Synthesis, molecular structure, and solution-dependent behavior of nickel complexes chelating anilido-imine donors and their catalytic activity toward olefin polymerization

Article abstract of DOI:10.1021/om049367t

A series of novel nickel complexes (1-4) bearing anilido-imine ligands, [(Ar¹N=CHC₆H₄-NAr²)NiBr] ₂ (Ar¹ = Ar² = 2,6-dimethylphenyl, 1; Ar ¹ = 2,6-dimethylphenyl, Ar² = 2,6-diisopropylphenyl, 2; Ar¹ = Ar² = 2,6-diisopropylphenyl, 3; Ar¹ = 2,6-diisopropylphenyl, Ar² = 2,6-dimethylphenyl, 4), have been synthesized and characterized. The solid-state structures of the complexes 1, 2, and 4 were confirmed by X-ray single-crystal analyses to be in the form of a dinuclear and bromine-bridged structure. However, there is an equilibrium that shifts between the monomer and dimer in solution, which has been monitored using ¹H NMR and UV-vis spectrophotometry. The themodynamic parameters for the equilibriums were calculated to be ΔH = +13.68 kJ/mol and ΔS = 40.32 J/(mol K) for 1 and ΔH = +8.35 kJ/mol and ΔS = 15.21 J/(mol K) for 3. All nickel complexes show low activities for ethylene oligomerization with MAO as cocatalyst but high catalytic activities for norbornene polymerization in the presence of MAO.

Full text of DOI:10.1021/om049367t

Organometallics 2004, 23, 6273-6280
6273
Synthesis, Molecular Structure, and Solution-Dependent
Behavior of Nickel Complexes Chelating Anilido-Imine
Donors and Their Catalytic Activity toward Olefin
Polymerization
Haiyang Gao, Wenjuan Guo, Feng Bao, Guoqiu Gui, Junkai Zhang,
Fangming Zhu, and Qing Wu*
Institute of Polymer Science, School of Chemistry and Chemical Engineering,
Sun Yat-Sen (Zhongshan) University, Guangzhou 510275, China
Received August 14, 2004
A series of novel nickel complexes (1-4) bearing anilido-imine ligands, [(Ar1NdCHC6H4-
NAr2)NiBr]2 (Ar1 ) Ar2 ) 2,6-dimethylphenyl, 1; Ar1 ) 2,6-dimethylphenyl, Ar2 ) 2,6-
diisopropylphenyl, 2; Ar1 ) Ar2 ) 2,6-diisopropylphenyl, 3; Ar1 ) 2,6-diisopropylphenyl, Ar2
) 2,6-dimethylphenyl, 4), have been synthesized and characterized. The solid-state structures
of the complexes 1, 2, and 4 were confirmed by X-ray single-crystal analyses to be in the
form of a dinuclear and bromine-bridged structure. However, there is an equilibrium that
1
shifts between the monomer and dimer in solution, which has been monitored using H
NMR and UV-vis spectrophotometry. The themodynamic parameters for the equilibriums
were calculated to be ∆H ) +13.68 kJ/mol and ∆S ) 40.32 J/(mol K) for 1 and ∆H ) +8.35
kJ/mol and ∆S ) 15.21 J/(mol K) for 3. All nickel complexes show low activities for ethylene
oligomerization with MAO as cocatalyst but high catalytic activities for norbornene
polymerization in the presence of MAO.
Introduction
membered chelate ring.3 Later, late-transition-metal
complexes chelating six-membered rings were less
frequently reported until neutral nickel complexes
chelating salicylaldiminate ligands were reported by the
Grubbs group to have high activity in polymerizing
olefin and polar monomer.4,5 Recently, six-membered
anionic â-diketiminate ligands has been dramatically
applied in bioinorganic and transition-metal chemis-
try,6,7 and bulky â-diketiminato nickel complexes have
been prepared.7c,e Our groups and others have also
found that some â-diketiminato nickel complexes show
good activity toward polymerizations of norbornene and
ethylene.8
Over the past decade, late-transition-metal catalysts
for olefin polymerization have received increasing at-
traction, for they are much less oxophilic and more
tolerant of polar functional groups than the catalysts
ordinarily used.1 Brookhart and his collaborators suc-
cessfully developed bulky R-diimine nickel and pal-
ladium complexes, which show high catalytic activity
for R-olefin polymerization.1a Subsequently, R-diimine
nickel and palladium complexes chelating five-mem-
bered rings were fully investigated in R-olefin polym-
erization.1,2 Feldman et al. reported that nickel and
palladium complexes chelating six-membered neutral
â-diketimine ligands showed less activity for ethylene
polymerization than R-diimine nickel and palladium
complexes, due to the change from a five- to six-
(2) (a) Brookhart, M.; Rix, F. C.; DeSimone, J. M. J. Am. Chem. Soc.
1992, 114, 5894. (b) Rix, F. C.; Brookhart, M. J. Am. Chem. Soc. 1995,
117, 1137. (c) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem.
Soc. 1996, 118, 4746. (d) Shultz, C. S.; DeSimone, J. M.; Brookhart,
M. Organometallics 2001, 20, 16. (e) Small, B. L.; Brookhart, M.;
Bennett, A. M. A. J. Am. Chem. Soc. 1998, 120, 4049. (f) Dias, E. L.;
Brookhart, M.; White, P. S. Organometallics 2000, 19, 4995.
(3) Feldman, J.; McLain, S. J.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(4) (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460. (b) Wang,
C.; Friedrish, S.; Younkin, T. R.; Grubbs, R. H. Organometallics 1998,
17, 3149.
* To whom correspondence should be addressed. Fax: (086)-020-
84112245. Tel: (086)-020-84113250. E-mail: ceswuq@zsu.edu.cn.
(1) (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem.
Soc. 1995, 117, 6414. (b) Johnson, L. K.; Mecking, S.; Brookhart, M.
J. Am. Chem. Soc. 1996, 118, 267. (c) Killian, C. M.; Tempel, D. J.;
Johnson, L. K.; Brookhart, M. J. Am. Chem. Soc. 1996, 118, 11664.
(d) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometallics 1997,
16, 2005. (e) McLain, S. J.; Feldman, J.; McCord, E. F.; Gardner, K.
H.; Teasley, M. F.; Coughlim, E. B.; Sweetman, K. J.; Johnson, L. K.;
Brookhart, M. Macromolecules 1998, 31, 6705. (f) Tempel, D. J.;
Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart, M. J. Am. Chem.
Soc. 2000, 122, 6686. (g) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.;
Kimerley, B. S.; Maddox, P. J.; Mastroianni, S.; McTavish, S. J.;
Redshaw, C.; Solan, G. A.; Stroemberg, S.; White, A. J. P.; Williams,
D. J. J. Am. Chem. Soc. 1999, 121, 8728. (h) Britovsek, G. J. P.; Gibson,
V. C.; Kinberley, B. S. Chem. Commun. 1998, 849. (i) He, X.-H.; Yao,
Y.-Z.; Luo, X.; Zhang, J.; Liu, Y.; Zhang, L.; Wu, Q. Organometallics
2003, 22, 4952. (j) He, X.-H.; Yao, Y.-Z.; Wu, Q. Polym. Mater. Sci.
Eng. 2003, 89. (k) Luo, X.; Zhang, J.-K.; Wu, Q. Polym. Prepr. 2002,
43(2), 1161.
(5) (a) Li, X.-F.; Li, Y.-S. J. Polym. Sci., Part A: Polym. Chem. 2002,
40, 2680. (b) Sun, W.-H.; Yang, H.-J.; Li, Z.-L.; Li, Y. Organometallics
2003, 22, 3678.
(6) (a) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev.
2002, 102, 3031. (b) Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc.
1999, 121, 7270. (c) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G.
Eur. J. Inorg. Chem. 1998, 1485. (d) Spencer, D. J. E.; Reynolds, A.
M.; Holland, P. L.; Jazdzewski, B. A.; Duboc-Toia, C.; Page, L. L.;
Yokota, S.; Tachi, Y.; Itoch, S.; Tolman, W. B. Inorg. Chem. 2002, 41,
6307. (e) Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland,
P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. (f) Dove, A.
P.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.; Williams, D. J. Dalton
2004, 570.
10.1021/om049367t CCC: $27.50 © 2004 American Chemical Society
Publication on Web 11/17/2004

6274 Organometallics, Vol. 23, No. 26, 2004
Gao et al.
Table 1. Crystallographic Data for Complexes 1, 2,
and 4
Scheme 1. Preparation of Nickel Complexes 1-4
1
2
4
empirical formula
C
46H46Br2-
C54H62Br2-
N4Ni2
C54H62Br2-
N4Ni2
N4Ni2
formula wt
temp (K)
cryst syst
space group
a (Å)
932.11
293(2)
monoclinic
P21/n
9.208(3)
11.424(3)
20.779(6)
90
1044.32
293(2)
triclinic
P1h
9.008(1)
11.122(1)
13.541(2)
73.925(2)
6.381(2)
84.357(2)
1266.1(3)
1
1044.32
293(2)
monoclinic
P21/c
13.674(5)
13.350(5)
16.997(7)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
100.503(5)
90
125.038(6)
90
2149.2(11)
2
2540.6(16)
2
Z
Dt (Mg/m3)
1.440
1.370
2.36
540
1.365
abs coeff (mm-1
F(000)
)
2.771
2.352
952
1080
cryst size (mm)
0.49 × 0.44 × 0.50 × 0.20 × 0.49 × 0.42 ×
0.31
0.07
1.6-27.1
0.35
1.82-27.06
θ range (deg)
index ranges
1.99-27.05
-11 e h e 11 -11 e h e 11 -17 e h e 17
-6 e k e 14
-14 e k e 14 -11 e k e 17
-26 e l e 26 -17 e l e 17 -21 e l e 16
In a comparison of salicylaldiminate ligands with
â-diketiminate ligands, the former have better conjuga-
tion and more easily modified features than the latter,
but â-diketiminate ligands have greater steric effect,
because two substituted aryl rings attached directly to
nitrogen atoms are close to the metal center. When the
steric effect of the â-diketiminate ligand is combined
with the more easily modified features of the salicyl-
aldiminate ligand, the result could be that bulky anilido-
imine compounds would find application in many areas
of inorganic and organometallic chemistry. More re-
cently, it has been reported that organoyttrium cations
chelating bulky anilido-imine ligands showed more
stability than â-diketiminato yttrium complexes.9
Herein the present contribution first reports the
syntheses and solid-state structure characterizations of
nickel complexes chelating bulky anilido-imine ligands
and investigates their interesting solution behavior.
Additionally, preliminary results from the complexes
catalyzing ethylene and norbornene polymerizations
after activation with methylaluminoxane (MAO) are
also shown.
no. of params
184
282
1.00
286
1.025
goodness of fit on F2 1.053
final R indices
0.0560, 0.1458 0.033, 0.078 0.0313, 0.0706
(I > 2σ(I))a
R indices (all data)a 0.0738, 0.1587 0.059, 0.090 0.0529, 0.0790
largest diff peak
1.257, -0.967 0.37, -0.38
0.552, -0.352
and hole (e/ Å-3
)
a R )∑llFol - lFcll∑lFol; Rw )[∑w(Fo - Fc )2/∑w(Fo2)2]1/2
.
2
2
o-fluorobenzaldehyde. In the second step, the anilido-
imine ligands can be obtained via a nucleophilic aro-
matic displacement of fluorine using LiN(H)Ar. Al-
though both of the reagents are reasonably sterically
bulky, the reaction occurs in good yield and is no doubt
aided by the electron-withdrawing nature of the neigh-
boring imine group. It is noteworthy that the steric
bulkiness of the ligands could be controlled easily by
changing various bulky arylamines, and nonsymmetric
ligands also could be synthesized by using various
arylamines at each step.10 All of these ligands have been
confirmed by EIMS, 1H NMR, 13C NMR, and elemental
analyses.
After the anilido-imine ligands were treated with
n-butyllithium in toluene, 1.1 equiv of (1,2-dimethoxy-
ethane)nickel(II) bromide ((DME)NiBr2) was added to
the solutions and the nickel complexes 1-4 were
obtained as dark green solids. The structures of anilido-
imino nickel complexes 1-4 were confirmed by elemen-
Results and Discussion
Ligands and Complex Syntheses. The three new
anilido-imine ligands L1, L2, and L4 were synthesized,
but L3 has been reported before.9 A general synthetic
route for these complexes is shown in Scheme 1. The
imine formation occurs smoothly at room temperature,
using the corresponding 2,6-substituted anilines and
1
tal analyses and EIMS and H NMR spectra (see the
Experimental Section).
Structural Features. Crystals of complexes 1, 2, and
4 suitable for single-crystal X-ray diffraction analyses
were grown from their hexane/toluene solutions. The
data collection and refinement data of the analyses are
summarized in Table 1. ORTEP diagrams are given in
Figures 1-3, respectively.
These three complexes exist as dimers in the solid
state with tetrahedral geometries about nickel and a
crystallographic C2 axis of symmetry that makes the two
units equivalent. As reported in the literature,3,7c the
nickel complex chelating a neutral â-diketimine ligand
has a nonplanar boat conformation, but the â-diketimi-
(7) (a) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416. (b) Panda, A.;
Stender, M.; Wright, R. J.; Olmstead, M. M.; Klavins, P.; Power, P. P.
Inorg. Chem. 2002, 41, 3909. (c) Eckert, N., A.; Bones, E., M.;
Lachicotte, R. J.; Holland, P. L. Inorg. Chem. 2003, 42, 1720. (d) Minas
da Piedade, M. E.; Simoes, J. A. M. J. Organomet. Chem. 1996, 518,
167. (e) Carey, D. T.; Cope-Eatough, E. K.; Vilaplana-Mafe˘ , E.; Mair,
F. C.; Pritchard, R. G.; Warren, J. E.; Woods, R. J. Dalton 2003, 1083.
(8) (a) Wu, Q.; Zhang, J.-K.; He, X.-H. German-Chinese Bilateral
Symposium on Organometallic Catalysts and Olefin Polymerization;
German Chemistry Society, Mu¨lheim, Germany, 2003; p 41. (b) Zhao,
D.; Jin, G.-X.; Weng, L.-H.; Wang, F.-S. Organometallics 2004, 23,
3270. (c) Wiencko, H. L.; Kogut, E.; Warren, T. H. Inorg. Chim. Acta
2003, 345, 199.
(9) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers,
W. E.; Parvez, M. Organometallics 2003, 22, 1577.
(10) Gao, H.-Y.; Wu, Q.; Ng, S. W. Acta Crystallogr. 2004, E60, o193.

Ni Complexes Chelating Anilido-Imine Ligands
Organometallics, Vol. 23, No. 26, 2004 6275
Figure 1. ORTEP plot of complex 1. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): Ni(1)-N(2), 1.886(4); Ni(1)-N(1), 1.942(4); Ni(1)-
Br(1)#1, 2.4135(8); Ni(1)-Br(1), 2.4464(8); N(2)-Ni(1)-
N(1), 94.28(17); N(2)-Ni(1)-Br(1)#1, 124.43(15); N(1)-
Ni(1)-Br(1)#1, 119.07(12); N(2)-Ni(1)-Br(1), 115.63(12);
N(1)-Ni(1)-Br(1), 114.48(11); Br(1)#1-Ni(1)-Br(1), 90.74-
(3); Ni(1)#1-Br(1)-Ni(1), 89.26(3); C(9)-N(1)-Ni(1), 122.0-
(4); C(1)-N(1)-Ni(1), 120.5(3); C(15)-N(2)-Ni(1), 127.0(4);
C(16)-N(2)-Ni(1), 113.6(4).
Figure 3. ORTEP plot of complex 4. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): Ni(1)-Br(1), 2.4415(7); Ni(1)-Br(1)#1, 2.4481(9); Ni-
(1)-N(1), 1.8861(18); Ni(1)-N(2), 1.9440(18); N(1)-Ni(1)-
N(2), 94.32(8); N(1)-Ni(1)-Br(1), 120.26(6); N(2)-Ni(1)-
Br(1), 116.23(6); N(1)-Ni(1)-Br(1)#1, 119.74(6); N(2)-
Ni(1)-Br(1)#1, 119.98(6); Br(1)-Ni(1)-Br(1)#1, 88.81(3);
Ni(1)-Br(1)-Ni(1)#1, 91.19(3); C(1)-N(1)-Ni(1), 128.70-
(15); C(7)-N(1)-Ni(1), 113.72(14); C(15)-N(2)-Ni(1),
123.36(16); C(16)-N(2)-Ni(1), 121.73(15).
unbalanced, owing to the difference in distance. The
complex 2 contains a more bulky aryl group attached
to the aniline than does the complex 4, implying that
there is a more crowded steric environment of the Ni
atom for 2 than for 4, even though these two complexes
have the same composition. Though there is an unbal-
anced steric effect of the N-aryl groups, the bite angles
(N-Ni-N) of the complexes are nearly the same. The
Ni-Br distances are longer than typical NiII-Br bonds.3
The planes (Ni-Br-Ni-Br) slightly deviate from a
rectangle. The bite angle (Br-Ni-Br) is slightly less
than 90° (87.29(1)° for 2 and 88.81(3)° for 4). In contrast
to complexes 2 and 4, the bite angle (Br-Ni-Br) of 1 is
slightly more 90° (90.74(3)°), which resulted from the
different steric effects of 2,6-substituents. The Ni-Ni
distances of complexes are over 3 Å, suggesting that
there is no direct metal-metal interaction.
Properties of Nickel Complexes in Solution. The
nickel complexes are sensitive to air and moisture and
show interesting solvent-dependent behavior. In the
solid state, these nickel complexes are dark green.
However, dissolution in toluene, benzene, and methyl-
ene chloride gave a green solution. At the same concen-
tration and temperature, the color of the anilido-imino
nickel complex 1 solution persists longer than that of
3, indicating that complex 3 is more unstable because
of the bulky 2,6-substituents.
Though anilido-imino nickel complexes are four-
coordinate dinuclear species in the solid state that
exhibit an electronic absorption at λmax 517 nm in UV-
vis spectrophotometry (see Figure 4), there is an equi-
librium that shifts between the three-coordinate mono-
mer and four-coordinate dimer in solution (Scheme 2),
which could be observed by UV-vis spectrophotometry.
Figure 4 shows UV-vis spectra of nickel complex 1 in
different solvents. There is a weak electronic absorption
at 517 nm (dimer) and an intense electronic absorption
at 708 nm (monomer), which support the monomer/
dimer equilibrium in solution.
Figure 2. ORTEP plot of complex 2. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles
(deg): Ni(1)-Br(1)A, 2.4520(5); Ni(1)-Br(1), 2.4468(4); Ni-
(1)-N(1), 1.888(2); Ni(1)-N(2), 1.951(2); Ni(1)-Br(1)-Ni-
(1)A, 92.71(1); Br(1)-Ni(1)-Br(1)A, 87.29(2); Br(1)-Ni(1)-
N(1), 124.27(6); Br(1)-Ni(1)-N(2), 112.00(6); Br(1)A-
Ni(1)-N(1), 128.18(6); Br(1)-Ni(1)-N(2), 112.38(6); N(1)-
Ni(1)-N(2), 93.76(9); C(13)-N(1)-Ni(1), 128.7(2); C(1)-
N(1)-Ni(1), 114.9(2); C(19)-N(2)-Ni(1), 124.3(2); C(20)-
N(2)-Ni(1), 119.1(2).
nato nickel complex has a planar â-diketiminate skel-
eton. Similar to the â-diketiminato nickel complex, the
anilido-imine skeleton also is a plane, but the benzene
ring plane slightly swings the chelate plane (N1CCCN2).
The interplanar angle between the benzene ring and the
chelate plane is 4.8° for 1, 2.1° for 2, and 1.6° for 4,
respectively. The nickel atom lies 0.1416 Å out of the
chelate plane for 1, 0.130 Å for 2, and 0.120 Å for 4,
respectively. Unlike the â-diketiminato complexes, the
anilido-imino complexes are more localized and the two
nitrogens bond to nickel with different bond lengths, and
the N(amine)-Ni bond lengths are invariably shorter
than the N(imine)-Ni bond lengths. The steric effects
of the two N-aryl groups upon the nickel atom are also

6276 Organometallics, Vol. 23, No. 26, 2004
Gao et al.
Table 2. 1H NMR Chemical Shifts (ppm) of the
Complex 1 in C6D6 at 18 °C
chem shift (ppm)
monomer dimer
49.99
proton
imine (CHdN)
substituent methyl (Me) 43.63, 38.29
55.13
38.68, 32.43
m-aryl
p-aryl
46.09, 32.56
29.12, 7.02
47.67, 31.93
31.93, 10.57
backbone benzene
-13.00, -28.40,
-59.47, -74.10
-12.90, -29.73,
-76.06, -86.57
Table 3. Equilibrium Constants (Keq) for the
Dissociation of Dimer into Monomer at Various
Temperatures in Toluene-d8 Solutiona
Keq
temp (°C)
1
3
-15
0
28
50
0.2308
0.2880
0.5217
0.8181
-2.0541
-1.8326
-1.5686
-1.2384
Figure 4. UV-vis spectra of 1 in various solvents. The
solid-state spectrum is on an arbitrary scale.
Scheme 2. Monomer/Dimer Equilibria of
a Concentrations of complexes are 45 mM for 1 and 25 mM
for 3.
Anilido-Imino Nickel Complexes
+13.68kJ/mol and ∆S ) 40.32 J/(mol K) for 1 and ∆H
) +8.35 kJ/mol and ∆S ) 15.21 J/(mol K) for 3,
respectively. As observed with other transition-metal
dimer/monomer equilibria, the equilibrium is enthalpi-
cally disfavored but entropically favored.7d In compari-
son with the monomer/dimer equilibrium reported for
â-diketiminato nickel halide complexes,7c the equilibri-
um for the anilido-imino nickel complexes in solution
showed smaller ∆H values, which suggests that anilido-
imino nickel complexes have a smaller tendency to
dimerize than do â-diketiminato nickel halide com-
plexes. In addition, the ∆H value of complex 1 in
solution is larger than that of complex 3. It seems that
the greater steric effect of complex 3 would make the
equilibrium shift to a monomer.
Olefin Polymerization. Preliminary experiments
indicated that no solid polymer was obtained, while
complexes 1-4 catalyzed ethylene polymerization in the
presence of MAO at atmospheric pressure or 10 atm
pressure of ethylene. It is noteworthy that a small
amount of oligomeric products were formed. GC-MS
analysis (see the Supporting Information) confirmed
that oligomers mainly contained dimers (butene) and
trimers (hexene), and only traces of tetramers and
higher oligomers were detected, which is a result of
rapid â-H elimination in the process of the ethylene
polymerization.
However, the anilido-imino nickel complexes showed
high catalytic activities for norbornene polymerization
after activation with MAO. The results of norbornene
polymerizations using complexes 1-4 activated with
MAO are summarized in Table 4. In general, the steric
structure of the nickel complexes slightly influences
their catalytic activities. The complex with bulky N-aryl
groups exhibits higher catalytic activity. For example,
at 70 °C, complex 3 with two 2,6-diisopropyl N-aryl
groups has the highest activity (4.60 × 106 g of PNBE/
((mol of Ni) h)) for norbornene polymerization, while
complex 1 with two 2,6-dimethyl N-aryl groups has the
lowest activity, which is in accord with the steric effect
of the four complexes (3 > 4 ≈ 2 > 1). However, the
1H NMR spectra also further explain this equilibrium.
Similar to â-diketiminato nickel complexes,6d,7c the
anilido-imino nickel complexes exhibit strongly broad-
ened 1H NMR spectra from 60 to -90 ppm, due to their
paramagnetism. As a result of the paramagnetism
effect, the four protons of the backbone benzene ring
shifted intensely upfield, but the protons of the substi-
tuted aryl ring shifted to low field, and the proton of
imine intensely shifted to low field to ∼50 ppm. In the
spectra of the complexes, a series of broadened major
signals and minor signals were observed. These signals
can be clearly divided into two sets: one set is assigned
to the monomer and the other set to the dimer. As an
example, Figure 5 shows the 1H NMR spectrum of
complex 1 in C6D6 at 18 °C, and the assignments of
signals are summarized in Table 2. The intensity ratio
of the monomer signals to dimer signals is 5:1, implying
the molar ratio of monomer to dimer in 10:1 under this
conditions.
To further examine these equilibria in solution, we
monitored 1H NMR spectra of complexes 1 and 3 at
temperatures of -15 to 50 °C in toluene-d8 solution.
Above 70 °C, only monomer was detected at the con-
centration used. The equilibrium constants for the
dissociation of dimer into monomer (Keq; see Scheme 2)
1
were obtained from the data of H NMR spectra (see
Table 3). The ln Keq vs 1/T plots are shown in Figure 6.
On the basis of the data of Keq at various temperatures,
the values of enthalpy and entropy can be calculated
according to the van’t Hoff equation11,12 to be ∆H )
(11) (a) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem.
Soc. 1998, 120, 4049. (b) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan,
G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523. (c)
Mecking, S. Coord. Chem. Rev. 2000, 203, 325.
(12) Institute of inorganic chemistry of Tianjian University. Inor-
ganic Chemistry; Academic Press: Beijing, 1994; p 30.

Ni Complexes Chelating Anilido-Imine Ligands
Organometallics, Vol. 23, No. 26, 2004 6277
Figure 5. 1H NMR spectrum of complex 1 in 35 mM benzene-d6 solution at 18 °C using benzene-d6 (7.15 ppm) as internal
standard. The ratio of integration (m/d) is ∼5:1, where m refers to the monomer and d refers to the dimer.
Table 4. Norbornene Polymerization with
Anilido-Imino Nickel Complexes 1-4/MAOa
d
entry complex Al/Nib yield (%) activityc Mw
Mw/Mn
1
2
3
4
5
6
7
8
1
2
3
4
3
3
3
3
3000
3000
3000
3000
0
1200
2100
5800
39.5
48.5
57.5
55.9
0
12.3
39.0
84.5
3.16
3.88
4.60
4.47
0
0.98
3.12
6.76
1.21
1.38
1.39
1.37
2.25
3.17
2.90
2.49
1.60
1.51
1.18
2.53
2.64
3.20
a Polymerization conditions: polymerization temperature 70 °C;
polymerization time 0.5 h; nickel complex 1 µmol; monomer
concentration [NBE] ) 0.2 g/mL, solvent toluene, total volume 20
mL. b In units of mol/mol. c In units of 10-6 g of PNBE/((mol of
Ni) h). d In units of 10-6 g/mol. Molecular weights were determined
by GPC, and calibration was carried out with polystyrene stan-
dards.
Figure 6. van’t Hoff plots of complex 1 (45 mM) and
complex 3 (25 mM) in toluene-d8.
The IR spectra of the obtained polymer reveal no
traces of double bonds that often appear at 1620-1680,
735, and 966 cm-1 14a (see the Supporting Information),
and the 1H NMR spectra (Figure 7) also supply the same
information.14b This ensures the occurrence of vinyl-type
polymerization rather than ring-opening metathesis
polymerization (ROMP).3g TGA curves of all the ob-
tained polymers show that all of the polymer samples
were very stable up to 450 °C. All polymers are soluble
steric structure of the nickel complexes does not practi-
cally influence the molecular weight of the produced
polymer.
It is necessary to use an excessive amount of MAO
for good to high activities. With an increased ratio of
Al/Ni of 5800, the catalytic activity increased signifi-
cantly up to 6.8 × 106 g of PNBE/((mol of Ni) h). In
contrast, the molecular weights (Mw) of the polymers
decreased with an increasing Al/Ni ratio. This result can
be ascribed to the chain transfer to AlMe3 which is
usually contained in MAO.13
(14) (a) IR (KBr, cm-1): 2945.91 (vs), 2867.38 (vs), 1474.12 (s),
1452.82 (s), 1375.19 (m), 1294.28 (m), 1257.47 (m), 1222.05 (m), 1189.09
(m), 1146.26 (m), 1107.66 (m), 1040.52 (w), 940.94 (m), 891.32 (m). (b)
1H NMR (500 MHz, o-dichlorobenzene-d4, room temperature, TMS as
internal standard): 0.831, 0.847, 0.858, 0.870, 1.125, 1.238, 1.561,
2.214, 2.293.
(13) Wu, Q.; Gao, Q.; Lin, S. J. Appl. Polym. Sci. 1998, 70, 765.

6278 Organometallics, Vol. 23, No. 26, 2004
Gao et al.
the water source. The initial [H2O]/[TMA] molar ratio was 1.3.
Other commercially available reagents were purchased and
used without purification.
Measurement. Elemental analyses were performed on a
Vario EL microanalyzer. Mass spectra were measured on a
LC/MS instrument using electrospray ionization (EI). NMR
spectra were carried out on an INOVA 500 Hz instrument at
room temperature in CDCl3 solution for ligands, C6D6 and C7D8
solutions for complexes, and o-dichlorobenzene solution for
polymers (using solvent as the internal standard for 1H NMR).
IR spectra were recorded on a Nicolet NEXUS-670 FT-IR
spectrometer. UV-vis spectra were measured on a UV-2450
spectrophotometer. Analysis of ethylene oligomers was per-
formed by GC-MS on a Voyager GC-8000 TOP gas chromato-
graph-mass spectrometer. The following temperature pro-
gram of the oven was adopted: 40 °C for 5 min, the temperature
was increased by 8 °C/min heating to 110 °C, and then the
temperature was increased by a 15 °C/min heating until 180
°C was reached; this value was kept constant for a further 5
min. Gel permeation chromatography (GPC) analyses of the
molecular weight and molecular weight distribution of the
polymers were performed on a Waters 150C instrument using
standard polystyrene as the reference and with chlorobenzene
as the eluent at 40 °C. TGA data were measured with a TG-
290C thermal analysis system instrument.
Syntheses of Ligands. o-C6H4F(CHdNC6H3Me2-2,6). A
solution of 11.68 g of o-fluorobenzaldehyde (10 mL, 94.21
mmol) and 10.38 g of 2,6-diisopropylaniline (10.55 mL, 85.65
mmol) in n-hexane (40 mL) was stirred for 2 h before MgSO4
was added. The mixture was then filtered, and the bright
yellow solution was evaporated to dryness in vacuo to give a
yellow oil. The oil was distilled under reduced pressure, and
a light yellow distillate at 162-163 °C/5 mmHg was collected.
Yield: 14.34 g (73.7%). EI-MS (m/z): 228.2 [M]+. 1H NMR (500
MHz, CDCl3): 8.529(s, 1H, CHdNAr), 8.238 (dt, 7 Hz, 2 Hz,
1H, Ph), 7.441(q, J ) 7.5 Hz, 1H, Ph), 7.223 (t, J ) 8.0 Hz,
1H, Ph), 7.112-7.036 (m, 3H, Ph), 6.32 (t, J ) 7.5 Hz, 1H,
Ph), 2.144 (s, 6H, CH3). 13C NMR (125 Hz, CDCl3): 163.793
(d, J ) 252 Hz, CF), 156.099, 151.208, 132.917, 128.048,
127.569, 126.896, 124.401, 123.836, 115.927, 18.187. Anal.
Calcd for C15H14FN: C, 79.22; H, 6.27; N, 6.16. Found: C,
79.07; H, 6.21; N, 6.01.
Figure 7. 1H NMR spectrum of polynorbornene prepared
from 3/MAO at 70 °C.
in chlorobenzene, o-dichlorobenzene, and cyclohexane
at room temperature, which indicates a low stereoregu-
larity.
Conclusion
Anilido-imino nickel complexes exist in the form of
dinuclear bromine-bridged structures with tetrahedral
geometries about nickel in the solid state. Due to the
unbalanced steric effects of the N-aryl groups, there is
a more crowded steric environment of the nickel atom
for 2 than for 4, even though these two complexes have
the same composition. However, there is an equilibrium
that shifts between the monomer and dimer depending
on solvent, concentration, and temperature. Equilibrium
constants and themodynamic parameters (∆H, ∆S) are
consistent with the proposed equilibria. Complex 1 with
both 2,6-dimethyl substituted aryls has a greater ten-
dency to dimerize in solution than complex 3 with both
2,6-diisopropyl substituted aryls under the same condi-
tions, which can be attributed to the steric effects of aryl
groups. The anilido-imino nickel complexes show low
activities for ethylene oligomerization but high activities
up to 6.80 × 106 g of PNBE/((mol of Ni) h) for nor-
bornene polymerization after activation with MAO. The
steric effect slightly influenced their catalytic activities.
The obtained homopolymers are vinyl-addition polynor-
bornene and show low stereoregularity.
o-C6H4{NH(C6H3Me2-2,6)}(CHdNC6H3Me2-2,6)
(L1).
Ligand L1 was prepared by a similar method reported previ-
ously.9 A 9.9 mL portion of an n-butyllithium solution in
hexane (2.6 M) was added to a solution of 2,6-dimethylaniline
(3.3 mL) in THF (30 mL) at -78 °C, and the mixture was
warmed to room temperature overnight. The resulting solution
of LiNHAr was cannula-transferred into a solution of o-C6H4F-
(CHdNC6H3Me-2,6) (5 mL) in 30 mL of THF at 25 °C. After
the reaction mixture was stirred for 1 h, it was quenched with
15 mL of H2O, extracted with n-hexane, and evaporated to
dryness in vacuo. The resulting yellow oil was dissolved in hot
methanol (∼500 mL) and then cooled slowly to -10 °C to give
3.18 g of pale yellow crystals that were dried in vacuo. Yield:
41.3%. EI-MS (m/z): 329.2 [M]+. 1H NMR (500 MHz, CDCl3):
10.495 (s, 1H, NH), 8.367 (s, 1H, CHdNAr), 7.345 (dd, J )
7.5 Hz, 1.5 Hz, 1H, Ph), 7.182-7.077 (m, 6H, Ph), 6.961 (t, J
) 7.5 Hz, 1H, Ph), 6.285 (d, J ) 8.5 Hz, 1H, Ph), 2.241 (s, 6H,
CH3), 2.190 (s, 6H, CH3). 13C NMR (125 Hz, CDCl3): 165.932,
150.777, 148.464, 137.475, 136.747, 134.527, 132.192, 128.352,
128.092, 127.638, 126.370, 123.783, 116.706, 115.344, 111.756,
18.500. Anal. Calcd for C23H24N2: C, 84.04; H, 7.43; N, 8.52.
Found: C, 84.24; H, 7.51; N, 8.52.
Experimental Section
General Considerations. All manipulations involving air-
and moisture-sensitive compounds were carried out under an
atmosphere of dried and purified nitrogen using standard
Schlenk and vacuum-line techniques. Toluene, hexane, and
THF were dried over sodium metal and distilled under
nitrogen; benzene-d6 and toluene-d8 (Aldrich) were dried over
CaH2. 2-Fluorobenzaldehyde (97%), 1,2-dimethoxyethane (99%),
anhydrous nickel(II) bromide (99%), 2,6-diisopropylaniline
(90%), and 2,6-dimethylaniline were bought from Aldrich
Chemical Co. and used without further purification. The
n-butyllithium solution in hexane (2.6 M) was purchased from
Aldrich. Norbornene (bicyclo[2.2.1]hept-2-ene; Acros) was puri-
fied by distillation over potassium and used as a solution (0.4
g/mL) in toluene. (DME)NiBr2 was synthesized by the reaction
of 1,2-dimethoxyethane with anhydrous nickel(II) bromide,
according to the report in the literature.15 Methylaluminoxane
(MAO) was prepared by partial hydrolysis of trimethylalumi-
num (TMA) in toluene at 0-60 °C with Al2(SO4)3‚18H2O as
i
o-C6H4{NH(C6H3 Pr2-2,6)}(CHdNC6H3Me2-2,6) (L2). The
synthesis of ligand L2 was carried out as described for ligand
L1. A 5.0 mL portion of o-C6H4F(CHdNC6H3Me-2,6), 5.1 mL
of 2,6-diisopropylaniline, and 9.9 mL of n-butyllithium (2.6 M)
were converted to L2, and 3.99 g of pale yellow crystals was
obtained. Yield: 44.4%. EI-MS (m/z): 385.2 [M]+. 1H NMR (500
MHz, CDCl3): 10.515 (s, 1H, NH), 8.371 (s, 1H, CHNAr),
(15) Hart, W. X. Doctoral Dissertation, University of Massachusetts,
1981.

Ni Complexes Chelating Anilido-Imine Ligands
Organometallics, Vol. 23, No. 26, 2004 6279
7.340-7.292 (m, 2H, Ph), 7.246-7.243 (m, 2H, Ph), 7.147 (dt,
J ) 8.5 Hz, 1.5 Hz, 1H, Ph), 7.090 (d, J ) 8.0 Hz, 2H, Ph),
6.960 (t, J ) 7.5 Hz, 1H, Ph), 6.689 (dt, J ) 7.5 Hz, 1 Hz, 1H,
Ph), 6.289 (d, J ) 7.5 Hz, 1H, Ph), 3.201 (sp, J ) 7.0 Hz, 2H,
CH(CH3)2), 2.185 (s, 6H, CH3), 1.151 (d, J ) 6.0 Hz, 12H, CH-
(CH3)2). 13C NMR (125 Hz, CDCl3): 166.018, 150.879, 149.941,
147.489, 134.621, 134.441, 132.178, 128.070, 127.638, 127.472,
123.761, 116.296, 115.114, 112.022, 28.545, 24.704, 22.982,
18.385. Anal. Calcd for C27H32N2: C, 84.26; H, 8.46; N, 7.28.
Found: C, 84.21; H, 8.48; N, 7.06.
low volume in vacuo, and then n-hexane (20:1) was added.
Solvent was removed from the precipitate via cannula filtra-
tion, and the residual black green solid was washed with
n-hexane (3 × 5 mL). Drying in vacuo produces the desired
nickel complex. The nickel complex was dissolved in hot
hexane/toluene (15:1) solution and cooled in a freezer several
days to afford the product as dark green crystals.
[Ni(2-C6H4{N(C6H3Me2-2,6)}(CHdNC6H3Me2-2,6))Br]2 (1).
The general procedure was employed with 1.10 g of ligand L1,
1.3 mL of n-butyllithium solution (2.6 M) and 1.04 g of (DME)-
NiBr2 to afford 1.22 g (77.9%) of the desired complex as a dark
green solid. EI-MS (m/z): 465, 466, 467, 468, 469, 470 (isotope,
[M]+); 383, 384, 385, 386, 387 (isotope, [M - Br]+); 329
(ligand+). 1H NMR (C6D6, 500 MHz, 18 °C): 55.134 (0.2H, CHd
N), 49.996 (1H, CHdN), 47.672 (0.4H, Ph), 46.091 (2H, Ph),
43.632 (6H, CH3), 38.680 (1.2H, CH3), 38.268 (6H, CH3), 32.810
(0.2H, Ph), 32.557 (2H, Ph), 32.433 (1.2H, CH3), 31.929 (0.4H,
Ph), 29.115 (1H, Ph), 10.574 (0.2H, Ph), 7.015 (1H, Ph),
-12.902 (0.2H, backbone benzene), -13.002 (1H, backbone
benzene), -28.397 (1H, backbone benzene), -29.728 (0.2H,
backbone benzene), -59.472 (1H, backbone benzene), -74.096
(1H, backbone benzene), -76.055 (0.2H, backbone benzene),
-86.565 (0.2H, backbone benzene). In benzene-d6, monomer
and dimer were observed in a ∼10:1 ratio on the basis of
integration. 1H NMR (C7D8, 500 MHz, 28 °C): 58.974 (0.15H,
CHdN), 53.174 (1H, CHdN), 51.037 (0.3H, Ph), 49.215 (2H,
Ph), 47.105 (6H, CH3), 41.475 (6H + 0.9H, CH3, overlap),
34.939 (0.9H, CH3), 34.768 (0.15H, Ph), 34.698 (2H, Ph), 34.021
(0.3H, Ph), 30.486 (1H, Ph), 10.569 (0.15H, Ph), 7.010 (1H,
Ph), -14.599 (1H + 0.15H, backbone benzene), -31.118 (1H,
backbone benzene), -32.679 (0.15H, backbone benzene),
-64.951 (1H, backbone benzene), -81.089 (1H, backbone
benzene), -83.183 (0.15H, backbone benzene), -96.982 (0.15H,
backbone benzene). The ratio of monomer and dimer is ∼40:
3. Anal. Calcd for C46H46N4Ni2Br2: C, 59.00; H, 4.97; N, 6.01.
Found: C, 58.53; H, 5.14; N, 6.19.
i
o-C6H4F(CHdNC6H3 Pr2-2,6). The synthesis was carried
out as described for o-C6H4F(CHdNC6H3Me2-2,6), but 2,6-
diisopropylaniline was used in place of 2,6-dimethylaniline.
A mixture of 11.5 g of o-fluorobenzaldehyde (9.85 mL, 92.8
mmol) and 18.1 g of 2,6-diisopropylaniline (19.25 mL, 102
mmol) in n-hexane (40 mL) was stirred for 2 h before MgSO4
was added. The mixture was then filtered; the bright yellow
solution was cooled to -10 °C to give 13.46 g of large yellow
blocklike crystals. The filtrate was condensed to lower volume
and cooled to -10 °C to give an additional 4.3 g of pure
crystals. Total yield: 17.76 g (68%). EI-MS (m/z): 284.3 [M]+.
1H NMR (500 MHz, CDCl3): 8.509 (s, 1H, CHdNAr), 8.224
(dt, J ) 7.5 Hz, 2.0 Hz, 1H, Ph), 7.481 (q, J ) 7.5 Hz, 1H, Ph),
7.273 (t, J ) 7.5 Hz, 1H, Ph), 7.241-7.084 (m, 4H, Ph), 2.957
(sp, J ) 7.0 Hz, 2H, CHMe2), 1.185 (d, J ) 6.5 Hz, 12H,
CHMe2). 13C NMR (125 Hz, CDCl3): 163.865 (d, J ) 252 Hz,
CF), 155.670, 149.306, 137.558, 132.989, 127.754, 124.565,
124.329, 123.814, 123.057, 116.056, 27.955, 23.464. Anal. Calcd
for C19H22NF: C, 80.53; H, 7.83; N, 4.94. Found: C, 80.37; H,
7.54; N, 4.73.
i
i
o-C6H4{NH(C6H3 Pr2-2,6)}(CHdNC6H3 Pr2-2,6) (L3). The
synthesis of ligand L3 has been reported,9 which was carried
out as described for ligand L1. A 10 g portion of o-C6H4F(CHd
i
NC6H3 Pr-2,6), 7.65 mL of 2,6-diisopropylaniline, and 14.8 mL
of n-butyllithium (2.6 M) were converted to L3, A 6.3 g amount
of pale yellow small crystals were obtained. Yield: 41%. EI-
MS (m/z): 441.4 [M]+. 1H NMR (500 MHz, CDCl3): 10.497 (s,
1H, NH), 8.353 (s, 1H, CHdNR), 7.348 (dd, J ) 7.5, 1.5 Hz,
1H, Ph), 7.319-7.288 (m, 1H, Ph), 7.242-7.222 (m, 3H, Ph),
7.169-7.091 (m, 4H, Ph), 6.693 (dt, J ) 8 Hz, 1.1, 1H, Ph),
6.289 (d, J ) 8.5 Hz, 1H, Ph), 3.215, 3.109 (sp, J ) 7.0 Hz, 2
× 2H, CHMe2), 1.183 (d, J ) 6.5 Hz, 12H, CHMe2), 1.154, 1.140
(d, J ) 5.5 Hz, 12H, CHMe2). 13C NMR (125 Hz, CDCl3):
165.810, 149.978, 148.684, 147.526, 138.223, 134.533, 134.476,
132.224, 127.504, 124.372, 123.800, 123.049, 116.192, 115.177,
112.030, 28.569, 28.076, 24.580, 23.543, 23.085. Anal. Calcd
for C31H40N2: C, 84.49; H, 9.15; N, 6.36. Found: C, 84.45; H,
9.43; N, 6.11.
i
[Ni(2-C6H4{N(C6H3 Pr2-2,6)}(CHdNC6H3Me2-2,6))Br]2 (2).
The general procedure was employed with 1.21 g of ligand L2,
1.7 mL of n-butyllithium (2.6 M), and 1.35 g of (DME)NiBr2
to afford 1.51 g (66.0%) of the desired complex as a dark green
solid. EI-MS (m/z): 521, 522, 523, 524, 525, 526 (isotope, [M]+);
439, 440, 441, 442, 443 (isotope, [M - Br]+); 385 (ligand+). 1H
NMR (C6D6, 500 MHz, 18 °C): 56.854 (1H, CHdN), 51.446
(0.3H, CHdN), 49.697 (2H, Ph), 47.194 (0.6H, Ph), 41.375
(2H+0.3H, Ph, overlap), 34.981 (1.8H, CH3), 34.405 (6H +
0.6H, 2CH3 + 2H, overlap), 33.736 (2H, Ph), 31.255 (0.3H, Ph),
19.311 (0.6H, CH(CH3)2), 16.833 (2H, CH(CH3)2), 8.362 (6H,
CH(CH3)2), 7.409 (1.8H, CH(CH3)2), 4.613 (1.8H, CH(CH3)2),
3.978 (6H, CH(CH3)2), -13.454 (1H, backbone benzene),
-15.015 (0.30H, backbone benzene), -27.803 (0.30H, backbone
benzene), -32.271 (1H, backbone benzene), -64.329 (0.30H,
backbone benzene), -79.472 (0.30H, backbone benzene),
-96.295 (1H, backbone benzene). The ratio of monomer and
dimer is ∼20:3. Anal. Calcd for C54H62N4Ni2Br2: C, 62.10; H,
5.99; N, 5.36. Found: C, 61.52; H, 6.08; N, 5.01.
i
o-C6H4{NH(C6H3Me2-2,6)}(CHdNC6H3 Pr2-2,6) (L4). The
synthesis of ligand L4 was carried out as described for ligand
i
L1. A 4.4 g portion of o-C6H4F(CHdNC6H3 Pr-2,6), 2.2 mL of
2,6-dimethylaniline, and 6.5 mL of n-butyllithium (2.6 M) were
converted to ligand L4; 2.82 g of pale yellow crystals was
obtained. Yield: 47.2%. EI-MS (m/z): 385.2 [M]+. 1H NMR (500
MHz, CDCl3): 10.556 (s, 1H, NH), 8.351 (s, 1H, CHdNAr),
7.349 (dd, J ) 7.5 Hz, 1.5 Hz, 1H, Ph), 7.215-7.085 (m, 7H,
Ph), 6.705 (dt, J ) 8.0 Hz, 1.0 Hz, 1H, Ph), 6.278 (d, J ) 8 Hz,
1H, Ph), 3.092 (sp, J ) 7 Hz, 2H, CHMe2), 2.210 (s, 6H, CH3),
1.186 (d, J ) 7 Hz, 12H, CH(CH3)2). 13C NMR (125 Hz,
CDCl3): 165.667, 148.734, 148.577, 138.058, 137.048, 136.900,
134.619, 132.259, 128.398, 128.467, 124.329, 123.028, 116.614,
115.377, 111.701, 28.112, 23.450, 18.237. Anal. Calcd for
C27H32N2: C, 84.26; H, 8.26; N, 7.28. Found: C, 84.34; H, 8.47;
N, 7.11.
Syntheses of Complexes. Ligands were dissolved in 40
mL of toluene in a flame-dried Schlenk flask, and an n-
butyllithium solution (2.6 M) was injected in a -78 °C dry ice/
acetone bath, which was warmed to room temperature over-
night. (DME)NiBr2 was added and then stirred for 24 h at 80
°C; the crude reaction mixture was followed by hot filtration
under nitrogen. The dark green solution was evaporated to
i
i
[Ni(2-C6H4{N(C6H3 Pr2-2,6)}(CHdNC6H3 Pr2-2,6))Br]2 (3).
The general procedure was employed with 1.14 g of ligand L3,
1.0 mL of n-butyllithium (2.6 M), and 0.795 g of (DME)NiBr2
to afford 0.67 g (45.0%) of the desired complex as a dark green
solid. EI-MS (m/z): 577, 579, 580, 581, 582, 583 (isotope, M+);
495, 496, 497, 498, 499 (isotope, [M - Br]+); 441 (ligand+). 1H
NMR (C6D6, 500 MHz, 18 °C): 53.367 (0.16H, CHdN), 47.470
(1H, CHdN), 45.904 (0.32H, Ph), 43.129 (2H, Ph), 33.164
(0.16H, Ph), 31.574 (2H + 0.32H, Ph, overlap), 29.116 (1H,
Ph), 26.560 (2H, CH(CH3)2), 20.736 (0.32H, Ph), 18.079 (2H,
CH(CH3)2), 15.461 (0.32H, CH(CH3)2), 10.772 (0.16H, Ph),
8.245 (1H, Ph), 7.271-5.926 (18H + 2.88H, CH3), 4.349-4.199
(6.96H, CH3), -11.620 (1.16H, backbone benzene, overlap),
-24.796 (1H, backbone benzene), -26.954 (0.16H, backbone
benzene), -56.986 (1H, backbone benzene), -69.933 (1H,
backbone benzene), -75.320 (0.16H, backbone benzene),

6280 Organometallics, Vol. 23, No. 26, 2004
Gao et al.
-88.030 (0.16H, backbone benzene). The ratio of monomer and
dimer is ∼12.5:1. 1H NMR (C7D8, 500 MHz, 28 °C): 57.146
(0.2H, CHdN), 50.838 (1H, CHdN), 49.146 (0.4H, Ph), 46.243
(2H, Ph), 35.404 (0.2H, Ph), 33.711 (2H + 0.4H, Ph, overlap),
33.218 (0.4H, Ph), 30.830 (1H, Ph), 28.574 (2H, CH(CH3)2),
21.862 (0.4H, CH(CH3)2), 19.074 (2H, CH(CH3)2), 16.421 (0.4H,
CH(CH3)2), 10.772 (0.2H, Ph), 9.162 (1H, Ph), 7.239-6.321
(18H + 3.6H, CH3), 4.408 (6H + 1.2H, CH3), -12.526 (0.2H,
backbone benzene), -13.228 (1H, backbone benzene), -27.471
(1H, backbone benzene), -29.900 (0.2H, backbone benzene),
-62.745 (1H, backbone benzene), -77.233 (1H, backbone
benzene), -82.241 (0.2H, backbone benzene), -96.143 (0.2H,
backbone benzene). The ratio of monomer and dimer is ∼10:
1. Anal. Calcd for C62H78N4Ni2Br2: C, 64.39; H, 6.80; N, 4.84.
Found: C, 63.68; H, 7.01; N, 4.62.
Norbornene Polymerization. In a typical procedure, the
appropriate methylaluminoxane (MAO) solid was introduced
into the round-bottom glass flask, and then 10 mL of a toluene
solution of norbornene (0.4 g/mL) was added via syringe.
Toluene (14 mL) and 1 mL of the nickel complex solution (1
mM) were syringed into the well-stirred solution in order, and
the reaction mixture was continuously stirred for an appropri-
ate period at the polymerization temperature. Polymerizations
were terminated by addition of 200 mL of the acidic ethanol
(ethanol-HCl, 95:5). The resulting precipitated polymers were
collected and treated by filtering, washing with ethanol several
times, and drying under vacuum at 60 °C to a constant weight.
Crystal Structure Determination. The crystals were
mounted on a glass fiber using the oil drop scan method.16 Data
obtained with the ω-2θ scan mode were collected on a Bruker
SMART 1000 CCD diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) at 293 K. The
structures were solved using direct methods, while further
refinement with full-matrix least squares on F2 was obtained
with the SHELXTL program package.17,18 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
introduced in calculated positions with the displacement
factors of the host carbon atoms.
i
[Ni(2-C6H4{N(C6H3 Pr2-2,6)}(CHdNC6H3Me-2,6))Br]2 (4).
The general procedure was employed with 1.27 g of ligand L4,
1.3 mL of n-butyllithium (2.6 M), and 1.02 g of (DME)NiBr2
to afford 0.98 g (56.9%) of the desired complex as a dark green
solid. EI-MS (m/z): 521, 522, 523, 524, 525, 526 (isotope, [M]+);
439, 440, 441, 442, 443 (isotope, [M - Br]+); 385 (ligand+). 1H
NMR (C6D6, 500 MHz, 18 °C, saturated solution): 57.494 (1H,
CHdN), 52.101 (0.8H, CHdN), 48.542 (2H, Ph), 48.180 (1.6H,
Ph), 45.792 (4.8H, CH3), 38.963 (6H, CH3), 34.214 (2H, Ph),
33.672 (2H, Ph), 29.802 (1.6H, Ph), 28.776 (1.6H, Ph), 23.575
(2H + 1.6H, CH(CH3)2, overlap), 7.980 (6H, CH(CH3)2), 6.615
(4.8H, CH(CH3)2), 6.302 (4.8H, CH(CH3)2), 5.270 (6H, CH-
(CH3)2), -12.133 (0.8H, backbone benzene), -13.230 (1H,
backbone benzene), -30.067 (0.8H, backbone benzene), -31.287
(1H, backbone benzene), -62.696 (0.8H, backbone benzene),
-78.229 (0.8H, backbone benzene), -81.565 (1H, backbone
benzene), -92.919 (1H, backbone benzene). The ratio of
monomer and dimer is ∼5:2 in saturated benzene solution.
Anal. Calcd for C54H62N4Ni2Br2: C, 62.10; H, 5.99; N, 5.36.
Found: C, 61.45; H, 6.17; N, 5.01.
Acknowledgment. Supports by the National Natu-
ral Science Foundation of China (NSFC) and SINOPEC
(Joint Project 20334030), the Science Foundation of
Guangdong Province (Projects 039184 and 013173) and
the Ministry of Education of China (Foundation for
Ph.D. Training) are gratefully acknowledged. We thank
Prof. Jiwen Cai, Prof. Ng Seik Weng, and Dr. Xingqiang
Lu¨ for single-crystal X-ray technical assistance.
Supporting Information Available: Tables and figures
giving X-ray crystallographic details for 1, 2, and 4 as CIF
files and figures giving GC-MS spectra of oligomers and FT-
IR spectra of the polynorbornene in PDF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
Ethylene Polymerization. A 50 mL stainless steel auto-
clave was charged with 25 mL of a toluene solution of MAO
under 1 atm of ethylene at initialization temperature. The
system was maintained by continuously stirring for 30 min,
and then 5 mL of the nickel complex solution (5 mM) was
charged into the autoclave under 1 atm of ethylene. The
ethylene pressure was raised to the specified value, and the
reaction was carried out for a certain time. Polymerizations
were terminated by addition of ethanol after releasing ethylene
pressure.
OM049367T
(16) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615.
(17) SHELXTL, Version 5.1; Bruker AXS, Madison, WI, 1998.
(18) Sheldrick, G. M. SHELXL-97, Program for X-ray Crystal
Structure Solution and Refinement; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1998.