Synthesis and characterization of 2-imino-indole nickel complexes and their ethylene oligomerization study

Article abstract of DOI:10.1016/j.inoche.2003.08.018

A series of 2-imino-indole derivatives and their neutral nickel complexes were synthesized and characterized. A single-crystal X-ray analysis of [Ni(C₁₀H₇)(C₁₈H₁₆ClN ₂)(PPh₃)] shows the nickel center adopted a square-planar coordination geometry. The nickel complexes act solely as effective catalysts for ethylene oligomerization with the activity up to 2.05 × 10 ⁴ g ethylene mol^-1 h^-1.

Full text of DOI:10.1016/j.inoche.2003.08.018

Inorganic Chemistry Communications 6 (2003) 1372–1374
www.elsevier.com/locate/inoche
Synthesis and characterization of 2-imino-indole nickel
complexes and their ethylene oligomerization study
a
Jitai Li , Tielong Gao , Wen Zhang , Wen-Hua Sun
a
b
b,
*
a
College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China
b
State Key Laboratory of Engineering Plastics and The Center for Molecular Sciences, Institute of Chemistry,
The Chinese Academy of Sciences, Beijing 100080, China
Received 26 June 2003; accepted 23 August 2003
Published online: 23 September 2003
Abstract
A series of 2-imino-indole derivatives and their neutral nickel complexes were synthesized and characterized. A single-crystal X-
ray analysis of [Ni(C10H7)(C18H16ClN2)(PPh3)] shows the nickel center adopted a square-planar coordination geometry. The nickel
complexes act solely as effective catalysts for ethylene oligomerization with the activity up to 2.05 ꢀ 104 g ethylene molꢁ1 hꢁ1
.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Neutral nickel complex; Indole; Schiff base; Ethylene oligomerization; Crystal structure
There has been an increasing interest in the devel-
opment of late-metal complexes as catalysts for ethylene
polymerization or oligomerization under moderate
conditions [1,2]. The significant notable are Ni(II)- and
Pd(II)-based Brookhard cationic catalysts [ArN ¼
C(R)C(R) ¼ NAr]MCHþ3 with bulky substituents on the
diimine ligands, as well as numerous late-metal com-
plexes as catalytic precursors [3,4]. Extensively neutral
nickel complexes had been developed by DuPont com-
pany [5] and Grubbs group [6] based upon the salicyl-
aldiminato ligands. By placing bulky groups to the ortho
position of phenoxy, Grubbs reported the salicylaldim-
inato catalysts could proceed polymerization without
additional activator [6] and showed interesting proper-
ties for copolymerization [7]. Back to 1980s, ylide-nickel
catalysts already showed good activities for ethylene
polymerization without cocatalysts [8]. Considering to
the industrial application and environmental friendship,
the single-component catalyst without adding cocatalyst
has gained great attentions. Several series of nickel
catalysts for ethylene activities have been investigated in
our group [9]. However, none of them could perform
ethylene activity without cocatalyst. Herein we demon-
strate the new neutral nickel complexes containing
2-N-iminoindolyl lignads are capable of ethylene oligo-
merization without cocatalyst.
The synthetic procedure of ligands (L, 2-imino-
3-chloro-1H-indole derivatives) and their neutral nickel
complexes is generally shown in Scheme 1. Ligands L
were prepared in good yields (65–81%) by the conden-
sation reaction of one equivalent of the appropriate
aniline with one equivalent of 3-chloro-1H-indole-
2-carboxaldehyde [10], yielding pale yellow crystalline
products after purified through re-crystallization in eth-
1
anol. Complexes 1–6 were synthesized in reasonable
1
Elemental analyses and IR spectra for complexes 1–6.
1: C49H44ClN2NiP Calc. (found): C, 74.88 (74.57); H, 5.64 (5.71); N,
3.56 (3.48). IR(cmꢁ1, KBr): 3227, 1587. 2: C45H36ClN2NiP Calc.
(found): C, 74.05 (73.90); H, 4.97 (4.82); N, 3.84 (3.96). IR(cmꢁ1, KBr):
1582. 3: C46H38ClN2NiP ꢂ THF Calc. (found): C, 73.96 (73.59); H,
5.21(5.09); N, 3.45(3.66.). IR(cmꢁ1, KBr): 1585. 4: C47H40ClN2NiP
Calc. (found): C, 74.48 (74.39); H, 5.32 (5.26); N, 3.70 (3.82). IR(cmꢁ1
KBr): 1588. 5: C43H31ClN3NiO2P.0.5H2O Calc. (found): C, 68.33
(68.35); H, 4.27 (4.55); N, 5.56 (5.45). IR(cmꢁ1
KBr): 1567.
,
,
* Corresponding author. Tel.: +86-10-62557955; fax: +86-10-
62566383.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
6: C43H29ClF3N2NiP Calc. (found): C, 68.33 (68.20); H, 3.87 (3.76);
N, 3.71 (3.85). IR(cmꢁ1, KBr): 1581. The synthetic details of ligands
and the complexes are available in the supplementary materials.
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.08.018

J. Li et al. / Inorganic Chemistry Communications 6 (2003) 1372–1374
1373
Scheme 1. Synthesis of complexes (isolated yield). Reagents and conditions: (i) EtOH, p-TsOH; (ii) THF, NaH, C10H7NiCl(PPh3)2.
Table 1
The activity of complexes and distribution of oligomers
Temperature Activitya
Catalyst
Distribution of the
oligomers. (%)
(°C)
Complex (lmol)
C4
C6
1
2
2
2
2
3
3
3
4
5
6
5
5
5
5
5
5
5
5
5
5
5
80
15
40
60
80
40
60
80
80
80
80
0.28
0.50
0.80
0.84
0.99
0.77
0.94
1.20
0.72
2.05
0.42
32.31
85.20
56.76
85.77
91.00
81.20
86.00
88.20
77.30
79.75
72.83
67.69
14.80
43.24
14.23
9.00
18.80
14.00
11.80
22.7
Fig. 1. Crystal structure of complex 3, 30% probability ellipsoids,
ꢀ
20.25
27.17
H atoms omitted for clarity. Selected bond lengths (A) and angles (°):
Ni1–C34 1.890(6), Ni1–N2 2.003(3), Ni1–N1 1.984(3), Ni1–P1
2.1652(15), C34–Ni1–N1 168.6(3), N1–Ni1–N2 83.01(15), N1–Ni1–P1
102.40(11), C34–Ni1–N2 90.37(19), C34–Ni1–P1 84.37(16), N2–Ni1–
P1 174.56(12).
Toluene solvent, 1 atm of ethylene, reaction time 1 h.
ꢀ 104 g molꢁ1 hꢁ1
a
.
sition trans to the triphenylphosphine ligand with a
nearly linear P1–Ni1–N2 angle (174.56(12)°). The
naphthyl group lays trans to N1 with an N1–Ni1–C34
yields (60–78%) by deprotonation of L with NaH in THF
and then reacted with C10H7NiCl(PPh3)2 [11]. The re-
sulting solutions were dried under vacuum, and the
formed complexes were re-crystallized in diethyl ether.
Complexes 1–6 are air-stable solids, and soluble in most
organic solvents, such as diethyl ether, CH2Cl2, ethanol,
CHCl3 and acetonitrile. The complexes obtained were
fully characterized by IR spectra and elemental analysis.
To confirm their structure, complex 3 2 was subjected
to single-crystal X-ray diffraction study (Fig. 1). The
nickel atom adopts a square-planar coordination ge-
ometry. The bulky 2,4,6-trimethylanil occupies the po-
ꢀ
angle of 168.6(3)°. The Ni1–P1 bond of 3 (2.1652(15) A)
is similar to that of reported nickel complexes [6]. The
Ni–N bonds are slightly different due to nitrogen atoms
ꢀ
of aryl ring and imide, the Ni1–N2 bond (2.003(3) A) is
ꢀ
ꢀ
0.02 A longer than the Ni1–N1 bond (1.984(3) A).
It is noteworthy that complexes 1–6 are active for
ethylene oligomerization without additional activator.
Catalyst activities are calculated on the base of GC
analysis, and their activities and oligomersÕ distributions
are listed in Table 1. It is notable of the activity de-
creasing during the oligomerization reaction, and the
final activity is only 10–15% of its beginning value in one
hour oligomerization under a constant pressure of one
atmosphere of ethylene. The nature of the ligand has a
major influence on the catalytic activity. Seen from the
Table 1, the order of their activities is listed as
5 > 3 > 2 > 4 > 6 > 1. The higher reaction temperature
(ꢃ80 °C) is the better catalytic activity appears. At this
2
Complex 3: C40H40ClN2NiP, M ¼ 673:87, triclinic, a ¼ 9:260ð2Þ,
ꢀ
b ¼ 9:517ð2Þ, c ¼ 21:916ð4Þ A, a ¼ 99:37ð3Þ, b ¼ 97:81ð3Þ, c ¼
3
ꢀ
98:20ð3Þ°, V ¼ 1860:9ð7Þ A , T ¼ 123ð2Þ K, Space group P ꢁ 1,
Z ¼ 2, Number of collected reflections ¼ 7882, Number of indepen-
dent reflections ¼ 2332, RðF 2Þ ¼ 0:0568, wR ¼ 0:0652. Full crystallo-
graphic detail was deposited at the Cambridge Crystallographic Data
Centre with number CCDC 213625.

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J. Li et al. / Inorganic Chemistry Communications 6 (2003) 1372–1374
C.M. Killian, D.J. Tempel, L.K. Johnson, M. Brookhart, J. Am.
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moment, the activity of complex 5 was obtained with a
h
ꢁ1, which leads
to oligomerize ethylene without additional cocatalyst.
Further detail investigation, including varying reaction
conditions and modifying coordinational ligands, is
under way.
moderate activity of 2.05 ꢀ 104 g molꢁ1
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