Two bis-[1-(aryliminomethyleny)-2-oxy-naphthalen] nickel catalysts for the polymerization of methyl methacrylate

Article abstract of DOI:10.1016/j.jorganchem.2008.11.006

Two bis-(1-arylliminomethylenyl-2-oxy-naphthalen) nickel complexes (aryl = 2-methylphenyl, complex 1; aryl = 2,6-diisoproylphenyl, complex 2) were reacted with alkylaluminium in presence of equimolar PPh₃ and tested as catalysts in methyl metha

Full text of DOI:10.1016/j.jorganchem.2008.11.006

Journal of Organometallic Chemistry 694 (2009) 366–372
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Two bis-[1-(aryliminomethyleny)-2-oxy-naphthalen] nickel catalysts
for the polymerization of methyl methacrylate
c
Yang-Jian Hu a,b, Hua Hong Zou a, Ming-Hua Zeng a, , Ng Seik Weng
*
a Key Laboratory of Medicinal Chemical Resources and Molecular Engineering, Department of Chemistry and Chemical Engineering, Guangxi Normal University, 15 Yucai Rd.,
Guilin 541004, PR China
b Department of Chemistry, Huaihua College, Huaihua 418000, PR China
c Department of Chemistry, University of Malaya, 0603 Kuala Lumpur, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 August 2008
Received in revised form 31 October 2008
Accepted 4 November 2008
Available online 8 November 2008
Two bis-(1-arylliminomethylenyl-2-oxy-naphthalen) nickel complexes (aryl = 2-methylphenyl, complex
1; aryl = 2,6-diisoproylphenyl, complex 2) were reacted with alkylaluminium in presence of equimolar
PPh3 and tested as catalysts in methyl methacrylate (MMA) polymerization. The two nickel catalysts
can initiate polymerization of MMA with good to high activity, the highest activity reaching
1.1 Â 105 g PMMA/(mol Ni Á h) by less bulky complex 1 at 0.8 mol/L of MMA, 400 of Al/Ni ratio and
0 °C. In addition, the structures of nickel complexes and polymerization conditions, such as monomer
concentration, polymerization temperature and Al/Ni molar ratio on catalytic activity of polymerization
have great influences on catalytic activity and product properties.
Keywords:
Nickel complex
MMA
Alkylaluminium
Polymerization
Cocatalyst
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
gands to [Ni(cod)2] (cod = 1,5-cyclooctadiene) and subsequent
activation with MAO [14,15]. The systems of some naphtocyi-
Studies have been directed on the synthesis of the transition
metal complexes of multifunctional ligands for catalysis [1]; in
particular, the nickel complexes that are linked to ligands through
N, O or N, N atoms [2,3] possess exceptional catalytic activity for
the polymerization of MMA (methyl methacrylate), such as, Ni(II)
[4,5], and Pd(II) complexes containing N,O-chelate atoms [6–10]
served as catalysts for copolymerization. Some of the features are
necessary for the manifestation of such behavior include, for exam-
ple, high electrophilicity, a positive charge on the metal center it-
self, and sterically-bulky N,O- and/or N,N-chelating ligands. A
number of reports have documented the last-mentioned feature
[11]. Ni(acac)2/MAO (acac = diacetate; MAO = methylaluminoxane)
is a common system for the polymerization of MMA [12]. However,
the nickel compounds that are particularly useful are the b-ketoa-
mino type, and mixed-ligands compounds are excellent catalysts
for the production of highly syndiotactic PMMA [13].
mine-nickel complexes/MAO were reported that can catalyze nor-
bornene to polymerization with high catalytic activity [16,17], but
there are little reports that these catalyst systems are utilized for
polymerization of MMA. Other systems are known [18] but gener-
ally, activation by MAO is necessary. Unfortunately, MAO is an
expensive chemical and is not easy to prepare. We have engaged
in investigations on an alkylaluminium in place of MAO as activa-
tor [19], this is the main difference from aforementioned catalyst
systems. Moreover, our catalyst system can give low molecular
weight PMMA, which favor the serialization and differentiation
of product. To assist in an understanding of the polymerization
of MMA by the late transition metal catalysts, we have chosen to
study the nickel system instead and have examined catalytic
behavior from the angle of the bulkiness of substituents in the
ortho aryl position (Scheme 1) and the influence of reaction condi-
tions on catalytic activity and properties of polymers obtained by
these nickel complexes.
The present study reports two bis(1-aryliminomethylenyl-
naphthalen-2-oxy)nickel complexes and their abilities to catalyze
MMA. All nickel complexes were characterized by their IR, NMR
spectra and elemental analyses. In addition, X-ray structure analy-
ses were performed for complex 2. After being activated with
alkylaluminium, these nickel(II) complexes can be used as catalysts
for the polymerization of methyl methacrylate (MMA) to produce
Recently Carlini used bis(salicylideneiminato)nickel(II) complex
as catalyst precursor activated by MAO for polymerizing MMA to a
prevailing syndiotactic polymer, exhibiting high catalytic activity,
and are able also to give copolymers of MMA with ethylene. These
systems were obtained by oxidative addition of salicylaldimine li-
* Corresponding author. Fax: +86 773 5812 383.
E-mail address: zmh@mailbox.gxnu.edu.cn (M.-H. Zeng).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.006

Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
367
Table 1
Structure parameters of the complex 2.
Empirical formula
C46H48N2O2Ni
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
719.55
Triclinic
ꢀ
P1 (No. 2)
9.397(3)
9.721(3)
11.454(4)
80.710(5)
72.356(5)
82.996(5)
981.0(6)
1
Scheme 1. The nickel complexes with different substituents in the ortho aryl
position.
a
(°)
b (°)
c
(°)
syndiotactic-rich PMMA. Catalytic activities and the degree of syn-
diotacticity of PMMA have been investigated for various reaction
conditions.
V (Å3)
Z
Temperature (K)
293
F(000)
382
1.218
1.05
1.9, 26.0
0.28, À0.18,
0.533
Dcalcd. (g cmÀ3
)
2. Experiment
Goodness-of-fit (GOF) on F2
Theta range (°)
Fmax/Fmin (e ÅÀ3
)
The synthesis was performed under nitrogen in Schlenk-type
vessels, and water- and oxygen-free reagents and solvents were
used throughout. 1H NMR spectra were recorded on a Bruker-300
spectrometer. The 13C NMR spectra of PMMA were obtained in
CDCl3 on Varian INOVA-500 NMR spectrometer. Gel permeation
chromatography (GPC) analyses of the molecular weight and
molecular weight distribution of the polymers were performed
on a Waters 150C instrument, and standard polystyrene was the
reference and with chloroform as the eluent. Diethylaluminum
chloride (AlEt2Cl), triethyl aluminum (AlEt3) and triisobutyl alumi-
num (Al(i-Bu)3) were taken as 350 g/L solutions in n-heptane,
respectively. The other chemicals were commercially procedure.
l
(mmÀ1
)
Total reflections
Unique reflections
Observed data [I > 2.0
7765
3813
3463
0.016
0.0368
0.0971
r(I)]
[R(int)
R1 [I P 2
wR2 (all data)
]
r(I)]
PMMA as a precipitate. The polymer was filtered and washed with
water–ethanol several times, and dried in vacuum at 50 °C for 12 h.
2.3. X-ray crystallography measurement
2.1. Preparation of nickel complexes
Suitable crystals of complex 2 for X-ray diffraction were ob-
tained by slow evaporation of the compound from n-heptane. The
X-ray diffraction measurements were carried out at on a Bruker
SMART 1000 CCD diffractometer fitted with graphite monochro-
The two nickel complexes were synthesized by using a modifi-
cation of a reported procedure [20].
2.1.1. Bis[(N-2-methyl-phenylimino)-2-oxy-1-
naphthylmethylene]nickel(II)
matic Mo K
a radiation (k = 0.71073 Å). The structure was solved
by direct methods, and refined by full-matrix least-squares on F2.
Hydrogen atoms were placed in calculated positions, and were re-
fined using a riding model. All nonhydrogen atoms were refined
anisotropically. Relevant crystal data are summarized in Table 1.
Nickel acetate tetrahydrate (2.48 g, 10 mmol) and 2-hydroxy-1-
naphthaldehyde (1.74 g, 10 mmol) were heated in ethanol
(100 mL) along with 2-methylaniline (3.21 g, 30 mmol) for 2 h.
The solvent was removed to give a dark green solid; the compound
1 was purified by crystallization from n-heptane. CHN Anal. Calc.
for C36H28N2NiO2: N, 4.83; C, 74.63; H, 4.87. Found: N, 4.67; C,
74.44; H, 5.06%. 1H NMR (CDCl3, 300 MHz): 1.20–1.26 (m, 6H),
5.58 (d, 2H), 6.78–7.65 (m, 18H), 7.95 (d, 2H) ppm. IR (KBr):
3. Results and discussion
3.1. Characterization of complexes
1625 cmÀ1
(mC@N).
The ready solubility of the two compounds implicates a mono-
meric nature for both. Element analysis revealed that the polycrys-
talline compound 1 is structurally similar to compound 2, only the
latter is suitable for single-crystal X-ray diffraction analysis, so that
the structure of 2 is described here. For the complex 2, the crystal
2.1.2. Bis[(N-2,6-diisopropylphenylimino)-2-oxy-1-
naphthylmethylene]nickel(II)
Compound 2 was similarly prepared and was also obtained as
green crystals. CHN Elemental Anal. Calc. for C46H48N2NiO2: N,
3.90; C, 76.99; H, 6.46. Found: N, 3.69; C, 76.72; H, 6.62%. 1H
NMR (CDCl3, 300 MHz): 1.23 (d, 24H), 4.27–4.34 (m, 4H), 5.69
(d, 2H), 7.13-7.67 (m, 16H), 8.15 (s, 2H) ppm. IR (KBr):
1628 cmÀ1
(mC@N).
2.2. General procedure for polymerization of MMA
Polymerizations were carried out in a 250 mL Schlenk flask fit-
ted with a magnetic stir. The flask was filled with 50 mL of n-hep-
tane; AlEt2Cl dissolved in n-heptane was injected into the reaction
solution. The solution of catalyst and an equimolar quantity of PPh3
were then added and the reactor was heated to the polymerization
temperature, after which the monomer was added. After 4 h, the
polymerization was quenched by addition of ethanol. The reaction
solution was poured into an excess of 10% HCl–EtOH to afford
Fig. 1. The coordination environment of NiII in compound 2.

368
Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
Table 2
Table 3
Selected bond distances (Å) and bond angle (°) for complex 2.
Polymerization of MMA by the catalytic system of complexes 1 and 2.
Bond distances
Run Cat. Al/
Ni
T
(°C)
Cocat.
Yielda/
%
Activityb Mn
Mw
Mn/
Mw
c
Ni(1)–O(1)
Ni(1)–N(1)
O(1)–C(10)
N(1)–C(11)
N(1)–C(12)
C(1)–C(2)
C(1)–C(10)
C(1)–C(11)
C(2)–C(3)
1.814(1)
1.892(1)
1.296(3)
1.301(2)
1.450(2)
1.452(3)
1.392(3)
1.417(2)
1.395(3)
C(2)–C(7)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(12)–C(13)
1.407(3)
1.370(4)
1.371(3)
1.344(4)
1.407(3)
1.417(3)
1.343(4)
1.431(3)
1.391(3)
1
2
3
1
1
1
400
400
400
30
30
30
AlEt2Cl
AlEt3
Al(i-
69
71
62
8.3
8.2
6.6
1572 1967 1.25
1783 2349 1.31
1812 2669 1.47
Bu)3
4
5
6
7
8
9
1
1
1
2
2
2
200
600
800
400
400
400
30
30
30
30
30
30
AlEt3
AlEt3
AlEt3
AlEt2Cl
AlEt3
Al(i-
41
70
72
67
68
61
3.8
8.1
7.8
7.6
6.9
6.2
1876 2685 1.43
1774 2461 1.38
1712 2338 1.36
2349 3508 1.49
3491 5419 1.55
3556 6255 1.75
Bond angles
O(1)–Ni(1)–N(1)
O(1)–Ni(1)–O(1a)
O(1)–Ni(1)–N(1a)
O(1a)–Ni(1)–N(1)
N(1)–Ni(1)–N(1a)
O(1a)–Ni(1)–N(1a)
92.40(6)
180.00
87.60(6)
87.60(6)
180.00
Ni(1)–O(1)–C(10)
Ni(1)–N(1)–C(11)
Ni(1)–N(1)–C(12)
C(11)–N(1)–C(12)
O(1)–C(10)–C(1)
O(1)–C(10)–C(9)
131.1(1)
125.3(1)
119.2(1)
115.4(1)
124.3(2)
116.1(2)
Bu)3
10
11
12
1
1
1
400
400
400
0
50
70
AlEt3
AlEt3
AlEt3
72
62
61
11.0
4.8
4.2
2937 5036 1.71
1653 2037 1.23
1511 1897 1.25
92.40(6)
Conditions: [MMA] = 0.8 mol/L; [Ni] = 0.0003–0.0004 mol/L, time = 4 h; solvent: n-
heptane.
a
Yield is defined as the mass of dry polymer recovered/mass of monomer used.
structure shows the nickel atom at a center-of-inversion in a trans-
N2O2Ni square-planar geometry (Fig. 1 and Table 2). On the basis of
the crystal structure, the complex 2 is also assigned a square-pla-
nar geometry at Ni(II) ion. The chelate ring with Ni(II) ion is planar,
and is co-planar with the naphthalene fused-ring. The reason for
the four-coordinate geometry is evident from the 2,4,6-trimethyl-
phenyl substituents as they block any attempt by other Lewis-ba-
sic sites to interact with Ni. Such a geometry has also been noted
in, for example, the bis-[N-(substituted methyl)-salicylideneimina-
to] nickel [21]. The Ni–O and Ni–N bond lengths are 1.814(2),
1.892(2) Å, respectively, which are essentially the same as in the
complexes of tetrahedral NiII, showing that coordination of the N,
O chelating function. The adjacent molecules are stacked with re-
spect to each other only by van der Waals interactions. It is mainly
raised by the sterically hindered ligands which impose the geome-
try on the isolate molecules.
b
104 g PMMA/mol Ni Á h.
c
Determined by means of GPC.
they are highly active and syndiotactic for the reaction in heptane
(Table 3). In fact, their activities exceed that of nickel
a-diimine
catalysts (6.9 Â 103 g PMMA/mol Ni Á h) [3a] and about equal to
that of the bis(a-ketoamino)nickel(II)/MAO system [13]. Compared
with phenoxyimine/Ni(cod)2/MAO systems, despite their good cat-
alytic activity (up to 1.5 Â 105 g PMMA/mol Ni Á h) [15a], Ni(cod)2
is known to be very expensive and extremely sensitive to air,
humidity and protic impurities. The somewhat higher activity of
complex 1 (Table 3) can be rationalized in terms of the bulkiness
of the substituents. The complex 1 has the less bulky methyl sub-
stituent whereas the complex 2 has the more bulky diisopropyl
substituent. Accumulated studies [3,20,22] have shown that the
Ni center should be able to expand its coordination number, at
least in the transition state, something the first compound can do
better than the second. However, despite the decreased activity,
the average molecular weight of PMMA for the bulkier Ni com-
pound is higher, which suggests that steric bulk protruding into
the ‘axial’ sites above and below the square plane retards the
3.2. Polymerization of MMA
3.2.1. Catalyst
The two complexes function as excellent as initiators in pres-
ence of alkylaluminium for the polymerization of MMA to PMMA;
R
R
R'
N
O
N
O
O
N
I
PPh3
PPh3
Ni
Ni
AlR'3 or AlR'2Cl
PPh3
CO2Me
R
II
R'
R'
N
N
1,2
OMe
OMe
Ni
Ni
O
ins.
R
O
O
O
R'
N
O
Ni
R'
nMMA
N
N
R'
CO2Me
2,1
OMe
Ni
Ni
O
ins.
O
OMe
O
O
Me
R'
(MMA)n
N
β
CO2Me
N
-H elimination
H
P
P
CO2Me
CO2Me
Ni
Ni
+
+
Me
O
O
CO2Me
CO2Me
N
N
P
R'=ethyl or isobutyl; =growing chain;
=
O
O
Scheme 2. Proposed mechanism of MMA polymerization.

Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
369
termination of progapation chain. Before the onset of polymeriza-
tion added PPh3 then serves as promoter for formation of activity
centers [20a] that accelerate the polymerization process. To check
if the addition of PPh3 should be requisite, we performed the con-
trast experiment with complex 1 and 2/AlEt3 in the absence of PPh3
under the same conditions adopted for the polymerization experi-
ments of MMA under dry nitrogen. The results showed that two
catalytic systems had very low catalytic activity and only traces
of product were found independently. Therefore, this indicates that
PPh3 can serve as ancillary ligand to stabilize the activity centers.
This result also confirms that in the presence of an alkylating agent
one of the two imine-naphtholato ligands is released, with the for-
mation of an alkylnickel species, which is stabilized by the coordi-
nation of the phosphine to give rise to the species II (Scheme 2). In
order to confirm the formation of the above species II, we have
investigated the interaction of the equimolar complex 2/PPh3 mix-
ture with Et3Al (1:1:50) in heptane solution under nitrogen atmo-
sphere, and then detect if the species II (C43H44NOPNi, molecular
weight is 679) has formed in the reaction by ESI-MS (LCQ DECA
XP, mobile phase is n-hexane and THF of 9:1). The result showed
that the species II existed in catalyst system (Fig. 2, the peaks at
about 679 contain nickel and its isotope complexes). The addition
to the catalyst of an equimolar amount of PPh3 (Table 3) allowed
to conclude that the activity remained extremely high
(1.1 Â 105 g/mol Ni Á h) (entry 10), thus indicating that the phos-
phine, in the presence of an excess of alkylaluminum, does not be-
have as a poison for the nickel sites, the alkylaluminum Lewis
acidity probably weakening the coordinative interaction of the
phosphine to the metal.
entry 10
entry 8
18
20
22
24
26
28
30
time/minutes
Fig. 3. The GPC elution curves of entry 8 and 10.
merely either AlEt3 or Al(i-Bu)3 and AlEt2Cl as cocatalysts for the
polymerization of MMA. Polymerization to produce PMMA and
the effect of three cocatalysts on MMA polymerization with an
Al/Ni ratio 400 and at 30 °C furnishes results (Table 3) that prove
that the three alkylaluminiums can initiate the reaction. The cata-
lytic activity of two catalysts with Al(i-Bu)3 is lowest, a possible
reason being a trialkylaluminum being bulkier and therefore hin-
ders access of the monomer to the site of activity.
3.2.3. Al/Ni ratio
Catalytic activity increased with the increasing Al/Ni molar ra-
tios, reaching highest at 400 (Table 3). For complex 1, the activity
increases to a maximum of 8.3 Â 104 g PMMA/mol Ni Á h at a ratio
at an Al/Ni 400, possibly arising from that the effect this ratio has
on the active site. Most likely, too little aluminum reagent cannot
completely balance the polarity of the nickel complex, which is
necessary for the formation of the active nickel species. Any further
So the proposed mechanism is as follows.
3.2.2. Cocatalyst
Unlike other reported catalytic nickel complexes with O,N-con-
taining ligands [13,14], the present two nickel complexes require
Fig. 2. ESI mass spectrum of products of reaction.

370
Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
increase in the quantity of the aluminum reagent will hasten chain
transfer on alkylaluminium, thereby decreasing the catalytic
activity.
decreased with an increase of the temperate of polymerization.
At around 70 °C, the yield of PMMA is low, being only
4.2 Â 104 g PMMA/molNiÁh. Obviously, with increasing tempera-
ture, the rate of polymerizatiom quickly decreases. These
results suggests that higher polymerization temperature may
influence the number of active sites formed in situ for the poly-
merization or that the alkylaluminium strongly interacts with the
active site.
3.2.4. Polymerization temperature (Tp)
The highest activity for complex 1 was observed at 0 °C, at
nearly 1.10 Â 105 g PMMA/mol Ni Á h (Table 3). Catalytic activity
(a)
(b)
(c)
(d)
δ (α-CH3)
s
δ (α-CH3)
a
δ (CH3-O)
a
δ (α-CH3)
s
ν (C=O)
skeletal
1800
1700
1600
1500
1400
1300
1200
1100
1000
cm-1
Fig. 4. IR spectra of PMMA produced by 1/AlEt3 catalyst at Tp (a) 0 °C, (b) 30 °C, (c) 50 °C, (d) 70 °C. Polymerization conditions are given in Table 1.
rr
mr
a
mm
CH3
e
b
( CH2 C )
n
c
C=O
O
46.0
45.8
45.6 45.4
45.2
45.0
ppm
44.8
44.6
44.4
44.2
44.0
rrrr
d
CH3
mrrr
mrrm
mmmr
179.0
178.5
178.0
177.5
177.0
176.5
176.0
175.5
175.0
220
200
180
160
140
120
100
80
60
40
20
ppm
Fig. 5. 13C NMR spectrum of entree 8.

Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
371
Table 4
Triad and pendant fractions of PMMA obtained with complexes 1 and 2.
Entrya
Triad fractions(%)b
Penendant fractions(%)c
mm
mr
rr
rmmr
rmrr + mmrr
mmrm + rmrm
rrrr
rrrm
mrrm
2
8
10
11
12
10.9
8.7
8.5
8.1
7.3
23.0
21.1
18.2
28.4
31.3
66.1
70.2
73.3
63.5
61.4
0.6
1.2
1.5
0.9
1.1
20.2
19.5
19.2
20.8
21.3
5.8
5.2
4.6
5.4
6.2
49.1
51.3
52.4
47.5
45.4
20.2
19.3
18.5
21.1
21.6
4.1
3.5
3.9
4.3
4.4
a
Entry numbers are common to Table 3.
b
c
Observed in 13C NMR spectra of quaternary carbon resonance; from low to high field in the spectra (=47.3–43.5 ppm) [22].
Observed in 13C NMR spectra of quaternary carbon resonance; from low to high field in the spectra (=178.3–176.1 ppm) [22].
3.3. Microstructure of PMMA
similar pathways for all bis(naphtocyimine) nickel(II)/alkylalumi-
num catalyst systems used in this study.
The average molecular weight (Mw) of products as determined
by GPC ranged from 1967 to 6255 (Fig. 3), which are lower than
those reported in the literature [13,14]. It also decreased with
increasing of temperature (Table 3). Possibly, chain transfer in
the catalytic systems is faster than chain propagation so that only
low molecular weight polymers are formed.
The complex 1 with the methyl substituent gave PMMA of
broad polydispersity whereas the diisopropyl substituent analog
gave PMMAs with of a narrow polydispersity at all Tps. On the aver-
age, the polydispersities obtained of both types of PMMA were nar-
rower than those resulting from other late transition metal
catalysts such as Ni(acac)2/MAO [12], phenoxyimine-nickel/MAO,
as well as neutral Pd(II) and Ni(II) acetylide [13–15].
The infrared spectra of PMMA by the complex 1 (Fig. 4) are sen-
sitive to tacticity [23,24] and although the polymers showed the
bands characteristic of syndiotactic PMMA, the detailed micro-
structure could not, unfortunately, be differentiated. The micro-
structure of PMMA was, however, eluciated from the 13C NMR
spectra of PMMA [25–28]. All the above catalyst systems produced
PMMAs with similar microstructures. Fig. 5 is the 13C NMR spec-
trum of entry 8. It shows the characteristic chemical-shift signals
of the carbon types in MMA units. The chemical-shift signals
appearing around 176.10–178.3 ppm (c), 18.25–22.24 ppm (a),
52.97–54.92 ppm (e), 50.64–52.86 ppm (d) and 43.51–47.31 ppm
4. Conclusions
In summary, common alkylaluminums such as AlEt3, Al(i-Bu)3
and AlEt2Cl are efficient cocatalysts to activate bis(1-arylimino-
methylenyl-naphthalen-2-oxy)nickel complexes for MMA poly-
merization without MAO. The complexes 1, 2 that were activated
with general alkylaluminium in presence of equimolar PPh3
showed high catalytic activities for the polymerizations of MMA,
producing PMMA with lower molecular weight. The polymeriza-
tion temperature and the Al/Ni molar ratio were found also to be
the main factors that influence catalyst efficiency. Determinated
by GPC, the average molecular weight (Mw) of products range from
1967 to 6255 and dispersity index (Mw/Mn) from 1.25 to 1.75. It
was found that the syndiotactic content of PMMA was predomi-
nant by 13C NMR and higher polymerization temperature favour-
able to atactic content of PMMA.
Acknowledgements
This research was funded by the Scientific Foundation of Guan-
gXi Province (No. 0832001Z), Fok Ying Tung Education Foundation
(No. 111014) and the Program for New Century Excellent Talents in
University of the Ministry of Education China (NCET-07-217).
(b) can be assigned to the resonances of ester carbonyl (C@O),
methyl ( -CH3), methoxy (–OCH3), methenes (–CH2–) and quater-
nary carbons in MMA units, respectively. The chemical-shift signal
at about 14.20 ppm can be assigned to -methyl( -CH3), which is
a-
a
Appendix A. Supplementary material
c
c
one end of PMMA chain from the Et3Al when chain initiating
(Scheme 2). The signals of 127.12–131.22 can be assigned to an-
other chain end in which a double bond can be contained from
chain termination by b-H elimination.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.11.006.
References
The triad and pendant content tests of the PMMA samples
(Table 4) show that the two nickel complexes furnish syndiotac-
tic-rich PMMA, and structural variations of the catalyst and poly-
merization temperature should have some degree of influence on
the microstructure of PMMA. On the basis of the racemic triad val-
ues, the more crowded catalyst yielded PMMA of a higher syndio-
tacticity at the same Tp. For example, the rr triad content in PMMA
of entry 2 reached 73% relative 66% of entry 8. Such a difference is
again attributed to the steric environment around the metal center.
With increasing temperature, the rr triad content decreases
although the antactic content in PMMA increases. The complex 2
shows stereoregularity in from 0 °C to 70 °C, the rr triad content
reaching 73%. The complex 1 shows relatively low selectivity as
it generates syndio-rich or atactic PMMA at normal temperature.
The polydispersity of the PMMA is relatively narrow (ranging from
1.232 to 1.759). The similarity in polymer microstructures suggests
that chain initiation and chain growth most likely proceed along
[1] (a) L.S. Boffa, B.M. Novak, Chem. Rev. 100 (2000) 1479–1494;
(b) S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169–1204;
(c) L.T.J. Evans, M.P. Coles, F. Geoffrey, N. Cloke, P.B. Hitchcock, Dalton Trans.
(2007) 2707–2717;
(d) D.B. Liu, S.B. Wang, H.T. Wang, W. Chen, J. Mole. Catal. A: Chem. 246 (2006)
53–58;
(e) W.H. Sun, P. Hao, S. Zhang, Q.S. Shi, W.W. Zuo, X.B. Tang, X. Lu,
Organometallics 26 (2007) 2720–2734;
(f) M. Zhang, P. Hao, W.W. Zuo, S.Y. Jie, W.H. Sun, J. Organomet. Chem. 693
(2008) 483–491.
[2] (a) C.N. Elia, A. Sen, A.C. Albeniz, P. Espinet, in: Proceedings of the ACS National
Meeting, Washington, August 2000, pp. 20–24.;
(b) G.R. Tang, G.X. Jin, Dalton Trans. (2007) 3840–3846.
[3] (a) I. Kim, J.M. Hwang, K.L. Jin, Macromol. Rapid Commun. 24 (2003) 508–511;
(b) M. Zhang, S. Zhang, P. Hao, S.Y. Jie, W.H. Sun, P.Z. Li, X.M. Lu, Eur. J. Inorg.
Chem. (2007) 3816–3826;
(c) S. Adewuyi, G. Li, S. Zhang, W.Q. Wang, P. Hao, W.H. Sun, N. Tang, J.J. Yi, J.
Organomet. Chem. 692 (2007) 3532–3541.
[4] (a) G.J.P. Brltovsek, V.C. Gibson, D.M. Wass, Angew. Chem., Int. Ed. 38 (1999)
428–447;

372
Y.-J. Hu et al. / Journal of Organometallic Chemistry 694 (2009) 366–372
(b) S. Meking, Coord. Chem. Rev. 203 (2000) 325–351;
(c) S. Meking, Angew. Chem., Int. Ed. 40 (2001) 534–540.
(b) C. Carlini, M. Martinelli, A.M.R. Galletti, G. Sbrana, J. Polym. Sci. Part A:
Polym. Chem. 41 (2003) 1716–1724.
[5] (a) B.Y. Lee, G.C. Bazan, J. Vela, Z.J.A. Komon, X. Bu, J. Am. Chem. Soc. 123
(2001) 5352–5353;
[16] F. Chang, D.H. Zhang, G.Y. Xu, H.J. Yang, J.T. Li, H.B. Song, W.H. Sun, J.
Organomet. Chem. 689 (2004) 936–946.
(b) F.A. Hicks, M. Brookhart, Organometallics 20 (2001) 3217–3219;
(c) D. Zhang, G.X. Jin, Appl. Catal. A: Gen. 262 (2004) 13–18;
(d) S.Y. Jie, S. Zhang, W.H. Sun, Eur. J. Inorg. Chem. (2007) 5584–5598.
[6] M. Peukert, W. Keim, Organometallics 2 (1983) 594–597.
[7] B. Reuben, H.J. Wittcoff, J. Chem. Educ. 65 (1988) 605–607.
[8] C. Wang, S. Friedrich, T.R. Younkin, R.T. Li, R.H. Grubbs, D.A. Bansleben, M.W.
Day, Organometallics 17 (1998) 3149–3151.
[9] H. Sun, Q. Shen, X. Peng, M. Yang, Catal. Lett. 80 (2002) 11–13.
[10] T. Younkin, E.F. Connor, J.I. Henderson, S.K. Friedrich, R.H. Grubbs, D.A.
Bansleben, Science 287 (2000) 460–462.
[11] G.Q. Gui, F. Bao, H.Y. Gao, F.M. Zhu, Q. Wu, Appl. Organomet. Chem. 19 (2005)
627–632.
[12] (a) F.M.B. Coutinho, M.A.S. Costa, L.F. Monteiro, L.C. Maria, Polym. Bull. 38
(1997) 303–309;
(b) K. Endo, A. Inukai, Polym. Int. 49 (2000) 110–114.
[13] (a) X.H. He, Y.Z. Yao, X. Luo, J.K. Zhang, Y.H. Liu, L. Zhang, Q. Wu,
Organometallics 22 (2003) 4952–4957;
[17] J.X. Hou, S.Y. Jie, W.J. Zhang, W.H. Sun, J. Appl. Polym. Sci. 102 (2006) 2233–
2240.
[18] C. Mast, M. Krieger, K. Dehnicke, A. Greiner, Macromol. Rapid Commum. 20
(1999) 232–235.
[19] X.G. Fan, H.H. Wang, Z.H. Hu, M.P. Hu, Q.X. Zhang, Polym. Mater. Sci. Eng. 20
(2004) 94–96.
[20] (a) S. Borkar, P.K. Saxena, Polym. Bull. 44 (2000) 167–169;
(b) O.A. Osipov, V.I. Minkin, N.R. Kalnitskii, Z.A. Tumakova, Zh. Neorg. Khim. 12
(7) (1967) 1867–1876.
[21] H. Yang, W. Sun, F. Chang, Y. Li, Appl. Catal. A: Gen. 252 (2003) 261–
267.
[22] R.J. Maldanis, J.S. Wood, A. Chandrasekaran, M.D. Rausch, J.C.W. Chien, J.
Organomet. Chem. 645 (2002) 158–167.
[23] C. Carlo, I. Mauro, L. Vincenzo, et al., Appl. Catal. A: Gen. 231 (2002) 307–320.
[24] J.M. O’Reilly, R.A. Mosher, Macromolecules 14 (1981) 602–608.
[25] T. Konishi, Y. Tamai, M. Fuji, Y. Einaga, H. Yamakawa, Polym. J. 21 (1989) 329–
334.
(b) X. He, Q. Wu, Appl. Organomet. Chem. 20 (2006) 264–271.
[14] C. Carlini, V.D. Luise, M. Martinelli, A.M.R. Galletti, G. Sbrana, J. Polym. Sci. Part
A: Polym. Chem. 44 (2006) 620–633.
[26] S. Collins, D.G. Ward, J. Am. Chem. Soc. 114 (1992) 5460–5462.
[27] H. Yasuda, H. Yamamoto, K. Yokota, S. Miyake, A. Nakamura, J. Am. Chem. Soc.
114 (1992) 4908–4910.
[15] (a) C. Carlini, M. Martinelli, A.M.R. Galletti, G. Sbrana, J. Polym. Sci. Part A:
Polym. Chem. 41 (2003) 2117–2124;
[28] H. Yasuda, H. Yamamoto, M. Yamashita, K. Yokota, A. Nakamura, S. Miyake, Y.
Kai, N. Kanehisa, Macromolecules 26 (1993) 7134–7143.