecular weight increases and branching density
decreases.
The pentafluorophenyl substituted catalysts such as phenoxy-
imine titanium or nickel catalyst featured the best property in
ethylene polymerization in terms of molecular weight,[23,69] thereby
the meta-F atoms were further introduced into Ni-3F' and the per-
fluorinated -diimine Ni(II) catalyst Ni-5F was investigated. To our
surprise, compared with Ni-3F' without meta-F atoms, catalytic
activity and polyethylene molecular weight obviously declined
using Ni-5F at all polymerization temperatures, and branching
density increased slightly (Table 1, entries 14, 15 and 18 vs. 26-
28). Decline on polymer molecular weight and catalytic activity
should be attributed to the presence of the remote meta-F
substituent in Ni-5F (relative to Ni-3F'), which leads to a reduced
coordination/stabilization towards the cationic nickel center. Both
decrease on activity and molecular weight and increase on
branching density using Ni-5F agree with the trend using Ni-2F.
Since Ni-3F' produced remarkably higher molecular weights,
more details were further studied. Ni-3F' showed an excellent
time-dependence at 0 oC (Table 1, entries 13 and 20-23). As
depicted in Figure 3a, the yield linearly increased with prolonging
polymerization time from 10 to 120 minutes, which means that
catalytic activity can be maintained within two hours or even a
longer reaction time. Most importantly, the polymer molecular
weight (Mw) also increased significantly to reach an amazing
value of 8,216 kDa with the prolonged reaction time (Figure 3b).
Notably, the polymer yield of 24.45 g corresponded to a very high
turnover number (TON = 8.7  105), namely 14.2 kg polymer can
be produced from 1 g of nickel catalyst or 414.4 kg polymer can
be produced from 1 g of nickel. This polymer molecular weight
was also beyond the detector limit (10,000 kDa) of the GPC
instrument using in this work (Table 1, entry 23). Likewise, at
higher temperature of 60 oC (Table 1, entries 15-17) the yield and
the polymer molecular weight also rationally increased from 10
min, 20 min to 40 min (Figure 3c and 3d). Combined with the data
at 120 oC (Table 1, entry 19), Ni-3F' could be acted as a thermally
robust catalyst.
Figure 2. Plots of molecular weight, activity, branching density, and melting
point of polyethylenes generated versus polymerization temperature with the
fluorine-substituted Ni(II) catalysts Ni-0F~Ni-5F (polymerization time: 10min).
Subsequently, eight ortho-F atoms and four para-F atoms were
introduced into the catalyst Ni-0F, and thus comprehensive
studies of Ni-3F' were conducted to have a more insight into the
role of ortho-F atoms in ethylene polymerization (Figure 2). Under
otherwise identical conditions, compared with these catalysts Ni-
0F~Ni-3F without ortho-F substituents, Ni-3F' produced
polyethylenes with much higher molecular weights (up to 664 kDa
at 30 oC) and far lower branching densities (6.3/1000 C at 30 oC).
The polymerization results resemble those previously reported in
ortho-F substituted nickel catalysts.[69,76] However, catalytic
activities of Ni-3F' were significantly lower than those of Ni-0F~Ni-
3F, which are similar with that by the ortho-F substituted
cyclophane -diimine Ni(II) catalyst,[76] but are opposite to that by
the ortho-F substituted phenoxy-imine nickel catalyst.[69] As we
know, catalytic activity depends on the rate of ethylene
Increasing ethylene pressure from 8 bar to 20 bar resulted in
the increase of catalytic activities and molecular weights (Table 1,
entries 21 vs. 24, 22 vs. 25). The obtained polyethylene molecular
weight of 8,703 kDa was extremely high, which is much higher
than the value of around 5,000 kDa produced by other nickel
catalysts.[8,21,48,73,78,79] Even for the classic early transition metal
catalysts it is not so easy.[80] As expected, branching densities
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
dropped at elevated ethylene pressure due to the reduced rate of
chain isomerization relative to the rate of trapping of monomer.
The branching distribution based on the 13C NMR analysis for the
sample from Table 1, entry 24 could be referred in supporting
information.
copolymerization of ethylene and polar monomers. As the most
popular polar monomers applied in -diimine Ni(II) catalyzed
olefin copolymerization,[52,56,57,62,63,65,81-85] the long-chain polar
monomers including methyl 10-undecenoate (UCOOMe), 10-
undecen-1-ol (UOH), 10-undecenoic acid (UCOOH), and the
common monomer vinyltriethoxysilane (VTEoS) were studied in
ethylene copolymerizations using the fluorinated Ni(II) catalysts.
Under the activation of AlEt2Cl, Ni-3F without ortho-F substituents
produced the copolymer with the highest incorporation of
comonomer but the lowest activity (Table 2, entry 4). Ni-3F' and
Ni-5F containing ortho-F substituents generated notably higher
molecular weight (Mw up to 493 kDa) copolymers at the expense
of incorporations (Table 2, entries 5 and 6). These results
indicated that the presence of ortho-F substituent was
unfavorable for the incorporation in copolymerization. Notably,
copolymerization activity, molecular weight, and comonomer
incorporation decreased consistently at elevated temperature of
60 oC (Table 2, entries 1 vs. 7). As anticipated, the incorporation
further increased under the higher comonomer concentration at
the expense of catalytic activity. It should be noted that activities
of these copolymerization reactions were high relative to those
using the other -diimine nickel catalysts. Notably, Ni-0F was also
capable of promoting copolymerization of other more challenging
long-chain polar monomers. Under otherwise identical conditions,
the copolymerization reactions revealed the following trends in
activity: UCOOH > UOH > UCOOMe, comonomer incorporation:
UCOOH > UCOOMe > UOH (Table 2, entries 8, 10, and 11). This
result revealed that the acid functionalized UCOOH even
behaved better than the ester functionalized UCOOMe.[86]
Besides, vinyltriethoxysilane (VTEoS) was further employed in
the copolymerization reaction, which gave the lowest
incorporation and molecular weight compared to long-chain polar
monomers, although it displayed very high activity of up to 1.47 
106 g mol-1 h-1 (Table 2, entry 12).
Figure 3. (a, Top/left) Time-dependence curves, (b, Bottom/left) Polyethylene
Mw as
a function of time in Ni-3F' catalyzed ethylene polymerization,
polymerization temperature: 0 oC; (c, Top/right) Time-dependence curves, (d,
Bottom/right) Polyethylene Mw as a function of time in Ni-3F' catalyzed ethylene
polymerization, polymerization temperature: 60 oC.
Mechanical properties of the obtained polyethylenes.
Generally, both polymer branching density and molecular weight
are two key factors that determine mechanical properties of
polymers. Therefore, a series of tensile tests of polyethylenes
were carried out with different branching densities to examine
themechanical properties (Figure 4). The results demonstrated
that these polymer samples exhibited various strain values at
break over a wide range (182%~1895%), which raised greatly
with increasing branching density. Moreover, the stress values at
break also displayed a wide range from 3.8 MPa to 18.3 MPa, but
there was no obvious correlation between the polymer branching
density and the stress value at break. Overall, the microscopic
topological structure of polyethylene related to polymer physical
properties can be modulated by external reaction conditions and
catalyst structures.
To corroborate these copolymer microstructures, 1H NMR
spectra and representative 13C NMR spectra, plus IR spectra
were determined and analyzed as shown in Figure 5 and
Supporting Information. Although the incorporation of polar
monomer was relatively low, it is enough to alter the surface
property of polyethylene. Incorporating 0.58 mol% of UCOOMe,
0.42 mol% of UOH, and 0.70 mol% of UCOOH into pure
polyethylene decreased the water contact angles of 17.4°, 14.8°,
and 20.3°, respectively (Figure 6).
Figure 4. Stress−strain curves of polyethylenes with different branching
densities.
Effect of fluorine substituents on the copolymerization of
ethylene and polar monomers. In sharp contrast to studies of
fluorine effect on ethylene polymerization, there is much less
attention on the influence of fluorine effect on the
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
Conclusions
In summary, to probe the effect of fluorine substituents in olefin
polymerization catalysis, a new series of distinct fluorinated -
diimine nickel catalysts has been prepared and utilized in ethylene
polymerization and copolymerization with polar monomers. In
ethylene polymerization, rational conclusions can be drawn: 1)
the ortho-F substituent is the most important, which extremely
effectively suppresses the -H elimination pathway and thus
notably enhances polymer molecular weight and obviously
reduces branching density of polymer; however, catalytic activity
decreases probably because the proposed Ni···F interaction
competes with the coordination of ethylene; 2) the meta-F
substituent is slightly unfavorable in terms of polymer molecular
weight and catalytic activity; however, branching density raises
clearly. These results are entirely contrast to that in meta-
fluorinated phenoxy-imine nickel system; 3) the para-F
substituent mostly increases branching degree; 4) compared to
the ortho-F substituent, the pentafluoro substituent not only
reduces catalytic activity but also declines polymer molecular
weight. This again verifies the negative role of the meta-F
substituent. However, the pentafluoro substituent offers the
highest polymer molecular weight in the phenoxy-imine nickel
system. Moreover, in the copolymerization of ethylene with polar
monomer, the ortho-F substituent is definitely unfavorable for the
key incorporation of comonomer, and both the meta-F substituent
and the para-F substituent show a slight influence in terms of
incorporation. These findings indicate a unique fluorine effect in
the most studied -diimine catalysts. These insights endow a
broader perspective on the fluorine effect in olefin polymerization
catalysis.
Figure 5. 13C NMR spectrum of the ethylene/UCOOMe copolymer (Table 2,
entry 9).
Figure 6. Water contact angles (WCA) of copolymers (Table 2, entries 9-11).
Table 2. Copolymerization of ethylene and polar monomers with fluorinated nickel catalysts.[a]
[d]
Entry
1
Cat.
Comon.
CUA (mol L-1)
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.1
Yield (g)
4.49
4.97
2.83
0.74
4.60
2.92
4.16
3.76
1.28
4.42
6.35
7.35
Act. (105)[b]
X (mol %)[c]
Mw (104)[d]
7.1
Mw/Mn
2.03
1.88
1.79
1.74
1.19
1.28
1.89
1.93
1.77
2.11
1.96
2.02
brs[c]
40.0
46.9
64.1
58.9
12.4
14.1
47.9
43.4
29.1
47.4
47.8
51.7
Tm[e] (oC)
101.6
78.8
Ni-0F
Ni-1F
Ni-2F
Ni-3F
Ni-3F'
Ni-5F
Ni-0F
Ni-0F
Ni-0F
Ni-0F
Ni-0F
Ni-0F
UCOOMe
UCOOMe
UCOOMe
UCOOMe
UCOOMe
UCOOMe
UCOOMe
UCOOMe
UCOOMe
8.98
0.31
2
9.94
0.25
5.0
3
5.66
0.27
7.0
53.6
4
1.48
0.35
8.1
64.4
5
9.20
0.02
49.3
33.4
4.4
112.4
111.7
66.2
6
5.84
0.17
7[f]
8[f]
9[f]
10[f]
11[f]
12[f]
8.32
0.26
7.52
0.45
4.6
72.6
0.2
2.56
0.58
5.7
94.1
UOH
0.1
8.84
0.42
3.8
77.1
UCOOH
VTEoS
0.1
12.7
0.70
3.4
55.8
0.1
14.7
0.10
2.9
55.7
[a] Reaction conditions: Ni catalyst (5 μmol), AlEt2Cl (1000 equiv.), toluene/CH2Cl2 (23 mL/2 mL), polymerization time (30 min), polymerization temperature (30 oC),
polymerization pressure (4 bar), all entries are based on at least two runs, unless noted otherwise. [b] Activity is in unit of g mol-1 h-1. [c] X = Incorporation of polar
monomer, brs = Number of branches per 1000C, as determined by 1H NMR spectroscopy. [d] Determined by gel permeation chromatography (GPC) in
trichlorobenzene at 150 °C. [e] Determined by DSC (second heating). [f] Polymerization temperature (60 oC).
22001244 for Y. Zhang) and the Jilin Provincial Science and
Technology Department Program (No. 20200801009GH).
Acknowledgements
Keywords: fluorine effect • late transition metal catalysts •
homogeneous catalysis • olefin polymerization • UHMWPE
We are thankful for financial support from the National Natural
Science Foundation of China (Nos. 21871250 for Z. Jian,
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
[1] A. Nakamura, S. Ito, K. Nozaki, Chem. Rev. 2009, 109, 5215-5244.
[2] M. Stürzel, S. Mihan, R. Mülhaupt, Chem. Rev. 2016, 116, 1398-1433.
[3] M. C. Baier, M. A. Zuideveld, S. Mecking, Angew. Chem. Int. Ed. 2014,
53, 9722-9744; Angew. Chem. 2014, 126, 9878-9902.
[4] T. V. Tran, L. H. Do, Eur. Polym. J. 2020, 142, 110100.
[5] H. L. Mu, L. Pan, D. P. Song, Y. S. Li, Chem. Rev. 2015, 115, 12091-
12137.
[43] J. L. Rhinehart, L. A. Brown, B. K. Long, J. Am. Chem. Soc. 2013, 135,
16316-16319.
[44] D. Takeuchi, Y. Chiba, S. Takano, K. Osakada, Angew. Chem. Int. Ed.
2013, 52, 12536-12540; Angew. Chem. 2013, 125, 12768-12772.
[45] W. -J. Tao, R. Nakano, S. Ito, K. Nozaki, Angew. Chem. Int. Ed. 2016,
55, 2835-2839; Angew. Chem. 2016, 128, 2885-2889.
[46] Y. Konishi, W. -J. Ta, H. Yasuda, S. Ito, Y. Oishi, H. Ohtaki, A. Tanna,
T. Tayano, K. Nozaki, ACS Macro. Lett. 2018, 7, 213-217.
[47] B. S. Xin, N. Sato, A. Tanna, Y. Oishi, Y. Konishi, F. Shimizu, J. Am.
Chem. Soc. 2017, 139, 3611-3614.
[48] Q. H. Tran, M. Brookhart, O. Daugulis, J. Am. Chem. Soc. 2020, 142,
7198-7206.
[49] Y. P. Zhang, H. L. Mu, L. Pan, X. L. Wang, Y. S. Li, ACS Catal. 2018,
8, 5963-5976.
[50] X. Fu, L. J. Zhang, R. Tanaka, T. Shiono, Z. G. Cai, Macromolecules
2017, 50, 9216-9221.
[51] L. H. Guo, K. B. Lian, W. Y. Kong, S. Xu, G. R. Jiang, S. Y. Dai,
Organometallics 2018, 37, 2442-2449.
[52] L. Zhong, G. L. Li, G. D. Liang, H. Y. Gao, Q. Wu, Macromolecules
2017, 50, 2675-2682.
[53] H. L. Cheng, H. J. Wang, Y. Q. Lia, Y. M. Hu, X. Q. Zhang, Z. G. Cai,
J. Catal. 2018, 368, 291-297.
[54] J. X. Gao, B. P. Yang, C. L. Chen, J. Catal. 2019, 369, 233-238.
[55] L. Zhong, C. Du, G. F. Liao, H. Liao, H. D. Zheng, Q. Wu, H. Y. Gao,
J. Catal. 2019, 375, 113-123.
[6] C. Tan, C. L. Chen, Angew. Chem. Int. Ed. 2019, 58, 7192-7200;
Angew. Chem. 2019, 131, 7268-7276.
[7] S. Mecking, M. Schnitte, Acc. Chem. Res. 2020, 53, 2738–2752.
[8] C. Q. Wang, X. H. Kang, S. Y. Dai, F. C. Cui, Y. Q. Li, H. L. Mu, S.
Mecking, Z. B. Jian, Angew. Chem. Int. Ed. 2021, 60, 4018–4022; Angew.
Chem. 2021, 133, 4064-4068.
[9] Y. X. Zhang, C. Q. Wang, S. Mecking, Z. B. Jian, Angew. Chem. Int.
Ed. 2020, 59, 14296–14302; Angew. Chem. 2020, 132, 14402-14408.
[10] M. Chen, B. P. Yang, C. L. Chen, Angew. Chem. Int. Ed. 2015, 54,
15520-15524; Angew. Chem. 2015, 127, 15740-15744.
[11] M. H. Zhao, C. L. Chen, ACS Catal. 2017, 7, 7490-7494.
[12] W. C. Anderson Jr., B. K. Long, ACS Macro. Lett. 2016, 5, 1029-1033.
[13] W. C. Anderson Jr., J. L. Rhinehart, A. G. Tennyson, B. K. Long, J.
Am. Chem. Soc. 2016, 138, 774-777.
[14] M. Li, X. B. Wang, Y. Luo, C. L. Chen, Angew. Chem. Int. Ed. 2017,
56, 11604-11609; Angew. Chem. 2017, 129, 11762 –11767.
[15] D. Zhang, C. L. Chen, Angew. Chem. Int. Ed. 2017, 56, 14672-14676;
Angew. Chem. 2017, 129, 14864-14868.
[16] M. Delferro, T. J. Marks, Chem. Rev. 2011, 111, 2450-2485.
[17] H. Y. Suo, G. A. Solan, Y. P. Ma, W. -H. Sun, Coord. Chem. Rev.
2018, 372, 101-116.
[18] Z. T. Chen, X. X. Zhao, X. Y. Gong, D. Xu, Y. G. Ma, Macromolecules
2017, 50, 6561-6568.
[56] L. Zhong, H. D. Zheng, C. Du, W. B. Du, G. F. Liao, C. S. Cheung, H.
Y. Gao, J. Catal. 2020, 384, 208-217.
[57] J. Xia, Y. X. Zhang, S. Q. Kou, Z. B. Jian, J. Catal. 2020, 390, 30-36.
[58] J. Xia, Y. X. Zhang, J. F. Zhang, Z. B. Jian, Organometallics 2019, 38,
1118-1126.
[19] X. X. Zhao, Z. T. Chen, H. Li, Y. G. Ma, Macromolecules 2020, 53,
3806-3813.
[59] Y. D. Liao, Y. X. Zhang, L. Cui, H. L. Mu, Z. B. Jian, Organometallics
2019, 38, 2075-2083.
[20] D. Takeuchi, Y. Chiba, S. Takano, K. Osakada, Angew. Chem. Int. Ed.
2013, 52, 12536-12540; Angew. Chem. 2013, 125, 12768-12772.
[21] H. Makio, H. Terao, A. Iwashita, T. Fujita, Chem. Rev. 2011, 111,
2363-2449.
[60] J. Xia, Y. X. Zhang, X. Q. Hu, X. Ma, L. Cui, J. F. Zhang, Z. B. Jian,
Polym. Chem. 2019, 10, 546-554.
[61] H. L. Mu, G. L. Zhou, X. Q. Hu, Z. B. Jian, Coord. Chem. Rev. 2021,
435, 213802.
[22] J. Tian, P. D. Hustad, G. W. Coates, J. Am. Chem. Soc. 2001, 123,
[62] X. Q. Hu, Y. X. Zhang, Y. X. Zhang, Z. B. Jian, ChemCatChem. 2020,
5134-5135.
12, 2497-2505.
[23] M. Mitani, J. Mohri, Y. Yoshida, J. Saito, S. Ishii, K. Tsuru, S. Matsui,
R. Furuyama, T. Nakano, H. Tanaka, S. Kojoh, T. Matsugi, N. Kashiwa, T.
Fujita, J. Am. Chem. Soc. 2002, 124, 3327-3336.
[63] X. Q. Hu, C. Q. Wang, Z. B. Jian, Polym. Chem. 2020, 11, 4005-4012.
[64] X. Ma, Y. X. Zhang, Z. B. Jian, Polym. Chem. 2021, 12, 1236-1243.
[65] X. Q. Hu, X. H. Kang, Y. X. Zhang, Z. B. Jian, CCS Chem. 2021, DOI:
10.31635/ccschem.021.202100895.
[24] P. D. Hustad, J. Tian, G. W. Coates, J. Am. Chem. Soc. 2002, 124,
3614-3621.
[66] L. Cui, X. Q. Hu, Y. X. Zhang, Z. B. Jian, Acta Polym. Sin. 2021, 52,
[25] M. Mitani, T. Nakano, T. Fujita, Chem. Eur. J. 2003, 9, 2396-2403.
[26] R. Furuyama, M. Mitani, J. Mohri, R. Mori, H. Tanaka, T. Fujita,
Macromolecules 2005, 38, 1546-1552.
531-540.
[67] I. Göttker-Schnetmann, P. Wehrmann, C. Röhr, S. Mecking,
Organometallics 2007, 26, 2348-2362.
[27] S. -M. Yu, S. Mecking, J. Am. Chem. Soc. 2008, 130, 13204-13205.
[28] S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100, 1169-
1203.
[68] M. P. Weberski Jr., C. L. Chen, M. Delferro, C. Zuccaccia, A.
Macchioni, T. J. Marks, Organometallics 2012, 31, 3773-3789.
[69] J. C. Wang, E. D. Yao, Z. T. Chen, Y. G. Ma, Macromolecules 2015,
48, 5504-5510.
[29] Z. Wang, Q. B. Liu, G. A. Solan, W. -H. Sun, Coord. Chem. Rev. 2017,
350, 68-83.
[70] Z. Chen, M. Mesgar, P. S. White, O. Daugulis, M. Brookhart, ACS
Catal. 2015, 5, 631-636.
[71] P. Kenyon, S. Mecking, J. Am. Chem. Soc. 2017, 139, 13786-13790.
[72] P. Kenyon, M. Wörner, S. Mecking, J. Am. Chem. Soc. 2018, 140,
6685-6689.
[73] M. Schnitte, A. Staiger, L. A. Casper, S. Mecking, Nat. Commun. 2019,
10, 2592.
[30] A. Keyes, H. E. B. Alhan, E. Ordonez, U. Ha, D. B. Beezer, H. Dau,
Y.-S. Liu, E. Tsogtgerel, G. R. Jones, E. Harth, Angew. Chem. Int. Ed.
2019, 58, 12370-12391; Angew. Chem. 2019, 131, 12498-12520.
[31] Z. Chen, M. Brookhart, Acc. Chem. Res. 2018, 51, 1831-1839.
[32] L. K. Johnson, C. M. Killian, M. Brookhart, J. Am. Chem. Soc. 1995,
117, 6414-6415.
[33] T. R. Younkin, E. F. Connor, J. I. Henderson, S. K. Friedrich, R. H.
Grubbs, D. A. Bansleben, Science 2000, 287, 460-462.
[34] S. A. Svejda, L. K. Johnson, M. Brookhart, J. Am. Chem. Soc. 1999,
121, 10634-10635.
[35] M. D. Leatherman, S. A. Svejda, L. K. Johnson, M. Brookhart, J. Am.
Chem. Soc. 2003, 125, 3068-3081.
[74] M. Schnitte, J. S. Scholliers, K. Riedmiller, S. Mecking, Angew. Chem.
Int. Ed. 2020, 59, 3258-3263; Angew. Chem. 2020, 132, 3284-3289.
[75] D. Meinhard, M. Wegner, G. Kipiani, A. Hearley, P. Reuter, S. Fischer,
O. Marti, B. Rieger, J. Am. Chem. Soc. 2007, 129, 9182-9191.
[76] C. S. Popeney, A. L. Rheingold, Z. B. Guan, Organometallics 2009,
28, 4452-4463.
[36] D. P. Gates, S. A. Svejda, E. Oñate, C. M. Killian, L. K. Johnson, P. S.
White, M. Brookhart, Macromolecules 2000, 33, 2320-2334.
[37] D. H. Camacho, E. V. Salo, J. W. Ziller, Z. B. Guan, Angew. Chem.
Int. Ed. 2004, 43, 1821-1825; Angew. Chem. 2004, 116, 1857-1861.
[38] D. F, Zhang, E. T. Nadres, M. Brookhart, O. Daugulis, Organometallics
2013, 32, 5136-5143.
[77] T. Korenaga, T. Kosaki, R. Fukumura, T. Ema, T. Sakai, Org. Lett.
2005, 7, 4915-4917.
[78] Q. Muhammad, C. Tan, C. L. Chen, Sci. Bull. 2020, 65, 300-307.
[79] M. Schmid, R. Eberhardt, M. Klinga, M. Leskelä, B. Rieger,
Organometallics 2001, 20, 2321-2330.
[80] K. Patel, S. H. Chikkali, S. Sivaram, Prog. Polym. Sci. 2020, 109,
[39] T. Liang, S. B. Goudari, C. L. Chen, Nat. Commun. 2020, 11, 372.
[40] A. L. Kocen, M. Brookhart, O. Daugulis, Nat. Commun. 2019, 10, 438.
[41] L. H. Guo, S. Y. Dai, C. L. Chen, Polymers 2016, 8, 37.
[42] Q. Mahmood, Y. N. Zeng, E. L. Yue, G. A. Solan, T. L. Liang, W. -H.
Sun, Polym. Chem. 2017, 8, 6416-6430.
101290.
[81] S. Y. Dai, C. L. Chen, Angew. Chem. Int. Ed. 2016, 55, 13281-13285;
Angew. Chem. 2016, 128, 13475-13479.
[82] B. K. Long, J. M. Eagan, M. Mulzer, G. W. Coates, Angew. Chem. Int.
Ed. 2016, 55, 7106-7110; Angew. Chem. 2016, 128, 7222-7226.
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
[83] S. Y. Dai, S. K. Li, G. Y. Xu, C. L. Chen, Macromolecules 2020, 53,
2539-2546.
[84] S. Y. Dai, C. L. Chen, Macromolecules 2018, 51, 6818-6824.
[85] Y. F. Gong, S. K. Li, Q. Gong, S. J. Zhang, B. Y. Liu, S. Y. Dai,
Organometallics 2019, 38, 2919-2926.
[86] Y. F. Gong, S. K. Li, C. Tan, W. Y. Kong, G. Y. Xu, S. J. Zhang, B. Y.
Liu, S. Y. Dai, J. Catal. 2019, 378, 184–191.
This article is protected by copyright. All rights reserved.

10.1002/chem.202101521
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Insert graphic for Table of Contents here.
Fluorine effect in olefin polymerization: Fluorine substituents at various positions (ortho-, meta-, and para-) and with
different numbers (n = 0, 1, 2, 3, and 5) have been systematically studied for the first time in the nickel -diimine promoted
ethylene polymerization and copolymerization with polar monomer, which show great influence on catalytic activity, polymer
molecular weight, branching density, and incorporation of polar monomer.
This article is protected by copyright. All rights reserved.