Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins

Article abstract of DOI:10.1002/pola.23868

A series of vanadium(V) complexes bearing tetradentate amine trihydroxy ligands [NOOO], which differ in the steric and electronic properties, have been synthesized and characterized. Single crystal X-ray analysis showed that these complexes are five or si

Full text of DOI:10.1002/pola.23868

Vanadium(V) Complexes Containing Tetradentate Amine Trihydroxy
Ligands as Catalysts for Copolymerization of Cyclic Olefins
JI-QIAN WU,1,2 JING-SHAN MU,1,2 SEN-WANG ZHANG,1,2 YUE-SHENG LI1
1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun 130022, China
2Graduate School of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, China
Received 4 November 2009; accepted 5 December 2009
DOI: 10.1002/pola.23868
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A series of vanadium(V) complexes bearing tetra-
dentate amine trihydroxy ligands [NOOO], which differ in the
steric and electronic properties, have been synthesized and
characterized. Single crystal X-ray analysis showed that these
complexes are five or six coordinated around the vanadium
center in the solid state. Their coordination geometries are
octahedral or trigonal bipyramidal. In the presence of Et2AlCl,
these complexes have been investigated as the efficient cata-
lysts for ethylene polymerization and ethylene/norbornene
copolymerization at elevated reaction temperature and pro-
duced the polymers with unimodal molecular weight distribu-
tions (MWDs), indicating the single site behaviors of these
catalysts. Both the steric hindrance and electronic effect of the
groups on the tetradentate ligands directly influenced catalytic
activity and the molecular weights of the resultant (co)poly-
mers. Other reaction parameters that influenced the polymer-
ization behavior, such as reaction temperature, ethylene
pressure, and comonomer concentration, are also examined in
detail. Furthermore, high catalytic activities of up to 3.30 kg
polymer/mmolVꢀh were also observed when these complexes
were applied to catalyze the copolymerization of ethylene and
5-norbornene-2-methanol, producing the high-molecular-
weight copolymers (Mw
¼
157–400 kg/mol) with unimodal
MWDs (Mw/Mn ¼ 2.5–3.0) and high polar comonomer incorpo-
C
V
rations (up to 12.3 mol %).
2010 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 48: 1122–1132, 2010
KEYWORDS: catalysts; functional polymers; homogeneous catal-
ysis; polydentate ligands; polymerization; polyolefins; vana-
dium; Ziegler-Natta polymerization
INTRODUCTION One of the most exciting objects in the field
of transition metal catalysis, organometallic chemistry, and
polymer science in recent years has been the intensive inves-
tigation of olefin polymerization catalysts.1 Single-site and
well-defined catalysts have been extensively explored during
the last 2 decades to optimize polymer properties, resulting
in the establishment of the relationship between the nature
of catalysts and the features of the resultant polymers, and
thereby providing various opportunities to adjust the poly-
mer’s architecture.2 Among various classes of catalysts, vana-
dium catalysts have played a critically important role in pro-
ducing high-molecular-weight polymers with narrow
molecular weight distribution (MWD) as well as a-olefin or
cycloolefin copolymers with high comonomer incorpora-
tions.3 Nonetheless, the report on vanadium catalysts is lim-
ited owing to low activity, which is ascribed to their deacti-
vation during the polymerization, especially at high
polymerization temperature, due to reduction of catalytically
active vanadium species to low valent, less active, or inactive
species. In recent years, although a number of vanadium cat-
alysts have been studied,4–16 only a few reports regarding
highly active and well-defined vanadium catalysts were pub-
lished.4(c),7,11(a,d,e),13 Gambarotta and coworkers reported
that bis(imino)pyridine vanadium(III) complexes showed
high catalytic activity toward ethylene polymerization, but
produced bimodal MWD PEs.7(b) Gibson’s group found that
bis(benzimidazole)amine ligand can stabilize highly active
vanadium(III) and vanadium(V) catalysts for olefin polymeri-
zation.4(c) Nomura et al. investigated (arylimido)vanadium(V)
complexes containing aryloxide or phenoxyimine ligands as
the efficient catalysts for olefin polymerization.11 Redshaw
et al. applied vanadium(V) complexes with calixarene ligands
to catalyze ethylene (co)polymerization.13(c)
Despite the fact that some favorable vanadium catalysts have
been reported for promoting olefin polymerization, the
search for new vanadium catalysts that display excellent
thermal stability and generate polyolefins with high molecu-
lar weight (MW) and relative narrow MWD remains of keen
interest. It was proposed that ligand denticity played an im-
portant role in controlling the behavior of transition metal
catalysis.17–19 Previously, we found vanadium catalysts bear-
ing tridentate Schiff base ligands showed better thermal sta-
bility than the corresponding bidentate ligands chelated
Additional Supporting Information may be found in the online version of this article. Correspondence to: Y.-S. Li (E-mail: ysli@ciac.jl.cn)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1122–1132 (2010) 2010 Wiley Periodicals, Inc.
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ARTICLE
RESULTS AND DISCUSSION
Synthesis and Characterization of Oxovanadium(V)
Complexes
The tetradentate amine trihydroxy ligands 1a–d were pre-
pared via literature procedures by using a Mannich conden-
sation of the corresponding phenol with amine and formal-
dehyde (Scheme 1).20 A general synthetic route of the new
vanadium complexes used in this study is shown in Scheme
2. The reaction of ligands 1a–d with VO(OnPr)3 in dry
CH2Cl2 under dry argon at room temperature yielded com-
plexes 2a–d as deep-red crystalline solids in high yields
(76–98%). These complexes were identified by 1H, 13C, and
51V NMR, FTIR, mass spectra, and elemental analysis.
The crystals suitable for crystallographic study were grown
from the CH2Cl2–hexane mixture solution containing com-
pounds 2a–d, respectively, and their molecular structures
were further confirmed by X-ray crystallographic analyses.
The symmetry of 2a was higher than expected (rhombohe-
dral crystal system with R-3 space group). As shown in
Figure 1, binuclear complex 2a displayed a six-coordinate
distorted octahedral geometry around each V center, which
is surrounded by two ligands and is bound to each other by
two bridging O atoms (the isopropoxides arm), possessing a
dimeric structure. Attempt to isolate mononuclear species by
changing the recrystallization solvent was not successful,
probably because of the small steric hindrance of the two
isopropoxide arms. The bond lengths (see Fig. S1 in Support-
ing Information) between vanadium and bridged oxygen
SCHEME 1 General synthetic route of the tetradentate ligands.
ones.16(c) We thus are interested in investigating the vana-
dium catalysts bearing polydentate ligand, which efficiently
stabilize the active species and control over the MW and
MWD of the resultant polymer. Herein, we report the investi-
gation of versatile tetradentate amine trihydroxy ligands that
afford highly active catalysts for ethylene polymerization,
ethylene/norbornene, and ethylene/5-norbornene-2-metha-
nol copolymerizations when bound to vanadium(V).
SCHEME 2 General synthetic
route of the vanadium com-
plexes used in this study.
CATALYSTS FOR COPOLYMERIZATION OF CYCLIC OLEFINS, WU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 3 General synthetic route of the vanadium complex
used in this study.
careful examination of the X-ray structures of 2d reveals the
presence of weak intermolecular p–p contacts between two
phenol planes (Fig. S5). The planes defined by the benzene
rings are 3.606 Å apart, with a centroid–centroid distance of
3.706 Å.
FIGURE 1 Molecular structure of complex 2a. Thermal ellip-
soids are drawn at the 30% probability level and H atoms are
omitted for clarity.
Synthesis and Characterization of Imidovanadium(V)
Complex
(V(1)-O(3), 1.980(4) Å; V(1)-O(3A), 2.108(4) Å) are much
longer than those between vanadium and nonbridged oxygen
(V(1)-O(4), 1.846(4) Å). V(1)-N(1) bond distance of 2.335(5)
Å is somewhat shorter than those in the literature docu-
mented vanadium(V) amine tris(phenolate) complexes
(2.3765(14) and 2.4697(4) Å).13(b),19(a)
Tetradentate amine trihydroxy ligand 1a was deprotonated
by 3.0 equiv of NaH, followed by treating with 1.0 equiv of
VCl3(N-2,6-Me2C6H3)21 in Et2O at ꢂ30 ꢁC (Scheme 3). The
reaction product was isolated by recrystallization from a
ꢁ
mixture of Et2O and n-hexane at ꢂ30 C in glovebox. The X-
ray crystal structure of 3a was also determined. As shown in
Figure 3, the geometries at vanadium are approximately tri-
gonal bipyramidal with N-V-N as the axes. Noted that crystal
of 3a consists of two crystallographically different independ-
ent molecules in the unit cell (see Fig. S6 in Supporting In-
formation), in one molecule the N-aryl plane was almost in
parallel with the O-aryl plane in the tetradentate ligand,
whereas in the other one the N-aryl plane was almost verti-
cal to the O-aryl plane in the tetradentate ligand.
Pentacoordinate complexes 2b–d display distorted trigonal
bipyramidal geometry (Figs. 2 and S2–4 in Supporting Infor-
mation, respectively), with the oxo function occupying the
axial position, trans to the central nitrogen, as the evidence
from the OAVAN bond angle (O(1)-V(1)-N(1): 2b,
175.20(9)ꢁ) as well as the sum of bond angles around V
(e.g., in 2b: ca. 360ꢁ; O(2)-V(1)-O(3), 115.97(9)ꢁ; O(2)-V(1)-
O(4), 119.13ꢁ; O(3)-V(1)-O(4), 117.37(9)ꢁ). A comparison of
the V(1)-N(1) distances in the three structures shows that
2c has shorter V(1)-N(1) bond distance (2.408(3) Å com-
pared with 2.422(2) and 2.414(3) Å). The vanadyl VAO
bond lengths in 2d (1.595(3) and 1.606(3) Å) are longer
than the corresponding bond length in 2c (1.585(3) Å), high-
lighting the stronger electron donability of the OMe group in
comparison with the Me group on the phenols. In addition, a
FIGURE 2 Molecular structure of complex 2b. Thermal ellip-
soids are drawn at the 30% probability level and H atoms are
omitted for clarity.
FIGURE 3 Molecular structure of complex 3a. Thermal ellip-
soids are drawn at the 30% probability level and H atoms are
omitted for clarity.
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ARTICLE
TABLE 1 Ethylene Polymerization Catalyzed by 2a–d and 3aa
Activityb
Mw (kg/mol)
Mw/Mn
c
c
Entry
Catalyst (lmol)
Tp (ꢁC)
Al/V (molar ratio)
p (C2H4) (bar)
Polymer (g)
1
2a (0.5)
2b (0.5)
2c (0.5)
2c (0.2)
2c (0.2)
2c (0.2)
2c (0.2)
2c (0.5)
2c (0.5)
2c (0.5)
2c (0.5)
2c (0.5)
2d (0.5)
3a (0.5)
50
50
25
50
50
50
50
50
50
50
50
70
50
50
4,000
4,000
4,000
4,000
4,000
4,000
4,000
500
4.0
4.0
4.0
2.0
4.0
4.0
6.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
d
0.25
0.56
0.51
0.14
0.45
2.27
0.52
0.02
0.26
0.78
0.80
0.48
0.02
0.12
6.00
13.44
12.24
8.40
167
52.1
650d
305
2.4
2.6
2
3
4
2.7
3.0
5
6e
27.00
22.70
31.20
0.48
323
608d
460d
7
f
f
8
–
–
9
2,000
4,000
6,000
4,000
4,000
4,000
6.24
110
104
99.1
92.2
2.7
3.0
3.0
2.9
10
11
12
13
14
a
18.72
19.20
11.52
0.48
f
f
–
–
2.88
234
2.0
Conditions: toluene ¼ 50 mL, Al/V ¼ 4000 (mol/mol), ETA/V ¼ 300
Mv was measured in decalin at 135 ꢁC because polymer did not dis-
(molar ratio), polymerization 5 min.
b
solve in 1,2,4-trichlorobenzene.
e
Activity in kg polymer/(mmolVꢀh).
Polymerization 30 min.
c
f
GPC data in 1,2,4-trichlorobenzene versus polystyrene standard.
Not determined.
Ethylene Polymerization
ously when the vanadium(V) complexes were combined with
Oxovanadium(V) complexes 2a–d and imidovanadium(V)
complex 3a have been investigated as the effective catalysts
for ethylene polymerization in the presence of the cocatalyst
Et2AlCl and reactivating agent ethyl trichloroacetate (ETA).
The typical results are summarized in Table 1. We found
that ligand structure remarkably influenced catalytic activity
and polymer property. Under the similar conditions, the
higher activities were observed for complexes 2b and 2c,
which contain two aryloxides and one alkoxide, whereas the
lower activity was detected for complex 2a presumably
because of the higher electron-donating property of alkoxide
than aryloxide and the steric bulk of the ancillary ligands in
the oxo bridged structure. Higher MW polymers were pro-
duced by complex 2a, but not by complexes 2b and 2c, indi-
cating that chain transfer reactions were partly hindered in
the more crowded structure 2a. Compared with 2c, complex
2d exhibited much lower catalytic activity (0.48 kg PE/
mmolVꢀh), indicating that the ortho MeO group in the aryloxo
in the ligand is indispensable for high activity in this type of
catalyst. This result is different from the behavior of amine
tris(3,5-dimethylphenolate) vanadium(V) catalyst, which dis-
played high activity toward ethylene polymerization in the
presence of dimethylaluminum chloride and ETA.13(b)
Et2AlCl in the in situ NMR experiment.13(b,c)
We also observed a dependence of the catalytic activity of
complex 2c on the reaction parameters, such as reaction
temperature, ethylene pressure, catalyst and cocatalyst con-
centrations. The increase of ethylene pressure is beneficial to
productivities (entries 4, 5, and 7 in Table 1, from 8.40 to
31.2 kg PE/mmolVꢀh when ethylene pressure increases from
2 to 6 atm), and the MW of the resultant polymer was also
increased. The catalytic activity of 2c is found to be sensitive
to reaction temperature, with 50 ꢁC being the optimum.
However, the MW and MWD were only mildly influenced
when reaction temperature was elevated from 50 to 70 ꢁC,
indicating high thermal stability of the catalyst. Compared
with the Schiff base-chelated vanadium(III) previously
reported,16 catalyst 2c produced much higher MW polymers
at elevated reaction temperature. Both the catalytic activity
and the MW of resultant PEs were influenced by catalyst
concentration (entries 5 and 10). However, the MWDs of the
resultant PEs were independent of the catalyst concentration
used. Note that productivity was kept in high level (22.70 kg
ꢁ
PE/mmolVꢀh) in the 30-min polymerization at 50 C, suggest-
ing excellent thermal stability of the active species. As previ-
ously reported,11(a,d,e),13(c,d),16 cocatalyst dosage also played
an important role in the vanadium(V) catalytic systems stud-
ied. Although Al/V molar ratio remarkably influenced the
catalytic activity of 2c (entries 8–11 in Table 1), and the MW
and MWD of the PEs only slightly changed, which indicates
that the dominant chain transfer in this polymerization was
not chain transfer to Al. The dependence of the MW and
MWD of the PEs on monomer pressure (entries 4 and 5 in
Table 1) also indicates that the main chain transfer is not to
Al but to the monomer. This result was quite different from
Imidovanadium complex 3a bearing the same trihydroxy
ligand as oxovanadium complex 2a was less productive, but
produced polyethylenes with higher MW probably resulting
from the steric hindrance of aryl group (2,6-dimethylphenyl)
on the imido group. Similar result was reported in the O,N-
chelating aminophenolate vanadium catalysts system.8a It
should be noted that although the precursors are well
defined, the active species or the alkylation’s pass ways are
obscure because paramagnetic derivatives formed simultane-
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Copolymerization of Ethylene and Norbornene by 2a–d and 3aa
Activityb
NBE Contentc
Mw (kg/mol)
Mw/Mn
d
d
Entry
Cat. (lmol)
T (ꢁC)
NBE (mol/L)
Polymer (g)
1
2a (1.0)
2b (1.0)
2c (1.0)
2c (1.0)
2c (1.0)
2c (1.0)
2c (1.0)
2c (0.2)
2c (1.0)
2c (1.0)
2d (1.0)
3a (1.0)
50
50
50
50
50
50
50
50
25
70
50
50
0.5
0.5
0.1
0.3
0.5
0.7
0.9
0.9
0.5
0.5
0.5
0.5
0.30
2.32
1.43
2.08
2.73
2.27
1.51
0.42
0.52
1.88
0.02
0.17
1.80
13.9
8.58
12.5
16.4
13.6
9.06
12.6
3.12
11.3
0.12
1.02
15.1
17.9
5.50
10.5
15.7
20.4
22.3
22.9
9.78
17.8
210
235
132
301
341
248
207
183
396
93.8
2.1
2.8
3.0
2.8
2.5
2.0
1.7
1.8
9.5
2.3
2
3
4
5
6
7
8
9
10
11
12
a
e
e
e
–
–
–
12.3
292
1.8
c
Conditions: toluene þ comonomer ¼ 30 mL, ethylene ¼ 4 bar, coca-
talyst ¼ Et2AlCl, Al/V ¼ 4000 (molar ratio), ETA/V ¼ 300 (molar ratio),
10 min.
NBE content (mol %) estimated by 13C NMR spectra.
GPC data in 1,2,4-trichlorobenzene versus polystyrene standard.
Not determined.
d
e
b
Activity in kg polymer/(mmolVꢀh).
the vanadium(III)/Et2AlCl catalytic systems, which displayed
obvious chain transfer to Al.16 Other organoaluminum com-
pounds such as modified MAO, dry MAO, AlMe3, and AlEt3
were also tested as the cocatalyst in combination with com-
plex 2c. Only 2c/(modified MAO) system exhibited low activ-
ity (56 g PE/mmolVꢀh), and trace or even no polymer was
obtained using dry MAO, AlMe3, or AlEt3 as the cocatalyst.
decreased with the increase of NBE concentration. A steady
increase of NBE incorporations was observed when more
NBE was charged. Notably, there is a pronounced increase in
catalytic activity with increasing temperature from 25 to 50
ꢁC for catalytic system 2c/Et2AlCl, further elevating tempera-
ture to 70 ꢁC leading to slightly losing productivity. Similar
to the behavior of the tridentate Schiff base-chelated vana-
dium(III) catalysts, the MW of the resultant copolymers
obtained by 2c decreased with the elevation of reaction tem-
perature. Nevertheless, at high reaction temperature, catalyst
2c can produce much higher MW copolymers than vanadium
(III) catalysts (e.g., at 50 ꢁC, 2c, MW ¼ 341 kg/mol;
Copolymerization of Ethylene with Norbornene
As tetradentate amine trihydroxy vanadium(V) complexes
exhibited high catalytic activity for ethylene polymerization,
the copolymerizations of ethylene with norbornene (NBE) by
2a–d and 3a were thus explored. The typical results are
summarized in Table 2. As the ethylene polymerization, the
data listed in entries 1, 2, 5, 11, and 12 indicate that ligand
structure considerably affects the catalytic activity toward
the copolymerization. Under the same conditions, complex
2c showed the highest activity of 16.38 kg polymer/
mmolVꢀh, whereas complex 2d revealed the lowest activity of
0.12 kg polymer/mmolVꢀh. Imidovanadium complex 3a dis-
played slightly low catalytic activity than oxovanadium com-
plex 2a, but the MW of the resultant copolymer produced by
3a was higher than that obtained by 2a, indicating that
steric hindrance of aryl group (2,6-dimethylphenyl) on the
imido partly restrained the chain transfer reactions. Intro-
duction of an extra methyl group in the alkyloxide resulted
in the increase of both catalytic activity and the MW of the
copolymer produced, but a slight decrease of NBE incorpora-
tion (entry 2 vs. entry 5).
[OC6H4CH
¼
NCH2C5H4N]VCl2(THF), MW
¼
164 kg/
mol).16(c) The copolymer with broad MWD (Mw/Mn ¼ 9.5)
was obtained at 25 ꢁC, but surprisingly the MWD narrowed
with the increase of reaction temperature and unimodal
ꢁ
MWD can be available at 50 or 70 C (Mw/Mn ¼ 2.5 and 2.3,
respectively, GPC curves are listed as Fig. S7 in Supporting
Information). Much more NBE monomers were incorporated
into the polymer chain when the reaction temperature was
elevated from 25 to 70 ꢁC. The rational explanation is fol-
lowed: One is the higher barrier of NBE insertion than that
of ethylene insertion, and the another is that the copolymer-
ization was conducted at constant pressure of ethylene; the
increase of polymerization temperature caused the decrease
of ethylene concentration in the solution due to the decrease
in the partial pressure and the solubility of ethylene, which
also caused the increase of NBE content.
The microstructures of the copolymers have been investi-
gated by means of 13C NMR techniques (Fig. 4). It is found
that NBE was incorporated into polymer chains in an iso-
lated or alternating manner with a mixture of iso- and syn-
diotactic NBE configurations, and no NBE dyads (no peaks
at 33.5–35.0 ppm) were observed, which is similar to our
previous results.16(a,c) In contrast to the copolymer with 5.5
mol % NBE incorporation, an increase of the alternating
The effect of reaction conditions on the ethylene/NBE
copolymerization was also investigated using catalyst 2c. The
data listed in Table 2 indicate that catalytic activity, the
MWs, and MWDs of the resultant copolymers were directly
influenced by NBE concentration. The highest activity and
the highest MW copolymer appeared when 0.5 mol/L NBE
was in feed, whereas the MWDs of the resultant copolymers
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ARTICLE
FIGURE 4 13C NMR of ethyl-
ene/NBE copolymer using cat-
alyst 2c: (a) 5.5 mol % (entry 3)
and (b) 22.3 mol % (entry 7) in
Table 2.
sequences was observed with the sample of 22.3 mol % NBE
incorporated.
droxy-ligated vanadium(V) complexes in catalyzing the
copolymerization ethylene with polar norbornene derivative.
The steric protection of the functional group through alkyla-
luminum has been proved to be a successful method for the
prevention of catalyst deactivation.25 Herein, Et2AlCl was
chosen as both protecting agent and cocatalyst. The copoly-
merizations of ethylene with 5-norbornene-2-methanol (NB-
CH2OH) were carried out using vanadium(V) complexes 2a–
Copolymerization of Ethylene with 5-Norbornene-2-
methanol
Polyolefins with polar functional groups possess not only
modified surface properties, such as dyeability, adhesion, and
wettability, but also unique bulk properties.22 A number of
late transition metal catalysts have shown great potential to
catalyze the copolymerization of ethylene with polar como-
nomers and produce high MW functional polyolefins.23,24 In
contrast, reports on early transition metal catalysts are lim-
ited because they are typically oxophilic and thus are deacti-
vated in the presence of polar monomers.25 Considering va-
nadium possesses less oxophilic than group IV metals and
can efficiently catalyze ethylene/norbornene copolymeriza-
tion, we also explored the behaviors of the amine trihy-
c, 3a, and vanadium(III) complex
I
([OC6H4CH
¼
NCH2C5H4N]VCl2(THF)) as a comparison. The typical copoly-
merization results are summarized in Table 3. Under the
same conditions, complex 2b showed the highest activity
(3.30 kg polymer/mmolVꢀh) among the five complexes,
whereas the much lower catalytic activities were observed
when tetradentate phenol bialkanol amine ligand supported
complexes 2a and 3a were applied. Note that the catalytic
TABLE 3 Copolymerization of Ethylene and 5-Norbornene-2-methanol (NB-CH2OH) by 2a–d and 3aa
NB-CH2OH
(mol/L)
NB-CH2OH
Contentc
Activityb
Mw (kg/mol)
Mw/Mn
Tm (ꢁC)
d
d
e
Entry
Cat.
T (ꢁC)
Polymer (g)
1
2a
2b
2c
2c
2c
2c
3a
Ih
50
50
50
70
50
50
50
50
0.1
0.1
0.1
0.1
0.3
0.5
0.1
0.1
0.15
0.55
0.21
0.10
0.25
0.28
0.14
0.49
0.90
3.30
1.26
0.60
1.50
1.68
0.84
2.94
d
0.28
2.29
5.60
7.50
9.86
12.3
12.1
0.60
201
214
400
157
289
214
253
69.5
2.6
2.6
2.5
2.4
2.7
3.0
2.5
3.0
125.1
124.3
126.6
125.0
118.9
117.6
118.2
128.6
2
3
4
5f
6g
7
8
a
Conditions: toluene
þ
comonomer
¼
30 mL, ethylene
¼
4
bar,
GPC data in 1,2,4-trichlorobenzene versus polystyrene standard.
Determined by DSC.
e
f
catalyst ¼ 1.0 lmol, cocatalyst Et2AlCl ¼ 7 mmol, ETA/V ¼ 300 (molar
ratio), 10 min, 50 ꢁC.
Et2AlCl ¼ 13 mmol.
b
g
h
Activity in kg polymer/(mmolVꢀh).
Et2AlCl ¼ 19 mmol.
c
NB-CH2OH content (mol %) estimated by 1H NMR spectra.
I ¼ [OC6H4CH¼NCH2C5H4N]VCl2(THF).16(c)
CATALYSTS FOR COPOLYMERIZATION OF CYCLIC OLEFINS, WU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
higher comonomer incorporation (entries 3, 5, and 6, 5.60–
12.3 mol %), though the MW of the resultant copolymer
decreased (Mw from 400 to 214 kg/mol) and the MWD
slightly broadened (Fig. S8 in Supporting Information). In
addition, the copolymerization was also sensitive to reaction
temperature. The catalytic activity and the MW of the result-
ant copolymer decreased, but NB-CH2OH incorporation
increaꢁsed when reaction temperature was elevated from 50
to 70 C (entry 3 vs. entry 4).
FIGURE 5 1H NMR spectrum for the copolymer formed with
complex 2c (entry 6 in Table 3).
The ethylene/NB-CH2OH copolymers displayed melting tem-
perature in the range of 117.6–126.6 ꢁC, which was deter-
mined by means of DSC techniques at a heating rate of 10
ꢁC/min. All copolymers produced displayed single melting
temperature (see Supporting Information Figs. S9–11), indi-
cating that the components of the copolymers are homogene-
ous. These copolymers differ from those obtained by metal-
locene/MAO catalytic systems, which exhibit two melting
temperatures.25(c) The microstructures of the copolymers
have been investigated using NMR techniques (Figs. 5 and
6). The peak presented at 3.56 ppm in 1H NMR spectra is
assigned to ACH2OH, and the peaks at 67.37 and 64.84 ppm
in 13C NMR spectra indicate the exo and endo, respectively,
with regard to the ACH2OH substituent at the norbornene
backbone.25(d) These results represent the first examples of
vanadium(V) catalysts, which exhibit attractive performance
for the copolymerization of ethylene and functionalized
norbornene.
activities toward ethylene/NB-CH2OH copolymerization were
much lower than those toward ethylene/norbornene copoly-
merization by complex 2c under the similar conditions (e.g.,
entry 3 in Table 2 vs. entry 3 in Table 3), which presumably
because of the steric hindrance of the protecting group on
the NB-CH2OH. The GPC analyses reveal that the obtained
ethylene/NB-CH2OH copolymers display both high MWs (Mw
¼ 157–400 kg/mol) and unimodal MWDs (Mw/Mn ¼ 2.5–
3.0).
The data also show that the structure of the vanadium com-
plex considerably affects both comonomer incorporation and
the MW of the resultant copolymers. Much higher MW
copolymers with more NB-CH2OH incorporation were pro-
duced by complex 2c over complex 2b, indicating the influ-
ence of the methyl group on the alkoxide arm. A comparison
of the copolymers obtained by different vanadium catalysts
revealed that the copolymers produced by complex 3a dis-
played not only higher MW but also much higher incorpora-
tion than those by complex 2a, suggesting that the ancillary
effect of imido group. Noticeably, although high catalytic ac-
tivity toward the copolymerization was also observed by tri-
dentate vanadium(III) catalyst [OC6H4CH ¼ NCH2C5H4N]
VCl2(THF) as reported previously16(c) (entry 8), the MW and
the polar monomer content of the obtained copolymer were
much lower than those produced by vanadium(V) complexes
2b, 2c, or 3a, which indicates that the vanadium(V) com-
plexes are the more attractive catalysts for the copolymeriza-
tion of ethylene with functional norbornene.
CONCLUSIONS
We have synthesized and structurally characterized a series
of vanadium(V) complexes bearing tetradentate trihydroxy
amine ligands. The complexes displayed high catalytic activ-
ity toward ethylene polymerization in the presence of
Et2AlCl as a cocatalyst and Cl3CCOOEt as a reactivating agent
and produced high MW polyethylenes with unimodal MWD
even at elevated reaction temperature. Catalyst structure
plays an important role in tuning the catalytic activity and
controlling the MW of the resulting polyethylenes. Further
investigation shows that these complexes were also highly
active catalysts for the copolymerization of ethylene with
norbornene or 5-norbornene-2-methanol. Comonomer incor-
poration and polymer MW can be controlled in a wide range
by the variation of catalyst structure and the reaction param-
eters. To the best of our knowledge, this is the first report
Similar to the case of ethylene/norbornene copolymerization,
increasing the amount of charged NB-CH2OH resulted in the
FIGURE 6 13C NMR spectrum
for the copolymer formed with
complex 2c (entry 6 in Table
3).
1128
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ARTICLE
on vanadium(V) complexes exhibiting high activity toward
copolymerization of ethylene with polar norbornene
derivative.
(s, 2H, ArCH2), 2.62 (d, J ¼ 6.0 Hz, 4H, NCH2), 2.25 (s, 3H,
ArCH3), 1.12 (d, J ¼ 2.4 Hz, 6H, CHCH3). 13C NMR (75.5
MHz, CDCl3): d 147.92 (C), 143.97 (C), 128.80 (C), 123.22
(C), 122.44 (CH), 112.38 (CH), 66.64 (CH), 64.51 (CH), 63.80
(CH2), 62.31 (CH2), 59.43 (CH2), 58.39 (CH3), 56.21 (CH2),
21.37 (CH3), 21.10 (CH3), 20.90 (CH3). Anal. Calcd. for
EXPERIMENTAL
General Procedures and Materials
C
15H25NO4: C, 63.58; H, 8.89; N, 4.94. Found: C, 63.60; H,
All manipulation of air- and/or moisture-sensitive com-
pounds was carried out under a dry argon atmosphere using
standard Schlenk techniques or under a dry argon atmos-
phere in an MBraun glovebox unless otherwise noted. All
solvents were purified from an MBraun SPS system. The
NMR data of the ligand and vanadium complexes were
obtained on a Bruker 300 MHz spectrometer at ambient
temperature, with CDCl3 as a solvent. 51V NMR spectra were
collected on a Bruker 78.92 MHz spectrometer and refer-
enced to VOCl3 (d ¼ 0) as an external standard. The NMR
data of polymers were obtained on a Varian Unity-400 MHz
spectrometer at 135ꢁC, with o-C6D4Cl2 as a solvent. The IR
spectra were recorded on a Bio-Rad FTS-135 spectrophotom-
eter. Elemental analyses were recorded on an elemental
Vario EL spectrometer. Mass spectra were obtained using
electron impact (EI-MS) and LDI-1700 (Linear Scientific).
The DSC measurements were performed on a Perkin-Elmer
8.94; N, 4.90.
1b
1
ꢁ
Yield 70%. H NMR (CDCl3, 25 C): d 6.61 (s, 2H, Ar-H), 6.56
(s, 2H, Ar-H), 3.83 (s, 6H, OCH3), 3.82 (s, 4H, ArCH2), 3.79 (t,
J ¼ 3.0 Hz, 2H, OCH2), 2.75 (t, J ¼ 6.0 Hz, 4H, NCH2), 2.25 (s,
6H, ArCH3). 13C NMR (75.5 MHz, CDCl3): d 147.46 (C),
143.35 (C), 129.12 (C), 122.97 (C), 122.08 (CH), 112.18 (CH),
60.40 (CH2), 56.23 (CH2), 55.74 (CH3), 21.39 (CH3). Anal.
Calcd. for C20H27NO5: C, 66.46; H, 7.53; N, 3.88. Found: C,
66.42; H, 7.55; N, 3.82.
1c
1
ꢁ
Yield 69%. H NMR (CDCl3, 25 C): d 6.61 (s, 2H, Ar-H), 6.54
(s, 2H, Ar-H), 4.13 (sept, J ¼ 6.0 Hz, 1H, CHCH3), 3.85 (s, 6H,
OCH3), 3.78 (br, 4H, ArCH2), 2.53 (m, 2H, NCH2), 2.25 (s, 6H,
ArCH3), 1.08 (d, J ¼ 6.0 Hz, 3H, CHCH3). 13C NMR (75.5
MHz, CDCl3): d 147.47 (C), 143.34 (C), 128.93 (C), 122.92
(C), 122.71 (CH), 112.10 (CH), 65.59 (CH), 61.99 (CH2),
56.73 (CH3), 56.19 (CH2), 21.38 (CH3), 20.96 (CH3). Anal.
Calcd. for C21H29NO5: C, 67.18; H, 7.79; N, 3.73. Found: C,
67.21; H, 7.73; N, 3.78.
ꢁ
Pyris 1 Differential Scanning Calorimeter at a rate of 10 C/
min. The weight-average MW (Mw) and the polydispersity
index of polymer samples were determined at 150 ꢁC by a
PL-GPC 220 type high-temperature chromatograph equipped
with three Plgel 10 lm Mixed-B LS type columns. 1,2,4-Tri-
chlorobenzene was used as the solvent at a flow rate of 1.0
mL/min. The calibration was made by polystyrene standard
EasiCal PS-1 (PL Ltd). The intrinsic viscosity of the polymer
sample was measured in decalin at 135 ꢁC using an
Ubbleohed viscometer, and the viscosity-average MW was
calculated using the following equation.26
1d
1
ꢁ
Yield 78%. H NMR (CDCl3, 25 C): d 6.77 (s, 2H, Ar-H), 6.56
(s, 2H, Ar-H), 4.10 (sept, J ¼ 6.0 Hz, 1H, CHCH3), 3.65 (br,
4H, ArCH2), 2.41 (m, 2H, NCH2), 2.12 (s, 6H, ArCH3), 2.10 (s,
6H, ArCH3), 1.06 (d, J ¼ 6.0 Hz, 3H, CHCH3). 13C NMR (75.5
MHz, CDCl3): d 152.4 (C), 131.34 (C), 129.93 (C), 125.92 (C),
122.79 (CH), 114.16 (CH), 66.59 (CH), 61.57 (CH2), 51.19
(CH2), 24.38 (CH3), 22.92 (CH3), 14.58 (CH3). Anal. Calcd. for
½gꢃ ¼ 6:2 ꢄ 10ꢂ4Mv0:7
C
21H29NO3: C, 73.44; H, 8.51; N, 4.08. Found: C, 73.50; H,
Ethyl trichloroacetate (ETA) was purchased from Aldrich,
dried over calcium hydride at room temperature, and then
distilled. VOCl3, VO(OnPr)3, phenol compounds, and amine
compounds were purchased from Aldrich. Diethylaluminium
chloride was obtained from Albemarle Corp. Literature pro-
cedures were used to synthesize amine trihydroxy ligands27
and VCl3(N-2,6-Me2C6H3).21
8.56; N, 4.03.
Synthesis of Oxovanadium(V) Complexes
To a stirred solution of VO(OnPr)3 (244 mg, 1.0 mmol) in
dried CH2Cl2 (20 mL) was added slowly a solution of ligand
1a (283 mg, 1.0 mmol) in CH2Cl2 (20 mL). After stirring for
4 h at room temperature, the red reaction mixture was con-
centrated to about 5 mL. Crystallization by diffusion of n-
hexane (10 mL) into the clear solution yielded red black
crystals of 2a (264 mg, 76%). Compounds 2b–d were pre-
pared analogously.
Synthesis of Trihydroxy Amine Ligands (1a–d)
To a stirred solution of 2-methoxy-4-methylphenol (2.76 g,
20 mmol) in CH3OH (25 mL) was added bis(2-hydroxypro-
pyl)amine (2.66 g, 20 mmol) and paraformaldehyde (0.6 g,
20 mmol). After refluxing 72 h, the evaporation of the sol-
vent under reduced pressure gave black oil, which was puri-
fied by column chromatography on silica gel using petroleum
ether/methanol (5/1) as an eluent to give the product as
white powder (4.25 g, 15 mmol) in 75% yield. Ligands 1b–d
were prepared analogously.
2a
1
ꢁ
H NMR (CDCl3, 25 C): d 6.68 (s, 2H, Ar-H), 6.65 (s, 2H, Ar-
H), 6.53 (s, 2H, Ar-H), 6.49 (s, 2H, Ar-H), 5.03 (sept, J ¼ 4.2
Hz, 2H, CH), 4.64 (sept, J ¼ 4.2 Hz, 2H, CH), 3.88 (s, 6H,
OCH3), 3.74 (penta, J ¼ 55.8 Hz, 4H, ArCH2), 2.71 (d, J ¼
12.0 Hz, 4H, NCH2), 2.51 (d, J ¼ 12.0 Hz, 4H, NCH2), 2.28 (s,
6H, ArCH3), 1.22 (m, 12H, CHCH3). 13C NMR (75.5 MHz,
CDCl3): d 156.28 (C), 145.96 (C), 133.05 (C), 126.03 (C),
122.37 (CH), 113.09 (CH), 82.86 (CH), 59.90 (CH), 56.68
1a
1
ꢁ
H NMR (CDCl3, 25 C): d 6.64 (s, 1H, Ar-H), 6.47 (s, 1H, Ar-
H), 3.99 (sept, J ¼ 6.0 Hz, 2H, CH), 3.81 (s, 3H, OCH3), 3.79
CATALYSTS FOR COPOLYMERIZATION OF CYCLIC OLEFINS, WU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
(CH2), 56.58 (CH2), 56.39 (CH3), 21.53 (CH3). 51V NMR
(78.92 MHz, CDCl3): d ꢂ368. IR (KBr pellets): m 2923, 2856,
1581, 1483, 1367, 1326, 1243, 1160, 1103, 967, 850, 643
cmꢂ1. EI-MS (70 ev): m/z ¼ 694 [Mþ]. Anal. Calcd. for
recrystallized in Et2O/n-hexane yielded 157 mg of the pure
complex as red crystal (35%).
1H NMR (CDCl3, 25 ꢁC): d 6.64–6.81 (m, 3H, Ar-H), 6.65 (s,
1H, Ar-H), 6.59 (s, 1H, Ar-H), 6.41 (s, 1H, Ar-H), 5.03 (sept, J
¼ 4.2 Hz, 1H, CH), 4.90 (sept, J ¼ 4.2 Hz, 1H, CH), 3.74 (s,
3H, OCH3), 3.72 (br flat, 2H, ArCH2), 2.71 (d, J ¼ 12.0 Hz,
2H, NCH2), 2.74 (s, 6H, ArCH3), 2.51 (m, 4H, NCH2), 2.21 (s,
3H, ArCH3), 1.22 (d, J ¼ 3.0 Hz, 3H, CHCH3), 1.01 (d, J ¼ 3.0
Hz, 3H, CHCH3). 13C NMR (75.5 MHz, CDCl3): d 159.92 (C),
147.97 (C), 134.75 (C), 128.87 (CH), 128.23 (CH), 126.75
(C),126.69 (CH), 125.88 (C), 122.06 (CH), 113.69 (CH), 81.58
(CH), 78.41 (CH), 61.13 (CH2), 59.71 (CH2), 59.43 (CH2),
56.48 (CH3), 55.63 (CH2), 21.64 (CH3), 20.82 (CH3), 18.40
(CH3). 51V NMR (78.92 MHz, CDCl3): d ꢂ249. IR (KBr pel-
lets): m 2961, 2919, 2851, 1579, 1484, 1314, 1250, 1160,
1125, 1104, 1070, 990, 955, 842, 669, 641 cmꢂ1. EI-MS
(70ev): m/z ¼ 450 [Mþ]. Anal. Calcd. for C23H31N2O4V: C,
61.33; H, 6.94; N, 6.22. Found: C, 61.18; H, 6.90; N, 6.27.
C30H44N2O10V2: C, 51.88; H, 6.93; N, 4.03. Found: C, 51.94;
H, 6.95; N, 3.98.
2b
1
ꢁ
Yield 83%. H NMR (CDCl3, 25 C): d 6.60 (s, 2H, Ar-H), 6.49
(s, 2H, Ar-H), 4.82 (br, 2H, OCH2), 3.85 (s, 6H, OCH3), 3.45
(br, 4H, ArCH2), 2.72 (br, 2H, NCH2), 2.26 (s, 6H, ArCH3). 13C
NMR (75.5 MHz, CDCl3): d 155.73 (C), 145.50 (C), 132.74
(C), 125.72 (C), 122.00 (CH), 112.54 (CH), 56.20 (CH2), 55.75
(CH2), 53.05 (CH3), 21.19 (CH3). 51V NMR (78.92 MHz,
CDCl3): d ꢂ364. IR (KBr pellets): m 2919, 2850, 1602, 1581,
1462, 1366, 1322, 1242, 1160, 1100, 954, 857, 618, 540
cmꢂ1. EI-MS (70 ev): m/z ¼ 425 [Mþ]. Anal. Calcd. for
C20H24NO6V: C, 56.47; H, 5.69; N, 3.29. Found: C, 56.41; H,
5.66; N, 3.34.
2c
1
ꢁ
Yield 98%. H NMR (CDCl3, 25 C): d 6.60 (s, 2H, Ar-H), 6.37
(s, 2H, Ar-H), 5.16 (sept, J ¼ 6.0 Hz, 1H, CHCH3), 3.85 (d, J ¼
6.0 Hz, 6H, OCH3), 3.72 (br, 4H, ArCH2), 2.52 (br, 2H, NCH2),
2.26 (d, J ¼ 12.0 Hz, 6H, ArCH3), 1.16 (d, J ¼ 6.0 Hz, 3H,
CHCH3). 13C NMR (75.5 MHz, CDCl3): d 156.13 (C), 146.44
(C), 133.23 (C), 125.80 (C), 123.05 (CH), 112.31 (CH), 84.54
(CH), 60.31 (CH), 56.78 (CH2), 55.54 (CH2), 55.35 (CH3),
21.57 (CH3). 51V NMR (78.92 MHz, CDCl3): d ꢂ365. IR (KBr
pellets): m 2958, 2919, 2852, 1604, 1581, 1482, 1369, 1328,
1243, 1160, 1101, 1053, 964, 859, 643, 618 cmꢂ1. EI-MS
(70 ev): m/z ¼ 439 [Mþ]. Anal. Calcd. for C21H26NO6V: C,
57.41; H, 5.96; N, 3.19. Found: C, 57.51; H, 5.91; N, 3.14.
General Procedure for Ethylene (Co)Polymerization
Ethylene polymerizations were conducted in toluene by
using a 100-mL scale autoclave. Toluene, Et2AlCl, ETA, and
comonomer were charged into the autoclave in sequence in
the drybox. The autoclave was placed under ethylene atmos-
phere (1 atm). After the addition of a toluene solution con-
taining a prescribed amount of catalyst via a syringe, the re-
actor was sealed and pressurized to the desired level, and
then the stirring motor was engaged. After the prescribed
reaction time, the stirring motor was stopped and the reac-
tor was vented, and the resulted mixture was added to acidic
ethanol. The solid polymer was isolated by filtration, washed
2d
1
ꢁ
ꢁ
Yield 88%. H NMR (CDCl3, 25 C): d 6.88 (s, 2H, Ar-H), 6.64
(s, 2H, Ar-H), 5.19 (sept, J ¼ 6.0 Hz, 1H, CHCH3), 3.73 (br,
2H, ArCH2), 2.51 (br, 2H, NCH2), 2.34 (d, J ¼ 12.0 Hz, 6H,
ArCH3), 2.23 (d, J ¼ 12.0 Hz, 6H, ArCH3), 1.18 (d, J ¼ 6.0 Hz,
3H, CHCH3). 13C NMR (75.5 MHz, CDCl3): d 159.20 (C),
148.23 (C), 133.55 (C), 126.60 (C), 124.45 (CH), 114.35 (CH),
86.62 (CH), 61.39 (CH), 56.97 (CH2), 54.44 (CH2), 23.35
(CH3), 21.57 (CH3), 14.57 (CH3). 51V NMR (78.92 MHz,
CDCl3): d ꢂ364. IR (KBr pellets): m 2977, 2918, 2851, 1605,
1472, 1449, 1371, 1239, 1218, 1159, 1077, 949, 862, 751,
641, 614 cmꢂ1. EI-MS (70 ev): m/z ¼ 407 [Mþ]. Anal. Calcd.
for C21H26NO4V: C, 61.91; H, 6.43; N, 3.44. Found: C, 61.82;
H, 6.38; N, 3.39.
with ethanol, and dried at 60 C for 12 h in vacuo.
Crystallographic Studies
Crystals for X-ray analysis were obtained as described in the
preparations. The crystallographic data, collection parame-
ters, and refinement parameters are listed in Supporting In-
formation (Table S1). The crystals were manipulated in a
glovebox. The intensity data were collected with the x scan
mode (186K) on a Bruker Smart APEX diffractometer with
CCD detector using Mo Ka radiation (k ¼ 0.71073Å). Lor-
entz, polarization factors were made for the intensity data,
and absorption corrections were performed using SADABS
program. The crystal structures were solved using the
SHELXTL program and refined using full matrix least
squares. The positions of hydrogen atoms were calculated
theoretically and included in the final cycles of refinement in
a riding model along with attached carbons.
Synthesis of (Arylimido)vanadium(V) Complex 3a
To a slurry of NaH (26.4 mg, 1.1 mmol) in Et2O (10 mL) was
added to a solution of ligand 1a (283 mg, 1.0 mmol) in Et2O
ꢁ
(10 mL) at ꢂ30 C. The resulting suspension was warmed to
room temperature and stirred for 4 h. Then, the white mix-
ture was slowly transferred to an Et2O solution (20 mL) con-
taining VCl3(N-2,6-Me2C6H3) (276 mg, 1.0 mmol) at ꢂ30 ꢁC.
The reaction mixture was warmed slowly to room tempera-
ture (25 ꢁC), and the mixture was stirred over night. The
reaction mixture was condensed and filtered to remove NaCl
and the excess NaH. The filtrate was concentrated and
The authors are grateful for subsidy provided by the National
Natural Science Foundation of China (Nos. 20734002 and
20923003), and by the Special Funds for Major State Basis
Research Projects (No. 2005CB623800) from the Ministry of
Science and Technology of China.
1130
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ARTICLE
Katao, S.; Fujiki, M.; Nomura, K. Organometallics 2008, 27,
2590–2596; (h) Nomura, K.; Onishi, Y.; Fujiki, M.; Yamada, J.
Organometallics 2008, 27, 3818–3824; (i) Zhang, W.; Yamada, J.;
Nomura, K. Organometallics 2008, 27, 5353–5360.
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