Synthesis and characterization of N-(2-pyridyl)benzamide-based nickel complexes and their activity for ethylene oligomerization

Article abstract of DOI:10.1016/j.jorganchem.2003.12.022

A series of N-(2-pyridyl)benzamides (1)-(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-μ-bromide dibromide (12)-(16) and (aryl)[N-(2-pyridyl)benzamido] (triphenylphosphine)nickel(II) (17)-(24), were synthesized and characterized.

Full text of DOI:10.1016/j.jorganchem.2003.12.022

Journal of Organometallic Chemistry 689 (2004) 917–929
www.elsevier.com/locate/jorganchem
Synthesis and characterization of
N-(2-pyridyl)benzamide-based nickel complexes and their activity
for ethylene oligomerization
a,
a
a
a
a
Wen-Hua Sun *, Wen Zhang , Tielong Gao , Xiubo Tang , Liyi Chen ,
a
Yan Li , Xianglin Jin
b
a
State Key Laboratory of Engineering Plastics and The Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Zhongguancun, Beiyijie, Beijing 100080, China
b
Institute of Physical Chemistry, Peking University, Beijing 100871, China
Received 4 September 2003; accepted 16 December 2003
Abstract
A series of N-(2-pyridyl)benzamides (1)–(11) and their nickel complexes, [N-(2-pyridyl)benzamide]dinickel(II) di-l-bromide
dibromide (12)–(16) and (aryl)[N-(2-pyridyl)benzamido](triphenylphosphine)nickel(II) (17)–(24), were synthesized and character-
ized. The single-crystal X-ray analysis revealed that 12 and 14 are binuclear nickel complexes bridged by bromine atoms and each
nickel atom adopts a distorted trigonal bipyramidal geometry. The key feature of the complexes 17, 19 and 23 is each has a six-
membered nickel chelate ring including a deprotonated secondary nitrogen atom and an O-donor atom. The nickel complexes show
moderate to high catalytic activity for ethylene oligomerization with methylaluminoxane (MAO) as cocatalyst. The activity of 12–
16/MAO systems is up to 3.3 ꢀ 104 g molꢁ1 hꢁ1 whereas for 17–24/MAO systems it is up to 4.94 ꢀ 105 g molꢁ1 atmꢁ1 ꢁ1. The
h
influence of Al/Ni molar ratio, reaction temperature, reaction period and PPh3/Ni molar ratio on catalytic activity was investigated.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: N-(2-Pyridyl)benzamide ligand; Nickel complexes; Crystal structures; Ethylene oligomerization
1. Introduction
nickel(II) catalysts is the SHOP-type [12–18]. These
nickel complexes contain an anionic [P, O] chelate ring
and show high activity and selectivity for the conversion
of ethylene to linear a-olefins and polymers. Neutral
nickel(II) catalysts containing anionic [N, O] chelate
ring were also largely reported in recent years [19–24].
One such type of catalyst is the neutral salicylaldimine
nickel complex, reported by GrubbsÕ group, having the
highest activity of 1.3 ꢀ 105 mol ethylene (mol Ni h)ꢁ1
for ethylene polymerization [21]. In addition, other li-
gands such as phosphinooxazoline [25], dithio-b-diket-
onate [26], iminophosphine [27], monoiminopyridine
[28], bis(pyrazolyl)methane [29], a-nitroketonate [30],
bis(2-diphenylphosphinoethyl)methylamine [31], etc.
have also been employed with late-metals as homoge-
neous catalysts.
The past decade has witnessed a significant progress
in late-metal complexes for oligomerization and poly-
merization of olefins [1–6]. a-Diimine nickel/palladium
complexes and bis(imino)pyridyl iron/cobalt complexes
are the two kinds of well-known catalysts [7,8] used for
oligomerization/polymerization of olefins. By tuning the
steric and electronic properties of the active center, the
catalytic products of the metal complexes differently
suitable for polyethylene and oligomers [9–11] can be
obtained. Recently, neutral nickel(II) complexes have
attracted much attention because they are less sensitive
to protonic solvents and polar monomers than cationic
nickel analogues. The most famous example of neutral
* Corresponding author. Tel.: +861062557955; fax: +861062618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
In exploring new catalysts for ethylene activation in our
laboratory, nickelcomplexescontaining8-aminoquinoline,
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.12.022

918
W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
2-(2-pyridyl)quinoxaline, 2,6-bis(imino)phenol, 2,9-bis-
(imino)-1,10-phenathroline and hydrazone derivatives
were investigated [32]. To the best of our knowledge, there
is no report on using pyridylcarboxamide metal com-
plexes for ethylene oligomerization. In this paper, N-(2-
pyridyl)benzamides (1)–(11) and their two kinds of nickel
complexes 12–24 were synthesized and characterized, and
the catalytic properties of these complexes for ethylene
oligomerization are reported.
When dried in vacuo, the Na salt was combined with
trans-[NiCl(Naph)(PPh3)2] or trans-[NiCl(Ph)(PPh3)2]
in toluene. The mixture was stirred at room temperature
for several hours resulting a clear solution. After filtra-
tion, concentration and precipitation by pentane, the
crude product was obtained in satisfactory yield. Com-
plexes 17–24 are all air-stable yellow to red powders and
highly soluble in toluene, CH2Cl2 and CHCl3, and in-
soluble in alkanes. The naphthyl-containing complexes
17–22 are very stable in solutions when exposed to air,
but the phenyl-containing complexes 23–24 soon de-
composed in solution after several hours.
2. Results and discussion
In IR spectra of 1–5, the weak and broad bands ob-
served between 3183 and 3343 cmꢁ1 are ascribed to the
stretching vibration of N–H. The 1H NMR spectra
show a broad singlet peak in the range 8.05–8.65 ppm
confirming the existence of the hydrogen of secondary
amide. In IR spectra of the corresponding complexes
12–16, the strong absorption bands in the range 1624
and 1636 cmꢁ1 are ascribed to the C@O stretching vi-
bration. However, these values are found to be higher
field (1652–1677 cmꢁ1) for the original ligands 1–5. The
stretching vibration of pyridine ring at 1421–1459 cmꢁ1
for 1–5 shifted to 1446–1461 cmꢁ1 for their corre-
sponding complexes 12–16. This spectral data show that
the nickel atom coordinates with the nitrogen atom of
the pyridyl ring and the oxygen atom of the carbonyl
group. In far infrared spectra of the complexes, the
absorption bands between 123 and 95 cmꢁ1 are ascribed
to bridging Br–Ni stretching vibrations and bands be-
tween 237 and 185 cmꢁ1 to terminal Br–Ni stretching
vibrations [34]. These observations reveal that the
complexes have a binuclear structure in solid state,
which is confirmed by X-ray analysis of 12 and 14.
In IR spectra of 17–24, a group of strong bands ap-
pears in the range 1300–1600 cmꢁ1 for the stretching
vibration of aromatic rings, and there are no C@O
stretching vibrations of the corresponding ligands in the
range 1659–1691 cmꢁ1. In 31P NMR spectra of naph-
2.1. Synthesis and spectroscopic characterization
Compounds 1–11 were prepared in good yields
through the condensation reaction of 2-aminopyridines
and benzoic chloride or 4-nitrobenzoic chloride ac-
cording to a modified procedure [33]. The reaction was
smoothly performed in pyridine at room temperature.
The resulting mixtures were quenched with water, fil-
tered, and the white solid was thoroughly washed with
1
water and dried in vacuum oven over night. H NMR
spectra and elemental analyses showed the products
were pure enough for subsequent reactions.
The nickel complexes 12–16 were synthesized by
mixing the THF solutions of (DME)NiBr2 (DME ¼
ethylene glycol dimethyl ether) and the corresponding
ligands 1–5, respectively (see Scheme 1). The resulting
complexes were precipitated from reaction solutions
after several minutes. They are all air-stable yellow to
yellow-brown powders which can be easily recrystallized
from acetone–ether solutions.
The neutral nickel complexes 17–24 were synthesized
according to a reported method [21a]. When NaH was
added to the THF solution of the corresponding ligand,
many bubbles were produced immediately. The color of
the resulting solution varied from colorless to orange
according to the different substituents on the ligand.
Scheme 1. The synthesis of the nickel complexes 12–24.

W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
919
Table 1
thyl-containing complexes 17–22, the chemical shift of P
ꢀ
Selected bond lengths (A) and angles (°) for 12 and 14
atom is between 28.20 and 28.82 ppm compared to the
value of 22.16 ppm of trans-[NiCl(Naph)(PPh3)2]. It is
affected by the substituent on the pyridyl and phenyl
rings of the ligand as shown in the following order:
19 < 17 < 18 and 22 < 20 < 21. As to the phenyl-con-
taining complexes 23–24, the peak of P atom is at 29.22
and 29.45 ppm, respectively, a little higher than the
values of 17–22. The MALDI-TOF MS of 18 showed
the most abundant peak at m=z 659.4, which is desig-
nated to the ionic molecule (m=z 659.2). This means the
neutral nickel(II) complex is stable in organic solvents.
It is noteworthy that the ortho-alkyl substituent on
the pyridyl ring in 1–11 played an important role for the
formation of the desired nickel complexes. In the reac-
tion of (DME)NiBr2 and other N-(2-pyridyl)benzamide
ligands (L) without alkyl substituent on the ortho-posi-
tion of the pyridyl ring, L2NiBr2-type complexes were
formed with a six-coordinate configuration around the
nickel atom [35]. However, the expected neutral nickel
complexes were not observed by using N-(2-pyr-
idyl)benzamide ligands containing ortho-alkyl sub-
stituent on the pyridyl ring. The reason perhaps may be
the adjacent steric interference between the ortho sub-
stituent and the R group (naphthyl or phenyl).
Complex 12
Complex 14
Bond lengths
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(1)–O(1)
Ni(1)–N(1)
Ni(1)–Br(1A)
2.5874(12) Ni(1)–Br(1)
2.4887(10) Ni(1)–Br(20)
2.4379(15)
2.4744(17)
1.934(6)
1.944(3)
2.029(4)
2.4708(10) Ni(1)–Br(1A)
Ni(1)–O(1)
Ni(1)–N(2)
1.991(6)
2.5700(17)
Bond angles
Ni(1)–Br(1)–Ni(1A) 95.21(3)
O(1)–Ni(1)–N(1) 91.75(13)
Ni(1)–Br(1)–Ni(1A) 95.00(5)
O(1)–Ni(1)–N(2)
O(1)–Ni(1)–Br(1)
93.1(3)
104.67(17)
O(1)–Ni(1)–Br(1A) 97.76(9)
N(1)–Ni(1)–Br(1A) 167.35(11)
N(2)–Ni(1)–Br(1) 160.64(19)
O(1)–Ni(1)–Br(1A) 92.8(2)
N(2)–Ni(1)–Br(1A) 86.54(19)
Br(1)–Ni(1)–Br(1A) 85.00(5)
Br(2)–Ni(1)–Br(1A) 171.05(6)
O(1)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(1)
98.68(11)
85.55(11)
Br(1)–Ni(1)–Br(1A) 84.79(3)
Br(2)–Ni(1)–Br(1) 163.22(3)
Symmetry transformation used to generate equivalent atoms: A
ꢁx; ꢁy; ꢁz for 12; ꢁx; ꢁy þ 2; ꢁz for 14.
trigonal bipyramidal geometry, in which the equatorial
plane contains O(1), Br(1) and Br(2) atoms while the
other two atoms (N(1) and Br(1A)) occupy the axial
positions. The angle of N(1)–Ni(1)–Br(1A) is
167.35(11)° (smaller than 180°), and the Ni(1) atom lo-
ꢀ
cates 0.0163 A above the equatorial plane toward
Br(1A). The six-membered chelating ring of Ni(1)–N(1)–
C(6)–N(2)–C(7)–O(1) is a distorted hexagon where the
bond angle of O(1)–Ni(1)–N(1) is 91.75(13)°. The largest
2.2. Crystal structure
ꢀ
deviation of the plane is 0.0957 A for C(6). The intra-
Single crystals of 12 and 14 suitable for X-ray anal-
ysis were obtained by slow diffusion of ethyl ether into
their acetone solutions. The structure of 12 shows a
centro symmetric dinuclear nickel center (Fig. 1). Each
nickel atom is coordinated by two atoms (O(1) and
N(1)) of the ligand, one terminal bromine atom (Br(2))
and two bridging bromine atoms (Br(1) and Br(1A)).
The bond lengths of Ni(1)–O(1), Ni(1)–N(1), Ni(1)–
Br(1), Ni(1)–Br(2) and Ni(1)–Br(1A) are 1.944(3),
ꢀ
molecular distance of Ni–Ni is 3.736 A, which is longer
ꢀ
than the value of 3.686 A observed in other dinickel
complexes [36]. The ligand is nearly perpendicular to the
Br(1)–N(1)–Br(2)–Br(1A) plane with a dihedral angle of
92.4°.
Complex 14 has a similar structure to its analogue 12.
The bond lengths of Ni(1)–O(1), Ni(1)–N(2), Ni(1)–
Br(1), Ni(1)–Br(1A) and Ni(1)–Br(2) vary in the range
ꢀ
ꢀ
ꢀ
1.934(6)–2.570(2) A. The nickel atom locates 0.0011 A
above the equatorial plane of O(1), Br(1A) and Br(2),
toward Br(1). The bond angle of O(1)–Ni(1)–N(2) is
93.1(3)° in the six-membered chelating ring of Ni(1)–
N(2)–C(8)–N(1)–C(7)–O(1). The intramolecular dis-
2.029(4), 2.587(1), 2.489(1) and 2.471(1) A, respectively
(Table 1). The nickel atom adopts a slightly distorted
ꢀ
ꢀ
tance of Ni–Ni is 3.693 A, which is 0.043 A shorter than
that in 12. These differences between the two complexes
derive from the different ortho-alkyl substituent of the
pyridyl ring of them, i.e., ethyl group in 14 and methyl
group in 12.
In addition, hydrogen bonds are observed between
terminal bromine atom and hydrogen atom of the sec-
ondary amide in the solid state of 12 and 14. The 1-D
chain diagram of 12 is shown in Fig. 2. In 12, the hy-
drogen bond angle of N(2)–H(21)ꢂ ꢂ ꢂBr(2#) (#:
ꢁx; ꢁy; 1 ꢁ z) is 164(4)°. The distance of Hꢂ ꢂ ꢂBr is
ꢀ
ꢀ
2.60(5) A and N(H)ꢂ ꢂ ꢂBr is 3.560(4) A. In 14, the hy-
drogen bond angle of N(1)–H(15)ꢂ ꢂ ꢂBr(2#) (#:
ꢁx; 2 ꢁ y; ꢁ1 ꢁ z) is 160(11)°. The distance of Hꢂ ꢂ ꢂBr is
Fig. 1. Molecular structure of 12, showing 30% probability displace-
ment ellipsoids with hydrogen atoms omitted for clarity.

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W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
In 17, the nickel center adopts a square planar ge-
ometry. The PPh3 ligand takes the trans position to the
nitrogen atom of the pyridyl ring. The bond lengths of
Ni(1)–O(1), Ni(1)–N(1), Ni(1)–C(13) are found to be
ꢀ
similar with a value of 1.9 A while the Ni(1)–P(1) length
ꢀ
is 2.191(2) A. The pyridyl ring is nearly perpendicular to
the naphthyl ring with a dihedral angle of 81.3°. Obvi-
ously the repulsion between the two rings and the
bulkiness of the PPh3 ligand enlarge the bond angle of
C(13)–Ni(1)–N(1) to 95.26(18)° and reduce the bond
angles of O(1)–Ni(1)–P(1) and C(13)–Ni(1)–P(1) to
84.69(9)° and 87.90(14)°, respectively. The bond lengths
of O(1)–C(6), N(2)–C(6) and N(2)–C(5) are 1.275(4),
Fig. 2. The 1-D chain of 12.
ꢀ
ꢀ
2.81(10) A and N(H)ꢂ ꢂ ꢂBr is 3.575(7) A. The interaction
of hydrogen bonds between the two neighboring mole-
cules forms a 1-D infinite chain in the solid state struc-
tures of 12 and 14.
Single crystals of 17, 19 and 23 suitable for X-ray
analysis were obtained by slow diffusion of pentane into
toluene solutions. The structures of 17 and 23 are shown
in Figs. 3 and 4, respectively. The selected bond lengths
and angles are listed in Table 2.
ꢀ
1.299(4) and 1.366(5) A, respectively. They are shorter
ꢀ
than the typical single bond lengths (C–O 1.36 A and C–
ꢀ
N 1.45 A) but longer than the typical double bond
ꢀ
ꢀ
lengths (C@O 1.22 A and C@N 1.27 A). It means that
after the deprotonation of the ligand, the electron on the
amide nitrogen partly delocalizes on the chelate ring
O(1)–C(6)–N(2)–C(5)–N(1).
19 has a similar structure as 17, but the existence of
the nitro group on the 5-position of the pyridyl ring
exerts some influence on the bond lengths and angles.
The dihedral angle of the pyridyl ring and the naphthyl
ring is 100.3°, which is higher compared to the value of
17. The bond angle of C(13)–Ni(1)–N(1) increases a
little to 96.6(4)° while the values of O(1)–Ni(1)–P(1)
and C(13)–Ni(1)–P(1) are nearly equal (86.6(2)° and
86.3(3)°). The bond lengths of O(1)–C(6), N(2)–C(6) and
N(2)–C(1) of the chelate ring O(1)–C(6)–N(2)–C(5)–
ꢀ
N(1) are 1.240(8), 1.324(9) and 1.336(9) A. The little
difference of the bond lengths between O(1)–C(6) and
O@C shows that the double bond is largely kept be-
tween O(1) and C(6).
As to 23, the bond lengths between the nickel center
and coordination atoms change little compared to 17
and 19. The dihedral angle between the pyridyl ring and
the phenyl ring is 99.9°. The repulsion between the two
rings is less than that in 17 and 19, i.e., the bond angle of
C(13)–Ni(1)–N(1) changes to 93.75(9)° and the bond
angles of O(1)–Ni(1)–P(1) and C(13)–Ni(1)–P(1) change
to 86.24(5)° and 88.51(7)°, respectively. The bond
lengths of O(1)–C(6), N(2)–C(6) and N(2)–C(1) are
Fig. 3. Molecular structure of 17, showing 15% probability displace-
ment ellipsoids with hydrogen atoms omitted for clarity.
ꢀ
1.269(3), 1.314(3) and 1.347(3) A, respectively. Similar
to 17 and 19, the electron on the amide nitrogen of 23
partly delocalizes on the chelate ring O(1)–C(6)–N(2)–
C(1)–N(1).
2.3. Mass spectroscopy
Although the solid state structures of 12–16 were
confirmed by IR spectra and X-ray analysis, it is not
clear what kind of species really exist in solution. The
relatively weak interactions of the carbonyl oxygen
atom and the bridging bromine atoms with the nickel
atom would be somewhat destroyed by the solvents.
Fig. 4. Molecular structure of 23, showing 30% probability displace-
ment ellipsoids with hydrogen atoms omitted for clarity.

W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
921
Table 2
Selected bond lengths (A) and angles (°) for complex 17, 19 and 23
ꢀ
Complex 17
Complex 19
Complex 23
Bond lengths
Ni(1)–O(1)
Ni(1)–C(13)
Ni(1)–N(1)
Ni(1)–P(1)
O(1)–C(6)
N(2)–C(6)
N(2)–C(5)
1.865(3)
1.938(6)
1.951(3)
2.1908(15)
1.275(4)
1.299(4)
1.366(5)
Ni(1)–O(1)
Ni(1)–C(13)
Ni(1)–N(1)
Ni(1)–P(1)
O(1)–C(6)
N(2)–C(6)
N(2)–C(1)
1.874(5)
1.951(13)
1.976(6)
2.189(2)
1.240(8)
1.324(9)
1.336(9)
Ni(1)–O(1)
Ni(1)–C(13)
Ni(1)–N(1)
Ni(1)–P(1)
O(1)–C(6)
N(2)–C(6)
N(2)–C(1)
1.888(2)
1.887(2)
1.974(2)
2.1816(8)
1.269(3)
1.314(3)
1.347(3)
Bond angles
O(1)–Ni(1)–C(13)
O(1)–Ni(1)–N(1)
C(13)–Ni(1)–N(1)
O(1)–Ni(1)–P(1)
C(13)–Ni(1)–P(1)
N(1)–Ni(1)–P(1)
C(6)–N(2)–C(5)
O(1)–C(6)–N(2)
171.6(2)
O(1)–Ni(1)–C(13)
O(1)–Ni(1)–N(1)
C(13)–Ni(1)–N(1)
O(1)–Ni(1)–P(1)
C(13)–Ni(1)–P(1)
N(1)–Ni(1)–P(1)
C(6)–N(2)–C(1)
O(1)–C(6)–N(2)
172.4(4)
90.5(3)
96.6(4)
O(1)–Ni(1)–C(13)
O(1)–Ni(1)–N(1)
C(13)–Ni(1)–N(1)
O(1)–Ni(1)–P(1)
C(13)–Ni(1)–P(1)
N(1)–Ni(1)–P(1)
C(6)–N(2)–C(1)
O(1)–C(6)–N(2)
174.57(9)
92.10(13)
95.26(18)
84.69(9)
91.37(8)
93.75(9)
86.24(5)
88.51(7)
174.71(6)
123.9(2)
127.5(2)
86.63(17)
86.3(3)
87.90(14)
176.74(12)
124.2(3)
177.0(3)
120.7(7)
128.1(8)
126.6(4)
Mass spectroscopy of 12 in methanol and acetone were
studied. The results are presented in Table 3.
2.4. Ethylene oligomerization
2.4.1. Catalytic activity and oligomer distribution
From the ESI-MS values of the methanol solution of
12 ([L2Ni2Br4]), it is clearly evident that the relative
abundance of the binuclear species ([L2Ni2Br3]þ) is as
low as 5%. The mononuclear species ([LNiBr]þ) and its
methanol adduct ([LNiBr + CH3OH]þ) also have low
abundance with the values of 5% and 10%. The most
abundant species is the protonated ligand ([L + H]þ),
indicating the decomposition of the complex. [L2NiBr]þ
and [L2Ni–H]þ have high abundance (48% and 80%) in
methanol, suggesting that the [L2NiBr2] species is
formed in the course. The MALDI-TOF-MS of 12 re-
vealed a different map of the species existing in acetone.
The strongest peak of the species is at m=z 619.4, which
is ascribed to [L2NiBr + CH3COCH3]þ (calc. m=z 621.1).
There is no sign of the protonated ligand ([L + H]þ).
Owing to the insolubility of 12 in toluene, we could
not get a full knowledge of the real species of the com-
plex in toluene when performing ethylene oligomeriza-
tion. But the MS of 12 in polar solutions help us draw a
conclusion that the ligand would coordinate nickel atom
rather tightly and the binuclear species would be de-
composed into mononuclear species in a large degree.
The influence of cocatalyst MAO on catalytic activi-
ties and the distribution of resulting oligomers of 12–24
were carefully investigated. The results are summarized
in Table 4.
Most complexes show good activity in the Al/Ni
molar ratio of 300–1000. 18 showed the highest catalytic
activity of 4.94 ꢀ 105 g molꢁ1 atmꢁ1 hꢁ1 at the Al/Ni
molar ratio of 1000 at 22 °C. Reaction temperature
exerted great influence on catalytic activities of 12–24.
Optimal catalytic activities were observed between 18
and 40 °C.
The change of ligands also clearly affects the activity
of the corresponding complexes, i.e., the additional alkyl
substituents on the pyridine ring impaired the catalytic
activity for ethylene oligomerization. Under the mild
catalytic conditions (Al/Ni 500, reaction temperature 18
°C), 14 with 6-ethyl group on pyridyl ring showed a
catalytic activity of 3.3 ꢀ 104 g molꢁ1 hꢁ1 while 13 with
4,6-dimethyl groups on pyridyl ring showed a relatively
lower value of 1.3 ꢀ 104 g molꢁ1 ꢁ1. 15 and 16 con-
h
taining NO2-substituent on pyridine ring show relatively
Table 3
MS-species of 12 in methanol and acetone
Complex 12a (methanol)
m=z Calc. (found)
Abundance (%)
Complex 12b (acetone)
m=z Calc. (found)
Abundance (%)
[L2Ni2Br3]þ
[L2NiBr]þ
[L2Ni–H]þ
[LNiBr + CH3OH]þ
[LNiBr]þ
[L2Ni]2þ
[L + H]þ
780.8 (781.0)
563.0 (563.2)
481.1 (481.3)
383.0 (383.1)
350.9 (351.1)
241.1 (241.2)
213.1 (213.2)
5
48
80
10
5
[L2Ni2Br3]þ
780.8 (781.2)
701.9 (702.2)
621.1 (619.4)
510.8 (510.6)
390.4 (389.2)
9
10
[L2Ni2Br2–H]þ
[L2NiBr + CH3COCH3]þ
[LNiBr3]þ
100
21
[L2Ni2Br3]2þ
16
80
100
a ESI-MS.
b MALDI-TOF-MS.

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W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
Table 4
Ethylene oligomerization using 12–24/MAO systems and their oligomersÕ distribution
Distribution of oligomers (%)b
Entry
Complexa
Al/Ni (mol/mol)
Temp (°C)
Activity (104 g molꢁ1 hꢁ1
)
C4
C6
1
2
12
13
14
14
14
14
14
14
14
14
15
16
17
18
18
18
18
18
18
18
18
18
18
19
20
21
22
23
24
500
300
18
18
18
18
18
18
18
0
2.0
1.3
78
93
83
83
84
76
83
88
80
84
86
86
84
93
92
88
88
87
90
97
83
76
82
92
90
88
86
85
86
22
7
3
100
300
3.8
3.9
17
17
16
24
17
12
20
16
14
14
16
7
4
5
500
3.3
4.6
6
1000
2000
500
7
2.9
0.7
8
9
500
500
40
60
18
18
40
22
22
22
22
22
22
0
1.2
0.8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
300
3.1
2.1
1000
1000
100
33.3
0.8
300
500
10.9
41.9
49.4
36.2
23.9
16.7
33.7
21.3
7.4
8
12
12
13
10
3
1000
1500
2000
1000
1000
1000
1000
300
40
60
80
23
24
24
25
28
28
17
24
18
8
22.3
20.9
35.7
18.8
22.3
20.8
500
10
12
14
15
14
1000
2000
1000
1000
a Reaction condition: entry 1–12: 5 lmol catalyst, 40 ml toluene, 1 h, 1 atm ethylene; entry 13–29: 5 lmol catalyst, 30 ml toluene, 0.5 h, 1 atm
ethylene.
b Using toluene (entry 1–12) and pentane (13–29) as internal standard.
higher catalytic activity than the corresponding com-
plexes 12 and 13. These results agreed well with com-
putational conclusion on the relationship of catalytic
activity and net charge of late-transition metal com-
plexes [37]. As to 17–24, the introduction of nitro-group
into the ligands impaired the catalytic activity of the
corresponding complexes. The orders of the activity are
18 > 17 > 19, 21 > 22, 23 > 24 and 18 > 21.
hꢁ1 in 120 min, however, its activity was completely lost
in 3 h. The content of C4 decreased regularly from 92%
to 80% in the oligomers produced.
Table 5
Dependence of reaction time on catalytic activity
Entry Complexa Time
(min)
Activity
(104 g molꢁ1 hꢁ1
Distribution of
oligomers (%)b
)
C4
C6
The oligomerization products of 12–24 are mainly C4
and C6. In 14/MAO system, C4 is distributed in 40% of
2-methylpropene and 60% of trans-2-butene, while C6 in
6% of 3-methylpentene, 8% of 1-hexene and 86% of in-
ternal olefins (50% of 3-hexene, 10% of 2-hexene and
26% of 3-methyl-2-pentene). The b-hydrogen elimina-
tion and chain transformation perhaps play a major role
for the distribution of oligomers.
The dependence of catalytic activity on reaction time
was studied using 14 and 18/MAO systems (Table 5).
The catalytic activity of 14 decreased from 3.1 ꢀ 104 g
molꢁ1 hꢁ1 in 10 min to 1.2 ꢀ 104 g molꢁ1 hꢁ1 in 120 min,
and remained active in following hours with a little de-
crease. As to 18, its activity decreased from 15.2 ꢀ 105 g
molꢁ1 atmꢁ1 hꢁ1 in 5 min to 2.11 ꢀ 105 g molꢁ1 atmꢁ1
1
2
3
4
5
6
7
8c
9
14
14
14
14
14
18
18
18
18
18
18
10
30
60
90
120
5
3.1
2.3
88
87
87
85
87
92
86
88
81
82
80
12
13
13
15
13
8
1.9
1.3
1.2
152
94.8
49.4
31.3
20.9
21.1
15
30
60
90
120
14
12
19
18
20
10
11
a Reaction condition: entry (1–5) 5 lmol catalyst, 40 ml toluene, Al/
Ni 500, 1 h, 25 °C, 1 atm ethylene; entry (6–11) 5 lmol catalyst, 30 ml
toluene, Al/Ni 1000, 1 h, 30 °C, 1 atm ethylene.
b Using toluene (entry 1–5) and pentane (entry 6–11) as internal
standard.
c Reaction temperature, 22 °C.

W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
923
2.4.2. Effect of the addition of PPh3
atom. In fact, the new species is a kind of neutral nickel
complex [39].
The effect of PPh3 on the ethylene oligomerization
was investigated using 14/MAO system and compared
with (DME)NiBr2 (Table 6). The catalytic activity of 14
This proposal was confirmed by the syntheses of the
neutral complexes 17–24. It is noticeable that the cata-
lytic activity of the neutral nickel complexes is com-
monly one order of amount higher than the values of the
dinickel complexes. The effect of PPh3 was also tested
using 18/MAO system. With the increase of the P/Ni
molar ratio from 1 to 20, the catalytic activity of 18
continuously decreased from 4.82 ꢀ 105 to 1.39 ꢀ 105 g
was much improved from 3.3 ꢀ 104 to 1.94 ꢀ 105
g
molꢁ1 hꢁ1 when PPh3 was added. At the same time, a
small amount of octenes (ca. 3%) appeared. In com-
parison, the catalytic activity of (DME)NiBr2 is very
low with values of 0.8–5.4 ꢀ 104 g molꢁ1 hꢁ1
.
In order to elucidate the function of PPh3, 31P NMR
spectra of the reaction system of 14 were examined.
When one equivalent of PPh3 was added into the tolu-
ene solution of the complex, the color of the solution
turned from pale yellow to yellow. The 31P NMR
spectrum showed two peaks at )3.95 and 21.36 ppm,
which were attributed to the resonance of free and co-
ordinated PPh3, respectively. The injection of MAO into
the reactor made the color of the solution turned to
bright brown. In 31P NMR spectrum, the peak of free
PPh3 disappeared and a new peak at 37.69 ppm ap-
peared while the peak at 21.36 ppm shifted slightly to
20.93 ppm. The uptake of ethylene took place slowly at
the beginning and accelerated after several minutes.
The existence of the auxiliary PR3 ligand for the
SHOP-type catalysts mainly resulted in the stabilization
of the catalytic species [38] and a further report claimed
its influence on the ethylene oligomerization [12f]. So we
guess that a new kind of catalytic active species is
formed during the catalytic process of 14/MAO system.
At the beginning of the reaction, some portion of PPh3
coordinates to the nickel atom. The addition of MAO
depletes the weak acidic amide hydrogen of the ligand
and the catalytic active species is formed by the delo-
calization of the electron on the amide nitrogen to the
chelate ring and the coordination of PPh3 on nickel
molꢁ1 atmꢁ1 ꢁ1. At the same time, the content of C4
h
increased from 76% to 95%.
3. Experimental
3.1. General procedures
All manipulations for moisture-sensitive compounds
were carried out under an atmosphere of nitrogen using
standard Schlenk techniques. Melting points (MP) were
determined with a digital electrothermal apparatus
without calibration. The IR spectra were recorded on a
Perkin–Elmer FT-IR 2000 spectrophotometer using
KBr disc in the range of 4000–400 cmꢁ1 and on a Nic-
olet Magna-IR 750 in the range of 650–50 cmꢁ1. The 1H
NMR spectra were recorded on a Bruker DMX-300
instrument with TMS as the internal standard. The 31P
NMR spectra were recorded on a Varian XL-200 in-
strument with H3PO4 (85%) as the external standard.
Splitting patterns are designated as follows: s, singlet; bs,
broad singlet; d, doublet; dd, double doublet; t, triplet;
m, multiplet. The elemental analyses were performed on
a Flash EA 1112 microanalyzer. The ESI-MS was re-
corded on a Shimadzu LCMS-2010 spectrometer. The
Table 6
Effects of the addition of Ph3P on ethylene oligomerization
Distribution of oligomers (%)e
Entry
Complex
PPh3/Ni (mol/mol)
Activity (104 g molꢁ1 hꢁ1
)
C4
C6
C8
1
2
14a
0
0.5
1
3.3
12.8
19.4
10.1
6.6
84
84
74
94
93
89
91
76
78
86
92
95
16
13
23
4
14b
3
3
2
1
3
14b
14b
4
5
5
14b
(DME)NiBr2
10
0
6
c
c
6
0.8
5.4
11
9
7
(DME)NiBr2
1
8
18d
18d
18d
18d
18d
1
48.2
43.6
36.3
17.1
13.9
24
22
14
8
9
2
10
11
12
5
10
20
5
a Reaction condition: 5 lmol catalyst, 40 ml toluene, Al/Ni 500, 1 h, 18 °C, 1 atm ethylene.
b Reaction condition: 5 lmol catalyst, 40 ml toluene, Al/Ni 500, 1 h, 25 °C, 1 atm ethylene.
c Reaction condition: 10 lmol catalyst, 30 ml toluene, Al/Ni 1000, 1 h, 25 °C, 1 atm ethylene.
d Reaction condition: 5 lmol catalyst, 30 ml toluene, Al/Ni 1000, 0.5 h, 30 °C, 1 atm ethylene.
e Using toluene (entry 1–7) and pentane (entry 8–12) as internal standard.

924
W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
MALDI-TOF MS was recorded on a Bruker BIFLEX
III spectrometer. Distribution of oligomers obtained was
measured on a Varian VISTA 6000 GC spectrometer and
a HP 5971A GC-MS detector.
THF and toluene were refluxed over sodium-benzo-
phenone until purple color appeared and distilled under
nitrogen atmosphere prior to use. CH2Cl2 and pentane
were distilled under nitrogen from CaH2. Pyridine was
1601 (m), 1538 (m), 1449 (s), 1308 (s), 812 (s), 714 (s). 1H
NMR (300 MHz, CDCl3/ppm): 1.34 (t, 3H, J ¼ 7:61
Hz, CH3), 2.78 (dd, 2H, J ¼ 7:60 Hz, CH2), 6.99 (d, 1H,
J ¼ 7:50 Hz), 7.58 (m, 3H), 7.72 (t, 1H, J ¼ 7:87 Hz),
7.99 (d, 2H, J ¼ 7:36 Hz), 8.24 (d, 1H, J ¼ 8:23 Hz),
8.65 (bs, 1H, NH). Anal. Calc. for C14H14N2O (226.27):
C, 74.31; H, 6.24; N, 12.38. Found: C, 74.32; H, 6.22; N,
12.34%.
ꢀ
dried over solid KOH and kept with 4 A molecule sieves.
NaH was washed with pentane (3 ꢀ 20 ml) and dried
before use. trans-[NiCl(Naph)(PPh3)2] [40] and trans-
[NiCl(Ph)(PPh3)2] [41] were prepared according to lit-
erature procedure. (DME)NiBr2 and 2-aminopyridines
were purchased from Alfa Aesar and Aldrich Chem. Co.,
respectively. Methylaluminoxane (MAO, 1.4 mol lꢁ1
in toluene) was purchased from Albemarle Corp.
(USA). All other chemicals were obtained commercially
and used without further purification unless stated
otherwise.
3.2.4. N-(6-Methyl-2-pyridyl)-4-nitrobenzamide (4)
In a similar manner as described for 1, the compound
4 was prepared from 2-amino-6-methylpyridine and 4-
nitrobenzoic chloride as white solid in 97% yield (2.50
g). MP: 130–131 °C. FT-IR (KBr disc, cmꢁ1): 3343 (m),
1653 (s), 1602 (s), 1528 (s), 1453 (s), 1349 (m), 854 (m),
1
791 (m), 716 (m). H NMR (300 MHz, CDCl3/ppm):
2.49 (s, 3H, CH3), 6.99 (d, 1H, J ¼ 7:49 Hz), 7.69 (t, 1H,
J ¼ 7:91 Hz), 8.10 (d, 2H, J ¼ 8:59 Hz), 8.16 (d, 1H,
J ¼ 8:24 Hz), 8.36 (d, 2H, J ¼ 8:78 Hz), 8.58 (bs,
1H, NH). Anal. Calc. for C13H11N3O3 (257.24): C,
60.70; H, 4.31; N, 16.33. Found: C, 60.02; H, 4.24; N,
15.95%.
3.2. Synthesis of N-(2-pyridyl)benzamides
3.2.1. N-(6-Methyl-2-pyridyl)benzamide (1)
3.2.5. N-(4,6-Dimethyl-2-pyridyl)-4-nitrobenzamide (5)
In a similar manner as described for 1, the compound
5 was prepared from 2-amino-4,6-dimethylpyridine and
4-nitrobenzoic chloride as white solid in 83% yield (2.24
g). MP: 156–158 °C. FT-IR (KBr disc, cmꢁ1): 3326 (w),
1655 (s), 1606 (w), 1526 (s), 1439 (s), 1345 (s), 1285 (w),
Benzoic chloride (1.41 g, 1.2 ml, 10 mmol) in 10 ml of
THF was added dropwise to the solution of 2-amino-6-
methylpyridine (1.08 g, 10 mmol) in 10 ml of dry pyri-
dine at 20 °C. The reaction mixture was stirred for 12 h
at room temperature and quenched in water (400 ml) to
afford a white solid in 99% yield (2.05 g). MP: 78–80 °C.
FT-IR (KBr disc, cmꢁ1): 3192 (m), 1677 (s), 1577 (s),
1
849 (m), 716 (m). H NMR (300 MHz, CDCl3/ppm):
2.38 (s, 3H, CH3), 2.43 (s, 3H, CH3), 6.83 (s, 1H), 8.01
(s, 1H), 8.09 (d, 2H, J ¼ 8:75 Hz), 8.35 (d, 2H, J ¼ 8:65
Hz), 8.57 (bs, 1H, NH). Anal. Calc. for C14H13N3O3
(271.27): C, 61.99; H, 4.83; N, 15.49. Found: C, 61.59;
H, 4.80; N, 15.49%.
1
1459 (s), 1304 (s), 1129 (m), 790 (m), 719 (m). H NMR
(300 MHz, CDCl3/ppm): 2.47 (s, 3H, CH3), 6.94 (d, 1H,
J ¼ 7:43 Hz), 7.53 (m, 3H), 7.66 (t, 1H, J ¼ 7:85 Hz),
7.94 (d, 2H, J ¼ 7:61 Hz), 8.20 (d, 1H, J ¼ 8:29 Hz),
8.62 (bs, 1H, NH). Anal. Calc. for C13H12N2O (212.25):
C, 73.56; H, 5.70; N, 13.20. Found: C, 73.77; H, 5.73; N,
12.98%.
3.2.6. N-(2-Pyridyl)benzamide (6)
In a similar manner as described for 1, the compound
6 was prepared from 2-aminopyridine and benzoic
chloride as white solid in 63% yield (1.24g). MP: 68–70
°C. FT-IR (KBr disc, cmꢁ1): 3170 (br), 1674 (s), 1580
3.2.2. N-(4,6-Dimethyl-2-pyridyl)benzamide (2)
In a similar manner as described for 1, the compound
2 was prepared from 2-amino-4,6-dimethylpyridine and
benzoic chloride as white solid in 63% yield (1.43 g).
MP: 128–130 °C. FT-IR (KBr disc, cmꢁ1): 3183 (w),
1676 (s), 1614 (m), 1567 (s), 1421 (s), 1282 (s), 846 (w),
1
(s), 1531 (s), 1435 (s), 1305 (s), 777 (m), 722 (m). H
NMR (300 MHz, CDCl3/ppm): 7.09 (t, 1H, J ¼ 6:10
Hz), 7.45 –7.62 (m, 3H), 7.78 (t, 1H, J ¼ 7:47 Hz), 7.95
(d, 2H, J ¼ 7:48 Hz), 8.30 (d, 1H, J ¼ 4:72 Hz), 8.42 (d,
1H, J ¼ 8:33 Hz), 8.69 (bs, 1H, NH). Anal. Calc. for
C12H10N2O (198.22): C, 72.71; H, 5.08; N, 14.13.
Found: C, 72.88; H, 5.05; N, 13.83%.
1
706 (s). H NMR (300 MHz, CDCl3/ppm): 2.37 (s, 3H,
CH3), 2.43 (s, 3H, CH3), 6.78 (s, 1H), 7.52 (m, 3H), 7.93
(d, 2H, J ¼ 7:31 Hz), 8.05 (s, 1H), 8.45 (bs, 1H, NH).
Anal. Calc. for C14H14N2O (226.27): C, 74.31; H, 6.24;
N, 12.38. Found: C, 74.43; H, 6.24; N, 12.17%.
3.2.7. N-(4-Methyl-2-pyridyl)benzamide (7)
In a similar manner as described for 1, the compound
7 was prepared from 2-amino-4-methylpyridine and
benzoic chloride as white solid in 50% yield (1.07 g).
MP: 106–108 °C. FT-IR (KBr disc, cmꢁ1): 3308 (s), 1661
3.2.3. N-(6-Ethyl-2-pyridyl)benzamide (3)
In a similar manner as described for 1, the compound
3 was prepared from 2-amino-6-ethylpyridine and ben-
zoic chloride as white solid in 78% yield (1.76 g). MP:
80–82 °C. FT-IR (KBr disc, cmꢁ1): 3280 (m), 1652 (s),
1
(s), 1535 (s), 1411 (s), 1301 (s), 1164 (m), 705 (s). H
NMR (300 MHz, CDCl3/ppm): 2.44 (s, 3H, CH3), 6.93

W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
925
(d, 1H, J ¼ 5:03 Hz), 7.50–7.63 (m, 3H), 7.96 (d, 2H,
3.3. Synthesis of complexes
J ¼ 7:28 Hz), 8.14 (d, 1H, J ¼ 5:10 Hz), 8.28 (s, 1H),
8.74 (bs, 1H, NH). Anal. Calc. for C13H12N2O (212.25):
C, 73.56; H, 5.70; N, 13.20. Found: C, 73.74; H, 5.73; N,
12.84%.
3.3.1. [N-(6-Methyl-2-pyridyl)benzamide]dinickel(II) di-
l-bromide dibromide (12)
A solution of the ligand 1 (240 mg, 1.1 mmol) in THF
(10 ml) was added to the solution of (DME)NiBr2 (308
mg, 1 mmol) in THF (60 ml). The mixture was stirred at
room temperature for 12 h. The resulting precipitate was
filtered, washed with 5 ml of THF and dried in vacuo to
result a yellow powder in 83% yield (357 mg). MP: 290
°C (dec.). FT-IR (KBr disc, cmꢁ1): 3273 (br), 1626 (s),
1577 (w), 1533 (s), 1461 (m), 1417 (w), 1315 (m), 1228
(w), 797 (m), 706 (s), 237 (s), 111 (m). Anal. Calc. for
C26H24Br4N4Ni2O2 (861.50): C, 36.25; H, 2.81; N, 6.50.
Found: C, 36.99; H, 2.87; N, 6.59%.
3.2.8. N-(5-Nitro-2-pyridyl)benzamide (8)
In a similar manner as described for 1, the compound
8 was prepared from 2-amino-5-nitropyridine and ben-
zoic chloride as white solid in 96% yield (2.15g). MP:
165–167 °C. FT-IR (KBr disc, cmꢁ1): 3347 (m), 1689 (s),
1601 (s), 1514 (s), 1395 (m), 1343 (s), 1234 (s), 1120 (s),
1
852 (m), 716 (m). H NMR (300 MHz, CDCl3/ppm):
7.55 (t, 2H, J ¼ 7:49 Hz), 7.64 (t, 1H, J ¼ 7:21 Hz), 7.95
(d, 2H, J ¼ 7:61 Hz), 8.58 (m, 2H), 8.94 (bs, 1H, NH),
9.16 (s, 1H). Anal. Calc. for C12H9N3O3 (243.22): C,
59.26; H, 3.73; N, 17.28. Found: C, 59.22; H, 3.72; N,
16.91%.
3.3.2.[N-(4,6-Dimethyl-2-pyridyl)benzamide]dinickel(II)
di-l-bromide dibromide (13)
In a similar manner described for 12, the compound
13 was obtained from (DME)NiBr2 and ligand 2 as an
orange-red powder in 68% yield (303 mg). MP: 300 °C
(dec.). FT-IR (KBr disc, cmꢁ1): 3243 (br), 1629 (s), 1575
(s), 1530 (s), 1459 (s), 1310 (m), 847 (m), 706 (s), 231 (s),
95 (m). Anal. Calc. for C28H28Br4N4Ni2O2 (889.55): C,
37.81; H, 3.17; N, 6.30. Found: C, 37.57; H, 3.16; N,
6.18%.
3.2.9. N-(2-Pyridyl)-4-nitrobenzamide (9)
In a similar manner as described for 1, the compound
9 was prepared from 2-aminopyridine and 4-nitroben-
zoic chloride as white solid in 55% yield (1.25g). MP:
236–238 °C. FT-IR (KBr disc, cmꢁ1): 3347 (m), 1679 (s),
1584 (s), 1515 (s), 1438 (m), 1312 (s), 853 (m), 790 (m),
716 (m). 1H NMR (300 MHz, CDCl3/ppm): 7.11 (t, 1H,
J ¼ 6:10 Hz), 7.78 (t, 1H, J ¼ 7:89 Hz), 8.07 (d, 2H,
J ¼ 8:46 Hz), 8.33 (t, 4H, J ¼ 7:71 Hz), 8.58 (bs,
1H, NH). Anal. Calc. for C12H9N3O3 (243.22): C,
59.26; H, 3.73; N, 17.28. Found: C, 59.23; H, 3.73; N,
17.23%.
3.3.3. [N-(6-Ethyl-2-pyridyl)benzamide]dinickel(II) di-
l-bromide dibromide (14)
In a similar manner described for 12, the compound
14 was obtained from (DME)NiBr2 and 3 as a yellow
powder in 72% yield (322 mg). MP:>320 °C. FT-IR
(KBr disc, cmꢁ1): 3369 (br), 1624 (s), 1578 (w), 1534 (m),
1456 (s), 810 (w), 700 (m), 185 (s), 105 (m). Anal. Calc.
for C28H28Br4N4Ni2O2 (889.55): C, 37.81; H, 3.17; N,
6.30. Found: C, 37.77; H, 3.23; N, 6.01%.
3.2.10. N-(4-Methyl-2-pyridyl)-4-nitrobenzamide (10)
In a similar manner as described for 1, the compound
10 was prepared from 2-amino-4-methylpyridine and 4-
nitrobenzoic chloride as white solid in 90% yield (2.30
g). MP: 182–184 °C. FT-IR (KBr disc, cmꢁ1): 3347 (m),
1659 (s), 1606 (m), 1533 (s), 1349 (m), 1300 (m), 854 (m),
717 (m). 1H NMR (300 MHz, CDCl3/ppm): 2.43 (s, 3H,
CH3), 6.95 (d, 1H, J ¼ 4:95 Hz), 7.88–8.25 (m, 4H), 8.35
(d, 2H, J ¼ 8:63 Hz), 8.81 (bs, 1H, NH). Anal. Calc. for
C13H11N3O3 (257.24): C, 60.70; H, 4.31; N, 16.33.
Found: C, 59.90; H, 4.17; N, 15.81%.
3.3.4. [N-(6-Methyl-2-pyridyl)-4-nitrobenzamide]dinickel
(II) di-l-bromide dibromide (15)
In a similar manner described for 12, the compound
15 was obtained from (DME)NiBr2 and 4 as a yellow
powder in 50% yield (237 mg). MP: 305 °C (dec.). FT-IR
(KBr disc, cmꢁ1): 3372 (br), 1630 (s), 1604 (m), 1534 (s),
1461 (s), 1348 (s), 850 (m), 712 (m), 216 (s), 118 (m).
Anal. Calc. for C26H22Br4N6Ni2O6 (951.49): C, 32.82;
H, 2.33; N, 8.83. Found: C, 32.65; H, 2.39; N, 8.64%.
3.2.11. N-(5-Nitro-2-pyridyl)-4-nitrobenzamide (11)
In a similar manner as described for 1, the compound
11 was prepared from 2-amino-5-nitropyridine and 4-
nitrobenzoic chloride as white solid in 87% yield (2.46
g). MP: 216–218 °C. FT-IR (KBr disc, cmꢁ1): 3394 (m),
1691 (s), 1606 (s), 1513 (s), 1350 (s), 1299 (s), 1225 (m),
1118 (m), 850 (m), 714 (m). 1H NMR (300 MHz,
CDCl3/ppm): 6.94 (d, 1H, J ¼ 4:78 Hz), 7.87 –8.24 (m,
4H), 8.35 (d, 2H, J ¼ 8:46 Hz), 8.72 (bs, 1H, NH). Anal.
Calc. for C12H8N4O5 (288.22): C, 50.01; H, 2.80; N,
19.44. Found: C, 49.82; H, 2.57; N, 19.67%.
3.3.5. [N-(4,6-Dimethyl-2-pyridyl)-4-nitrobenzamide]di-
nickel(II) di-l-bromide dibromide (16)
In a similar manner described for 12, the compound
16 was obtained from (DME)NiBr2 and 5 as a yellow
powder in 68% yield (331 mg). MP: 290 °C (dec.). FT-IR
(KBr disc, cmꢁ1): 3386 (br), 1636 (s), 1530 (s), 1446 (m),
1345 (s), 851 (m), 711 (m), 228 (s), 123 (m). Anal. Calc.
for C28H26Br4N6Ni2O6 (979.55): C, 34.33; H, 2.68; N,
8.58. Found: C, 34.31; H, 2.78; N, 8.40%.

926
W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
3.3.6. (1-Naphthyl)[N-(2-pyridyl)benzamido](triphenyl-
phosphine)nickel(II) (17)
(782.49): C, 72.14; H, 4.89; N, 5.37. Found: C, 71.81; H,
4.93; N, 5.40%.
A flame-dried Schlenk tube was charged with 6 (198
mg, 1 mmol) and sodium hydride (64 mg, 2.7 mmol)
under nitrogen. THF (10 ml) was added to the mixture
at 0 °C. Many bubbles were immediately produced. The
resulting mixture was stirred at room temperature for
1 h, filtered, and evaporated. The solid was washed with
pentane and dried in vacuo. The Na salt was immedi-
ately used in the next step without further purification.
Solid trans-[NiCl(Naph)(PPh3)2] (746 mg, 1 mmol) was
added to the Schlenk tube under positive nitrogen flow.
The mixture was charged with toluene (30 ml) and
stirred at 20 °C for 16 h. Then, the reaction mixture was
filtered and the filtrate was concentrated in vacuo to ca.
5 ml. Hexane (50 ml) was added to this solution. A solid
was precipitated and isolated by cannula filtration to get
a yellow-brown powder in 79% yield (509 mg). MP: 200–
202 °C. FT-IR (KBr disc, cmꢁ1): 3429 (br), 3051 (w),
1559 (m), 1504 (m), 1436 (s), 1393 (m), 781(m), 696 (m).
1H NMR (300 MHz, CDCl3/ppm): 6.19 (t, 1H, J ¼ 6:54
Hz), 6.81 (t, 1H, J ¼ 7:43 Hz), 6.91 (d, 1H, J ¼ 6:60
Hz), 7.00 (t, 2H, J ¼ 7:61 Hz), 7.08–7.97 (m, 25H), 9.58
(d, 1H, J ¼ 8:06 Hz). 31P NMR (H3PO4 as external
standard, toluene/ppm): 28.25. Anal. Calc. for
C40H31N2NiOP (645.35): C, 74.44; H, 4.84; N, 4.34.
Found: C, 74.98; H, 5.22; N, 4.20%.
3.3.9. (1-Naphthyl)[N-(2-Pyridyl)-4-nitrobenzamido](tri-
phenylphosphine)nickel(II) (20)
In a similar manner described for 17, the compound
20 was obtained from trans-[NiCl(Naph)(PPh3)2] and 9
as a yellow powder in 68% yield (463 mg). MP: 200–202
°C. FT-IR (KBr disc, cmꢁ1): 3051 (w), 1566 (s), 1523 (s),
1457 (s), 1432 (s), 1344 (s), 696 (m). 1H NMR (300 MHz,
CDCl3/ppm): 6.25 (t, 1H, J ¼ 6:51 Hz), 6.81 (t, 1H,
J ¼ 7:37 Hz), 6.92 (d, 1H, J ¼ 7:37 Hz), 7.09–7.57 (m,
24H), 7.82 (d, 2H, J ¼ 8:62 Hz), 9.53 (d, 1H, J ¼ 8:62
Hz). 31P NMR (H3PO4 as external standard, toluene/
ppm): 28.57. Anal. Calc. for C40H30N3NiO3P (690.35):
C, 69.59; H, 4.38; N, 6.09. Found: C, 69.80; H, 4.40; N,
6.23%.
3.3.10. (1-Naphthyl)[N-(4-methyl-2-pyridyl)-4-nitrobenz-
amido](triphenylphosphine)nickel(II) (21)
In a similar manner described for 17, the compound
21 was obtained from trans-[NiCl(Naph)(PPh3)2] and 10
as a yellow powder in 68% yield (475 mg). MP: >196 °C
(dec.). FT-IR (KBr disc, cmꢁ1): 3429 (br), 3051 (w),
1577 (m), 1522 (m), 1455 (s), 1330 (s), 1105 (m), 695 (m).
1H NMR (300 MHz, CDCl3/ppm): 2.17 (s, 3H, CH3),
6.11 (d, 1H, J ¼ 6:09 Hz), 6.79–7.53 (m, 25H), 7.83 (d,
2H, J ¼ 8:71 Hz), 9.54 (d, 1H, J ¼ 8:05 Hz). 31P NMR
(H3PO4 as external standard, toluene/ppm): 28.69. Anal.
Calc. for C41H32N3NiO3P (704.38): C, 69.91; H, 4.58; N,
5.97. Found: C, 69.19; H, 4.53; N, 5.97%.
3.3.7. (1-Naphthyl)[N-(4-methyl-2-pyridyl)benzamido]
(triphenylphosphine)nickel(II) (18)
In a similar manner described for 17, the compound
18 was obtained from trans-[NiCl(Naph)(PPh3)2] and 7
as a yellow powder in 65% yield (430 mg). MP: 134–136
°C. FT-IR (KBr disc, cmꢁ1): 3432 (br), 3052 (w), 1556
3.3.11. (1-Naphthyl)[N-(5-nitro-2-pyridyl)-4-nitrobenz-
amido](triphenylphosphine)nickel(II) (22)
1
(m), 1500 (m), 1441 (s), 1379 (m), 697 (m). H NMR
In a similar manner described for 17, the compound
22 was obtained from trans-[NiCl(Naph)(PPh3)2] and 11
as a red powder in 53% yield (422 mg). MP: 230–232 °C.
FT-IR (KBr disc, cmꢁ1): 3429 (br), 3051 (w), 1577 (m),
1522 (m), 1455 (s), 1330 (s), 1130 (s), 1105 (m), 695 (m).
1H NMR (300 MHz, CDCl3/ppm): 6.92 (t, 1H, J ¼ 7:39
Hz), 7.15–7.74 (m, 24H), 7.87 (d, 2H, J ¼ 8:33), 8.18 (d,
1H, J ¼ 9:05 Hz), 9.40 (d, 1H, J ¼ 7:69 Hz). 31P NMR
(H3PO4 as external standard, toluene/ppm): 28.42. Anal.
Calc. for C40H29N4NiO5P (735.35): C, 65.33; H, 3.98; N,
7.62. Found: C, 64.98; H, 3.85; N, 7.76%.
(300 MHz, CDCl3/ppm): 2.14 (s, 3H, CH3), 6.03 (d, 1H,
J ¼ 6:40 Hz), 6.74 (d, 1H, J ¼ 6:55Hz), 6.78 (t, 1H,
J ¼ 7:45 Hz), 6.97 (t, 3H, J ¼ 7:55 Hz), 7.06–7.56 (m,
23H), 9.55 (d, 1H, J ¼ 8:04 Hz). 31P NMR (H3PO4
as external standard, toluene/ppm): 28.82. Anal. Calc.
for C41H33N2NiOP (659.38): C, 74.68; H, 5.04; N, 4.25.
Found: C, 75.13; H, 5.14; N, 4.03%. Positive MALDI-
TOF MS: ion at m=e 659.4 {[C41H33N2NiOP]þ,
100%}.
3.3.8. (1-Naphthyl)[N-(5-nitro-2-pyridyl)benzamido](tri-
phenylphosphine)nickel(II) (19)
3.3.12. [N-(5-Nitro-2-pyridyl)benzamido](phenyl)(tri-
phenylphosphine)nickel(II) (23)
In a similar manner described for 17, the compound 19
was obtained from trans-[NiCl(Naph)(PPh3)2] and 8 as a
red powder in 62% yield (520 mg). MP: 156–158 °C. FT-
IR (KBr disc, cmꢁ1): 3053 (w), 1570 (m), 1490 (m), 1459
In a similar manner described for 17, the compound
23 was obtained from trans-[NiCl(Ph)(PPh3)2] and 8 as a
red powder in 58% yield (371 mg). MP: 174 °C (dec.).
FT-IR (KBr disc, cmꢁ1): 3445 (br), 3053 (w), 1568 (m),
1492 (m), 1433 (s), 1328 (s), 1107 (m), 698 (m). 1H NMR
(300 MHz, CDCl3/ppm): 6.71 (m, 3H), 7.04–7.60 (m,
24H), 7.99 (s, 1H), 8.19 (dd, 1H, J ¼ 9:15 Hz). 31P
NMR (H3PO4 as external standard, toluene / ppm):
1
(m), 1433 (s), 1331 (s), 696 (m). H NMR (300 MHz,
CDCl3/ppm): 6.64 (t, 1H, J ¼ 7:41 Hz), 6.79–7.70 (m,
27H), 8.03 (d, 1H, J ¼ 8:80 Hz), 9.35 (d, 1H, J ¼ 7:64
Hz). 31P NMR (H3PO4 as external standard, toluene/
ppm): 28.20. Anal. Calc. for C40H30N3NiO3P ꢂ C7H8

Table 7
Crystal data and structure refinement for 12, 14, 17, 19 and 23
Complex
12
14
17
19
23
Formula
Formula weight
Temperature (K)
C26H24Br4N4Ni2O2
861.56
293(2)
C28H28Br4N4Ni2O2
889.55
293(2)
C40H31N2NiOP
649.35
293(2)
C40H30N3NiO3P ꢂ C4H8O
C36H28N3NiO3P
640.29
293(2)
762.45
293(2)
ꢀ
Wavelength (A)
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
Crystal system
Space group
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
P1
8.683(2)
P1
8.644(2)
P1
10.650(2)
P1
11.420(2)
P1
10.672(3)
ꢀ
a (A)
ꢀ
b (A)
9.413(2)
10.622(2)
9.523(2)
10.637(2)
11.314(2)
14.858(3)
12.927(3)
14.748(3)
12.192(4)
12.658(4)
ꢀ
c (A)
a (°)
b (°)
c (°)
112.31(3)
93.64(3)
69.10(3)
74.00(3)
93.07(3)
109.00(3)
75.44(3)
78.87(3)
100.802(5)
90.173(4)
113.64(3)
711.6(2)
72.82(3)
767.1(3)
103.49(3)
1629.6(6)
73.66(3)
2004.5(7)
106.390(4)
1549.3(8)
3
ꢀ
Volume (A )
Z
1
2.011
6.970
1
1.926
6.469
2
1.334
0.680
2
1.263
0.569
2
1.373
0.719
Dcalc (Mg mꢁ3
)
l (mmꢁ1
)
Crystal size (mm3)
0.223 ꢀ 0.218 ꢀ 0.122
2.63–27.45
ꢁ10 6 h 6 11;
ꢁ12 6 k 6 12; ꢁ13 6 l 6 13
4765
0.307 ꢀ 0.205 ꢀ 0.118
2.09–27.48
0 6 h 6 11;
ꢁ11 6 k 6 12; ꢁ12 6 l 6 13
5968
0.528 ꢀ 0.407 ꢀ 0.266
2.53–27.49
0 6 h 6 13; ꢁ14 6 k 6 14;
ꢁ19 6 l 6 18
6388
0.355 ꢀ 0.200 ꢀ 0.141
1.68–27.48
ꢁ14 6 h 6 14; ꢁ15 6 k 6 16;
ꢁ18 6 l 6 19
11546
0.24 ꢀ 0.22 ꢀ 0.20
1.99–26.39
ꢁ13 6 h 6 12; ꢁ8 6 k 6 15;
ꢁ15 6 l 6 15
8991
h Range (°)
Limiting indices
Reflections collected
Unique reflections
3149 [Rint ¼ 0:0436]
96.6 (h ¼ 27:45°)
ABSCOR
3229 [Rint ¼ 0:0884]
92.1 (h ¼ 27:48°)
ABSCOR
6388 [Rint ¼ 0:0405]
85.4 (h ¼ 27:49°)
ABSCOR
8209 [Rint ¼ 0:1635]
89.4 (h ¼ 27:48°)
ABSCOR
6275[Rint ¼ 0:0181]
99.6 (h ¼ 25:00°)
SADABS
Completeness to h (%)
Absorption correction
Maximum/minimum
transmission
1.2650/0.7147
1.5527/0.3311
1.3088/0.6989
1.4561/0.5982
1.0000/0.8783
Data/restraints/parameters
Goodness-of-fit on F 2
R indices [I > 2rðIÞ]
R indices (all data)
3149/0/177
0.790
3229/0/185
0.813
6388/0/406
0.713
8209/9/478
0.646
6275/0/397
1.013
R1 ¼ 0:0392, wR2 ¼ 0:0679
R1 ¼ 0:0805, wR2 ¼ 0:0736
0.676 and )0.532
R1 ¼ 0:0652, wR2 ¼ 0:1351
R1 ¼ 0:1313, wR2 ¼ 0:1511
1.200 and )0.863
R1 ¼ 0:0479, wR2 ¼ 0:0900
R1 ¼ 0:1969, wR2 ¼ 0:1131
0.311 and )0.175
R1 ¼ 0:0685, wR2 ¼ 0:1177
R1 ¼ 0:3519, wR2 ¼ 0:1625
0.324 and )0.237
R1 ¼ 0:0379, wR2 ¼ 0:0828
R1 ¼ 0:0634, wR2 ¼ 0:0941
0.275 and )0.249
Largest difference peak and
hole (e Aꢁ3
)

928
W.-H. Sun et al. / Journal of Organometallic Chemistry 689 (2004) 917–929
29.22. Anal. Calc. for C36H28N3NiO3P (640.29): C,
67.53; H, 4.41; N, 6.56. Found: C, 67.82; H, 4.48; N,
6.76%.
4. Supplementary material
Crystallographic data have been deposited to the
Cambridge Crystallographic Data Center, CCDC
212587 for 12, 212588 for 14, 223946 for 17, 223945 for
19 and 223947 for 23. Copies of the information may be
obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.ac.uk), upon request.
3.3.13. [N-(5-Nitro-2-pyridyl)-4-nitrobenzamido](phenyl)
(triphenylphosphine)nickel(II) (24)
In a similar manner described for 17, the compound
24 was obtained from trans-[NiCl(Ph)(PPh3)2] and 11 as
a red powder in 61% yield (418 mg). MP: 180 °C (dec.).
FT-IR (KBr disc, cmꢁ1): 3431 (br), 3053 (w), 1578 (m),
1523 (m), 1456 (s), 1328 (s), 1107 (m), 696 (m). 1H NMR
(300 MHz, CDCl3/ppm): 6.62 (m, 3H), 7.08–7.76 (m,
21H), 7.95 (s, 1H), 8.17 (d, 1H, J ¼ 7:58 Hz). 31P NMR
(H3PO4 as external standard, toluene/ppm): 29.45. Anal.
Calc. for C36H27N4NiO5P (685.29): C, 63.10; H, 3.97; N,
8.18. Found: C, 63.25; H, 3.98; N, 8.07%.
Acknowledgements
The authors are grateful to the National Natural
Science Foundation of China for the financial support
with Grant No. 20272062 and Polymer Chemistry
Laboratory, Chinese Academy of Sciences and China
Petro-Chemical Corporation for their help.
3.4. X-ray crystal structure determination of 12, 14, 17,
19 and 23
Intensity datasets of 12, 14, 17 and 19 were collected at
293 K on a Rigaku RAXIS pid IP diffractometer with
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