Trans-1,2-diphenylethylene linked isoindoline-salicylaldiminato nickel(II) halide complexes: Synthesis, structure, dehydrogenation, and catalytic activity toward olefin homopolymerization

Article abstract of DOI:10.1002/ejic.201201331

Tridentate ligands 4-R¹-6-R²-2-{[trans-2-(isoindolin- 2-yl)-1,2-diphenylethylimino]methyl}phenol [R¹ = R² = H, H(L^a); R¹ = R² = tert-butyl, H(L^b); R¹ = Ph, R² = H, H(L^c)] in which a substituted salicylaldimine moiety and an isoindoline are linked by a trans-1,2- diphenylethylene moiety have been prepared. Deprotonation of these tridentate ligands H(L^a)-H(L^c) by NaH at room temperature in tetrahydrofuran (THF), followed by treatment with 1 equiv. of [(PPh ₃)₂NiX₂] (X = Cl, Br, I) at room temperature afforded the desired nickel complexes [(L)NiX] (X = Cl, L = L^a, 1; X = Cl, L = L^b, 2; X = Cl, L = L^c, 3; X = Br, L = L ^b, 4; X = I, L = L^b, 5) in moderate yields. The structures of 2 and 4 were unequivocally confirmed by single-crystal X-ray diffraction in the solid state. The metal atom has a distorted square-planar coordination geometry and is coordinated to the two nitrogen atoms and one oxygen atom from the tridentate ligand and one halide atom. Dehydrogenation of the chelate tridentate ligand (L^b) in the presence of oxygen afforded the corresponding nickel complexes [(L^b*)NiX] (X = Br, 6; X = I, 7). X-ray analysis showed that in these complexes the two bridged benzylic carbon atoms of (L^b)^- were oxidized and a cis-stilbene moiety, which includes a C=C double bond (1.205-1.268 A) was formed. These nickel complexes with such trans-1,2-diphenylethylene bridged tridentate ligands proved to be active catalysts for ethylene oligomerization in the presence of methylaluminoxane (MAO) and produced butene and hexene with catalytic activities of 0.49 × 10⁵-3.25 × 10⁵ g mol^-1 Ni h^-1 at 30 °C, under 20 bar of ethylene, and with an MAO/Ni ratio of 250. They were also active catalysts for the homopolymerization of norbornene and styrene and displayed activities of up to 1.89 × 10⁵ and 7.36 × 10⁵ g mol^-1 Ni h^-1, respectively. Copyright

Full text of DOI:10.1002/ejic.201201331

FULL PAPER
DOI:10.1002/ejic.201201331
trans-1,2-Diphenylethylene Linked Isoindoline–
Salicylaldiminato Nickel(II) Halide Complexes: Synthesis,
Structure, Dehydrogenation, and Catalytic Activity toward
Olefin Homopolymerization
Jinyang Wang,[a][‡] Li Wan,[a][‡] Dao Zhang,*[a] Quanrui Wang,[a]
and Zhenxia Chen[a]
Keywords: Tridentate ligands / Nickel / Solid-state structures / Oligomerization / Polymerization
Tridentate ligands 4-R1-6-R2-2-{[trans-2-(isoindolin-2-yl)-1,2-
diphenylethylimino]methyl}phenol [R1 = R2 = H, H(La); R1
ation of the chelate tridentate ligand (Lb) in the presence of
oxygen afforded the corresponding nickel complexes [(Lb*)-
NiX] (X = Br, 6; X = I, 7). X-ray analysis showed that in these
complexes the two bridged benzylic carbon atoms of (Lb)–
were oxidized and a cis-stilbene moiety, which includes a
C=C double bond (1.205–1.268 Å) was formed. These nickel
complexes with such trans-1,2-diphenylethylene bridged tri-
dentate ligands proved to be active catalysts for ethylene
oligomerization in the presence of methylaluminoxane
(MAO) and produced butene and hexene with catalytic ac-
tivities of 0.49ϫ105–3.25ϫ105 gmol–1 Nih–1 at 30 °C, under
20 bar of ethylene, and with an MAO/Ni ratio of 250. They
were also active catalysts for the homopolymerization of nor-
bornene and styrene and displayed activities of up to
1.89ϫ105 and 7.36ϫ105 gmol–1 Nih–1, respectively.
=
R2 = tert-butyl, H(Lb); R1 = Ph, R2 = H, H(Lc)] in which a sub-
stituted salicylaldimine moiety and an isoindoline are linked
by a trans-1,2-diphenylethylene moiety have been prepared.
Deprotonation of these tridentate ligands H(La)–H(Lc) by
NaH at room temperature in tetrahydrofuran (THF), followed
by treatment with 1 equiv. of [(PPh3)2NiX2] (X = Cl, Br, I) at
room temperature afforded the desired nickel complexes
[(L)NiX] (X = Cl, L = La, 1; X = Cl, L = Lb, 2; X = Cl, L = Lc,
3; X = Br, L = Lb, 4; X = I, L = Lb, 5) in moderate yields. The
structures of 2 and 4 were unequivocally confirmed by sin-
gle-crystal X-ray diffraction in the solid state. The metal atom
has a distorted square-planar coordination geometry and is
coordinated to the two nitrogen atoms and one oxygen atom
from the tridentate ligand and one halide atom. Dehydrogen-
action mechanisms, electronic and/or steric influence of
these nickel and palladium derivatives because of better
catalytic performances.[1a,1b] Functional olefin copolymers
with hydroxy, epoxide, and carbohydrate groups were suc-
cessfully controlled by copolymerization of ethylene with
polar olefins by using a palladium–diimine chain-walking
catalyst.[6] Soon after that, single-component neutral
salicylaldiminato nickel catalysts[7] and SHOP-type phos-
phane–sulfonato palladium catalysts[8] were discovered in
succession; they showed excellent performance in ethylene
(co)polymerization.
To date, the quest for novel catalytic system involves the
search for new ligand structures. However, this search was
found to be empirical in nature; recent developments have
provided somewhat more comprehensive guidelines for the
design of metal catalysts. Several nickel and palladium com-
plexes supported by tridentate [ONX] ligands [X = O, N, P,
N-heterocyclic carbene (NHC)] have been found to be
active for the oligomerization of ethylene and the polymeri-
zation of norbornene and acrylates to afford higher α-ole-
fins or vinyl-addition polymers.[9] As part of our ongoing
research project on group 10 and group 4 metal complexes
and their application as catalysts for olefin polymeriza-
Introduction
The utilization of d8 metal complexes for ethylene oligo-
merization and olefin (co)polymerization has been studied
intensely in both academic and industrial fields over the
past decades.[1] Traditionally, d8 late-transition-metal cata-
lysts were only found to produce dimers or low-molecular-
weight oligomers owing to chain termination by β-hydride
elimination.[2] For example, the Shell higher olefin process
(SHOP), based on the nickel catalyst [Ph2–PC(R)=C(R)O]-
Ni(Ph)L, was developed to oligomerize ethylene to higher
α-olefins.[3] At the end of last century, Brookhart and co-
workers developed a series of cationic bis(imino) nickel-
(II)[4] and palladium(II)[5] catalysts, which have been suc-
cessfully used as highly effective precatalysts for olefin
(co)polymerization reactions in this field. Extensive investi-
gations have subsequently favored the active species and re-
[a] Department of Chemistry, Fudan University,
Handane Road 220, Shanghai, P. R. China
Fax: +86-21-65641470
E-mail: daozhang@fudan.edu.cn
Homepage: http://www.chemistry.fudan.edu.cn/
teacher.asp?tno=zhangdao
[‡] These authors contributed equally to this work.
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tion,[10] we prepared a series of nickel complexes with chiral
tridentate ligands, H(La)–H(Lc), in which a substituted sal-
icylaldiminato moiety and an isoindoline are linked by a
trans-1,2-diphenylethylene group (Scheme 1).[11] Initially,
these chiral nickel complexes were tested in the polymeriza-
tion of styrene. Unfortunately, the tacticity of the obtained
polymer was very low. As the results were not good, we
turned to the homogeneous polymerization of ethylene and
norbornene. We found that this kind of monoanionic tri-
dentate ligand L– can be used to create an appropriate envi-
ronment around the coordination sphere of the nickel atom
for ethylene oligomerization and norbornene polymeriza-
tion. This tridentate fragment obviously results in a higher
coordination number than an ordinary bidentate salicylald-
iminato ligand. The third nitrogen donor atom of isoind-
oline will tend to compete against olefin monomers to coor-
dinate the metal center during polymerization, and the
trans-1,2-diphenylethylenediamine linker makes the coordi-
nation mode more flexible, which may or may not be bene-
ficial to the polymerization reaction.
Herein, we wish to report the synthesis, characterization,
and dehydrogenation of these nickel complexes and their
catalytic activities toward ethylene oligomerization and nor-
bornene and styrene homopolymerization with methylalu-
minoxane (MAO) as cocatalyst.
Results and Discussion
Synthesis of Tridentate Ligands and Their Nickel
Complexes
The tridentate ligands 4,6-disubstituted-2-{(trans-2-
(isoindolin-2-yl)-1,2-diphenylethylimino)methyl}phenol
[H(La)–H(Lc)] were synthesized as outlined in Scheme 1.
Racemic trans-diphenylethylenediamine (DPEDA) was
used as the starting material. One of the amine groups of
DPEDA was firstly protected with 1,3-dimethyl-5-acetyl-
barbituric acid[12] to form compound A, followed by alkyl-
ation of the other primary amine group with o-xylylene di-
bromide to give B in high yield.[13a] Deprotection of the
amine group of B with ethanolamine gave the monoamine
compound C,[13b] and further straightforward Schiff base
Scheme 1. Synthesis of tridentate ligands H(La)–H(Lc) and their
nickel complexes 1–5; reaction conditions: (i) THF, 3 d, yield: 91%.
(ii) (1,2-Dibromomethyl)benzene, diisopropylethylamine, N,N-di-
methylformamide (DMF), 40 °C, 2 d, yield: 72%. (iii) Ethanol-
amine, ethanol, yield: 77%. (iv) 3,5-Disubstituted salicylaldehyde,
ethanol, reflux, yields: 57 [H(La)], 86 [H(Lb)], and 89% [H(Lc)]. (v)
a) NaH, THF, room temp.; b) [(PPh3)2NiX2] (X = Cl, Br, I), THF,
room temp., yields: 56 (1), 63 (2), 69 (3), 67 (4), and 65% (5).
1
The H NMR spectra of the ligands H(L) are indicative
condensation of the terminal primary amine with 3,5-disub- of a trans-1,2-diphenylethylene linked isoindoline–salicyl-
stituted salicylaldehyde gave the corresponding crude prod- aldiminato fragment. For example, ligand H(Lb) exhibits
ucts, which were purified by silica gel chromatography to two doublets at δ = 4.27 and 4.93 ppm with a coupling con-
afford the pure tridentate ligands H(La)–H(Lc) as yellowish stant of J = 1.7 Hz that is attributable to the two inequiva-
solids in good yields (57–89%).
lent protons (Ha and Hb) of the CH group adjacent to the
1
The ligands H(La)–H(Lc) were treated with excess so- nitrogen atoms, and this H NMR spectrum also displays
dium hydride in tetrahydrofuran (THF) at room tempera- two doublets at δ = 3.98 and 3.99 ppm (J = 11.1 Hz), which
ture under argon to afford the corresponding sodium salts is characteristic of the CHcHdN protons of a five-member
[(L)Na(THF)], which subsequently reacted with [(PPh3)2- heterocyclic ring (Figure 1).
NiX2] (X = Cl, Br, I) to give the desired nickel complexes
From the IR spectra, the νC=N band obviously shifts
[(L)NiX] (X = Cl, L = La, 1; X = Cl, L = Lb, 2; X = Cl, L from 1628–1630 cm–1 for H(L) to 1599–1605 cm–1 for nickel
= Lc, 3; X = Br, L = Lb, 4; X = I, L = Lb, 5) in moderate complexes 1–5. The NMR spectra of these nickel complexes
yields (56–67%, Scheme 1). All nickel complexes were char- showed no complexity; the broad singlet resonance assigned
acterized by NMR and FTIR spectroscopy, elemental to the ArOH protons was not present and the resonances
analysis, and single-crystal X-ray diffraction analysis.
corresponding to the ligand protons were observed. It
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Figure 1. Selected region (δ = 6.5–3.5 ppm) of the 1H NMR spectra
of ligand H(Lb) (above) and complex 2 (below) in CDCl3 solutions
at 20 °C. 1H Chemical shifts referenced to residual undeuterated
chloroform solvent signal (δ = 7.26 ppm).
Figure 2. Molecular structure of 2.
should be noted that the CH and CH2N groups of the
nickel complexes revealed six broad singlets in the range δ
= 6.12–3.88 ppm, which are quite different from those of
free ligands (Figure 1). It is the inability of this ligand frag-
ment to rotate with regard to the C–N bond (as a conse-
quence of coordination) that causes the inequivalence of
these nuclei. Variable-temperature NMR experiments re-
vealed that the rotation of this part of the ligand could not
proceed even at higher temperatures. As complexes of
Ni(II) with square-planar geometry are expected to be dia-
magnetic, this observation implies that these complexes are
distorted from the ideal geometry in solution. We tried but
failed to observe an electron paramagnetic resonance (EPR)
signal at room temperature. Inspection of 2 in the solid state
also indicates a somewhat distorted structure, which is in
agreement with this observation (see below).
Figure 3. Molecular structure of 4.
Table 1. Selected bond lengths [Å] and angles [°] for 2, 4, 6, and 7.
2 (X = Cl) 4 (X = Br) 6 (X = Br) 7 (X = I)
Bond lengths
X-ray Crystal Structural Analysis
Ni–N[a]
Ni–N[b]
Ni–O[c]
Ni–X
1.976(10)
1.850(8)
1.866(10)
2.215(3)
1.473(13)
–
1.960(12)
1.817(13)
1.815(9)
2.362(2)
1.481(13)
–
1.988(5)
1.822(6)
1.819(5)
2.3647(13) 2.5485(11)
–
1.984(5)
1.849(5)
1.833(4)
Crystals of 2 and 4 suitable for single-crystal X-ray dif-
fraction analysis were obtained as orange blocks by diffus-
ing hexane into the corresponding toluene solution of the
metal complexes. The ORTEP drawings of 2 and 4 are pre-
sented in Figures 2 and 3, and selected bond lengths and
angles for these complexes are summarized in Table 1.
ORTEP views reveal that the molecular structures of these
two complexes are similar to each other. Each consists of
one tridentate chelate ligand and a halide anion that form
a distorted square-planar coordination geometry, and the
nickel atoms are nearly coplanar.
C–C[d]
C=C[e]
–
1.205(9)
1.268(10)
Bond angles
N[a]–Ni–N[b] 86.5(4)
85.6(5)
93.6(4)
86.0(3)
94.8(3)
174.6(5)
179.4(3)
85.8(2)
93.6(2)
86.86(14)
94.63(15)
172.9(2)
172.2(3)
85.9(2)
N[b]–Ni–O[c] 92.9(4)
94.43(19)
84.96(13)
94.78(15)
177.0(2)
177.71(19)
O[c]–Ni–X
X–Ni–N[a]
87.3(3)
87.3(3)
N[a]–Ni–O[c] 174.8(4)
X–Ni–N[b]
178.0(2)
[a] Amine nitrogen atom. [b] Imine nitrogen atom. [c] Phenol oxy-
gen atom. [d] C–C single bond of two bridged benzylic carbon
atoms. [e] C=C double bond of cis-stilbene moiety in (Lb*).
For 2, the Nimine–Ni–Cl [178.0(2)°] and Ophenol–Ni–
Namine [174.8(4)°] angles are close to linear, and the two
angles are almost perpendicular to each other. The C(9)
phenyl ring and C(16) phenyl ring of the tridentate ligand
(Lb) are in a staggered configuration with regard to the nickel complexes.[7,9] The Ni–Namine distance of 1.976(10) Å
C(8)–C(15) bond, and the C(9)–C(8)–N(1) [115.8(7)°] and is longer than the Ni–Nimine distance [1.850(8) Å]. The for-
C(16)–C(15)–N(2) [115.9(8)°] bond angles are similar. The mer is close to the Ni–N(1) distance [2.005(2) Å] in [(η3:η1-
Ni–Ophenol distance of 1.866(10) Å is within the typical indenyl(CH2)2NMe2)Ni(PPh3)][BPh4],[14] and the latter is
range for Ni–O distances in square planar salicylaldiminato comparable to that of Ni–N(2) in [(L)NiCl] {1.858(8) Å, L
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=
4,6-di-tert-butyl-2-[N-(quinolin-8-yl)iminomethyl]phen-
olato}.[9d] The C(8)–C(15) distances of 1.473 (13) Å are nor-
mal for a C–C single bond.
For 4, the Ni–Br distance [2.36(2) Å] is naturally longer
than the Ni–Cl distance [2.215(3) Å] of 2. Noticeably, the
Ni–Nimine, Ni–Namine, and Ni–Ophenol bond lengths in 4 are
shorter than those in 2, and the differences are in the order
Ni–Namine (0.016 Å) Ͻ Ni–Nimine (0.033 Å) Ͻ Ni–Ophenol
(0.051 Å). Complex 4 has a less ideal coordination plane
surrounding the metal center than that of 2; the Namine–Ni–
Nimine [85.6(5)°], Namine–Ni–Ophenol [93.6(4)°], Ophenol–Ni–
Br [86.0(3)°], and Br–Ni–Namine [94.80°] bond angles devi-
ate from the ideal 90° more seriously than the equivalent
angles in 2 [86.5(4), 92.9(4), 87.3(3), and 87.3(3)°, respec-
tively]. The trend of bond length shortening and bond angle
deviation is attributed to the bromide coligand as it has a
relatively large atomic radius.
Figure 4. Molecular structure of 6.
Dehydrogenation of the Chelated Ligand (Lb)
Unlike nickel chloride complexes 1–3, when the bromide
(4) and iodide (5) complexes bearing (Lb) ligands were pre-
pared in the presence of O2 at an elevated temperature of
40 °C or were exposed to air at 40 °C, complexes of the type
[(Lb*)NiX] (X = Br, 6; X = I, 7) could be obtained
1
(Scheme 2). The H NMR spectra of these complexes ap-
parently lack signals attributable to methyne protons (CH)
on the diamine moiety, which are observed in the spectra
of H(Lb) at δ = 4.27 and 4.93 ppm. This indicates that dehy-
drogenation of the coordinated tridentate ligand took place
at the bridged carbon atoms to form the cis-stiblene moiety.
Figure 5. Molecular structure of 7.
of a metal ion to an unstable higher oxidation state, fol-
lowed by oxidation of the ligand and reduction of the metal
ion. Therefore, oxidation reagents are necessary for the oxi-
dation of the metal ion. We also found that the dehydroge-
nation reactions of Lb in 4–5 did not directly occur under
an argon atmosphere, but that oxygen is necessary for the
oxidation. Control NMR-tube experiments showed that
heating the THF solution of 4 for a long time in the pres-
ence of O2 could give 6 very slowly, whereas a relatively
short time is sufficient for 5. This result suggested that, in
addition to oxygen, something else (e.g., coordinated an-
ionic groups Cl–, Br–, and I–) might play a role in the above
one-pot dehydrogenation of 4. Moreover, several control ex-
periments were performed to exclude the influence of NaH
in the first step. Ligand H(Lb) reacted with excess NaH in
THF at elevated temperature (less than 60 °C) in the pres-
ence of oxygen to give the salt [(Lb)Na(THF)]; no corre-
sponding salt of the dehydrogenated chelate ligand could
Scheme 2.
Single-crystal X-ray diffractions analyses (Table 1, Fig-
ures 4 and 5) were performed to confirm the dehydrogena-
tion of the chelate ligand. Complexes 6 and 7 have similar
solid-state structures to those of 2 and 4. Four atoms coor-
dinate to the NiII center to create five- and six-member
metallacycles. Notably, the two benzylic carbon atoms were
oxidized and a C=C double bond [1.205 Å for C(9)–C(16)
of 6, 1.268(10) Å for C(1)–C(8) of 7] formed in the five-
membered metal–chelate ring.
Similar dehydrogenation of coordinated tetradentate
salen-like ligands derived from 1,2-diphenyl-1,2-ethanedi-
amine by using oxidation reagents such as molecular oxy-
gen and heating of their nickel complexes for prolonged
periods has been reported.[15] This kind of dehydrogenation
1
be detected by H NMR spectroscopy. However, the role
of O2, coordinated halides, and the nickel centers in these
complexes still remains unclear.
Ethylene Oligomerization
The catalytic performances of the obtained nickel com-
reaction is usually considered to involve the prior oxidation plexes in the homopolymerization of ethylene and nor-
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bornene have been evaluated with MAO as cocatalyst. To polymerization of norbornene (NB). Polynorbornene
show the differences in catalytic behavior of the present (PNB) formed immediately after MAO was added to a mix-
complexes and previously known Ni catalysts, we prepared ture of norbornene and nickel complex in toluene. The
a simpler nickel complex 8 with a similar NNO ligand steric effect of the diphenyl-substituted C–C linker nega-
(ethylenediamine-linked salicilaldiminato–diethylamine) ac- tively impacts the catalytic activity. Under the same polyme-
cording to ref.[16]
rization conditions, complex 2 showed a catalytic activity
As shown in Table 2, nickel complexes 1–5 catalyzed eth- of 0.12–1.89ϫ105 gmol–1 Nih–1, which is much lower than
ylene oligomerization with activities of 0.49ϫ105– that of 8 [5.90ϫ105 gmol–1 Nih–1] and other previously
3.25ϫ105 gmol–1 Nih–1 at 30 °C under 20 bar of ethylene known Ni catalysts [Ͼ106 gmol–1 Nih–1].[9d]
with an MAO/Ni ratio of 250. Complexes 6 and 7 with
chelated ligand (Lb*) revealed much lower activity and only
trace C6 product could be detected (Table 2, Entries 6 and
7). The ethylenediamine-bridged [ONN] nickel complex 8
showed good catalytic activity of 1.02ϫ105 gmol–1 Nih–1
for ethylene dimerization (Table 2, Entry 12).
Table 3. Norbornene polymerization with 2/MAO system.[a]
[c]
[c]
Entry Ni [μmol]
T
[°C]
Yield Activity[b]
[g]
Mw
Mw/Mn
(ϫ106)
1
2
4
4
4
4
2
0
4
50 0.070
30 0.355
10 0.753
10 0.421
10 0.048
0.17
0.89
1.89
1.05
0.12
–
–
0.82
1.06
1.32
–
–
–
–
1.59
1.72
2.07
–
–
–
3
4[d]
5
Table 2. Ethylene oligomerization with 1–7/MAO system.[a]
Entry Cat. Al/Ni P [atm] Activity[b] Selectivity [%]
6[e]
10
0
[c]
[d]
7[f]
10 1.180
5.90
C4
1-C4 C6
[a] Polymerization conditions: [Ni]: 1.0ϫ10–3 m in CH2Cl2, MAO:
2.2 m in toluene, Al/Ni: 1100, norbornene: 2 g, time: 30 min, Vtotal
= 15 mL. [b]ϫ105 gmol–1Nih–1. [c] Determined by high tempera-
ture GPC at 150 °C. [d] Al/Ni: 550. [e] Blank experiment with only
MAO. [f] Complex 8 as precatalyst.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
2
2
2
2
8
250
250
250
250
250
250
250
250
250
500
500
250
20
20
20
20
20
20
20
5
1.59
3.14
3.30
3.28
3.25
0.77
0.49
0.55
3.28
0.34
0.06
1.02
97.8
98.3
97.1
97.9
97.2
Ͼ99
Ͼ99
98.0
98.5
97.0
99.8
Ͼ99
75.3
86.3
83.2
85.5
85.5
–
2.2
1.7
2.9
2.1
2.1
–
–
–
Further study showed that the polymerization conditions
strongly influenced the activities (Table 3). For example,
decreasing the reaction temperature from 50 to 10 °C re-
sulted in an improvement of activity from 0.17 to
1.89ϫ105 gmol–1 Nih–1 (Table 3, Entries 1–3). A low ac-
tivity of 1.05ϫ105 gmol–1 Nih–1 was observed in the pres-
ence of a low Al/Ni molar ratio of 550 (Table 3, Entries 3
and 4), which indicates that more MAO was required to
stabilize the active species for norbornene polymerization.
Moreover, a low initial nickel catalyst concentration caused
a low polymer yield (Table 3, Entry 5). The blank experi-
ments showed that no polymers were produced in the ab-
sence of 2 (Table 3, Entry 6).
64.2
92.1
42.6
66.9
–
2.0
1.5
3.0
0.2
–
9
40
5
5
10[e]
11
12
40
[a] Reaction conditions: 50 mL of toluene, 10 μmol of Ni, 30 °C,
30 min. The results shown are representative of at least duplicated
experiments. [b] ϫ105 gmol–1 Nih–1, as determined by quantitative
gas–liquid chromatography (GLC). [c] Butene. [d] Several isomers
of hexene were detected by GLC. [e] 60 °C.
Complex 2 was carefully studied for further optimiza-
tion, and the influence of temperature, Al/Ni mol ratio, and
ethylene pressure was investigated (Table 2, Entries 8–11).
From the representative results, several points can be con-
cluded. Firstly, the oligomerization rate logically increased
with ethylene pressure; the activities varied from 0.55ϫ105
to 3.28ϫ105 gmol–1 Nih–1 from 5 to 40 bar (Table 2, En-
tries 8 and 9). Secondly, increasing the oligomerization tem-
perature caused an increase of the selectivity for 1-butene,
along with a more balanced 2-butene isomeric ratio (cis vs.
trans, Table 2, Entries 10 and 11). Finally, a greater load of
MAO led to lower activity (Table 2, Entries 11 and 8). At
the same time, increasing the ration from 250 to 500 equiv.
led to slightly improved selectivity for both the C4 fraction
(98.0 to 99.8%) and 1-butene (64.2 to 66.9%).
The molecular weights (Mw) of the polynorbornenes ob-
tained range from 0.82ϫ105 to 1.32ϫ105 gmol–1 with very
low molecular weight distribution (1.59 to 2.07). The ab-
1
sence of resonances at δ = 5.0–6.0 ppm in the H NMR
spectra revealed that the obtained polynorbornene pos-
sesses a vinyl addition structure but not a ring opening me-
tathesis polymerization (ROMP) structure.[17] In the 13C
NMR spectra, the main four groups of resonances at δ =
52.8–47.7 ppm for the backbone carbon atoms and 39.8–
35.5, 31.5, and 30.0–29.8 ppm for the bridge carbon atoms
also agree with this.[18]
Styrene Polymerization
Norbornene Addition Polymerization
Nickel complex 2 was found to actively catalyze the poly-
On the basis of the preliminary results for ethylene oligo- merization of styrene in the presence of MAO (Table 4).
merization, complex 2 was selected for further investigation The activities decreased with prolongation of the polymeri-
in norbornene polymerization (Table 3). In the presence of zation time probably owing to the increased viscosity of the
MAO, complex 2 proved to be an active catalyst for the quickly formed polystyrene solution, which might block
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catalytic species (Table 4, Entries 1–4). Increased polymeri-
Experimental Section
zation temperature slightly improved the activity (Table 4,
Entries 4 and 5). Further study showed that the Al/Ni mo-
lar ratio strongly influenced the activities, which decreased
quickly from 3.24ϫ105 to 0.49ϫ105 gmol–1 Nih–1 with a
decrease of MAO loading (Table 4, Entries 5–7). The opti-
mum Al/Ni value was about 1100 and lower catalyst load-
ing decreased the catalytic ability (Table 4, Entries 5–8).
Unlike norbornene polymerization, complex 2 revealed a
slightly higher activity [3.57ϫ105 gmol–1 Nih–1] than the
ethylenediamine-linked salicylalidiminato–diethylamine Ni
complex 8 [2.94ϫ105 gmol–1 Nih–1] under the same condi-
tions (Table 4, Entries 4 and 9). Although the nickel com-
plex is active for styrene polymerization, the tacticity of the
obtained polystyrene is very low because these polymer are
very soluble in 2-butanone.[19] Polystyrene samples at the
various Al:Ni ratios as well as reaction temperature were
analyzed by gel permeation chromatography (GPC,
Table 4). Both the molecular weight (Mw) and polydisper-
sity index (PDI, 4.20ϫ 104 gmol–1 and 1.54, respectively)
of the polymer obtained increase with a decrease of polyme-
rization temperature from 60 to 5 °C (6.67ϫ 104 gmol–1 and
1.62) and a decrease of the Al/Ni molar ratio from 1100 to
550 (4.72ϫ 105 gmol–1 and 1.714).
General: Unless otherwise noted, all manipulations of air- and/or
water-sensitive compounds were carried out under an inert atmo-
sphere by using standard Schlenk techniques. Toluene, THF, and
hexane were distilled from sodium benzophenone ketyl under nitro-
gen. Dichloromethane was distilled from CaH2. CDCl3 was dried
and distilled before use. 1,3-Dimethyl-5-acetylbarbituric acid
(DAB),[12]
B
[13a], C[13b] (Scheme 1), 3,5-disubstituted salicylalde-
hyde,[20] [(PPh3)2NiX2] (X = Cl, Br, I),[21] and 8[16] were prepared
according to published procedures. MAO was purchased from
Akzo Chemical as a 2.2 m toluene solution. Other commercially
available reagents were purchased and used without further purifi-
cation.
NMR spectra were recorded with Bruker DMX-500 (500 MHz, 1H;
125 MHz, 13C) and Jeol ECA 400 spectrometers (400 MHz, 1H;
100 MHz, 13C). Chemical shifts (δ) for 1H and 13C spectra are refer-
enced to internal solvent resonances and are reported relative to
tetramethylsilane (TMS). NMR experiments on air-sensitive sam-
ples were conducted in Teflon-valve-sealed sample tubes (J. Young).
IR spectra were recorded with a Nicolet AV-360 spectrometer. Ele-
mental analyses for C, H, and N were performed with a Vario EL
1
III analyzer. H and 13C NMR spectra of polymers were acquired
in 1,2-[D4]dichlorobenzene at 120 °C. GPC for polynorbornenes
was carried out in 1,2,4-trichlorobenzene at 150 °C with a Waters
high-temperature GPC 2000 instrument equipped with a set of
three PLgel 10 μm mixed-B columns. GPC for polystyrenes was
carried out in THF at 40 °C with a Waters Ultrastyra GPC instru-
ment.
Table 4. Styrene polymerization with 2/MAO system.[a]
[c]
[c]
Entry
Ni
Al/ Time Yield Activity[b] Mw
Mw/Mn
[μmol] Ni [min] [g]
(ϫ104)
General Procedure for the Synthesis of 4,6-Disubstituted 2-{(trans-
2-(Isoindolin-2-yl)-1,2-diphenylethylimino)methyl}phenol
[H(La)–
1
2
3
2
2
2
2
2
2
2
1
8
1100 15 0.368
1100 30 0.503
1100 45 0.621
1100 60 0.713
1100 60 0.757
7.36
5.03
4.14
3.57
3.79
0.49
3.24
3.27
2.94
–
–
–
4.20
6.67
4.72
–
–
–
–
1.54
1.62
1.71
–
H(Lc)]: To a mixture of 1,3-dihydro-α,β-diphenyl-2H-isoindole-2-
ethanamine C, 3,5-disubstitutedsalicylaldehyde (equivalent to C),
and several 4 Å molecular sieves in a septum capped Schlenk tube
was added anhydrous ethanol (ca. 10 mL per mmol of C) with a
syringe at 20 °C with stirring under nitrogen. After the resulting
mixture was stirred overnight, the solvent was removed under vac-
uum, and the residue was purified by flash chromatography on sil-
ica gel (Vethyl acetate/Vpetroleum ether = 1:20) to give the yellow to
brown target ligands H(La)–H(Lc).
4
5[d]
6
550
60 0.097
7
2200 60 0.648
1100 60 0.654
1100 60 0.588
8
–
–
–
–
9[e]
[a] Polymerization conditions: [Ni]: 1.0ϫ10–3 m in CH2Cl2, MAO:
2.2 m in toluene, styrene: 1 mL, temperature: 24 °C, Vtotal = 4.0 mL.
[b] 105 gmol–1 Nih–1. [c] Determined by GPC at 40 °C. [d] Polymeri-
zation temperature: 5 °C. [e] Complex 8 as precatalyst.
2-{(trans-2-(Isoindolin-2-yl)-1,2-diphenylethylimino)methyl}phenol
[H(La)]: Yellowish white crystalline solid, yield: 0.422 g, 57%. 1H
NMR (500 MHz, CDCl3): δ = 3.99 (d, J = 12.0 Hz, 2 H, CHHЈ),
4.11 (d, J = 12.0 Hz, 2 H, CHHЈ), 4.22 (s, 1 H, NCHCHN=CH),
4.96 (s, 1 H, NCHCHN=CH), 6.87 (t, J = 7.0 Hz, 1 H, ArH), 6.98
(d, J = 8.0 Hz, 1 H, ArH), 7.08 (s, 2 H, ArH), 7.09 (d, JH,H
=
Conclusions
2.0 Hz, 2 H, ArH), 7.13–7.17 (m, 7 H, ArH), 7.19 (s, 4 H, ArH),
7.32 (t, J = 7.0 Hz, 1 H, ArH), 8.49 (s, 1 H, N=CH), 13.41 (br. s,
1 H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ = 58.5, 76.1, 117.0,
122.2, 128.1, 129.7, 137.0, 140.1, 161.1, 165.1 ppm. FTIR (Nujol):
We have synthesized a class of trans-1,2-diphenyl-
ethylenediamine-linked salicylaldiminato–isoindoline li-
gands and their nickel complexes. These compounds were
characterized by NMR and FTIR spectroscopy and ele-
mental analysis. Single-crystal X-ray analysis confirms the
formation of complexes in which the metal center is coordi-
nated with the oxygen and nitrogen atoms of the tridentate
ligands. Dehydrogenation of the chelated tridentate ligand
took place and the two bridged benzylic carbon atoms of a
CH–CH single bond were oxidized to form the cis-stilbene
moiety with a C=C double bond. The nickel complexes
were active for ethylene oligomerization and the homopoly-
merization of norbornene and styrene with MAO as cocata-
lyst.
ν = 1629 (νC=N) cm–1. C29H26N2O (418.53): calcd. C 83.22, H 6.26,
˜
N 6.69; found C 83.19, H 6.31, N 6.75.
4,6-Di-tert-butyl-2-{(trans-2-(isoindolin-2-yl)-1,2-diphenylethyl-
imino)methyl}phenol [H(Lb)]: Yellowish white crystalline solid,
yield: 0.630 g, 86%. 1H NMR (500 MHz, CDCl3): δ = 1.29 [s, 9 H,
C(CH3)3], 1.47 [s, 9 H, C(CH3)3], 4.01 (d, J = 12.0 Hz, 2 H, CHHЈ),
4.10 (d, J = 12.0 Hz, 2 H, CHHЈ), 4.22 (d, J = 6.0 Hz, 1 H,
NCHCHN=CH), 4.93 (s, J = 6.0 Hz, 1 H, NCHCHN=CH), 7.08–
7.18 (m, 15 H, ArH), 7.39 (d, J = 2.0 Hz, 1 H, ArH), 8.52 (s, 1 H,
N=CH), 13.64 (s, 1 H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ
= 21.4, 29.4, 31.4, 33.7, 35.2, 59.1, 64.2, 74.0, 78.9, 121.3, 127.0,
128.5, 129.4, 136.6, 137.3, 159.5, 163.3 ppm. FTIR (Nujol): ν =
˜
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1628 (νC=N) cm–1. C37H42N2O (530.74): calcd. C 83.73, H 7.98, N
5.28; found C 83.69, H 8.00, N 5.41.
6.90 (m, 2 H, ArH), 6.80 (m, 1 H, ArH), 6.72 (m, 2 H, ArH), 6.22
(br. s, 1 H), 5.82 (br. s, 1 H), 5.01 (br. s, 1 H), 4.30 (br. s, 2 H),
4.12 (br. s, 1 H), 3.55 (br. s, 1 H), 1.73 [s, 9 H, C(CH3)3], 1.13 [s, 9
6-Phenyl-2-{[trans-2-(isoindolin-2-yl)-1,2-diphenylethylimino]-
methyl}phenol [H(Lc)]: Yellowish white crystalline solid, yield:
0.478 g, 89 %. 1H NMR (500 MHz, CDCl3): δ = 3.98 (d, J =
11.0 Hz, 2 H, CHHЈ), 4.08 (d, J = 11.0 Hz, 2 H, CHHЈ), 4.27 (d, J
= 6.7 Hz, 1 H, NCHCHN=CH), 4.93 (d, J = 6.7 Hz, 1 H,
H, C(CH ) ] ppm. FTIR (Nujol): ν = 1603 (νC=N) cm–1
.
˜
3
3
C37H41BrN2NiO (668.33): calcd. C 66.49, H 6.18, N 4.19; found C
66.24, H 6.39, N 4.28.
{N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylethyl]-[3,5-bis(tert-butyl)-
NCHCHN=CH), 6.95 (t, J = 7.5 Hz, 1 H, ArH), 7.07–7.17 (m, 15 salicylaldiminate]}NiIII (5): Orange-red solid, yield: 0.464 g, 65%.
H, ArH), 7.35 (t, J = 8.5 Hz, 2 H, ArH), 7.41 (d, J = 7.5 Hz, 1 H,
1H NMR (500 MHz, 25 °C, CDCl3): δ = 7.76 (br. s, 1 H, CH=N),
ArH), 7.45 (t, J = 7.5 Hz, 2 H, ArH), 7.65 (d, J = 8.5 Hz, 1 H, 7.34 (s, 6 H, ArH), 7.14 (d, J = 6.4 Hz, 2 H, ArH), 7.00 (s, 3 H,
ArH), 8.55 (s, 1 H, N=CH), 13.91 (s, 1 H, OH) ppm. 13C NMR ArH), 6.91 (m, 2 H, ArH), 6.76 (m, 1 H, ArH), 6.70 (m, 2 H, ArH),
(125 MHz, CDCl3): δ = 58.3, 77.7, 118.7, 119.2, 122.2, 126.7, 127.1,
127.4, 127.8, 128.0, 128.1, 128.2, 128.3, 128.5, 129.3, 129.4, 129.7,
6.22 (br. s, 1 H), 5.83 (br. s, 1 H), 5.02 (br. s, 1 H), 4.25 (br. s, 2
H), 4.11 (br. s, 1 H), 3.53 (br. s, 1 H), 1.72 [s, 9 H, C(CH3)3],
129.8, 131.2, 133.6, 137.8, 140.3, 158.5 ppm. FTIR (Nujol): ν =
1.12 [s, 9 H, C(CH ) ] ppm. FTIR (Nujol): ν = 1605 (νC=N) cm–1.
˜
˜
3 3
1630 (νC=N) cm–1. C35H30N2O (494.63): calcd. C 84.99, H 6.11, N
C37H41IN2NiO (715.33): calcd. C 62.12, H 5.78, N 3.92; found C
62.09, H 5.80, N 4.00.
5.66; found C 85.03, H 6.17, N 5.74.
General Synthesis of Complex {N-[trans-2-(Isoindolin-2-yl)-1,2-di- General Dehydrogenation Synthesis of Complex {N-[trans-2-(Iso-
phenylethyl]-[3,5-bis(substituent)salicylaldiminate]}NiIIX (1–5): To a
stirred suspension of NaH (5.0 mmol) in THF (5 mL) at 0 °C was
added dropwise a solution of H(L) (1.0 mmol) in THF (10 mL).
After the resulting mixture was warmed to room temperature and
stirred for 2 h, the excess NaH was removed by centrifugation. The
resultant clear yellow-green THF solution of sodium complex of
H(L) was transferred into a Schlenk tube containing [(PPh3)2NiX2]
(X = Cl, Br, I, 1.0 mmol). After the mixture was stirred overnight,
the solvent was evaporated under vacuum to afford a solid residue,
which was washed with hexane (2ϫ5 mL). The residue was ex-
indolin-2-yl)-1,2-diphenylvinyl]-[3,5-bis(substituent)salicylaldimin-
ate]}NiIIX (6–7): To a stirred suspension of NaH (5.0 mmol) in
THF (5 mL) at room temperature was added dropwise a solution
of H(Lb) (1.0 mmol) in THF (10 mL). The resulting mixture was
warmed to room temperature and stirred for 2 h. The reaction mix-
ture was centrifugated to remove excess NaH. The obtained clear
yellow-green THF solution of the sodium salt was transferred to a
Schlenk tube containing [(PPh3)2NiX2] (X = Br, I, 1.0 mmol) under
an O2 atmosphere. The resulting mixture was stirred overnight, and
the solvent was removed under vacuum to afford a solid residue.
tracted with toluene (2ϫ5 mL) to afford a dark red solution. The The residue was washed with hexane (2ϫ5 mL) and then extracted
toluene was removed in vacuo to give pure nickel complexes 1–5.
with toluene twice (2ϫ5 mL) to produce a dark red solution, which
was layered with hexane (10 mL) to give red crystals of pure prod-
uct.
{N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylethyl]-(salicylaldimin-
ate)}NiIICl (1): Orange-red solid, yield: 0.286 g, 56%. 1H NMR
(500 MHz, CDCl3): δ = 8.13 (br. s, 1 H, CH=N), 7.35 (s, 6 H, {N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylvinyl]-[3,5-bis(tert-butyl)-
ArH), 7.17 (d, J = 6.4 Hz, 2 H, ArH), 7.05 (s, 3 H, ArH), 6.90 (m, salicylaldiminate]}NiIIBr (6): Red crystals, yield: 0.379 g, 57% yield.
2 H, ArH), 6.80 (m, 1 H, ArH), 6.72 (m, 2 H, ArH), 6.12 (br. s, 1 1H NMR (500 MHz, CDCl3): δ = 8.12 (br. s, 1 H, CH=N),
H), 5.80 (br. s, 1 H), 5.35 (br. s, 1 H), 4.92 (br. s, 1 H), 4.28 (br. s, 7.62–6.69 (m, 16 H, ArH), 5.92 (br., s, 2 H, CH2), 4.18 (br., s, 2 H,
1 H), 3.88 (br. s, 1 H) ppm. FTIR (Nujol): ν = 1603 (νC=N) cm–1.
C29H25ClN2NiO (511.67): calcd. C 68.07, H 4.92, N 5.47; found C
67.88, H 5.17, N 5.63.
CH2), 1.34 [s, 9 H, C(CH3)3], 1.18 [s, 9 H, C(CH3)3] ppm.
C37H39BrN2NiO (666.32 g): calcd. C 66.69, H 5.90, N 4.20; found
C 66.77, H 5.97, N 4.30.
˜
{N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylethyl]-[3,5-bis(tert-
butyl)salicylaldiminate]}NiIICl (2): Orange-red solid, yield: 0.370 g,
63%. H NMR (500 MHz, CDCl3): δ = 8.24 (br. s, 1 H, CH=N),
{N-[trans-2-(isoindolin-2-yl)-1,2-diphenylvinyl]-[3,5-bis(tert-butyl)-
salicylaldiminate]}NiIII (7): Red crystals, yield: 0.392 g, 55% yield.
1H NMR (500 MHz, CDCl3): δ = 8.11 (br. s, 1 H, CH=N), 7.62–
1
7.35 (s, 6 H, ArH), 7.17 (d, J = 6.4 Hz, 2 H, ArH), 7.05 (s, 3 H, 6.67 (m, 16 H, ArH), 5.94 (br., s, 2 H, CH2), 4.13 (br., s, 2 H, CH2),
ArH), 6.90 (m, 2 H, ArH), 6.80 (m, 1 H, ArH), 6.72 (m, 2 H, ArH), 1.35 [s, 9 H, C(CH3)3], 1.19 [s, 9 H, C(CH3)3] ppm. C37H39IN2NiO
6.12 (br. s, 1 H), 5.80 (br. s, 1 H), 5.35 (br. s, 1 H), 4.92 (br. s, 1 (713.32): calcd. C 62.30, H 5.51, N 3.93; found C 62.17, H 5.47, N
H), 4.28 (br. s, 1 H), 3.88 (br. s, 1 H), 1.34 [s, 9 H, C(CH3)3], 4.00.
1.19 [s, 9 H, C(CH ) ] ppm. FTIR (Nujol): ν = 1599 (vC=N) cm–1.
C37H41ClN2NiO (623.88): calcd. C 71.23, H 6.62, N 4.49; found C
71.19, H 6.57, N 4.62.
˜
3 3
General Procedure for Ethylene Oligomerization by Ni Catalysts 1–
7/MAO: A 150 mL stainless autoclave equipped with a mechanical
stirrer and a continuous feed of ethylene was used. The reactors
were dried in an oven at 120 °C for 12 h prior to each run and
then placed under vacuum for 30 min. After toluene and the proper
{N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylethyl]-(3-phenylsalicylald-
iminate)}NiIICl (3): Orange-red solid, yield: 0.430 g, 69%. 1H NMR
(500 MHz, CDCl3): δ = 8.22 (br. s, 1 H, CH=N), 7.48–7.45 (m, 3 amount of MAO cocatalyst were introduced into the reactor under
H, ArH), 7.32–7.30 (m, 3 H, ArH), 7.23–7.21 (m, 5 H, ArH), 7.12 argon, the system was closed and saturated with ethylene, and the
(d, J = 6.4 Hz, 4 H, ArH), 7.07 (m, 2 H, ArH), 6.94–6.92 (m, 5 H, oligomerization reaction was started by introduction of the nickel
ArH), 6.14 (br. s, 1 H), 5.79 (br. s, 1 H), 5.37 (br. s, 1 H), 4.92 (br.
complex dissolved in toluene. The ethylene was continuously fed in
order to maintain the ethylene pressure at the desired value. After
a certain time, the reaction was stopped by cooling the system to
0 °C, depressurizing, and introducing 1 mL of ethanol. An exact
amount of cyclohexane was introduced (as an internal standard),
and the mixture was analyzed by quantitative GLC.
s, 1 H), 4.27 (br. s, 1 H), 3.88 (br. s, 1 H) ppm. FTIR (Nujol): ν =
˜
1603 (νC=N) cm–1. C35H29ClN2NiO (587.76): calcd. C 71.52, H
4.97, N 4.77; found C 71.79, H 5.07, N 4.95.
{N-[trans-2-(Isoindolin-2-yl)-1,2-diphenylethyl]-[3,5-bis(tert-butyl)-
salicylaldiminate]}NiIIBr (4): Orange-red solid, yield: 0.447 g, 67%.
1H NMR (500 MHz, CDCl3): δ = 7.81 (br. s, 1 H, CH=N), 7.35
(s, 6 H, ArH), 7.17 (d, J = 6.4 Hz, 2 H, ArH), 7.05 (s, 3 H, ArH),
General Procedure for Norbornene Addition Polymerization by Ni
Catalysts 1–5/MAO: To a solution of norbornene (2 g) and precata-
Eur. J. Inorg. Chem. 2013, 2093–2101
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FULL PAPER
Table 5. Crystal data and structure refinements of complexes 2, 4, 6, and 7.
2
4·0.5(CH2Cl2)
6
7·0.5(C7H8)
Formula
C37H41ClN2NiO
623.88
0.32ϫ0.20ϫ0.10
triclinic
C37.50H42BrClN2NiO
710.80
0.25ϫ0.15ϫ0.06
triclinic
C74H78Br2N4Ni2O2
1332.64
C40.50H43IN2NiO
759.38
Formula weight
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
0.20ϫ0.18ϫ0.16
triclinic
0.12ϫ0.08ϫ0.01
triclinic
¯
¯
P1
P1
P1
P1
10.808(4)
12.766(5)
14.958(6)
97.559(5)
99.404(5)
105.708(5)
1926.4(12)
2
10.674(4)
12.857(5)
13.632(5)
86.610(5)
70.852(5)
74.666(5)
1703.5(11)
2
12.807(6)
16.046(8)
21.378(10)
84.819(8)
78.323(7)
74.385(8)
4141(3)
12.937(6)
13.214(6)
13.310(6)
89.462(5)
61.739(5)
66.565(5)
1793.2(13)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
2
ρcalcd. [Mgm–3]
F(000)
1.076
660
1.386
738
1.069
1384
1.406
778
T [K]
293(2)
0.599
293(2)
1.852
293(2)
1.458
293(2)
1.435
μ [mm–1]
θ range [°]
Reflections collected
Data/restraints/parameters
Goodness of fit
R indices [IϾ2σ(I)]
1.40 to 25.01
8004
8004/9/770
0.913
R1 = 0.0621
wR2 = 0.1496
R1 = 0.0813,
wR2 = 0.1599
1.58 to 25.01
7092
7092/21/784
1.022
R1 = 0.0636
wR2 = 0.1805
R1 = 0.0796
wR2 = 0.2059
1.152 and –1.089
1.67 to 25.01
17262
14301/37/746
0.788
R1 = 0.0773
wR2 = 0.1718
R1 = 0.1472
wR2 = 0.1868
1.092 and –0.689
1.72 to 25.01
7451
6189/6/429
1.012
R1 = 0.0600
wR2 = 0.1495
R1 = 0.0943
wR2 = 0.1653
0.925 and –0.736
R indices (all data)
Largest diff. peak and hole eÅ–3 0.9425 and 0.8314
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|, wR2 = [Σ(|Fo|2 – |Fc|2)2/Σ(Fo2)]1/2
.
lyst (4 μmol) in CH2Cl2 was added MAO (2.2 m in toluene) by sy-
ringe. After the desired run time, the reactor was vented, and the
reaction mixture was quickly quenched with 10% HCl in methanol.
The precipitated polymer was stirred for several hours, collected by
filtration, and washed with methanol. It was then dried under high
vacuum at 40 °C overnight.
Acknowledgments
This work was financially supported by National Natural Science
Foundation of China (NSFC) (grant numbers 20972031 and
21272040).
General Procedure for Polymerization of Styrene: To a solution of
styrene (1 mL) and precatalyst (2 μmol) in CH2Cl2 was added
MAO (2.2 m in toluene) by syringe. After the desired time, the reac-
tion mixture was quenched by adding acidified EtOH (5 mL,
EtOH/concentrated HCl, 10:1 v/v). The mixture was poured into a
solution of concentrated HCl in EtOH (5% v/v) and stirred for
12 h. The polymer was collected by filtration, washed with EtOH,
and dried under reduced pressure at 40 °C to constant weight.
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Received: November 2, 2012
Published Online: February 12, 2013
Eur. J. Inorg. Chem. 2013, 2093–2101
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim