Synthesis, crystal structure, and olefin oligomerization activity of neutral arylnickel(II) phosphine catalyst with 2-oxazolinylphenolato N-O chelate ligand

Article abstract of DOI:10.1016/j.inoche.2003.12.003

A novel neutral arylnickel(II) phosphine complex 1 bearing 2-oxazolinylphenolato ligand is synthesized by the reaction of trans-Ni(Ph)(Cl (PPh₃)₂ with 2-(4,5-dihydro-oxazol-2-yl)phenol in the presence of NEt₃, and the molecular structure is determined by X-ray single crystal diffraction. Complex 1 exhibits high activity and selectivity in catalyzing olefin oligomerization when various organoaluminum cocatalysts or Ni(COD)₂ are used (TOF values up to 507 kg oligomers/(molNi·h) ).

Full text of DOI:10.1016/j.inoche.2003.12.003

Inorganic Chemistry Communications 7 (2004) 459–461
www.elsevier.com/locate/inoche
Synthesis, crystal structure, and olefin oligomerization activity
of neutral arylnickel(II) phosphine catalyst with
2-oxazolinylphenolato N–O chelate ligand q
*
Yanlong Qian, Wei Zhao, Jiling Huang
Laboratory of Organometallic Chemistry, East China University of Science and Technology, 130 Meilong Road,
Shanghai 200237, People’s Republic of China
Received 19 August 2003; accepted 5 December 2003
Dedicated to Professor Yanlong Qian
Published online: 4 February 2004
Abstract
A novel neutral arylnickel(II) phosphine complex 1 bearing 2-oxazolinylphenolato ligand is synthesized by the reaction of trans-
Ni(Ph)(Cl)(PPh3)2 with 2-(4,5-dihydro-oxazol-2-yl)phenol in the presence of NEt3, and the molecular structure is determined by
X-ray single crystal diffraction. Complex 1 exhibits high activity and selectivity in catalyzing olefin oligomerization when various
organoaluminum cocatalysts or Ni(COD)2 are used (TOF values up to 507 kg oligomers/(mol Niꢀh)).
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Nickel complex; Oxazoline ligand; Crystal structure; Olefin oligomerization
Recently, due to some potential application values in
both academic and commercial fields, many attentions
are focused on the olefin oligomerization and polymer-
ization catalyzed by late transition metal complexes [1–
3]. Compared with early transition metal complexes, late
transition metal complexes are generally more tolerant
of polar media because of their less oxophilic nature.
Therefore, it is possible for them to catalyze olefin
polymerization, polar-functionlized a-olefin polymeri-
zation as well as copolymerization of ethylene and a-
olefin. Keim [4] firstly revealed that the late transition
metal nickel catalysts [(PONi(R)(L)] containing a-keto-
ylide ligands could oligomerize ethylene to produce
linear a-olefin, and also could polymerize ethylene in the
presence of phosphine scavenger [5]. Brookhart and
co-workers [6] reported that nickel and palladium
complexes bearing a-diimine ligands could convert eth-
ylene to highly branched polymers. Furthermore, the
cationic (a-diimine) nickel catalysts had the ability to
copolymerizing ethylene and polar-functionlized a-
olefins [7]. A series of salicylaldiminato nickel catalysts
with bulky imino substituents were described by Grubbs
[8]. These neutral nickel catalysts exhibited high activity
in ethylene polymerization, and excellent tolerance to
polar functional groups. Recently, arylnickel phosphine
complexes are paid more attention because of their
various catalytic polymerization behavior besides olefin
polymerization and oligomerization [9–12]. Therefore, it
is the tendency in exploring some novel ligands for
arylnickel(II) phosphine catalysts.
We report here the synthesis of the nickel-oxazoline
olefin oligomerization catalyst 1 (Scheme 1). The reac-
tion of trans-Ni(Ph)(Cl)(PPh3)2 with 2-(4,5-dihydro-
oxazol-2-yl)phenol in the presence of NEt3 gives out the
target complex 1 in moderate yields. Although it also
gives out the by-product 2, the separation of these two
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.inoche.2003.12.003.
* Corresponding author. Tel.: +862164253519; fax: +862154282375.
E-mail address: qianling@online.sh.cn (J. Huang).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.12.003

460
Y. Qian et al. / Inorganic Chemistry Communications 7 (2004) 459–461
with the triphenylphosphane ligand in the trans-position
to the N atom, which is similar to some known neutral
arylnickel(II) phosphine complexes. We note that the
O
O
O
N
trans-Ni(Ph)(Cl)(PPh )
3 2
N
O
O
N
+
O
N
Ni
NEt toluene
Ni
3
OH
O
ꢀ
bond lengths of Ni–O(2) (1.891(2) A), and Ni–N(1)
Ph P
3
Ph
ꢀ
(1.907(2) A) are shorter than that of known (NO)Ni
1 (57%)
2 (21%)
ꢀ
ꢀ
complexes which are 1:906–1:931 A and 1:921–1:975 A
[14–16], respectively. These facts suggest that the p back-
bonding from metal atom to the ligand is stronger than
that of other nickel complexes. It should also be noted
that there are seven rings in the molecular: five phenyl
groups, one oxazoline group, and one six-membered
chelate ring containing the metal atom. Therefore, it is
possible to form a large plane composed of 15 atoms in
complex 1. The large rigid p-coplanar structure may
have dramatic effects on the catalytic activity in the
formation of low carbon oligomers by decreasing the
steric hindrance.
Scheme 1.
complexes is very easy according to their different sol-
ubility in toluene.
The single crystal X-ray diffraction result confirms the
structure of 1 [13] (Fig. 1). In solid-state, the coordina-
tion geometry around Ni atom is typically square-planar
Complex 1 exhibits considerable activity and high
selectivity for ethylene oligomerization (Table 1). The
highest activity up to 507 kg oligomers/(mol Niꢀh) can
be achieved by treatment with 1/MAO catalytic sys-
tem. The activities of 1/DIBAL-H and 1/AlEt3 are
slightly lower than that of 1/MAO in the formation
of ethylene oligomers. At the same time, the activities of
1/organoaluminum catalytic system are almost 10 times
as high as that of 1/Ni(COD)2 catalytic system. In
contrast, no oligomers are obtained when cocatalysts
or phosphine scavenger are absent from the catalytic
system.
Table 1 also shows that the product distribution
greatly depends on the kinds of cocatalysts or phos-
phine scavenger. In 1/MAO, C6-olefin is the major
product, while C4-olefin (2-methylpropylene) is the
major product in 1/AlEt3. Ni(COD)2 being a phosphine
scavenger has better selectivity in the formation of C8-
olefin. 84.9% (wt%) 1-octene is obtained in the catalytic
system.
Table 2 verifies that 1 is an efficient catalyst for se-
lective propylene dimerization to C6-olefin in the pres-
ence of various cocatalysts or phosphine scavenger. The
dimerization activities increase in the order of
ꢀ
Fig. 1. the molecular structure of complex 1. Selected bond lengths (A)
and angles (°): Ni–C(10) 1.884(3), Ni–O(2) 1.891(2), Ni–N(1) 1.907(2),
Ni–P 2.1709(9), O(2)–C(9) 1.291(4), N(1)–C(3) 1.282(4), C(10)–Ni–
O(2) 175.08(13), N(1)–Ni–P 177.37(8), C(10)–Ni–N(1) 91.53(11), O(2)–
Ni–N(1) 91.49(10), C(10)–Ni–P 86.13(9), O(2)–Ni–P 90.76(7).
Table 1
Ethylene oligomerization with complex 1a
Entry
Activityb
Reaction conditions
Cocatalystc
Distribution of oligomers (%)
Ratiod
C4
C6
C8
1
2
3
4
5
DIBAL-H
MAO
AlEt3
500
1300
500
2
487
507
364
54.0
12.6
61.8
–
28.7
77.3
11.1
15.1
–
17.4
10.0
27.1
84.9
–
Ni(COD)2
–
55.6
0
–
–
a Conditions: 1.63 lmol of complex 1, solvent: toluene, total volume: 30 ml, ethylene pressure: 12 atm, temperature: 25 °C, reaction time: 0.5 h.
b kg oligomers/(mol Niꢀh).
c DIBAL-H is diisobutylaluminum hydride, MAO is methylaluminoxane, and Ni(COD)2 is di(1,5-cyclooctadiene)nickel.
d The ratio of cocat. and cat.

Y. Qian et al. / Inorganic Chemistry Communications 7 (2004) 459–461
461
Table 2
Propylene dimerization with complex 1a
Entry
Activityb
Reaction conditions
Distribution of C6-olefin (%)
Cocatalyst
Ratioc
1-Hexene
Others
1
2
3
4
MAO
AlEt3
Ni(COD)2
–
1000
500
2
132
38.1
24.3
0
78.4
26.5
76.0
–
21.6
73.5
24.0
–
–
a Conditions: 1.74 lmol of complex 1, solvent: toluene, total volume: 30 ml, propylene pressure: 1 atm, temperature: 25 °C, reaction time: 0.5 h.
b kg oligomers/(mol Niꢀh).
c The ratio of cocat. and cat.
MAO > AlEt3 > Ni(COD)2. Amongst them, 1/MAO
catalytic system shows the highest activity up to 132 kg
oligomers/(mol Ni h) (entry 1). Notably, 1-hexene is the
major product in entries 1 and 3. The fact that 1 can give
out low carbon olefins indicates the consequence
that chain transfer is faster than chain propagation in
ethylene and propylene oligomerization because of
the elimination of axial steric bulk in d8 square-planar
system [17].
References
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In summary, neutral arylnickel(II) phosphine com-
plex 1 with chelating oxazoline ligand represents a novel
kind of efficient olefin oligomerization catalyst. The
molecular weight distribution of olefin oligomers greatly
depends on the selection of cocatalysts or phosphine
scavenger in catalytic system. A series of study on neu-
tral nickel(II) catalysts containing substituted 2-oxaz-
olinylphenolato ligand towards olefin oligomerization
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€
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ꢂ
[13] Crystal data for 1: triclinic, space group P1; a ¼ 9:5314ð13Þ;
ꢀ
b ¼ 12:5616ð17Þ; c ¼ 13:6247ð19Þ A, a ¼ 70:768ð3Þ; b ¼ 79:498ð2Þ;
3
ꢁ1
.
ꢀ
c ¼ 81:044ð3Þ°; V ¼ 1506:4ð4Þ A , Z ¼ 2, and l ¼ 0:731 mm
Acknowledgements
The structure was solved by direct methods and refined by full
matrix least-squares procedures: R1 ¼ 0:0502, Rw ¼ 0:0883 for
6704 reflections.
We gratefully acknowledge financial support from the
Special Funds for Major State Basic Research Projects
(1999064801), the National Natural Science Foundation
of China (20072004), and the research fund for the
doctoral program of higher education (20020251002).
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