Vinyl polymerizations of norbornene catalyzed by nickel complexes with acetoacetamide ligands

Article abstract of DOI:10.1002/aoc.3067

On the basis of a remote effect, a series of acetoacetamide ligands and corresponding nickel complexes N-(R-phenyl) acetoacetamide Ni(CH₂Ph) (PMe₃) (R = H, 1; R = 2-methyl, 2; R = 2,6-dimethyl, 3; R = 2,6-diisopropyl, 4; R = 4-NO₂, 5) were synthesized and characterized. The solid structure of complex 3 was confirmed by X-ray single-crystal analysis to be of cis form. ¹H and ³¹P NMR spectroscopy confirmed that cis and trans isomers of nickel complexes were present in solution. Norbornene polymerizations with acetoacetamide nickel complexes activated with modified methylaluminoxane (MMAO) were investigated in detail. Remote steric and electronic effects of acetoacetamide ligand on catalytic activity and molecular weight of polynorbornenes (PNBs) were observed. Characterizations of the obtained PNBs show that the obtained polymer products are non-crystalline vinylic-addition polynorbornenes. Copyright

Full text of DOI:10.1002/aoc.3067

Full Paper
Received: 12 July 2013
Revised: 19 August 2013
Accepted: 23 August 2013
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3067
Vinyl polymerizations of norbornene catalyzed
by nickel complexes with acetoacetamide
ligands
Qian Fenga,b, Dajun Chena*, Danyang Fenga, Libin Jiaoa, Zhigang Pengc
and Lixia Peid
On the basis of a remote effect, a series of acetoacetamide ligands and corresponding nickel complexes N-(R-phenyl)
acetoacetamide Ni(CH2Ph) (PMe3) (R = H, 1; R = 2-methyl, 2; R = 2,6-dimethyl, 3; R = 2,6-diisopropyl, 4; R = 4-NO2, 5) were
synthesized and characterized. The solid structure of complex 3 was confirmed by X-ray single-crystal analysis to be of cis
form. 1H and 31P NMR spectroscopy confirmed that cis and trans isomers of nickel complexes were present in solution.
Norbornene polymerizations with acetoacetamide nickel complexes activated with modified methylaluminoxane (MMAO)
were investigated in detail. Remote steric and electronic effects of acetoacetamide ligand on catalytic activity and molecular
weight of polynorbornenes (PNBs) were observed. Characterizations of the obtained PNBs show that the obtained polymer
products are non-crystalline vinylic-addition polynorbornenes. Copyright © 2013 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: norbornene; acetoacetamide; nickel catalyst; vinyl polymerization
polymerization.[36,38] In this paper, we synthesized novel [O,O]
acetoacetamide ligands and corresponding nickel complexes,
Introduction
Olefin polymerization based on late-transition-metal catalysts has
been one of the most exciting developments in the area of
catalysis, organometallic chemistry and polymer science in recent
years.[1–3] Interest in polymers of cyclic olefins such as
norbornene (NB) (bicyclo[2.2.1]hept-2-ene) has increased
dramatically because of the attractive properties of this addition
type of polymer such as high chemical resistance, good UV
resistance, low dielectric constant, high glass transition
temperature, excellent transparency, large refractive index and
low birefringence.[4–10] Up to now, vinyl-addition polymerization
of norbornene has been reported using many transition metal
catalysts, including Ti,[11,12] Zr,[13,14] Fe,[15] Ni,[15–21] Pd,[22–24]
Co,[25,26] Cu[27–30] and Cr.[31,32] Janiak and Bao have given a full
literature and patent account on the work describing the
addition polymerization of norbornene.[33,34] Among these
catalysts, late transition metal catalysts (Ni and Pd) exhibited
especially high activity.[33] It is known that the polynorbornenes
(PNBs) catalyzed by palladium-based catalysts are usually
insoluble in common solvents,[22,24,33] whereas those obtained
by-nickel based catalysts are soluble in chlorohydrocarbons.[15–21]
Therefore, nickel-based catalysts show great potential for
application in norbornene homopolymerization.
and studied their catalytic properties toward norbornene
polymerization. The influence of polymerization parameters such
as polymerization temperature and Al/Ni molar ratio on
norbornene polymerization with acetoacetamide nickel catalysts
was examined in detail. More importantly, remote steric and
electronic effects on catalytic activity and molecular weight of
the produced polymer were observed, which provides visible
access to facilely tuning steric and electronic effects of [O,O]
acetylacetone type ligand.
Experimental
All manipulations involving air- and moisture-sensitive
compounds were carried out under an atmosphere of dried and
purified nitrogen with standard vacuum line, Schlenk or glovebox
techniques.
*
Correspondence to: Dajun Chen, College of Chemistry and Chemical
Engineering, Southwest Petroleum University, Chengdu 610500, China. Email:
swpuchendajun@126.com
a College of Chemistry and Chemical Engineering, Southwest Petroleum
Currently, nickel complexes bearing chelate [N,O] and [N,N]
ligands are mostly synthesized and applied for norbornene
polymerization.[18–21,26–29] Compared to these two types of
ligand, [O,O] ligand has rarely been used to coordinate nickel
for norbornene polymerization because of the difficultly in
modifying features for steric and electronic effects.[35–39] Indeed,
the reported literature has addressed that nickel catalyst bearing
[O,O] ligands can also show very high activity toward norbornene
University, Chengdu 610500, China
b Institute of Oil Production Technology, Shengli Oilfield, Dongying 257000,
China
c
Institute of Drilling Technology, Shengli Oilfield, Dongying 257000, China
d School of Chemistry and Chemical Engineering, South China University of
Technology, Guangzhou 510641, China
Appl. Organometal. Chem. 2014, 28, 32–37
Copyright © 2013 John Wiley & Sons, Ltd.

Polymerization of norbornene with acetoacetamide nickel
Materials
Synthesis of Ligand
Toluene, THF and hexane were dried over sodium metal and
distilled under nitrogen. Dichloromethane and chlorobenzene
were dried and distilled from calcium hydride. Ethyl acetoacetate
was purchased from Alfa Aesar. 2,6-Diisopropylaniline (90%;
Aldrich) and 2,6-dimethylaniline (97%; Aldrich) were distilled
prior to use. Norbornene (bicyclo-[2.2.1]hept-2-ene; Acros) was
purified by distillation over potassium and used as a solution in
chlorobenzene. Modified methylaluminoxane (MMAO; 7 wt% Al
in heptane) was purchased from Akzo-Nobel and used as
received. (η1-CH2Ph)NiCl(PMe3)2 was synthesized according to a
previous method.[40] Other commercially available reagents were
purchased and used without purification.
Acetoacetanilide ligands were prepared by condensation
reaction of substituted anilines with ethyl acetoacetate by the
microwave irradiation method. Ethyl acetoacetate (5.20 g), the
desired amount of substituted amines (1.2 equiv.) and a catalytic
amount of potassium tert-butoxide were added to the tube and
the reaction was irradiated in a domestic microwave oven. After
1 h, the reaction mixture was cooled and triturated with ice-cold
ether. The product separated was filtered, washed with small
portions of ice-cold ether and dried. Purification by recrystalliza-
tion from ethanol afforded a colorless or yellow crystalline solid.
L1, L2 and L5 are known compounds and characterization data
can be seen in the supporting information.
N-Phenyl acetoacetamide (L1)
Norbornene Polymerization
4.46 g aniline was used in the reaction. Yield 5.88 g, 83%.
N-(2-Methylphenyl) acetoacetamide (L2)
In a typical procedure, the appropriate MMAO solution was
introduced into a chlorobenzene solution of norbornene in a
50 ml round-bottom glass flask. Chlorobenzene and nickel
complex solution were syringed into the well-stirred solution in
order, and the total reaction volume was kept at 25 ml. The
reaction was continuously stirred for 20 min at polymerization
temperature. Polymerization was terminated by addition of acidic
methanol (methanol–HCl, 90:10). The resulting precipitated
polymer was collected and treated by filtering, washing with
methanol several times and drying under vacuum at 60 °C to
constant weight.
5.14 g 2-methylaniline was used in the reaction. Yield 6.19 g, 81%.
N-(2,6-Dimethylphenyl) acetoacetamide (L3)
5.81 g 2,6-dimethylaniline was used in the reaction. Yield 6.48 g,
79%. IR (KBr): 3290 (N―H), 3062 (C―H, Ph), 1775 (C O amide),
1
1587 (C O) cmÀ1. H NMR (CDCl3, 400 MHz), δ (ppm): 9.12 (s, 1H,
CO―NH), 7.16 (m, 1H, 4-H on Ph), 7.09 (m, 2H, 3,5-H on Ph),
3.65 (s, 2H, CH2), 2.35 (s, 3H, CO―CH3), 2.21 (s, 3H, Ph―CH3).
13C NMR (CDCl3, 100 MHz), δ (ppm): 205.3 (CH3C O), 166.2
(HN―C O), 133.6 (1-C on Ph), 131.2 (2,6-C on Ph), 127.9 (3,5-C
on Ph), 126.1 (4-C on Ph), 50.0 (CH2), 31.3 (CH3―CO), 18.6
(CH3―Ph). EI-MS (m/z): 206 [M+]. Anal. Calcd for C12H15NO2: C,
70.22; H, 7.37; N, 6.82%. Found: C, 70.08; H, 7.25; N, 6.70%.
Characterization
Elemental analyses were performed on a Vario EL microanalyzer.
Electron impact (EI) mass spectra were obtained with a Shimazu
1
LCMS-2010A instrument. H, 13C and 31P NMR spectra of ligands
N-(2,6-Diisopropylphenyl) acetoacetamide (L4)
and complexes were obtained using
a Bruker 400 MHz
instrument at room temperature in CDCl3 or benzene-d6. 1H
NMR and 13C NMR spectra of PNBs in o-dichlorobenzene-d4 were
recorded on a Bruker 500 MHz spectrometer. Analysis by gel
permeation chromatography (GPC) of the molecular weight and
molecular weight distribution (MWD) of the PNBs was performed
using a PL-GPC 220 instrument with standard polystyrene as
the reference and with 1,2,4-trichlorobenzene (TCB) as the
eluent at 150 °C. FT-IR spectra were recorded on a Nicolet Nexus
670 FT-IR spectrometer. Differential scanning calorimetry (DSC)
analysis was conducted with a PerkinElmer DCS-7 system. The
DSC curve was recorded at a heating rate of 10 °C minÀ1. The
cooling rate was 10 °C minÀ1. TGA data was measured with a
TG-290C thermal analysis system instrument under a nitrogen
atmosphere up to 600 °C with heating rate of 10 °C minÀ1. A
wide-angle X-ray diffraction (WAXD) curve of the polymer pow-
der was obtained using a D/Max-IIIA powder X-ray diffractometer.
8.50 g 2,6-diisopropylaniline was used in the reaction. Yield
7.41 g, 71%. IR (KBr): 3298 (N―H), 3071 (C―H, Ph), 1780 (C O
amide), 1562 (C O) cmÀ1 1H NMR (CDCl3, 400 MHz), δ (ppm):
.
10.60 (s, 1H, CO―NH), 7.21–7.14 (m, 3H, Ph), 3.35 (s, 2H, CH2),
3.16 (sp, J = 7.6 Hz, 2H, CH), 2.36 (s, 3H, CO―CH3), 1.24–1.19 (d,
J = 7.6 Hz 24H, CH3). 13C NMR (CDCl3, 100 MHz), δ (ppm): 205.4
(CH3C O), 166.5 (HN―C O), 144.9 (2,6-C on Ph), 131.8 (1-C on Ph),
125.1 (4-C on Ph), 123. 6 (3,5-C on Ph), 50.4 (CH2), 31.4 (CH3―CO),
28.3 (CH), 23.5 (CH3―Ph). EI-MS (m/z): 217 [M+]. Anal. Calcd for
C16H23NO2: C, 73.53; H, 8.87; N, 5.36%. Found: C, 73.46; H, 8.76; N,
5.50%.
N-(4-Nitrophenyl) acetoacetamide (L5)
6.62 g 2-nitroaniline was used in the reaction. Yield 4.80 g, 54%.
Synthesis of nickel complex
Ligand was dissolved in 20 ml THF in a flame-dried Schlenk flask,
and a desired amount of KH (1.1 equiv.) was added. After 4 h, the
solution was obtained by filtration and (η1-CH2Ph)NiCl(PMe3)2
was added. The mixture was stirred at room temperature
overnight, and the crude reaction mixture was followed by
filtration to remove inorganic salt under nitrogen. The solution
was evaporated to low volume under vacuum and then n-hexane
(20:1) was added. Solvent was removed from the precipitate
via cannula filtration, and the residual solid was washed with
n-hexane (3 × 5 ml). Drying under vacuum afforded the desired
nickel complex. The nickel complex was dissolved in hot
Crystal Structure Determination
Crystal data obtained with the ω-2θ scan mode were collected on
a
Bruker SMART 1000 CCD diffractometer with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 293 K. The
structure was solved using direct methods, while further
refinements with full-matrix least squares on F2 were obtained
with the SHELXTL program package. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were introduced
in calculated positions with the displacement factors of the host
carbon atoms.
Appl. Organometal. Chem. 2014, 28, 32–37
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

Q. Feng et al.
hexane/toluene solvents and cooled in a freezer for several days
to afford the product as brown crystals.
Calcd for C26H38NNiO2P: C, 64.22; H, 7.88; N, 2.88%. Found: C,
64.54; H, 7.94; N, 3.03%.
Nickel complex 1
Nickel complex 5
The general procedure was employed with 0.885 g ligand L1,
0.22 g KH and 1.68 g (η1-CH2Ph)NiCl(PMe3)2 to afford 1.64 g
(82%) of the desired complex 1. H NMR (C6D6, 400 MHz, 20 °C):
The general procedure was employed with 1.11 g ligand L5,
0.22 g KH and 1.68 g (η1-CH2Ph)NiCl(PMe3)2 to afford 0.96 g
(52%) of the desired complex 5. H NMR (C6D6, 400 MHz, 20 °C):
1
1
7.76 (d, J = 8.0 Hz, 2H, 2,6-H on Ph, major), 7.29–6.78 (m, 8H, Ph,
major + minor), 5.30 (s, 1H, NH, minor), 5.01 (s, 1H, NH, minor),
4.64, (s, 1H, CH, major), 4.31(s, 1H, CH, major), 2.32 (s, 3H, CO―Me,
major), 2.14 (s, 3H, CO―Me, minor), 1.70 (s, 2H, CH2Ph, major),
1.58 (s, 2H, CH2Ph, minor), 0.74 (d, J = 8.0 Hz, 9H, P(Me)3, major),
0.43 (d, J = 8.0 Hz, 9H, P(Me)3, minor). 31P NMR (C6D6, 162 MHz,
20 °C): À72.1, À75.0. The ratio of cis to trans complex was ~1/1.
EI-MS (m/z): 403, 402, 401, 325, 177. Anal. Calcd For
C20H26NNiO2P: C, 59.74; H, 6.52; N, 3.48%. Found: C, 59.60; H,
6.68; N, 3.50%.
7.80 (d, J = 8.0 Hz, 2H, 2,6-H on Ph, major), 7.26–6.74 (m, 8H, Ph,
major + minor), 5.38 (s, 1H, NH, minor), 5.12 (s, 1H, NH, minor),
5.09, (s, 1H, CH, major), 4.72(s, 1H, CH, major), 4.36 (s, 1H, CH,
major), 2.40 (s, 3H, CO―Me, major), 2.32 (s, 3H, CO―Me, minor),
1.86 (s, 2H, CH2Ph, major), 1.72 (s, 2H, CH2Ph, minor), 0.80
(d, J = 8.0 Hz, 9H, P(Me)3, major), 0.51 (d, J = 8.0 Hz, 9H, P(Me)3,
minor).31P NMR (C6D6, 162 MHz, 20 °C): À72.5, À75.7. The ratio
of cis to trans complex is ~1/1. EI-MS (m/z): 449, 448, 447, 371,
222. Anal. Calcd for C20H26N2NiO4P: C, 53.61; H, 5.85; N, 6.25%.
Found: C, 53.17; H, 5.93; N, 6.48%.
Nickel complex 2
Results and Discussion
The general procedure was employed with 0.955 g ligand L2,
0.22 g KH and 1.68 g (η1-CH2Ph)NiCl(PMe3)2 to afford 1.66 g
(80%) of the desired complex 2. H NMR (C6D6, 400 MHz, 20 °C):
Synthesis of Nickel Complex and Molecular Structure
1
7.75 (d, J = 8.0 Hz, 2H, 2,4-H on Ph, major), 7.30–6.80 (m, 6H, Ph,
major + minor), 5.31 (s, 1H, NH, minor), 5.04 (s, 1H, NH, minor),
4.72, (s, 1H, CH, major), 4.40 (s, 1H, CH, major), 2.26 (s, 3H,
CO―Me, major), 2.18 (s, 3H, CH3Ph, minor), 2.10 (s, 3H, CO―Me,
minor), 1.96 (s, 3H, CH3Ph, major), 1.73 (s, 2H, CH2Ph, major), 1.60
(s, 2H, CH2Ph, minor), 0.75 (d, J = 8.0 Hz, 9H, P(Me)3, major), 0.42
(d, J = 8.0 Hz, 9H, P(Me)3, minor). 31P NMR (C6D6, 162 MHz, 20 °C):
À72.0, À74.9. The ratio of cis to trans complex was ~5/4. EI-MS
(m/z): 418, 417, 416, 340, 191. Anal. Calcd for C21H29NNiO2P: C,
60.47; H, 7.01; N, 3.36%. Found: C, 60.72; H, 7.25; N, 3.28%.
Previously, acetoacetanilide ligands have been synthesized by
conventional methods under the condition of reflux of
solvent.[41–43] Herein, the microwave irradiation method without
any solvents was used to prepare the target product. The
reaction was performed in a microwave oven for 1 h. In
comparison with the conventional method, there are many
virtues of microwave irradiation reaction, including no solvent,
high isolated yield, short time and easy work-up. Two new
acetoacetanilide ligands L2 and L3 were synthesized by the
microwave irradiation method, but L1, L4 and L5 compounds
were reported previously. The structures of ligand L1, L4 and
L5 were confirmed by comparing their 1H and 13C NMR with
those found in the literature.[41–43] Ligands L2 and L3 were fully
characterized by FT-IR, 1H and 13C NMR, EI-MS and elemental
analysis (EA).
Nickel complex 3
The general procedure was employed with 1.03 g ligand L3,
0.22 g KH and 1.68 g (η1-CH2Ph)NiCl(PMe3)2 to afford 1.69 g
1
(79%) of the desired complex 3. H NMR (C6D6, 400 MHz, 20 °C):
7.74 (d, J = 8.0 Hz, 2H, 3,5-H on Ph, major), 7.31–6.82 (m, 4H, Ph,
major + minor), 5.33 (s, 1H, NH, minor), 5.06 (s, 1H, NH, minor),
4.83, (s, 1H, CH, major), 4.52 (s, 1H, CH, major), 2.18 (s, 3H,
CO―Me, major), 2.10 (s, 6H, CH3Ph, minor), 2.04 (s, 3H, CO―Me,
minor), 1.94 (s, 6H, CH3Ph, major), 1.75 (s, 2H, CH2Ph, major), 1.62
(s, 2H, CH2Ph, minor), 0.75 (d, J = 8.0 Hz, 9H, P(Me)3, major), 0.41
(d, J = 8.0 Hz, 9H, P(Me)3, minor). 31P NMR (C6D6, 162 MHz, 20 °C):
À72.0, À74.8. The ratio of cis to trans complex was ~3/2. EI-MS
(m/z): 431, 430, 429, 354, 205. Anal. Calcd for C22H30NNiO2P: C,
61.43; H, 7.03; N, 3.26%. Found: C, 61.64; H, 7.14; N, 3.19%.
After the obtained ligands were treated with KH in THF,
(η1-CH2Ph)NiCl(PMe3)2 was added to the solution and corre-
sponding nickel complexes were obtained in good yields
(Scheme 1). New nickel complexes bearing acetoacetamide
ligands were characterized by EA and NMR. Note that two
isomers of nickel complexes are present in solution on the basis
of two sets of resonances in 1H NMR spectroscopy (see
Experimental section), which is a result of the orientation of the
η1-benzyl and phosphine ligands. The 31P NMR spectrum also
revealed two PMe3 signals, which further supports the presence
of cis and trans isomers in solution (Scheme 1).[40] A clear
tendency is that the ratio of cis isomer to trans isomer increases
(1/1, 5/4, 3/2, 2/1) with an increase in the steric hindrance of
the aniline moiety from H atoms to 2,6-diisopropyl groups (1 to
4), which may be attributed to a steric effect. However, introduc-
tion of an electron-withdrawing nitro group on the aryl ring has
no influence on the ratio of cis isomer to trans isomer in solution.
A crystal of complex 3 suitable for X-ray diffraction analysis was
obtained by slow diffusion of n-hexane into nickel complex
solution in CH2Cl2. The molecular structure of the nickel complex
supports the O,O-bound connectivity pattern deduced from
NMR analysis in solution. Data collection and refinement data
are summarized in Table 1. The ORTEP diagram of complex 3 is
shown in Fig. 1, along with selected bond lengths and
bond angles. The nickel complex 3 adopts a slightly distorted
Nickel complex 4
The general procedure was employed with 1.08 g ligand L4,
0.22 g KH and 1.68 g (η1-CH2Ph)NiCl(PMe3)2 to afford 1.65 g
1
(68%) of the desired complex 4. H NMR (C6D6, 400 MHz, 20 °C):
7.72 (d, J = 8.0 Hz, 2H, 3,5-H on Ph, major), 7.35–6.86 (m, 6H, Ph,
major + minor), 5.65 (s, 1H, NH, major), 5.37 (s, 1H, NH, minor),
5.03, (s, 1H, CH, major), 4.61 (s, 1H, CH, minor), 3.25 (sp,
J = 7.6 Hz, 2H, CH(Me3)2, major), 2.93 (sp, J = 7.6 Hz, 2H, CH(Me3)2,
minor), 2.04 (s, 3H, CO―Me, major), 1.77 (s, 2H, CH2Ph, major),
1.64 (s, 2H, CH2Ph, minor), 1.45 (s, 3H, CO―Me, minor),
1.16–1.02 (m, 12H, CH(CH3)2 major + minor), 0.75 (d, J = 8.0 Hz,
9H, P(Me)3, major), 0.41 (d, J = 8.0 Hz, 9H, P(Me)3, minor). 31P
NMR (C6D6, 162 MHz, 20 °C): À71.8, À74.6. The ratio of cis to trans
complex was ~2/1. EI-MS (m/z): 487, 486, 485, 409, 261. Anal.
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 32–37

Polymerization of norbornene with acetoacetamide nickel
Scheme 1. Synthesis of acetoacetamide nickel complex.
Table 1. Crystal data and structure refinement for nickel complex 3
Figure 1. ORTEP plots of complex 3. Hydrogen atoms are omitted for
clarity. Selected bond distances (Å) and angles (°): Ni―O(1), 1.9090(14);
Ni―O(2), 1.9042(15); Ni―C(13), 1.957(2); Ni―P, 2.1467(7); O(1)―Ni―O
(2), 92.97(6); O(1)―Ni―C(13), 88.72(8); O(2)―Ni―C(13), 169.87(9); O(1)
―Ni―P, 169.94(5); O(2)―Ni―P, 87.02(5); C(13)―Ni―P, 93.05(7).
Empirical formula
C22H30NNiO2P
430.15
Formula weight
Crystal system
Tetragonal
P4(3)
Space group
a (Å)
12.4576(16)
12.4576(16)
14.424(4)
b (Å)
Table 2. Norbornene polymerizations with nickel complexes 1–5/
MMAO under various conditionsa
c (Å)
α (°)
β (°)
γ (°)
90
c
Entry Catalyst
Tp
(°C)
Al/Ni
(mol/mol)
Activityb
Mn
Mw/Mn
90
90
Volume (Å3)
Z
2238.5(7)
1
1
1
1
1
2
3
3
3
3
4
4
4
4
4
4
4
5
0
25
50
75
50
0
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
500
8.9
14.3
26.2
23.1
32.8
9.6
384
432
315
257
362
438
526
401
287
471
683
506
348
495
585
257
388
2.62
2.36
2.14
2.53
2.12
2.54
2.28
2.09
2.46
2.43
2.26
2.06
2.39
1.94
2.04
3.78
2.44
4
2
D (calc.) (g cmÀ3
F (000)
)
1.276
3
912
4
Crystal size (mm)
θ range (°)
Index ranges
0.36 × 0.25 × 0.22
2.16–26.75
À15 ≤ h ≤ 15
À15 ≤ k ≤ 15
À17 ≤ l ≤ 18
15 000/4539
[R(int) = 0.0223]
98.2 %
5
6
7
25
50
75
0
25.3
45.6
38.5
12.2
34.7
68.1
52.4
21.0
54.1
48.9
43.9
8
9
Reflections collected/unique
10
11
12
13
14
15
16
17
25
50
75
50
50
50
50
Data completeness
Data/restraints/parameters
Goodness-of-fit on F2
4539/ 1/251
1.039
Final R indices [I > 2σ (I)]
R indices (all data)
Largest diff. peak and hole (e ÅÀ3
R1 = 0.0263, wR2 = 0.0664
R1 = 0.0279, wR2 = 0.0677
0.200, À0.184
1500
3500
2500
)
aPolymerization conditions: reaction time, t = 20 min; Ni catalyst
addition, 1 μmol; co-catalyst, MMAO; norbornene addition, 4 g;
solvent, 25 ml chlorobenzene. À1
square-planar coordination geometry around the nickel center
with a cis relationship between PMe3 group and the carboxamide
oxygen. Because of the conjugate effect of the acetoacetate ring,
the two bond lengths of O―Ni are similar (Ni―O1, 1.9090 Å;
Ni-O2, 1.9042 Å). The PMe3 ligand is tilted 11.3° out of the six-
membered chelate plane, while the benzyl group is tilted
9.3° out of the chelate ring.
bIn units of 106 g PNB (mol Ni h)
.
cIn units of kg molÀ1, determined by high-temperature GPC.
an important role in the catalytic performances. Under the
same polymerization conditions, complex
4 with N-2,6-
diisopropylphenyl groups shows the highest activity, up to
68.1 × 106 g PNB (mol Ni h)À1, while complex 1 with N-phenyl
groups exhibits the lowest activity. This result clearly supports a
positive steric effect on catalytic activity for norbornene polymer-
ization, although the bulky substituent on the N-aryl moiety is
remote from the nickel center. Compared with 1, electron-
deficient complex 5 with NO2 can exhibit a higher catalytic
activity for norbornene polymerization. This result shows that a
Norbornene Polymerization
A series of norbornene polymerizations were carried out using
acetoacetamide nickel catalyst precursors 1, 2, 3, 4 and 5 under
various conditions (Table 2). In the presence of MMAO, five
nickel complexes 1–5 exhibited very high activities for
norbornene polymerization. Figure 2 demonstrates that
remote steric characteristic of the acetoacetamide ligand plays
a
Appl. Organometal. Chem. 2014, 28, 32–37
Copyright © 2013 John Wiley & Sons, Ltd.
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Q. Feng et al.
remote electronic effect can also work on the nickel active center
for norbornene polymerization. Currently, [O,O] ligands are rarely
used to coordinate nickel for olefin polymerization because this
type of ligand is hardly modified from steric and electronic
effects. Our study herein provides a visible access to tuning steric
and electronic effects of [O,O] acetylacetone type ligand by a
remote effect. Besides, the steric characteristic of the chelate
ligand has the same tendency to influence the molecular weight
of the obtained PNB (Fig. 2). The highest molecular weight of the
produced polymer is achieved using complex 4/MMAO catalytic
system under the same conditions, suggesting that a remote
effect can suppress the occurrence of chain transfer/termination.
The reaction temperature also strongly affects catalytic activity,
and the results of norbornene polymerizations using 1, 3, 4/
MMAO at various temperatures are summarized in Table 2. For
1, 3 and 4/MMAO catalytic systems, the lowest catalytic activities
are observed when the reaction temperature is 0 °C. With an
increase in reaction temperature, the catalytic activity obviously
increases. Three nickel complexes show the highest activity
for norbornene polymerization at 50 °C. A higher temperature
(75 °C) causes a decrease in the catalytic activity for norbornene
polymerization because of the instability or decomposition of
the active species. Therefore, the optimum polymerization
temperature is 50 °C. The polymerization temperature also
affects the molecular weights of the obtained polymers. A
basic tendency is observed for the Mn value of the obtained
polymer to increase, and then decrease with an increase in
the reaction temperature. When polymerizations are carried
out at 25 °C, the highest molecular weights of the obtained
PNB are observed. Further increasing the temperature to 75°C
leads to decreasing molecular weight, suggesting that chain
transfer or termination begins to accelerate above 25 °C.
Influence of Al/Ni molar ratio is typically investigated using the
4/MMAO catalytic system at a fixed temperature of 50 °C, and the
results are summarized in Table 2 (entries 12 and 14–16). When
the Al/Ni molar ratio is 500, a low activity for norbornene
polymerization is observed. With an increase in Al/Ni molar ratio
from 500 to 3500, the catalytic activity for norbornene polymeri-
zation increases and then decreases. An optimum Al/Ni molar
ratio is 2500 for 4/MMAO catalytic systems. Moreover, Al/Ni molar
ratio also influences the molecular weight of the obtained PNB.
With an increase in Al/Ni molar ratio, the molecular weight of
PNB increases and then decreases. When the Al/Ni molar ratio
is 1500, the highest molecular weight is observed. This result
suggests that excess MMAO (Al/Ni > 1500) gives rise to easy
chain transfer.
Figure 2. Influence of catalyst structure on norbornene polymerization
with nickel complexes 1–5/MMAO. Polymerization conditions: catalyst
addition, 1 μmol; Al/Ni = 2500; polymerization temperature, 50 °C; reaction
time, t = 20 min; norbornene addition, 4 g; solvent, 25 ml chlorobenzene.
Polynorbornene Characterizations
All of the obtained PNBs catalyzed by acetoacetamide nickel
catalytic systems are soluble in organic solvents such as
chlorobenzene, 1,2-dichlorobenzene and 1,2,4-trichlorobenzene,
which is consistent with previous observations.[18,19,21] The FT-IR
spectrum of PNB (Fig. 3) clearly shows no traces of double bond,
which is present at 1680–1620, 966 and 735 cmÀ1. A vibration
band of bicyclics of the norbornene unit is clearly observed at
941 cmÀ1, proving that the obtained PNB is a vinyl-addition
polymer.
Figure 3. FT-IR spectrum of PNB (entry 12).
Figure 4. 1H and 13C NMR spectra of PNB (entry 12).
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Polymerization of norbornene with acetoacetamide nickel
1
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As showed in Fig. 4(a), the H NMR spectrum of PNB is in a
range of chemical shift from 0.5 to 3.0 ppm, and no traces of
any double bond at 5.0–7.0 ppm are observed. The absence of
double bond further supports the occurrence of vinyl-type
polymerization rather than ring-opening metathesis polymeriza-
tion. The 13C NMR spectrum (Fig. 4b) also further confirms that
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observed from 25 to 55 ppm. According to previous assignment
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appear at 28.5–33.0 ppm for C5 and C6, 35.0–38.0 ppm for C7,
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The DSC spectrum of the PNB cannot show well-defined
endothermic signals upon heating to the decomposition
temperature, and no glass transition temperature (Tg) of PNB
from DSC curve is observed. The TGA curve shows that the PNB
sample is stable up to 450 °C (see supporting information). The
WAXD analysis of the obtained PNB shows two major broad
peaks (2θ = 9–11° and 17–19°), which implies that the obtained
PNB is non-crystalline (see supporting information).
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In summary, a series of acetoacetamide nickel complexes has
been successfully synthesized and characterized. The solid
structure of complex 3 is confirmed by X-ray single-crystal
analysis to be a cis form, while there are two isomers in solution.
Acetoacetamide nickel complexes activated by MMAO are highly
active toward norbornene polymerization. Obvious steric and
electronic effects of acetoacetamide ligand on catalytic activity
and molecular weight for norbornene polymerization can be
observed, although substituents on the N-aryl moiety are remote
from the nickel center. Our study provides a visible access to
tuning steric and electronic effects of [O,O] acetylacetone type
ligand by a remote effect.
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Financial support by NSFC (Project 51206053) is gratefully
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CCDC 948848 contains the supplementary crystallographic data
for complex 3. The data can be obtained free of charge via
http://www.ccdc.cam.ac.uk, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Appl. Organometal. Chem. 2014, 28, 32–37
Copyright © 2013 John Wiley & Sons, Ltd.
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