Binuclear neutral nickel complexes bearing bis(bidentate) salicylaldiminato ligands: Synthesis, structure and ethylene polymerization behavior

Article abstract of DOI:10.1016/j.inoche.2006.02.015

Reaction of sodium salts of the bridging [O,N,N,O]-type bisalylaldimine ligands [O,N,N,O = [3-phenyl-2-OH-(CH{double bond, long}N)]₂-L (L = CH₂CH₂CH₂ 3a, 1,4-C₆H₄ 3b)] with trans-bis(triphe

Full text of DOI:10.1016/j.inoche.2006.02.015

Inorganic Chemistry Communications 9 (2006) 548–550
www.elsevier.com/locate/inoche
Binuclear neutral nickel complexes bearing bis(bidentate)
salicylaldiminato ligands: Synthesis, structure and
ethylene polymerization behavior
*
Wei-Hua Wang, Guo-Xin Jin
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200 433, China
Received 24 December 2005; accepted 20 February 2006
Available online 3 April 2006
Abstract
Reaction of sodium salts of the bridging [O,N,N,O]-type bisalylaldimine ligands [O,N,N,O = [3-phenyl-2-OH-(CH@N)]2-L
(L = CH2CH2CH2 3a, 1,4-C6H4 3b)] with trans-bis(triphenylphosphane)phenylnickel (II) chloride result in neutral bis(bidentate) binu-
clear nickel (II) complexes 4a and 4b. The structure of 4b has been confirmed by X-ray crystallography. 4a shows moderate activity for
polymerization of ethylene in the presence of methylaluminoxane (MAO). Catalytic activities, molecular weights and molecular weight
distribution of polyethylene have been investigated under the various reaction conditions.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Nickel; Catalyst; Binuclear; Molecular structure; Polymerization of ethylene
Late transition metal catalysts for polymerization of ole-
fins have attracted more and more attention over the past
decade [1–4]. Due to the less oxophillic properties of late
transition metal, these catalysts are more tolerate to polar
functional groups in the monomers than those metallocene
olefin polymerization catalysts, therefore, the copolymeri-
zation of olefins with polar monomers become possible
[5–7]. Among them, neutral salicylaldimine based nickel
(II) catalysts developed by Grubbs and coworkers are of
high importance [8], which can produce polyethylene with
high molecular weight. Grubbs reported that introducing
bulky substituent into the ortho position of the phenoxyl
group can retard the rate of chain termination and increase
the catalytic activity [8]. But the influence of the modifica-
tion at the other side of the imino fragment have been
rarely investigated [9]. Here we report new neutral binu-
clear nickel (II) complexes with [N,O,O,N]-type bridging
di(bidentate) ligands and their catalysis properties for eth-
ylene polymerization.
The free ligands 3a–b were prepared by condensation of
1,3-diaminopropane (2a) or p-diaminobenzene (2b) and the
substituted salicylaldehyde (1) in appropriate yields
(Scheme 1). The substituted salicylaldehyde 1, containing
bulky aromatic phenyl group was prepared by formylation
of the corresponding phenol with paraformaldehyde with
the catalysis of SnCl4 according to reference [10].
Binuclear complexes 4a–b were prepared in a similar
procedure of reference [8], by the reaction of 2 equiv of
trans-[Ni(PPh3)2(Ph)Cl] with the sodium salts of the free
ligands 2a–b, which were obtained via deprotonation by
excess sodium hydride in anhydrous tetrahydrofuran at
room temperature. After several times of recrystallization
in hexane/benzene, pure powders of 4a–b were obtained,
which are light brown and dark brown respectively. Com-
plexes 4a and 4b are neutral, diamagnetic and air-sensitive
in solution, and insoluble in n-hexane, soluble in CH2Cl2 or
THF.
Crystals of 4b suitable for X-ray structure determination
were grown from slow diffusion of hexane into a benzene
solution of 4b [11]. The molecular structure of 4b is
depicted in Fig. 1.
*
Corresponding author. Tel.: +86 21 65643776; fax: +86 21 65641740.
E-mail address: gxjin@fudan.edu.cn (G.-X. Jin).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.02.015

W.-H. Wang, G.-X. Jin / Inorganic Chemistry Communications 9 (2006) 548–550
549
OH
CHO
OH
L
N
CH
Ph
CH
OH
N
H+
2
L
NH2
H2N
+
CH3CH2 OH
Ph
Ph
2a-b
1
3a-b
H
Ph
Ph
Ph3P
N
O
Ni
trans-[Ni(PPh3)2(Ph)Cl]
benzene
NaH
THF
L
Ni
O
N
Ph
Ph
PPh3
CH2CH2CH2
a: L =
b: L =
H
4a-b
Scheme 1. Synthesis of complexes 4a–4b.
˚
Fig. 1. Molecular structure of complex 4b. Selected distances (A) and angles(ꢁC):Ni(1)AC(1) = 1.891(6), Ni(1)AO(1) = 1.910(4), Ni(1)AN(1) = 1.926(4),
Ni(1)AP(1) = 2.1735(18); C(1)ANi(1)AO(1) = 165.0(2), C(1)ANi(1)AN(1) = 90.6(2), O(1)ANi(1)AN(1) = 92.74(17), C(1)ANi(1)AP(1) = 89.63(17),
O(1)ANi(1)AP(1) = 89.87(12), N(1)ANi(1)AP(1) = 168.99(15).
In the solid state, the molecule adopts a nearly square-pla-
nar coordination geometry with both Ni atoms displaced
catalysts with bulky phenyl group or larger groups at the
ortho position of the phenoxy group can catalyze ethylene
polymerization without cocatalyst [8]. It is clear that binu-
clear 4a–b are different from mononuclear Grubbs’ cata-
lysts. When activated with MAO, complex 4b still show
no catalytic activity to polymerization of ethylene, which
is agree to the case of neutral nickel complexes reported
by Li and coworkers [12] and is similar to the case of the
neutral palladium complexes reported by Novak and
coworkers [13].
The ration of Al/Ni is essential for complex 4a to poly-
merize ethylene. Under 1 bar ethylene pressure, only trace
product was obtained at 1000:1 ratio, while activity of
3.76 · 105 gPE/mol Ni Æ h was obtained when the Al/Ni
was increased to 2000:1. At high pressure of 10 bar, less
MAO was needed to activate the catalyst precursor 4a.
At the Al/Ni ratio of 400:1, complex 4a showed an activity
of 2.67 · 104 gPE/mol Ni Æ h. When the Al/Ni ratio was
increased to 2000:1, the according activity was increased
˚
˚
approximately 0.067 A (Ni1) and 0.078 A (Ni2) from the
planes of their ligands respectively. Meanwhile, the bridging
phenyl plane is almost perpendicular to the two coordination
planes with Ni centers. The triphenylphosphine occupies the
position trans to the N atom with a nearly linear
N(1)ANi(1)AP(1) angle (168.99(15)ꢁ). The phenyl group
attached to Ni lies trans to O atom with an C(1)ANi(1)AO(1)
angle of 165.0(2)ꢁ. The Ni(1)AO(1), Ni(1)AN(1),
Ni(1)AP(1) and Ni(1)AC(1) bond distances are similar to
those in known neutral nickel complexes [9,12].
The tests of ethylene polymerization with complexes 4a–
b were carried out by dissolving the corresponding catalysts
in toluene, followed by the injection of a toluene solution
of different amount of MAO. The results of polymeriza-
tions are listed in Table 1.
Neither complexes 4a nor 4b could be used as single
component catalyst to polymerize ethylene, while Grubbs’

550
W.-H. Wang, G.-X. Jin / Inorganic Chemistry Communications 9 (2006) 548–550
Table 1
Results of polymerization of ethylenea
Entry
Complex (amt, lmol)
Al/Ni
T (ꢁC)
P (bar)
Yield (g)
Activity (gPE/mol Ni Æ h)
Mw
Mw/Mn
1
2
3
4
5
6
a
4a (13.625)
4a (3.406)
4a (3.406)
4a (3.406)
4a (3.406)
4b (13.625)
0
40
25
25
40
40
40
10
1
1
10
10
10
0
0
–
–
–
–
–
1000:1
2000:1
400:1
2000:1
0
Trace
1.282
0.091
2.262
0
3.76 · 105
2.67 · 104
6.71 · 105
0
440000
n.d.b
n.d.b
–
2.2
n.d.b
n.d.b
–
Conditions: Total volume of toluene, 50 ml; Cocatalyst, MAO; 800 rpm; Time of polymerization, 30 min.
Not determined due to poor solubility in 1,2,4-trichlorobenzene.
b
to 6.71 · 105 gPE/mol Ni Æ h, which is higher than that of
1 bar ethylene pressure (entry 3).
Appendix A. Supplementary data
GPC analysis of polyethylene obtained employing com-
plexes 4a at 1 bar ethylene pressure revealed molecular
weight of 4.4 · 105g/mol (Mw), which is higher than that
of polyethylenes obtained by Grubbs’ catalysts [8] and a
moderate molecular weight distribution of 2.2, which is sim-
ilar to those of Brookhart’s mononuclear nickel catalyst
with anilinotropone ligand [6] amd Li’s binuclear neutral
nickel catalyst [12]. However, polyethylenes obtained under
10 bar ethylene pressure are difficult to dissolve in 1,2,4-tri-
chlorobenzene, implying that the molecular weights may be
higher. High-temperature 13C NMR spectra showed that the
polymers which was produced by the catalyst 4a (entry 3) are
moderately branched. Methyl branches predominate with
ca. 15 methyl branches per 1000 carbon atoms. Additional
weak signals suggested that higher branches, such as butyl,
are also present.
New type of neutral di(bidentate) binuclear nickel (II)
complexes 4a and 4b were synthesized, and the structure
of 4b has been determined by X-ray crystallography. When
activated with methylaluminoxane (MAO), 4a shows mod-
erate activity for polymerization of ethylene (3.71 · 105
gPE/mol Ni Æ h). The molecular weight of the obtained
polyethylene of up to 440 000 g/mol was observed. Cata-
lytic activities, molecular weights and molecular weight dis-
tribution of polyethylene have been investigated under the
various reaction conditions.
Details on experimental section are deposited. Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2006.02.015.
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˚
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Acknowledgement
Financial support by the National Science Foundation
of China for Distinguished Young Scholars (20421303,
20531020) and by the National Basic Research Program
of China (2005CB623800) is gratefully acknowledged.
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