Design ,synthesis and investigation of α-diimine,
β-diimine and benzoxazolyl ligands formed series of
Ni（II） complexes
Zhuofeng Ke, Junkai Zhang*, Qing Wu*
Contribution from the Department of Polymer and Materials, School of Chemistry and Chemical Engineering, Zhongshan
University, China
Abstract
α-diimine,β-diimine and benzoxazoyl ligands to form series of
and synthesized in this article. copolymerization of
Ni complexes were designed
ethylene/norbornene, ethylene/acrylate,
norbornene/acrylate can be carried out in good active to get saturated new materials with super properties
of optics, stable in size, manufacture.
Comparing with the different characteristics of synthesis and isolation between these ligands, the project
provides a series of conventional one-step preparation methods to synthesize the ligands mentioned ahead.
Then identified the compounds with MS (FAB) and element analysis. α-diimine ligands can be prepared
by one-step method in methanol medium, using anhydrous Na2SO4 to absorb the water of the system. The
catalysts can obtain recrystallization with n-hexane. β-diimine ligands can reacted in one-step in toluene
medium, removing water of the system by boiling with toluene. Catalyst can also obtain with n-hexane.
Benzoxazolyl ligands can be prepared first adding a small quantity of water to urge the transesterificatio
reaction then removing water to
initiate cyclization reaction in the mixed of tetrahydrofuran and toluene.
Mixture of toluene and tetrahydrofuran is the best solvent to crystallization. Identification result indicated
that α-diimine and β-diimine ligands have the respondent structure and pure, benzoxazolyl ligands need
isolation farther。
Keywords
α-diimine ligands,β-diimine ligands, benzoxazoyl ligands. Ni complexes.
Introduction
Since the discovery of the Ziegler–Natta catalyst in the 1950s, highly active MgCl2-supported Ti catalysts, displaying
high catalytic performance, havebeen developed to simplify the production process in order to save resources and energy as
well as toimprove properties of produced polymers [1–3]. By using these MgCl2-supported Ti catalysts, many polymers,
such as high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and isotactic polypropylene (i-PP),
have been industrially produced. However, the catalyst design for tailored polyolefins
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170
has not yet been perfected, because of the existence of multiple active sites on these solid catalysts.
Single-site catalysts possess potential for controlling polymer structure while displaying high
polymerization activity by changing the ligand structure and co-catalyst. Thus, research and development of
transition metal complexes for olefin polymerization, aiming at high performance single-site catalysts, made a
dramatic impact on the polyolefin industry, as demonstrated by the discovery of highly active group 4
metallocene catalyst systems [4–7]. So far, by employing group 4 metallocenes, the industrial production of
LLDPE, isotactic and syndiotactic polypropylene (i-PP, s-PP), etc., has been commercially successful.
Therefore, after the discovery of the group 4 metallocene catalyst systems, transition metal complexeshave been
intensively investigated as post-metallocene candidates [8–14], and since 1995, some excellent new catalysts
have been developed.
In 1995, Brookhart [15] reported that a nickel complex possessing a diimine ligand (a) produced branched
polyethylene in the absence of a co-monomer with considerable activity for ethylene polymerization. And, in
1996, Brookhart [16-18] established ethylene/methyl acrylate co-polymerization using the corresponding
palladium complex bearing the same ligand (b), as the nickel complex. This is the first example of
ethylene/methyl acrylate co-polymerization via coordination polymerization. In 1998, Brookhart and Gibson
[19,20] independently discovered a new series of iron complexes
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Williams, 1998 Chem. Commun. 849.
171
possessing
Imine–pyridine ligands (c). These complexes displayed very high ethylene polymerization activity
comparable to that of metallocenes. This is fantastic, since they say that metallocenes exhibit the highest
polymerization activity and that no catalysts can exceed metallocene activity. Additionally, a titanium complex
with a di-amide ligand displaying excellent properties for higher olefin polymerization (d) [21-23], and a nickel
complex with a phenoxy–imine ligand exhibiting high ethylene polymerization activity and high functional
group tolerance (e), have also been reported [24,25]. Late-transition
metal catalyst remains the characteristics of metallocene catalysts, such as narrow molecular weight
distribution, potential for controlling polymer structure, being a tailor-polymerization. It is also a single-site
catalyst and has many other advantages compared with other catalysts mentioned ahead. The post- transition
metal catalysts are steadier, which make them easier to be stored and transported. The catalyst system can be
used to copolymerize polar monomer or norbornene and olefins to produce materials with superior properties,
using less or no co-catalyst MAO, which has more commercial value because MAO is usually expensive.
Researchers have been making great strides in the field of late-transition metal catalysts with modification of
ligands.
The purpose of this project was the development of highly active post-metallocenes based on transition
metal complexes, especially the metal nickel, which combined the diimine ligands. Considering that α-diimine
complexes can avoidβ-H transfer at polymerization of ethylene, and thatβ-ketoamine complexes are high
active to polymerize norbornene, β -diimine complexes is designed to polymerize norbornene and
copolymerize based on norbornene.
A catalyst with appropriate substituents eliminating the β-H transfer to increasing molecular weight, with
β-diimine ligand eliminating H on the secondary carbon, the anion carbon and the coordination metal ion to
form a electronic unite, which maybe do a dramatic electron effect on the polymerization.
Additionally we design new ligands with stable substituent benzoxazole. With all the catalysts designed we
will study the activity of catalysts in various homopolymerizations and copolymerizations, especial the
norbornene based copolymerization with ethylene, propylene or other α-olefins, styrene and other polar
fu
nctional monomer, comparing with the different effect distributed by different catalysts, studying
polymerizations under different reaction conditions, investigating the different reaction mechanism.
The result and discussion
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[24] C. Wang, S.K. Friedrich, T.R. Younkin, R.T. Li, R.H. Grubbs, D.A. Bansleben, M.W. Day,
Organometallics1998. 17
[25] T.R. Younkin, E.F. Connor, J.I. Henderson, S.K. Friedrich, R.H. Grubbs, D.A. Bansleben, Science 2000.
287. 460.
172
The synthesis of α-diimine ligands. Theα-diimine ligands investigated in this study were
synthesized via a modification of a procedure described by Matei and Lixandru [26]. The result of this
procedure was unsatisfied because of acid liquid medium. Another procedure to synthesize α-diimine ligands
with alcohol gave an better result in the experiment prepared by a similar method described [27,28], in which
the respective ligand was first formed via an acid catalyzed condensation between the aniline and the diketone.
Preparation of ligand (R=CH3) and ligand (R=phenyl) are all nucleophilic reactions that the single
substituting forms the sub-conduct. Considering it, feeding excessive 2,6-diisopropylaniline to prevent single
substitute and extending the reaction time for adequate conversion. The experiment was ever done with a
reaction time of 8 hours affording very little deposition, which is very difficult to recrystallize. But the single
substituting is impossible to avoid absolutely. Due to the transition state of this nucleophilic reaction the
transition state is instable, neutralization the solution with triethyl amine must be processed in time, or the
deposition will reduce sharply. Putting filter paper tube filled with anhydrous Na 2SO4 in the filter to absorb
water in the reflux liquid is very Important to increase the conversion ratio, which is a improvement of the
procedure [27,28]. High conversion ratio is not our main aim. Pure ligands were necessary to form the nickel
complex that recrystallization must be operated again and again, which will of course decrease quantity of the
product. Toluene, n-hexane and ethyl ether were used as solvents for crystallization. Ether solution is difficult to
crystallize.
The synthesis of β-diimine ligands. The preparation ofβ-diimine ligands is a new research
field to form Ni complexes. Ligand was first prepared according to the literature methods [29,30] and then tried
in the preparation method ofα-diimine [27,28]. The results were unsatisfied. The reaction temperature is too
high under which the malonic acid will decompose. Polyphosphoric acid is very difficult to isolated as the
reaction medium. Considering the same nucleophilic reaction mechanism. A similar procedure to chapter 2.3
was carried out except the way to get rid of produced water. Toluene was used as the azeotropes with water,
which was distilled out of the reaction solution when refluxing. During the reaction water appeared in the
bottom of the filter.
To get pure catalysts, Toluene, n-hexane, methane, tetrahydrofuran were all tried to cresytallize. Methane is
good enough to remove the impurities, but the solubility is too favorable; crystallization is difficult in the
tetrahydrofuran solution; the shape of the
crystal in the toluene is bad; n-hexane is the best solvent
we had tried. But catalyst of ligand (R=CH3) was still unsatisfied as too tiny like wool compared
with ligand
[26] T. Matei, T. Lixandru, Bul. Inst. Politeh. Iasi 13 (1967) 245; Chem. Abstr. 1969.70. 3623m.
[27] S.A. Svejda, M. Brookhart, Organometallics. 1999. 18. 65;
[28] C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J.Am. Chem. Soc. 1996. 118. 11664.
[29] A. Vogler, H. Kunkely, J. Hlavatsch, A. Merz, Inorg. Chem. 1984. 23. 506.
[30] R. Benedix, H. Henning, Inorg. Chim. Acta 1988. 141. 21.(R=phenyl)
The synthesis of benzoxazolyl ligands
173
As usual, the preparation of benzoxazole derivatives was used poly phosphoric acid as reaction medium,
from 2-nitrophenol or 2-aminophenol with carboxylic
acid derivatives. The reaction temperature is usually up
to 250oC [31-33] (Scheme 1). It is an extremely
convenient one–step procedures and easy to be carried
out in scale. As for ligand (d), malonic acid and
2-aminophenol were heated under 250oC in PPA
(polyphosphoric acid). The post-procedure was very
Scheme 1
difficult, and nothing obtained in the end. As for ligand (c), two-step
reaction was tried. 2-aminophenol reacted with acetonitrile to form 2-methyl benzoxazole, which was then
reacted with benzoyl chloride. This procedure is troubleThere are two steps reaction in the mechanism of the
procedure in chapter 2.7 and 2.8.
The first one is transesterificatio reaction; the second one is cyclization reaction. Because the reaction
mechanism is complex，it is difficult to control the reaction to obtain the ligand. If the nucleophilic reaction
between hydroxyl and the carbonyl take place first, the benzoxazolyl can’t be formed. Due to the mechanism
ahead, we added some water in the system before reaction occurring, which could prevent the nucleophilic
reaction. When the transesterificatio reaction processed in a good degree, we increased the reaction temperature
to boiling out the water to improve conversion of the cyclization reaction. And the time of first step reaction
must be enough. It meant that the system’s color had changed or the system produced deposition. Figure 5 and 6
is the early catalyst produced without adding water in advance. Catalyst obtained according to procedure
illustrated in chapter 2.7 and 2.8 is still need to recrystallize.
R
R
R
R
O
Ar
N
N
Ar
N
N
N
Ar
O
N
R
O
O
N
Ar
¦Á -benzoxazolyl-one
R = CH3,
Ar = 2,6-diisopropyl-aniline
(a)
R = CH3,
Ar = 2,6-diisopropyl-aniline
Bis(benzoxazolyl)methane
(b)
(c)
Scheme 2
[31] S. Chiou, H.J. Shine, J. Heterocycl. Chem. 1989. 26. 125.
[32] F. Eloy, R. Lenaers, Chem. Rev.1962. 62 155.
[33] K.P. Flora, B. Reit, G.L. Wampler, Cancer Res. 1978. 38 1291
Experimental section
174
R = CH3,
(d)
We have synthesized 6 ligands by now. (Scheme
2)
α-diimine ligands (a) as to R=CH3,
before the reaction was took place, the capacity
must be dried with infrared light and replace the air in
it with nitrogen 2~3 times to form a closed system
(scheme 3) with inert nitrogen air. Carefully fed in the
single-neck flask 13.5ml 2,6-diisopropylaniline, 3ml
butanedione, a little hydrochloric acid as initiation
catalyst and 15~20ml methanol, from the branch pipe
with injection. The stirred solution was heated at
scheme 3
reflux for 36 hours till the color of the homogeneous solution didn’t changed and the quantity of the
deposition didn’t increasing any more. Neutralized the solution with triethyl amine and collected the
tan powder deposition by filtering under nitrogen atmosphere. Condensed the filtrate in vacuo to get
more products, Collecting solvent using cold trap under liquid nitrogen bath. The rough wet powder
was then recrystallized with toluene once and n-hexane there times affording 6.5001g yellow crystals
after being washed and dried in vacuo. The conversion ratio is 47.4%. MS (FAB): M/z 405 (30) found
(M+H)+ ion CH3CN(C12H17)CN(C12H17); M/z 202 (100) found ion (M)+ CH3C+N(C12H17)
α-diimine ligands (a) as to R=phenyl, rejected 3.5ml dibenzoyl, 11.5ml 2,6-diisopropylaniline,
a little hydrochloric acid as initiation catalyst and 15~20ml methanol .The reaction time was 38 hours. The
rough wet yellow catalyst produced was then recrystallized once with toluene and twice with n-hexane
affording 4.7274g agglomerate pure golden crystals after being washed and dried in vacuo. The conversion ratio
is 43.7%. The product must be restored in an isolated capacity full of inert nitrogen gas. MS (FAB): M/z 370
(12) found (M+H)+ ion C6H5COCN(C12H17)C6H5; M/z 264 (40) found (M’)+ ion (C12H17)NC+C6H5; M/z 211 (12)
found (M+H)+ ion C6H5COCOC6H5; M/z 105 (100),M+ ion C6H5C+O.
β -diimine ligands (b) as to R=CH3
refering to scheme 4, Carefully fed in the single-neck
flask from the branch pipe with injection, 10ml
2,6-diisopropylaniline, 2.45ml acetylactone, a little
hydrochloric acid as initiation catalyst, 15~20ml toluene,
which must make the reagents into a homogeneous
solution. The stirred solution was heated at reflux for 15
hours. Neutralized the solution with triethyl amino till
the pH=7.0 in time. The reaction solution turned turbid.
Filtered the solution to collect gray powder, which was
Scheme 4
175
then recrystallized with mixed solvent of n-hexane and methanol then with n-hexane another time.
White tiny needles appeared. After being filtered, washed and dried in vacuo, the 6.2433g weight
product was stored in an isolated capacity full of inert nitrogen gas. The conversion ratio is 41.7%.
M/z 419 (31) found (M+H)+ ion CH3CN(C12H17)CH2(C12H17)NCCH3; M/z 202 (100) found
(M)+ ion CH3COCH2OCCH3
β -diimine ligands (b) as to R ＝ phenyl ， rejected 3.5ml dibenzoyl methane, 8ml
2,6-diisopropylaniline, a little hydrochloric acid as initiation catalyst and 15~20ml toluene carefully in turn。
Neutralized the solution with trithyl amine and collected the deposition after 17 hours The rough catalyst was
then recrystallized twice with n-hexane affording 4.3952g pure granule crystals after being washed and dried in
vacuo. The conversion ratio is 42.2%. M/z 384 (4) found (M+H) + ion C6H5COCH2(C12H17)NCC6H5; M/z 279
(18) found (M’)+ ion CH2(C12H17)NC+C6H5; M/z 225 (100) found (M+H)+ ion C6H5COCH2COC6H5; M/z 105
(69),M+ ions. M+ C6H5C+O.
As to ligand (c), refer to the scheme 4, carefully fed in the single-neck flask from the branch pipe with
injection, 10.8ml ethyl acetoacetate, 5ml tetrahydrofuran, 1.5ml H2O, a little p-toluenesulfonic acid as initiation
catalyst. The stirred mixture was added 20mol tetrahydrofuran and heated for 5 hours till changed into
homogeneous rufous solution. Added 20ml toluene each for twice, Increased the temperature to 130oC, the
system continued to react under reflux. To get rid of the water easier, 22ml toluene was added into the system
again. After seven hours, collected the deposition by filtering with Scheck filter under the protection of inert
nitrogen gas after condensing in vacuo. The rough light rufous tiny catalyst was recrystallized with
tetrahydrofuran once time and with n-hexane twice, and then washed carefully. The weight is 6.2433g after
drying and the conversion ratio is 41.7%.
As to ligand (d), Carefully fed in the single-neck flask from the branch pipe with
injection, 9.5ml diethyl malonate, 30ml tetrahydrofuran, 2.4ml H2O, a little p-toluenesulfonic acid as
initiation catalyst. the catalyst is pure tiny white catalyst if you recrystallize the rough product with
mixed solvent n-hexane and tetrahydrofuran, then washed carefully.
Peaks in the MS (FAB) of ligand (c) and ligand (d) are unable to identify. The reactive species is too many
to control the reaction without effective method. Study of the preparation must carry on.
Acknowledgement.
I would like to thank Wu Qing and Zhang Junkai for their guide. I would also like to thank Zhang Ling, He
Xiaohui, Luo Xiang, Liu Yunhai and Huang Shengjian for their technical assistant.
176
Ligand (a) R=CH3
Ligand (a) R=phenyl
177
Ligand (b) R=CH3
Ligand (b) R=phenyl
178
Ligand (c)
Ligand (d)
179
1200
HEMA+1173 in air
HEMA+1173 in N2
HEMA+1173+BPO
HEMA+1173 in O2
complete inibition
dH/dt(J/s*mol)
1000
800
600
α-二亚氨类、β-二亚氨类、苯并噁唑类配体系列
NI（II）配合物的设计合成及其表征
400
200
0
0
100
200
300
400
500
600
700
time(s)
柯卓锋，张军凯*，伍青*
(中山大学高分子研究所， 广州， 510275)
摘要 本论文根据后过渡金属催化剂有较低的亲氧性，能聚合可结构控制的含有极性官能团、高分
子量共聚物，及其对环烯烃聚合具有的特殊活性，结合过渡金属（Ni、Pd 等）阳离子周围的空间位
阻对α-烯烃等聚合时β-氢转移的成功规避以及β-酮胺类后过渡金属（Ni、Pd 等）催化剂体系对降
冰片烯的良好催化活性的特点，设计合成α-二亚氨类、β-二亚氨类、苯并噁唑基类配体等一系列
NI（II）配合物。达到实现乙烯-降冰片烯、乙烯-丙烯酸酯类、降冰片烯-丙烯酸酯类共聚合，得到
完全饱和、光学性能好、尺寸稳定性好、具有可加工性能的新材料的目的。
参考比较各种配体的合成分离提纯特性, 本论文设计了一系列方便的一步合成方法，合成了上述配
体。并且用 MS（FAB），元素分析，1HNMR 对催化剂配体进行表征。表明：
α-二亚氨类配体可以在甲醇介质，通过 Na2SO4 吸附反应生成的水较好的一步反应。用正己烷重结
晶得到晶体。β-二亚氨类配体通过甲苯共沸除去反应生成水，在甲苯介质中一步反应，用正己烷重
结晶得到晶体。苯并噁唑基类配体通过加少量水促进酯交换反应然后除水促使成环，在四氢呋喃和
甲苯介质中一步反应得到配体。用四氢呋喃和正己烷重结晶。表征结果表明α-二亚氨类，β-二亚
氨类配体结果较好。苯并噁唑类配体需要进一步分离纯化。
关键词
α-二亚氨类配体， β-二亚氨类配体， 苯并噁唑基类配体，
化学与化学工程学院 2001 年度创新基金项目，项目号：01023
180