Highly active single-component neutral nickel ethylene polymerization catalysts: The influence of electronic effects and spectator ligands

Article abstract of DOI:10.1021/om100658j

A series of neutral nickel complexes [6-CHN(2,6-ⁱPr ₂C₆H₃)-2-(2-NO₂C₆H ₄)-C₆H₃O-κ²- N,O]Ni(Ph)(PPh₃) (6a), [6-CHN(2,6-ⁱPr₂C ₆H₃)-2-(C₆F₅)-C₆H ₃O-κ²-N,O]Ni(R)(L) (R = Ph, L = PPh₃ (6b-PPh₃); R = Me, L = pyridine (6b-Py); R = CH₂Ph, L = PMe₃ (6b-¹Bz); R = η³-CH₂Ph (6b-³Bz)), and [6-CHN(2,6-ⁱPr₂C ₆H₃)-2-(2-OCH₃C₆H ₄)-C₆H₃O-κ²-N,O]Ni(Ph) (PPh₃) (6c) based on 2-nitrophenyl-, pentafluorophenyl-, and 2-methoxyphenyl-substituted salicylaldimine ligands, respectively, have been synthesized and characterized by ¹H NMR, ¹³C NMR, and elemental analysis. The solid structures of 6a, 6b-PPh₃, 6b-Py, and 6b-¹Bz have been further confirmed by X-ray crystallography. By combining the benefits of both electronic and steric factors, all the complexes with electron-withdrawing groups proved to be highly active single-component catalysts for ethylene polymerization, producing polymer with moderate molecular weights. Among these catalysts, 6b-PPh₃ exhibited very high productivity of up to 5.87 × 10⁶ g PE/mol_Ni·h under optimal conditions. Compared with 6b-PPh₃ and 6b-Py, 6b- ³Bz requires lower temperature and ethylene pressure to show high productivity. The branching number, M_w, and T_m of the polymer can be readily manipulated by variation of reaction conditions and catalyst structure.

Full text of DOI:10.1021/om100658j

6282 Organometallics 2010, 29, 6282–6290
DOI: 10.1021/om100658j
Highly Active Single-Component Neutral Nickel Ethylene
Polymerization Catalysts: The Influence of Electronic Effects and
Spectator Ligands
Hong-Liang Mu,†,‡ Wei-Ping Ye,† Dong-Po Song,†,‡ and Yue-Sheng Li*,†
†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, Changchun Branch, People’s Republic of China
Received July 7, 2010
A series of neutral nickel complexes [6-CHN(2,6-iPr2C6H3)-2-(2-NO2C6H4)-C6H3O-κ2- N,O]Ni-
(Ph)(PPh3) (6a), [6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-κ2-N,O]Ni(R)(L) (R = Ph, L = PPh3
(6b-PPh3); R=Me, L=pyridine (6b-Py); R=CH2Ph, L=PMe3 (6b-1Bz); R=η3-CH2Ph (6b-3Bz)),
and [6-CHN(2,6-iPr2C6H3)-2-(2-OCH3C6H4)-C6H3O-κ2-N,O]Ni(Ph)(PPh3) (6c) based on 2-nitrophenyl-,
pentafluorophenyl-, and 2-methoxyphenyl-substituted salicylaldimine ligands, respectively, have been synthe-
sized and characterized by 1H NMR, 13C NMR, and elemental analysis. The solid structures of 6a, 6b-PPh3,
6b-Py, and 6b-1Bz have been further confirmed by X-ray crystallography. By combining the benefits of both
electronic and steric factors, all the complexes with electron-withdrawing groups proved to be highly active
single-component catalysts for ethylene polymerization, producing polymer with moderate molecular weights.
Among these catalysts, 6b-PPh3 exhibited very high productivity of up to 5.87 ꢀ 106 g PE/molNi h under
3
optimal conditions. Compared with 6b-PPh3 and 6b-Py, 6b-3Bz requires lower temperature and ethylene
pressure to show high productivity. The branching number, Mw, and Tm of the polymer can be readily
manipulated by variation of reaction conditions and catalyst structure.
Introduction
investigated,4 and the corresponding computational and
mechanistic studies have also been conducted.5,6 Their nickel
counterparts, however, met only limited success in the field
of the copolymerization of olefins with polar monomers due
to higher oxophilicity of the metal center relative to the
palladium catalysts. Neutral nickel catalysts are promising
candidates, compared with their cationic analogues, for the
copolymerization of olefins with polar monomers7 and can
Late metal catalysts for olefin polymerization have been
investigated intensely,1 stimulated by Brookhart’s seminal
work on cationic Ni(II) and Pd(II) catalysts for the poly-
merization of ethylene and R-olefins2 and, remarkably, the
copolymerization of olefins with methyl acrylate.3 Since
then, the coordination copolymerization of ethylene with
polar monomers by cationic Pd(II) catalysts has been well
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*To whom correspondence should be addressed. Fax: þ86-431-
85262039. E-mail: ysli@ciac.jl.cn.
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pubs.acs.org/Organometallics
Published on Web 11/02/2010
2010 American Chemical Society

Article
Chart 1. Examples of Previously Reported Neutral
Nickel Catalysts
Organometallics, Vol. 29, No. 23, 2010 6283
Scheme 1. Syntheses of Ligands 5a-c
be used even in aqueous media.7g,8 It is also of great academic
and industrial interest that some neutral nickel complexes
are single-component catalysts benefiting from their labile
pendant ligands.7c,l,9 This greatly simplifies the polymeriza-
tion reaction without the need for expensive MAO or borates
as cocatalyst. The single-component neutral nickel catalyst B
bearing a bulky anthryl group reported by Grubbs7c (Chart 1)
displays a good tolerance to polar additives and high activity
toward ethylene homo- and copolymerization,7c,f which
stimulated a search for other neutral nickel catalysts. For
example, Brookhart designed and synthesized neutral nickel
complexes C and D based on anilinotropone and anilinoper-
inaphthenone ligands.9a,d These complexes, even without
bulky substituents proximate to the metal center, can pro-
mote ethylene polymerization as single-component catalysts
nickel-methyl pyridine catalysts with bulky terphenyl
anilines.8k,9i,9l,10 Recently, binuclear neutral nickel catalysts
were reported by Marks7o to exhibit high levels of acrylate
incorporation (up to 11%) in the copolymerization of eth-
ylene with methyl methacrylate, which was ascribed to the
cooperative effect between the two nickel centers.
with very high productivity of up to 8.8 ꢀ 106 g PE/molNi h.
3
Bulky substituents in the backbone of the ligand are gen-
erally considered to be necessary for late metal catalysts,2,7c,11
especially for neutral nickel catalysts,7c,11b,11d to attain good
activity and yield high molecular weight polymer. In addi-
tion, the electronic effect of the ligand also drastically influ-
ences the performance of the catalysts. Tremendous efforts
were focused on the modifications of the bulky N-aryl moiety
of the ligand by Mecking’s group,8n,p,9i,9l,10,12 verifying that
electron-donating or -withdrawing substituents on N-aryl
groups of the ligands can control the catalytic activity of the
neutral nickel complexes and the microstrucutre of the resu-
lting polymer.10 However, examples of electronic modifications
toward the ortho-phenoxy aryl groups are rare.9j,12b,12d Re-
cently, our group reported a free hydroxyl group-containing
neutral nickel complex,9j,12b,12d and as a single-component
catalyst, it is very active toward ethylene polymerization due
to the hydrogen bond between the free hydroxyl group and
the coordinating oxygen atom, which lowered the electron
density in the metal center and consequently enhanced the
chain propagation rate. Given the above examples
of neutral nickel catalysts, we wish to combine the benefits
of both electronic effects and proper steric bulk, and thus our
particular interests lie in the influence of electron-withdrawing
or -donating substituents directly linked to the ortho-phenoxy
phenyl groups (proper steric hindrance) on the performance
of the resultant catalysts. For this reason, we designed a series
of substituted salicylaldimine ligands differing in electronic
Bazan reported a series of neutral or zwitterionic benzyl
nickel catalysts for ethylene polymerization with or without
an activator1e and the quasi-living copolymeriza-
tion of ethylene with functionalized norbornenes using the
R-iminocarboxamide neutral nickel complex E/Ni(COD)2
system.7h,i,n Mecking reported a family of efficient neutral
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G.; Rosenfeldt, S.; Ballauff, M.; Harnau, L.; Gottker-Schnetmann, I.; Tong,
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B. Z. Anorg. Allg. Chem. 2005, 631, 2775. (h) Chen, Q. H.; Yu, J.; Huang,
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6284 Organometallics, Vol. 29, No. 23, 2010
Mu et al.
Scheme 2. Syntheses of Neutral Nickel(II) Catalysts 6a and 6c
In the 1H NMR spectra, the downfield shift of the septets of
CH(CH3)2 to 4.22 (6a), 4.11 (6b-PPh3), and 4.20 ppm (6c)
and the splitting of CH(CH3)2 into two doublets reveal the
successful coordination. The methyl nickel(II) complex 6b-
Py was synthesized according to Mecking’s method via the
reaction of the ligand 5b with NiMe2(Py)2 in toluene. After
filtration and removal of all volatiles under vacuum, the
complex was obtained in nearly quantitative yield as a red
solid. The η1-benzyl nickel(II) complex stabilized by the
PMe3 ligand was synthesized according to the literature
through the reaction of Ni(η3-CH2C6H5)Cl(PMe3) with the
sodium salt of the ligand in toluene at room temperature.16
After removal of the resultant NaCl and concentration of the
filtrate followed by layer diffusion with hexane, the target
complex was obtained in high yield as dark red crystals. In
the 1H NMR spectrum, the sharp doublet of P(CH3)3 at 0.41
ppm indicates the coordination of the PMe3 ligand. The
downfield shift of the septets of CH(CH3)2 to 4.14 ppm, split
of the CH(CH3)2 hydrogens into two doublets at 1.06 and
1.25 ppm, and the presence of the singlet of the -CH2Ph
hydrogen at 0.91 ppm confirmed the formation of η1-benzyl
nickel(II) trimethylphosphine complex 6b-1Bz. With regard
to the syntheses of neutral η3-benzyl nickel(II) complexes,
two published methods proved to be effective: by direct
reaction of Ni(COD)2, benzyl chloride, and the salt of the
ligand or by abstracting the phosphine ligand, which stabi-
lizes the corresponding η1-benzyl nickel complex to complete
the transformation from the η1- to the η3-benzyl coordina-
tion mode. Our initial attempts to synthesize complex 6b-3Bz
by the reaction of Ni(COD)2, benzyl chloride, and the
sodium salt of the ligand led to the formation of the bis-
Scheme 3. Syntheses of Pentafluorophenyl-Based Neutral
Nickel(II) Catalysts
properties of the ortho-phenoxy phenyl groups and corre-
sponding neutral nickel complexes, and studied their cataly-
tic performance toward ethylene polymerization.
1
ligated complex 6b-Bis, which was confirmed by H NMR
and X-ray diffraction analyses. This may be due to the low
steric hindrance of the ligand. Formation of bis-ligated
complexes was also observed by Lee in the syntheses of η3-
benzyl nickel complexes with less bulky ligands.17 The target
complex was finally obtained via the second method, that is,
abstracting the PMe3 ligand with B(C6F5)3 from the η1-
benzyl nickel complex 6b-1Bz synthesized via the reaction
of the sodium salt of the ligand and the nickel source Ni(η3-
CH2C6H5)Cl(PMe3). The disappearance of the sharp doub-
let of the P(CH3)3 hydrogen shows the absence of the PMe3
ligand, and the upfield shift of the septets of the CH(CH3)2
hydrogen from 4.14 ppm of η1-benzyl nickel to 3.64 ppm
indicates the formation of a η3-benzyl complex.7l
Solid-state characterization by single-crystal X-ray dif-
fraction further confirmed the structures of 6a, 6b-PPh3, 6b-
Py, 6b-1Bz, and 6b-Bis. Single crystals suitable for X-ray
crystallography were obtained by slow diffusion of hexane to
the toluene or THF (for 6b-PPh3) solution and by slow
evaporation of the solvent (hexane) for the bis-ligated com-
plex 6b-Bis. Suitable single crystals of 6b-PPh3 were very
difficult to obtain due to the high propensity of twinning.
Very thin plate crystals were chosen to avoid twinning, which
caused the poor diffraction data. The data collection and the
refinement parameters of the analyses are summarized in
Table S1. The ORTEP diagrams together with selected bond
lengths and angles for 6a, 6b-PPh3, 6b-Py, 6b-1Bz, and 6b-Bis
are shown in Figures 1-5. Complex 6b-Py exhibits a near
Results and Discussion
1. Synthesis and Characterization of the Neutral Nickel
Complexes. The ligands were synthesized according to
Scheme 1. Convenient palladium-catalyzed Suzuki coupling
of pentafluorobromobenzene or 2-nitrobromobenzene with
2-methoxybenzeneboronic acid in the presence of K2CO3
gave the substituted anisoles in good yields. After the
demethylation of 2a and 2b in high yields in CH2Cl2 at room
temperature,13 the resultant phenols were reacted with par-
aformaldehyde and anhydrous MgCl2 in THF, yielding 4a
and 4b.14 Suzuki coupling of 2-methoxybenzeneboronic acid
with 3-bromosalicylaldehyde directly afforded the substi-
tuted salicylaldehyde 4c.15 The target ligands were finally
obtained via facile Schiff base condensation of 2,6-diisopro-
pylaniline with the corresponding substituted salicylalde-
hydes 4a-c in the presence of catalytic amounts of formic
acid in methanol.
Synthetic routes to the neutral nickel(II) complexes are
depicted in Schemes 2 and 3. The phenyl nickel(II) complexes
6a, 6b-PPh3, and 6c were prepared by the reaction of the
sodium salts of the respective free ligands with one equiva-
lent of trans-NiCl(Ph)(PPh3)2 in toluene in moderate yields.
(13) Bauer, U.; Amaro, A. R.; Robertson, L. W. Chem. Res. Toxicol.
1995, 8, 92.
(14) Hansen, T. V.; Skattebøl, L. Org. Synth. 2005, 82, 64.
(15) (a) Flegel, M.; Lukeman, M.; Huck, L.; Wan, P. J. Am. Chem.
Soc. 2004, 126, 7890. (b) Duffy, K. J.; Shaw, A. N.; Delorme, E.; Dillon,
S. B.; Erickson-Miller, C.; Giampa, L.; Huang, Y. F.; Keenan, R. M.; Lamb,
P.; Liu, N. N.; Miller, S. G.; Price, A. T.; Rosen, J.; Smith, H.; Wiggall, K. J.;
Zhang, L. H.; Luengo, J. I. J. Med. Chem. 2002, 45, 3573.
(16) Lee, B. Y.; Bazan, G. C.; Vela, J.; Komon, Z. J. A.; Bu, X. H.
J. Am. Chem. Soc. 2001, 123, 5352.
(17) Shim, C. B.; Kim, Y. H.; Lee, B. Y.; Dong, Y.; Yun, H.
Organometallics 2003, 22, 4272.

Article
Organometallics, Vol. 29, No. 23, 2010 6285
Figure 3. ORTEP plot of 6b-Py. Ellipsoids are shown with 30%
probability. Hydrogen atoms are omitted for clarity. Selected
˚
bond distances (A) and angles (deg): Ni1-C31 = 1.9209(19),
Figure 1. ORTEP plot of 6a. Ellipsoids are shown with 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
distances (A) and angles (deg): Ni1-C26 = 1.881(4), Ni1-O1=
1.895(3), Ni1-N1 = 1.945(3), Ni1-P1 = 2.1851(11), P1-C44 =
1.816(4), O1-C7 = 1.298(4), N1-C1 = 1.298(5), C1-C2 =
1.422(5), N1-C14 = 1.452(5), C6-C8 = 1.500(5), N2-C9 =
1.476(6), O2-N2 =1.210(5), O3-N2 = 1.211(5), C26-Ni1-
O1 = 169.34(15), C26-Ni1-N1 = 93.01(15), O1-Ni1-N1 =
92.90(13), C26-Ni1-P1 = 86.56(12), O1-Ni1-P1 = 88.74(8),
N1-Ni1-P1=172.43(10).
Ni1-N1 = 1.8948(15), Ni1-N2 = 1.9110(15), Ni1-O1 =
1.9222(13), O1-C15 = 1.290(2), N1-C1 = 1.457(2), N1-
C13 = 1.304(2), C13-C14 = 1.432(3), C16-C20 = 1.486(3),
F1-C21=1.346(2), N1-Ni1-C31=93.14(8), N1-Ni1-N2=
171.31(7), N2-Ni1-C31=90.11(8), N1-Ni1-O1=93.63(6),
N2-Ni1-O1=84.16(6), C31-Ni1-O1=170.42(7).
˚
Figure 4. ORTEP plot of 6b-1Bz. Ellipsoids are shown with 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
distances (A) and angles (deg): Ni1-O1=1.9137(19), Ni1-N1=
1.955(2), Ni1-P1 = 2.1646(9), Ni1-C26 = 1.955(3), N1-C1 =
1.298(3), O1-C7 = 1.294(3), O1-Ni1-C26 = 164.35(11),
N1-Ni1-P1 = 163.26(7), O1-Ni1-N1 = 93.36(8), C26-Ni1-
P1 = 90.94(10), O1-Ni1-P1 = 85.65(6), C26-Ni1-N1 =
94.23(11), Ni1-C26-C27=112.1(2).
Figure 2. ORTEP plot of 6b-PPh3. Ellipsoids are shown with
30% probability. Hydrogen atoms are omitted for clarity. One
molecule in the asymmetric unit is shown here. Selected bond
˚
˚
distances (A) and angles (deg): Ni1-P3=2.168(4), Ni1-N1=
1.884(9), Ni1-O1 1.914(7), Ni1-C75 = 1.908(10), N1-Ni1-
O1 = 93.0(3), N1-Ni1-C75 = 94.8(4), O1-Ni1-C75 =
162.1(4), N1-Ni1-P3 = 165.2(3), O1-Ni1-P3 = 89.0(2),
C75-Ni1-P3=87.4(4).
˚
for 6b-Py, 1.897(2) and 1.912(2) A for the latter). The data for
square-planar coordination geometry around the nickel center,
evidenced by almost linear N1-Ni1-N2 (171.31(7)°) and
O1-Ni1-C31 (170.42(7)°) bond angles. The pyridine ligand
is trans to the bulky N-aryl group, similar to other methyl nickel
pyridine complexes reported by Mecking.9i The bond distance
6a, 6b-PPh3, and 6b-1Bz also reveal their distorted square-
planar geometry. The phosphine ligand in the three complexes
is situated in the trans position of the N-aryl group, respectively,
as in the case of B7c and R-iminocarboxamide-based benzyl
nickel trimethylphosphine complexes.16 Comparing the
Ni-PPh3 distances of 6b-PPh3 (2.165(4) A) (two independent
molecules with slightly different bond lengths and angles crystallized
in the asymmetric unit, and the average values were used for
˚
˚
of Ni1-O1 (1.9222(13) A) is slightly longer than that of the
complex with a 9-anthryl group,9i and the Ni1-N1 and
˚
Ni1-N2 distances are similar (1.8948(15) and 1.9110(15) A

6286 Organometallics, Vol. 29, No. 23, 2010
Mu et al.
Table 1. Preliminary Screening Results Using 6a, 6b-PPh3,
and 6ca
c
temp
P
yield
Mw
entry
cat.
(°C) (atm) (g) productivityb (kg/mol)
PDIc
1
2
3
4
5
6
6a
6a
46-52 10 1.53
53-58 10 1.47
4.59
4.41
5.31
12.6
0.99
3.90
40.5
65.2
34.7
18.2
28.8
11.5
bimodal
bimodal
2.2
2.1
2.0
6b-PPh3 46-52 10 1.77
6b-PPh3 53-62 10 4.20
6c
6c
46-47 10 0.33
53-59 10 1.30
1.9
a Reaction conditions: 60 mL of toluene, 10 μmol of catalyst, 20 μmol
of B(C6F5)3, polymerization for 20 min. b In units of 105 g PE/molNi h.
3
c Determined by GPC.
6b-Py, which may be due to the loss of base that donates an
electron to the nickel center.21
Figure 5. ORTEP plot of 6b-Bis. Ellipsoids are shown with 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
distances (A) and angles (deg): Ni1-O1 = 1.839(2), Ni1-N1 =
1.901(2), O1-C1=1.312(3), N1-C25=1.302(4), N1A-Ni1-N1=
157.69(14), N1A-Ni1-O1 = 94.17(9), N1-Ni1-O1=89.09(9),
O1-Ni1-O1A=163.10(12).
2. Ethylene Polymerization. Preliminary screening was
first carried out using the Grubbs-type neutral nickel com-
plexes 6a and 6c, and the typical results are summarized in
Table 1. These data indicate that an electron-withdrawing
nitro group may contribute to the higher activity of complex
6a than 6c (entries 1, 2 vs 5, 6). Thus, we also synthesized 6b-
PPh3 with a fluorinated ligand, which was found to be even
more active than 6a. We chose the most active catalyst, 6b-
PPh3, in a preliminary screening to catalyze the polymeriza-
tion of ethylene as a single-component catalyst, and the
results are given in Table 2, from which we can see sub-
stantial influence of the reaction conditions upon the beha-
vior of the catalysts and the molecular weights as well as the
microstructure of the polymer. Considering the crucial role
of the labile pendant ligands in neutral nickel catalysts,
complexes 6b-Py, 6b-1Bz, and 6b-3Bz were also synthesized
and assessed for ethylene polymerization as a comparison
and further modification of catalyst 6b-PPh3.
˚
comparison) with reported complexes bearing similar steric
hindrance, we found that the distances are shorter than the
˚
nitro-bearing complex 6a(2.1851(11) A), cyclohexyl-substituted
complex [6-CHdN(2,6-iPr2C6H3)-3-Cy-5-Me-C6H3O-κ2-N,
7j
O]Ni(Ph)(PPh3) (2.182(2) A), phenyl-substituted complex
˚
9c
(2.1838(12) A), and the complex with no substituent in the
˚
18
C3 position (2.1833(5) A), which implies that the electron-
˚
withdrawing group in 6b-PPh3 may strengthen the Ni-PPh3
bond and consequently hamper the initiation process. As for
6b-1Bz, the wide angles of O1-Ni1-C26 (164.35(11)°) and
N1-Ni1-P1 (163.26(7)°) also reveal a slightly distorted square-
planar geometry and the trans arrangement of the PMe3 and
˚
Compared with cationic catalysts that need cocatalysts,
single-component neutral nickel catalysts, especially those
with electron-withdrawing groups, generally require higher
temperatures to generate the active sites by removing the
pendant ligands from the complexes.8p,12b In our case, with-
out any activator, 6b-PPh3-initiated polymerizations give
very little polymer below 50 °C. Only at temperatures higher
than 55 °C is 6b-PPh3 able to be an efficient single-compo-
nent catalyst (Table 2, entry 3). The polymer productivities
increase with reaction temperature from 55 to 70 °C (entries
3-5), and decrease at higher temperature (entry 7). Different
from the neutral nickel catalysts reported by Grubbs,7c,20 6b-
PPh3 exhibits good productivities under relatively higher
temperature. This probably originates from the electron-
withdrawing character of the ligand, which increases the
electrophilic nature of the metal center, and thus the PPh3
pendant ligand binds more tightly to the nickel center than in
catalysts A and B. However, once the pendant PPh3 dissoci-
ates from 6b-PPh3, the more electrophilic nature will lead to
a more electron-deficient active site and thus be beneficial to
chain growth. Since 6b-PPh3 is highly active only under
elevated temperature, attempts to yield more polymer will
be at the expense of the molecular weights (Table 2, entry 1 vs
entry 2). Thus, analogous catalyst 6b-Py with pendant
pyridine was synthesized to overcome this shortcoming
(Table 3). Its productivities also increase with the enhance-
ment of reaction temperature and attain the maximum value
at 60 °C (Table 3, entries 3-5, 7). The comparison of the
polymerization results under similar conditions indicates
that the pyridine-coordinated catalyst is more readily initiated
N-aryl moieties. The Ni-PMe3 bond length (2.1646(9) A) is
longer than that in the R-iminocarboxamide-based complex
(2.1483(8) A), which indicates the weaker binding of the
16
˚
phosphine to the metal center in 6b-1Bz. The Ni1-O1
˚
˚
(1.9137(19) A) and Ni1-N1 (1.955(2) A) distances are similar
to the reported 4-(2,6-diisopropylphenylimino) acetylacetonate-
˚
based PMe3-coordinated complex (1.907(2) and 1.954(2) A,
respectively).19 An obviously longer Ni-N distance of 6b-1Bz
than that of 6b-PPh3 (1.955(2) vs 1.918(9) A) may originate
˚
from the more donating nature of PMe3 that increases the
electron density on the nickel center, which subsequently weak-
ens the Ni-N bond in 6b-1Bz.9c,20 This phenomenon was also
observed in the literature when the more basic and electron-
donating 1,3,5-triaza-7-phosphaadamantane (PTA) replaced
PPh3.21 In 6b-Bis, the two diisopropyl groups are trans to each
other for steric reasons. The angle between the N-Ni-O planes
defined by the two ligands is 27.2°, which is similar to the value
reported for the phenyl-substituted analogue (28°).22 The dis-
˚
˚
tances of Ni1-O1(1.839(2) A) and Ni1-N1(1.901(2) A) are
similar to analogous bis-ligated complexes reported22 and are
obviously smaller than that in complexes 6b-PPh3, 6b-1Bz, and
(18) Zeller, A.; Eickerling, G.; Herdtweck, E.; Schmidt, M. U.;
Strassner, T. J. Organomet. Chem. 2007, 692, 4725.
(19) Chen, Y. F.; Wu, G.; Bazan, G. C. Angew. Chem., Int. Ed. 2005,
44, 1108.
(20) Wang, C. M.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs,
R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149.
(21) Darensbourg, D. J.; Ortiz, C. G.; Yarbrough, J. C. Inorg. Chem.
2003, 42, 6915.
(22) Foley, S. R.; Stockland, R. A.; Shen, H.; Jordan, R. F. J. Am.
Chem. Soc. 2003, 125, 4350.

Article
Organometallics, Vol. 29, No. 23, 2010 6287
Table 2. Ethylene Polymerization Results Using PPh3-Stabilized Catalysts (A, 6c, and 6b-PPh3)
e
Mw
(kg/mol)
branchesg /
1000C
entry
cat.
temp. (°C)
P (atm)
yield (g)
productivityd
PDIe
Tmf (°C)
1a
6b-PPh3
6b-PPh3
6b-PPh3
6b-PPh3
6b-PPh3
6b-PPh3
6b-PPh3
6b-PPh3
A
55
68
55
60
70
70
80
70
47
55
55
55
10
10
30
30
30
30
30
50
30
30
30
30
0.24
2.37
7.01
8.00
8.13
10.09
4.87
19.56
1.55
3.23
3.95
5.51
0.72
7.11
17.5
24.0
24.5
15.1
14.6
58.7
4.64
9.69
11.9
8.27
15.6
7.3
2.1
1.9
2.2
2.0
2.0
1.8
2.0
2.2
2.9
2.0
2.2
2.0
102
87
2a
3b
22.9
20.9
15.4
15.7
7.9
17.8
98.8
29.5
52.5
55.4
111
108
104
104
96
105
121
111
118
118
4b
22
25
5b
6c
7b
37
26
8b
9b
10b
11b
12c
A
6c
6c
a Reaction conditions: 60 mL of toluene, 10 μmol of catalyst, polymerization for 20 min. b Reaction conditions: 100 mL of toluene, 10 μmol of catalyst,
polymerization for 20 min. c Reaction for 40 min. d In units of 105 g PE/molNi h. e Determined by GPC. f Determined by DSC. g Calculated from 13
NMR.
C
3
Table 3. Ethylene Polymerization Results Catalyzed by Pyridine-Stabilized Catalyst 6b-Pya
Mw
(kg/mol)
branchesf /
1000C
d
entry
P (atm)
temp (°C)
yield (g)
productivityc
PDId
Tm
e
1
2
3
4
5
6b
7
8
9
10
20
30
30
30
30
30
30
40
60
60
40
50
60
60
70
80
60
5.76
6.16
4.30
4.44
8.55
13.05
7.67
3.94
8.72
17.3
19.9
12.9
13.3
25.7
19.6
23.0
11.8
26.2
12.3
17.6
99.7
34.4
29.0
28.7
18.1
9.3
1.8
1.8
2.6
2.0
1.9
1.8
2.0
2.0
1.9
96
102
119
110
107
109
102
98
13
17
24
38
17
30.1
109
a Reaction conditions: 100 mL of toluene, 10 μmol of catalyst, polymerization for 20 min. b Reaction for 40 min. c In units of 105 g PE/molNi h.
3
d Determined by GPC. e Determined by DSC. f Calculated from 13C NMR.
than the phosphine analogue. Even under a low temperature of
40 °C, catalyst 6b-Py still shows high productivity up to 106 g
increase of the productivity to 5.87 ꢀ 106 g PE/molNi h,
3
which is even higher than that of B (3.7 ꢀ 106 g PE/molNi
h
3
PE/molNi h (Table 3, entry 3) for ethylene polymerization
under optimized conditions), although under higher ethylene
pressure. This result indicates that catalyst 6b-PPh3 is far
from saturation, and the system still rests between Ni(alkyl)-
(ethylene) and Ni(alkyl)(PPh3) species. With the increase of
ethylene pressure, the molecular weights (Mw) of the polymer
increase from 7.3 kg/mol (10 atm, Table 2, entry 2) to 15.4 kg/
mol (30 atm, Table 2, entry 5) to 17.8 kg/mol (50 atm,
Table 2, entry 8). These data indicate that chain transfer to
monomer may limit the Mw at higher ethylene pressure.
Complex 6b-Py shows similar polymerization behavior un-
der various ethylene pressures. For example, under 60 °C, the
molecular weights of the polymer vary from 17.6 kg/mol (20
atm, Table 3, entry 2) to 29.0 kg/mol (30 atm, Table 3, entry 5)
to 30.1 kg/mol (40 atm, Table 3, entry 9). Catalyst 6b-Py differs
from 6b-PPh3 in that the former can exhibit high productivity at
relatively lower ethylene pressure (Table 3, entry 1). This result
again verifies that the pyridine in 6b-Py is more labile than
triphenylphosphine in 6b-PPh3, enabling the equilibrium
to favor the ethylene-coordinated species Ni(alkyl)(ethylene) to
a greater extent in 6b-Py.
For ethylene polymerizations using single component
neutral nickel catalysts, the generation of active species
requires dissociation of the pendant ligands, which still stay
in the reaction system resulting in equilibria between ligand
coordinated and dissociated species. The competition of
strong nitrogen or phosphine ligand with ethylene for
coordination largely limits the polymerization rate and
the molecular weights of the polymer. To overcome this
disadvantage, we also synthesized the η3-benzyl-coordinated
nickel complex 6b-3Bz based on the pentafluorophenyl substituted
3
without any activator, while polymerizations using 6b-PPh3
under 50 °C yield only a trace amount of solid polymer even
using high ethylene concentration, which indicates the more
labile character of pyridine than that of triphenylphosphine as a
pendant ligand in the two catalysts, respectively. The same
phenomenon was also previously reported.7a The molecular
weights of the resultant polyethylene decrease dramatically with
increasing temperature for both 6b-PPh3 and 6b-Py (Table 2,
entries 4, 5, 7 and Table 3, entries 3-5, 7, 8). As expected,
increasing the temperature from 60 to 80 °C also results in the
enhancement of the polymer branching numbers using 6b-PPh3
(Table 2, entries 4-5, 7, from 22 branches/1000C to 37
branches/1000C) and 6b-Py (Table 3, entries 5, 7, 8, from 17
branches/1000C to 38 branches/1000C) together with decreases
in Tm values (from 108 to 96 °C and 107 to 98 °C, respectively).
These results indicate that fast chain transfer occurs under
elevated temperature for this family of catalysts.
Generally, polymerizations catalyzed by neutral nickel
catalysts always require relatively higher ethylene pressure
to ensure the coordination of ethylene monomer due to the
less electrophilic nature of the active center than the cationic
catalysts and the severe coordinative competition of the
pendant ligands with the monomer. Under an ethylene
pressure of 10 atm, 6b-PPh3 shows productivity of lower
than 106 g PE/molNi h (Table 2, entries 1, 2). By increasing
3
the ethylene pressure to 30 atm (Table 2, entries 3-7), 6b-
PPh3 exhibits high productivity up to 2 ꢀ 106 g PE/molNi h.
3
Further enhancing ethylene pressure to 50 atm under the
optimized temperature of 70 °C (Table 2, entry 8) leads to an

6288 Organometallics, Vol. 29, No. 23, 2010
Table 4. Ethylene Polymerization Results Using Benzyl Nickel Complexes (6b-1Bz and 6b-3Bz)a
Mu et al.
d
Mw
(kg/mol)
branchesf /
1000C
e
Tm
entry
cat.
P (atm)
temp (°C)
yield (g)
productivityc
PDId
1
2
3
4
5
6
7
6b-1Bz
6b-1Bz
6b-1Bz
6b-1Bz
6b-1Bz
6b-3Bz
6b-3Bz
6b-3Bz
6b-3Bz
6b-3Bz
10
20
30
30
30
30
30
30
30
30
60
60
50
65
75
30
50
65
65
75
1.28
2.47
1.42
7.66
5.15
1.33
5.50
9.58
11.7
1.97
3.84
7.41
4.26
23.0
15.4
3.99
16.5
28.7
17.5
5.91
13.5
14.7
47.7
20.0
12.1
96.5
46.3
21.7
24.5
16.6
1.9
1.9
2.0
2.0
2.0
2.1
1.9
1.9
1.8
1.9
96
100
113
105
100
119
112
106
108
102
24
13
21
9
8
18
9b
10
a Reaction conditions: 100 mL of toluene, 10 μmol of catalyst, polymerization for 20 min. b Reaction for 40 min. c In units of 105 g PE/molNi h.
3
d Determined by GPC. e Determined by DSC. f Calculated from 13C NMR.
the PMe3-stabilized η1-benzyl complex. Especially, this
preactivation plays a more important role in complex
6b-3Bz, since the electron-withdrawing groups in the com-
plex will render the coordination of pendant leaving li-
gands more tightly. It is also noteworthy that the base-free
catalyst 6b-3Bz is, as expected, less stable than the base-
stabilized 6b-PPh3 and 6b-Py (over time crystallizations
lead to the formation of bis-ligated complex 6b-Bis), which
may limit the activity of the catalyst and molecular weights
of the produced polymer.
Lifetime experiments for catalysts with electron-with-
drawing (6b-PPh3, 6b-Py, 6b-3Bz) and electron-donating
(6c) groups were conducted. We found obvious decreases
in productivity when the polymerization time was extended
to 40 min, and the decreasing percentages of productivity
were used to characterize their lifetimes. Comparing the two
triphenyphosphine-stabilized catalysts, 6c, with an electron-
Figure 6. 13C NMR of polyethylene with different branching
donating methoxy group, exhibited a higher lifetime than its
electron-withdrawing anologue 6b-PPh3 (productivity decrease
percentage 30.5% vs 38.2%, Table 2, entries 11, 12 vs 5, 6).
Actually, 6b-PPh3 produced only less than 2 g of polymer within
numbers produced by 6b-1Bz under different pressure and
temperature: (a) Table 4, entry 1; (b) Table 4, entry 4; and (c)
Table 4, entry 3.
ligand. Complex 6b-3Bz was synthesized by treatment of PMe3
stabilized complex 6b-1Bz with B(C6F5)3, and the latter behaves
similarly to 6b-PPh3 as a single-component ethylene polymeri-
the latter 20 min of the 40 min trial, which is about one-quarter
of that produced in the former 20 min polymerization. The base-
free catalyst 6b-3Bz exhibited a lifetime similar to 6b-PPh3
(productivity decrease percentage 40.3%, Table 4, entries 8,
9). 6b-Py showed the longest lifetime among these catalysts, and
the productivity decreased only 23.7% (Table 3, entries 5, 6) in
the 40 min trial. These data indicate that both the backbone and
the spectator ligand, especially the latter, considerably influence
catalyst lifetime. That complex 6b-Py displayed a longer lifetime
may originate from the low steric hindrance of the pyridine
ligand, which may be beneficial to the stabilization of the active
site during chain growth. Due to the high steric hindrance of the
growing polymer chains, it is difficult for the dissociated bulky
PPh3 ligand of 6b-PPh3 to stabilize the active site. Likely, also
due to the failure of stabilization by base, complex 6b-3Bz
showed a shorter lifetime than 6b-Py. The temperature rise
(caused by reaction heat of polymerization) of the system during
polymerization also provided some information about the life-
time of the catalysts. Actually, in less than 25 min, the tempera-
ture of the systems 6b-PPh3 (16 min), 6b-3Bz (15 min), and 6c
(18 min) became stable, and the temperature controls require no
cooling water, which indicates the slowing of the reactions. For
catalyst 6b-Py, however, the cooling water was still needed
through 38 min. This may also indicate that the reaction began
to slow if reaction time was further extended, and no experi-
ments for longer time were conducted.
zation catalyst with respect to the molecular weights and the
branching numbers of the produced polymer (Table 4). Repre-
sentative examples for the influence of temperature and ethylene
pressure on the branching numbers produced by 6b-1Bz are
shown in Figure 6. Under 50 °C and 30 atm ethylene pressure,
this catalyst produces polyethylene with almost exclusively
methyl branches, and the total number of branches is low (13
branches/1000C) (Figure 6c). When the temperature is pro-
moted to 65 °C under identical ethylene pressure, the total
branching numbers increase to 21 branches/1000C with the
emergence of ethyl and longer branches (Figure 6b). Compared
with the significant influence of reaction temperature, ethylene
pressure only slightly influences branching numbers of the
polymer (10 atm ethylene pressure, 60 °C, 24 branches/1000C)
(Figure 6a). Polymerization results show that complex 6b-3Bz is
a highly active single-component catalyst for ethylene polymer-
ization under lower temperature, which enables the formation of
relatively lower branched and higher molecular weight polymer
(Table 4, entry 6) than those produced using 6b-PPh3 and 6b-Py.
This reveals that the base-free η3-benzyl-coordinated nickel
center can be more readily transformed to the active site for
ethylenesubstrate than the base-stabilized nickel complexes
6b-PPh3 and 6b-Py. The η3-benzyl complex 6b-3Bz, in some
sense, may be seen as the preactivated catalyst derived from

Article
In general, these catalysts produce polymer with narrow
Organometallics, Vol. 29, No. 23, 2010 6289
Experimental Section
PDIs, indicating a single-site mechanism. Reaction tempera-
ture seems to be a key to the initiation process of the catalysts
and exerts a great influence on the molecular weights and
branching numbers of the polymer. Given the proper tem-
perature to initiate the polymerizations, ethylene pressure
greatly influences the productivity. It was reported by Mecking
that the complexes with electron-withdrawing groups in the
aniline groups showed high productivities and produced higher
molecular weight polymer than those with electron-donating
groups in the same positions.10 Huang also reported that bi-
nuclear neutral nickel complexes with nitro groups in the ligand
backbone are highly active toward ethylene polymerization and
yield polymer with higher molecular weights.9h In our case,
however, the molecular weight are relatively lower. Even the
highest molecular weights of the polymer produced (Mw=96.5
kg/mol, PDI=2.1, using 6b-3Bz under 30 °C, Mw=99.7 kg/mol,
PDI=2.6, using 6b-Py under 40 °C) are still lower than that
produced with catalyst B (Mw=236 kg/mol, PDI=2.2) and
even A (Mw=207 kg/mol, PDI=2.2), with lower steric bulk.
Apart from steric factors, we tentatively ascribed the relatively
lower molecular weight of the polymer to the high initiation
temperature of our catalysts caused by the electron-withdrawing
character of the ligand. Under higher temperature, chain trans-
fer was more severe, which limited the molecular weight of the
polymer. On the other hand, we noticed that ethylene polymer-
izations using 6b-Py under 40 °C produced polymer with Mw
similar to that using catalyst A under 47 °C under otherwise
identical conditions (Table 2, entry 8 and Table 3, entry 3). This
reveals that, in addition to the factor of temperature, the more
electrophilic nature of the nickel center may also contribute to
the lower molecular weights, presumably by accelerating the
β-H elimination process.
General Procedures and Materials. All manipulations invol-
ving air- and/or moisture-sensitive compounds were performed
under dry nitrogen or argon atmosphere using standard Schlenk
and glovebox techniques. Toluene, n-hexane, diethyl ether,
tetrahydrofuran, and methylene dichloride were purified by an
MBraun solvent purification system (SPS), benzyl chloride was
distilled under reduced pressure after drying over MgSO4, and
pyridine was distilled from sodium/benzophenone ketyl under
nitrogen prior to use.
Sodium hydride and 2,6-diisopropylaniline were purchased
from Acros. Anhydrous MgCl2, 1-bromo-2-nitrobezene, and
methyllithium (1.6 M in diethyl ether) were used as received
from Alfa Aesar. B(C6F5)3 was obtained from Strem. Literature
procedures were employed for the preparation of the following
compounds: Ni(COD)2,23 Pd(PPh3)4,24 Ni(η3-CH2C6H5)Cl-
(PMe3),25 NiMe2(Py)2,26 trans-NiCl(Ph)(PPh3)2,27 2-methoxy-
benzeneboronic acid,28 3-bromosalicylaldehyde.14 All the other
chemical products were purchased from commercial vendors
and used without further purification.
The NMR spectra of polyethylene samples were all recorded
on a Varian Unity 400 MHz spectrometer with o-dichloroben-
zene as the solvent at 120 °C. The other NMR data of the ligands
and the complex were obtained on a Bruker 300 MHz spectro-
meter or a Varian Unity 400 MHz spectrometer at ambient
temperature with CDCl3 or C6D6 as the solvent. The DSC
measurements were performed on a Perkin-Elmer Pyris 1 differ-
ential scanning calorimeter at a heating rate of 10 °C/min. The
weight-average molecular weight (Mw) and the polydispersity
index (PDI) values of polyethylene samples were determined via
high-temperature GPC in which 1,2,4-trichlorobenzene was
used as mobile phase at a flow rate of 1.0 mL/min.
Synthesis of Nickel Complexes. [[6-CHN(2,6-iPr2C6H3)-
2-(2-NO2C6H4)-C6H3O-K2-N,O]Ni(Ph)(PPh3)] (6a). To a 50 mL
Schlenk flask containing NaH (72.0 mg, 3.00 mmol) and 5 mL of
THF was added ligand 5a (0.40 g, 1.00 mmol, dissolved in 10 mL of
THF). The suspension was stirred at room temperature for 4 h, then
filtrated to remove excess NaH, and the filtrate was evaporated to
dryness. To the resultant yellow solid were added trans-PhNi-
(PPh3)2Cl (696 mg, 1.00 mmol) and 15 mL of toluene. The reaction
mixture was stirred overnight at room temperature and filtrated.
The filtrate was concentrated under vacuum to a small volume (ca. 3
mL), and 6 mL of hexane was added to yield complex 6a as dark
yellow crystals (0.59 g, 70%). 1H NMR (300 MHz, C6D6):δ8.03 (d,
J=8.7 Hz, 1H), 7.56 (t, J=8.4 Hz, 6H), 7.41 (dd, J=8.1, 0.9 Hz,
1H), 7.07-6.92 (m, 16H), 6.77 (dd, J=7.5, 1.5 Hz, 1H), 6.50 (t, J=
7.5 Hz, 1H), 6.42-6.25 (m, 5H), 4.22 (sept, J = 6.6 Hz, 2H,
iPr2-CH), 1.30 (d, J=6.6 Hz, 6H, iPr-CH3), 1.17 (d, J=6.6 Hz,
6H, iPr2-CH3) 13C NMR (75 MHz, C6D6): δ 166.60 (CdN), 157.76
(O-C), 150.20, 149.44, 140.92, 137.35, 135.07, 134.70, 134.56,
134.22, 133.38, 132.37, 131.79, 130.87, 129.79, 128.00, 126.45,
126.30, 125.52, 123.94, 123.16, 121.54, 120.35, 114.42, 29.29 (iPr2-
CH), 25.90 (iPr-CH3), 23.00 (iPr-CH3). Anal. Calcd for
C49H45N2NiO3P: C, 73.61; H, 5.67; N, 3.50. Found: C, 73.58; H,
5.62; N, 3.46.
Conclusions
With the expectation that integrating both electronic and
proper steric effects into the C3 position of the ligands may
have a significant influence on the performance of the
catalysts, complexes 6a, 6b (6b-PPh3, 6b-Py, 6b-1Bz, 6b-3Bz),
and 6c were synthesized. Under temperatures of 60 to 70 °C, 6a
and 6b, bearing electron-withdrawing groups, exhibit high
productivities for ethylene polymerization as single-component
catalysts, which are on the same order as that of the anthryl-
bearing catalyst B and much higher than the phenyl-substituted
catalyst A. The preactivation of 6b-1Bz afforded base-free
catalyst 6b-3Bz, which can catalyze the polymerization of
ethylene under lower temperature, yielding higher molecular
weight polymer with fewer branches. Compared with catalysts
A and B, Mw of the produced polymer is slightly lower, which is
probably attributable to the less steric hindrance and also to the
electron-withdrawing character that strengthens the coordina-
tion of the leaving pendant ligands, making the catalysts
effective only under higher reaction temperature. Alternatively,
the relatively lower molecular weights may result from an
accelerated rate of β-H elimination due to the more electrophilic
nickel center. Catalyst 6b-Py exhibited the longest lifetime
among the catalysts we reported. We ascribed the relatively
longer lifetime to the success of active site stabilization during
polymerization due to the lower steric hindrance of the pyridine
spectator ligand. The properties of the polyethylene produced
using these catalysts, namely, branching numbers, Mw, and Tm,
can be readily manipulated by variation of reaction tempera-
ture, ethylene pressure, and/or catalyst structure.
[[6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-K2-N,O]Ni(Ph)(PPh3)]
(6b-PPh3). Following the procedure for the synthesis of 6a,
complex 6b-Ph was obtained as red crystals in 56.9% yield. H
1
NMR (300 MHz, C6D6): δ 8.04 (d, J=9.0 Hz, 2H, NdCH), 7.57(t,
(23) Tenorio, M. J.; Puerta, M. C.; Salcedo, I.; Valerga, P. J. Chem.
Soc., Dalton Trans. 2001, 653.
(24) Coulson, D. R. Inorg. Synth. 1990, 28, 107.
(25) Carmona, E.; Paneque, M.; Poveda, M. L. Polyhedron 1989, 8,
285.
ꢀ
ꢀ
(26) Campora, J.; Conejo, M. D.; Mereiter, K.; Palma, P.; Perez, C.;
Reyes, M. L.; Ruiz, C. J. Organomet. Chem. 2003, 683, 220.
(27) Schunn, R. A. Inorg. Synth. 1971, 13, 124.
(28) Rashkin, M. J.; Hughes, R. M.; Calloway, N. T.; Waters, M. L.
J. Am. Chem. Soc. 2004, 126, 13320.

6290 Organometallics, Vol. 29, No. 23, 2010
Mu et al.
J=8.8, 6H, Ar-H), 7.18-6.91 (m, 16H, Ar-H), 6.61 (t, J=7.5 Hz,
1H), 6.40-6.26 (m, 3H), 4.11 (sept, J=6.9 Hz, 2H, iPr-CH), 1.30
[[6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-K2-N,O]2Ni] (6b-Bis).
1H NMR (300 MHz, CDCl3): δ 7.33 (s, 1H), 7.06-6.80 (m, 5H),
6.47 (t, J=7.5 Hz, 1H), 4.34 (sept, J=6.9 Hz, 2H, iPr-CH), 1.31 (d,
(d, J=6.9 Hz, 6H, iPr-CH3), 1.12 (d, J=6.9 Hz, 6H, iPr-CH3). 13
C
NMR (75 MHz, C6D6): δ 166.67, 163.76, 150.12, 146.26, 145.58,
142.84, 140.75, 137.67, 136.63, 134.50, 134.42, 131.91, 131.32,
130.04, 128.06, 126.55,125.50, 123.14, 121.71, 120.49, 119.83,
114.11, 119.84, 29.22, 25.81, 22.91. Anal. Calcd for C49H41F5-
NNiOP: C, 69.69; H, 4.89; N, 1.66. Found: C, 69.80; H, 4.84;
N, 1.62.
J=6.9 Hz, 6H, iPr-CH3), 1.17 (d, J=6.6 Hz, 6H, iPr-CH3). 13
C
NMR (75 MHz, CDCl3): δ 165.5, 161.1, 146.3, 146.7, 142.4, 141.5,
139.4, 137.9, 136.1, 135.3, 126.2, 123.1, 121.5, 119.0, 115.0, 29.56,
24.72, 22.55. Anal. Calcd for C50H42F10N2NiO2: C, 63.11; H, 4.45;
N, 2.94. Found: C, 63.03; H, 4.46; N, 2.87.
[[6-CHN(2,6-iPr2C6H3)-2-(2-OCH3C6H4)-C6H3O-K2-N,O]-
Ni(Ph)(PPh3)] (6c). Following the procedure for the synthesis of
6a, complex 6c was obtained as yellow crystals in 52.4% yield. 1H
NMR (400 MHz, C6D6): δ 8.10 (d, J=9.2 Hz, 1H), 7.74-7.59
(m, 7H), 7.15-6.92 (m, 15H), 6.84-6.75 (m, 2H), 6.72 (t, J=7.5
Hz, 1H), 6.54 (d, J=8.1 Hz, 1H), 6.43 (t, J=7.0 Hz, 1H), 6.34 (t,
J=7.3Hz, 2H), 6.15 (t, J=7.3 Hz, 1H), 4.20(sept, J=7.3 Hz, 2H,
iPr2-CH), 3.40 (s, 3H, OCH3), 1.34 (d, J=6.8 Hz, 6H, iPr-CH3),
1.20 (d, J=6.8 Hz, 6H, iPr-CH3). 13C NMR (75 MHz, C6D6): δ
166.81, 164.26, 157.00, 150.47, 147.08, 146.32, 141.12, 137.54,
137.36, 134.81, 134.67, 134.22, 133.00, 132.65, 131.70, 129.59,
128.02, 127.06, 126.32, 125.33, 123.08, 121.46, 120.01, 114.09,
111.08, 55.31 (OCH3), 29.16 (iPr2-CH), 25.89 (iPr-CH3), 22.99
(iPr-CH3). Anal. Calcd for C50H48NNiO2P: C, 76.54; H, 6.17; N,
1.79. Found: C, 76.40; H, 6.14; N, 1.76.
[[6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-K2-N,O]Ni(CH3)-
(pyridine)] (6b-Py). The mixture of ligand 5b (0.12 g, 0.27 mmol)
and NiMe2(Py)2 (0.07 g, 0.28 mmol) was stirred in 15 mL of
toluene at room temperature to give a red solution, which turned
dark as the reaction proceeded. After 4 h, the mixture was
filtrated to remove nickel black, and the filtrate was directly
taken to dryness, affording complex 6b-Py as dark red solid
1
(0.153 g, yield 95.6%). H NMR (300 MHz, C6D6): δ 8.48 (d,
J=5.1 Hz, 2H), 7.55 (s, 1H), 7.24-6.94 (m, 6H), 6.54 (dt, J=
30.0, 7.5 Hz, 2H), 6.30 (t, J=6.6 Hz, 2H), 4.20 (sept, J=6.9 Hz,
i
i
2H, Pr2-CH), 1.57 (d, J = 6.9 Hz, 6H, Pr-CH3), 1.12 (d, J =
i
6.9 Hz, 6H, Pr-CH3), -0.59 (s, 3H, Ni-CH3). 13C NMR (75
MHz, C6D6): δ 166.50, 164.67, 151.58, 150.09, 146.65, 143.44,
141.56, 141.12, 139.17, 136.2, 126.87, 123.81, 123.13, 120.85,
119.04, 113.50, 28.70, 24.98, 23.27. Anal. Calcd for C31H29-
F5N2NiO: C, 62.13; H, 4.88; N, 4.67. Found: C, 62.10; H, 4.92;
N, 4.64.
Ethylene Polymerization. A 100 or 200 mL autoclave was
heated under vacuum up to 130 °C for 4 h and then was cooled to
and maintained at the desired reaction temperature. The reactor
was charged with toluene under vacuum, and then the stirring
motor was engaged to facilitate heat transfer. For single-com-
ponent trials, a toluene solution of the catalyst was injected into
the reactor; for cocatalyst-activated trials, a toluene solution of
B(C6F5)3 was also added, after which ethylene was fed continu-
ously, which was manually adjusted to maintain a desired
constant pressure. Temperature control (for the 200 mL auto-
clave) was conducted by internal cooling water coils. After the
prescribed reaction time, the stirring motor was stopped, and the
reactor was vented. The solid polyethylene was obtained by
filtration after precipitation from ethanol, washed with ethanol
and acetone, and dried at 60 °C for 10 h under vacuum.
Crystallographic Studies. Crystals suitable for X-ray analysis
were manipulated in a glovebox. The intensity data were collected
with the ω scan mode (186K) on a Bruker Smart APEX diffract-
[[6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-K2-N,O]Ni(CH2Ph)-
(PMe3)] (6b-1Bz). To a flask containing ligand 5b (0.19 g, 0.43
mmol) and NaH (0.02 g, 0.86 mmol) was added 15 mL of THF, and
the suspension was stirred for 4 h and filtrated to remove excess
NaH. The filtrate was taken to dryness to give the yellow sodium salt
of the ligand, to which were added complex Ni(η3-CH2C6H5)Cl-
(PMe3) (0.11 g, 0.43 mmol) and 5 mL of toluene. The resultant dark
red solution was stirred for 3 h and then filtrated. Dark red crystals
(0.18 g, yield 62.3%) were obtained by crystallization with toluene
and hexane. 1H NMR (300 MHz, C6D6): δ 7.86 (s, 1H), 7.76 (d, J=
6.3 Hz, 2H), 7.20-6.94 (m, 8H, Ar-H), 6.52 (t, J=7.2 Hz, 1H), 4.15
(sept, J=6.9 Hz, 2H, iPr2-CH), 1.25 (d, J=6.9 Hz, 6H, iPr-CH3),
1.06 (d, J=6.9 Hz, 6H, iPr-CH3), 0.91 (s, 2H, benzyl-CH2), 0.41 (d,
J=6.9 Hz, 9H, PMe3-CH3). 13C NMR (75 MHz, C6D6): δ 165.57,
164.50, 150.07, 149.34, 146.87, 143.65, 141.73, 139.61, 138.57,
136.70, 136.34, 129.71, 127.02, 123.92, 120.89, 119.34, 113.81,
28.85, 25.22, 23.54, 11.58 (d, J = 100.5 Hz, PMe3-CH3), 8.68 (d,
J=129.3 Hz, benzyl-CH2). Anal. Calcd for C35H37F5NNiOP: C,
62.52; H, 5.55; N, 2.08. Found: C, 62.73; H, 5.47; N, 2.10.
[[6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-K2-N,O]Ni(η3-CH2Ph)]
(6b-3Bz). The η1-benzyl complex 6b-1Bz (0.07 g, 0.1 mmol) and one
equivalent of B(C6F5)3 (53.5 mg, 0.1 mmol) were mixed and stirred
˚
ometer with CCD detector using Mo KR radiation (λ=0.71073 A).
Absorption corrections were performed using the SADABS pro-
gram. The crystal structures were solved using the SHELXTL-97
program and refined on F2 using full matrix least-squares techni-
ques. The positions of hydrogen atoms were calculated theoreti-
cally and included in the final cycles of refinement in a riding model
along with attached carbons.
in 3 mL of toluene for 3 h, after which the resulting PMe3 B(C6F5)3
3
was filtered off and the filtrate was taken to dryness to give red solid
6b-3Bz in nearly quantitative yield. 1H NMR (300 MHz, C6D6): δ
7.53 (s, 1H), 7.43 (t, J=7.4 Hz, 1H), 7.07-7.01 (m, 4H), 6.94-6.83
(m, 4H), 6.53 (d, J=7.5 Hz, 2H), 6.44 (t, J=7.5 Hz, 1H), 3.64 (sept,
J=6.8 Hz, 2H, iPr2-CH), 1.24 (d, J=6.8 Hz, 6H, iPr-CH3), 0.88 (d,
Acknowledgment. The authors are grateful for the
subsidy provided by the National Natural Science Foun-
dation of China (Nos. 20734002 and 20923003).
i
J = 6.8 Hz, 6H, Pr-CH3), 0.78 (s, 2H, CH2-Ph). 13C NMR
Supporting Information Available: CIF files giving X-ray
crystallographic data (6a, 6b-Py, 6b-PPh3, 6b-1Bz, and 6b-Bis),
details for the synthesis and characterization of the ligands, and
a table of crystallographic parameters. This material is available
free of charge via the Internet at http://pubs.acs.org.
(75 MHz, C6D6): δ 164.8, 163.7, 152.4, 147.0, 144.8, 143.7, 141.8,
139.8, 136.3, 136.0, 134.8, 126.7, 123.8, 113.9, 108.0, 28.5, 27.8
(CH2-Ph), 25.1, 23.1. Anal. Calcd for C32H28F5NNiO: C, 64.46; H,
4.73; N, 2.35. Found: C, 64.60; H, 4.68; N, 2.38.