Synthesis and characterization of tridentate nickel complexes bearing P∧N∧N and P∧N∧P ligands and their catalytic property in ethylene oligomerization

Article abstract of DOI:10.1021/om0507979

A series of nickel(II) complexes ligated by the N-(1-(2-(diarylphosphino) phenyl)methylidene)quinolin-8-amines (P∧N∧N) and 2-(diphenylphosphino)- N-[2-(diarylphosphino)benzylidene]anilines (P∧N∧P) were synthesized and characterized by elemental analysis, spectroscopy, and X-ray crystallography. X-ray crystallographic analyses reveal complexes 16 and 20 as having a five-coordinated distorted trigonal-bipyramidal geometry, while complex 12 displays a distorted square-pyramidal geometry and complex 13 is distorted square planar. Upon activation with MAO and AlEtCl₂, these complexes exhibited considerably high activity (up to 1.34 × 10⁶ g·mol^-1(Ni)·h^-1) of ethylene oligomerization. It was found that ligand environment and reaction conditions significantly affect the activity of the catalysts. In addition, a cobalt analogue with a distorted tetrahedral coordination geometry was investigated, which showed low activity of ethylene oligomerization.

Full text of DOI:10.1021/om0507979

236
Organometallics 2006, 25, 236-244
Synthesis and Characterization of Tridentate Nickel Complexes
Bearing P∧N∧N and P∧N∧P Ligands and Their Catalytic Property in
Ethylene Oligomerization
Junxian Hou,† Wen-Hua Sun,*,† Shu Zhang,† Hongwei Ma,† Yuan Deng,‡ and
Xiaoming Lu‡
Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, People’s Republic of China, and Department of Chemistry, Capital Normal UniVersity,
Beijing 100037, People’s Republic of China
ReceiVed September 16, 2005
A series of nickel(II) complexes ligated by the N-(1-(2-(diarylphosphino)phenyl)methylidene)quinolin-
8-amines (P∧N∧N) and 2-(diphenylphosphino)-N-[2-(diarylphosphino)benzylidene]anilines (P∧N∧P) were
synthesized and characterized by elemental analysis, spectroscopy, and X-ray crystallography. X-ray
crystallographic analyses reveal complexes 16 and 20 as having a five-coordinated distorted trigonal-
bipyramidal geometry, while complex 12 displays a distorted square-pyramidal geometry and complex
13 is distorted square planar. Upon activation with MAO and AlEtCl2, these complexes exhibited
considerably high activity (up to 1.34 × 106 g‚mol-1(Ni)‚h-1) of ethylene oligomerization. It was found
that ligand environment and reaction conditions significantly affect the activity of the catalysts. In addition,
a cobalt analogue with a distorted tetrahedral coordination geometry was investigated, which showed
low activity of ethylene oligomerization.
of the ligand backbone on the catalysis behavior or mechanism
of the catalysts.
1. Introduction
Ethylene oligomerization represents a major industrial process
for the production of linear R-olefins, which are extensively
used in the preparation of detergents, plasticizers, and fine
chemicals and as monomers for copolymerization with ethylene
in the production of linear low-density polyethylene (LLDPE).
The linear R-olefins were originally manufactured by the Ziegler
(Alfen) process,1 and current industrial catalysts include either
alkylaluminum compounds or a combination of alkylaluminum
compounds and early transition metal compounds or nickel(II)
complexes containing bidentate monoanionic [P,O] ligands (the
SHOP process).2 The discovery of the cationic (diimino NiCl2)
complexes3 as effective catalysts for ethylene oligomerization
and polymerization resurrected interest in designing new
catalysts of late-transition metal complexes with various ligands,
such as diimine,4 unsymmetrical pyridylimine,5 salicylaldimine,6
and 8-iminoquinoline.7 Although only a few examples of the
catalysts were found to be comparable to Brookhart’s diimine-
Ni(II) complexes in terms of their catalytic activities,8 these
numerous studies have enriched the knowledge of the effects
Following the success of the SHOP process,2 nickel com-
plexes containing phosphine ligands have drawn much attention.
These complexes contain either bridged bidentate ligands9 or
auxiliary ligands of PPh3 and exhibit high catalytic activity for
ethylene oligomerization.5d,9h,10 The P∧N∧N nickel complexes
(A) perform well as catalysts in the oligomerization of ethyl-
ene,11 and the metal complexes containing various P∧N∧P
† Key Laboratory of Engineering Plastics, Chinese Academy of Sciences.
‡ Capital Normal University.
(1) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: New York,
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Int. Ed. Engl. 1978, 17, 466. (b) Keim, W.; Behr, A.; Limbacker, B.; Kruger,
C. Angew. Chem., Int. Ed. Engl. 1983, 22, 503. (c) Keim, W.; Behr, A.;
Kraus, G. J. Organomet. Chem. 1983, 251, 377. (d) Klabunde, U.; Itten, S.
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10.1021/om0507979 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/24/2005

Tridentate Nickel Complexes
Organometallics, Vol. 25, No. 1, 2006 237
Scheme 1. Synthesis of 2-(Diarylphosphino)benzaldehyde
Scheme 2. Synthesis of Nickel Complexes 12-19
(1-5) and 2-(Diphenylphosphino)acetophenone (6)
in the synthesis of N-(1-(2-(diarylphosphino)phenyl)methylidene)-
quinolin-8-amines as the P∧N∧N ligands. However, these
compounds tend to decompose when separated by column
chromatography. Therefore, the nickel complexes (12-19) were
prepared through a one-pot template reaction, in which the
central metal ion was introduced in situ in the condensation
reaction of o-phosphinoaldehydes and 8-aminoquinolines (Scheme
2). Stoichiometric amounts of the o-phosphinoaldehydes, 8-ami-
noquinolines, and (DME)NiBr2 were mixed and refluxed in
acetic acid for 1 h, giving a dark red solution. The obtained
complexes (12-19) were soluble in acetic acid, but did not
dissolve in hexane. Therefore, the complexes were precipitated
by the addition of hexane after the reaction solution was
concentrated in vacuo to ca. 0.5 mL, and the complexes were
obtained in high yields. All complexes were characterized with
elemental analysis and IR spectroscopy. The NMR data were
not obtained due to the paramagnetic nature of nickel complexes.
Their structures were confirmed by single-crystal X-ray crystal-
lography.
A crystal of 12 was grown by layering hexane on a methanol
solution at room temperature under a nitrogen atmosphere. The
single crystals of 13 and 16 suitable for X-ray crystallography
were grown by layer diffusion of diethyl ether into their
dichloromethane solutions. Complex 12 displays a distorted
square-pyramidal geometry. The coordination geometry around
the nickel atom for complex 13 is distorted square planar. The
bromine atom in complexes 12 and 13 acts as a counterion
relatively far from the nickel atom Ni(II) (Ni- - -Br distances
are 2.891and 5.498 Å, respectively).
ligands such as the chromium (B12 and C13) and cobalt analogues
(D)14 have also been developed as catalysts for oligomerization
and polymerization of ethylene. To study [P∧N∧N] and [P∧N∧P]
metal complexes for ethylene oligomerization and polymeriza-
tion, one important research step is to design and synthesize
various compounds that will provide the tridentate coordination
sites in the complexes, such as the [P∧N∧N] or [P∧N∧P] ligands.
In this study, nickel complexes containing N-(1-(2-(diarylphos-
phino)phenyl)methylidene)quinolin-8-amines (P∧N∧N) and
2-(diphenylphosphino)-N-[2-(diaryl-phosphino)benzylidene]-
anilines (P∧N∧P) were synthesized, and their catalytic properties
for ethylene activation were investigated under various reaction
conditions.
2. Results and Discussion
2.1. Synthesis and Characterization. 2.1.1. Synthesis and
Characterization of the Benzaldehydes and Ketone. The
2-(diarylphosphino)benzaldehydes (1-5) and 2-(diphenylphos-
phino)acetophenone (6) were prepared via a modified literature
procedure (Scheme 1).15 All compounds were fully confirmed
with their analytic data. The compounds 1 and 6 were reported
with basic analysis data without any NMR data of 6 and 31P
NMR of 1.15 The compounds 1-6 display a singlet in their 31
P
NMR spectra at δ -11.2, -29.0, -36.8, -31.6, -32.9, and
-2.3, respectively.
2.1.2. Synthesis and Characterization of the Nickel Com-
plexes Containing the P∧N∧N Ligand. Much effort was spent
For complex 16 (Figure 3), the coordination geometry around
the nickel can be described as distorted trigonal bipyramidal,
in which the N(2)-Ni(1)-P angle is 151.85(10)° as a result of
the strain imposed by the five-membered chelate rings. As noted,
the distances between Ni and the two Br atoms are very close,
at 2.4471(10) and 2.4789(9) Å, respectively, and the Ni-P bond
length in 12 (2.1600(14) Å), 13 (2.1801(8) Å), and 16 (2.4108-
(13) Å) increases in the same order as the bulky aryl group on
the phosphorus atom.
2.1.3. Synthesis and Characterization of 2-(Diphenylphos-
phino)-N-[2-(diarylphosphino)benzylidene]anilines (P∧N∧P).
The designed compounds (7-11) were synthesized in satisfac-
tory yields (74.7-81.6%) through the Schiff-base condensation
of (o-aminophenyl)diphenylphosphine with the corresponding
o-phosphinoaldehydes in the presence of a catalytic amount of
toluene-p-sulfonic acid (p-TsOH) in refluxing toluene (Scheme
3) as described above. All compounds were characterized and
confirmed by elemental analysis, 1H NMR, 13C NMR, 31P NMR,
and IR spectroscopy.
(9) (a) Daugulis, O.; Brookhart, M. Organometallics 2002, 21, 5926.
(b) Sun, W.-H.; Li, Z.; Hu, H.; Wu, B.; Yang, H.; Zhu, N.; Leng, X.; Wang,
H. New J. Chem. 2002, 26, 1474. (c) Daugulis, O.; Brookhart, M.; White,
P. S. Organometallics 2002, 21, 5935. (d) Speiser, F.; Braunstein, P.;
Saussine, L.; Welter, R. Organometallics 2004, 23, 2613. (e) Speiser, F.;
Braunstein, P.; Saussine, L. Organometallics 2004, 23, 2625. (f) Speiser,
F.; Braunstein, P.; Saussine, L. Organometallics 2004, 23, 2633. (g)
Heinicke, J.; Ko¨hler, M.; Peulecke, N.; Kindermann, M. K.; Keim, W.;
Ko¨ckerling, M. Organometallics 2005, 24, 344. (h) Tang, X.; Zhang, D.;
Jie, S.; Sun, W.-H.; Chen, J. J. Organomet. Chem. 2005, 690, 3918.
(10) Sun, W.-H.; Zhang, W.; Gao, T.; Tang, X.; Chen, L.; Li, Y.; Jin,
X. J. Organomet. Chem. 2004, 689, 917.
(11) Speiser, F.; Braunstein, P.; Saussine, L. Dalton 2004, 1539.
(12) Bluhm, M.; Walter O.; Do¨ring M. J. Organomet. Chem. 2005, 690,
713.
(13) (a) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Hu, C.; Englert,
U.; Dixon, J. T.; Grove, C. Chem. Commun. 2003, 334. (b) McGuinness,
D. S.; Wasserscheid, P.; Morgan, D. H.; Dixon, J. T. Organometallics 2005,
24, 552.
(14) Wang, M.; Yu, X.; Shi, Z.; Qian, M.; Jin, K.; Chen, J.; He, R. J.
Organomet. Chem. 2002, 645, 127.
(15) (a) Schiemenz, G. P.; Kaack, H. Liebigs Ann. Chem. 1973, 1480.
(b) Hoots, J. E.; Rauchfuss, T. B.; Wrobleski, D. A.; Knachel, H. C. Inorg.
Synth. 1982, 21, 175.

238 Organometallics, Vol. 25, No. 1, 2006
Hou et al.
Figure 1. Molecular structure of 12 (thermal ellipsoids at 30%
probability, hydrogen atoms and solvent have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ni(1)-N(1)
) 1.951(4), Ni(1)-N(2) ) 1.931(3), Ni(1)-P(1) ) 2.1600(14),
Ni(1)-Br(1) ) 2.3176(11); N(1)-Ni(1)-N(2) ) 84.00(15); N(2)-
Ni(1)-P(1) ) 90.33(10), N(1)-Ni(1)-P(1) ) 166.62(12), Br(1)-
Ni(1)-N(1) ) 92.77(12), Br(1)-Ni(1)-N(2) ) 167.79(10), Br(1)-
Ni(1)-P(1) ) 90.24(4). The interaction distance of the Ni cation
and bromide anion: Ni(1)- - -Br(2) ) 2.891 Å.
Figure 3. Molecular structure of 16 (thermal ellipsoids at 30%
probability, hydrogen atoms and solvent have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ni-N(2) )
2.054(3), Ni-N(1) ) 2.103(3), Ni-P ) 2.4108(13), Ni-Br(1) )
2.4471(10), Ni-Br(2) ) 2.4789(9); N(2)-Ni-N(1) ) 80.07(13),
N(1)-Ni-P ) 82.76(9), N(2)-Ni-P ) 151.85(10), Br(1)-Ni-
Br(2) ) 102.68(4), Br(1)-Ni-N(2) ) 94.14(10), Br(1)-Ni-N(1)
) 166.47(9), Br(1)-Ni-P ) 97.53(4), Br(2)-Ni-N(2) ) 94.14-
(10), Br(2)-Ni-N(1) ) 90.20(9), Br(2)-Ni-P ) 105.48(4).
Scheme 3. Synthesis of Nickel Complexes
Figure 2. Molecular structure of 13 (thermal ellipsoids at 30%
probability, hydrogen atoms and solvent have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ni-N(1) )
1.979(2), Ni-N(2) ) 1.899(2), Ni-P ) 2.1801(8), Ni-Br(1) )
2.2885(5); N(1)-Ni-N(2) ) 83.41(11), N(2)-Ni-P ) 88.28(7),
N(1)-Ni-P ) 165.97(10), Br(1)-Ni-N(1) ) 93.74(9), Br(1)-
Ni-N(2) ) 176.11(8), Br(1)-Ni-P ) 95.03(3). The interaction
distance of Ni cation and bromide anion: Ni- - -Br(2) ) 5.498 Å.
were determined by elemental analysis and IR. The elemental
analysis results reveal that the components of these complexes
are in accord with the formula MLBr2. The IR spectra of the
ligands show that the CHdN stretching frequencies appear in
the range 1619-1620 cm-1, while the CHdN stretching
vibrations in complexes 20-24 shift toward lower frequencies
between 1575 and 1590 cm-1 with weak intensities, which
indicate the effective coordination interaction between the imino
nitrogen atoms and nickel center in the complexes.
Crystals of 20 suitable for X-ray crystallography were grown
by layer diffusion of diethyl ether into their dichloromethane
solutions. The molecular structure of 20 is depicted in Figure
4. In complex 20, the coordination geometry around the nickel
can be described as distorted trigonal bipyramidal, in which there
is a trans arrangement of phosphorus atoms with the P(2)-Ni-
(1)-P(1) angle 150.23(8)°. The C(20)-N(1), C(19)-N(1), and
C(18)-C(19) bond lengths of 1.492(9), 1.275(9), and 1.441-
(10) Å are typical of single and double bonds, respectively, and
there is little electron delocalization through the imine system.
The two Ni-P distances are very close (2.154(2) and 2.1972-
(19) Å) despite the chemical inequivalence of the two P atoms.
2.1.4. Synthesis and Characterization of the Nickel Com-
plexes Containing P∧N∧P Ligands. The nickel complexes 20-
24 were easily prepared by combining a CH2Cl2 solution of
(DME)NiBr2 with 1 equiv of the corresponding P∧N∧P com-
pounds (7-11) at room temperature (Scheme 3). The resulting
nickel complexes were soluble in CH2Cl2, but did not dissolve
in diethyl ether. Therefore, anhydrous diethyl ether was added
to precipitate the nickel complexes. After washing with diethyl
ether, the nickel complexes 20-24 were obtained as dark brown
powders in good yields (typically 80.0-85.0%) and high
purities. These complexes are air-stable in the solid state, but
the solutions of these complexes turned from dark brown to
red when exposed to air for a few days, most likely due to the
oxidation of P(III) to P(V). The structures of these complexes

Tridentate Nickel Complexes
Organometallics, Vol. 25, No. 1, 2006 239
Table 1. Ethylene Oligomerization with 12-19 at 1 atm of
Ethylenea
oligomer distribution (%)
com-
temp time
linear
entry plex Al/Nid (°C) (min) activitye C4/∑C C6/∑C Cg8/∑C R-olefin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
12b 1000 20
13b 1000 20
14b 1000 20
15b 1000 20
30
30
30
30
30
30
30
30
30
30
30
30
15
30
60
2.31
2.78
3.10
4.73
4.01
5.24
2.07
5.86
1.55
1.47
8.37
9.34
13.4
12.2
8.31
4.94
11.2
81.7
98.0
87.3
91.1
94.2
97.0
96.8
61.1
98.6
95.8
23.3
28.5
36.7
24.5
23.6
22.7
26.5
48.8
45.0
67.6
53.2
11.6
2.0
4.3
4.4
3.2
1.8
1.6
25.2
1.4
4.2
23.5
30.4
26.4
23.5
24.1
25.8
30.1
37.6
31.3
18.4
24.1
6.7
0
8.4
4.5
2.6
1.2
1.6
13.7
0
0
53.2
41.1
36.9
52.0
52.3
51.5
43.4
13.6
23.7
14.0
22.7
98
97
74
92
92
93
98
99
85
87
69
78
75
72
73
71
71
59
67
64
55
16b
250 20
16b 1000 20
16b 2000 20
16c
20 20
17b 1000 20
18b 1000 20
19b
19b
150 20
250 20
Figure 4. Molecular structure of 20 (thermal ellipsoids at 30%
probability, hydrogen atoms and solvent have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Ni(1)-P(1)
) 2.1972(19), Ni(1)-P(2) ) 2.154(2), Ni(1)-N(1) ) 1.956(6),
Ni(1)-Br(1) ) 2.3222(11), Ni(1)-Br(2) ) 2.7754(11); N(1)-Ni-
(1)-P(1) ) 92.33(17), N(1)-Ni(1)-P(2) ) 88.25(18), P(1)-Ni-
(1)-P(2) ) 150.23(8), Br(1)-Ni(1)-Br(2) ) 93.98(4), Br(1)-
Ni(1)-P(1) ) 91.56(6), Br(1)-Ni(1)-N(1) ) 172.46(17), Br(1)-
Ni(1)-P(2) ) 85.17(6), Br(2)-Ni(1)-P(1) ) 95.99(6), Br(2)-
Ni(1)-N(1) ) 92.05(16), Br(2)-Ni(1)-P(2) ) 113.74(6).
19b 1000 20
19b 1000 20
19b 1000 20
19b 1000 20 120
19b 1000
0
30
30
30
30
30
19b 1000 40
19b 2000 20
4.86
4.29
7.52
9.77
19c
19c
10 20
20 20
a General conditions: 5 µmol of catalyst, 30 mL of toluene, 0.5 h. b MAO
as cocatalyst. c AlEtCl2 as cocatalyst. d Ratio in moles. e 105g mol-1 h-1
.
2.2. Ethylene Oligomerization. 2.2.1. Ethylene Oligomer-
ization Behavior of the Nickel Complexes Bearing P∧N∧N
Ligands. The nickel(II) complexes 12-19 were systematically
investigated for the oligomerization of ethylene by using MAO
or AlEtCl2 as cocatalyst. Various activators and experimental
conditions were employed to improve the productivity and
selectivity of the catalysts. In most cases, dimerization and
trimerization of ethylene are the major reactions, and the
selectivity of R-olefin products in total is modest to high
according to GC and GC-MS analysis. The results with ambient
pressure of ethylene are collected in Table 1.
Effect of Ligand Environment. As shown in Table 1, the
bulkiness of the ligands in the complex affect the catalytic
activity of ethylene oligomerization. Among complexes 12-
16, 16, with the isopropyl group in the ortho-position of the
phenyl ring, showed the highest activity, and the activity
decreases in the order 16 > 15 > 14 > 13 > 12 under identical
reaction conditions. Oligomerization results with 12-16 indicate
that the introduction of steric hindrance on the phosphorus atom
has little influence on the selectivity of R-olefin formation.
Increased substitution at the carbon â to phosphorus leads to
poor selectivities for R-olefin in the oligomerization of ethylene
in the presence of 1000 equiv of MAO. For the purpose of
increasing the ligand dimension furthermore, 2-methyl-8-
aminoquinoline was introduced into the ligand backbone.
Unexpectedly, the activities of the catalytic system with MAO
of 17 and 18 are both lower than the analogues 12 and 16,
respectively. The ketimine-derived catalyst 19 was substantially
more active than aldimine-derived catalysts 12-18. Catalyst 19/
MAO produced oligomers ranging from C6 to C22 with a low
selectivity for R-olefins (50-80%).
Figure 5. Molecular structure of 25 (thermal ellipsoids at 30%
probability, hydrogen atoms and solvent have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Co-Cl(1) )
2.228(3), Co-Cl(2) ) 2.237(3), Co-P(1)) 2.380(3), Co-P(2))
2.367(3); Cl(1)-Co-Cl(2) ) 110.24(13), Cl(1)-Co-P(1) )
107.05(12), Cl(1)-Co-P(2) ) 103.67(12), Cl(2)-Co-P(1) )
109.04(11), Cl(2)-Co-P(2) ) 111.99(11), P(1)-Co-P(2) )
114.59(11). The interaction distance of cobalt and nitrogen atoms:
Co- - -N ) 2.877 Å.
2.1.5. Synthesis and Characterization of the Cobalt
Analogue Containing the P∧N∧P Ligand. To examine the
influence of the metal cation on the catalytic properties of the
resulting complex, cobalt analogues containing P∧N∧P ligands
were explored, which showed low catalytic activities for
ethylene activations. The cobalt complex 25 was studied in detail
for the structural determination and analysis. The cobalt complex
(L)CoCl2 (25, L ) 7) was prepared by stirring equal amounts
of 7 and CoCl2 in EtOH at 25 °C for 2 h. After workup, the Co
complex was isolated in 78.1% yield. The X-ray structural
determination of 25 reveals that the cobalt(II) complex is four-
coordinate with a distorted tetrahedral coordination geometry
(Figure 5). The imine 2-PPh2(C6H4NdCHC6H4)2-PPh2 acts as
a bidentate ligand through two phosphorus atoms, and the
distance of Co- - -N (2.877 Å) is too long to be considered as
a bond. The Co-P distances of 2.379(3) and 2.367(3) Å in 25
are significantly longer than the typical Co-P bond length (2.1-
2.3 Å) reported for many cobalt(II) phosphine complexes.16
Effects of Reaction Parameters. The influences of the Al/
Ni molar ratio and the reaction temperature on ethylene
oligomerization were investigated in detail with complex 19.
Variation of the Al/Ni molar ratio in the range 150-2000
significantly affects the oligomerization activity and oligomer
distribution, and the highest oligomerization activity was
(16) (a) Boyter, H. A.; Swisher, R. G.; Sinn, E.; Grimes, R. N. Inorg.
Chem. 1985, 24, 3810. (b) Liebeskind, L. S.; Baysdon, S. L.; Goedken, V.;
Chidambaram, R. Organometallics 1986, 5, 1086.

240 Organometallics, Vol. 25, No. 1, 2006
Hou et al.
Table 2. Ethylene Oligomerization of 12-19/MAO at 10 atm
Table 4. Ethylene Oligomerization Using the 20-24/AlEtCl2
of Ethylenea
Systemsa
oligomer distribution (%)
oligomer distribution (%)
activity (105 g
linear
g8/∑C R-olefin
activity (105 g
linear
g8/∑C R-olefin
entry complex
mol-1 h-1
)
C4/∑C C6/∑C
C
entry complex
mol-1 h-1
)
C4/∑C C6/∑C
C
1
2
3
4
5
6
7
8
12
13
14
15
16
17
18
19
3.51
8.35
13.3
7.62
8.08
5.22
2.13
11.5
77.9
97.8
95.9
98.1
46.8
96.7
98.5
54.5
19.5
2.2
4.1
1.9
33.9
3.3
2.6
0
0
0
19.3
0
99
98
99
97
97
99
99
77
1
2
3
4
5
20
21
22
23
24
1.04
2.78
3.33
3.24
3.74
66.7
72.2
79.1
76.9
69.6
21.2
24.3
19.7
14.3
25.4
12.1
3.5
1.2
8.8
5.0
98
99
99
98
99
a Reaction conditions: 5 µmol of catalyst, Al/Ni ) 20, 20 °C, 30 mL of
toluene, 0.5 h, 1 atm ethylene.
1.5
27.6
0
17.9
a Reaction conditions: 5 µmol of catalyst, Al/Ni ) 1000, 20 °C, 120
ization activity. The selectivity of R-olefins with the catalytic
system of complexes 20-24/MAO is generally high. The main
products formed during the oligomerization reactions were C4
and C6. 24, with an isopropyl substituent on the phenyl ring,
showed the highest activity under identical reaction conditions.
Precatalyst 22 generated a large quantity of octenes, while the
selectivity for R-olefins was poor. As shown in Table 3, the
activity increases in the order of increased ligand bulk: 24 >
23 > 22 > 21 > 20. These results resemble the catalytic
activities obtained with four-membered diphosphine nickel(II)
chelates.17
Effects of Reaction Parameters. The influences of the Al/
Ni molar ratio and the reaction temperature on ethylene
oligomerization were investigated in detail with complex 24.
Varying the Al/Ni molar ratio in the range 250-1000 had little
effect on the oligomerization activity and oligomer distribution,
and the highest oligomerization activity was observed when the
Al/Ni molar ratio is 500.
When AlEtCl2 was used as the cocatalyst, all nickel com-
plexes performed well as catalysts for ethylene oligomerization,
with high selectivity of R-olefins and considerably high activity.
Collected in Table 4 are the results obtained with complexes
20-24 as the catalysts and 20 equiv of AlEtCl2.
2.2.3. Test of Ethylene Activation on the Cobalt Complex
Bearing a P∧N∧P Ligand. General scanning work has been
done to test cobalt complexes bearing various PNP ligands;
however, all the cobalt complexes were inactive in the presence
of MAO or AlEt3. In the presence of 20 equiv of AlEtCl2,
mL of toluene, 0.5 h.
Table 3. Ethylene Oligomerization Using the 20-24/MAO
Systemsa
oligomer distribution (%)
com-
entry plex Al/Ni (°C)
temp activity (104 g
linear
g8/∑C R-olefin
mol-1 h-1
)
C4/∑C C6/∑C
C
1
2
3
4
5
6
7
8
9
20 1000 20
21 1000 20
22 1000 20
23 1000 20
3.16
3.94
5.58
7.72
10.2
11.4
7.44
3.52
9.33
85.9
85.1
50.4
84.5
80.1
83.8
87.8
92.1
81.6
11.1
9.6
3.0
5.3
14.5
4.2
5.6
6.1
0
98
97
94
98
98
98
96
97
98
35.1
11.3
14.3
10.1
12.2
7.9
24
24
24
24
250 20
500 20
500
0
500 40
0
7.2
24 1000 20
11.2
a Reaction condition: 5 µmol of catalyst, 30 mL of toluene, 0.5 h, 1
atm ethylene.
observed at the Al/Ni molar ratio of 1000. The catalyst 19
showed higher oligomerization activity at lower temperature,
and elevating the reaction temperature to 40 °C led to the
remarkable reduction in activity (entry 18, Table 1), which may
be attributable to the decomposition of the active catalytic sites
and lower ethylene solubility at higher temperature. The
oligomerization activity progressively decreased when the
reaction was prolonged from 15 to 60 min and finally to 120
min, which indicates that the catalyst lifetime is relative short.
Recently Braunstein’s group reported that N∧P-coordinated
nickel complexes show high ethylene oligomerization activity
upon activation with a slight excess of AlEtCl2.9d-f,11 Therefore,
oligomerization with complexes 16 and 19 was investigated by
using AlEtCl2 instead of MAO as cocatalyst. It was observed
that complex 19 displays high activity with only 20 molar equiv
of AlEtCl2 as the cocatalyst (entry 21, Table 1).
Effects of Ethylene Pressure. The complexes 12-19 were
also examined for ethylene oligomerization at 10 atm of ethylene
pressure, and the results are summarized in Table 2. These data
suggest that increased ethylene pressure results in slightly higher
catalytic activity, and the effect of the ligand environments on
the oligomerization activity is similar to that observed at 1 atm.
In addition, the percentages of the higher carbon number olefins
in the oligomers are much lower than those obtained at 1 atm
of ethylene pressure, while the similar tendency of selectivity
for R-olefin was observed at elevated ethylene pressure.
2.2.2. Ethylene Oligomerization Behavior of the Nickel
Complexes Bearing P∧N∧P Ligands. The complexes 20-25
were investigated for their ethylene oligomerization behavior
upon activation with MAO and AlEtCl2, and the results are listed
in Tables 3 and 4, respectively. In all cases, dimers and trimers
of ethylene are the main products. According to GC and GC-
MS results, the selectivity of R-olefins in total olefins is high.
Effect of Ligand Environment. The bulkiness of the ligand
in the nickel complex slightly affects the ethylene oligomer-
precatalyst 25 showed an activity of 7.4 × 104 g mol-1 h-1
.
Dimerization (92.1%) and trimerization (7.9%) of ethylene
dominated, and a selectivity for 1-butene within the C4 fraction
of 94% was observed. Therefore there is less interest for the
Co(II) complexes for ethylene activity. That might be caused
by the ligand being bidentate instead of tridentate.
3. Conclusion
A series of nickel(II) complexes ligated by N-(1-(2-(di-
arylphosphino)phenyl)methylidene)quinolin-8-amines (P∧N∧N)
and 2-(diphenylphosphino)-N-[2-(diarylphosphino)benzylidene]-
anilines (P∧N∧P) were synthesized and characterized. The
P∧N∧N ligands are not stable, and their complexes were
synthesized through metal-induced template reaction. Activated
by MAO and AlEtCl2, all nickel complexes exhibited consider-
ably high catalytic activity for ethylene oligomerization, with
the dimers and trimers of ethylene as the major products. In
the presence of 1000 equiv of MAO, complex 19 showed an
(17) (a) Cooley, N. A.; Green, S. M.; Wass, D. F.; Heslop, K.; Orpen,
A. G.; Pringle, P. G. Organometallics 2001, 20, 4769. (b) Dennett, J. N.
L.; Gillon, A. L.; Heslop, K.; Hyett, D. J.; Flemming, J. S.; Lloyd-Jones,
C. E.; Orpen, A. G.; Pringle, P. G.; Wass, D. F. Organometallics 2004, 23,
6077.

Tridentate Nickel Complexes
Organometallics, Vol. 25, No. 1, 2006 241
activity of 1.34 × 106 g‚mol-1(Ni)‚h-1. Interestingly, the
selectivities of R-olefins are modest to high, which will be
further investigated. The ethylene oligomerization activity was
found to be affected by the substituents in the ligands’
framework. Incorporation of bulky groups of ligands led to an
increase in catalytic activity of ethylene oligomerization.
p-Toluenesulfonic acid monohydrate (0.57 g, 3.0 mmol) was added,
and the solution was refluxed for 8 h. During this time, the yellow
color of the final product developed. The product mixture was
separated by column chromatography over silica gel (petroleum
ether/ethyl acetate, 8/1). Rf (petroleum ether/ethyl acetate, 2/1):
0.86. To obtain pure product, the yellow crystals were recrystallized
from petroleum ether/ethyl acetate, affording 2-(di-o-tolylphosphi-
no)benzaldehyde (13.4 g, 42.1 mmol, 78.7%). Mp: 120.0-120.5
4. Experimental Section
1
°C. H NMR (CDCl3) δ: 2.43 (s, 6H, CH3), 6.68-6.72 (m, 2H,
Ph), 6.92-6.96 (m, 1H, Ph), 7.07 (t, 2H, Ph, J ) 7.5 Hz), 7.22-
7.30 (m, 4H, Ph), 7.43-7.53 (m, 2H, Ph), 7.99-8.02 (m, 1H, Ph),
10.58 (d, 1H, CHO, J(PH) ) 6.0 Hz). 13C NMR (CDCl3) δ: 55.5,
110.2, 121.0, 123.5, 123.6, 128.3, 128.6, 130.5, 133.3, 134.0, 138.7,
138.9, 140.7, 141.0, 161.0, 161.2, 191.7, 192.0. Anal. Calcd for
C21H19OP: C, 79.23; H, 6.02. Found: C, 79.09; H, 6.27. 31P NMR
(CDCl3) δ: -29.0 (s). IR (KBr): 1696 (νCdO), 1648, 1584, 1562,
General Considerations. All manipulations involving air- or
moisture-sensitive compounds were carried out under an atmosphere
of nitrogen using standard Schlenk techniques. All solvents were
dried and distilled using common techniques unless otherwise stated.
All Grignard reagents were prepared by slow addition of the
corresponding aryl bromides or chlorides to a suspension of
magnesium in THF. The magnesium was activated by adding some
iodine crystals. (DME)NiBr2,18 2-(diphenylphosphino)benzaldehyde
(1) (31P NMR (CDCl3) δ: -11.2 (s)),15 2-(2-bromophenyl)-1,3-
dioxolane,15 2-{bis(2-methylphenyl)}chlorophosphine,19a and (o-
aminophenyl)diphenylphosphine (31P NMR (CDCl3) δ: -19.9 (s))19b
were prepared according to the literature methods. Methylalumi-
noxane (MAO) was purchased from Albemarle as a 1.4 M toluene
solution. AlEtCl2 was purchased from Fluka as a 1.0 M hexane
solution. IR spectra were recorded on a Perkin-Elmer system 2000
FT-IR spectrometer. The chemical shifts of the NMR spectra were
measured with a Bruker BMX-300 MHz instrument and were
referenced against residual solvent peaks (1H, 13C) or H3PO4 (31P).
Elemental analysis was performed by using a HP-MOD 1106
microanalyzer. GC analyses were performed with a Carlo Erba
Strumentazione gas chromatograph equipped with a flame ionization
detector and a 30 m (0.25 mm i.d., 0.25 µm film thickness) DM-1
silica capillary column.
1451, 1391, 1288, 1264, 1200, 1166, 1120, 1066, 1037 cm-1
.
2-(Bis(2-methoxyphenyl)phosphino)benzaldehyde (3). The
2-(bis(2-methoxyphenyl)phosphino)benzaldehyde was prepared ac-
1
cording to a literature method.20 Mp: 176.0-176.5 °C. H NMR
(CDCl3) δ: 3.74 (s, 6H, CH3), 6.68-6.71 (m, 2H, Ph), 6.84-6.93
(m, 4H, Ph), 7.01-7.03 (m, 1H, Ph), 7.33-7.45 (m, 4H, Ph), 7.98-
8.00 (m, 1H, Ph), 10.78 (d, 1H, CHO, J(PH) ) 7.0 Hz). 13C NMR
(CDCl3) δ: 52.2, 54.4, 108.9, 116.3, 119.9, 122.5, 122.6, 124.7,
125.9, 126.0, 127.0, 127.1, 127.5, 128.3, 129.2, 129.4, 131.1, 131.5,
131.6, 132.1, 132.7, 133.0, 135.8, 135.9, 136.3, 136.5, 138.4, 138.6,
152.6, 152.8, 157.1, 157.5, 159.9, 160.1. Anal. Calcd for
C21H19O3P: C, 71.99; H, 5.47. Found: C, 71.86; H, 5.36. 31P NMR
(CDCl3) δ: -36.8 (s). IR (KBr): 1692 (νCdO), 1645, 1579, 1463,
1428, 1393, 1275, 1242, 1196, 1172, 1132, 1070, 1017 cm-1
.
2-(Bis(2-ethylphenyl)phosphino)benzaldehyde (4). The 2-eth-
ylphenyl Grignard reagent was prepared by the dropwise addition
of 22.15 g (0.120 mol) of 1-bromo-2-ethylbenzene in 60 mL of
anhydrous THF to 3.38 g (0.139 mol) of magnesium turnings in
40 mL of THF under reflux conditions (in a 250 mL three-neck
flask fitted with a pressure-equalizing dropping funnel, magnetic
stirrer, and condenser). After the addition was complete (ca. 1 h)
the solution was refluxed for a further 1 h, at which stage little
magnesium metal still remained. At this time the Grignard was
cooled in an ice bath. To a three-neck 1 L flask was added 7.83 g
(0.057 mol) of phosphorus trichloride in 120 mL of anhydrous THF.
The solution was cooled in a dry ice/acetone bath. The Grignard
solution was then transferred under nitrogen through a tube into a
pressure-equalizing dropping funnel. Then the Grignard solution
was added slowly in a dropwise manner over a 1 h period to the
solution of phosphorus trichloride with the aid of a magnetic stirrer.
After the addition was complete, the solution was slowly warmed
to room temperature overnight. The solution was then heated to
reflux for 1 h. The solvent was removed by distillation, and the
product extracted with hexane. Distillation of the extracts gave a
light yellow liquid that solidified overnight. The phosphine was
added dropwise to the stirred solution of 2-(2-bromophenyl)-1,3-
dioxolane Grignard reagent (0.05 mol) in THF (100 mL) while the
temperature was maintained at ca. 5 °C. After the addition was
complete, the reaction was heated to reflux for 10 h. The cooled
reaction was cautiously quenched with 30 mL of 10% aqueous NH4-
Cl, and the nonaqueous extracts were further extracted with 35 mL
of saturated aqueous NaCl. The combined aqueous extracts were
washed with 100 mL of diethyl ether. The combined nonaqueous
extracts were dried over anhydrous Na2SO4 and then concentrated
to an oily liquid on a rotary evaporator. The mixture was separated
by column chromatography over silica gel (petroleum ether/ethyl
acetate, 10/1) to give (2-(1,3-dioxolan-2-yl)phenyl)bis(2-ethylphen-
yl)phosphine (13.0 g, 66.6%). Rf (petroleum ether/ethyl acetate,
4.1. Synthesis of the o-Phosphinoaldehydes. 2-(Di-o-tolylphos-
phino)benzaldehyde (2). Magnesium (0.15 mol) and 200 mL of
THF were placed into a 1000 mL, three-neck flask equipped with
a mechanical stirrer, a condenser, and a pressure-equalizing addition
funnel. The addition funnel was charged with 27.5 g (0.12 mol)
2-(2-bromophenyl)-1,3-dioxolane. The reaction was initiated with
a crystal of I2 and a few milliliters of the dioxolane. The remaining
dioxolane was added slowly in 3 mL aliquots from the addition
funnel, and the reaction was then heated to reflux for 30 min. The
clear, brownish solution was cooled in an ice bath while a solution
of chloro-di(o-tolyl)phosphine (0.12 mol) in 200 mL of anhydrous
THF was prepared in the addition funnel. The phosphine was added
dropwise to the stirred Grignard reagent while the temperature was
maintained at ca. 5 °C. After the addition was complete, the reaction
was heated to reflux for 10 h. The cooled reaction was cautiously
quenched with 75 mL of 10% aqueous NH4Cl, and the nonaqueous
extracts was further extracted with 100 mL of saturated aqueous
NaCl. The combined aqueous extracts were washed with 200 mL
of diethyl ether. The combined nonaqueous extracts were dried over
anhydrous Na2SO4 and then concentrated to an oily liquid on a
rotary evaporator. The produced mixture was separated by column
chromatography over silica gel (petroleum ether/ethyl acetate, 8/1)
to give (2-(1,3-dioxolan-2-yl)phenyl)di-o-tolylphosphine (19.4 g,
1
44.6%). Rf (petroleum ether/ethyl acetate, 2/1): 0.81. H NMR
(CDCl3) δ: 2.36 (s, 6H, CH3), 3.96-4.10 (m, 4H, O-CH2CH2-
O), 6.45-6.47 (m, 1H, PhCH), 6.72-6.74 (m, 2H, Ph), 6.86-6.89
(m, 1H, Ph), 7.08-7.11 (m, 2H, Ph), 7.23-7.25 (m, 5H, Ph), 7.40-
7.45 (m, 1H, Ph), 7.71-7.72 (m, 1H, Ph).
(2-(1,3-Dioxolan-2-yl)phenyl)di-o-tolylphosphine (19.4 g, 53.5
mmol) was added to 400 mL of acetone in a 1000 mL, round-
bottomed flask equipped with a magnetic stirrer and a condenser.
1
3/1): 0.78. H NMR (CDCl3) δ: 1.13 (t, 6H, CH3, J ) 7.6 Hz,),
(18) Cotton, F. A. Inorg. Synth. 1971, 13, 160.
(19) (a) Clark, P. W.; Mulraney, B. J. J. Organomet. Chem. 1981, 217,
51. (b) Cooper, M. K.; Downes, J. M.; Duckworth, P. A.; Tiekink, E. R. T.
Aust. J. Chem. 1992, 45, 595.
(20) Beuken, E. K.; Smeets, W. J. J.; Spek, A. L.; Feringa, B. L. Chem.
Commun. 1998, 223.

242 Organometallics, Vol. 25, No. 1, 2006
Hou et al.
2.75-2.83 (q, 4H, CH2, J ) 7.4 Hz), 3.89-4.13 (m, 4H,
O-CH2CH2-O), 6.41 (d, 1H, Ph-CH, J ) 5.5 Hz), 6.74-6.78
(m, 2H, Ph), 6.86-6.88 (m, 1H, Ph), 7.06 (t, 2H, Ph, J ) 7.3 Hz),
7.22-7.29 (m, 4H, Ph), 7.36-7.38 (m, 2H, Ph), 7.67-7.69 (m,
1H, Ph).
(2-(1,3-Dioxolan-2-yl)phenyl)bis(2-isopropylphenyl)phosphine
(11.4 g, 27.2 mmol) was added to 250 mL of acetone in a 500 mL,
round-bottomed flask equipped with a magnetic stirrer and a
condenser. p-Toluenesulfonic acid monohydrate, 0.38 g (2.0 mmol),
was added, and the solution was refluxed for 8 h. During this time,
the yellow color of the final product developed. The product mixture
was separated by column chromatography over silica gel (petroleum
ether/ethyl acetate, 20/1). Rf (petroleum ether/ethyl acetate, 6/1):
0.64. To obtain pure product, the yellow crystals were recrystallized
from petroleum ether/ethyl acetate, affording 2-(bis(2-isopropyl-
phenyl)phosphino)benzaldehyde (6.34 g, 62.1%). Mp: 158.0-158.5
(2-(1,3-Dioxolan-2-yl)phenyl)-bis(2-ethylphenyl)phosphine (13.0
g, 33.3 mmol) was added to 250 mL of acetone in a 500 mL, round-
bottomed flask equipped with a magnetic stirrer and a condenser.
p-Toluenesulfonic acid monohydrate, 0.38 g (2.0 mmol), was added,
and the solution was refluxed for 8 h. During this time, the yellow
color of the final product developed. The warm solution was diluted
with 50 mL of H2O, concentrated to 60 mL, and cooled overnight
at -20 °C. The precipitated yellow crystals were filtered from the
cold solution. To obtain pure product, the yellow crystals were
recrystallized from CH2Cl2/MeOH, affording 2-(bis(2-ethylphenyl)-
1
°C. H NMR (CDCl3) δ: 1.11 (d, 6H, CH3, J ) 6.5 Hz), 1.19 (d,
6H, CH3, J ) 6.7 Hz), 3.67-3.73 (m, 2H, CH(CH3)2), 6.75-6.77
(m, 2H, Ph), 6.93-6.96 (m, 1H, Ph), 7.04 (t, 2H, Ph, J ) 7.3 Hz),
7.31-7.36 (m, 4H, Ph), 7.44-7.48 (m, 2H, Ph), 7.97-8.00 (m,
1H, Ph), 10.54 (d, 1H, CHO, J(PH) ) 6.0 Hz). 13C NMR (75 MHz,
CDCl3) δ: 23.8, 24.0, 31.4, 31.6, 125.6, 126.3, 128.8, 129.7, 130.0,
133.7, 134.2, 134.4, 138.3, 138.4, 141.8, 141.9, 153.3, 153.5, 191.6,
191.8. Anal. Calcd for C25H27OP: C, 80.19; H, 7.27. Found: C,
79.95; H, 7.24. 31P NMR (CDCl3) δ: -32.9 (s). IR (KBr): 1697
(νCdO), 1647, 1583, 1469, 1435, 1384, 1290, 1259, 1201, 1163,
1
phosphino)benzaldehyde (8.08 g, 70.0%). Mp: 82.0-82.5 °C. H
NMR (CDCl3) δ: 1.14 (t, 6H, CH3, J ) 7.2 Hz), 2.81-2.86 (q,
4H, CH2, J ) 7.4 Hz), 6.70-6.73 (m, 2H, Ph), 6.87-6.90 (m, 1H,
Ph), 7.03 (t, 2H, Ph, J ) 7.6 Hz), 7.23-7.30 (m, 4H, Ph), 7.38-
7.46 (m, 2H, Ph), 7.93-7.96 (m, 1H, Ph), 10.52 (d, 1H, CHO,
J(PH) ) 6.0 Hz). 13C NMR (CDCl3) δ: 15.3, 27.5, 27.8, 126.3,
128.5, 128.8, 129.4, 129.8, 129.9, 133.7, 133.9, 134.0, 134.2, 138.4,
138.5, 141.2, 141.4, 148.6, 148.8, 191.6, 191.8. Anal. Calcd for
C23H23OP: C, 79.75; H, 6.69. Found: C, 79.41; H, 6.86. 31P NMR
(CDCl3) δ: -31.6 (s). IR (KBr): 1696 (νCdO), 1642, 1580, 1463,
1113, 1054, 1029 cm-1
.
2-(Diphenylphosphino)acetophenone (6). The 2-(diphenylphos-
phino)acetophenone was prepared according to a literature method,15a
but without the detailed analysis data in the literature. Mp: 137.0-
1
137.5 °C. H NMR (CDCl3) δ: 2.59 (s, 3H, CH3), 7.01-7.04 (m,
1436, 1388, 1286, 1259, 1197, 1161, 1131, 1112, 1027 cm-1
.
1H, Ph), 7.26-7.47 (m, 12H, Ph), 7.94-7.97 (m, 1H, Ph). 31P NMR
(CDCl3) δ: -2.3 (s). IR (KBr): 1668 (νCdO), 1585, 1559, 1477,
2-(Bis(2-isopropylphenyl)phosphino)benzaldehyde (5). The
2-isopropylphenyl Grignard reagent was prepared by the dropwise
addition of 59.73 g (0.300 mol) of 1-bromo-2-isopropylbenzene in
120 mL of anhydrous THF to 8.51 g (0.350 mol) of magnesium
turnings in 60 mL of THF under reflux conditions in a 500 mL
three-neck flask fitted with a pressure-equalizing dropping funnel,
magnetic stirrer, and condenser. After the addition was complete
(ca. 1 h) the solution was refluxed for a further 1 h, at which stage
little magnesium metal still remained. At this time the Grignard
was cooled in an ice bath. To a three-neck 1000 mL flask was
added 19.61 g (0.143 mol) of phosphorus trichloride in 200 mL of
anhydrous THF. The solution was cooled in a dry ice/acetone bath.
The Grignard solution was then transferred under nitrogen through
a tube into a pressure-equalizing dropping funnel. Then the Grignard
solution was added slowly in a dropwise manner over a 1 h period
to the solution of phosphorus trichloride with the aid of a magnetic
stirrer. After the addition was complete, the solution was slowly
warmed to room temperature overnight. The solution was then
heated to reflux for 1 h. The solvent was removed by distillation,
and the product extracted with hexane. Distillation of the extracts
gave a light yellow liquid that solidified overnight. The phosphine
was added dropwise to the stirred solution of 2-(2-bromophenyl)-
1,3-dioxolane Grignard reagent (0.10 mol) in THF (200 mL) while
the temperature was maintained at ca. 5 °C. After the addition was
complete, the reaction was heated to reflux for 10 h. The cooled
reaction was cautiously quenched with 60 mL of 10% aqueous NH4-
Cl, and the nonaqueous extracts was further extracted with 70 mL
of saturated aqueous NaCl. The combined aqueous extracts were
washed with 200 mL of diethyl ether. The combined nonaqueous
extracts were dried over anhydrous Na2SO4 and then concentrated
to an oily liquid on a rotary evaporator. The mixture was separated
by column chromatography over silica gel (petroleum ether/ethyl
acetate, 8/1) to give (2-(1,3-dioxolan-2-yl)phenyl)bis(2-isopropy-
lphenyl)phosphine (11.4 g, 27.2%). Rf (petroleum ether/ethyl acetate,
10/1): 0.52. 1H NMR (300 MHz, CDCl3): δ 1.10 (d, 6H, J ) 6.8
Hz, CH3), 1.19 (d, 6H, J ) 7.2 Hz, CH3), 3.63-3.76 (m, 2H,
CH(CH3)2), 3.92-4.12 (m, 4H, O-CH2CH2-O), 6.39 (s, 1H, Ph-
CH), 6.70-6.74 (m, 2H, Ph), 6.93-6.96 (m, 1H, Ph), 7.00-7.03-
(m, 2H, Ph, J ) 7 Hz), 7.31-7.42 (m, 6H, Ph), 7.68-7.71 (m,
1H).
1431, 1355, 1252, 1204, 1092, 1022 cm-1
.
4.2. Synthesis of the Nickel Complexes Containing P∧N∧N
Ligands (12-19). Complexes 12-19 were prepared with the same
method, and the typical procedure is described as follows. An
orange suspension of aldehyde 7 (0.5806 g, 2.00 mmol), 8-ami-
noquinoline (0.2884 g, 2.00 mmol), and (DME)NiBr2 (0.6180 g,
2.00 mmol) in glacial acetic acid (12 mL) was refluxed for 2 h,
giving a dark red solution. The solution was concentrated in vacuo
to ca. 1 mL. Hexane (10 mL) was added to precipitate the complex.
After filtration and washing with hexane, 12 was obtained as a
purple powder in 89.7% yield. Mp: 218 °C (dec). IR (KBr): 1603,
1556, 1507, 1480, 1434, 1406, 1315, 1231, 1187, 1136, 1098, 1050
cm-1. Anal. Calcd for C28H21Br2N2NiP: C, 52.96; H, 3.33; N, 4.41.
Found: C, 52.51; H, 3.60; N, 4.37.
Complex 13 was obtained as an orange powder in 94.2% yield.
Mp: 259 °C (dec). IR (KBr): 1605, 1558, 1504, 1435, 1407, 1311,
1230, 1202, 1130, 1076, 1030 cm-1. Anal. Calcd for C30H25Br2N2-
NiP‚2H2O: C, 51.55; H, 4.18; N, 4.01. Found: C, 51.29; H, 3.92;
N, 4.19.
Complex 14 was obtained as an orange powder in 90.4% yield.
Mp: 257 °C (dec). IR (KBr): 1603, 1585, 1506, 1475, 1431, 1280,
1244, 1165, 1135, 1075, 1013 cm-1. Anal. Calcd for C30H25Br2N2-
NiO2P‚2H2O: C, 49.29; H, 4.00; N, 3.83. Found: C, 49.48; H,
4.03; N, 3.86.
Complex 15 was obtained as an orange powder in 87.1% yield.
Mp: 220 °C (dec). IR (KBr): 1602, 1558, 1506, 1467, 1435, 1377,
1316, 1236, 1168, 1075, 1049 cm-1. Anal. Calcd for C32H29Br2N2-
NiP‚2H2O: C, 52.86; H, 4.57; N, 3.85. Found: C, 51.93; H, 4.48;
N, 4.21.
Complex 16 was obtained as an orange powder in 90.7% yield.
Mp: 238 °C (dec). IR (KBr): 1600, 1557, 1506, 1471, 1434, 1408,
1382, 1317, 1269, 1237, 1213, 1165, 1088, 1032 cm-1. Anal. Calcd
for C34H33Br2N2NiP: C, 56.79; H, 4.63; N, 3.90. Found: C, 56.71;
H, 4.29; N, 3.51.
Complex 17 was obtained as a green powder in 90.7% yield.
Mp: 300 °C (dec). IR (KBr): 1593, 1557, 1505, 1478, 1432, 1408,
1373, 1320, 1295, 1242, 1213, 1147, 1093, 1029 cm-1. Anal. Calcd
for C29H23Br2N2NiP: C, 53.67; H, 3.57; N, 4.32. Found: C, 53.44;
H, 3.62; N, 4.22.

Tridentate Nickel Complexes
Organometallics, Vol. 25, No. 1, 2006 243
Complex 18 was obtained as a green-gray powder in 91.5% yield.
Mp: 282 °C (dec). IR (KBr): 1607, 1560, 1503, 1468, 1433, 1377,
1326, 1292, 1242, 1210, 1164, 1114, 1073, 1029 cm-1. Anal. Calcd
for C35H35Br2N2NiP‚0.5H2O: C, 56.64; H, 4.89; N, 3.77. Found:
C, 56.62; H, 4.87; N, 3.81.
Complex 19 was obtained as an orange powder in 84.4% yield.
Mp: 244 °C (dec). IR (KBr): 1628, 1571, 1504, 1473, 1393, 1318,
1260, 1210, 1168, 1134, 1076, 1021 cm-1. Anal. Calcd for C29H23-
Br2N2NiP: C, 53.67; H, 3.57; N, 4.32. Found: C, 53.47; H, 3.71;
N, 4.16.
6.75-6.82 (m, 4H, Ph), 7.04-7.10 (m, 3H, Ph), 7.19-7.36 (m,
17H, Ph), 7.95-7.97 (m, 1H, Ph), 8.91 (d, 1H, CHdN, J ) 5.7
Hz). 13C NMR (CDCl3) δ: 15.4, 27.6, 27.8, 117.3, 125.9, 126.4,
127.5, 128.3, 128.4, 128.5, 128.6, 128.7, 128.8, 129.4, 129.7, 130.9,
132.5, 132.7, 132.8, 133.2, 133.6, 133.7, 133.8, 134.0, 134.3, 134.6,
137.0, 137.1, 138.0, 138.1, 139.1, 139.2, 148.5, 148.8, 154.1, 154.3,
158.3, 158.6. Anal. Calcd for C41H37NP2‚0.5H2O: C, 80.11; H, 6.23;
N, 2.28. Found: C, 80.21; H, 6.43; N, 2.57. 31P NMR (CDCl3): δ
-33.4 (s), -13.9(s). IR (KBr): 1621 (νCHdN), 1565, 1464, 1433,
1366, 1264, 1191, 1160, 1092, 1025 cm-1
.
4.3. Synthesis of the Nickel Complexes Containing P∧N∧P
Ligands (20-24). 2-(Diphenylphosphino)-N-[2-(diphenylphos-
phino)benzylidene]aniline (7). This compound was prepared
according to a literature method.21 Mp: 185.0-185.5 °C. 1H NMR
(CDCl3) δ: 6.45-6.49 (m, 1H, Ph), 6.73-6.85 (m, 2H, Ph), 7.06
(t, 1H, J ) 7.4 Hz, Ph), 7.21-7.36 (m, 23H, Ph), 7.94-7.98 (m,
1H, Ph), 8.93 (d, 1H, CHdN, J ) 5.5 Hz). 31P NMR (CDCl3) δ:
-14.5 (s), -13.8 (s). IR (KBr): 1619 (νCHdN), 1561, 1469, 1431,
2-(Diphenylphosphino)-N-[2-(di(o-isopropylphenyl)phosphi-
no)benzylidene]aniline (11). Using the same procedure as for the
synthesis of 10, 11 was obtained as a yellow powder in 67.7%
1
yield. Mp: 166.0-166.5 °C. H NMR (CDCl3) δ: 1.11 (d, 6H,
CH3, J ) 5.8 Hz), 1.20 (d, 6H, CH3, J ) 6.5 Hz), 3.62-3.71 (m,
2H, CH), 6.19-6.23 (m, 1H, Ph), 6.71-6.80 (m, 4H, Ph), 7.00-
7.07 (m, 3H, Ph), 7.13-7.40 (m, 17H, Ph), 7.88-7.92 (m, 1H,
Ph), 8.86 (d, 1H, CHdN, J ) 5.7 Hz). 13C NMR (CDCl3) δ: 23.8,
24.1, 31.4, 31.6, 53.5, 117.3, 125.4, 125.5, 125.9, 126.4, 127.4,
128.3, 128.4, 128.5, 128.7, 129.6, 130.8, 132.4, 132.6, 132.7, 133.1,
133.3, 134.0, 134.2, 134.7, 136.9, 137.1, 138.6, 138.7, 138.9, 153.3,
153.5, 154.1, 154.3, 158.4, 158.7. Anal. Calcd for C43H41NP2: C,
81.49; H, 6.52; N, 2.21. Found: C, 81.21; H, 6.80; N, 2.29. 31P
NMR (CDCl3) δ: -34.3 (s), -13.3 (s). IR (KBr): 1617 (νCHdN),
1564, 1467, 1433, 1361, 1264, 1190, 1163, 1113, 1094, 1059, 1027
1361, 1307, 1266, 1229, 1186, 1157, 1091, 1069, 1025 cm-1
.
2-(Diphenylphosphino)-N-[2-(di(o-methylphenyl)phosphino)-
benzylidene]aniline (8). A solution of (o-aminophenyl)diphen-
ylphosphine (0.555 g, 2.0 mmol), 2-(di-o-tolylphosphino)benzal-
dehyde (0.634 g, 2.0 mmol), and a catalytic amount of p-
toluenesulfonic acid in toluene (60 mL) was refluxed for 10 h. After
solvent evaporation, the crude product was purified by column
chromatography on silica gel with petroleum ether/ethyl acetate
(15/1) as eluent to afford a yellow oil. This was dissolved in a
minimum amount of dichloromethane, then methanol was added
until crystallization began. The pale yellow crystals were isolated
and dried in vacuo. Yield: 0.739 g (64.0%). Mp: 82.0-82.5 °C.
1H NMR (CDCl3) δ: 2.37 (s, 6H, CH3), 6.46-6.49 (m, 1H, Ph),
6.71-6.77 (m, 4H, Ph), 7.05-7.08 (m, 3H, Ph), 7.22-7.34 (m,
17H, Ph), 7.97-8.00 (m, 1H, Ph), 8.93 (d, 1H, CHdN, J ) 5.5
Hz). 13C NMR (CDCl3) δ: 21.2, 21.5, 117.3, 126.0, 126.4, 127.6,
128.3, 128.4, 128.5, 129.1, 129.8, 130.2, 131.1, 132.5, 132.7, 132.9,
133.4, 133.7, 133.9, 134.0, 134.1, 134.3, 136.7, 136.9, 137.1, 139.6,
139.9, 142.3, 142.7, 154.0, 154.3, 158.1, 158.5. Anal. Calcd for
C39H33NP2‚H2O: C, 78.64; H, 5.92; N, 2.35. Found: C, 78.50; H,
5.85; N, 2.54. 31P NMR (CDCl3) δ: -31.1 (s), -13.8(s). IR
(KBr): 1619 (νCHdN), 1564, 1464, 1433, 1361, 1307, 1267, 1191,
cm-1
.
Complexes 20-24 were prepared with the same method, and
the typical procedure is described as follows. Compound 7 (0.3297
g, 0.60 mmol) and (DME)NiBr2 (0.1852 g, 0.60 mmol) were added
to a Schlenk tube under nitrogen, followed by the addition of freshly
distilled dichloromethane (20 mL) with rapid stirring at room
temperature. The solution turned dark red immediately. The reaction
mixture was stirred for 5 h at room temperature and then
concentrated to ca. 4 mL. Hexane (10 mL) was added to precipitate
the complex. After filtration and washing with hexane, 20 was
obtained as a purple powder in 75.6% yield. Mp: 190 °C (dec). IR
(KBr): 1575, 1550, 1479, 1432, 1307, 1270, 1220, 1184, 1154,
1097, 1069, 1026 cm-1. Anal. Calcd for C37H29Br2NNiP2: C, 57.86;
H, 3.81; N, 1.82. Found: C, 57.95; H, 3.83; N, 1.73.
Complex 21 was obtained as an orange powder in 83.2% yield.
Mp: 192 °C (dec). IR (KBr): 1555, 1469, 1436, 1383, 1302, 1275,
1234, 1200, 1183, 1164, 1133, 1099, 1068, 1027 cm-1. Anal. Calcd
for C39H33Br2NNiP2‚0.5CH2Cl2: C, 56.57; H, 4.09; N, 1.67.
Found: C, 56.76; H, 4.21; N, 1.76.
Complex 22 was obtained as a purple powder in 79.5% yield.
Mp: 191 °C (dec). IR (KBr): 1583, 1553, 1472, 1432, 1337, 1277,
1245, 1164, 1134, 1099, 1073, 1012 cm-1. Anal. Calcd for C39H33-
Br2NNiO2P2‚0.75CH2Cl2: C, 53.53; H, 3.90; N, 1.57. Found: C,
53.61; H, 4.07; N, 1.62.
Complex 23 was obtained as an orange powder in 77.1% yield.
Mp: 167 °C (dec). IR (KBr): 1589, 1553, 1468, 1435, 1376, 1304,
1266, 1231, 1165, 1133, 1098, 1068, 1025 cm-1. Anal. Calcd for
C41H37Br2NNiP2‚0.75CH2Cl2: C, 56.48; H, 4.37; N, 1.58. Found:
C, 56.27; H, 4.66; N, 1.47.
Complex 24 was obtained as a purple powder in 70.4% yield.
Mp: 180 °C (dec). IR (KBr): 1589, 1555, 1471, 1435, 1386, 1305,
1269, 1230, 1164, 1137, 1099, 1068, 1027 cm-1. Anal. Calcd for
C43H41Br2NNiP2‚0.5CH2Cl2: C, 58.40; H, 4.73; N, 1.57. Found:
C, 58.04; H, 5.05; N, 1.57.
4.4. Synthesis of the Cobalt Analogue Containing the P∧N∧P
Ligand (25). To a solution of compound 7 (0.3297 g, 0.60 mmol)
in degassed ethanol (10 mL) was added CoCl2 (0.0774 g, 0.60
mmol), and the solution was stirred for 2 h at room temperature.
After 3 min, a color change from purple to blue was observed.
The solvent was evaporated under reduced pressure. The blue
residue was dissolved in CH2Cl2 (10 mL), and this solution was
filtered. The filtrate was evaporated, giving the product as a blue
1160, 1123, 1092, 1065, 1028 cm-1
.
2-(Diphenylphosphino)-N-[2-(di(o-methoxyphenyl)phosphino)-
benzylidene]aniline (9). Using the same procedure as for the
synthesis of 8, 9 was obtained as yellow crystals in 71.4% yield.
1
Mp: 206.0-206.5 °C. H NMR (CDCl3) δ: 3.71 (s, 6H, CH3),
6.64-6.74 (m, 4H, Ph), 6.81-6.91 (m, 5H, Ph), 7.04 (t, 1H, Ph, J
) 7.2 Hz), 7.19-7.36 (m, 15H, Ph), 7.95-7.99 (m, 1H, Ph), 9.11
(d, 1H, CHdN, J ) 6.2 Hz). 13C NMR (CDCl3) δ: 21.2, 21.5,
117.3, 126.0, 126.4, 127.6, 128.3, 128.4, 128.5, 129.1, 129.8, 130.2,
131.1, 132.5, 132.7, 132.9, 133.4, 133.7, 133.9, 134.0, 134.1, 134.3,
136.7, 136.9, 137.1, 139.6, 139.9, 142.3, 142.7, 154.0, 154.3, 158.1,
158.5. Anal. Calcd for C39H33NO2P2‚H2O: C, 74.63; H, 5.62; N,
2.23. Found: C, 74.55; H, 5.41; N, 2.06. 31P NMR (CDCl3): δ
-37.7 (s), -14.1(s). IR (KBr): 1620 (νCHdN), 1578, 1461, 1427,
1393, 1242, 1196, 1172, 1132, 1070, 1016 cm-1
.
2-(Diphenylphosphino)-N-[2-(di(o-ethylphenyl)phosphino)-
benzylidene]aniline (10). A solution of (o-aminophenyl)diphen-
ylphosphine (0.555 g, 2.0 mmol), 2-(di(o-ethylphenyl)phosphino)-
benzaldehyde (0.693 g, 2.0 mmol), and a catalytic amount of
p-toluenesulfonic acid in toluene (60 mL) was refluxed for 10 h.
After solvent evaporation, the crude product was purified by column
chromatography on silica gel with petroleum ether/ethyl acetate
(10/1) as eluent to afford a yellow powder. Yield: 0.756 g (62.4%).
Mp: 163.0-163.5 °C. 1H NMR (CDCl3) δ: 1.19 (t, 6H, CH3, J )
7.5 Hz), 2.85(q, 4H, CH2, J ) 7.4 Hz), 6.34-6.37 (m, 1H, Ph),
(21) Ainscough, E. W.; Brodie, A. M.; Buckley, P. D.; Burrell, A. K.;
Kennedy, S. M. F.; Waters, J. M. Dalton 2000, 2663.

244 Organometallics, Vol. 25, No. 1, 2006
Table 5. Crystallographic Data of Complexes 12, 13, 16, 20, and 25
Hou et al.
12‚CH3OH
13‚H2O
16‚CH2Cl2
20‚0.5CH2Cl2‚0.5Et2O
25‚CH2Cl2
formula
fw
cryst syst
space group
a (Å)
C29H25Br2N2NiOP
667.01
triclinic
P1h
10.109(2)
11.233(2)
13.541(3)
82.68(3)
70.56(3)
63.38(3)
1295.8(4)
2
C30H27Br2N2NiOP
681.04
C35H35Br2Cl2N2NiP
804.05
triclinic
P1h
11.298(2)
11.879(2)
14.045(3)
91.99(3)
97.91(3)
114.07(3)
1696.1(6)
2
C39.50H35Br2ClNNiO0.50P2
847.61
C38H31Cl4CoNP2
764.31
triclinic
P1h
10.475(2)
13.575(3)
13.657(3)
75.02(3)
73.06(3)
88.40(3)
1792.3(6)
2
monoclinic
P2(1)/n
16.5092(4)
10.1035(2)
16.9507(5)
90.00
104.7810(10)
90.00
2733.82(12)
4
monoclinic
P2(1)/n
11.4617(17)
28.609(4)
12.1638(18)
90
94.501(3)
90
3976.3(10)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calc, (g cm-3
)
1.710
3.921
668
1.655
3.718
1368
1.574
3.160
812
1.416
2.674
1712
1.416
0.895
782
abs coeff, µ (mm-1
F(000)
)
λ (Å)
0.71073
1.60 to 27.48
5887
0.71073
1.54 to 28.28
6753
0.71073
1.47 to 27.48
6896
0.71073
1.42 to 25.01
20 121
0.71073
1.55 to 25.49
5978
θ range (deg)
no. of data collected
no. of unique data
3891
4192
4970
7014
3562
R
Rw
0.0509
0.1181
1.099
0.0383
0.0845
1.096
0.0506
0.1115
0.966
0.0572
0.1527
1.065
0.0986
0.2645
1.097
goodness of fit
powder in 78.1% yield. Mp: 179 °C. IR (KBr): 1616 (νCHdN),
1577, 1559, 1474, 1433, 1394, 1301, 1265, 1184, 1163, 1095, 1068,
1026 cm-1. Anal. Calcd for C37H29Cl2CoNP2: C, 65.41; H, 4.30;
N, 2.06. Found: C, 65.25; H, 4.30; N, 1.96.
solution was vigorously stirred under 1 atm of ethylene for the
desired period of time. The oligomerization reaction was quenched
by the addition 60 mL of 10% HCl solution. About 1 mL of organic
solution was dried by anhydrous Na2SO4 for GC analysis. No
polyethylene formation was observed after pouring the remaining
solution into 100 mL of ethanol.
The oligomerization with 10 atmospheric pressure of ethylene
was performed in a stainless steel autoclave (0.25 L capacity)
equipped with gas ballast through a solenoid clave for continuous
feeding of ethylene at constant pressure. A 137 mL amount of
toluene containing the catalyst precursor was transferred to the fully
dried reactor under nitrogen atmosphere, and 13 mL of MAO in
toluene solution was then injected into the reactor using a syringe.
As the prescribed temperature was reached, the reactor was
pressurized to 10 atm. After stirring for 30 min, the reaction was
quenched and worked up using the same method as described above
for the 1 atm reaction.
4.5. X-ray Crystallographic Studies. Single-crystal X-ray
diffraction for complexes 12, 16, and 25 was carried out on a Rigaku
R-AXIS Rapid IP diffractometer with graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å) at 293(2) K. Intensity data of crystal
13 were collected on a Bruker P4 diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å) at 293(2) K.
Intensity data of crystal 20 were collected on a Bruker SMART
1000 CCD diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å) at 293(2) K. Cell parameters were
obtained by global refinement of the positions of all collected
reflections. Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures were solved by
direct methods and refined by full-matrix least-squares on F2. All
non-hydrogen atoms were refined anisotropically. All hydrogen
atoms were placed in calculated positions. Structure solution and
refinement were performed by using the SHELXL-97 package.
Crystal data and processing parameters for complexes 12, 13, 16,
20, and 25 are summarized in Table 5.
Acknowledgment. This project was supported by NSFC
Nos. 20272062 and 20473099 along with National 863 Project
(2002AA333060). We thank Dr. Jinkui Niu for English cor-
rection.
4.6. Procedure for Ethylene Oligomerization. The oligomer-
ization with 1 atm of ethylene was carried out as follows. Complex
(5 µmol) was added to a Schlenk type flask under nitrogen. The
flask was back-filled three times with N2 and twice with ethylene
and then charged with toluene and cocatalyst solution in turn under
ethylene atmosphere. Under the prescribed temperature, the reaction
Supporting Information Available: Crystallographic data for
12, 13, 16, 20, and 25. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM0507979