Synthesis and characterization of nickel(II) complexes bearing 2-(imidazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles and their polymerization of norbornene

Article abstract of DOI:10.1016/j.ica.2009.02.026

Series of 2-R₁-6-(1-R₂-4,5-diphenyl-1H-imidazol-2-yl)pyridin e (R₁ = R₂ = H, L1; R₁ = Me, R₂ = H, L2; R₁ = H, R₂ = Me, L3; R₁ = R₂ = Me, L4), 2-(

Full text of DOI:10.1016/j.ica.2009.02.026

Inorganica Chimica Acta 363 (2010) 1970–1978
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and characterization of nickel(II) complexes bearing
2-(imidazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles
and their polymerization of norbornene
Abiodun O. Eseola a,b, Min Zhang a, Jun-Feng Xiang a, Weiwei Zuo a, Yan Li a, Joseph A.O. Woods b,
Wen-Hua Sun a,
*
a Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, No. 2, Beiyijie, Zhongguancun,
Haidian-Sub., Beijing 100190, China
b Inorganic Chemistry Group, Department of Chemistry, University of Ibadan, Ibadan, Nigeria
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 January 2009
Received in revised form 15 February 2009
Accepted 19 February 2009
Available online 28 February 2009
Series of 2-R1-6-(1-R2-4,5-diphenyl-1H-imidazol-2-yl)pyridine (R1 = R2 = H, L1; R1 = Me, R2 = H, L2;
R1 = H, R2 = Me, L3; R1 = R2 = Me, L4), 2-(6-R1-pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (R1 = H,
L5; R1 = Me, L6) and 2-(pyridin-2-yl)phenanthro[9,10-d]oxazole (L7) were synthesized and used to pre-
pare their corresponding dihalonickel complexes (C1–C9). All organic compounds and nickel complexes
were characterized by elemental and spectroscopic analyses. Molecular structures of C1, C4, C5 and C8
were confirmed by the single-crystal X-ray diffraction analysis. The single-crystal X-ray analysis revealed
complex C1 as a distorted octahedral geometry, complex C4 as a distorted square pyramidal geometry,
complex C5 as a distorted trigonal bipyramidal configuration, and complex C8 as a tetrahedral geometry.
Upon activation with methylaluminoxane (MAO), the nickel complexes showed good activity towards
norbornene polymerization through main additional and minor ring-opening metathesis. The reaction
parameters such as norbornene concentration, reaction temperature and different coordinate environ-
ments caused by the ligands affected their catalytic performances.
Dedicated to Prof. R.J. Puddephatt.
Keywords:
Nickel
Catalyst
Molecular structure
Vinyl polymerization
Norbornene
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
with high activities by neutral salicylaldiminato nickel complexes
[12] and nickel complexes bearing bis(salicylaldimine) [13] or
The polymerization of norbornene (bicyclo[2.2.1]heptane) has
occurred with two major mechanisms: ring-opening metathesis
and vinyl addition. The ring-opening metathesis polymerization
(ROMP) of norbornene was initially reported by Andersen and
Merckling in 1950s [1], and has extensively investigated [2] with
great achievements as part work of Noble Award in 2005 [3,4].
Vinyl polymerization of norbornene was traced back to early
1960s [5], and some efforts were made on considering their poten-
tially advantageous properties by chemists both from industry [6]
and the academia [7–11].
The scarcity of data such as molecular weight and molecular
weight distribution of polymer presented the problem of evaluat-
ing and controlling the physical properties of polynorbornene ob-
tained. Consequently, the case was that scientists could not
measure the molecular weights and molecular weight distribu-
tions of polynorbornene obtained by vinyl polymerization. In our
efforts to copolymerize ethylene with norbornene, the homopoly-
merization (vinyl polymerization) of norbornene only happened
2-methyl-8-(diphenylphosphino)quinolines [14], and resultant
polynorbornenes were measured for their molecular weights and
distributions [15]. During the same period and before, there were
some works employing nickel complexes as catalysts for vinyl
polymerization of norbornene without measuring the molecular
weights of polynorbornene obtained by GPC [16–18]. It would be
fair to mention that the polynorbornenes obtained by titanium
complex catalysts were reported with molecular weights and dis-
tributions in the same period [19].
Inspired by these achievements, search for new nickel com-
plexes as catalysts for norbornene polymerization has become a
hot topic in our [20–24] and other groups [25–29]. After we solved
the problem of reactor fouling by supporting nickel catalysts on
spherical MgCl2 [30], we attended to their properties and applica-
tion. Unfortunately, there is no melting point observable for such
polymers. Therefore, further papers were not submitted even
though an invited lecture was delivered [31].
Recently, it was reported that norbornene polymerization cata-
lyzed by some iridium complexes proceeded by both ROMP and vi-
nyl-polymerization styles [32,33]. Such phenomenon has also been
described for cobalt [34] and palladium [35] precursors. However,
* Corresponding author. Tel.: +86 10 62557955; fax: +86 10 62618239.
E-mail address: whsun@iccas.ac.cn (W.-H. Sun).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.02.026

A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
1971
2. Experimental
R2
Y
N
N
N
All air- or moisture-sensitive manipulations were carried out
under an atmosphere of nitrogen using standard Schlenk tech-
niques. IR spectra were obtained on a Perkin–Elmer FT-IR 2000
spectrophotometer by using KBr disks in the range of 4000–
400 cmÀ1. NMR spectra were recorded with a Bruker ARX 400
spectrometer with TMS as the internal standard. Solid state 13C
spectra were obtained on a Bruker AVANCE III 400 WB spectrome-
ter by using cptoss pulse program, in which the delay time is 3 s
and the spectra are accumulated for 1024 scans with spinning rate
is 5 kHz. Elemental analysis was carried out using a Flash EA 1112
microanalyzer. Toluene was refluxed over sodium-benzophenone
and distilled under nitrogen prior to use. Methylaluminoxane
(MAO, 1.46 M in toluene) was purchased from Akzo Nobel Corp.
Norbornene (bicyclo-[2.2.1]hept-2-ene; Acros) was refluxed over
sodium for 12 h and distilled under nitrogen, and applied as tolu-
ene solution. All other chemicals are commercially available and
used without further purification unless stated otherwise.
N
N
R1
R1
(a)
(b)
Scheme 1. Ligand frameworks in this work.
it is taken for granted that norbornene polymerization mediated by
nickel systems involves only vinyl-type polymerization mode. The
occurrences of the two active species for polymerization may lead
to bimodal molecular weight distributions [36], but bimodal distri-
butions could also result from pure vinyl polymerization in the
presence of different active site types [29].
Though the recent progress made on nickel catalytic system, it
is usual to explore nickel complexes for their catalytic behaviours
regardless of whether they are more active than literature findings.
This is so because academic understanding on polymerization
mechanisms and the nature of the active species in relation to
activity trends is still largely lacking. One of the few reported con-
clusions, ‘trigger’ mechanism [37], proposed that norbornene
monomer always occupies coordination site on active species,
and that the complexed norbornene monomer will only undergo
incorporation into the polymer chain via Ni–C cis–exo insertion
only if triggered by a new monomer that is accessing the active
site. Therefore, it is conceivable that productivity and polymer
molecular weight should increase at increasing temperatures
and/or increasing monomer concentrations. Such a trend is ob-
served for some nickel complexes (e.g. anilido–imino nickel com-
plexes [29]), but may be inadequate to explain active site
characteristics for higher catalytic activities and polymer molecu-
lar weight increase that is favoured at reducing temperatures.
Moreover, the blocked polynorbornenes are expected for making
parts without constrained rings in order to have the polymer
chains foldable and possible for their melting points of such
polymers. In our on going syntheses of 2-(4,5-diphenyl-imidazol-
2-yl)pyridines (a) or 2-(pyridin-2-yl)phenanthroimidazoles/oxaz-
oles (b) (Scheme 1), their corresponding dihalonickel complexes
showed good activities toward norbornene polymerization, in
which polynorbornenes have some remaining double bonds and
indicate the polymerization through major additional and minor
ring-opening metathesis. Herein we report syntheses, character-
ization and norbornene polymerization behaviour of dihalonickel
complexes based on pyridine derivatives such as 2-(imidazol-
2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/oxazoles
Scheme 2.
3. Synthesis of pyridine derivatives and nickel complexes
3.1. Synthesis of pyridine derivatives (L1–L7)
3.1.1. 2-(4,5-Diphenyl-1H-imidazol-2-yl)pyridine (L1)
Benzil (3.00 g, 14.27 mmol) and ammonium acetate (11.00 g,
0.14 mol) were put into a flask and after filling with nitrogen,
20 mL each of ethanol and dichloromethane were added. While
stirring at reflux, 2-pyridinecarboxaldehyed (1.6 mL, 17.12 mmol)
was added followed by catalytic amount of glacial acetic acid
(0.5 mL) and 2 h reflux. The reaction solution was cooled, extracted
trice with 100 mL portions of dichloromethane, and the combined
extracts was washed with 10 mL water, dried and purified on silica
gel column with petroleum ether/ethyl acetate/dichloromethane
(10:1:1) as eluent. Compound L1 was isolated as white crystalline
solid (0.85 g, 20.7%). Melting point (M.p.) 174–176 °C. Selected IR
peaks (KBr disc, cmÀ1):
m 3050vs, 1601s, 1590s, 1581s, 1567s,
1475vs, 768s, 739s, 697vs. 1H NMR (400 MHz, TMS, CDCl3): d
10.56(s, br, 1H); 8.51(d, J = 4.8 Hz, 1H); 8.29(d, J = 8.0 Hz, 1H);
7.78(dd, J = 7.6 Hz, 1H); 7.76(s, br, 2H); 7.49(s, br, 2H); 7.34(m,
br, 6H), 7.22(dd, J = 5.0 Hz, 1H). 13C NMR (100 MHz, TMS, CDCl3);
148.7, 148.2, 145.4, 137.1, 128.6, 127.9, 123.2, 120.1. Anal. Calc.
for C20H15N3: C, 80.78; H, 5.08; N, 14.13. Found; C, 80.99; H,
5.01; N, 14.38%.
3.1.2. 2-Methyl-6-(4,5-diphenyl-1H-imidazol-2-yl)pyridine (L2)
Benzil (2.06 g, 9.78 mmol), 6-methyl-2-pyridinecarboxaldehyde
(1.18 g, 9.78 mmol), ammonium acetate (7.0 g, 90.81 mmol) and
catalytic amount of glacial acetic acid (1 mL) were treated in the
same manner as for compound L1 above, except that petroether/
ethyl acetate/dichloromethane (2:2:1) was employed for column
R2
C1 C2 C3 C4 C5 C6
R2
N
N
R1
R2
X
H
H
H
Me Me Me
H
Me
H
H
Me
H
N
N
(DME)NiBr2
Cl Cl Br Cl Cl Br
N
R1
N
n
R1
or NiCl2 6H2O
n
2
2
2
1
1
1
Ni
L1-L4
X
X
Solvent
Y
C7 C8 C9
Y
R1
Y
H
Me
H
O
N
N
N
N
NH NH
R1
R1
Ni
L5-L7
Cl
Cl
Scheme 2. General synthetic routes to the complexes C1–C9.

1972
A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
chromatography. The imidazole product (L2) was isolated as white
solid (1.44 g, 47.3% yield). M.p. 198–200 °C. Selected IR peaks (KBr
8.64(d, J = 4.8 Hz, 1H); 8.53(d, J = 8.0 Hz, 1H); 8.08(s, br, 1H);
7.89(dd, 7.7 Hz, 1H); 7.71(s, br, 2H); 7.64(m, 2H); 7.34(dd,
J = 4.9 Hz, 1H). 13C NMR (CDCl3, 100 MHz, TMS); 149.02, 148.57,
148.38, 137.31, 127.08, 125.61, 123.90, 121.18. Anal. Calc. for
C20H13N3.0 Á 25H2O: C, 80.11; H, 4.54; N, 14.01. Found: C, 79.60;
H, 4.63; N, 14.14%.
disc, cmÀ1):
m 3061s, 2959s, 1597s, 1572s, 1501m, 1474vs, 1454vs,
765vs, 697vs. 1H NMR (400 MHz, TMS, CDCl3); d 10.50(s, br, 1H);
8.09(d, J = 7.8 Hz, 1H); 7.67(m, 3H); 7.50(br, d, J = 5.9 Hz, 2H);
7.32(m, br, 6H); 7.09(d, J = 7.6 Hz, 1H); 2.61(s, 3H). 13C NMR
(100 MHz, TMS, CDCl3): 157.7, 147.5, 145.5, 137.4, 128.5, 127.9,
127.1, 122.8, 117.1, 24.2. Anal. Calc. for C21H17N3: C, 81.00; H,
5.50; N, 13.49 Found: C, 80.56; H, 5.59; N, 13.86%.
3.1.6. 2-(6-Methylpyridin-2-yl)-1H-phenanthro[9,10-d]imidazoles
(L6)
Obtained 0.61 g, 41.0%. M.p. 218–220 °C. Selected IR peaks (KBr
3.1.3. 2-(1-Methyl-4,5-diphenyl-1H-imidazol-2-yl)pyridine (L3)
In acetone (30 mL), 2-(4,5-diphenyl-1H-imidazol-2-yl)pyridine
(0.44 g, 1.47 mmol) and K2CO3 (0.41 g, 2.95 mmol) were refluxed
for 30 min. On cooling, iodidomethane (0.13 mL, 2.06 mmol) was
added and the reaction mixture stirred at room temperature for
24 h. Removal of solvent under vacuum followed by addition of
about 50 mL water gave white particles which were filtered,
washed with water and dried. This was purified on silica gel column
with ethyl acetate/petroleum ether (1:5) to obtain compound L3
(0.34 g, 71.4%). M.p. 121–123 °C. Selected IR peaks (KBr disc,
disc, cmÀ1):
m 3435s, 3072s, 1615m, 1595s, 1573vs, 1516m,
1461vs, 1450vs, 1427vs, 1235s, 1120m, 1038s, 796s, 752vs,
723vs. 1H NMR (CDCl3, 400 MHz, TMS): 11.45(s, br, 1H); 8.74(m,
3H); 8.34(d, J = 7.8 Hz, 1H); 8.12(d, J = 6.4 Hz, 1H); 7.76(m, 2H),
7.64(m, 3H); 7.20(d, J = 7.3 Hz, 1H); 2.66(s, 3H). 13C NMR (CDCl3,
100 MHz, TMS): 158.1, 148.5, 147.8, 137.5, 128.6, 127.1, 125.5,
123.6, 122.5, 118.2, 24.31. Anal. Calc. for C21H15N3 Á 0.9H2O: C,
76.62; H, 5.27; N, 12.77. Found: C, 76.65; H, 5.18; N, 12.79%.
3.1.7. 2-(Pyridin-2-yl)phenanthro[9,10-d]oxazole (L7)
cmÀ1):
m
3104m, 3034m, 2953w, 1606s, 1573m, 799s, 700vs. 1H
Obtained 2.50 g, 58.6%. M.p. 199–201 °C. Selected IR peaks (KBr
NMR (400 MHz, TMS, CDCl3): d 8.62(d, J = 4.8 Hz, 1H); 8.32(d,
J = 8.0 Hz, 1H); 7.81(dd, J = 7.7 Hz, 1H); 7.55(d, J = 7.2 Hz, 2H);
7.48(m, 3H); 7.41(m, 2H); 7.24(m, 1H); 7.22(dd, J = 7.2 Hz, 2H);
7.16(d, 7.2 Hz, 1H); 3.91(s, 3H). 13C NMR (100 MHz, TMS, CDCl3):
151.0, 148.3, 145.0, 137.9, 136.6, 134.7, 132.2, 131.0, 129.0, 128.7,
128.1, 126.9, 126.4, 123.7, 122.5, 34.1. Anal. Calc. for C21H17N3: C,
81.00; H, 5.50; N, 13.49. Found: C, 81.03; H, 5.52; N, 13.32%.
disc, cmÀ1):
m 3056m, 1615m, 1589vs, 1566s, 1455vs, 1425vs,
1251s, 1234s, 1082vs, 757vs, 724vs. 1H NMR (CDCl3, 400 MHz,
TMS): 8.89(d, J = 4.8 Hz, 1H); 8.73(m, 3H); 8.47(m, 2H); 7.94(dd,
J = 7.6 Hz, 1H), 7.73(m, 4H); 7.46(dd, J = 4.8 Hz, 1H). 13C NMR
(CDCl3, 100 MHz, TMS): 160.7, 150.4, 146.4, 145.7, 137.1, 135.6,
129.9, 129.2, 127.9, 127.4, 126.9, 126.4, 126.2, 125.0, 123.8,
123.5, 123.2, 123.1, 121.4, 121.1. Anal. Calc. for C20H12N2O: C,
81.07; H, 4.08; N, 9.45. Found: C, 80.84, H, 4.20, N, 9.41%.
3.1.4 2-Methyl-6-(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)pyridine
(L4)
3.2. Syntheses of Ni(II) complexes C1–C9
In 30 mL solvent, the reactants 2-methyl-6-(4,5-diphenyl-1H-
imidazol-2-yl)pyridine (0.44 g, 1.40 mmol), K2CO3 (0.39 g,
2.79 mmol) and methyliodide (0.12 mL, 1.95 mmol) were subjected
to similare procedure as for compound L3 to obtain compound L4
(0.27 g, 66.1%). M.p. 120–122 °C. Selected IR peaks (KBr disc,
3.2.1. Complex C1 (L12NiCl2)
The dichloromethane (10 mL) solution of L1 (0.13 g, 0.45 mmol)
was added in drops to a stirring solution of NiCl2 Á 6H2O (54.0 mg,
0.225 mmol) in ethanol (6 mL) at room temperature. The stirring
continued for 12 h after which the resultant particles were filtered
to give C1 as light blue micro-crystals (0.13 g, 73.4%). Decomposi-
cmÀ1):
m
3100m, 3056w, 3030w, 2987w, 1604s, 1573s, 790vs. 1H
NMR (400 MHz, TMS, CDCl3): d 8.08(d, J = 7.8 Hz, 1H); 7.69(dd,
J = 7.8 Hz, 1H); 7.53(d, J = 7.3 Hz, 2H); 7.46(m, 3H); 7.40(m, 2H);
7.21(dd, J = 7.2 Hz, 2H); 7.13(dd, J = 7.6 Hz, 2H); 3.88(s, 3H);
2.60(s, 3H). 13C NMR (100 MHz, TMS, CDCl3): 157.1, 150.3, 145.2,
137.8, 137.0, 134.7, 132.0, 131.1, 131.0, 129.0, 128.6, 128.1, 127.0,
126.3, 122.0, 120.7, 34.0, 24.5. Anal. Calc. for C22H19N3: C, 81.20;
H, 5.89; N, 12.91. Found: C, 81.36; H, 5.92; N, 12.78%.
tion point (D.p.) >302 °C. Selected IR peaks (KBr, cmÀ1):
m 3285m,
3055vs, 1615vs, 1585vs, 1573s, 1535s, 1475vs, 1459vs, 774vs,
696vs. Anal. Calc. for C41H36Cl2N6NiO2: C, 63.59; H, 4.69; N,
10.85. Found: C, 63.30; H, 4.66; N, 10.58%.
3.2.2. Complex C2 (L32NiCl2)
Compounds L5–L7 were also obtained by similar procedure for
preparation of compound L1. The general procedure is as follows:
Phenanthrenequinone and the corresponding aldehyde (1 M e-
quiv.) were refluxed for 3 h in the presence of ammonium acetate
(10 M equiv.) and glacial acetic acid (0.5–1.0 mL) as catalyst. The
reaction solution was cooled and stirred with a few drops of con-
centrated aqueous ammonia at room temperature to neutralize
residual acid. The mixture was extracted 2ce with dichlorometh-
ane (60 mL and 20 mL) and the combined organic extract concen-
trated under vacuum was purified on silica gel column using
petroleum ether/dichloromethane (1:4) as eluent. The eluent por-
tions containing the respective products were collected and con-
centrated under vacuum. Addition of petroleum ether
precipitated the products which were filtered washed with petro-
leum ether and dried under vacuum at 60 °C. Reaction and analyt-
ical data for the respective ligands are as follows.
NiCl2 Á 6H2O (46.0 mg, 0.20 mmol) and L3 (0.12 g, 0.40 mmol)
were reacted in a similar manner as for C1 to obtain C2 as a blue
powder (0.15 g, 85.2%). D.p. >394 °C. Selected IR peaks (KBr,
m 3104m, 3034m, 2953w, 1606s, 1573m, 799s, 700vs. Anal.
Calc. for C42H36Cl2N6NiO: C, 65.48; H, 4.71; N, 10.91. Found: C,
cmÀ1):
65.54; H, 4.53; N, 10.87%.
3.2.3. Complex C3 (L12NiBr2)
To a THF (2 mL) solution of (DME)NiBr2 (90.0 mg, 0.29 mmol),
the THF (4 mL) solution of L1 (0.19 g, 0.64 mmol) was added in
drops and stirring continued for 12 h at room temperature. Diethyl
ether (5 mL) was added to precipitate the blue powder, which was
filtered, washed with THF/diethyl ether mixture, and dried under
vacuum to give C3 as blue powder (0.24 g, 78.8%). D.p. >312 °C. Se-
lected IR peaks (KBr, cmÀ1):
m 3433m(br), 3321m, 3106s, 3056s,
3009m, 1614s, 1584m, 1574m, 1507m, 773s, 695vs. Anal. Calc.
for C40H34Br2N6NiO2: C, 56.57; H, 4.04; N, 9.90. Found: C, 56.46;
H, 3.79; N, 9.47%.
3.1.5. 2-(Pyridin-2-yl)-1H-phenanthro[9,10-d]imidazoles (L5)
Obtained 0.48 g, 11.3%. M.p. 200–202 °C. Selected IR peaks (KBr
disc, cmÀ1):
m
3434vs, 3052s, 1614w, 1594vs, 1566s, 1455vs,
3.2.4. Complex C4 (L2NiCl2)
1445vs, 1426s, 1396m, 1234s, 1144m, 788s, 758vs, 725vs. 1H
NMR (CDCl3, 400 MHz, TMS): 11.34(s, br, 1H); 8.73(s, br, 3H);
NiCl2 Á 6H2O (0.15 g, 0.65 mmol) and L2 (0.20 g, 0.65 mmol)
were reacted in a similar manner as for C1 to obtain C4 as a yellow

A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
1973
powder (0.26 g, 91.2%). D.p. >216 °C. Selected IR peaks (KBr, cmÀ1):
3348s (br), 3066vs, 1615m, 1603m, 1568s, 1478vs, 1247s, 805s,
765s, 694vs. Anal. Calc. for C21H19Cl2N3NiO: C, 54.95; H, 4.17; N,
1445, 1428, 1299, 1161, 788, 750, 718. Anal. Calc. for
C20H13Cl2N3Ni Á H2O: C, 54.23; H, 3.41; N, 9.49. Found: C, 54.30;
H, 3.17; N, 9.37%.
m
9.15. Found: C, 54.74; H, 4.24; N, 8.62%.
3.2.8. Complex C8 (L6NiCl2)
3.2.5. Complex C5 (L4NiCl2)
Compound L6 (0.10 g, 0.32 mmol) and NiCl2 Á 6H2O (76.8 mg,
0.32 mmol) were reacted in the same manner as for complex C1
above to obtain C8 as a yellow powder (0.12 g, 87.9%). D.p.
NiCl2 Á 6H2O (0.1 g, 0.40 mmol) and L4 (0.13 g, 0.40 mmol) were
reacted in a similar manner as for C1 to obtain C5 as a yellow pow-
der (0.16 g, 88.2%). Dp. >214 °C. Selected IR peaks (KBr, cmÀ1):
m
>390 °C. Selected IR peaks (KBr disc, cmÀ1):
m
3045m, 2950m,
3100m, 3056w, 3030w, 2987w, 1604s, 1573s, 790vs. Anal. Calc.
for C22H19Cl2N3Ni Á (1/2)H2O: C, 56.95; H, 4.34; N, 9.06. Found: C,
56.88; H, 4.18; N, 9.11%.
1654m, 1591vs, 1491vs, 1279s, 775vs, 711s. Anal. Calc. for
C21H19Cl2N3NiO2: C, 53.10; H, 4.03; N, 8.85. Found: C, 52.75; H,
3.49; N, 8.50%.
3.2.6. Complex C6 (L2NiBr2)
3.2.9. Complex C9 (L7NiCl2)
(DME)NiBr2 (0.28 g, 0.92 mmol) in THF (2 mL) and L2 (0.32 g,
1.02 mmol) were reacted according to procedure for preparation
of C1 to give C6 as yellow cake (0.50 g, 95.3%). D.p. >220 °C. Se-
Compound L7 (0.20 g, 0.68 mmol) and NiCl2 Á 6H2O (0.16 g,
0.68 mmol) were reacted in the same manner as for complex C1
above to afford C9 as light green powder (0.26 g, 90.4%). D.p.
lected IR peaks (KBr, cmÀ1):
m
3435s(br), 3160m, 3138m, 3064m,
>422 °C. Selected IR peaks (KBr disc, cmÀ1):
m 3483s, 3302vs(br),
2978m, 2874m, 1616s, 1566s, 806s, 695vs. Anal. Calc. for
C21H17Br2N3Ni Á (1/2)(C2H5)2O: C, 48.73; H, 3.91; Br, 28.19; N, 7.4.
Found: C, 48.80; H, 3.92; N, 6.96%.
3074m, 1638vs, 1615s, 1543vs, 1478s, 1439vs, 1292s, 1167s,
788s, 759vs. Anal. Calc. for C20H12Cl2N2NiO Á (1/2)H2O:C, 55.23; H,
3.01; N, 6.44. Found: C, 55.50; H, 3.77; N, 6.36%.
4. Polymerization of norbornene
3.2.7. Complex C7 (L5NiCl2)
Compound L5 (0.13 g, 0.43 mmol) taken up in dichloromethane
(10 mL) was added in drops and at room temperature to a stirring
solution of NiCl2 Á 6H2O (0.10 g 0.43 mmol) in ethanol (6 mL). The
stirring continued for 12 h after which the reaction solution was
diluted with diethyl ether and the resultant light green powder fil-
tered. The product was washed with diethyl ether and dried under
vacuum at 60 °C to obtain C7 (0.33 g, 78.1%). D.p. 402 °C. Selected
In the polymerization experiment, the general procedure is as
follows: the catalyst (2.0 lmol Ni) was weighed into Schlenk-type
glassware, charged with nitrogen and the appropriate volume of
norbornene solution in toluene was added via syringe through a
rubber septum. Necessary amount of toluene was added to reactor
to achieve the total reaction volume, which was typically 10 mL.
Polymerization reaction was initiated by addition of corresponding
volume of 1.46 M solution of MAO in toluene. After respective
IR peaks (KBr disc, cmÀ1):
m 3363, 3096, 3039, 1608, 1521, 1455,
Table 1
Crystal data for processing parameters for C1, C4, C5 and C8.
C1 Á CH3OH
C4 Á 2CH3OH
C5
C8 Á DMF
Formula
Formula weight
T (K)
C40H30N6NiCl2ÁCH3OH
756.33
173(2)
C21H17N3NiCl2Á2CH3OH
C22H19N3NiCl2
455.01
173(2)
C21H15N3NiCl2ÁDMF
505.07
512.07
173(2)
173(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
0.71073
monoclinic
P2(1)/n
10.665(2)
9.794(2)
22.088(4)
90
91.05(3)
90
2306.8(8)
4
1.454
0.71073
triclinic
P1
8.4913(2)
11.359(2)
12.622(3)
66.09(3)
86.66(3)
70.65(3)
1046.0(4)
2
1.445
0.71073
monoclinic
P2(1)/n
13.437(3)
9.7111(2)
18.033(4)
90
108.43(3)
90
triclinic
ꢀ
ꢀ
P1
11.933(2)
12.526(3)
15.126(3)
102.72(3)
96.03(3)
116.59(3)
1917.7(7)
2
a
(°)
b (°)
c
(°)
V (Å3)
2232.4(8)
4
1.524
Z
DCalc (g mÀ3
)
1.310
0.685
l
(mmÀ1
)
1.098
1.195
1.134
F(000)
784
1048
468
1056
Crystal size (mm)
h Range (°)
Limiting indicates
0.46 Â 0.46 Â 0.29
1.42–25.00
À14 6 h 6 14
À14 6 k 6 14
À17 6 l 6 17
12553
0.42 Â 0.26 Â 0.24
2.14–25.00
À12 6 h 6 12
À11 6 k 6 11
À26 6 l 6 26
12132
0.10 Â 0.10 Â 0.10
2.08–25.00
À10 6 h 6 10
À13 6 k 6 13
À14 6 l 6 14
6844
0.53 Â 0.47 Â 0.28
1.66–27.39
À17 6 h 6 17
À12 6 k 6 12
À23 6 l 6 23
9623
Number of reflections collected
Number of unique reflections
R(int)
6744
0.0311
4054
0.0577
3683
0.0279
5079
0.0265
Completeness to h (%)
Number of parameters
Goodness-of-fit (GOF) on F2
99.9 (h = 25.00)
464
1.152
99.6 (h = 25.00)
289
1.337
99.9 (h = 25.00)
254
1.130
99.8 (h = 27.39)
300
1.352
Final R indices (I > 2
r
(I))
R1 = 0.0507
wR2 = 0.1031
R1 = 0.0647
wR2 = 0.1074
0.657, À0.457
R1 = 0.0607
wR2 = 0.1087
R1 = 0.0728
wR2 = 0.1126
0.559, À0.763
R1 = 0.0555
wR2 = 0.1167
R1 = 0.0688
wR2 = 0.1222
1.019, À0.561
R1 = 0.0622
wR2 = 0.1276
R1 = 0.0795
wR2 = 0.1382
0.438, À0.506
R indices (all data)
Largest difference in peak and hole (e ÅÀ3
)

1974
A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
durations, the polymerization was terminated by pouring into
100 mL acidic ethanol (ethanol:conc. HCl = 95:5). The polymer
was isolated by filtration, washed with ethanol, and dried in vac-
uum at 60 °C overnight. All polynorbornenes showed the almost
same IR spectra. IR (KBr disc, cmÀ1): 2945 (vs), 2867 (vs), 1477
(m), 1452 (s), 1374 (w), 1294 (m), 1257 (m), 1222 (w), 1146 (m),
1108 (w), 1084 (w), 1022 (w), 939 (m), 891 (m), 739 (s), 702 (w),
648(w).
cur in a faster step relative to formation of the N–N species. Similar
mechanism was upheld by Stein and Day [41].
5.2. Syntheses of the Ni(II) complexes
All nickel complexes were obtained in good yields by routinely
reacting appropriate ratios of NiCl2 Á 6H2O or (DME) NiBr2 to the
respective ligands at room temperature. They were characterized
by FT-IR and elemental analyses. Peaks assignable to the C@N dou-
ble bonds were shifted to lower wavenumbers in the complexes
compared to the ligand IR peak positions for similar vibrations. Sin-
gle-crystal X-ray diffraction experiments were performed for C1,
C4, C5 and C8. Attempts to prepare the mono-ligated analogues
of C1, C2 and C3 proved abortive as we observed that coordination
of L1 and L3 with nickel halides displayed a preference for the bis-
ligand structures even when deliberate slight excess of nickel salt
was experimented. It is note worthy that all the case of bis-che-
lated nickel complexes were distinguishable by their characteristic
blue color and higher CHN values of elemental analyses (EA) in
contrast to the bright yellow shades of mono-ligated complexes
C4, C5 and C6 with lower EA values. It is also observable that all
bis-coordinated compounds resulted from ligands without ortho-
methyl group to the pyridyl nitrogen, which probably hindered
the phenomenon in the instances of complexes derived from L2
and L4. In general, this phenomenon suggests the importance of
its steric influence of the ligand system. In contrast, the phenan-
thro-substituted ligands conformed to 1:1 complexation regardless
of whether R1 is methyl or proton. Therefore, it is considered that
the constrained ring of phenanthro-ring play roles in such
coordination.
4.1. X-ray crystallographic studies
Single-crystal X-ray diffraction studies for complexes C1, C4, C5
and C8 were done on a Rigaku R-AXIS Rapid IP diffractometer with
graphite monochromated Mo Ka radiation (k = 0.71073 Å). Intensi-
ties were corrected for Lorentz and polarization effects and empir-
ical absorption. A direct method was applied in solving the
structural data and refinement done by full-matrix least-squares
on F2. All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were placed in calculated positions except for
the imidazole and DMF carbonyl protons which were assigned
based on identified peak positions during refinement. Structure
solution and refinement were performed using the SHELXL-97 pack-
age [45]. Crystal data and processing parameters for C1, C4, C5 and
C8 are presented in Table 1.
5. Results and discussions
5.1. Syntheses of pyridine derivatives (L1–L7)
Using modified literature method [38], the imidazole ligands
(L1, L2, L5 and L6) and an oxazole analogue (L7) were synthesized
in appreciable to good yields by refluxing the respective a-diones,
5.3. Molecular structure of complexes
appropriate pyridinecarboxaldehyde and ten fold ammonium ace-
tate in ethanol/dichloromethane solvent mixture (1:1, v/v) in the
presence of catalytic amount of glacial acetic acid. Bearing in mind
the intention to tune the electronic properties of the imidazole
ring, L3 and L4 were prepared in good yields by respective methyl-
ation of 1-imidazole position on L1 and L2 using K2CO3 as base and
CH3I as alkylating agent in acetone. All the obtained compounds
were fully characterized by IR, 1H NMR, 13C NMR and elemental
analyses. According to the method of Steck and Day [38], prepara-
Single crystals of C1 suitable for X-ray diffraction were grown
by slow diffusion of diethyl ether into its methanol solution. The
molecular structure is shown in Fig. 1. The distorted octahedral
coordination environment of complex C1 consists of two units of
ligand L1, one chloride and an oxygen atom from adducted meth-
anol group. The chelating ligands provided four N atoms such that
the two pyridyl rings are trans-displaced (N1–Ni(1)–N4 =
175.66(9)°) while the imidazolyl nitrogen donors are cis-placed
(N2–Ni–N5 = 84.30°). The chloride and oxygen atoms are located
cis- to each other and form an approximate right angle
(84.32(9)°). The second chloride anion is detached from metal
center and located within the crystal lattice mediating H-bond net-
works. The Ni–N bond lengths (Ni(1)–N1 = 2.095(3) Å, Ni(1)–
N2 = 2.095(3) Å), which are equal, Ni(1)–Cl1 = 2.4668(9) Å and
Ni(1)–O1 = 2.071(3) Å are similar to those nickel analogues ob-
served in the literatures [42–44], and in the typical range for nickel
complexes. In each ligand, the pyridyl and imidazolyl ring together
with the chelating ring are almost in the same plane, while
dihedral angles between the substituent phenyl groups and the
five-membered ring randomly varied; planes (C9–C10–C11–C12–
C13–C14) and (C15–C16–C17–C18–C19–C20) of one ligand unit
formed dihedral angles of 71.2° and 14.6°, respectively, with their
imidazole ring (N2–C6–N3–C8–C7), while planes (C49–C50–C48–
C47–C46–C45) and (C39–C44–C43–C42–C41–C40) of the second
ligand unit formed dihedral angles 43.1o and 30.1o with their imid-
azole plane (N6–C36–C38–C37–N5), respectively.
tion of imidazoles by coupling
a-diones with aldehydes in the
presence of excess ammonium acetate is usually conducted by
refluxing in glacial acetic acid serving the dual purpose of solvent
as well as reaction catalyst. Attempts to prepare L1, L2 and L5–
L7 in glacial acetic acid as solvent usually gave a mixture of many
products and no appreciable amount of the target ligands even
when conducted under nitrogen protection. To the best of our
knowledge, detailed synthetic protocol is unavailable for oxazole
and/or imidazole ring synthesis by condensation of a-diones with
aldehyde-substituted pyridines. Our careful examination of 1H
NMR data for the only known condensation attempt reveals that
the oxazole derivative was obtained, but was thought to be and re-
ported as the target imidazole ligand [39]. Attempt to use either
ethanol or dichloromethane as a single solvent reaction system
gave insignificant yields obviously because of difference in solubil-
ity of benzil or phenanthrene on the one hand and ammonium ace-
tate on the other hand. Phenanthrenequinone formed both oxazole
(major) and imidazole products. However, the oxazole analogue
was not noticed when benzil was employed as reactant under sim-
ilar reaction action conditions. This can be rationalized from the
close proximity and alignment of the two carbonyl groups in phen-
anthrenequinone relative to that in benzil, which has O–O dihedral
angle as large as 90° [40]. Cyclic coupling of N–O phenanthrene
intermediates with the aldehyde moieties is, thus, suggested to oc-
The steric demands caused by ortho-substituent methyl group
on the pyridyl ring lead to mono-ligand structures. From the ORTEP
plot of C4 (Fig. 2), the Ni center can best be described as square
pyramidal. The square plane consists of the trans-chloride atoms,
pyridyl N(1) and O(1) of coordinated methanol and the angles be-
tween diagonals of the tetragonal plane are all close to right an-
gles: N(1)–Ni(1)–Cl(2) = 91.02(9); N(1)–Ni(1)–Cl(1) = 86.79(9);

A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
1975
Single crystals of C5 were obtained by layering diethyl ether on
the methanol solution of the complex. The molecular structure is
shown in Fig. 3. Coordination of each nickel center can be de-
scribed as distorted trigonal bipyramidal. Each nickel center is
coordinated to two nitrogen atoms, one terminal chloride and
two bridging chlorides. The distance between nickel and the termi-
nal chloride (Ni(1)–Cl(2)) is 2.3429(2) Å, while the bond lengths
between Ni and the bridged chlorides differ: (Ni(1)–
Cl(1) = 2.3140(12) Å and Ni(1)–Cl(1A) = 2.4466(18) Å. The bridging
ring is planar with a Ni(1)–Ni(1A) distance of 3.568 Å and located
approximately perpendicular to both chelating rings with dihedral
angles of 90.7° on either sides.
Crystals of C8 obtained as brown blocks were grown by slow
diffusion of diethyl ether into DMF solution of the complex
(Fig. 4). One DMF molecule was found to be hydrogen bonded to
the imidazole proton was. The nickel center has a distorted tetra-
hedral coordination environment consisting to two ligand donor
nitrogen and the two chloride atoms. The pyridyl ring (C2–C3–
C4–C5–N1–C1) is almost co-planar with the phenanthrene rings
(C6–N3–C7–C8–N2) with dihedral angle 1.08°. The Ni–N bond
lengths (Ni(1)–N(1) = 2.022(3) Å; Ni(1)–N(2) = 1.996(3) Å) are al-
most similar to those observed in C4. The two Ni–Cl lengths
(Ni(1)–Cl(1) = 2.2404(9) Å, Ni(1)–Cl(2) = 2.1873(9) Å) are slightly
different, but shorter than those in C4 (2.3370(9) and
2.3591(9) Å). Comparison of the structures of C4 and C8 reveals
that the two nickel centers possess only a slight difference in steric
properties. Thus, it is probable that the structural difference and
difference in their catalytic performances are influenced by steric
effects inherent in the respective ligands.
Fig. 1. Molecular structure of complex C1. Thermal ellipsoids are drawn at 30%
probability level. Crystallized methanol and all hydrogen atoms have been omitted
for clarity. Selected bond lengths (Å): Ni(1)–O(1) = 2.071(3), Ni(1)–N(2) = 2.095(3),
Ni(1)–N(1) = 2.095(3), Ni(1)–N(5) = 2.106(2), Ni(1)–N(4) = 2.112(3), Ni(1)–Cl(1) =
2.4668(1). Selected bond angles (°): O(1)–Ni(1)–N(2) = 169.40(2), O(1)–Ni(1)–
N(1) = 90.54(1), N(2)–Ni(1)–N(1) = 79.36(1), O(1)–Ni(1)–N(5) = 94.29(2), N(2)–
Ni(1)–N(5) = 84.32(1), N(1)–Ni(1)–N(5) = 99.60(1), O(1)–Ni(1)–N(4) = 85.25(2),
N(2)–Ni(1)–N(4) = 104.79(1),
N(1)–Ni(1)–N(4) = 175.66(1),
N(5)–Ni(1)–N(4) =
79.73(1), O(1)–Ni(1)–Cl(1) = 91.97(8), N(2)–Ni(1)–Cl(1), = 91.08(7), N(1)–Ni(1)–
Cl(1) = 88.97(7), N(5)–Ni(1)–Cl(1) = 169.32(7), N(4)–Ni(1)–Cl(1) = 92.20(8).
O(1)–Ni(1)–Cl(2) = 86.19(9); O(1)–Ni(1)–Cl(1) = 91.28(9). The axial
position is occupied by the imidazole donor nitrogen which also
formed angles 111.29(13)°, 100.71(10)°, 100.79(9)° and
80.97(12)° with donors on the tetragonal plane. A free methanol
molecule was observed in the crystal lattice of C4. Angle between
the two chlorides, Cl(1)–Ni(1)–Cl2(1), is 157.75(4)°. Generally, the
distances between Ni center and the O or N atoms are similar to
those found in C1, while the Ni–Cl bond lengths found in C4
(Ni(1)–Cl(1) = 2.3370(9) Å; Ni(1)–Cl(2) = 2.3591(9) Å) are slightly
shorter compared to observed value for C1 (2.4668(9) Å). In C4,
the dihedral angle between the two phenyl rings (C9–C10–C11–
C12–C13–C14 and C15–C16–C17–C18–C19–C20) and the imidazo-
lyl ring (N2–C6–N3–C8–C7) are 61.1° and 19.8°, respectively.
5.4. Norbornene polymerization
To study the trends with influences of reaction parameters on
catalytic performance of norbornene polymerization, the catalyst
precursor C4 was typically used. Increasing the monomer concen-
trations with fixed amount of C4 (i.e. increase in M/Ni ratio) re-
sulted in a dramatic increase of catalytic activity (Table 2).
Activity increase up to 3.78 Â 106 g PNB/(mol Ni h) was observed
for M/Ni ratio of 32000 from the value of 1.93 Â 105 g PNB/(mol -
Ni h) for M/Ni ratio of 4000 (Table 2, Entry 1 versus Entry 4). Mean-
while, higher molecular weight and broader molecular weight
polydispersity were obtained with the elevation of the monomer
concentration (Table 2, Entries 1–4).
Fig. 2. Molecular structure of complex C4. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms and methanol solvent have been omitted for
clarity. Selected bond lengths (Å): Ni(1)–O(1) = 2.013(3), Ni(1)–N(2) = 2.014(3),
Ni(1)–N(1) = 2.075(3), Ni(1)–Cl(1) = 2.3370(11), Ni(1)–Cl(2) = 2.3591(1). Selected
bond angles (°): O(1)–Ni(1)–N(2) = 111.29(1), O(1)–Ni(1)–N(1)=167.73(12), N(2)–
Ni(1)–N(1) = 80.97(1), O(1)–Ni(1)–Cl(1) = 91.28(9), N(2)–Ni(1)–Cl(1) = 100.71(1),
Fig. 3. Molecular structure of complex C5. Thermal ellipsoids are shown at the 30%
probability level. All hydrogen atoms and most atomic labels for the second
complex unit have been omitted for clarity. Selected bond lengths (Å): Ni(1)–
N(2) = 2.012(3), Ni(1)–N(1) = 2.035(3), Ni(1)–Cl(1) = 2.3140(1), Ni(1)–Cl(2) =
2.3429(2), Ni(1)–Cl(1A) = 2.4466(2). Selected bond angles (°): N(2)–Ni(1)–N(1) =
80.92(1), N(2)–Ni(1)–Cl(1) = 130.38(1), N(1)–Ni(1)–Cl(1) = 147.42(1), N(2)–Ni(1)–
Cl(2) = 97.23(1), N(1)–Ni(1)–Cl(2) = 91.42(1), Cl(1)–Ni(1)–Cl(2) = 92.76(5), N(2)–
Ni(1)–Cl(1A) = 91.05(1).
N(1)–Ni(1)–Cl(1) = 86.79(9),
O(1)–Ni(1)–Cl(2) = 86.19(9),
N(2)–Ni(1)–Cl(2) =
100.79(9), N(1)–Ni(1)–Cl(2) = 91.02(9), Cl(1)–Ni(1)–Cl(2) = 157.75(4).

1976
A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
the mono-ligand precursors C4–C6 (Entries 1–3 versus Entries 4–
6, Table 4). This is probably as a result of less favourable generation
of active components due to the number of coordination sites al-
ready claimed by the four N donors of the ligands. Moreover,
broader molecular weight distributions were obtained with C1–
C3 in comparison with those of C4–C6 (Entries 1–3 versus Entries
4–6, Table 4).
Complex C8 (R1 = Me) showed higher activity than C7 (R1 = H)
(Entry 8 versus Entry 7, Table 4), which indicates that the incorpo-
ration of a methyl group on the six-position of the pyridyl ring in
the complex caused slightly higher activity together with compara-
ble molecular weight and molecular weight distribution (Entry 8
versus Entry 7, Table 4).
Comparison of the productivity of C1 (R1 = R2 = H) with C2
(R1 = H, R2 = Me) or C4 ((R1 = R2 = H) with C5 (R1 = R2 = Me) reveal
that the introduction of a methyl group on the N atom of imidazole
leads to a decrease in the catalytic activity (Entry 1 versus Entry 2,
or Entry 4 versus Entry 5, Table 4). Complexes C1 and C4 contain-
ing N–H group showed higher activities than their N-alkylated ana-
logues C2 and C5. Tentatively, these results suggest that N–H
functionality is essential for high activity with this ligand system,
which could be caused by their deprotonation to give anionic
amide ligands when activated by MAO. The anionic amide ligands
could be free or form N–Al species (anion–cation pair) to increase
their catalytic activity. The observation is in agreement with our
previous result in ethylene polymerization catalyzed by (2-benz-
imidazolyl)pyridyl nickel systems [44].
Complexes C8 containing phenanthrene group exhibited much
lower activity than its 4,5-diphenyl analogue C4, which may be
attributed to the fact that the two steric bulky phenyl groups can
flexibly protect the active species from C4. However, the bulky
phenanthrene group is rigid and tends to be coplanar with the
imidazole ring, and thus support relatively less steric hindrance
to protect the active species from C8.
Fig. 4. Molecular structure of complex C8. Thermal ellipsoids are shown at the 30%
probability level. Hydrogen atoms and the hydrogen bonded DMF have been
omitted for clarity. Selected bond lengths (Å): Ni(1)–N(2) = 1.996(3), Ni(1)–
N(1) = 2.022(3), Ni(1)–Cl(2) = 2.1873(1), Ni(1)–Cl(1) = 2.2404(1). Selected bond
angles (°): N(2)–Ni(1)–N(1) = 82.38(1), N(2)–Ni(1)–Cl(2) = 118.81(8), N(1)–Ni(1)–
Cl(2) = 127.97(8), N(2)–Ni(1)–Cl(1) = 104.53(8), N(1)–Ni(1)–Cl(1) = 97.65(8), Cl(2)–
Ni(1)–Cl(1) = 118.34(4).
Table 2
Effect of norbornene concentration on activity of C4.a
c
Entry
M/Ni
PNB (g)
Yield (%)
Activityb
Mw
Mw/Mn
1
2
3
4
4000
8000
16000
32000
0.193
0.412
1.38
26.6
27.3
45.7
62.0
1.93
4.12
13.8
37.8
5.43
9.01
20.8
23.3
2.06
2.33
3.05
3.36
3.78
a
Condition: 2.0 lmol C4; MAO/Ni = 2000; total solution volume 10 mL ; 30 min;
20 °C.
b
c
105 g PNB/(mol Ni h).
105 g/mol.
The results on effect of reaction temperatures are presented in
Table 3. The catalytic system displayed good activity over the stud-
ied range of reaction temperatures and the reaction temperature
showed limited influence on the catalytic activities. The catalytic
activities increase initially with temperature from 0 to 20 °C and
reach a maximum around 20 °C. However, as reaction temperature
increases from 20 to 80 °C, the activity of the catalyst decreases
gradually. It is noteworthy that the molecular weight (Mw) contin-
ually decreased coupled with narrowing molecular weight polydis-
persity (Mw/Mn) at increasing reaction temperature (Table 3,
Entries 1–5). Nickel b-diketiminates [45] and (benzamidina-
to)(acetylacetonato) nickel complexes [46] were found to exhibit
higher productivities and higher polymer molecular weights at
reducing temperatures, but this is in direct contrast with behaviour
of anilido–imino nickel [29] for which trigger mechanism [37] was
proposed.
Additionally, the variation of heteroatoms in the five-mem-
bered donor ring exhibited influence on the catalytic performance.
Complex C9 containing an oxazole ring showed higher activity
than C7 bearing an imidazole ring under the same reaction condi-
tions (Entry 9 versus Entry 7, Table 4). Higher activity on reduction
of donor capacity of the five-membered ring donor nitrogen is im-
plied in both cases and agrees with the literature findings [47]. It is
interesting to note that the bromide complexes yielded obvious
higher molecular weight polymers and wider molecular weight
distributions relative to their chloride counterparts (Entry 1 versus
Entry 3, Entry 4 versus Entry 6, Table 4).
5.5. 13C NMR characterization of polynorbornene
Two representative samples of polynorbornenes obtained in the
current experiments were characterized by solid state 13C NMR
The polymerization data for C1–C9 are presented in Table 4. The
coordination environment obviously has effect on the catalytic
performances of the activated complexes. The bis-ligand com-
plexes, C1–C3, presented lower productivity results compared to
Table 4
Activities of complexes C1–C9 for the polymerization of norbornene.a
Activityb
Mw
Mw/Mn
c
Entry
Cat.
PNB (g)
Yield (%)
Table 3
1
2
3
4
5
6
7
8
9
C1
C2
C3
C4
C5
C6
C7
C8
C9
0.403
0.393
0.539
0.896
0.562
0.679
0.353
0.427
0.423
27.3
26.6
32.5
60.6
38.1
46.0
23.9
28.9
28.6
4.03
3.93
5.39
8.96
5.62
6.79
3.53
4.27
4.23
1.53
5.25
16.8
9.01
7.91
11.5
12.9
12.6
10.7
3.01
2.70
4.12
2.33
1.52
2.62
2.24
2.34
2.15
Influence of reaction temperatures on the activity of complex C4.a
Activityb
Mw
Mw/Mn
c
Entry
T (°C)
PNB (g)
Yield (%)
1
2
3
4
5
0
0.650
0.896
0.490
0.455
0.388
44.0
60.6
33.2
30.8
26.3
6.50
8.96
4.90
4.55
3.88
12.7
9.01
5.61
3.88
3.17
2.42
2.33
2.16
1.90
1.75
20
40
60
80
a
a
Conditions: 2.0
lmol C4; MAO Al/Ni = 2000; Norbornene/Ni = 8000; total
Condition: 2.0 lmol precursors; MAO/Ni = 2000; Norbornene/Ni = 8000; total
solution volume 10 mL, 30 min.
solution volume 10 mL; 30 min; 20 °C.
b
b
105 g PNB/(mol Ni h).
105 g PNB/(mol Ni h).
105 g/mol.
105 g/mol.
c
c

A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
1977
Fig. 5. Solid state 13C NMR spectra of polynorbornenes obtained by C4 (a), C5 (b) and literature catalyst (c)12
.
measurements. Main signals occurred in the ranges of 50 ppm
through 30 ppm with peaks at 48.5, 38.8 and 31.7 ppm for samples
(Entries 4 and 5, Table 4) obtained by C4 (Fig. 5a) and C5 (Fig. 5b),
however, surprisingly the observable signals around the 130 ppm
region indicated C@C bonds remaining in the polymeric samples.
In fact, two samples are with relative narrow molecular weight dis-
tributions, and it could be figured out that the impurity or by-prod-
uct of polymers appeared. In another word, the resultant polymers
in norbornene polymerization are unique polymers instead of
combined polymers. Therefore, there are double bonds remaining
in resulting polymers, and the double bonds could only occurred
through partly happened ring-open metathesis polymerization of
norbornene.
complexes, while mono-ligated complexes were obtainable from
L2, L4 and L5–L7. Moreover, X-ray analysis revealed that slight
variations on ligand structures informed definite preference of
coordination geometry about the nickel centers from tetrahedral
structure, through trigonal bipyramid and square pyramid to octa-
hedral assemblies. The tetrahedral structure of C8 showed that the
phenanthro-derived ligand formed their own class of robust donor
ability; an indication of significant difference in steric attribute of
this group of ligands.
In the presence of MAO as cocatalyst, these nickel systems
showed good to high activities for norbornene polymerization.
The bis-chelated nickel complexes (C1, C2 and C3) showed rela-
tively lower catalytic activities with broader molecular weight dis-
tributions than their mono-ligand counterparts (C4, C5 and C6).
Presence of a protective methyl group ortho- to pyridyl donor
nitrogen generally improved catalytic productivity. Higher activity
with less donating oxazole ring relative to imidazole was observed.
The polynorbornenes obtained in current system would be new
type blocked polymers through mainly vinyl-type and minor
ring-opening metathesis polymerization of norbornene.
To approve this point, the solid state 13C NMR of polynorborn-
ene obtained according to our previous work (Entry 4 of Table 3
of literature [12]) is carefully investigated, and its spectrum ap-
peared as Fig. 5c. It is no doubt that the polynorbornene through
vinyl-type polymerization do not have any C@C bond, though such
polynorbornene had wide molecular weight distributions [12].
According to the comparisons of the solid state 13C NMR spec-
tra, the polynorbornenes were obtained through mainly vinyl-type
and minor ring-opening metathesis polymerization of norbornene.
The nature of blocked polymer is proposed on the base of the uni-
modal GPC curves and yet narrow PDIs of obtained polymers. The
resultant polynorbornenes would be new type blocked polymers
with potential advantage of having melting points if the C@C bonds
in polymer chain could be reductive and foldable. Experiments per-
taining to the ratios and possibility of tuning the ratios would be
undergoing.
Acknowledgements
This work was supported by NSFC No. 20674089. A.O.E. is grate-
ful to the Chinese Academy of Science (CAS) and The Academy of
Science for The Developing World (TWAS) for the Postgraduate
Fellowships.
Appendix A. Supplementary material
CCDC 714491, 714492, 714493 and 714494 contain the supple-
mentary crystallographic data for C1, C4, C5 and C8. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2009.02.026.
6. Conclusions
A series of new nickel complexes bearing 2-(4,5-diphenyl-imi-
dazol-2-yl)pyridines or 2-(pyridin-2-yl)phenanthroimidazoles/
oxazole was synthesized and fully characterized. Reaction of L1
and L3 with nickel dihalides selectively formed blue, bis-ligated

1978
A.O. Eseola et al. / Inorganica Chimica Acta 363 (2010) 1970–1978
[24] W. Zhang, W.-H. Sun, S. Zhang, J. Hou, K. Wedeking, S. Schultz, R. Frohlich, H.
References
Song, Organometallics 25 (2006) 1961.
[25] Q.-S. Shi, W.-W. Zuo, Chin. J. Polym. Sci. 26 (2008) 561.
[26] N.H. Tarte, H.Y. Cho, S.I. Woo, Macromolecules 40 (2007) 8162.
[27] Y. Wang, S. Lin, F. Zhu, H. Gao, Q. Wu, Eur. Polym. J. 44 (2008) 2308.
[28] F.-B. Han, Y.-L. Zhang, X.-L. Sun, B.-G. Li, Y.-H. Guo, Y. Tang, Organometallics 27
(2008) 1924.
[29] H. Gao, J. Zhang, Y. Chen, F. Zhu, Q. Wu, J. Mol. Catal. A 240 (2005) 178.
[30] J. Hou, S. Jie, W. Zhang, W.-H. Sun, J. Appl. Polym. Sci. 102 (2006) 2233.
[31] Q. Shi, S. Jie, S. Zhang, H. Yang, W.-H. Sun, Macromol. Symp. 260 (2007) 74.
[32] X. Meng, G.R. Tang, G.-X. Jin, Chem. Commun. (2008) 3178.
[33] W.-G. Jia, Y.-B. Huang, Y.-J. Lin, G.-X. Jin, Dalton Trans. (2008) 5612.
[34] F. Blank, C. Janiak, Coord. Chem. Rev. 253 (2009) 827.
[35] T.F.A. Haselwandel, W. Heitz, Macromol. Rapid Commun. 18 (1997) 689.
[36] M.C. Sacchi, M. Sonzogni, S. Losio, F. Forlini, P. Locatelli, I. Tritto, M. Licchelli,
Macromol. Chem. Phys. 202 (2001) 2052.
[37] M. Ystenes, Makromol. Chem. Macromol. Symp. 66 (1993) 71.
[38] E.A. Steck, A.R. Day, J. Am. Chem. Soc. 65 (1943) 452.
[39] K. Wang, L. Gao, G. Bai, L. Jin, Inorg. Chem. Commun. 5 (2002) 841.
[40] K. Mizuno, N. Kamiyama, N. Ichinose, Y. Otsuji, Tetrahedron 41 (1985) 2207.
[41] C.W.C. Stein, A.R. Day, J. Am. Chem. Soc. 64 (1942) 2567.
[42] W.-H. Sun, P. Hao, S. Zhang, Q. Shi, W. Zuo, X. Tang, Organometallics 26 (2007)
2720.
[1] A.W. Andersen, N.G. Merkling, US Patent 2721189, to DuPont, Chem. Abstr. 50
(1954) 3008i.
[2] R.H. Grubbs, Tetrahedron 60 (2004) 7117.
[3] R.R. Schrock, Angew. Chem., Int. Ed. 45 (2006) 3748.
[4] R.H. Grubbs, Angew. Chem., Int. Ed. 45 (2006) 3760.
[5] G. Sartori, F.C. Ciampelli, N. Cameli, Chim. Ind. (Milan) 45 (1963) 1478.
[6] B.L. Good, in: B. Rieger, L.S. Baugh, S. Kacker, S. Striegler (Eds.), Late Transition
Metal Polymerization Catalysts, Wiley-VCH, Weinheim, 2003, p. 101.
[7] C. Janiak, P.G. Lassahn, J. Mol. Catal. A: Chem. 166 (2001) 193.
[8] C. Janiak, P.G. Lassahn, Macromol. Rapid Commun. 22 (2001) 479.
[9] M. Arndt, I. Beulich, Macromol. Chem. Phys. 199 (1998) 1221.
[10] S. Ahmed, S.A. Bidstrup, P.A. Kohl, P.J. Ludovice, J. Phys. Chem. B 102 (1998)
9783.
[11] B.S. Heinz, F.P. Alt, W. Heiz, Macromol. Rapid Commun. 19 (1998) 251.
[12] W.-H. Sun, H. Yang, Z. Li, Y. Li, Organometallics 22 (2003) 3678.
[13] H. Yang, W.-H. Sun, F. Chang, Y. Li, Appl. Catal. A 252 (2003) 261.
[14] H. Yang, Z. Li, W.-H. Sun, J. Mol. Catal. A 206 (2003) 23.
[15] W.-H. Sun, H.-J. Yang, Z.-L. Li, Chin. Patent 02 1 263 18.3, 2002.
[16] X. Mi, Z. Ma, N. Cui, L. Wang, Y. Ke, Y. Hu, J. Appl. Polym. Sci. 88 (2003).
[17] X.-F. Li, Y.-S. Li, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 2680.
[18] C. Mast, M. Krieger, K. Dehnicke, A. Greiner, Macromol. Rapid Commun. 20
(1999) 232.
[43] W.-H. Sun, K. Wang, K. Wedeking, D. Zhang, S. Zhang, J. Cai, Y. Li,
Organometallics 26 (2007) 4871.
[44] P. Hao, S. Zhang, W.-H. Sun, Q. Shi, S. Adewuyi, X. Lu, P. Li, Organometallics 26
(2007) 2439.
[45] Y. Li, M. Gao, Q. Wu, Appl. Organometal. Chem. 21 (2007) 965.
[46] E. Nelkenbaum, M. Kapon, M.S. Eisen, Organometallics 23 (2005) 2645.
[47] J.A. Casares, P. Espinet, J.M. Martín-Alvarez, J.M. Martínez-Ilarduya, G. Salas,
Eur. J. Inorg. Chem. (2005) 3825.
[19] Q. Wu, Y.-Y. Lu, J. Polym. Sci. Part A: Polym. Chem. 40 (2002) 1421.
[20] F. Chang, D. Zhang, G. Xu, H. Yang, J. Li, H. Song, W.-H. Sun, J. Organomet. Chem.
689 (2004) 936.
[21] D. Zhang, S. Jie, H. Yang, F. Chang, W.-H. Sun, Chin. J. Polym. Sci. 23 (2005) 619.
[22] J. Hou, W.-H. Sun, D. Zhang, L. Chen, W. Li, D. Zhao, H. Song, J. Mol. Catal. A 231
(2005) 221.
[23] D. Zhang, S. Jie, T. Zhang, J. Hou, W. Li, D. Zhao, W.-H. Sun, Acta Polym. Sinica 5
(2004) 758.