Polymerization of methyl methacrylate catalyzed by nickel complexes with hydroxyindanone-imine ligands

Article abstract of DOI:10.1039/b708048d

A series of new hydroxyindanone-imine ligands [PhNCC₂H ₃(CH₃)C₆H₂(CH₃)OH] (HL₁) and [ArNCC₂H₃(CH₃)C ₆H₂(R)OH] (Ar = 2,6-i-Pr₂C₆H ₃, R = Me (HL₂), R = H (HL₃), and R = Cl (HL₄)) were synthesized and characterized. Reactions of hydroxyindanone-imines with Ni(OAc)₂·4H₂O result in the formation of the trinuclear hexa(indanone-iminato)tri(nickel(ii)) complex Ni₃[PhNCC₂H₃(CH₃)C₆H ₂(CH₃)O]₆ (1) and the mononuclear bis(indanone-iminato)nickel(ii) complexes Ni[ArNCC₂H ₃(CH₃)C₆H₂(R)O]₂ (Ar = 2,6-i-Pr₂C₆H₃, R = Me (2), R = H (3), and R = Cl (4)). All nickel complexes were characterized by their IR, NMR spectra and elemental analyses. In addition, X-ray structure analyses were performed for complexes 1 and 2. After being activated with methylaluminoxane (MAO), these nickel(ii) complexes can be used as catalysts for the polymerization of methyl methacrylate (MMA) to produce syndiotactic-rich PMMA. Catalytic activities and the degree of syndiotacticity of PMMA have been investigated for various reaction conditions. The Royal Society of Chemistry.

Full text of DOI:10.1039/b708048d

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PAPER
www.rsc.org/dalton | Dalton Transactions
Polymerization of methyl methacrylate catalyzed by nickel complexes with
hydroxyindanone-imine ligands†
Guangrong Tang and Guo-Xin Jin*
Received 29th May 2007, Accepted 6th July 2007
First published as an Advance Article on the web 2nd August 2007
DOI: 10.1039/b708048d
=
A series of new hydroxyindanone-imine ligands [PhN CC2H3(CH3)C6H2(CH3)OH] (HL1) and
=
[ArN CC2H3(CH3)C6H2(R)OH] (Ar = 2,6-i-Pr2C6H3, R = Me (HL2), R = H (HL3), and R = Cl
(HL4)) were synthesized and characterized. Reactions of hydroxyindanone-imines with Ni(OAc)2·4H2O
result in the formation of the trinuclear hexa(indanone-iminato)tri(nickel(II)) complex
=
Ni3[PhN CC2H3(CH3)C6H2(CH3)O]6 (1) and the mononuclear bis(indanone-iminato)nickel(II)
=
complexes Ni[ArN CC2H3(CH3)C6H2(R)O]2 (Ar = 2,6-i-Pr2C6H3, R = Me (2), R = H (3), and R = Cl
(4)). All nickel complexes were characterized by their IR, NMR spectra and elemental analyses. In
addition, X-ray structure analyses were performed for complexes 1 and 2. After being activated with
methylaluminoxane (MAO), these nickel(II) complexes can be used as catalysts for the polymerization
of methyl methacrylate (MMA) to produce syndiotactic-rich PMMA. Catalytic activities and the
degree of syndiotacticity of PMMA have been investigated for various reaction conditions.
distribution activated with MAO. Recently several reports had also
appeared claiming coordination polymerization of MMA based
on copper(II) complexes.12
Introduction
Stereospecific polymerization of methyl methacrylate (MMA) has
attracted increasing attention from both academia and industry.
Noteworthy successes in this regard included the discoveries by
Yasuda et al.1 and Collins and Ward2 that lanthanocenes3 and
zirconocenes4 were efficient initiators for the controlled polymer-
ization of MMA, providing isotactic or syndiotactic PMMA based
on the ligand structures.
Our group have designed and synthesized a number of the early
transition metal and late transition metal complexes based on
[O, N], [N, N], [C, N] and [N, P] ligands for polymerization of
ethylene and norbornene.13 Herein, we reported the synthesis of
a series of nickel(II) complexes bearing hydroxyindanone-imine
ligands. After activation with MAO, those nickel(II) complexes can
be used as catalysts for the polymerization of MMA, providing the
syndiotactic-rich PMMA.
Late transition metal complexes are generally considered to be
more tolerant toward polar functional monomers due to their less
oxophilic nature relative to early transition metal complexes, and
make them likely targets for the development of catalysts for the
polymerization of the polar monomers including MMA.5 Never-
theless, there are few reports on stereospecific polymerization of
MMA catalyzed by late transition metal complexes with methyla-
luminoxane (MAO) systems. The Ni(acac)2/MAO catalyst system
was first found to be an effective catalyst for the polymerization of
MMA.6 A series of nickelocene complexes evidenced good activity
in the polymerization of MMA with syndiotactic-rich PMMA.7
Carlini et al.8 reported the polymerization of MMA catalyzed by
nickel complexes based on salicylaldimine ligands, which provided
syndiotactic-rich PMMA with high molecular weight and broad
polydispersity index. Kim et al.9 reported that late transition metal
complexes such as (a-diimine)nickel, (pyridyl bisimine)iron(II) and
(pyridyl bisimine)cobalt(II), which were widely used for the olefin
polymerization,10 polymerized MMA in combination with MAO
to give syndiotactic-rich PMMA. Wu and co-workers11 reported
bis(b-ketiminato)nickel complexes could polymerize MMA to give
syndiotactic-rich PMMA with relatively wide molecular weight
Results and discussion
Synthesis of ligands HL1–HL4 and complexes 1–4
The hydroxyindanone-imine ligands HL1–HL4 can be obtained by
the condensation reaction of the corresponding hydroxyindanone
with aniline or 2,6-diisopropylaniline. According to a modified
method,14 ligand HL1 without substituted groups on aniline can
be obtained in 80% yield by the condensation of corresponding
hydroxyindanone with aniline in ethanol using formic acid as
a catalyst, and ligands HL2–HL4 were synthesized in about
40% yield by the Schiff base condensation of the corresponding
hydroxyindanone with 2,6-diisopropylaniline in toluene using
TiCl4 as a Lewis acid catalyst (Scheme 1).
Like the procedure of preparing bis(salicylaldiminato) nickel(II)
complexes,15 nickel complexes 1–4 were prepared by the reaction
of Ni(OAc)2·4H2O with two equivalents of the correspond-
ing hydroxyindanone-imine. Green trinuclear nickel complex 1
was synthesized from ligand HL1, while brown mononuclear
nickel complexes 2–4 were synthesized from ligands HL2–HL4
(Scheme 1). This is due to the steric hindrance of substituted
groups at the 2- and the 6-position of aniline. All complexes are
stable in dry air. They are readily soluble in dichloromethane,
toluene and THF, but sparingly soluble in ethanol and methanol.
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,
Department of Chemistry, Fudan University, Shanghai, 200433, P. R. China.
E-mail: gxjin@fudan.edu.cn; Fax: (+86)21-65643776
† CCDC reference numbers 633235 and 633236. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b708048d
3840 | Dalton Trans., 2007, 3840–3846
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Scheme 1 The synthesis of ligands HL1–HL4 and complexes 1–4.
Table 1 Crystallographic data and structure refinement details for 1
and 2
The trinuclear complex 1 is paramagnetic, while mononu-
clear complexes 2–4 are diamagnetic. The H NMR spectra of
1
complexes 2–4 show signals at d 5.3–5.4 ppm (d 5.35 (2), 5.41
(3), 5.34 ppm(4)) assigned to the phenoxy C2–H signals, while
the C2–H signals of the ligands HL2–HL4 were found at about
d 6.8 ppm (d 6.77 (HL2), 6.84 (HL3), 6.82 ppm(HL4)). The
shift to high field results from the ring current, formed by the
delocalized p electrons of the phenyl of N-aryl system to other
hydroxyindanone-imine moiety. Compared to bis(indaniminato)-
nickel(II) complexes, the signals of aromatic protons of bis[(N-2,6-
diisopropylphenyl)salicylaldiminate] nickel(II) complex ranged be-
tween d 6.9 and 7.3 ppm,16 which indicates no presence of any ring
current.
Complex
1
2
Formula
Fw
T/K
C102 H96 N6 Ni3 O6
1677.98
293(2)
Trigonal
P3(1)21
0.40 × 0.40 × 0.30
22.826(4)
22.826(4)
17.511(4)
90
90
120
7901(2)
3
1.058
0.579
1.03–25.01
33593
9289
0.1222
0.818
0.0522
0.1370
−0.01(2)
C46 H56 N2 Ni O2
727.64
293(2)
Triclinic
P-1
0.20 × 0.15 × 0.10
9.878(4)
11.226(5)
19.901(9)
79.860(7)
78.497(7)
72.554(6)
2047.0(15)
2
1.181
0.512
1.05–25.01
8640
7129
0.0991
0.861
0.0692
0.1783
Crystal system
Space group
Crystal size/mm3
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
X-Ray single crystal structures of complexes 1 and 2
Z
qcalcd/g cm−3
l/mm−1
Crystals suitable for X-ray crystallography of 1 was obtained
by slow diffusion of ethanol into a dichloromethane solution of
complex 1. The crystallographic data and processing parameters
are given in Table 1. The ORTEP diagram of 1 is presented in
Fig. 1. The X-ray structure analysis clearly indicates that complex
1 is octahedral and trimeric, the two terminal nickel atoms (Ni(2)
and Ni(2A)) are symmetrical. The molecular structure shows the
six-coordinate geometry about every nickel atom, in which each
terminal nickel atom is tri-chelated and the central one is not part
of any chelate ring, with six oxygen donor atoms only. The Ni–O
h range/◦
Reflections collected
Independent reflections
Rint
GOF on F2
R1
wR2
Absolute structure
parameter
—
R1 = R(| | Fo|–| Fc| |)/R| Fo|, wR2 = [R(| Fo|2 -| Fc|2)2/R(Fo2)]1/2
.
˚
distances vary from 2.053(4) to 2.075(4) A, the mean distance of
˚
Ni(1)–O is similar to that of Ni(2)–O (2.0607(4) and 2.0597(4) A,
˚
respectively). The Ni(2)–N distances vary from 2.108 to 2.127 A.
The Ni(1)–Ni(2) and Ni(1)–Ni(2A) distances are 2.8258(9) and
2. The crystallographic data and processing parameters are
given in Table 1. For complex 2, there are two independent
molecules in the crystal cell, and the nickel atoms Ni(1) and
Ni(2) lie on independent inversion centers. The ORTEP diagram
of one of two molecules of complex 2 is shown in Fig. 2.
Each nickel coordinates the two ligands in a planar fashion
with a trans-N2O2 arrangement of the donor atoms. The N-
2,6-diisopropylphenyl groups are also roughly perpendicular to
the remainder of the ligand L, making an angle of 93.6◦ With
˚
2.8257(9) A, respectively. The Ni–Ni distance is shorter than
˚
the sum of the nickel(II) atomic van der Waals radii, 3.3 A,
at which point the chemical interaction may be considered to
be insignificant.17 It indicates that there is direct chemical Ni-
Ni interactions in the structure of complex 1. The Ni(2)–Ni(1)–
Ni(2A) angle is 175.57 (6)◦. The trimeric nickel complex 1 is an
approximately linear Ni3 cluster.
˚
Crystals of 2 suitable for X-ray crystallography were obtained
by slow diffusion of ethanol into a toluene solution of complex
the hydroxyindanone-imine residues. The Ni(1)–O (1.837(3) A)
˚
and Ni(1)–N (1.926(3)A) distances are slightly longer than those
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Fig. 1 Molecular structure of complex 1 with 30% probability (the
hydrogen atoms are omitted for clarity). The additional “A” letter
indicates the symmetry operation (–x + 2, −x + y + 1, −z + 7/3).
Fig. 2 Molecular structure of complex 2 with 30% probability (the
hydrogen atoms are omitted for clarity). The additional “A” letter indicates
˚
the symmetry operation (−x+ 1, −y + 1, −z + 1). Selected bond lengths (A)
◦
˚
Selected bond lengths (A) and angles ( ): Ni(1)–O(1) 2.054(4), Ni(1)–
O(2) 2.053(4), Ni(1)–O(3) 2.075(4), Ni(2)–O(1) 2.056(4), Ni(2)–O(2)
2.055(4), Ni(2)–O(3) 2.068(4), Ni(2)–N(1) 2.119(5), Ni(2)–N(2)
2.127(5), Ni(2)–N(3) 2.108(5), Ni(1)–Ni(2) 2.8258(9), Ni(1)–Ni(2A)
2.8257(9); O(1)–Ni(1)–O(2) 79.07(15), O(1)–Ni(1)–O(3) 77.45(16), O(1)–
Ni(1)–O(1A) 168.4(3), O(1)–Ni(1)–O(2A) 93.96(15), (1)–Ni(1)–O(3A)
110.36(17), O(2)–Ni(1)–O(3) 77.76(16), O(2)–Ni(1)–O(2A) 106.9(2),
(2)–Ni(1)–O(3A) 169.48(16), O(3)–Ni(1)–O(3A) 99.3(2), O(1)–Ni(2)–N(1)
90.34(19), O(2)–Ni(2)–O(2) 89.2(2), O(3)–Ni(2)–N(3) 91.3(2) and
Ni(2)–Ni(1)–Ni(2A) 175.57(6).
and angles (◦): Ni(1)–O(1) 1.837(3), Ni(1)–N(1) 1.926(3); O(1)–Ni(1)–N(1)
94.74(13), O(1)–Ni(1)–N(1A) 85.26(13), N(1)–C(7)–C(6) 125.1(4).
result showed that MAO is indispensable for the activation of the
nickel complexes 1–4 for MMA polymerization.
Table 2 shows polymerization results using Ni(II) complexes 1–
4 activated with MAO. After activation with MAO, all Ni (II)
complexes can catalyze the polymerization of MMA to produce
syndiotactic-rich PMMA with high activities. The results suggest
that the structure of the complex has a significant affect on the
activity, stereotacticity, molecular weight and molecular weight
distribution. At the same polymerization conditions, the trinuclear
complex 1 showed the lowest activity, while the mononuclear
complex 2 showed the highest activity of 4.25 × 104 g PMMA
mol−1 Ni h−1 (Table 2, run 2). All complexes produced a polymer
with a rather high degree of syndiotacticity, and the highest degree
of syndiotacticity (rr triads up to 79.0%) was observed in PMMA
produced by complex 3 (Table 2, run 3). All polymers obtained
showed high number-average molecular weight (Mn = 5.7–10.6 ×
104 g mol−1) and relatively wide molecular weight distribution
(Mw/Mn = 4.0–6.0). Taking into account that the viscosity of
the medium gradually increased during polymerization, diffusion
phenomena could be responsible for the wide molecular weight
distribution.
˚
˚
(1.8285(9) A and 1.9087(11) A, respectively) found in the bis[(N-
2,6-diisopropylphenyl)salicylaldiminate]nickel(II) complex.16 The
O(1)–Ni(1)–N(1) angle (94.74(13)◦) is bigger than the angle
of 93.03(4)◦ for the bis[(N-2,6-diisopropylphenyl) salicylaldimi-
nate]nickel(II) complex.16 The N(1)–C(7)–C(6) angle (125.1(4)◦)
is smaller than the angle (126.27(12)◦) found in the bis[(N-
2,6-diisopropylphenyl) salicylaldiminate]nickel(II) complex, which
indicates the orientation of nitrogen atom in the space is limited
due to the presence of five-membered ring. It indicates that
the structures of nickel complexes with hydroxyindanone-imine
ligands are very different from those of nickel complexes with
salicylaldimine ligands with the introduction of the five-membered
ring.
The polymerization temperature also affects considerably the
catalytic activities and molecular weight as well as molecular
weight distribution (Table 3). For both complexes 1 and 2, the
catalytic activities first increased and then sharply decreased with
increasing polymerization temperature, and the highest activity
Polymerization of methyl methacrylate (MMA)
Prior to this study, an attempt to polymerize MMA by using the
nickel complexes 1–4 or MAO alone was made. Due to the reaction
conditions, no polymer was obtained in any of these cases. This
Table 2 Polymerization of MMA with different nickel complexesa
cd
c
Run
Catalyst
Yield/g
Activityb
%mm
%mr
%rr
Mn
Mw/Mn
1
2
3
4
1
2
3
4
0.54
0.85
0.78
0.61
2.70
4.25
3.90
3.05
9.1
3.1
1.9
4.6
22.1
27.7
19.1
20.5
68.8
69.2
79.0
74.9
5.7
10.6
6.5
4.8
4.0
5.1
6.0
7.2
a Polymerization conditions: Ni = 20 lmol, Al/Ni = 150, MMA = 18.6 mmol, toluene = 10 ml, T = 60 ◦C, time = 1 h. b 104 g PMMA mol−1 Ni h−1
.
c Determined by GPC analysis. d 104 g mol−1
.
3842 | Dalton Trans., 2007, 3840–3846
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Table 3 Influence of the polymerization temperature on the polymerization of MMAa
cd
c
Run
Catalyst
T/◦C
Yield/g
Activityb
%mm
%mr
%rr
Mn
1.5
Mw/Mn
1
2
3
4
5
6
1
1
1
2
2
2
20
60
90
20
60
90
0.094
0.54
0.21
0.24
0.85
0.34
0.47
2.70
1.05
1.20
4.25
1.70
9.4
9.1
5.2
5.0
3.1
6.9
31.4
22.1
25.7
27.7
27.7
26.5
59.2
68.8
69.1
67.3
69.2
66.6
4.1
4.8
5.0
10.0
4.0
6.0
5.7
2.9
2.8
10.6
4.3
a Polymerization conditions: Ni = 20 lmol, Al/Ni = 150, MMA = 18.6 mmol, toluene = 10 ml, time = 1 h. b 104 g PMMA mol−1 Ni h−1
.
c Determined
by GPC analysis. d 104 g mol−1
.
Table 4 Influence of Al/Ni on the polymerization of MMAa
cd
c
Run
Catalyst
Al/Ni
Yield/g
Activityb
% mm
% mr
% rr
Mn
Mw/Mn
1
2
3
4
5
2
2
2
3
3
50
100
150
50
0.45
0.64
0.85
0.62
0.78
2.25
3.20
4.25
3.10
3.90
2.8
6.1
3.1
3.2
1.9
17.1
16.0
27.7
19.5
19.1
80.1
77.9
69.2
77.3
79.0
7.6
6.7
6.4
4.0
5.4
5.1
8.1
10.6
4.2
150
6.5
a Polymerization conditions: Ni = 20 lmol, MMA = 18.6 mmol, toluene = 10 ml, T = 60 ◦C, time = 1 h. b 104 g PMMA mol−1 Ni h−1
.
c Determined by
GPC analysis. d 104 g mol−1
.
values were achieved at 60 ◦C (Table 3, run 2 and 5). The number-
average molecular weight obviously depended on the polymeriza-
tion temperature. However, the degree of syndiotacticity showed
slightly variation under different polymerization temperature.
For a binary catalyst system, the ratios of Al/Ni will influ-
ence the catalytic activities, stereotacticity, molecular weight and
molecular weight distribution (Table 4). For both complexes 2 and
3, when the Al/Ni ratio increased from 50 to 150, an improvement
of both the activity and number-average molecular weight was
observed, but a decrease in molecular weight distribution was ob-
served. For complex 2, the degree of syndiotacticity decreased with
increasing the ratio of Al/Ni, the highest degree of syndiotacticity
(rr = 80.1%) was obtained at the Al : Ni ratio of 50 : 1 (Table 4, run
1). For complex 3, the varied trend of the degree of syndiotacticity
was contrary to that of complex 2.
To investigate the catalytic lifetime of complex 2, the polymeri-
zations of MMA were conducted for 1, 2, 4, and 12 h. The
relationship between the polymerization time and the polymer
yield indicates that the 2/MAO has a catalytic lifetime of about
2 h, as shown in Table 5. With increasing polymerization time, the
degree of syndiotacticity first increases and then decreased.
In the above polymerization reactions (Tables 2–5), the nickel
precursor was dissolved at room temperature in toluene, then
MMA and MAO were added in that order (see Experimental).
When MAO was allowed to react with complex 2 before the
introduction of MMA, an improvement in the activity and
degree of syndiotacticity was observed (Table 6, run 2). When
the activation was performed under an ethylene atmosphere, the
activity sharply increased up to 6.35 × 104 g PMMA mol−1 Ni h−1
(Table 2, run 2), agreed with the results reported by Carlini et al.8
The activation effect caused by the presence of ethylene might
be attributed to the fact that the olefin helps MAO to remove
one chelate ligand from the metal nickel and at the same time
stabilizes the resulting active species by coordination to the center
metal nickel, increasing the concentration of active sites capable
of polymerizing MMA.8c Finally, some polymerization reactions
were performed by the amount of the nickel complex and/or
MMA monomer being reduced to decrease the polymerization
rates (Table 6, run 4–6). When both nickel complex and MMA
monomer were reduced to 1/4, the polymerization reaction did
not occur (Table 6, run 4). The decrease in activity was observed
when reducing the nickel complex or MMA monomer by 75%
(Table 6, run 5 and 6). However, the degree of syndiotacticity
varied slightly.
Table 6 Influence of other polymerization conditions on the polymeriza-
tion of MMA catalyzed by complex 2/MAOa
Run
Yield/g
Activityb
% mm
% mr
% rr
Table 5 Influence of polymerization time on the polymerization of MMA
catalyzed by complex 2/MAOa
1
0.85
0.91
1.27
0.0
0.65
0.25
4.25
4.55
6.35
—
3.26
1.25
3.1
11.9
8.3
—
8.6
4.3
27.7
15.0
17.7
—
24.2
23.1
69.2
73.1
74.0
—
67.2
72.6
2c
3d
4e
5f
6g
Run Time/h
Yield/g Activityb
% mm % mr
% rr
1
2
3
4
1
2
4
0.85
0.96
0.98
1.02
4.25
2.40
1.22
0.42
3.1
3.4
5.2
5.8
27.7
23.2
17.3
22.8
69.2
73.4
77.5
71.4
a Polymerization conditions: Ni = 20 lmol, Al/Ni = 150, MMA =
18.6 mmol, toluene = 10 ml, T = 60 ◦C, time = 1 h. b 104 g PMMA
12
mol−1 Ni h−1 c The order is Ni, MAO, MMA. d The catalyst was prepared
.
a Polymerization conditions: Ni = 20 lmol, MMA = 18.6 mmol, toluene =
in the presence of an ethylene atmosphere. e Ni = 5.0 lmol, MMA =
10 ml, T = 60 ◦C. b 04 g PMMA mol−1 Ni h−1
.
4.65 mmol. f Ni = 5.0 lmol. g MMA = 4.65 mmol.
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774 (m), 735 (w), 705 (m) cm−1; Anal. Calc. for C17H17NO: C 81.24,
H 6.82, N 5.57; Found: C 80.98, H 6.74, N 5.59%.
Conclusion
In this report, a series of nickel(II) complexes containing
hydroxyindanone-imine ligands were synthesized and character-
ized, which were air-stable. A combination of spectroscopic and X-
ray crystallographic studies confirmed the structure of these nickel
complexes. After activation with MAO, the resulting nickel(II)
complexes can be used as catalysts for the polymerization of
MMA to produce syndiotactic-rich PMMA. The degree of syn-
diotacticity and molecular weight of polymer can be controlled by
the structure of nickel complexes and polymerization parameters
including polymerization temperature and the ratio of Al/Ni.
Synthesis of 7-hydroxy-3,4-dimethylindan-1-(N-2,6-diisopropyl-
phenylimine) (HL2). To a stirred solution of 2,6-diisopro-
pylaniline (8.6 mL, 45.4 mmol) in toluene (40 mL) was added
TiCl4 (1.3 mL, 11.4 mmol) in toluene (30 mL) at room temperature
during 30 min. The resulting mixture was stirred at 90 ◦C for
30 min followed by the addition of 7-hydroxy-3,4-dimethylindan-
1-one (2.0 g, 11.4 mmol). The mixture was stirred for 48 h at
90 ◦C, poured into saturated Na2CO3 solution, and extracted with
ethyl ether. The organic phase was dried over anhydrous Mg2SO4.
Evaporating the solvent, purification by column chromatography
on silica gel using hexane : ethyl acetate (200 : 1) as eluent gave
1
Experimental
compound HL2 (1.54 g, 40%) as an orange-red oil. H NMR
(500 MHz, CDCl3, ppm): d 1.11–1.28 (m, 15H, CH3), 2.08 (dd,
1H, CH2), 2.30 (s, 3H, Me), 2.67 (dd, 1H, CH2), 2.84(m, 1H, CH),
2.96 (m, 1H, CH), 3.43 (m, 1H, CH), 6.77 (d, 1H, aromatic-H),
7.14–7.18 (m, 4H, aromatic-H), 11.78 (br, 1H, OH); 13C NMR
(125 MHz, CDCl3, ppm): d 17.4, 21.4, 22.6, 22.9, 23.1, 23.7, 23.9,
28.0, 28.4, 35.1, 39.7, 113.8, 118.6, 122.9, 123.3, 124.7, 132.5, 137.4,
General procedures
All air-sensitive experiments were carried out under nitrogen
using standard Schenk techniques. Toluene was dried over
sodium/benzophenone and distilled under nitrogen prior to use.
MMA was purified by drying from CaH2 and distilling under
vacuum. Methylaluminoxane (MAO) was purchased from Aldrich
as 10% weight of a toluene solution and used without further
purification. 2,6-Diisopropylaniline (90%) was purchased from
Lancaster. Other chemicals were of analytical grade and were
used as received. FTIR spectra were recorded on a Nicolet
FT-IR spectrometer. Element analyses were performed on an
Elementar vario EL III Analyzer. 1H and 13C NMR spectra
were carried out on a Bruker AC 500 spectrometer instrument
at room temperature in CDCl3 solution for ligands and polymers
using TMS as internal standard. Gel permeation chromatography
(GPC) analyses of the molecular weight and molecular weight
distribution of the polymers were performed on an Agilent 1100
instrument using standard polystyrene as calibration and with
THF as the eluent at 35 ◦C. The tacticity of PMMA was
=
145.4, 153.5, 156.1 (C-O), 178.9 (C N); IR (KBr): m 3060 (w), 2961
(s), 2868 (m), 1634 (s), 1594 (m), 1461 (m), 1381 (w), 1361 (w),
1319 (w), 1287 (m), 1253 (m), 1221 (m), 1184 (w), 1107 (w),
1050 (w), 933 (w), 900 (w), 823 (m), 764 (w), 733 (m), 691 (w) cm−1;
Anal. Calc. for C23H29NO: C 82.34, H 8.71, N 4.18; Found: C
82.22, H 8.78, N 4.22%.
Synthesis of 7-hydroxy-3-methylindan-1-(N-2,6-diisopropyl-
phenylimine) (HL3). Analogous synthesis to HL2, except
that 7-hydroxy-3-methylindan-1-one instead of 7-hydroxy-3,4-
dimethylindan-1-one was used. Purification by column chro-
matography on silica gel using hexane : ethyl acetate (200 : 1)
as eluent gave compound HL3 (1.57 g, 43%) as a red-yellow solid.
1H NMR (500 MHz, CDCl3, ppm): d 1.13–1.30 (m, 15H, CH3),
2.05 (dd, 1H, CH2), 2.67 (dd, 1H, CH2), 2.89 (m, 2H, CH), 3.41 (m,
1
determined by the methyl resonance of H NMR. 7-Hydroxy-
1H, CH), 6.84–7.40 (m, 6H, aromatic-H), 11.78 (br, 1H, OH); 13
C
3-methylindan-1-one, 7-hydroxy-3,4-dimethylindan-1-one and 4-
chloro-7-hydroxy-3- methylindan-1-one were prepared according
to literature procedures.18
NMR (125 MHz, CDCl3, ppm): d 22.8, 23.2, 24.2, 28.7, 35.9, 39.7,
113.9, 115.4, 118.8, 122.8, 123.1, 123.6, 125.1, 132.5, 134.6, 137.6,
=
145.7, 156.2 (C–O), 158.3, 178.8 (C N); IR (KBr): m 3062 (w),
2962 (s), 2927 (m), 2869 (m), 1640 (s), 1596 (m), 1471 (m), 1437 (w),
1382 (w), 1362 (m), 1318 (w), 1290 (m), 1263 (m), 1216 (m),
1184 (m), 1158 (w), 1106 (w), 1051 (w), 955 (w), 879 (w), 835 (w),
796 (m), 741 (m), 690 (w) cm−1; Anal. Calc. for C22H27NO: C 82.20,
H 8.46, N 4.36; Found: C 81.92, H 8.41, N 4.40%.
Synthesis of 7-hydroxy-3,4-dimethylindan-1-(N-phenylimine)
(HL1). To a stirred mixture of 7-hydroxy-3,4-dimethylindan-1-
one (2 g, 11.4 mmol) and molecular sieves 4A (0.7 g) in ethanol
(30 mL) was added aniline (1.4 mL, 15.0 mmol) and formic
acid (0.10 mL) at room temperature. The mixture was refluxed
˚
˚
for 48 h and filtered. The molecular sieves 4A were washed
Synthesis of 4-chloro-7-hydroxy-3-methylindan-1-(N-2,6-diiso-
propylphenylimine) (HL4). Analogous synthesis to HL1, ex-
cept that 4-chloro-7-hydroxy-3-methylindan-1-one instead of 7-
hydroxy-3,4-dimethylindan-1-one was used. Purification by col-
umn chromatography on silica gel using hexane : ethyl acetate
(200 : 1) as eluent gave compound HL4 (1.62 g, 40%) as a red-
yellow solid. 1H NMR (500 MHz, CDCl3, ppm): d 1.12–1.35 (m,
15H, CH3), 2.14 (dd, 1H, CH2), 2.69 (dd, 1H, CH2), 2.80 (m,
1H, CH), 2.91 (m, 1H, CH), 3.50 (m, 1H, CH), 6.82 (d, 1H,
aromatic-H), 7.14–7.31 (m, 4H, aromatic-H), 11.76 (br, 1H, OH);
13C NMR (125 MHz, CDCl3, ppm): d 20.7, 22.9, 23.1, 23.8, 23.9,
28.5, 35.7, 39.4, 115.8, 120.9, 123.5, 125.0, 134.3, 137.4, 144.9,
with ethyl acetate (15 mL). The combined organic filtrates were
concentrated under reduced pressure and allowed to crystallize
at −20 ◦C. Purification by recrystallization from diethyl ether
1
gave compound HL1 (2.3 g, 80%) as yellow crystals. H NMR
(500 MHz, CDCl3, ppm): d 1.27 (d, 3H, CH3), 2.35 (s, 3H, CH3),
2.40 (dd, 1H, CH2), 3.06 (dd, 1H, CH2), 3.45 (m, 1H, CH), 6.74
(d, 1H, aromatic-H), 7.03 (m, 2H, aromatic-H), 7.14 (m, 2H,
aromatic-H), 7.37 (m, 2H, aromatic-H), 11.14 (br, 1H, OH); 13C
NMR (125 MHz, CDCl3, ppm): d 17.5, 21.2, 35.4, 38.9, 113.8,
121.3, 122.7, 124.5, 124.7, 129.2, 135.6, 149.5, 153.1, 156.0 (C–O),
177.9 (C N); IR (KBr): m 3048 (w), 2956 (w), 1642 (s), 1593 (m),
1484 (m), 1444 (m), 1374 (w), 1344 (w), 1284 (w), 1257 (m),
1209 (m), 1162 (w), 1069 (w), 1018 (w), 915 (w), 861 (w), 818 (m),
=
=
151.9, 156.8 (C–O), 178.3 (C N); IR (KBr): m 3062 (w), 2962
(s), 2927 (m), 2869 (m), 1640 (s), 1596 (m), 1471 (m), 1437 (w),
3844 | Dalton Trans., 2007, 3840–3846
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1382 (w), 1362 (m), 1318 (w), 1290 (m), 1263 (m), 1216 (m),
1184 (m), 1158 (w), 1106 (w), 1051 (w), 955 (w), 879 (w), 835 (w),
796 (m), 741 (m), 690 (w) cm−1; Anal. Calc. for C22H26ClNO: C
74.24, H 7.36, N 3.94; Found: C 74.11, H 7.29, N 3.90%.
Polymerization of MMA
In a typical procedure (Table 1, run 2), 20.0 lmol of nickel(II)
complex 2 in 2.0 mL of toluene, 18.6 mmol (2.0 mL) of MMA
and 10 mL toluene were added into a polymerization bottle with
a strong stirred◦under a nitrogen atmosphere. After the mixture
was kept at 60 C for 5 min, 2.0 mL of MAO was charged into
the polymerization system by means of a syringe and the reaction
was initiated. After 1 h, acidic methanol (Vethanol : Vconcd.HCl = 10 :
1) was added to terminate the reaction. The polymer was isolated
Synthesis of nickel(II) complexes (1–4). 7-hydroxy-3,4-dime-
thylindan-1-(N-phenylimine) (0.245 g, 0.98 mmol) was allowed
to react with Ni(OAc)2·4H2O (0.122 g, 0.49 mmol) in anhydrous
ethanol (20 mL) at the refluxing temperature for 3 h. After cooling,
the solid was filtered and recrystallized from a dichloromethane–
ethanol solution at room temperature to give complex 1 (0.33 g,
20%) as light green crystals. The other nickel complexes 2–4 were
prepared by the same procedure.
◦
by filtration, washed with methanol and dried at 80 C for 48 h
under vacuum.
X-Ray crystallography
Complex 1: IR (KBr): m 3058 (w), 2960 (w), 2922 (w), 2868 (w),
1609 (s), 1555 (m), 1474 (m), 1395 (w), 1336 (m), 1259 (w),
1207 (m), 1165 (w), 1098 (m), 1022 (m), 917 (w), 868 (w), 803 (m),
747 (w), 708 (m) cm−1; Anal. Calc. for C102H96N6Ni3O6: C 73.01,
H 5.77, N 5.01; Found: C 73.01, H 5.69, N 5.04%.
Complex 2: Complex 2 was obtained from a toluene–ethanol
solution at room temperature as brown crystals (0.50 g, 70%).
1H NMR (500 MHz, CDCl3, ppm): d 1.09–1.56 (m, 30H, CH3),
1.93 (dd, 2H, CH2), 2.06 (s, 6H, CH3), 2.51 (dd, 2H, CH2), 3.20
(m, 2H, CH), 3.81–4.15 (m, 4H, CH), 5.35 (d, 2H, aromatic-H),
6.68 (d, 2H, aromatic-H), 7.10–7.26 (m, 6H, aromatic-H); 13C
NMR (125 MHz, CDCl3, ppm): d 15.7, 19.8, 23.2, 23.4, 27.6,
34.4, 43.2, 116.0, 116.7, 121.9, 122.2, 124.3, 136.2, 139.8, 140.4,
Diffraction data of complexes 1 and 2 were collected on a Bruker
Smart APEX CCD diffractometer with graphite-monochromated
˚
Mo Ka radiation (k = 0.71073 A). All data were collected at room
temperature and the structures were solved by direct methods
and subsequently refined on F2 by using full-matrix least-squares
techniques (SHELXL),19 absorption corrections were applied to
the data. The non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were located at calculated positions.
CCDC reference numbers 633235 (1) and 633236 (2). For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b708048d.
=
141.9, 151.8, 158.7 (C–O), 176.6 (C N); IR (KBr): m 3052 (w),
Acknowledgements
2959 (m), 2866 (w), 2924 (w), 1607 (s), 1561 (m), 1482 (m),
1403 (w), 1352 (m), 1252 (m), 1184 (w), 1161 (w), 1101 (w), 909 (w),
869 (w), 818 (w), 777 (w) cm−1; Anal. Calc. for C46H56N2NiO2: C
75.93, H 7.76, N 3.85; Found: C 75.85, H 7.69, N 3.87%.
Financial support by the National Science Foundation of China
for Distinguished Young Scholars (20531020, 20421303), by the
National Basic Research Program of China (2005CB623800) and
by Shanghai Science and Technology Committee (05JC14003,
06XD14002) is gratefully acknowledged.
Complex 3: Complex 3 was obtained from a THF–ethanol
solution at room temperature as brown crystals (0.52 g, 75%). 1H
NMR (500 MHz, CDCl3, ppm): d 1.12–1.53 (m, 30H, CH3), 1.84
(dd, 2H, CH2), 2.50 (dd, 2H, CH2), 3.12 (m, 2H, CH), 3.92–4.06
(m, 4H, CH), 5.41 (d, 2H, aromatic-H), 6.21 (d, 2H, aromatic-H),
7.11–7.25 (m, 8H, aromatic-H). 13C NMR (125 MHz, CDCl3,
ppm): d 21.1, 23.9, 24.4, 28.8, 36.0, 43.0, 108.6, 116.8, 123.0,
123.9, 125.6, 135.0, 141.1, 141.3, 142.8, 156.4 (C–O), 161.4, 177.7
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(C N). IR (KBr): m 3058 (w), 2959 (m), 2924 (w), 2866 (w), 1605
(s), 1598 (s), 1567 (m), 1470 (m), 1413 (w), 1381 (w), 1359 (m),
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4.00; Found: C 75.47, H 7.45, N 4.03%.
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solution at room temperature as brown crystals (0.64 g, 87%). 1H
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(m, 4H, CH), 5.34 (d, 2H, aromatic-H), 6.78 (d, 2H, aromatic-H),
7.09–7.27 (m, 6H, aromatic-H). 13C NMR (125 MHz, CDCl3,
ppm): d 19.0, 22.6, 23.2, 27.7, 34.8, 41.9, 113.0, 117.7, 122.0,
123.4, 124.8, 134.4, 139.6, 140.1, 141.2, 150.3, 159.1 (C–O), 176.6
=
(C N). IR (KBr): m 3059 (w), 2959 (m), 2923 (w), 2865 (w), 1611
(s), 1591 (m), 1560 (m), 1467 (s), 1406 (w), 1370 (w), 1360 (m),
1324 (w), 1247 (m), 1171 (m), 1113 (w), 1060 (w), 935 (w),
882 (w), 819 (m), 799 (w), 742 (w), 686 (w) cm−1; Anal. Calc.
for C44H50Cl2N2NiO2: C 68.77, H 6.56, N 3.64; Found: C 68.69, H
6.49, N 3.69%.
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