Novel vanadium(iii) complexes with bidentate N,N-chelating iminopyrrolide ligands: Synthesis, characterization and catalytic behaviour of ethylene polymerization and copolymerization with 10-undecen-1-ol

Article abstract of DOI:10.1039/b909495d

A series of novel vanadium(iii) complexes bearing iminopyrrolide chelating ligands [2-(RNCH)C₄H₃N]V(THF)₂Cl₂ (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr₂C₆H ₃; 2d: R = p-CF<

Full text of DOI:10.1039/b909495d

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www.rsc.org/dalton | Dalton Transactions
Novel vanadium(III) complexes with bidentate N,N-chelating iminopyrrolide
ligands: synthesis, characterization and catalytic behaviour of ethylene
polymerization and copolymerization with 10-undecen-1-ol†
Bao-Chang Xu,a,b Tao Hu,a Ji-Qian Wu,a,b Ning-Hai Hua and Yue-Sheng Li*a
Received 13th May 2009, Accepted 25th August 2009
First published as an Advance Article on the web 7th September 2009
DOI: 10.1039/b909495d
A series of novel vanadium(III) complexes bearing iminopyrrolide chelating ligands
=
[2-(RN CH)C4H3N]V(THF)2Cl2 (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr2C6H3; 2d: R =
p-CF3C6H4; 2e: R = C6F5) have been synthesized and characterized. Single-crystal X-ray diffraction
revealed that complexes 2a, 2c and 2e adopt an octahedral geometry around the vanadium center. In
the presence of Et2AlCl as a co-catalyst, these complexes displayed high catalytic activities up to 48.6 kg
PE mmolV h-1 bar-1 for ethylene polymerization, and produced high molecular weight polymers.
-1
2a–e/Et2AlCl catalytic systems were tolerant to elevated temperature (70 ◦C) and yielded unimodal
polyethylenes, indicating the single site behaviour of these catalysts. By pre-treating with equimolar
amounts of alkylaluminums, functional a-olefin 10-undecen-1-ol can be efficiently incorporated into
polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 15.8 mol% under the mild
conditions. When compared with VCl3(THF)3 or rac-Et[Ind]2ZrCl2, these vanadium(III) complexes
exhibited higher activities towards the copolymerization, and can incorporate more 10-undecen-1-ol
into polymer chains under the similar conditions.
bidentate, tridentate, or polydentate ligands.7–23 Gambarotta and
Introduction
co-workers synthesized six-membered chelating (b-diketonate)3V
complexes with different ligands and found that they exhibited
high catalytic activities towards ethylene polymerization.8a The
bis(benzimidazole) amine vanadium catalysts found by Gibson
and colleagues displayed high catalytic activity for ethylene
(co)polymerization, affording high molecular weight polymers
with unimodal distribution.11 Redshaw et al. reported various
aryloxide-based vanadium complexes, which exhibited excellent
performance for catalyzing ethylene polymerization.18 Nomura
obtained many different (arylimino) vanadium complexes con-
taining aryloxo and alkoxo ligands, which possessed excellent
efficiency towards olefin (co)polymerization.20 Recently, our group
reported various vanadium catalysts featuring b-enaminoketonato
or salicylaldiminato ligands, which also displayed remarkable
catalytic activity for ethylene (co)polymerization.6,23
Although many vanadium catalysts with high performances
have been published, most of the reported highly active “non-
metallocene” vanadium complexes are six-membered chelates,
and five-membered chelating vanadium(III) complexes are still
rare.24 This urged us to investigate if the five-membered chelating
vanadium(III) complexes are more active catalysts for olefin
polymerization. Therefore, we sought to design a ligand which
bears the donor atoms able to stabilize the intermediate oxidation
state of the vanadium center and can form a five-membered
chelate. The iminopyrrolide moieties were chosen for this purpose
because they contain the desired chelating ring and the nitrogen
donor atom bears stronger ability to stabilize the intermediate
oxidation state of the vanadium center than oxygen atom.7b
Besides, iminopyrrolide ligands have been used in group 4,25 group
6,26 and group 1027 metal systems and have already been shown to
afford highly active olefin polymerization and copolymerization
A great amount of success has been made in the field of
olefin coordination polymerization in the past decades since
the invention of Zieglar–Natta catalysts. Many well-defined
and highly active homogeneous catalysts were synthesized by
modifying ligand frameworks. These successes stimulated the
progress of organometallic chemistry and catalyst chemistry.1
Vanadium catalysts, one of the first homogeneous Ziegler–Natta
catalysts,2 also attracted much interest and got great development
presumably due to their extensive uses in the production of
high molecular weight polyethylene,3 ethylene/propylene copoly-
mer or ethylene/propylene/diene elastomer,4 and syndiotactic
polypropylene.5 However, thermal instability is an issue for
vanadium catalysts due to the reduction of the catalytically active
vanadium species to low-valent, less active, or inactive species. For
example, when the polymerization was performed at 25 ◦C, a high
activity of 20.4 kg of PE mmolV h-1 bar-1 can be achieved, how-
-1
ever, the activity can reduce up to 50% when the polymerization
◦
temperature increased to 70 C.6 The introduction of ancillary
ligand to stabilize the active metal center is an effective way of im-
proving the performance of the vanadium catalysts. In recent years,
in the field of olefin polymerization and copolymerization, some
studies on vanadium catalytic system with impressive advances in
catalytic activity and thermal stability involved complexes having
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun,
130022, China. E-mail: ysli@ciac.jl.cn; Fax: +86-431-85262039
bGraduate School of the Chinese Academy of Sciences, Changchun Branch,
Changchun, 130022, China
† CCDC reference numbers 725659–725661. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b909495d
8854 | Dalton Trans., 2009, 8854–8863
This journal is
The Royal Society of Chemistry 2009
©

catalysts. Thus, employing these ligands with different imines, we
reported herein that the syntheses of a series of five-membered
N,N-chelating vanadium(III) complexes and their behaviours of
ethylene polymerization. Considering the lower oxophilic nature
of vanadium than group IV metals, we also investigated if
chelated vanadium(III) complexes are effective catalysts for the
copolymerization of ethylene with functional a-olefin. To the best
of our knowledge, this is the first example using homogeneous
non-metallocene vanadium catalysts for the copolymerization of
ethylene and an a,w-olefinic alcohol.
Results and discussion
Synthesis and characterization of vanadium(III) complexes
A general synthetic route for the vanadium complexes used in
this study is shown in Scheme 1. Pyrrolide-imine ligands 1a–
d were obtained in good yields (1a, 87%; 1b, 90%; 1c, 93%;
2d, 90%) via the reaction of pyrrole-2-carboxaldehyde with the
corresponding amine in methanol containing a little formic acid
as a catalyst according to the procedure reported.25b,27a 1e was not
obtained via the same procedure probably due to the low basicity
of pentafluoroaniline. This compound was prepared in a moderate
yield (50%) by the reaction of pyrrole-2-carboxaldehyde with
pentafluoroaniline in toluene containing a little p-toluenesulfonic
acid monohydrate as a catalyst. The vanadium complexes 2a–e
were prepared under moderate conditions in good yields (2a, 75%;
2b, 69%; 2c, 63%; 2d, 72%; 2e, 45%) by the reaction of VCl3(THF)3
with one equivalent of the lithium salts of pyrrolide-imine in
dry tetrahydrofuran. The resulting complexes were isolated from
the chilled concentrated mixture of THF and hexane solution
as dark red or brown crystalline solids. These complexes were
identified by FTIR and mass spectra as well as elemental analyses.
In the MALDI-TOF-MS spectra of complexes 2a–e, there were
no peaks of 2 : 1 or 0 : 1 ligand-to-V(III) complexes, indicating
the complexes displayed high purity. The resonances broadened
Fig. 1 ORTEP view of complex 2a. Thermal ellipsoids are drawn at the
30% probability level and H atoms are omitted for clarity.
1
to an unobservable extent in the H (or 13C) NMR spectra for
these complexes in CD2Cl2 or C6D6 and indicate that they are
paramagnetic species.
Fig. 2 ORTEP view of complex 2c. Thermal ellipsoids are drawn at the
30% probability level and H atoms are omitted for clarity.
angles are given in Table 1. Crystals of 2a and 2c consist of
two crystallographically independent molecules in the unit cell,
while crystal of 2e contains one crystallographically independent
complex molecule and one THF molecule in the unit cell. As
shown in Fig. 1–3, complexes 2a, 2c and 2e have a six-coordinate
distorted octahedral geometry around the V metal center. The
two chlorine atoms are situated in the cis-position, while two
THF molecules are in the trans-position to each other. However,
in our previous work, mono(b-enaminoketonato) vanadium(III)
complexes and salicylaldiminato vanadium(III) complexes possess
a reverse configuration. Complexes 2a (N(1)–V–N(2), 78.39◦),
2c (N(1)–V–N(2), 77.84◦) and 2e (N(1)–V–N(2), 78.02◦) show
smaller N(1)–V–N(2) angles over the corresponding mono(b-
enaminoketonato) vanadium(III) complexes and salicylaldiminato
vanadium(III) complexes which the N–V–O angles are approxi-
mately 90◦.6,23a These differences are due to pyrrolide-imine ligands
Scheme 1
The molecular structures of complexes 2a, 2c and 2e were
confirmed by single-crystal X-ray structure analyses. Crystals
suitable for X-ray diffraction were grown from a THF–hexane
mixture solution at -20 ◦C. The molecular structures of 2a, 2c
and 2e are shown in Fig. 1–3 and pertinent bond lengths and
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8854–8863 | 8855
©

◦
˚
Ethylene polymerization
Table 1 Selected bond distances (A) and angles ( ) for complexes 2a, 2c
and 2e
Co-catalysts, especially alkylaluminiums, play an irreplaceable role
in the olefin polymerization promoted by vanadium catalysts,
and the performance of catalysts depended very much on the
nature of the co-catalyst.28 In this paper, we investigated the
performance of complex 2b catalyzing ethylene polymerization
with the aid of various kinds of alkylaluminiums such as mod-
ified methylaluminoxane (MMAO), AlMe3, AlEt3, AliBu3 and
Et2AlCl. Cl3CCOOEt (ETA) was used as a reactivating agent to
reactivate the low-valent, less active or inactive species to active
vanadium(III) species.7b,29 The typical results of the polymerization
are collected in Table 2. The data in Table 2 (entries 1–5) indicate
that Et2AlCl is the most effective co-catalyst among the five
alkylaluminiums under the same conditions. 2b/Et2AlCl displayed
2a
2c
2e
V(1)–O(2)
V(1)–N(1)
V(1)–O(1)
V(1)–N(2)
V(1)–Cl(1)
V(1)–Cl(2)
O(2)–V(1)–N(1)
O(2)–V(1)–O(1)
N(1)–V(1)–O(1)
O(2)–V(1)–N(2)
N(1)–V(1)–N(2)
O(1)–V(1)–N(2)
O(2)–V(1)–Cl(1)
N(1)–V(1)–Cl(1)
O(1)–V(1)–Cl(1)
N(2)–V(1)–Cl(1)
O(2)–V(1)–Cl(2)
N(1)–V(1)–Cl(2)
O(1)–V(1)–Cl(2)
N(2)–V(1)–Cl(2)
Cl(1)–V(1)–Cl(2)
2.028(4)
2.028(5)
2.027(4)
2.147(4)
2.064(3)
2.037(3)
2.058(3)
2.170(3)
2.3203(12)
2.3512(12)
90.27(11)
175.24(11)
86.14(12)
87.64(11)
77.84(12)
94.66(11)
93.34(8)
168.58(9)
90.78(8)
91.47(9)
86.85(8)
92.24(9)
90.15(8)
168.63(9)
98.77(5)
2.017(6)
2.044(4)
2.046(6)
2.129(4)
2.3365(14)
2.3401(15)
89.2(2)
179.13(15)
90.0(2)
90.5(2)
2.3501(18)
2.3729(18)
93.59(17)
178.09(16)
88.23(17)
87.86(17)
78.39(18)
91.93(17)
90.22(12)
174.71(15)
87.93(12)
98.11(13)
90.22(12)
89.76(13)
90.81(12)
168.62(14)
93.03(6)
78.02(15)
89.7(2)
90.80(14)
170.17(12)
90.01(16)
92.16(11)
89.99(15)
92.17(12)
89.61(17)
170.17(11)
97.65(6)
the◦highest catalytic activity of 31.0 kg PE mmolV h-1 bar-1 at
-1
50 C when the Al–V molar ratio equalled 2000 (entry 5), while
a much lower activity was obtained using MMAO or AlMe3 or
AlEt3 as a co-catalyst, and even no polymer was formed using
AliBu3 as a co-catalyst, due to the strong reducibility. Thus,
we further examined the effect of Et2AlCl dosage on ethylene
polymerization behaviour of complexes 2b at 25 ◦C. With an
increase of the Al–V molar ratio, a significant increase of the
catalytic activity was observed, and a significant decrease of the
molecular weights (MWs) of polymers was detected, as shown
in Fig. 4. Catalytic activity of 9.6 kg PE mmolV h-1 bar-1 was
-1
obtained when the Al–V molar ratio was 500, and enhancing
the Al–V molar ratio to 2000, a higher activity of 33.0 kg PE
mmolV h-1 bar-1 was achieved. However, further increasing the
-1
Et2AlCl dosage, the catalytic activity only slightly increased. This
result is quite different from that of mono(b-enaminoketonato)
vanadium(III) catalysts which the maximum activity was achieved
when the Al–V molar ratio equalled 4000.23a
Fig. 3 ORTEP view of complex 2e and one molecule of THF. Thermal
ellipsoids are drawn at the 30% probability level and H atoms are omitted
for clarity.
coordinated with vanadium atoms forming five-membered rings
whereas b-enaminoketonato ligands and salicylaldiminato ligands
forming six-membered rings with vanadium atoms. Compared
˚
˚
with 2a (V–N(2), 2.147 A) and 2c (V–N(2), 2.170 A), 2e showed
˚
shorter V–N(2) bond distance (2.129 A), which is probably due to
Fig. 4 Plots of catalytic activity of complex 2b and weight-average
molecular weight of the polymers obtained vs. Al–V molar ratio. Reaction
conditions: 0.2 mmol vanadium complex, Cl3CCO2Et 0.06 mmol, ethylene
1 atm, toluene 50 mL, at 25 ◦C polymerization for 5 min.
electronic effects of fluorine atoms. In complex 2c, the O(1)–V–
O(2) angle (175.24◦) is narrower than those in 2a (178.09◦) and 2e
(179.13◦), which derives from the steric hindrance effect caused by
the isopropyl groups in the ligand. The Cl(1)–V–Cl(2) bond angle
of 2a (93.03◦) is smaller than those of 2c (98.77◦) and 2e (97.65◦),
while the Cl(1)–V–N(2) bond angle of 2a (98.11◦) is larger than
those of 2c (91.47◦) and 2e (92.16◦). These differences originate
from the repulse effect to chlorine atom caused by cyclohexyl
group of the ligand.
Although going on increasing the concentration of co-catalyst
(Et2AlCl) could only play slim effect on the catalytic activity
when Al–V was more than 2000, it still brought a great influence
to the MWs and MWDs of the polymers especially at elevated
temperature. Increasing Et2AlCl dosage from 2000 to 4000, the
8856 | Dalton Trans., 2009, 8854–8863
This journal is
The Royal Society of Chemistry 2009
©

a
Table 2 Typical results of ethylene polymerization catalyzed by 2a–e and VCl3(THF)3
c
c
Entry
Catalyst
Catalyst/mmol
Co-catalyst
Al–V (m/m)
T/◦C
Polymer/g
Activityb
0.7
Mw (¥104)
Mw/Mn
1
2
3
4
5
6
7
8
2b
0.5
0.5
0.5
0.5
0.5
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
MMAO
AliBu3
AlEt3
2000
2000
2000
2000
2000
4000
4000
4000
4000
2000
2000
2000
4000
4000
4000
4000
4000
4000
4000
4000
4000
4000
4000
4000
50
50
50
50
50
50
70
50
70
25
50
70
25
50
70
50
70
50
70
70
70
25
50
70
0.03
Trace
0.01
0.21
1.29
0.63
0.53
0.47
0.32
0.63
0.74
0.45
0.66
0.81
0.57
0.55
0.39
0.65
0.48
0.92
1.29
0.43
0.39
0.21
2b
2b
0.2
5.0
2b
AlMe3
2b
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
31.0
37.8
31.8
28.2
19.2
37.8
44.4
27.0
39.6
48.6
34.2
33.0
23.4
39.0
28.8
18.4
12.9
25.8
23.4
12.6
8.8
4.3
1.6
3.5
1.3
11.8
9. 9
10.0
6.3
2.5
1.0
4.4
2.0
3.0
1.4
2.3
2.7
22.7
13.4
9.9
4.0
2.2
1.7
2.1
1.9
2.6
5.3
7.8
2.4
1.7
2.2
2.4
2.2
1.9
1.7
2.3
2.4
2.8
5.8
21.9
2b
2b
2a
9
2a
10
11
12
13
14
15
16
17
18
19
20d
21e
22
23
24
2c
2c
2c
2c
2c
2c
2d
2d
2e
2e
2a
2a
VCl3(THF)3
VCl3(THF)3
VCl3(THF)3
-1
a Reaction conditions: 1 atm ethylene pressure, ETA–V molar ratio = 300, toluene 50 mL, polymerization for 5 min. b kg of PE mmolV h-1 bar-1.
c Weight-average molecular weight and polydispersity index of the resultant polyethylene determined by high temperature GPC using polystyrene
standard. d Polymerization for 15 min. e Polymerization for 30 min.
MWs of the polymers produced by complex 2c decreased sharply,
and the MWDs of polyethylenes became much narrower (entries
10–12 vs. entries 13–15 in Table 2, respectively). This indicates
that the increase of Et2AlCl concentration can speed up the chain
transfer reaction velocity and restrain the appearance of new active
centers.
and the MWD remained 2.4 even at 30 min, which suggested 2b
seems to be still single site catalyst even at 70 ◦C.
Compared with complex 2b, complex 2c bearing two ortho-
isopropyls substituted iminopyrrolide ligand exhibited higher
catalytic activity, indicating that steric hindrance effect can
improve the catalytic performance of the iminopyrrolide vanadium
complexes by retarding the bimolecular deactivation of vanadium
catalysts.11a,b When the phenyl of the imine-moiety of complex 2b
was replaced by non-conjugated cyclohexyl to form complex 2a,
lower activity was observed, which is probably due to the lack
of the stabilization of phenyl to metal center. Interestingly, the
introduction of electron-withdrawing groups into the iminopy-
rrolide ligand will bring different results on the performance of
the vanadium catalysts. For example, with trifluoromethyl at the
para-position on the N-aryl moiety, complex 2d showed lower
catalytic activity than complex 2b. However, when five fluorine
atoms were introduced into the N-aryl moiety to form complex 2e,
the comparable activity was afforded under the same conditions.
Compared with mono(salicylaldiminato) vanadium(III) com-
plexes previously reported,6 vanadium(III) complexes bearing
iminopyrrolide ligands exhibited higher catalytic activities toward
ethylene polymerization under the similar conditions, which
indicates that nitrogen donor atom in this kind of ligands bear
stronger ability than oxygen donor related ligands to stabilize the
vanadium active species during the catalytic reaction.
With the feed of 4000 equivalents of Et2AlCl, complexes 2a–e
were highly active towards ethylene polymerization at elevated
temperature. When the polymerizations were conducted at 50 ◦C,
all the complexes showed their highest catalytic activities, and
the highest activity of 2c could be up to 48.6 kg PE mmolV h-1
-1
bar-1 (entry 14 in Table 2). Increasing reaction temperature to
70 ◦C, the catalytic activities of these complexes were still higher
than that of VCl3(THF)3 although they were lower than that at
50 ◦C. Furthermore, the MWDs almost kept fixedness, and the
polydispersity indexes remained in the range of 1.7–2.4 although
the MWs of polymers produced by 2a–e decreased with the
increase of reaction temperature. In contrast, the MWDs of the
polymers obtained by VCl3(THF)3 remarkably broadened under
the same conditions (entries 22–24 in Table 2). This result indicates
that the iminopyrrolide ligands can stabilize the vanadium active
center, and complexes 2a–e are tolerant to elevated tempera-
ture, and they are single site catalysts even at high reaction
temperature.
◦
Ethylene polymerization lifetime study of catalyst 2b at 70 C
during 5–30 min was conducted for verifying their deactivation
process (entries 7, 20 and 21 in Table 2) and found that there was
a remarkable decrease in catalytic activity. At 30 min a net 60%
of catalytic activity was reduced in contrast with at 5 min. Not
only the deactivation of the catalyst can lead to the decrease of the
activity, but the mass-transfer limitation is also a factor. However,
the MWs of the resultant polymers increased with reaction time
Copolymerization of ethylene with 10-undecen-1-ol
Because the formation of stable complexes between the cat-
alytic species and the functional hydroxyl can deactivate the
active centers and inhibit the polymerization when functional
monomers were directly reacted with ethylene, it is necessary to
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8854–8863 | 8857
©

Table 3 Results of the copolymerization of ethylene/10-undecen-1-ola
Protecting Al/V (molar Comonomer/
Polymer/g Activityc Incorp.d (mol%) Tme/◦C
Mwf(¥103) Mw/Mn
f
Entry Catalyst
reagentb
ratio)
mol L-1
1
2
3
2b
AliBu3
AlEt3
AlMe3
Et2AlCl
AliBu3
AlEt3
AlMe3
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
Et2AlCl
2000
2000
2000
2000
2000
2000
2000
2000
500
4000
6000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.05
0.20
0.50
0.10
0.50
0.10
0.50
0.10
0.50
0.10
0.50
0.10
0.10
0.10
0.18
0.15
0.49
1.41
Trace
Trace
Trace
1.17
0.66
1.44
1.51
1.85
1.14
0.24
1.44
0.22
1.68
0.29
1.14
0.75
1.86
0.31
0.71
Trace
0.35
1.1
0.9
2.9
8.5
—
—
—
7.0
4.0
8.6
9.1
11.1
6.8
1.4
8.6
1.3
10.1
1.7
6.8
4.5
11.2
1.9
4.3
—
1.9
1.7
2.1
3.5
—
—
—
2.9
3.4
3.6
3.7
2.4
7.0
15.8
3.4
14.7
3.7
14.2
3.9
11.1
3.3
14.6
3.1
—
118.7
116.5
117.5
111.8
—
—
—
112.8
113.5
111.6
111.5
115.2
104.7
14.8
6.4
8.0
15.5
—
—
1.9
1.6
2.0
2.2
—
—
—
2.0
3.9
2.1
1.9
2.1
2.1
1.8
1.9
1.8
2.0
1.9
2.0
1.8
2.2
1.9
2.0
—
2b
2b
4
2b
5g
2b
6g
2b
7g
2b
—
8g
2b
13.7
52.2
11.8
11.2
18.9
7.9
3.1
15.7
3.4
13.3
3.5
12.3
5.1
15.9
3.3
10.4
—
9
2b
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24h
25h,i
2b
2b
2b
2b
2b
2a
112.1
111.3
110.9
113.7
2a
2c
2c
2d
2d
2e
2e
VCl3(THF)3
112.5
—
114.7
rac-Et[Ind]2ZrCl2 Et2AlCl
rac-Et[Ind]2ZrCl2 Et2AlCl
0.4
2.8
10.5
1.9
a Reaction conditions: 1 mmol catalyst, ETA/V molar ratio = 300, Vtotal = 50 mL, 1 atm ethylene pressure, copolymerization at 50 ◦C in toluene for
10 min. b [Protecting reagents]/[10-undecen-1-ol] = 1 : 1, except for entries 5–8. c Activity in kg mmolV h-1 bar-1 or kg mmolZr h-1 bar-1. d Determined
by 1H NMR. e Determined by DSC. f Determined by GPC. g 2.0 equivalents of alkylaluminiums added as protecting reagents. h MMAO as a co-catalyst.
i 5 mmol catalyst used.
-1
-1
pre-treat the functional monomers using protecting reagents. In
our experiments, we masked the functional groups with various
alkylaluminiums including AliBu3, AlEt3, AlMe3 and Et2AlCl, and
the typical results of ethylene/10-undecen-1-ol copolymerizations
are summarized in Table 3. The data in Table 3 (entries 1–4)
show that the alkylaluminiums considerably affect the catalytic
activity, comonomer incorporation and the MWs of the copoly-
mers. The catalytic activity towards the copolymerization and
the comonomer incorporation exhibited the same sequence of
Et2AlCl > AlMe3 > AliBu3 > AlEt3. The highest activity of
polymer was obtained. In the case of Et2AlCl, the catalytic
activity just decreased slightly (entry 8 in Table 3), and 10-
undecen-1-ol incorporation decreased from 3.5 mol% to 2.9 mol%.
GPC analysis showed that the MW and polydispersity index of
the resultant polymer decreased slightly with increasing Et2AlCl
amounts.
As references, the copolymerizations of ethylene with 10-
undecen-1-ol were also carried out by rac-Et[Ind]2ZrCl2/MMAO
and VCl3(THF)3/Et2AlCl using Et2AlCl as the protecting reagent.
The catalytic activities, functional monomer incorporation, MWs
and polydispersity indexes are all summarized in Table 3. For
the rac-Et[Ind]2ZrCl2/MMAO system (entries 24 and 25), no
copolymer can be obtained when 1 mmol rac-Et[Ind]2ZrCl2 was
added. Even if the catalyst dosage increased to 5 mmol, only a low
complex 2b towards the copolymerization of 8.5 kg mmolV h-1
-1
bar-1 and the highest comonomer incorporation of 3.5 mol%
was detected when 10-undecen-1-ol was masked by Et2AlCl.
The reducibility of alkylaluminiums and the steric effect of
masked comonomers, can be used to explain this sequence. The
reducibility of alkylaluminiums can deactivate active centers of
the catalyst, thus causing the catalytic activity and the comonomer
incorporation to have a sequence of Et2AlCl > AlMe3 > AlEt3 >
AliBu3. The steric effect of masked comonomers can restrain the
coordination between vanadium active center and oxygen atom
so as to improving the copolymerization activity as well as the
comonomer incorporation to a sequence of AliBu3 > AlEt3 >
Et2AlCl > AlMe3. The joint influences of these two factors
resulted in the sequence of the activity of copolymerization and
the comonomer incorporation. Compared with AlEt3 and AlMe3,
the copolymers with higher MWs can be afforded when AliBu3
and Et2AlCl were used as protecting reagents.
activity of 0.4 kg mmolZr h-1 bar-1 could be afforded, which is
-1
much lower than that of 2b/Et2AlCl system (entry 4). In addition,
10-undecen-1-ol incorporation and MW of the copolymer by rac-
Et[Ind]2ZrCl2 were also lower than those by 2b. These inferiorities
of rac-Et[Ind]2ZrCl2/MMAO system are thought to be due to the
stronger oxophilicity of Zr metal center. For VCl3(THF)3/Et2AlCl
system (entry 23), the catalytic activity, the MW of the copolymer
and functional monomer incorporation are all lower as compared
with 2b/Et2AlCl system, which is due to lack of the stabilization
of iminopyrrolide ligands to V metal center.
In order to get the optimized reaction condition, the effect
of Al–V molar ratio and functional monomer dosage on the
copolymerization were further examined. Just as shown in Table 3
(entries 4, 9, 10 and 11), the copolymerization expressed a
high activity when Al–V increases to 2000 : 1, and there is no
When 10-undecen-1-ol was protected with 2 equivalents of
AliBu3, AlEt3 and AlMe3, respectively, trace amounts or no
8858 | Dalton Trans., 2009, 8854–8863
This journal is
The Royal Society of Chemistry 2009
©

precipitously increase of activity going on enhancing Et2AlCl
concentration. This phenomenon is similar to the case of ethylene
polymerization catalyzed by the same catalyst. The MWs and
polydispersity indexes of the copolymers decreased gradually with
the increase of Et2AlCl concentration. Whereas, the functional
monomer incorporation almost kept constant, indicating that the
concentration of Et2AlCl is not an important factor to control
comonomer incorporation.
Noteworthy, when the comonomer concentration in the feed
increased from 0.05 to 0.5 mol L-1, the catalytic activity of complex
2b decreased almost 90%, while the comonomer incorporation
of copolymer increased 5.6 times (entries 4, 12, 13 and 14). The
decline of catalytic activity maybe ascribe to the low speed of polar
monomer insertion or long-time interaction between protected
heteroatom and metal center which hindering the insertion of
ethylene or 10-undecen-1-ol. When 0.5 mol L-1 of 10-undecen-1-ol
was feeded, the 10-undecen-1-ol incorporation could be up to 15.8
mol%. The MWs of the copolymers decreased with the increase
of the 10-undecen-1-ol concentration in the feed, but the MWDs
were independent of comonomer concentration. In addition, DSC
analyses showed that the melting temperatures of the resultant
polymers gradually decreased with the increase of initial 10-
undecen-1-ol concentration, and only one melting temperature
was observed, indicating the components of the copolymers are
homogeneous.
Fig. 5 1H NMR spectrum of poly(ethylene-co-10-undecen-1-ol) (entry 4
in Table 3).
The ligand structure also considerably influences catalytic
activity and comonomer incorporation. Just as shown in Table 3
(entries 4, 14-22), when 0.1 mol L-1 of 10-undecen-1-ol was feeded,
complex 2e containing five fluorine atoms exhibited the highest
Fig. 6 13C NMR spectra of poly(ethylene-co-10-undecen-1-ol): A,
3.5 mol% (entry 4 in Table 3); B, 15.8 mol% (entry 14 in Table 3).
catalytic activity (11.2 kg mmolV h-1 bar-1), while complex 2d
-1
bearing trifluoromethyl on its ligand showed the lowest catalytic
activity (6.8 kg mmolV h-1 bar-1). However, only slim changes
-1
increased up to 15.8 mol%, which is similar to the previous result
by stereorigid bridged zirconocene/MAO system.30a
can be found for the functional monomer incorporation. Besides,
all the complexes can afford copolymers with high MWs and
unimodal MWDs. When the concentration of 10-undecen-1-ol
increased to 0.5 mol L-1, complex 2d displayed higher catalytic
Conclusions
activity (4.5 kg mmolV h-1 bar-1), while lower comonomer
We have synthesized and characterized a series of vanadium(III)
complexes bearing bidentate iminopyrrolide ligands (2a–e), which
were highly air and moisture sensitive. In the presence of Et2AlCl as
a co-catalyst and Cl3CCOOEt as a reactivating agent, these com-
plexes displayed high activities towards ethylene polymerization,
and produced high molecular weight polyethylenes with unimodal
MWDs. The five-membered N,N-chelating iminopyrrolide ligands
can increase the activity and stabilize the active vanadium species
inthe polymerization. 2a–e/Et2AlCl catalytic systems showedhigh
activity even at 70 ◦C. The steric hindrance effect can improve the
catalytic performance of the iminopyrrolide vanadium complexes,
and complex 2c bearing two ortho-isopropyls substituted iminopy-
rrolide ligand exhibited higher catalytic activity than complex 2b.
Introduction of electron-withdrawing groups into iminopyrrolide
ligand will bring different effects on the performance of vanadium
pre-catalysts. With trifluoromethyl at the para-position on the
N-aryl moiety, complex 2d showed lower catalytic activity than
complex 2b. In contrast, when five fluorine atoms were introduced
into the N-aryl moiety of the ligand to form complex 2e, the
comparable activity was afforded under the same conditions.
Moreover, this type of vanadium complex can efficiently cat-
alyze the copolymerization of ethylene with 10-undecen-1-ol by
masking the functional group with alkylaluminiums. Et2AlCl was
-1
incorporation (11.1 mol%) than other four complexes. The highest
comonomer incorporation of 15.8 mol% can be observed when the
copolymerization was catalyzed by complex 2b.
The successful copolymerization of ethylene with 10-undecen-
1
1-ol was confirmed by H NMR spectra. As shown in Fig. 5,
the signals for unsaturated end-group of 10-undecen-1-ol at 4.5–
6.5 ppm disappeared, and the chemical shift at 3.6 ppm described
to the characteristic resonance for the hydroxymethyl group in the
incorporated 10-undecen-1-ol groups was observed, suggesting
that 10-undecen-1-ol units were incorporated into the PE back-
bone. The microstructure of the copolymer was established by
13C NMR in o-C6D4Cl2 at 135 ◦C, with the assignment of the
microstructure following previous work reported by Imuta, Kojoh
and Toda.30 As shown in Fig. 6, the characteristic resonance for
the carbon of the hydroxymethyl group appeared at 63.2 ppm
and there were no peaks that were attributable to the carbon of
vinyl (ca. 115 ppm) group derived from the comonomer or the
chain transfer reaction caused by monomer and/or hydride b-
elimination, suggesting that true copolymer was produced and the
chain transfer reaction to Et2AlCl is the main terminating manner.
Compared with the spectrum A, spectrum B shows that UU and
UUU sequences appeared when the comonomer incorporation
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8854–8863 | 8859
©

proved out the best protecting reagent because of its weaker
reductive ability than AlMe3, AlEt3 and AliBu3. The formation
of true copolymer was clearly certified from the 1H and 13C
NMR analyses. Under the mild conditions, the incorporation of
10-undecen-1-ol can be up to 15.8 mol%.
(CDCl3): d 110.88 and 111.40 (pyrrole C2, C3), 118.30 (pyrrole C4),
121.23 (phenyl C2, C6), 124.37 (CF3), 126.47 and 126.52 (phenyl
=
C3, C5), 129.81 (phenyl C4), 130.41 (pyrrole C1), 151.48 (CH N),
179.62 (phenyl C1).
=
Synthesis of iminopyrrolide ligand 2-(C6F5N CH)C4H3NH (1e)
Experimental
To a stirred solution of pyrrole-2-carboxyaldehyde (2.38 g,
25 mmol) and pentafluoroaniline (4.58 g, 25 mmol) in dried
toluene (40 mL), p-toluenesulfonic acid monohydrate (30 mg) as a
catalyst was added at room temperature. The mixture was stirred
for 6 h at 60 ◦C, and then the toluene was evaporated in reduced
All manipulations of air- and/or moisture-sensitive compounds
were carried out under a dry argon atmosphere by using standard
Schlenk techniques or under a dry argon atmosphere in an
MBraun glovebox unless otherwise noted. All solvents were
purified from an MBraun SPS system. Commercial ethylene was
directly used for polymerization without further purification. 10-
Undecen-1-ol and ethyl trichloroacetate (ETA) were purchased
from Aldrich, dried over calcium hydride at room temperature and
◦
pressure at 60 C to give a residue. The residue was dissolved in
dried toluene (40 mL) and stirred for 4 h at 60 ◦C. Then the toluene
was evaporated in reduced pressure to give the crude product.
The crude product was purified by column chromatography on
silica gel with petroleum ether–ethyl acetate (200 : 1) as an eluent,
=
then distilled. Iminopyrrolide ligands 2-(C6H11N CH)C4H3NH
=
=
(1a), 2-(C6H5N CH)C4H3NH (1b) and 2-(2,6-iPr2C6H3N CH)
C4H3NH (1c) were prepared with good yields (1a, 87%; 1b, 90%;
1c, 93%) according to the procedure reported.25b,27a VCl3(THF)3
was purchased from Aldrich. Et2AlCl, AlMe3, AlEt3, and AliBu3
were purchased from Albemarle Corporation. Modified methy-
laluminoxane (MMAO, 7% aluminum in heptane solution) was
purchased from Akzo Nobel Chemical Inc. The other reagents
and solvents were commercially available.
=
affording 2-(C6F5N CH)C4H3NH (1e) (3.25 g, 12.5 mmol) as a
brown solid in 50% yield. H NMR (CDCl3): d 6.35–6.38 (m,
1
pyrrole-H), 6.79 (m, pyrrole-H) 7.10 (m, pyrrole-H), 8.36 (s, 1 H,
CH N), 9.51 (br, 1 H, N-H). 13C NMR (CDCl3): d 110.26 (pyrrole
=
C2, C3), 118.34 (pyrrole C4), 129.09 (pyrrole C1), 124.07 (phenyl
C1), 135.09 and 135.29 (phenyl C3, C5), 138.04–138.59 (phenyl C2,
=
C6), 141.33 (phenyl C4), 155.76 (CH N).
NMR data of the ligands were obtained on a Bruker 300 MHz
spectrometer at ambient temperature with CDCl3 as a solvent
Synthesis of vanadium complex
1
13
˚
(dried by MS 4 A). The H NMR, C NMR data of the copolymers
were obtained on a Varian Unity-400 MHz spectrometer at 135 ◦C,
with o-C6D4Cl2 as a solvent. The IR spectra were recorded on a
Bio-Rad FTS-135 spectrophotometer. Elemental analyses were
recorded on an elemental Vario EL spectrometer. MALDI-TOF
MS was performed on a Voyager DE-STR instrument (Applied
Biosystems, Foster City, CA) equipped with a 337 nm pulsed
nitrogen laser. DSC measurements were performed on a Perkin-
Elmer Pyris 1 Differential Scanning Calorimeter at a rate of
10 ◦C min-1. The weight-average molecular weights (Mws) and the
polydispersity indexes (PDIs) of polymer samples were determined
at 150 ◦C by a PL-GPC 220 type high-temperature chromatograph
equipped with three Plgel 10 mm Mixed-B LS type columns. 1,2,4-
Trichlorobenzene (TCB) was employed as the solvent at a flow
rate of 1.0 mL min-1. The calibration was made by polystyrene
standard EasiCal PS-1 (PL Ltd).
=
[2-(C6H5N CH)C4H3N]VCl2(THF)2 (2b)
To a stirred solution of ligand 1b (170 mg, 1 mmol) in dried THF
◦
(20 mL) at -78 C, a 2.5 mol L-1 n-butyllithium hexane solution
(0.44 mL, 1.1 mmol) was added dropwise over 5 min. The mixture
was allowed to warm to room temperature slowly and stirred for
2.5 h. The resultant mixture was added dropwise to VCl3(THF)3
(374 mg, 1 mmol) in dried THF (20 mL) at -78 ◦C over 30 min.
The mixture was allowed to warm to room temperature slowly
and stirred overnight. Evaporation of the solvent under reduced
pressure yielded a crude product. To the crude product, dried
toluene (20 mL) was added, and the mixture was stirred for 10 min,
and then filtered. The filtrate was concentrated to 10 mL under
reduced pressure. Crystallization by diffusion of n-hexane (20 mL)
into the clear solution yielded red-black crystals of 2b (0.30 g,
69%). IR (KBr pellets, cm-1): n 3056, 2972, 2920, 2851, 1663,
1558, 1429, 1391, 1330, 1280, 1259, 1179,1 151, 1090, 1037, 1014,
987, 924, 910, 885, 856, 776, 754, 746, 695, 607, 598, 565, 497, 416.
EI-MS (70 eV): m/z = 434 [M+]. Anal. calcd for C19H25Cl2N2O2V:
C 52.43, H 5.79, N 6.44%. Found: C 52.31, H 5.73, N 6.38%.
=
Synthesis of iminopyrrolide ligand 2-(4-CF3C6H4N CH)C4H3NH
(1d)
To a stirred solution of pyrrole-2-carboxyaldehyde (2.85 g, 30
mmol) in dried ethanol (40 mL), p-trifluoromethylaniline (4.83 g,
30 mmol) and formic acid (10 drops), as a catalyst, were added.
The reaction mixture was stirred for 48 h at room temperature.
The solution was concentrated to 15 mL and placed in the freezer
(-20 ◦C) overnight. The resulting mixture was filtrated through a
glass filter. The solid was washed with 5 mL cold ethanol. 2-(4-
Synthesis of vanadium complex
=
[2-(C6H11N CH)C4H3N]VCl2(THF)2 (2a)
Complex 2a, as a red-black crystal in 75% yield, was prepared via
a procedure similar to that for 2b. IR (KBr pellets, cm-1): n 3106,
2967, 2871, 1646, 1593, 1562, 1490, 1460, 1442, 1428, 1391, 1363,
1326, 1282, 1259, 1166, 1143, 1109, 1092, 1032, 1015, 990, 933,
898, 858, 805, 775, 752, 683, 573, 447. EI-MS (70 ev): m/z = 440
[M+]. Anal. calcd for C19H31Cl2N2O2V: C 51.71, H 7.08, N 6.35%.
Found: C 51.58, H 7.04, N 6.38%.
=
CF3C6H4N CH)C4H3NH (1d) (6.42 g, 26.95 mmol) was afforded
as off-white crystalline solid in 90% yield. H NMR (CDCl3): d
1
6.34 (m, 1 H, pyrrole-H), 6.74 (m, 1 H, pyrrole-H), 7.02 (m, 1
H, pyrrole-H), 7.22–7.25 (d, 2 H, benzene-H), 7.60–7.63 (d, 2 H,
benzene-H), 8.24 (s, 1 H, CH N), 9.54 (br, 1 H, N-H). 13C NMR
=
8860 | Dalton Trans., 2009, 8854–8863
This journal is
The Royal Society of Chemistry 2009
©

Synthesis of vanadium complex
Ethylene polymerization
[2-(2,6-iPr2C6H3)C4H3N]VCl2(THF)2 (2c)
Polymerizations were carried out under atmospheric pressure in
toluene in a 150 mL glass reactor equipped with a mechanical
stirrer. The total volume of the liquid phase was 50 mL. The
prescribed amount of toluene was introduced into the nitrogen-
purged reactor and stirred vigorously (600 rpm). The toluene was
kept at a prescribed polymerization temperature, and then ethylene
gas feed was started. After 15 min, a solution of ETA in toluene
and a solution of Et2AlCl in toluene were added and stirred for
5 min. Then a toluene solution of the vanadium complexes was
added into the reactor with vigorous stirring (900 rpm) to initiate
polymerization. After a prescribed time, the ethylene gas feed was
stopped and acidic alcohol (10 mL) was added to terminate the
polymerization reaction. The resultant mixture was poured into
acidic alcohol (150 mL). The solid polyethylene was isolated by
filtration, washed with alcohol and acetone, and dried at 60 ◦C for
24 h in a vacuum oven.
Complex 2c, as a brown crystal in 63% yield, was prepared via a
procedure similar to that for 2b. IR (KBr pellets, cm-1): n 3106,
2926, 2852, 1663, 1581, 1496, 1450 1426, 1397, 1374, 1347, 1316,
1282, 1242, 1176, 1145, 1104, 1063, 1031, 989, 921, 892, 847, 817,
748, 696, 634, 602, 467, 411. EI-MS (70 eV): m/z = 518 [M+]. Anal.
calcd for C25H37Cl2N2O2V: C 57.81, H 7.18, N 5.39%. Found: C
57.62, H 7.13, N 5.42%.
Synthesis of vanadium complex
[2-(4-CF3C6H4)C4H3N]VCl2(THF)2 (2d)
Complex 2d, as a brown crystal in 72% yield, was prepared via a
procedure similar to that for 2b. IR (KBr pellets, cm-1): n 3105,
2920, 2851, 1663, 1616, 1599, 1570, 1514, 1482, 1433, 1416, 1391,
1325, 1301, 1280, 1175, 1121, 1068, 1038, 1015, 992, 963, 922, 899,
845, 791, 749, 686, 637, 605, 549, 511, 466, 423, 404. EI-MS (70
eV): m/z = 502 [M+]. Anal. calcd for C20H24Cl2 F3N2O2V: C 47.73,
H 4.81, N 5.57%. Found: C 47.59, H 4.75, N 5.50%.
Ethylene/10-undecen-1-ol copolymerization
Copolymerizations were carried out under atmospheric pressure
in toluene in a 150 mL glass reactor equipped with a mechanical
stirrer. The total volume of the liquid phase was 50 mL. The
nitrogen-purged reactor was charged with the prescribed amount
of toluene and the prescribed amount of 10-undecen-1-ol and
stirred vigorously (600 rpm). Then equivalent protecting reagent
(Et2AlCl or AlMe3 or AlEt3 or AliBu3) was added and the
ethylene gas feed was started followed by equilibration at desired
polymerization temperature. After 10 min, a solution of ETA in
toluene and a solution of Et2AlCl in toluene were added and
stirred for 5 min. Subsequently, a toluene solution of catalyst was
added into the reactor with vigorous stirring (900 rpm) to initiate
Synthesis of vanadium complex [2-(C6F5)C4H3N]VCl2(THF)2 (2e)
Complex 2e, as a brown crystal in 45% yield, was prepared via a
procedure similar to that for 2b. IR (KBr pellets, cm-1): n 3116,
2962, 2919, 2851, 2653, 1662, 1640, 1565, 1520, 1510, 1472, 1457,
1422, 1387, 1330, 1308, 1272, 1191, 1135, 1082, 1043, 1004, 984,
923, 857, 769, 728, 689, 662, 647, 604, 577, 484, 451, 414. EI-MS
(70 eV): m/z = 524 [M+]. Anal. calcd for C19H20Cl2 F5N2O2V: C
43.45, H 3.84, N 5.33%. Found: C 43.28, H 3.78, N 5.40%.
Table 4 Crystal data and structure refinements of complexes 2b, 2c and 2e
2a
2c
2e·THF
Empirical formula
FW/g mol-1
T/K
C19H31Cl2N2O2V
441.30
187(2)
C25H37Cl2N2O2V
519.41
187(2)
Monoclinic
P21/n
1.68743(11)
0.91538(6)
3.4753(2)
5.2261(6)
90.00
103.2050(10)
90.00
C23H28Cl2F5N2O3V
597.31
185(2)
Monoclinic
P21
8.3619(12)
15.214(2)
10.2809(14)
1305.3(3)
90.00
93.629(2)
90
Crystal system
Space group
a/nm
Triclinic
¯
P1
1.0282(3)
b/nm
1.4958(4)
1.4958(4)
2.1168(10)
78.948(4)
74.413(4)
74.413(4)
4
1.385
0.737
928
c/nm
V/nm3
a/◦
b/◦
g /◦
Z
8
2
D
calcd/Mg m-3
1.320
0.608
2192
1.520
0.648
612
0.26 ¥ 0.10 ¥ 0.10
1.98 to 25.50
7090 [Rint = 0.0416]
m/mm-1
F(000)
Crystal size/mm
0.10 ¥ 0.10 ¥ 0.08
1.43 to 24.99
7333 (Rint = 0.0522)
Semi-empirical from equivalents
0.9407 and 0.9287
Full-matrix least-squares on F2
R1 = 0.0739
0.26 ¥ 0.15 ¥ 0.07
1.50 to 26.04
10 299 (Rint = 0.0691)
q range/◦
No. of independent reflections
Absorbance correction
Max. and min. transmission
Refinement method
Final R indices [I > 2s(I)]
Semi-empirical from equivalents Semi-empirical from equivalents
0.9564 and 0.8589
0.9410 and 0.8516
Full-matrix least-squares on F2 Full-matrix least-squares on F2
R1 = 0.0668
R1 = 0.0592
wR2 = 0.1545
R1 = 0.1487, wR2 = 0.1805
0.588 and -0.523
wR2 = 0.1296
wR2= 0.1260
R indices (all data)
Largest diffraction peak and hole/e A
R1 = 0.1213, wR2 = 0.1527
0.575 and -0.319
R1 = 0.0844, wR2 =0.1357
0.559 and -0.281
-3
˚
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8854–8863 | 8861
©

polymerization. After a prescribed time, the ethylene gas feed
was stopped and acidic alcohol (10 mL) was added to terminate
the polymerization reaction. The resultant mixture was poured
into acidic alcohol (150 mL). The solid polymer was isolated by
filtration, washed with alcohol and acetone, and dried at 60 ◦C for
24 h in a vacuum oven.
2003, 237, 229–243; (c) P. D. Bolton and P. Mountford, Adv. Synth.
Catal., 2005, 347, 355–366.
8 (a) Y. L. Ma, D. Reardon, S. Gambarotta and G. Yap, Organometallics,
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Crystallographic studies
Crystals for X-ray analyses were obtained as described in the
preparations. The crystallographic data, collection parameters,
and refinement parameters are listed in Table 4. The crystals
were manipulated in a glovebox. The intensity data were collected
with the w scan mode (187 K) on a Bruker Smart APEX
diffractometer with CCD detector using Mo Ka radiation (l
˚
= 0.71073 A). Lorentz, 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 structures were solved by the direct method and refined by the
full-matrix least-squares on F2 using the SHELXTL-97 program.
The Flack parameter is 0.48 for Structure 725661, which means
that the crystal is thus twinned by inversion and the ratio of two
configurations is 0.48 : 0.52. The positions of hydrogen atoms
were calculated theoretically and included in the final cycles of
refinement in a riding model along with attached carbons.
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Acknowledgements
The authors are grateful for subsidy provided by the National Nat-
ural Science Foundation of China (no. 20734002 and 50525312),
and by the Special Funds for Major State Basis Research Projects
(no. 2005CB623800) from the Ministry of Science and Technology
of China.
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