Synthesis and ethylene polymerization activity of a novel, highly active single-component binuclear neutral nickel(II) catalyst

Article abstract of DOI:10.1021/om049223e

The novel binuclear neutral nickel(II) complex [((2,6-iPr₂C ₆H₃)NCH)C₆H₃ONi(PPh ₃)Ph]₂ (5), based on the 3,3′-bisalicylaldimine ligand, has been synthesized in high yield, and its structure has been confirmed by X-ray crystallography, elemental analysis, and ¹H NMR and ¹³C NMR spectra. Used in the polymerization of ethylene as an active single-component catalyst, the complex exhibited a high catalytic activity of up to 4.55 × 10⁵ g of PE/((mol of Ni) h), and polyethylenes with a weight-average molecular weight (M_w) of up to 487.7 kg/ mol and relatively broad molecular weight distribution (M_w/ M_n = 2.8-3.8) were produced.

Full text of DOI:10.1021/om049223e

2628
Organometallics 2005, 24, 2628-2632
Synthesis and Ethylene Polymerization Activity of a
Novel, Highly Active Single-Component Binuclear
Neutral Nickel(II) Catalyst
Tao Hu, Li-Ming Tang, Xiao-Fang Li, Yue-Sheng Li,* and Ning-Hai Hu
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China,
and Graduate School of the Chinese Academy of Sciences, Beijing 100039,
People’s Republic of China
Received October 7, 2004
The novel binuclear neutral nickel(II) complex [((2,6-iPr2C6H3)NCH)C6H3ONi(PPh3)Ph]2
(5), based on the 3,3′-bisalicylaldimine ligand, has been synthesized in high yield, and its
1
structure has been confirmed by X-ray crystallography, elemental analysis, and H NMR
and 13C NMR spectra. Used in the polymerization of ethylene as an active single-component
catalyst, the complex exhibited a high catalytic activity of up to 4.55 × 105 g of PE/((mol of
Ni) h), and polyethylenes with a weight-average molecular weight (Mh w) of up to 487.7 kg/
mol and relatively broad molecular weight distribution (Mh w/Mh n ) 2.8-3.8) were produced.
Introduction
polymers, but only under special conditions.21-23 Re-
cently, Grubbs and co-workers reported a series of
highly active neutral single-component salicylaldimine-
based nickel(II) catalysts (Grubbs catalysts) such as
1a-d (Chart 1) for ethylene polymerization, which
greatly stimulated research in this area.24-27 Subse-
quently, a large number of neutral nickel(II) and pal-
ladium(II) catalysts which can homopolymerize olefins
and copolymerize ethylene with polar monomers were
reported.28-39 They were so tolerant to the polar func-
Over the past decade, interest in late-transition-metal
olefin polymerization catalysts has mushroomed with
a major advance which came with Brookhart’s discovery
of cationic Ni(II) and Pd(II) catalysts.1-15 However, it
is difficult for electrophilic cationic nickel catalysts to
copolymerize olefins with polar monomers. Therefore,
a number of neutral nickel catalysts (less electrophilic)
have been developed to overcome this limitation. The
most industrially relevant neutral nickel catalysts are
the SHOP-type catalysts, developed for the conversion
of ethylene to linear R-olefins.16-20 Modified SHOP
catalysts convert ethylene to high-molecular-weight
(19) Ostoya Starzewski, K. A.; Witte, J. Angew. Chem., Int. Ed. Engl.
1985, 24, 599.
(20) Klabunde, U.; Mulhaupt, R.; Herskovitz, T.; Janowicz, A. H.;
Calabrese, J.; Ittel, S. D. J. Polym. Sci., Part A: Polym. Chem. 1987,
25, 1989.
(21) Keim, W. Ann. N. Y. Acad. Sci. 1983, 415, 191.
(22) Desjardins, S. Y.; Cavell, K. J.; Hoare, J. L.; Skelton, B. W.;
Sobolev, A. N.; White, A. W.; Keim, W. J. Organomet. Chem. 1997,
544, 163.
(23) Kurtev, K.; Tomov, A. J. Mol. Catal. 1994, 88, 141.
(24) Bansleben, D. A.; Grubbs, R. H.; Wang, C.; Friedrich, S.;
Younkin, T. R.; Li, R. T. New Late Transition Metal Catalysts for the
Polymerization of Ethylene; Proceedings of MetCon’98: “Polymers in
Transition”; June 10-11, 1998, Houston, TX; Paper II.3.
(25) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S.
K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
(26) Bansleben, D. A.; Friedrich, S. K.; Younkin, T. R.; Grubbs, R.
H.; Wang, C.; Li, R. T. U.S. Patent 6 410 664, 2002.
(27) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R.
H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(28) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217.
(29) Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22, 250.
(30) Hicks, F. A.; Jenkins, J. C.; Brookhart, M. Organometallics
2003, 22, 3533.
* To whom correspondence should be addressed. Fax: +86-431-
5685653. E-mail: ysli@ciac.jl.cn.
(1) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169.
(2) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(3) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(4) Boffa, L. S.; Novak, B. M. Chem. Rev. 2000, 100, 1479.
(5) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414.
(6) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. J. Am.
Chem. Soc. 1998, 120, 888.
(7) Gates, D. P.; Svejda, S. A.; Onate, E.; Killian, C. M.; Johnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320.
(8) Jenkins, J. C.; Brookhart, M. J. Am. Chem. Soc. 2004, 126, 5827.
(9) Brookhart, M. S.; Johnson, L. K.; Arthur, S. D.; Feldman, J.;
Kreutzer, K. A.; Bennett, A. M. A.; Coughlin, E. B.; Ittel, S. D.;
Parthasarathy, A.; Tempel, D. J. U.S. Patent 5 886 224, 1999.
(10) Brookhart, M.; DeSimone, J. M.; Grant, B. E.; Tanner, M. J.
Macromolecules 1995, 28, 5378.
(31) Schro¨der, D. L.; Keim, W.; Zuideveld, M. A.; Mecking, S.
Macromolecules 2002, 35, 6071.
(32) Li, X. F.; Li, Y. S. J. Polym. Sci., Part A: Polym. Chem. 2002,
40, 2680.
(11) Killian, C. M.; Johnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005.
(12) McLain, S. J.; Feldman, J.; McCord, E. F.; Gardner, K. H.;
Teasley, M. F.; Coughlin, E. B.; Sweetman, K. J.; Johnson, L. K.;
Brookhart, M. Macromolecules 1998, 31, 6705.
(33) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang, S. J.;
Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. J. Polym. Sci., Part A:
Polym. Chem. 2002, 40, 2842.
(13) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem.
Soc. 1998, 120, 4049.
(34) Tian, G. L.; Boone, H. W.; Novak, B. M. Macromolecules 2001,
34, 7656.
(14) Britovsek, G. J. P.; Gibson, V. C.; Kimberly, B. S.; Maddox, P.
J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1998, 849.
(35) Liang, H.; Liu, J. Y.; Li, X. F.; Li, Y. S. Polyhedron. 2004, 23,
1619.
(15) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(16) Keim, W.; Hoffman, B.; Lodewick, R.; Peiukert, M.; Schmitt,
G. J. Mol. Catal. 1979, 6, 79.
(36) Li, Y. S.; Li, Y. R.; Li, X. F. J. Organomet. Chem. 2003, 667,
185.
(37) Gibson, V. C.; Tomov, A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 2001, 719.
(17) Klabunde, U.; Ittel, S. D. J. Mol. Catal. 1987, 41, 123.
(18) Peuckert, M.; Keim, W. Organometallics 1983, 2, 594.
(38) Gibson, V. C.; Tomov, A. Chem. Commun. 2001, 1964.
10.1021/om049223e CCC: $30.25 © 2005 American Chemical Society
Publication on Web 04/29/2005

A Binuclear Neutral Nickel(II) Catalyst
Organometallics, Vol. 24, No. 11, 2005 2629
Table 1. Crystal Data and Structure Refinement
for Complex 5
Chart 1
empirical formula
fw
C86H82N2Ni2O2P2
1354.90
cryst syst
space group
a (Å)
triclinic
P1h
14.685(2)
b (Å)
14.691(2)
c (Å)
20.695(4)
V (Å3)
4171.6(12)
Scheme 1
R (deg)
â (deg)
γ (deg)
Z
95.985(3)
101.920(3)
104.487(3)
2
Dcalcd (Mg/m3)
1.079
abs coeff (mm-1
F(000)
)
0.532
1428
cryst size (mm)
θ range (deg)
0.34 × 0.21 × 0.09
1.63-26.09
no.of indep rflns
15 959 (Rint ) 0.0186)
semiempirical from equivalents
0.9536 and 0.8397
full-matrix least squares on F2
R1 ) 0.0647, wR2 ) 0.1738
R1 ) 0.0926, wR2 ) 0.1967
1.347 and -0.391
Bruker SMART
graphite
abs cor
max and min transmn
refinement method
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak and hole (e Å-3
type of diffractometer
monochromator
)
Results and Discussion
tional groups that some polymerizations can be con-
ducted in aqueous emulsion, affording stable polymer
lattices.40-43
Synthesis and Structure of the Binuclear Neu-
tral Nickel(II) Catalyst 5. The synthetic route for the
binuclear neutral nickel(II) catalyst 5 is shown in
Scheme 1. The free ligand 3 was synthesized via the
condensation reaction of the corresponding compound
2 and excess 2,6-diisopropylaniline in excellent yield.
The deprotonation of the free ligand 3 readily proceeded
with excess sodium hydride in anhydrous THF at room
temperature. The isolated sodium salt 4 reacted with 2
equiv of trans-NiCl(Ph)(PPh3)2 for 14 h in benzene to
afford the binuclear neutral nickel(II) catalyst 5. Usu-
ally in the syntheses of salicylaldimine-based neutral
Ni complexes, as the residual trans-NiCl(Ph)(PPh3)2 is
difficult to remove from the reaction system, its starting
quantity is slightly less than the stoichiometric am-
ount.27,32,36 In our case, however, it is clear that this
approach would result in a mixture of the binuclear Ni
complex and the mononuclear complex, and our multiple
attempts to separate these two complexes have not been
successful. Therefore, we found that it was critical that
2 equiv of trans-NiCl(Ph)(PPh3)2 should be used vs
salicylaldimine sodium salt 4. Nevertheless, multiple
recrystallizations in benzene/pentane remained neces-
sary to give brown-purple crystals of the binuclear Ni
complex 5. Surprisingly, the complex is so insensitive
to moisture that it can be exposed to ambient atmo-
sphere for several days without notable change.
Crystals of the binuclear neutral nickel(II) complex
suitable for X-ray diffraction analysis were obtained by
slow diffusion of pentane into a benzene solution of 5.
The crystallographic data together with the collection
parameters and the refinement parameters are sum-
marized in Table 1. As shown in Figure 1, in the solid
state, the molecule adopts a nearly square-planar
coordination geometry with two Ni atoms displaced
approximately 0.09 Å (Ni1) and 0.01 Å (Ni2) from the
plane of their ligands, respectively. Although the two
segments have almost the same Ni-P, Ni-N, Ni-O,
and Ni-C bond lengths and seemingly identical chemi-
cal environments, the coordination geometries of the two
It has been reported that complex 1a is not active for
ethylene polymerization as a single-component catalyst
because its deactivation easily occurs by a ligand
disproportionation and dimerization.24 Grubbs et al.
found that the introduction of a bulky substituent at
the ortho position of the phenoxy group not only blocks
the axial faces of the nickel center and retards the rate
of chain termination but also enhances the catalytic
activity by accelerating PPh3 dissociation and decreases
the rate of catalyst deactivation.24-27,44 For example,
catalyst 1d, with a bulky 9-anthracenyl at the ortho
position of the phenoxy group, displays a high activity
of up to 3.7 × 106 g of PE/((mol of Ni) h) under optimized
conditions.45 However, just as Mecking pointed out,46
the syntheses of the ligands containing a bulky ortho-
substituted group require multistep reactions in very
low yields. Furthermore, the starting material 2-bro-
mophenol is expensive.
In view of these, here we report the synthesis of the
binuclear Ni(II) complex 5, based on the 3,3′-bisalicy-
laldimine ligand, starting from the readily available 2,2′-
biphenol (Scheme 1) and its catalytic activity as a single-
component catalyst for ethylene polymerization. In this
complex, each salicylaldimine unit plays the role of a
bulky group at the C-3 position of the other unit.
(39) Zhang, D.; Jing, G. X. Organometallics 2003, 22, 2851.
(40) Held, A.; Bauers, F. M.; Mecking, S. Chem. Commun. 2000,
301.
(41) Bauers, F. M.; Mecking, S. Macromolecules 2001, 34, 1165.
(42) Tomov, A.; Broyer, J.-P.; Spitz, R. Macromol. Symp. 2000, 150,
53.
(43) Mecking, S.; Held, A.; Bauers, F. M. Angew. Chem. 2002, 114,
564; Angew. Chem., Int. Ed. 2002, 41, 544.
(44) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Waltman, A.
W.; Grubbs, R. H. Chem. Commun. 2003, 2272.
(45) In 58 °C and 400 psig of ethylene, 1d can produce PE with the
highest activity of 3.7 × 106 g of PE/((mol of Ni) h), but the Mw value
is only 85.9 kg/mol.27
(46) Zuideveld, M. A.; Wehrmann, P.; Ro¨hr, C.; Mecking, S. Angew.
Chem., Int. Ed. 2004, 43, 869.

2630 Organometallics, Vol. 24, No. 11, 2005
Hu et al.
Figure 1. ORTEP diagram of 5. (Two benzene solvent molecules of crystallization are omitted.) Selected bond distances
(Å) and angles (deg): Ni(1)-C(1) ) 1.896(3), Ni(1)-O(1) ) 1.903(2), Ni(1)-N(1) ) 1.932(3), Ni(1)-P(1) ) 2.1846(10), O(1)-
C(43) ) 1.309(4), N(1)-C(7) ) 1.449(4), N(1)-C(37) ) 1.305(4), C(37)-C(38) ) 1.420(5), P(1)-C(25) ) 1.841(4); N(1)-
Ni(1)-P(1) ) 162.45(9), N(2)-Ni(2)-P(2) ) 173.12(9), C(1)-Ni(1)-O(1) ) 158.61(13), C(44)-Ni(2)-O(2) ) 168.70(14),
O(1)-Ni(1)-P(1) ) 88.42(7), O(2)-Ni(2)-P(2) ) 84.97(8).
Table 2. Ethylene Polymerization Results Catalyzed by Catalyst 5a
entry reacn temp (°C) time (min) pressure (atm) yield (g) 10-5(activity)b 10-3Mh w PDI (Mh w/Mh n) Tm (°C) c branchesd/1000C
1
42
43
43
54
64
43
43
43
43
43
60
60
7
14
21
21
21
14
21
14
14
14
1.5
4.7
9.1
6.6
3.6
6.1
7.9
2.1
6.7
8.4
0.75
2.35
4.55
3.30
1.80
3.05
3.95
2.10
2.23
2.10
335.6
462.3
487.7
314.2
128.2
353.7
438.6
421.4
447.1
451.8
3.75
2.92
2.82
2.87
2.78
2.76
3.46
3.01
2.91
2.87
122
124
123
123
120
124
123
124
123
122
15
12
11
14
17
15
16
14
12
13
2
3
60
4
60
5
60
6e
7f
8
60
60
30
9
10
90
120
a Polymerizations run using 10 µmol of catalyst in 60 mL of toluene with a maximum exotherm of 2 °C. b In units of g of PE/((mol of
Ni) h). c Melting temperature is determined by DSC. d Determined by 1H NMR. e A 4.5 equiv portion of (COD)2Ni was used as phosphine
scavenger. f Without efficient cooling, exotherm from 43 to 55 °C.
Ni atoms are different. The bond angles of N(1)-Ni(1)-
P(1), C(1)-Ni(1)-O(1), and O(1)-Ni(1)-P(1) are all
different from the corresponding bond angles for Ni(2),
and the coplanarity of Ni(1) atom and the atoms around
it is not identical with that of Ni(2). The root-mean-
square (RMS) deviations from the planes for the atoms
Ni(1), O(1), N(1), C(37), C(38), C(43) and the atoms
Ni(1), O(1), N(1), P(1), C(1) are 0.0710 and 0.2631 Å,
respectively, while those for the atoms Ni(2), O(2), N(2),
C(80), C(81), C(86) and the atoms Ni(2), O(2), N(2), P(2),
C(44) are 0.0112 and 0.1018 Å, respectively.
Ethylene Polymerization Behavior of the Bi-
nuclear Neutral Nickel(II) Catalyst 5. According to
literature reports,24,25 in the absence of other added
activators, complex 1a exhibited no activity for ethylene
polymerization. Even when (COD)2Ni or B(C6F5)3 was
used as a phosphine acceptor, only a low catalytic
activity was observed.24-27 Interestingly, the binuclear
Ni complex 5, which may be treated as the product of
the two 1a molecules coupled at the ortho position of
the phenoxy group, is capable of polymerizing ethylene
with an activity of up to 4.55 × 105 g of PE/((mol of Ni)
h) without any cocatalyst. This activity is higher than
that of the sterically modified Grubbs catalysts reported,
such as 1b (1.0 × 105 g of PE/((mol of Ni) h)) and 1c
(3.1 × 105 g of PE/((mol of Ni) h)).24-27 Furthermore, in
comparison with the binuclear single-component neutral
nickel catalysts reported earlier, whose catalytic activi-
ties were up to 8.5 × 104 g of PE/((mol of Ni) h),39
catalyst 5 also has much higher activity. These results
clearly indicate that two separate Ni complex units act
as the mutual bulky ortho-substituted steric groups for
each other, which leads to the excellent catalytic per-
formance.
In our initial ethylene polymerization experiments
using 5 as a catalyst, the temperature increases were
not as rapid as those when highly active catalysts were
used, such as cationic Ni and Fe catalysts. For example,
using 10 µmol of catalyst loading, a polymerization
starting at 43 °C and 21 atm can heat up to 55 °C within
1 h without temperature control (Table 2 entry 7), and
the reaction temperature can continue to increase after
1 h. To accurately compare activities and lifetimes under
various reaction conditions, it is critical to control
reaction temperature for a highly active catalyst. Thus,
an autoclave with cooling water coils was used to control
the temperature of the reaction solutions. With circulat-
ing cooling water, the temperature increase can be

A Binuclear Neutral Nickel(II) Catalyst
Organometallics, Vol. 24, No. 11, 2005 2631
controlled to within 2 °C of the initial temperature as
the autoclave was pressurized and throughout the
polymerization runs.
In conclusion, a new binuclear 3,3′-bisalicylaldimine-
based neutral nickel(II) complex, derived from the
readily available 2,2′-biphenol, has been developed.
Employed as a single-component catalyst for ethylene
polymerization, this well-defined complex displayed a
high catalytic activity and produced high-molecular-
weight polyethylenes with broad molecular weight
distribution and moderate branching degree of ca. 10-
15 methyl branches per 1000 carbon atoms.
In a series of ethylene polymerization trials, the
temperature and ethylene pressure were found to have
a dramatic effect on catalyst activity. As can be seen in
Table 2, when the ethylene pressure increases from 7
to 21 atm, the catalyst activity rises from 0.75 × 105 to
4.55 × 105 g of PE/((mol of Ni) h) (entries 1-3). It is
also found that the catalyst activity decreases gradually
with temperature, increasing from 43 to 64 °C, and the
highest activity comes at 43 °C (entries 3-5). Moreover,
using (COD)2Ni as a phosphine scavenger increases the
catalyst activity and decreases the molecular weight of
the resultant polymer (entry 6), which is consistent with
what was found for Grubbs catalysts 1b-d. Addition-
ally, the activity of the catalyst remains essentially
same at 0.5, 1, 1.5, and 2 h runs under the same
conditions (entries 2 and 8-10), indicating that the
lifetime of catalyst 5 is longer than 2 h.
It is noteworthy that the PEs obtained using catalyst
5 display a molecular weight distribution (PDI > 2.8)
slightly broader than that for the PEs reported by
Grubbs using their catalysts (PDI < 2.2) under similar
conditions. A possible reason for this is that complex 5
is asymmetric in structure, as mentioned above. The two
Ni units are not identical, which may result in two
slightly different active sites during the polymerization.
The two different active species then lead to the
broadening of the molecular weight distribution, in
comparison to the scenario where there is only one
active species present. In addition, the binuclear Ni
complex 5 produces PEs of higher molecular weight than
Grubbs catalysts under similar conditions. With the
ethylene pressure increasing, weight-average molecular
weights of the polymers display an increasing trend and
are usually higher than 400 kg/mol, which are generally
higher than those of the PEs produced, employing
Grubbs catalysts.24-27 This suggests that the rate of
chain transfer for catalyst 5 is quite slow relative to the
rate of chain propagation.
Experimental Section
General Considerations. All manipulations of air- and/
or water-sensitive compounds were performed under a dry
nitrogen atmosphere using standard Schlenk techniques.
Toluene, benzene, n-pentane, diethyl ether, and tetrahydro-
furan were refluxed with sodium/benzophenone ketyl and were
distilled under nitrogen prior to use. Methylene dichloride was
distilled from drying CaH2 under nitrogen. Commercial eth-
ylene was directly used for polymerization without further
purification. 2,6-Diisopropylaniline and NaH were purchased
from Acros. trans-[Ni(PPh3)2PhCl]49 and (COD)2Ni (bis(1,5-
cyclooctadiene)nickel)50 were prepared according to the analog-
ous methods reported, respectively.
The NMR spectra of the polyethylenes were recorded on a
Varian Unity 400 MHz spectrometer with o-dichlorobenzene
as the solvent at 120 °C. The other NMR data of the ligands
and the complex were obtained on a Bruker 300 MHz
spectrometer at ambient temperature, with CDCl3 or C6D6 as
the solvent. The IR spectra were recorded on a Bio-Rad FTS-
135 spectrophotometer. The DSC measurements were per-
formed on a Perkin-Elmer Pyris 1 differential scanning
calorimeter at a heating rate of 10 °C/min. The weight-average
molecular weight (Mh w) and the polydispersity index (PDI) of
the polyethylene samples were determined via high-temper-
ature GPC according to the procedure reported previously.51
Elemental analyses were performed on a Perkin-Elmer Series
II CHN/O analyzer 2400.
Synthesis of Compound 2. In accordance with the re-
ported method,52 compound 2 was prepared from 2,2-biphenol.
1H NMR (CDCl3): δ 7.07 (t, 2H, Ar H), 7.56 (m, 4H, Ar H),
9.89 (s, 2H, dCHO), 11.3 (s, 2H, OH). IR (KBr) ν 3435 (OH),
1633 (CHdO), 1613, 1477, 1456 cm-1 (Ph). Anal. Calcd for
C14H10O4: C, 69.42; H, 4.16. Found: C, 69.36; H, 4.11.
Synthesis of Compound 3. To a stirred solution of
compound 2 (2.42 g, 10 mmol) in dried methylene dichloride
(40 mL) were added 2,6-diisopropylaniline (4.43 g, 25 mmol)
and formic acid (0.3 mL) as a catalyst. The mixture was
refluxed and stirred for 24 h. During the stirring period, a
yellow solution was formed. The evaporation of solvent gave
a yellow solid powder. The crude product was washed with
ethanol and dried. Yield: 5.1 g, 91%. 1H NMR (CDCl3): δ 1.09
High-temperature 13C NMR spectra show there are
few ethyl and longer branches besides methyl ones in
the resulting PE chains (cf. Figure 2 in the Supporting
Information). On the basis of Mandelken’s protocol,47
all of the corresponding carbon resonances can be
assigned unambiguously. Furthermore, in the high-
temperature 1H NMR spectrum (cf. Figure 3 in the
Supporting Information), the methyl resonance at δ 0.93
ppm splits into a doublet, which again indicates that
the branches in the polyethylenes are mainly CH3
branches. According to the 1H NMR result, the average
branching content of the PEs is around 10-15 branches
per 1000 carbon atoms,48 which is slightly higher than
those of the PEs produced using Grubbs catalysts (5-8
branches per 1000 carbon atoms) under similar condi-
tions. This may be the reason the melting temperatures
of our PEs are slightly lower (Tm ) 122-124 °C, vs 129.5
°C reported by Grubbs).
3
3
(d, J ) 6.8 Hz, 12H, CH3), 1.11 (d, J ) 6.8 Hz, 12H, CH3),
3
2.97 (sept, J ) 6.8 Hz, 4H, CH), 7.01 (t, 2H, Ar H), 7.13 (s,
6H, Ar H), 7.47 (d, 2H, Ar H), 7.53 (d, 2H, Ar), 8.33 (s, 2H, Ar
H). Anal. Calcd for C38H44N2O2: C, 81.39; H, 7.91; N, 5.00.
Found: C, 81.52; H, 7.86; N, 4.97.
Sodium Salt of Compound 3. A solution of 3 (0.43 g, 0.76
mmol) in anhydrous THF (15 mL) was added to sodium
hydride (46 mg, 1.9 mmol). The resultant mixture was stirred
at room temperature for 4 h and then filtered and evaporated.
The solid residue was immediately used in the next step
without further purification.
(49) Hidai, M.; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J. Organomet.
Chem. 1971, 30, 279-282.
(47) Axelson, D. E.; Levy, G. C.; Mandelkern, L. Macromolecules
1979, 12, 41.
(48) The branching numbers for polyethylene were determined by
1H NMR spectroscopy using the ratio of the number of methyl groups
to the overall number of carbons (e.g., methyl + methylene + methine)
and reported as branches per 1000 carbon atoms.7
(50) Wilke, G. Angew. Chem. 1960, 72, 581.
(51) Li, X. F.; Dai, K.; Ye, W. P.; Pan, L.; Li, Y. S. Organometallics
2004, 23, 1223.
(52) Zhang, H. C.; Huang, W. S.; Pu, L. J. Org. Chem. 2001, 66,
481.

2632 Organometallics, Vol. 24, No. 11, 2005
Hu et al.
Synthesis of Complex 5. The Na salt of 3 obtained above
and trans-[Ni(PPh3)2PhCl] (1.06 g, 1.52 mmol) were dissolved
in benzene (45 mL) in a Schlenk flask and stirred at room
temperature for 14 h. The resultant mixture was filtered, and
the filtrate was concentrated under vacuum to ca. 6 mL.
Pentane (30 mL) was added to the reaction mixture. A brown-
purple solid crystallized from solution and was isolated by
stirring motor was engaged. Temperature control was main-
tained by internal cooling water coils with temperature
increases within 2 °C in every case. After the prescribed
reaction time, the stirring motor was stopped, the reactor was
vented, and the polymer was isolated via precipitation from
ethanol and dilute HCl (10%). The solid polyethylene was
filtered, washed with ethanol, and dried at 60 °C for 10 h under
vacuum.
1
filtration to give 5. Yield: 0.73 g (71%). H NMR (300 MHz,
C6D6): δ 1.32 (d, JHH ) 6.6 Hz, 12H, CH3), 1.40 (d, JHH ) 6.3
Hz, 12H, CH3), 4.46 (m, 4H, CH), 5.54-7.81 (m, 52H, Ar H),
7.93 (d, 2H, JHP ) 9.3 Hz, NdCH). 13C NMR (C6D6): δ 23.2,
26.2, 29.3, 114.0, 119.9, 121.6, 123.2, 125.5, 126.4, 129.8, 130.5,
132.4, 132.8 (m), 134.8 (d, JCP ) 39 Hz), 137.2, 138.5, 141.3,
150.4, 164.0, 166.6. Anal. Calcd for C86H82N2Ni2O2P2: C, 76.23;
H, 6.10; N, 2.07. Found: C, 76.32; H, 6.06; N, 2.11.
Ethylene Polymerization. A 100 mL autoclave was
heated under vacuum up to 140 °C for 10 h and then was
cooled to the desired reaction temperature in an oil bath with
constant temperature. The vessel was purged three times with
ethylene and then was charged with toluene (50 mL) under
vacuum. A 10 µmol amount of catalyst dissolved in 10 mL of
toluene was added into the autoclave by syringe. The reactor
was sealed and pressurized to the desired level, and the
Acknowledgment. We are grateful for financial
support from the National Natural Science Foundation
of China and SINOPEC (No. 20334030) and from the
Special Funds for Major State Basis Research Projects
(No. G1999064801) from the Ministry of Science and
Technology of China.
Supporting Information Available: A CIF file giving
crystallographic data and a figure giving a crystal cell diagram
of complex 5 and figures giving the GPC and 1H NMR and 13
C
NMR spectra of a typical PE sample (entry 3). This material
is available free of charge via the Internet at http://pubs.acs.org.
OM049223E