Elaborate Tuning in Ligand Makes a Big Difference in Catalytic Performance: Bulky Nickel Catalysts for (Co)polymerization of Ethylene with Promising Vinyl Polar Monomers

Article abstract of DOI:10.1002/cctc.201900265

To reveal effect of electronic or steric modification of phosphino-phenolate nickel complex for preparing optimized catalysts, we take elaborated studies on structure-performance relationship by finely modifying substituents on ortho-phenoxy position or phosphorus moiety of this catalyst. It reveals that these newly synthesized complexes are thermally robust, and exhibits very high activity (up to 10⁷ g mol_Ni^?1 h^?1) in ethylene polymerization even at 120 °C. Associated with stoichiometric experiments, experimental results prove that nickel complexes bearing electron-withdrawing substituents on ortho-phenoxy position or electron-donating substituents on phosphorus atom show higher activity than contrastive catalysts toward ethylene polymerization and ethylene–methyl acrylate (MA) copolymerization. Among these catalysts, 3 g bearing a strong electron-withdrawing substituent on ortho-phenoxy position exhibits the highest activity, and produces copolymers with the highest molecular weight and analogous MA incorporation. Various challenging polar vinyl monomers, like polyethylene glycol monomethyl ether acrylate, can be efficiently copolymerized with ethylene.

Full text of DOI:10.1002/cctc.201900265

Accepted Article
Title: Elaborate Tuning in Ligand Makes Big Differences in Catalytic
Performance: Bulky Nickel Catalysts for (Co)polymerization of
Ethylene with Promising Vinyl Polar Monomers
Authors: Yanping Zhang, Hongliang Mu, Xuling Wang, Li Pan, and
Yuesheng Li
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Elaborate Tuning in Ligand Makes Big Differences in Catalytic
Performance: Bulky Nickel Catalysts for (Co)polymerization of
Ethylene with Promising Vinyl Polar Monomers
Yanping Zhang,[a] Hongliang Mu,[b] Xuling Wang,[a] Li Pan,*[a] Yuesheng Li*[a]
Abstract: To reveal effect of electronic or steric modification of
nickel catalyst thus attracted increasing attention in both industry
phosphino-phenolate nickel complex for preparing optimized catalysts, and academia.
we take elaborated studies on structure-performance relationship by
finely modifying substituents on ortho-phenoxy position or
phosphorus moiety of this catalyst. It reveals that these newly
synthesized complexes are thermally robust, and exhibits very high
activity (up to 107 g·molNi−1·h−1) in ethylene polymerization even at
120 °C. Associated with stoichiometric experiments, experimental
results prove that nickel complexes bearing electron-withdrawing
substituents on ortho-phenoxy position or electron-donating
substituents on phosphorus atom show higher activity than
contrastive catalysts toward ethylene polymerization and ethylene–
methyl acrylate (MA) copolymerization. Among these catalysts, 3g
bearing a strong electron-withdrawing substituent on ortho-phenoxy
position exhibits the highest activity, and produces copolymers with
the highest molecular weight and analogous MA incorporation.
Various challenging polar vinyl monomers, like polyethylene glycol
monomethyl ether acrylate, can be efficiently copolymerized with
ethylene.
Recently, nickel catalysts with various ligands, such as α-
diimine nickel cationic catalyst,[4] phosphine-sulfonate neutral
nickel catalyst,[5] salicylaldimine neutral nickel catalyst,[6] shell
higher olefin process (SHOP) catalyst,[7] have contributed a lot to
copolymerization of ethylene and various polar comonomer,
respectively. However, only those comonomers bearing a spacer
between C=C bond and polar group could be effectively
incorporated. The commercially available polar comonomer, such
as methyl acrylate (MA), with a polar group directly connected
with the C=C bond usually leads to severe catalyst poisoning
reaction.[8] To overcome this poisoning process, Chen group[8a]
and Shimizu group[8c] designed nickel catalysts (A and B in Chart
1) that could copolymerize ethylene with MA by using transient
interaction between metal center with other heteroatom,
respectively. Chen et al. also designed several nickel catalysts
based on rigid diphosphazane monoxide ligands of C (Chart 1),
and those could copolymerize ethylene with MA.[8b] Catalysts A
-
and C exhibited relative low catalytic activity (< 9.2 × 103 g molNi
h-1) and produced copolymer with molecular weight lower than
1
20.7 × 103, MA incorporation of about 6.5 mol%. While catalyst B
could only achieve ethylene–MA copolymerization under higher
ethylene pressure (30 atm) and a large dosage of catalysts (80
μmol). By introducing an axial bulky group of neutral catalyst D,
β-H elimination and biomolecular deactivation could be effectively
suppressed. This neutral catalyst exhibited high catalytic activity
(up to 105 g molNi-1 h-1) toward ethylene–MA copolymerization and
produced high-molecular-weight (Mw up to 108 × 103) copolymer
with high MA incorporation (7.4 mol%).[9] However, it is very
difficult for all the previously reported Ni catalysts to
simultaneously achieve high catalytic activity and produce high-
molecular-weight copolymer with good incorporation of polar unit.
Introduction
Late transition metal catalysts, bearing a low oxophilic metal
center, play a vital role in coordination-insertion copolymerization
of olefin and polar monomers which could produce high-valued
polyolefin with improved surface properties.[1] In past decades,
significant progresses have been achieved with the most
representative palladium catalysts,[2] and various polar vinyl
monomers have been effectively incorporated into polyethylene
main chain.[3] However, molecular weight of such copolymers
usually was severely suppressed to only several thousand by the
polar group, made it far from application as a useful polymer
material. Besides, cost of the palladium complex is still beyond
industrial expectation.[2h] As a competitive candidate, low-cost
[a]
[b]
Y. zhang, X. Wang, Prof. Dr. L. Pan and Prof. Dr. Y. Li
School of Material Science and Engineering and Collaborative
Innovation Center of Chemical Science and Engineering (Tianjin)
Tianjin University
Tianjin 300072, China
E-mail: lilypan@tju.edu.cn; ysli@tju.edu.cn
Dr. H.Mu
Polymer Composites Engineering Laboratory
Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences
Changchun 130022, China
Chart 1. Representative nickel catalysts for ethylene and polar monomer
Supporting information for this article is given via a link at the end of
the document.
copolymerization.
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Generally, catalytic properties are sensitive to electronic or
steric modification on its ligand.[6,7d-e,10-12] For example, Claverie[12]
and Klabunde[7d,7e] proved that an electron-withdrawing
copolymerization capability and good tolerance toward polar
group, we carried out in depth exploration on effect of electronic
or steric modification at different position of the frame of the
promising catalyst D.
substituent on the Cα or Cβ-P position of phosphors in SHOP-type
-P
catalyst was contributed to improving catalytic activity by two-
orders-of-magnitude. In some cases, higher molecular-weight
polyethylenes were obtained by introducing electron-withdrawing
substituents.[11b,13] For example, fluorine atom as an electron-
withdrawing substituent made a big difference on the high
molecular weight becuase of C−H···F−C interaction.[13a-c]
However, there was no clear trend between catalytic properties
and catalyst structures by tuning the electronic effect in some
reports.[14a-c] Chen[14d] also observed that different position of the
substituents also played an important role. Grubbs[6] and Li[10a] et
al. reported that neutral salicylaldiminato nickel catalyst bearing a
bulky substituent on ortho-phenoxy position displayed high
catalytic activity toward ethylene polymerization, and also
produced high-molecular-weight polymers. Mecking and his
coworkers also demonstrated that introducing an electron-
withdrawing remote substituent on N-aryl moiety substantially
enhanced the molecular weight and crystallinity of obtained
polyethylene.[11] Additionally, Heinicke et al. showed that
substituents on phosphorus atom played a key role on the
catalytic properties of SOHP-type catalyst, especially molecular
weight of polymer.[15] In a word, it is noteworthy that electronic or
steric effect always plays different roles in different catalyst
systems, and the influence of electronic or steric modification is
always intricate because of diverse structural coordination
environments. In addition, neutral nickel catalysts as single-
component catalysts are of great academic and industrial interest
benefiting from their labile ligands, such as pyridine,
triphenylphosphine, and dimethylsulfoxide, becuause they can
initiate polymerization reaction without expensive borates or MAO
as a cocatalyst.[6a,10a] Therefore, aiming to prepare optimized
netural catalysts with high thermostability, catalytic activity,
Results and Discussion
Ligands and Complexes Syntheses. Phosphino-phenolate
([P,O]) ligands with different electronic and steric substituents at
ortho-position of the oxygen donor were synthesized as
presented in Scheme 1. Tetrahydropyranyl (THP) ether
compounds a–g were lithiated by n-BuLi, and then reacted with
PAr1PhCl (Ar1 = 2-(2’,6’-(MeO)2-C6H3)-C6H4), thus obtaining
compounds 1a–g, respectively. Protective group (THP) of
complexes 1a–g could be easily removed to afford ligands 2a–g
by adding drops of hydrochloric acid. In the case of ligand 2g,
introduction of –C6F5 substituent was accomplished after
introduction of –PArPh moiety by F-Li exchange reaction. Ligand
2h was prepared via a procedure similar to 2a using PAr2PhCl
instead of PAr1PhCl. Complex PAr1PhCl (Ar1 = 2-(2’,6’-(MeO)2-
C6H3)-C6H4) was synthesized according to literature,[9] while
synthesis of PAr2PhCl (Ar2
= 2-(2’,6’-F2-C6H3)-C6H4) was
described in Supporting Information.
As far as we know, electronic modification on ortho-phenoxy
position makes a difference on the electric density of hydrogen
atom in phenolic hydroxyl group. Presence of an electron-
withdrawing group at ortho-position of phenolic hydroxyl group will
decrease electric density of hydrogen atom, thus the resonance
of –OH in 1H NMR spectrum shifts to low field. As observed,
chemical shifts of the hydroxyl proton from each ligand with
different substituent at ortho-position of the phenyl are in following
sequence: 2b (9.65 ppm) > 2a (9.46 ppm), 2d (9.24 ppm) > 2c
(8.33 ppm), 2g (8.98 ppm) > 2f (8.28 ppm).
Scheme 1. Synthesis of ligands 2a–h and corresponding nickel complexes 3a–h.
1
Nickel complexes 3a–h were synthesized by a facile one-step
reaction of corresponding phosphino-phenolate ligand 2a–h with
Py2NiMe2 in good yields (> 80%) as depicted in Scheme 1. All
nickel complexes were characterized by elemental analysis and
NMR spectroscopy. Presence of doublet peaks at negative field
in H NMR spectra, which is originated from spin-spin coupling
between the protons of Ni–CH3 and phosphorus atom, proves that
the phosphorus atom is coordinated to the Ni center. One doublet
peak can be observed in 31P NMR spectrum for complex 3b
because of the long-range spin-spin coupling between
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phosphorus and fluorine atom, while one singlet is deteceted for
all other complexes. It is also observed that resonances for
complexes with electron-withdrawing substituents on ortho-
phenoxy position (3b: 20.80, 3d: 19.92, 3g: 20.39 ppm, Figure 1)
slightly shift to higher field compared to the corresponding
electron-donating complex (3a: 21.09, 3c: 21.27, 3f: 21.28 ppm)
in 31P NMR spectra. This observation may be explained by that
introducing an electron-withdrawing substituent on ortho-phenoxy
position makes the metal center more electron-deficient, both σ-
donating of phosphine ligand and back donating bonding between
pz orbital of nickel center and empty dπ orbital of phosphorus atom
are therefore slightly weaken. Electronic density of phosphorus
atom is decreased by introducing an electron-withdrawing
substituent, as observed, corresponding resonance for electron-
poor complex 3h (24.68 ppm) in 31P NMR spectrum evidently
shifts to lower field compared to electron-efficient 3e (21.47 ppm).
Nickel complexes 3b, 3d and 3h were also exemplified by X-
ray diffraction analyses (3b and 3h is in Figure 2–3, respectively,
3d is in Figure S87). Generally, nickel center adopts a distorted
square-planner geometry, and labile ligand pyridine is located
trans to the phosphorus atom because of ‘trans effect’.[9] As
described in Figure
2
and 3, either bulky 2-(2,6-
(OCH3)2C6H3)C6H4– or 2-(2,6-F2-C6H3)C6H4– group effectively
shields the nickel center from axial position. Note that bond length
of Ni(1)–O(2) and Ni(1)–O(3) in 3b is 3.817 and 4.436 Å,
respectively, either is longer than the sum of the van der Waals
radii of nickel and oxygen (3.15 Å).[16] In addition, bond length of
Ni(1)–F(1) and Ni(1)–F(2) in 3h is 3.791 and 4.487 Å, respectively,
while the sum of van der Waals radii between Ni and F atom is
3.31 Å.[17] This result reveals that the interaction between –F or –
OMe group and the nickel center for both 3b and 3h is negligible.
Figure 3. ORTEP plot of complex 3h. Ellipsoids are shown with 30% probability.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles
(°): Ni(1)–O(1) 1.928(2), Ni(1)–N(1) 1.955(3), Ni(1)–P(1) 2.1080(11), Ni(1)–
C(34) 1.944(4), Ni(1)–F(1) 3.791, Ni(1)–F(2) 4.487. O(1)–Ni(1)–C(34)
179.67(15), O(1)–Ni(1)–N(1) 88.75(11), C(34)–Ni(1)–N(1) 91.58(15), O(1)–
Ni(1)–P(1) 86.68(8), C(34)–Ni(1)–P(1) 92.99(12), N(1)–Ni(1)–P(1) 175.18(10).
Figure 1. Chemical shifts of phosphorus atom for nickel complexes 3a–h in
31P NMR spectra.
Ethylene polymerization studies. Because of the great
academic and industrial interest, neutral [P,O] chelate cayalysts
3a-h were applied as single-component catalysts to promote
ethylene polymerization without any activator or scavenger at 10
bar of ethylene pressure under 80 °C. As shown in Table 1,
catalytic activity is markedly increased (entry 1 vs 2, 3 vs 4, and 6
vs 7) by introducing an electron-withdrawing substituent (–F, –CF3
or –C6F5) on ortho-phenoxy position. The most electron-deficient
complex 3g bearing a –C6F5 group exhibits the highest catalytic
activity among complexes 3a–d, 3f and 3g. Introduction of an
electron-withdrawing group on ortho-phenoxy position makes the
nickel center more electrophilic, and thus ethylene more easily
coordinating to it. Additionally, a steric bulky group on ortho-
phenoxy position also contributes to an increased catalytic activity.
Comparing the polymerization results of complexes 3a, 3c and 3e
will give us more insight into the effect of steric bulk. Complex 3e
bearing the bulkiest substituent (6-tBu) exhibits the highest
catalytic activity (up to 24.06 × 106 gPE molNi−1 h−1, entry 5), while
complex 3a shows the lowest catalytic activity of 3.54 × 106 gPE
Figure 2. ORTEP plot of complex 3b. Ellipsoids are shown with 30% probability.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles
(°): Ni(1)–O(1) 1.9314(16), Ni(1)–N(1) 1.9565(19), Ni(1)–P(1) 2.1206(6), Ni(1)–
C(32) 1.967(2), Ni(1)–O(2) 3.817, Ni(1)–O(3) 4.436. O(1)–Ni(1)–N(1) 88.69(7),
O(1)–Ni(1)–C(32) 177.57(8), N(1)–Ni(1)–C(32) 92.43(9), O(1)–Ni(1)–P(1)
87.56(5), N(1)–Ni(1)–P(1) 175.58(6), C(32)–Ni(1)–P(1) 91.23(7).
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−1
molNi h−1. In the case of complexes 3b, 3d and 3g, the similar
reasonable because basicity of phosphine moiety is decreased by
introducing an electron-withdrawing substituent, and ‘trans effects’
become weaker, thus making the liable ligand pyridine binds more
tightly to Ni center and decelerating the coordination-insertion
process.
trend can be observed that complex 3g bearing the bulkiest
substituent (6-C6F5) exhibits the highest catalytic activity (up to
17.04 × 106 gPE molNi−1 h−1, entry 7). It also indicates that a bulky
group can help to enhance the steric hindrance around the active
Ni site, thus the labile ligand pyridine (Py) readily dissociates from
Ni center, and then ethylene can easily go close to the Ni center.
Besides catalytic activities, molecular weights of the obtained
polymers can also be well controlled by tuning ligand structure of
Ni complex. In comparison of complex 3a with 3b, molecular
weight of resultant polymer decreases from 169.3 × 103 to 83.8 ×
103 (entry 1 vs entry 2, Table 1). Similar observations can also be
found in comparison between 3c and 3d (entry 3 vs 4, from 120.3
× 103 to 36.0 × 103) or 3f and 3g (entry 6 vs 7, from 74.8 × 103 to
53.7 × 103). All above comparisons reveal that molecular weight
of the synthesized polyethylene is declined by introducing an
electron-withdrawing substituent on ortho-phenoxy position, such
as –F, –CF3 or –C6F5 group, and this feature is in good
accordance with some previous reports.[15, 18, 19] However, higher
molecular weight polyethylene was obtained with an electron-
withdrawing substituent in some other reports.[11b,13] We speculate
the different influence trend originates from different ligand
skeleton. Generally, molecular weight of the obtained
polyethylene depends on the ratio of ethylene insertion rate
relative to chain transfer rate and chain termination rate. We thus
speculate that the decrease in molecular weight is originated from
the facilitated reductive elimination (β-H elimination) rate relative
to ethylene insertion rate by introducing an electron-withdrawing
substituent.[20]
Most previously reported nickel catalysts tended to decompose
beyond 60 °C,[21] while high reaction temperature (70–115 °C)
was essential condition for industrial gas-phase olefin
polymerizations.[22] To reveal the influences of reaction
temperature on catalytic performances and evaluate the thermal
stability of the representative catalyst, we conducted
polymerization under different temperatures at 10 bar of ethylene
using complex 3e (Table 2). Surprisingly, 3e is very active toward
ethylene polymerization in a very wide temperature window. As
the temperature elevated from 20 to 80 °C, the catalytic activity is
−1
dramatically enhanced from 2.88 × 106 to 24.06 × 106 gPE molNi
h−1 (entries 1–4). When reaction temperature further elevated
from 80 to 140 °C, catalytic activity is decreased to 2.76 × 106 gPE
molNi−1 h−1, which is very similar to that of polymerization at 20 °C.
It is notable that even at very high temperature of 120 °C, catalyst
3e still displays extremely high catalytic activity (up to 13.1 × 106
−1
gPE molNi h−1), and besides, yields polyethylene with relatively
high molecular weight (17.4 × 103). To our best knowledge, this is
the most thermally stable neutral nickel catalyst reported so far.[15,
19b, 21c, 22a, 22b] Molecular weight of resultant polyethylene is closely
related to reaction temperature. As displayed in Table 2,
polymerization can be initiated under 20 °C, and polyethylene with
very high molecular weight of 632.4 × 103 can be obtained with
narrow polydispersity index of 1.8. The highest molecular weight
of 717.1 × 103 emerges at 40 °C, then it is slightly decreased with
enhancement of reaction temperature till 60 °C. This catalyst
simultaneously possesses high catalytic activity and produces
high-molecular-weight polymer, and it is a very promising
breakthrough compared to all previously reported examples.[21b,
Table 1. Data of ethylene polymerization using neutral nickel catalysts 3a–h.[a]
[d]
[d]
[e]
Yield Act.[b] TOF[c] Mn
Mw
(103) (103) (103)
Tm
[d]
Entry
Cat.
Mw/Mn
(g) (103)
5.9 3540
17.3 10380
(°C)
21c, 22a]
1
2
3
4
5
6
7
8
3a (H)
3b (F)
126
370
276
516
859
504
609
722
74.4 169.3
38.1 83.8
30.4 120.3
2.3
2.2
3.9
3.9
2.4
2.0
2.3
2.2
134.4
132.6
135.2
128.5
130.0
129.6
127.0
131.1
Further enhancement in reaction temperature from 60 to
140 °C accelerates the decrease in molecular weight, but the
lowest weight average molecular weight is still relatively high (>
10 × 103). Decrease in molecular weight dominatingly results from
the facilitated rates of chain transfer reaction at elevated
temparatures.
3c (CH3) 12.9 7740
3d (CF3) 24.1 14460
9.3
36.0
3e (tBu)
3f (Ph)
40.1 24060
23.5 14100
18.1 43.6
36.9 74.8
23.4 53.7
13.2 29.2
In addition, We also carry out ethylene polymerization at 120 °C
3g (C6F5) 28.4 17040
using catalyst 3d bearing
a strong electron-withdrawing
3h (P-F) 33.7 20220
substituent –CF3 and the bulkeir catalyst 3g bearing another
strong electron-withdrawing substituent –C6F5. These two
catalysts show very high catalytic activity, and the bulkeir 3g
shows higher catalytic activity than 3d (Table 2, entry 8 vs 9). We
aslo explore the thermal stability of these nickel catalysts at longer
polymerization period under 120 °C. The selected catalyst 3e
shows increased catalytic activity and molecular weitht of polymer
with prolonged reaction time at 30 °C (Table S2, entry S5-S8).
Ethylene polymerization is also conducted with prolonged
reaction time at 120 °C using lower catalyst concentration to avoid
catalyst being enwrapped. As shown in the plots of TOF-time
(Figure S86), the TOF remains very similar value (134 × 103–144
× 103). To further explore the thermostability of catalyst 3e, we
also first carried out ethylene polymerization at 120 °C for 10 min,
then shutted off the ethylene gas for 20 or 40 min, respectively,
[a] 100 mL of toluene, 5 μmol of catalyst, 20 min, 10 bar of ethylene, 80 °C. [b] In
. ,
unit of gPE molNi−1 h−1 [c] TOF, turnover frequency, in unit of 103 molPE molNi−1 h−1
[d]
E, ethylene.
Determined by GPC in 1,2,4-trichlorobenzene at 150 °C vs
narrow polystyrene standard. [e] Determined by DSC, the second heating curve
at the rate of 20 °C min-1.
Influence of phosphine moiety electronic modification on
catalytic performance is also explored. Both catalytic activity and
molecular weight of polyethylene are decreased by introducing an
electron-withdrawing substituent on phosphine moiety.
Comparing the data of complex 3e and 3h in Table 1, catalytic
−1
activity is decreased from 24.06 × 106 to 20.22 × 106 gPE molNi
h−1. The molecuar weight of polyethene produced by 3e and 3f is
43.6 × 103 and 29.2 × 103, respectively. This observation is
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after that, charged the ethylene gas again to trigger the
polymerization for another 10 min. To our delight, after this
intermittent process, catalyst 3e still exhibits comparable catalytic
activity with the data of direct reaction for 20 min in Table 2, entry
6. All these data domenstrate that catalyst 3e exhibits excellent
thermal stability. All resultant polyethylene possesses highly
linear structure or only very few methyl branches (4/1000C)
produced at temperature over 120 °C as evidenced by 13C NMR
(Figure S62–63) and differential scanning calorimetry (DSC)
analyses (Tm = 126.2–138.5 °C).
accompanying decomposition reaction occurred quickly, however
these nickel complexes still display good tolerance to MA.
Table 2. Controlled ethylene polymerization by using catalyst 3e.[a]
[d]
[d]
[e]
T
(oC)
Yield Act.[b] TOF[c] Mn
Mw
Tm
[d]
Entry
Mw/Mn
(g) (103)
(103)
(103) (103)
(oC)
1
2
20
40
60
80
4.8 2880
8.1 4860
20.1 12000
40.1 24060
103
173
429
859
469
462
99
358.1 632.4
552.8 717.1
489.3 679.0
1.8
1.3
1.4
2.4
2.4
3.4
3.6
2.8
3.1
134.1
138.5
137.1
130.0
127.5
126.2
126.6
126.9
128.6
3
4
18.1
14.2
5.1
43.6
33.6
17.4
12.1
29.5
30.8
5
100 22.0 13120
120 21.6 12960
Figure 4. Selected 1H NMR spectra (expanded 2.2 to -1.1 ppm) of reaction of
nickel complexes 3c–g with 60 equivalents of methyl acrylate after 2 h at 25 °C.
6[f]
7[f]
8[g]
9[h]
140
4.6 2760
3.4
120 16.6 9960
120 18.9 11340
356
405
10.5
9.9
It is notable that apparent rate constant is the rate of equilibrium
reaction as shown below [19a]
:
[a] 100 mL of toluene, 5 μmol of catalyst 3e, 20 min, 10 bar of ethylene. [b] Unit of
−1
−1
gPE molNi h−1 [c] TOF, turnover frequency, in unit of 103 molE molNi h−1, E,
.
[P,O]Ni(CH3)(Py) + MA ⇄ [P,O]Ni–MA–CH3 + Py
ethylene. [d] Determined by GPC in 1,2,4-trichlorobenzene at 150 °C vs narrow
[e]
polystyrene standard. Determined by DSC, the second heating curve at the
Herein, the decay of Ni–CH3 resonance is used to estimate the
apparent rate constant of reaction between Ni complex and MA,
and the decay rate of the Ni–CH3 resonance is found to follow
first-order kinetics at 25 °C (Figure 5). Note that electron-poor
rate of 20 °C min-1. [f] 100 mL of naphthane. [g] 100 mL of naphthane, 5 μmol of
catalyst 3d; [h] 100 mL of naphthane, 5 μmol of catalyst 3g.
complex 3g displays the lowest apparent rate constant (kapp
=
Reaction of nickel complex with methyl acrylate (MA). To
understand the influence of steric or electronic modification on
tolerance and reactivity of nickel complexes with polar monomer,
reaction of different Ni complex (3c–h) with excess MA (60
equivalents of Ni) in the absence of ethylene were monitored by
NMR technique at 25 °C, respectively. As revealed, MA inserts
into Ni–CH3 bond mainly via 2,1-fashion to form [P,O]Ni–
CH(CO2CH3)CH2CH3 ([P,O]Ni–MA–CH3) and the resonance
intensity of Ni–CH3 at negative field is accordlingly decreased.[9,
3.94 × 10-5 s-1), which is significantly lower than that of complex
3f. Similarly, complex 3d (kapp = 4.61× 10-5 s-1) bearing an
electron-withdrawing –CF3 group also displays a lower rate
relative to 3c (kapp = 13.17 × 10-5 s-1). Evidently, electron-poor
nickel complexes show a slower rate of MA insertion into Ni–CH3
bond, in other words, the electron-poor nickel complexes show
better tolerance in presence of excess MA. Additionally, complex
3e bearing a bulkier group (6-tBu) undergoes a slower reaction
rate than complex 3c (6-CH3). The reactivity of nickel catalysts is
decreased in sequence: 3g > 3d > 3f > 3c; 3e > 3c. Substituent
on phosphorus atom also shows influence on reactivity in reaction
of MA and Ni complex. For instance, Ni–CH3 resonance of 3h
which is bearing 2’,6’-F2-substituted biphenyl group on P-aryl
19a]
The insertion product [P,O]Ni–MA–CH3 can undergo β-H
elimination to form free Ni–hydride and methyl crotonate.
Accompanying
bimolecular
decomposition
reaction
simultaneously occurs via reaction of free Ni-hydride with
[P,O]Ni–MA–CH3. This decomposition reaction can be further
evidenced by formation of methyl butyrate decomposition product. moiety nearly disappears after reaction for 13 h (Figure S85),
1
All H NMR spectra of reaction of 3c–g with MA after 2 h are
presented in Figure 4. The residue resonances of Ni–CH3 are still
distinct even after 2 h, indicating that these nickel complexes
exhibit excellent polar group tolerance. Besides, some new
resonances present at 2.02, 1.51, and 0.76 ppm can be ascribed
to the proton of –CH2CO2Me, –CH2CH3, and –CH3, respectively.
Characteristic resonances of [P,O]Ni–MA–CH3 are not very
prominent, and weak resonances at –0.29 and 0.36 ppm refer to
Ni–CH(CO2CH3)CH2CH3 and Ni–CH(CO2CH3)CH2CH3 can be
while Ni–CH3 resonance of 3e which is bearing 2’,6’-OMe2-
substituted biphenyl group on P-aryl moiety still exists after
reaction for 38 h (Figure S82). It is evident that an electron-
donating group on P-aryl moiety is helpful to enhance the catalyst
tolerance toward polar MA. After reaction of nickel complex with
MA for 30 h, the reaction mixture was also tried to initiate ethylene
polymerization. Surprisingly, 3d and 3g bearing an electron-
withdrawing substituent on ortho-phenoxy position still exhibits
−1
high catalytic activity (up to 1.56 × 106 g molNi h−1, Table S1,
further affirmed by H-1H COSY (Supporting Information, Figure
S51). These identifications suggest that above mentioned
1
entry S5) toward ethylene polymerization. This is a highly
persuasive evidence to prove that introducing an electron-
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10.1002/cctc.201900265
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−1
withdrawing substituent on ortho-phenoxy position is an effective
molNi h−1 for 3a, 3c and 3e, respectively) and molecular weight
(10.6 × 103, 43.3 × 103 and 59.3 × 103 for 3a, 3c and 3e,
respectively) of the resultant copolymers are also enhanced.
Furthermore, electronic modification of phosphorus moiety also
makes a dramatic effect on ethylene–MA copolymerization. It is
revealed that electron-rich catalyst 3e is more active than
electron-poor catalyst 3h, and 3e also produces much higher
molecular-weight copolymer (entry 5 vs 8, and 12 vs 15,
respectively). For example, catalytic activity of ethylene/MA
way to enhance tolerance of the Ni catalyst.
−1
copolymerization by catalyst 3e is up to 50.5 × 103 g molNi h−1
(entry 5), but catalytic activity by catalyst 3h is only about 32.9 ×
−1
103 g molNi h−1 (entry 8). The molecular weight of obtained
copolymers by catalysts 3e and 3h is 59.3 × 103 and 27.8 × 103,
respectively. However, complex 3h produces E-MA copolymer
with higher MA incorporation than complex 3e by 0.7 mol%.
Table 3. Copolymerization of ethylene and methyl acrylate (MA) by using
catalysts 3a–h.[a]
Figure 5. First order kinetic of the reaction of nickel complexes (3c–g) with 60
equivalents of methyl acrylate over 3 h: plots of decreasing intensity of
resonance of Ni–CH3 protons over time in 1H NMR spectra.
[e]
[f]
Yield
(g)
Act.[c]
(103)
Incorp.[d]
(mol%)
Mw
Tm
Entry
Cat.
[MA][b]
PDI[e]
(103)
(°C)
1
2
3a(H)
3b(F)
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.039
0.075
0.372
1.280
0.505
0.400
1.320
0.329
0.030
0.179
0.386
0.263
0.140
0.750
0.163
0.052
0.210
0.423
3.9
7.5
1.9
1.6
1.5
1.4
2.0
1.5
0.7
2.7
2.5
4.7
3.1
2.2
3.6
2.8
4.2
6.1
3.9
2.7
10.6
21.5
43.3
116.3
59.3
56.9
154.0
27.8
7.6
1.8
1.8
1.7
2.2
2.0
1.8
2.0
2.0
1.7
1.8
2.0
2.0
2.1
2.2
1.9
1.7
2.0
2.0
125.2
126.6
122.4
121.6
123.3
121.3
126.3
120.2
120.9
113.6
119.2
117.0
113.7
121.7
112.4
106.2
114.3
116.8
Copolymerization of ethylene and methyl acrylate.
Representative data of copolymerization of ethylene with methyl
acrylate promoted by all nickel complexes are tabulated in Table
3. Both catalytic activity and molecular weight of the resultant
copolymer are significantly increased by introducing an electron-
withdrawing substituent (–F, –CF3, or –C6F5) on ortho-phenoxy
position. For example, catalytic activity of complex 3d is much
higher than that of 3c (128 × 103 vs 37.2 × 103 g molNi−1 h−1, entry
4 vs 3), and molecular weight of copolymer yielded by complex
3d is two times higher than that by complex 3c (116.3 × 103 vs
43.3 × 103). Note that 3g bearing an electron-withdrawing group
3
3c(CH3)
3d(CF3)
3e(tBu)
3f(Ph)
37.2
128
50.5
40
4
5
6
7
3g(C6F5)
3h(P-F)
3a(H)
132
32.9
3.0
8
9
10
11
3c(CH3)
17.9
38.6
26.3
14
14.4
31.1
22.6
26.0
75.0
12.1
8.9
3d(CF3)
12[g] 3e(tBu)
13
3f(Ph)
14 3g(C6F5)
−1
–C6F5 shows the highest activity (up to 132 × 103 g molNi h−1,
75.0
16.3
5.2
entry 7) and produces highly linear copolymers with the highest
molecular weight (Mw up to154 × 103, entry 7). In addition, the
incorporation of MA is also affected by substituent type. The
influence is not very obvious in the presence of low MA
concentration. For instance, MA incorporation of copolymer by
complex 3a is 1.9 mol%, and this value is slightly higher than that
by complex 3b (1.6 mol%). Similar to this phenomena, complex
3d (1.4 mol%) or 3g (0.7 mol%) bearing a srtong electron-
withdrawing substituent –CF3 or –C6F5 on ortho-phenoxy position
produces E-MA copolymer with lower MA incorporation than the
corresponding complex 3c (1.5 mol%) or 3f (1.5 mol%). In the
presence of high MA concentration, as can be observed (Table 3,
10 vs 11, 13 vs 14), the influnce of electronic effect was more
obvious, and MA incorporation by a catalyst bearing an electron-
withdrawing substituent on ortho-phenoxy position is also lower
than that by contrastive catalysts. For example, MA incorporation
of copolymer produced by electron-deficient complex 3d and 3g
is 3.1 and 2.8 mol%, respectively, which is lower than that by
complex 3c (4.7 mol%, entry 10) and 3f (3.6 mol%, entry 13).
Ethylene is more nucleophilic to electron-deficient Ni center than
electron-deficient olefin (MA), and a little smaller than MA, thus it
is more easier for ethylene to insert into polymer chain during the
coordination-insertion process.[2a, 3a, 23]
15
16[h]
3h(P-F)
3f(Ph)
17[h] 3g(C6F5)
18[i]
3e(tBu)
210
21.2
18.0
20.5
Polymerization conditions:[a] 50 mL of toluene, 10 μmol of catalyst, 60 min, 50 °C,
10 bar of ethylene. [b] units of mol L-1. [c] In units of g molNi−1 h−1 [d] Determined
.
by 1H NMR spectroscopy at 120 °C. [e] PDI = Mw/Mn, determined by GPC in
1,2,4-trichlorobenzene at 150 °C vs narrow polystyrene standard. [f] Determined
by DSC, the second heating curve at the rate of 20 °C min-1. [g] Ref.[9]
[i] Reaction for 120 min.
.
[h] 5 bar.
In a word, the catalytic activity and molecular weight of resultant
copolymers increased in a sequence: 3g > 3d > 3f > 3c > 3b >
3a; 3e > 3c > 3a; 3e > 3h. The enhanced catalytic activity and
decreased insertion percentage of MA for catalysts bearing
electronic-withdrawing substituents in the copolymerization of
ethylene with MA could be also explained by a lower reaction rate
of catalyst (Figure 6) with MA for electron-deficient catalyst. The
sequence of catalytic activity is in good accordance with catalyst
tolerance in the presence of excess MA. Furthermore, 3d and 3g
bearing
a
strong electron-withdrawing substituent can
simultaneously achieve high catalytic activity, and produce higher
molecular weight copolymer with even higher MA incorporation
than that of our previously reported 3e, demonstrating that an
excellent catalyst system for copolymerization of ethylene with
While introducing a bulky group on ortho-phenoxy position,
both catalytic activity (3.9 × 103, 37.2 × 103, and 50.5 × 103 g
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10.1002/cctc.201900265
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vinyl polar monomer can be achieved via elaborately tuning
substituents on proper sites around Ni center.
complexes 3c–h (E/MA-3c–E/MA-3h, entry 10–15, Table 3) in
presence of 0.2 mol/L MA, respectively. We find that MA units are
mainly incorporated into the polymer main chain (in-chain MA)
and just a few located at the chain end (terminal MA). As shown
in Figure 6, ratio of terminal MA to total MA is 8.7% in both E/MA-
3c and E/MA-3f, however, it is 8.0% and 8.3% in E/MA-3d and
E/MA-3g, respectively. This result indicates that the percentage
of terminal MA is slightly decreased by introducing an electron-
withdrawing group on ortho-phenoxy position. That means, β-H
elimination reaction after 2,1-insertion of MA has been slightly
inhibited. In addition, terminal MA structure in E/MA-3h is slightly
increased by 0.3% by introducing an electron-withdrawing group
on the phosphorus atom relative to that in copolymer E/MA-3e.
As previously reported, MA incorporation could be enhanced
with increasing MA feed concentration, while the molecular weight
of copolymer was decreased, because β-H elimination was more
facilitated after insertion an MA unit.[9, 19a] In the case of low MA
concentrantion, for instence, catalyst 3g bearing a strong
electronic-withdrawing substituent –C6F5 on the ortho-phenoxy
position displays very high catalytic activity (up to 132 × 103 g
−1
molNi
h−1, entry 7) and produces high molecular-weight
copolymer (154.0 × 103), but MA incorporation in copolymer is
only 0.7 mol%. Howerver, in the precense of higher MA
concentration, MA incoropration in copolymer is increased from
0.7 to 2.8 mol%, while the catalytic activity significantly decreases
−1
to 75 × 103 g molNi h−1, and molecular weight of copolymer
declines to 75 × 103. The increase in MA incorporation and
decrease in catalytic activity are reasonable because the
possibility and ratio of MA coordinated with Ni center is increased
in higher MA concentration, and deactivation reaction becomes
more facilitated, thus resulting in lower catalytic activity and higher
MA incorporation. Furthermore, as observed, decreasing ethyele
pressure has similar effect on the catalytic activity, molecular
weight and MA incorporation (Table 3, entry 16 and 17).
We also perform copolymerization with longer time using
catalyst 3e. Catalyst 3e still displays high activity (up to 21.2 × 103
g molNi−1 h−1) even reacted for two hours (entry 18, table 3). This
value is only slightly decreased relative to the data of reacting for
one hour (26.3 × 103 g molNi h−1, entry 12, Table 3), and it is
−1
Figure 6. 1H NMR spectra (expanded 4.6 to 2.2 ppm) of ethylene–methyl
acrylate copolymers (E/MA-3c–E/MA-3h) obtained with complexes 3c–h (entry
10-15, Table 3), respectively.
indicative of an excellent thermal stability of 3e under 120C.
To shed light on the influence of catalyst structure tailor on the
microstructure of E–MA copolymer, [2a,2k ] we also made a detailed
analysis of the 1H NMR spectra of copolymers produced by
Table 4. Copolymerization of ethylene with challenging vinyl polar monomers by 3g.a)
d)
e)
Comonomer
(mol/L)
P
Yield
(g)
Act.b)
(104)
Incorp.c)
(mol%)
Mw
Tm
d)
Entry
Mw/Mn
(Bar)
(103)
(oC)
1
2
3
4
5
6
7
10
10
10
5
0.743
0.200
0.095
0.222
0.061
0.025
0.635
7.43
2.00
0.95
2.22
0.61
0.25
6.35
1.4
0.8
2.2
2.3
1.2
3.0
1.0
147.2
1.7
1.8
2.5
1.9
2.2
2.1
3.1
133
(0.2)
(0.1)
(0.2)
39.0
37.9
26.2
19.6
11.5
373.6
132
132
120
130
119
134
(0.2)
(0.1)
(0.2)
(0.1)
5
5
10
Polymerization conditions: a) 10 μmol of catalyst, 50 mL toluene, 60 min, 50 °C . b) In unit of g molNi−1 h−1 c) Determined by 1H NMR spectroscopy at 120 °C. d)
.
Determined by GPC in 1,2,4-trichlorobenzene at 150 °C vs narrow polystyrene standard. e) Determined by DSC, the second heating curve at the rate of 20 °C
min-1.
Copolymerization of ethylene and various promising and
challenging vinyl polar monomers. Complex 3g bearing an
electron-withdrawing substituent (6-C6F5) displays the highest
catalytic activity in copolymerization of ethylene with MA and
produces E–MA copolymer with the highest molecular weight.
Herein, we further explore copolymerization of ethylene with a
variety of challenging vinyl polar monomers, such as acrylamides
and macromonomer, respectively. Without any cocatalyst, 3g
shows relatively high activity toward copolymerization of ethylene
with butyl acrylate, N,N-dimethylacrylamide, or ethylene glycol
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10.1002/cctc.201900265
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monomethyl ether acrylate with 1–3 mol% of polar comonomer
incorporation. As shown in Table 4, catalytic activity for ethylene–
butyl acrylate copolymerization (entry 1 and 4) was much higher
than the corresponding values for acrylamide monomer (entry 2
and 5). 3g can also effectively catalyze copolymerization of
ethylene with ethyleneglycol monomethyl ether acrylate (EGMA),
giving copolymer with EGMA incorporation up to 3.0 mol%.
Besides, as a very important biocompatible and hydrophilic
macromonomer, polyethylene glycol monomethyl ether acrylate
macromonomer can also be efficiently incorporated into
polyethylene main chain by using 3g as a catalyst. As far as we
know, this is the first example of direct coordination-insertion
copolymerization of ethylene with these kinds of challenging vinyl
functional macromonomers.
drying over CaH2. Polyethylene glycol monomethyl ether acrylate
was synthesized by the reaction of acrylic acid with polyethylene
glycol monomethyl ether (Mn = 350). Compound 2e and complex
3e were synthesized according to our previous work.[9] NMR
experiments were conducted on a Bruker spectrometer (500 MHz
or 400 MHz) at 25 °C or 120 °C. The molecular weights of
polyethylenes or ethylene–vinyl polar monomer copolymers were
measured by gel permeation chromatography technique (1,2,4-
trichlorobenzene as mobile phase) through a high-temperature
chromatograph (PL-GPC 220 type) equipped with three PLgel 10
μm Mixed-B LS type columns. Melting temperatures of obtained
(co)polymers were measured via a Q2000 V24.11 Build 124
differential scanning calorimeter (DSC) at a rate of 20 °C min−1
under N2. Elemental analysis was performed on an elemental
spectrometer (Vario EL). The X-ray analysis data of crystals were
recorded on a Bruker Smart diffractometer (APEX) with CCD
detector using Mo K radiation (λ = 0.71073Å) with the  scan
mode at 186 K. The CCDC number for complex 3b, 3d and 3h is
1886371, 1886372, and 1886373, respectively. Representative
NMR spectra, GPC traces, DSC traces of the polymers, and X-
ray crystallography data are all provided in supporting information.
This material is available free of charge via the Internet at
https://onlinelibrary.wiley.com.
Conclusions
In conclusion, we present an excellent example to effectively
improve catalytic performances by fine modification of bulky
phosphino-phenolate neutral nickel catalyst structure. These
modified nickel complexes are very thermally robust and exhibit
high catalytic activity (up to 107 g·molNi−1·h−1) even at 120 °C.
Highly linear polyethylene with high molecular weight (up to 717.1
× 103) are obtained. Additionally, nickel complexes bearing an
electron-withdrawing group or a bulky group on ortho-phenoxy
position display increased catalytic activities toward not only
ethylene polymerization but also ethylene–methyl acrylate
copolymerization. More importantly, introducing an electronic-
withdrawing group on ortho-phenoxy position contributes to
enhance molecular weight at expense of MA incorporation.
Conversely, nickel complex bearing an electronic-donating
substituent on P-aryl moiety exhibits increased catalytic activity
and produces higher molecular-weight (co)polymer toward both
ethylene polymerization and copolymerization. Stoichiometric
NMR experiments reveal that nickel complexes bearing an
electron-withdrawing substituent on ortho-phenoxy position are
more tolerant in the presence of excess MA. Besides,
unprecedented copolymerization of ethylene and several very
challenging polar vinyl monomers (such as acrylamide, ethylene
glycol monomethyl ether acrylate, even polyethylene glycol
monomethyl ether acrylate macromonomer) can also be
efficiently achieved by the optimized Ni catalyst.
Syntheses of ligands. 2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-
C6H4OH (2a).
A flask was charged with 2-bromo-2’,6’-
dimethoxybiphenyl (3.4 g, 12 mmol) and 80 mL of dry THF, then
n
a solution of BuLi (14 mmol, 1.2 equivalents, 2.4 M) in hexane
was slowly added via a dry syringe at 25 °C. After stirred for 3 h,
reaction mixture was slowly transferred to another flask charged
with a solution of PPhCl2 (1.62 mL, 12 mmol) in 10 mL of THF via
a glass delivery tube under N2 atmosphere at 0 °C. Reaction
temperature was slowly warmed up to room temperature. After
reaction for 6 h, a clear solution A was formed. Meanwhile, a
solution of tetrahydropyranyl (THP) ether compound C6H5OTHP
(THP = –C5H9O, 2.14 g, 12 mmol) in diethyl ether was lithiated by
5.5 mL of nBuLi (13 mmol, 1.1 equivalents, 2.4 M in hexane) and
stirred for 4 h at room temperature, yielding suspension B. The
formed suspension B was slowly transferred to reaction mixture
A via a glass delivery tube at 0 °C. After reaction for 8 h at room
temperature, all solvents were removed under vacuum, and the
obtained
residue
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-
C6H4OTHP (1a) was used in next reaction step without purification.
The residue was dissolved in degassed ethyl acetate, and a few
drops of hydrochloric acid was added. After stirred for 3 h, the
protected group was completely removed by TLC monitoring.
Resultant mixture was quenched by aqueous NaHCO3 and
extracted with ethyl acetate. Organic phase was dried by
anhydrous magnesium sulfate, and pure target compound 2a was
obtained by column chromatography (petroleum ether/ethyl
acetate = 30/1) as white solids (2.5 g, 51 wt%). 1H NMR (400 MHz,
C6D6): δ 7.52–7.44 (m, 1H), 7.38–7.27 (m, 3H), 7.14–7.09 (m, 2H),
7.08–6.94 (m, 6H), 6.69 (td, J = 7.3, 1.2 Hz, 1H), 6.60 (d, J = 7.7
Hz, 1H), 6.32 (dd, J = 23.3, 8.3 Hz, 2H), 3.22 (s, –OCH3, 3H), 3.09
Experimental Section
General procedures and materials. All syntheses and
preparations involving air/moisture-sensitive were all carried out
in a glove-box (Etelux Lab 2000) under nitrogen or using standard
Schlenk techniques. All solvents, such as toluene, n-hexane,
diethyl ether, dichloromethane, were purified by Etelux solvent
purification system. Dry tetrahydrofuran was purchased form J&K
Chemicals, and used without any purification. Naphthane was
distilled under reduced pressure after drying over CaH2. Ethylene
(99.9%) was purchased form BF Special Gas Limited Company
and purified with a purification system (O2 ≤ 0.1 ppm, H2O ≤ 0.1
ppm, CO2 ≤ 0.1 ppm). Butyl acrylate, ethyleneglycol monomethyl
ether acrylate and N,N-dimethylacrylamide were all purchased
from J&K Chemicals and distilled under reduced pressure after
1
(s, –OCH3, 3H). H NMR (400 MHz, DMSO-d6): δ 9.46 (s, –OH,
1H), 7.38–7.18 (m, 6H), 7.17–7.01 (m, 4H), 6.95–6.90 (m, 1H),
6.78–6.66 (m, 2H), 6.62–6.56 (m, 2H), 6.53 (m, 1H), 3.47 (s, –
OCH3, 3H), 3.36 (s, –OCH3, 3H).13C NMR (101 MHz, C6D6): δ
142.5, 142.2, 135.6, 134.1, 133.9, 133.7, 133.5, 131.4 (d, J = 6.6
Hz), 130.8, 129.5, 129.3, 122.6, 120.5, 119.5, 115.6, 104.0, 103.9
(d, J = 13.0 Hz), 103.98, 55.4 (–OCH3), 55.2 (–OCH3). 31P NMR
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10.1002/cctc.201900265
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FULL PAPER
(162 MHz, C6D6): δ -35.99. Anal. calcd. for C26H23O3P: C, 75.35;
Hz), 120.06, 119.25 (d, J = 8.2 Hz), 117.20 (qd, J = 31.1, 2.0 Hz,
–CF3), 104.29 (d, J = 9.8 Hz), 55.39 (–OCH3), 55.16 (–OCH3). 31
P
H, 5.59. Found: C, 75.41; H, 5.64.
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-6-F-C6H3OH
(2b).
NMR (162 MHz, C6D6): δ -38.57. 19F NMR (376 MHz, C6D6): δ -
61.93. Anal. calcd. for C27H22F3O3P: C, 67.22; H, 4.60. Found: C,
67.27; H, 4.52.
Following a procedure similar to that for ligand 2a, using 2-F-
C6H4OTHP instead of C6H5OTHP, ligand 2b was obtained in yield
of 57 wt%. 1H NMR (400 MHz, C6D6): δ 7.44–7.39 (m, 1H), 7.37–
7.32 (m, 1H), 7.28 (m, 2H), 7.10 (t, J = 8.3 Hz, 1H), 7.00 (m, 4H),
6.80 (dd, J = 9.5, 1.4 Hz, 2H), 6.43 (td, J = 8.0, 4.6 Hz, 1H), 6.35-
6.32 (m, 2H), 6.28 (d, J = 8.3 Hz, 1H), 3.23 (s, –OCH3, 3H), 3.06
(s, –OCH3, 3H).1H NMR (400 MHz, DMSO-d6): δ 9.65 (s, –OH,
1H), 7.38–7.28 (m, 4H), 7.24 (t, J = 8.3 Hz, 2H), 7.17–7.01 (m,
4H), 6.91 (ddd, J = 7.7, 3.6, 1.4 Hz, 1H), 6.72 (tdd, J = 8.0, 4.8,
1.0 Hz, 1H), 6.59 (dd, J = 8.3, 4.9 Hz, 2H), 6.33 (dd, J = 7.5, 3.9
Hz, 1H), 3.47 (s, –OCH3, 3H), 3.38 (s, –OCH3, 3H). 13C NMR (101
MHz, C6D6): δ 158.45, 158.15, 152.77, 150.37, 147.45 (dd, J =
20.0, 11.2 Hz), 142.86, 142.51, 135.70 (dd, J = 16.9, 6.9 Hz),
134.64–133.42 (m), 131.83 (d, J = 6.5 Hz), 129.88, 129.63,
129.09, 126.75 (d, J = 12.3 Hz), 120.40 (d, J = 5.7 Hz), 119.74 (d,
J = 8.0 Hz), 117.00 (d, J = 18.1 Hz), 104.35 (d, J = 4.6 Hz), 55.50(–
OCH3), 55.12(–OCH3). 31P NMR (162 MHz, C6D6): δ -33.23 (d, J
= 8.7 Hz). 19F NMR (376 MHz, C6D6): δ -136.77 (d, J = 8.7 Hz).
Anal. calcd. for C26H22FO3P: C, 72.22; H, 5.13. Found: C, 72.03;
H, 5.20.
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-6-Ph-C6H3OH
(2f).
Following a procedure similar to that for ligand 2a, using 2-Ph-
C6H4OTHP instead of C6H5OTHP, ligand 2f was obtained in yield
of 53 wt%. 1H NMR (400 MHz, C6D6): δ 7.65–7.59 (m, 2H), 7.54
(dd, J = 8.2, 4.7 Hz, 1H), 7.41–7.31 (m, 3H), 7.29–7.10 (m, 10H),
6.78 (t, J = 7.5 Hz, 2H), 6.30 (dd, J = 10.3, 8.4 Hz, 2H), 3.16 (s, –
OCH3, 3H), 3.09 (s, –OCH3, 3H). 1H NMR (400 MHz, DMSO-d6):
δ 8.28 (s, –OH, 1H), 7.47–7.21 (m, 12H), 7.17 (dt, J = 7.4, 1.3 Hz,
1H), 7.15–7.08 (m, 3H), 6.98 (dd, J = 7.6, 2.6 Hz, 1H), 6.87 (t, J =
7.6 Hz, 1H), 6.65–6.55 (m, 3H), 3.50 (s, –OCH3, 3H), 3.39 (s, –
OCH3, 3H). 13C NMR (101 MHz, C6D6): δ 158.39, 158.19, 156.72,
156.52, 142.66, 142.33, 139.04 (d, J = 3.62), 136.14, 136.06,
136.03, 134.11–133.92(m), 132.44, 131.78 (d, J = 6.5 Hz), 129.98,
129.66 (d, J = 9.5 Hz, 5H), 128.91, 127.15, 123.70, 104.13 (d, J
= 9.0 Hz), 55.30 (–OCH3), 55.09 (–OCH3). 31P NMR (162 MHz,
C6D6): δ -35.52. Anal. calcd. for C32H27O3P: C, 78.35; H, 5.55.
Found: C, 78.25; H, 5.48.
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-6-C6F5-C6H3OH (2g).
A
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-6-CH3-C6H3OH
(2c).
flask was charged with complex 1a (1.8 g, 3.6 mmol) and 20 mL
of dry THF, cooled to 0 oC and a solution of nBuLi in hexane (2.4
M, 1.5 mL, 1.2 equivalents) was added dropwise. The formed
Following a procedure similar to that for ligand 2a, using 2-CH3-
C6H4OTHP instead of C6H5OTHP, ligand 2c was obtained in yield
1
o
of 45 wt%. H NMR (400 MHz, C6D6): δ 7.51 (ddd, J = 7.7, 4.2,
suspension was cooled to -50 C, followed by slow addition of
1.0 Hz, 1H), 7.37–7.27 (m, 3H), 7.11 (t, J = 8.3 Hz, 1H), 7.07–7.02
(m, 1H), 7.01–6.94 (m, 5H), 6.77 (d, J = 8.7 Hz, 1H), 6.69 (t, J =
7.5 Hz, 1H), 6.31 (dd, J = 26.2, 8.3 Hz, 2H), 3.23 (s, –OCH3, 3H),
3.06 (s, –OCH3, 3H), 2.28 (s, 3H, –CH3). 1H NMR (400 MHz,
DMSO-d6): δ 8.33 (s, –OH, 1H), 7.42–7.18 (m, 6H), 7.07 (dddd, J
= 15.9, 7.2, 4.8, 1.8 Hz, 4H), 6.92 (ddd, J = 7.7, 3.5, 1.4 Hz, 1H),
6.66 (t, J = 7.5 Hz, 1H), 6.58 (dd, J = 8.3, 2.2 Hz, 2H), 6.38 (ddd,
J = 7.8, 4.1, 1.7 Hz, 1H), 3.45 (s, –OCH3, 3H), 3.40 (s, –OCH3,
3H), 2.13 (s, –CH3, 3H).13C NMR (101 MHz, C6D6): δ 158.47,
158.16, 158.14, 157.96, 142.71, 142.37, 136.19, 136.12, 136.00
(d, J = 2.5 Hz), 134.10 (d, J = 1.7 Hz), 134.04, 133.85, 132.48,
132.18 (d, J = 2.1 Hz), 131.70 (d, J = 6.6 Hz), 129.74, 129.57,
128.47, 128.41, 128.00, 124.59 (d, J = 1.5 Hz), 121.97 (d, J = 6.0
Hz), 120.56 (d, J = 1.6 Hz), 119.70 (d, J = 8.0 Hz), 104.25, 104.09,
hexafluorobenzene (3.3 g, 18 mmol, 5 equivalents). After reaction
overnight, volatiles was removed by a rotary evaporator, and the
obtained residue was dissolved in degassed ethyl acetate. Few
drops of hydrochloric acid was added slowly. After stirring for 5 h,
the protected group was completely removed monitoring by TLC.
Resultant mixture was quenched by aqueous NaHCO3, and then
extracted with ethyl acetate. Organic phase was dried in
anhydrous magnesium sulfate, and concentrated by a rotary
evaporator. Pure target compound 2g was obtained by column
chromatography (petroleum ether/ethyl acetate = 15/1) as white
solids (1.5 g, 75 wt%). 1H NMR (400 MHz, C6D6): δ 7.45 (ddd, J =
7.6, 4.2, 1.0 Hz, 1H), 7.35–7.24 (m, 3H), 7.23–7.13 (m, 4H), 7.23–
7.06 (m, 5H), 7.10 (t, J = 8.4 Hz, 1H), 7.06–6.95 (m, 5H), 6.92 (d,
J = 7.9 Hz, 1H), 6.92 (d, J = 7.9 Hz, 1H), 6.73 (t, J = 7.6 Hz, 1H),
6.73 (t, J = 7.6 Hz, 1H), 6.35 (d, J = 8.3 Hz, 1H), 6.27 (d, J = 8.3
Hz, 1H), 3.19 (s,–OCH3, 3H), 3.06 (s, –OCH3, 3H). 1H NMR (400
MHz, DMSO-d6): δ 8.98 (s, –OH, 1H), 7.42–7.18 (m, 7H), 7.10 (m,
3H), 6.97 (dd, J = 8.0, 3.4 Hz, 1H), 6.92 (t, J = 7.6 Hz, 1H), 6.72–
6.64 (m, 1H), 6.60 (d, J = 8.4 Hz, 2H), 3.45 (s, –OCH3, 3H), 3.38
(s, –OCH3, 3H).13C NMR (101 MHz, C6D6): δ 158.37, 158.02,
157.37, 157.16, 146.06, 142.78, 142.45, 136.12, 135.09, 135.02,
134.05, 133.87, 133.04, 131.87 (d, J = 6.6 Hz), 130.14, 129.77,
128.72, 128.65, 124.47 (d, J = 9.3 Hz), 120.74, 119.45 (d, J = 8.1
Hz), 113.71, 104.31 (d, J = 11.3 Hz), 55.39 (–OCH3), 55.15 (–
OCH3). 31P NMR (162 MHz, C6D6): δ -36.13. 19F NMR (376 MHz,
C6D6): δ -140.36 (ddd, J = 100.8, 23.8, 8.0 Hz), -156.46 (t, J =
21.5 Hz), -163.35 – -163.72 (m). Anal. calcd. for C32H22F5O3P: C,
55.34 (–OCH3), 55.10 (–OCH3), 16.54 (d, J = 2.7 Hz, –CH3). 31
P
NMR (162 MHz, C6D6): δ -36.61. Anal. calcd. for C27H25O3P: C,
75.69; H, 5.88. Found: C, 75.55; H, 5.84.
2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-6-CF3-C6H3OH
(2d).
Following a procedure similar to that for ligand 2a, using 2-CF3-
C6H4OTHP instead of C6H5OTHP, ligand 2d was obtained in yield
of 42 wt%. 1H NMR (400 MHz, C6D6): δ 7.40–7.27 (m, 3H), 7.25
(d, J = 7.9 Hz, 1H), 7.22–7.11 (m, 3H), 7.09 (t, J = 8.4 Hz, 1H),
7.00–6.93 (m, 4H), 6.45 (t, J = 7.7 Hz, 1H), 6.28 (dd, J = 18.3, 8.3
Hz, 2H), 3.15 (s, –OCH3, 3H), 3.06 (s, –OCH3, 3H). 1H NMR (400
MHz, DMSO-d6): δ 9.24 (s, –OH, 1H), 7.52 (dd, J = 7.9, 1.7 Hz,
1H), 7.45–7.21 (m, 6H), 7.10 (dddd, J = 23.8, 7.2, 4.6, 2.4 Hz, 3H),
7.03–6.89 (m, 3H), 6.64 (d, J = 8.4 Hz, 1H), 6.55 (d, J = 8.4 Hz,
1H), 3.56 (s, –OCH3,3H), 3.28 (s, –OCH3,3H).13C NMR (101 MHz, 66.21; H, 3.82. Found: C, 66.11; H, 3.74.
C6D6): δ 158.27 (d, J = 0.8 Hz), 157.94 (d, J = 1.1 Hz), 157.78 (d,
J = 1.6 Hz), 157.56 (d, J = 1.6 Hz), 142.76, 142.42, 138.16, 134.85
(d, J = 1.1 Hz), 134.77, 134.70, 133.87, 133.72 (d, J = 1.7 Hz),
133.69, 131.89 (d, J = 6.8 Hz), 130.17, 129.88, 128.71, 128.64,
128.42, 126.04 (d, J = 2.7 Hz), 125.49, 125.39, 123.33 (d, J = 2.7
2-(2-(2’,6’-F2-C6H3)-C6H4)(Ph)P-6-tBu-C6H3OH
(2h).
The
synthetic procedure was similar to that for ligand 2a, except using
2-tBu-C6H4OTHP instead of C6H5OTHP. Note that the reaction of
2-bromo-2’,6’-difluorobiphenyl (2.7 g, 10 mmol) with nBuli was
carried out at -78 °C. 2h was obtained as withe solids in yield of
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10.1002/cctc.201900265
ChemCatChem
FULL PAPER
1
63 wt%. H NMR (400 MHz, C6D6): δ 7.37–7.32 (m, 1H), 7.28–
[6-CH3-2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H3O]Ni(Me)(Py)
(3c). Following the general procedure, complex 3c was prepared
from the reaction of Py2NiMe2 (0.12 g, 0.5 mmol, 1.2 equivalents)
with ligand 2c (0.17 g, 0.4 mmol) as a yellow solid (0.21 g, 89
wt%). 1H NMR (400 MHz, C6D6): δ 8.46 (d, J = 4.0 Hz, 2H), 7.69
(dt, J = 12.3, 8.5 Hz, 3H), 7.47 (dd, J = 7.0, 4.5 Hz, 1H), 7.27 (t, J
= 8.4 Hz, 1H), 7.24-7.29 (m, 1H), 7.17-7.12 (m, 3H), 7.03–6.93
(m, 8H (5H, toluene, 3H, Ar-H)), 6.81 (t, J = 6.6 Hz, 1H), 6.66–
6.45 (m, 4H), 6.37 (d, J = 8.3 Hz, 1H), 3.39 (s, 3H, –OCH3), 3.03
(s, 3H, –OCH3), 2.37 (d, J = 14.4 Hz, 3H), -0.87 (dd, J = 65.8, 4.2
Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ 175.5, 175.3 159.7,
158.4, 150.6, 141.7, 141.57, 137.9, 137.3, 136. 8, 136.1, 134.6,
133.4 (d, J = 9.2 Hz), 133.2, 132.8 (d, J = 9.5 Hz), 132. 6, 130.0
(d, J = 2.0 Hz), 129.7 (d, J = 1.1 Hz), 129.3, 129.2, 128.8 (d, J =
2.1 Hz), 126.7 (d, J = 6.6 Hz), 126.37 (d, J = 9.6 Hz), 125.7, 123.1,
120.2 (d, J = 5.1 Hz), 119.3, 118.8, 113.5 (d, J = 7.5 Hz), 103.2
(d, J = 23.0 Hz), 54.95(–OCH3), 54.17 (–OCH3), 17.5 (–CH3), -
13.9 (d, J = 37.1 Hz, Ni–CH3). 31P NMR (162 MHz, C6D6): δ 21.27.
Anal. calcd. for C33H32NNiO3P: C, 68.30; H, 5.56; N, 2.41. Found:
C, 68.22; H, 5.43; N, 2.34.
[6-CF3-2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H3O]Ni(Me)(Py)
(3d). Following the general procedure, complex 3d was prepared
from the reaction of Py2NiMe2 (0.12 g, 0.5 mmol, 1.2 equivalents)
with ligand 2d (0.19 g, 0.4 mmol) as a brown solid (0.22 g, 86
wt%). 1H NMR (400 MHz, C6D6): δ 8.41 (s, broad, 2H), 7.66–7.50
(m, 4H), 7.43 (dd, J = 6.7, 4.5 Hz, 1H), 7.32 (t, J = 8.3 Hz, 1H),
7.22–7.18 (m, 1H), 7.12 (t, J = 3.7 Hz, 1H), 7.08–6.91 (m, 5H),
6.83–6.72 (m, 1H), 6.50 (d, J = 8.3 Hz, 3H), 6.31 (dd, J = 12.6,
7.8 Hz, 2H), 3.36 (s, 3H, –OCH3), 3.08 (s, 1H, –OCH3), -0.77 (d,
J = 5.1 Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ 159.46,
158.25, 150.51, 141.91 (d, J = 17.2 Hz), 136.51, 136.07, 135.94,
135.44, 134.45, 133.61 (d, J = 9.3 Hz), 132.67 (d, J = 9.6 Hz),
132.03, 131.52, 130.35 (d, J = 2.0 Hz), 130.06 (d, J = 4.8 Hz),
129.57, 129.34, 129.18 (d, J = 1.8 Hz), 128.58 (d, J = 2.5 Hz),
128.50, 126.80 (d, J = 6.8 Hz), 125.70, 125.20, 124.71, 123.22,
119.65 (d, J = 5.3 Hz), 119.65 (d, J = 5.3 Hz), 112.07 (d, J = 6.9
Hz), 103.52, 103.25, 54.96 (–OCH3), 54.46 (–OCH3), -14.07 (d, J
= 37.6 Hz, Ni–CH3). 31P NMR (162 MHz, C6D6): δ 19.92. 19F NMR
(376 MHz, C6D6): δ -62.39. Anal. calcd. for C33H29F3NNiO3P: C,
62.49; H, 4.61; N, 2.21. Found: C, 62.43; H, 4.56; N, 2.18.
[6-Ph-2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H3O]Ni(Me)(Py)
(3f). Following the general procedure, complex 3f was prepared
from the reaction of Py2NiMe2 (0.12 g, 0.5 mmol, 1.2 equivalents)
with ligand 2f (0.20 g, 0.4 mmol) as a yellow solid (0.23 g, 90 wt %).
1H NMR (400 MHz, C6D6): δ 8.38 (dd, J = 4.9, 1.6 Hz, 2H), 7.97–
7.93 (m, 2H), 7.68 (m, 3H), 7.50–7.43 (m, 2H), 7.32–7.26 (m, 3H),
7.20 (d, J = 7.4 Hz, 2H), 7.14–6.95 (m, 10H), 6.83 (t, J = 7.6 Hz,
1H), 6.62 (td, J = 7.4, 1.9 Hz, 1H), 6.56–6.46 (m, 2H), 6.34 (d, J =
9.0 Hz, 2H), 3.38 (s, 3H, –OCH3), 3.01 (s, 3H, –OCH3), -0.75 (d,
J = 5.0 Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ 173.7 (d, J
= 21.2 Hz), 159.7, 158.3, 150.8, 141.9, 141.7, 136.7, 136.3, 134.5,
133.5 (d, J = 9.3 Hz), 132.8, 132.7, 132.5 (d, J = 5.2 Hz), 131.9,
130.1, 129.7, 129.6, 129.3, 129.0, 126.8 (d, J = 6.5 Hz), 125.8,
125.7, 123.0, 122.4, 121. 9, 120.0 (d, J = 5.2 Hz), 114.2 (d, J =
7.4 Hz), 103.4, 103.1, 54.9 (–OCH3), 54.6 (–OCH3), -14.1 (d, J =
36.8 Hz, Ni–CH3).31P NMR (162 MHz, C6D6): δ 21.28. Anal. calcd.
for C38H34NNiO3P: C, 71.05; H, 5.34; N, 2.18. Found: C, 71.97; H,
5.26; N, 2.04.
7.24 (m, 3H), 7.12–7.06 (m, 1H), 7.06–7.00 (m, 2H), 6.99–6.92
(m, 5H), 6.73 (t, J = 7.6 Hz, 1H), 6.70–6.63 (m, 1H), 6.52 (td, J =
8.4, 5.3 Hz, 2H), 1.45 (s, –C(CH3)3, 9H).13C NMR (101 MHz,
C6D6): δ 162.04 (d, J = 7.0 Hz), 161.59 (d, J = 7.1 Hz), 159.61,
159.16, 159.09, 159.05, 158.83, 137.26 (d, J = 3.8 Hz), 136.15,
135.60, 135.30, 134.46 (d, J = 1.8 Hz), 133.88, 133.66 (d, J = 7.8
Hz), 133.39, 131.37 (d, J = 5.7 Hz), 130.14 (t, J = 10.0 Hz), 129.47
(d, J = 4.8 Hz), 129.20 , 129.05–128.73 (m), 120.93 (d, J = 1.7
Hz), 120.44 , 118.62 (dd, J = 21.1, 7.5 Hz), 111.59 (d, J = 3.4 Hz),
111.50–111.30 (m), 111.20 (d, J = 3.5 Hz), 35.14 (d, J = 1.9 Hz,
–C(CH3)3), 29.83 (–C(CH3)3). 31P NMR (162 MHz, C6D6): δ -39.06
(t, J = 24.4 Hz). 19F NMR (376 MHz, C6D6): δ -110.38 (dd, J = 24.5,
4.8 Hz), -110.54 (dd, J = 24.5, 4.8 Hz). Anal. calcd. for
C28H25F2OP: C, 75.32; H, 5.64. Found: C, 75.38; H, 5.74.
General procedure for synthesis of nickel complexes. In a 50-
mL flask, Py2NiMe2 (0.15 g, 0.6 mmol, 1.2 equivalents) was
dissolved in 10 mL of dry toluene, a solution of respective
phosphino-phenolate ligand 2a-h in 15 mL of dry toluene was
slowly added under vigorous stirring at room temperature. After
reaction for 6 h, a black suspension was yielded. The suspension
was filtered to remove the black nickel. The red-brown filtrate was
concentrated to give crude product. Pure complex was obtained
by recrystallization from toluene/hexane.
[2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H4O] Ni(Me)(Py) (3a).
Following the general procedure, complex 3a was prepared from
the reaction of Py2NiMe2 (0.15 g, 0.6 mmol, 1.2 equivalents) with
ligand 2a (0.21 g, 0.5 mmol) as a yellow solid (0.23 g, 80 wt%).
1H NMR (400 MHz, C6D6): δ 8.43 (s, 2H), 7.78–7.60 (m, 3H),
7.49–7.46 (m, 1H), 7.37–7.32 (m, 1H), 7.08–6.96 (m, 8H), 6.62 (d,
J = 8.3 Hz, 1H), 6.55 (t, J = 7.3 Hz, 1H), 6.47–6.44 (m, 2H), 6.39
(d, J = 8.3 Hz, 1H), 3.39 (s, 3H, –OCH3), 3.13 (s, 3H, –OCH3), -
0.78 (d, J = 5.0 Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ
177.08, 159.81, 158.45, 141.81, 134.69, 133.47 (d, J = 9.2 Hz),
133.24 (d, J = 10.5 Hz), 132.74, 132.65, 132.07, 131.29, 130.77,
130.06, 126.74 (d, J = 6.6 Hz), 118.82 (d, J = 9.5 Hz), 113.53,
103.46, 103.18, 54.97 (–OCH3), 54.56(–OCH3), -14.00 (d, J =
36.8 Hz, Ni–CH3). 31P NMR (162 MHz, C6D6): δ 21.09. Anal. calcd.
for C32H30NNiO3P: C, 67.88; H, 5.34; N, 2.47. Found: C, 67.74; H,
5.44; N, 2.35.
[6-F-2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H3O]Ni(Me)(Py)
(3b). Following the general procedure, complex 3b was prepared
from the reaction of Py2NiMe2 (0.15 g, 0.6 mmol, 1.2 equivalents)
with ligand 2b (0.21 g, 0.5 mmol) as a yellow solid (0.22 g, 75
wt%). 1H NMR (500 MHz, C6D6): δ 8.45 (d, J = 4.1 Hz, 2H), 7.74–
7.55 (m, 3H), 7.44 (dd, J = 7.2, 4.5 Hz, 1H), 7.28–7.17 (m, 1H),
7.12–6.88 (m, 7H), 6.74 (t, J = 7.0 Hz, 1H), 6.58 (d, J = 8.3 Hz,
1H), 6.52–6.39 (m, 2H), 6.37 (d, J = 8.3 Hz, 1H), 6.35–6.25 (m,
1H), 3.38 (s, 1H, –OCH3), 3.15 (s, 1H, –OCH3), -0.78 (d, J = 5.1
Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ 159.66, 158.38,
150.58, 141.82 (d, J = 22.5 Hz), 136.35, 135.93–135.64 (m),
134.43, 133.51 (d, J = 8.5 Hz), 132.71 (d, J = 9.5 Hz), 132.07,
130.22, 129.45, 129.08, 127.19–126.49 (m), 124.77, 124.28,
123.34, 119.98, 117.39 (d, J = 18.0 Hz), 112.58, 103.60, 103.19,
54.98 (–OCH3), 54.39 (–OCH3), -13.90 (d, J = 37.5 Hz, Ni–CH3).
31P NMR (162 MHz, C6D6): δ 20.80 (d, J = 12.6 Hz). 19F NMR (376
MHz, C6D6): δ -137.77 (d, J = 12.4 Hz). Anal. calcd. for
C32H29FNNiO3P: C, 65.79; H, 5.00; N, 2.40. Found: C, 65.63; H,
5.07; N, 2.32.
[6-C6F5-2-(2-(2’,6’-(MeO)2-C6H3)-C6H4)(Ph)P-C6H3O]Ni(Me)(Py)
(3g). Following the general procedure, complex 3g was prepared
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10.1002/cctc.201900265
ChemCatChem
FULL PAPER
from the reaction of Py2NiMe2 (0.12 g, 0.5 mmol, 1.2 equivalents)
with ligand 2g (0.23 g, 0.4 mmol) as a reddish brown solid (0.26
g, 90 wt%). 1H NMR (500 MHz, C6D6): δ 8.31–8.20 (m, 2H), 7.64–
7.55 (m, 3H), 7.45 (ddd, J = 7.7, 4.5, 1.1 Hz, 1H), 7.35 (ddd, J =
9.4, 7.6, 1.7 Hz, 1H), 7.24–7.16 (m, 2H), 7.16–7.13 (m, 1H), 7.05–
6.92 (m, 4H), 6.74 (t, J = 7.6 Hz, 1H), 6.59–6.45 (m, 4H), 6.34 (d,
J = 8.0 Hz, 1H), 3.34 (s, 3H, –OCH3), 3.09 (s, 3H, –OCH3), -0.79
(d, J = 5.2 Hz, 3H, Ni–CH3). 13C NMR (101 MHz, C6D6): δ 173.43
(d, J = 21.3 Hz), 159.60, 158.33, 150.45, 141.87, 136.47, 134.80,
134.36, 134.13, 133.59 (d, J = 9.6 Hz), 132.44 (d, J = 9.6 Hz),
131.89, 130.37, 129.49, 129.11, 126.80 (d, J = 6.0 Hz), 123.10,
122.87, 122.39, 119.79 (d, J = 5.3 Hz), 115.18 (d, J = 10.5 Hz),
113.23 (d, J = 7.6 Hz), 103.37 (d, J = 31.0 Hz), 54.95 (–OCH3),
54.12 (–OCH3), -14.31 (d, J = 36.5 Hz, Ni–CH3). 31P NMR (162
MHz, C6D6): δ 20.39. 19F NMR (376 MHz, C6D6): δ -137.89 (dd, J
= 24.3, 7.7 Hz), -140.07 (dd, J = 24.5, 7.7 Hz), -159.95 (t, J = 21.4
Hz), -164.23–-166.63 (m). Anal. calcd. for C38H29F5NNiO3P: C,
62.33; H, 3.99; N, 1.91. Found: C, 62.24; H, 4.03; N, 1.83.
added under vacuum. A solution of certain amount nickel complex
in 10 mL of toluene or naphthane was quickly injected into the
reactor through a dry syringe under vigorous stirring. And then,
the reactor was quickly filled in ethylene and kept at required
pressure. After reaction for a desired period, stirrer was stopped,
and the remaining ethylene was allowed to exhaust. The resultant
polymer was filtered, washed several times with ethanol, and
dried in a vacuum drying oven for 8 h at 70 °C.
Copolymerization Procedure. For all the copolymerization
experiments, a 100-mL steel autoclave charged with a magnetic
stirrer maintained at required temperature after heating under
vacuum for 6 h at 130 °C. The autoclave was purged three times
with ethylene before 30 mL of toluene added under ethylene
atmosphere. A solution of comonomer in 10 mL of toluene and
fresh catalyst solution in 10 mL of toluene were added in
sequence under ethylene atmosphere. Ethylene was quickly filled
in the autoclave and kept at required pressure. After the
prescribed reaction time, the stirrer was stopped, and the
remaining ethylene was allowed to exhaust. The solid copolymer
was collected by filtration after precipitation from ethanol or
methanol, washed with acetone, dried in a vacuum drying oven
for 8 h to constant weight at 70 °C.
[6-tBu-2-(2-(2’,6’-F2-C6H3)-C6H4)PhP-C6H3O]Ni(Me)(Py)
(3h).
Following the general procedure, complex 3h was prepared from
the reaction of Py2NiMe2 (0.12 g, 0.5 mmol, 1.2 equivalents) with
ligand 2h (0.18 g, 0.4 mmol) as a yellowish brown solid (0.21 g,
1
90 wt%). H NMR (400 MHz, C6D6): δ 8.45 (d, J = 5.2 Hz, 2H),
7.82 (ddt, J = 10.1, 6.8, 1.6 Hz, 2H), 7.55 (t, J = 8.6 Hz, 1H), 7.32
(d, J = 7.2 Hz, 1H), 7.18–7.14 (m, 2), 7.11–7.00 (m, 4H), 6.94 (t,
J = 7.6 Hz, 1H), 6.84–6.76 (m, 2H), 6.69 (dt, J = 16.8, 8.2 Hz, 2H),
6.59 (td, J = 7.4, 2.2 Hz, 1H), 6.52–6.44 (m, 2H), 1.54 (s, 9H), –
0.53 (dd, J = 4.9, 2.8 Hz, 3H). 13C NMR (101 MHz, C6D6): δ 175.23
(d, J = 21.1 Hz), 163.14 (d, J = 6.9 Hz), 162.06 (d, J = 6.7 Hz),
160.65 (d, J = 7.3 Hz), 159.60 (d, J = 6.9 Hz), 150.65, 137.88 (d,
J = 9.2 Hz), 136.48, 135.29 (d, J = 15.5 Hz), 134.60, 134.48,
134.33 (d, J = 2.7 Hz), 134.13, 133.98, 133.43, 133.33, 132.62 (d,
J = 8.3 Hz), 130.75, 130.09, 129.77, 129.68, 129.58, 129.47,
128.72, 128.63, 128.21, 127.94, 123.17, 119.17, 118.66, 113.92
(d, J = 7.8 Hz), 111.77 (dd, J = 22.2, 3.4 Hz), 111.13 (dd, J = 22.1,
3.3 Hz), 35.16 (–C(CH3)3), 29.81 (–C(CH3)3), -13.50 (dd, J = 36.3,
3.4 Hz, Ni–CH3). 31P NMR (162 MHz, C6D6): δ 24.68. 19F NMR
(376 MHz, C6D6): δ -110.12 (dd, J = 26.6, 5.4 Hz), -110.51 (dd, J
= 22.1, 5.2 Hz). Anal. calcd. for C34H31F2NNiOP: C, 68.37; H, 5.23.
Found: C, 68.25; H, 5.14.
Synthesis of polyethylene glycol monomethyl ether acrylate
macromonomer. A 100 mL vial was charged with acrylic acid
(11.9 g, 0.165 mmol), polyethylene glycol monomethyl ether (Mn
= 350, 21 g, 0.600 mmol) and hydroquinone (0.32 g, 0.003 mmol).
The reaction system was heated up to 80 °C, p-toluenesulfonic
acid (0.34 g, 1 wt%) as catalyst was added. After reacted for 7 h
at 130 °C, reaction mixture was disolved in dichloromethane,
washed with sodium hydroxide dilute solution two times, and then
washed with water three times. Organic layer was collected, dried
in anhydrous sodium sulfate and concentrated by a rotary
evaporator. Pure target macromonomer was obtained by column
Acknowledgements
The authors are grateful for subsidy provided by the National
Natural Science Foundation of China (No. 21690071 and
21574097).
Keywords: catalyst design • electronic structure • ligand effects
• nickel • polymerization
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Entry for the Table of Contents
FULL PAPER
Newly synthesized bulky nickel
complexes are thermally robust, and
exhibits very high activity (up to 107
Yanping Zhang, Hongliang Mu, Xuling
Wang, Li Pan,* Yuesheng Li*
g·molNi−1·h−1)
in
ethylene
Page No. – Page No.
polymerization even at 120 °C, and
these complexes bearing electron-
withdrawing substituents on ortho-
phenoxy position or electron-
donating substituents on phosphorus
atom show higher activity than
contrastive catalyst toward ethylene
polymerization and ethylene–methyl
acrylate (MA) copolymerization.
Elaborate Tuning in Ligand Makes
Big
Differences
in
Catalytic
Performance: Bulky Nickel Catalysts
for (Co)polymerization of Ethylene
with
Promising
Vinyl
Polar
Monomers
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