Ligand steric and electronic effects on β-ketiminato neutral nickel(II) olefin polymerization catalysts

Article abstract of DOI:10.1021/om2010194

A series of novel neutral nickel complexes 3a-g and 4a-d bearing the β-ketiminato ligands [(2,6-ⁱPr₂C₆H ₃)N=CHCHC(R)O]Ni(R′)(L) (for 3a-g, R′ = Me, L = Py, and R = ^tBu (3a), Ph (3b), 1-naphthyl (3c), 9-anthryl (3d), PhNMe ₂(p) (3e), PhOMe(p) (3f), PhCF₃(p) (3g); for 4a-d, R′ = Ph, L = PPh₃, and ^tBu (4a), Ph (4b), 1-naphthyl (4c), 9-anthryl (4d)) have been synthesized and characterized. The molecular structures of 3b-d,f,g and 4a,c were further confirmed by X-ray crystallographic analysis. These complexes were employed in ethylene polymerization to systematically investigate ligand steric and electronic effects on the catalytic properties, including activity, molecular weight (MW), and branching number of the polyethylene obtained. The complexes bearing more bulky ligands showed higher activities and produced more branched polyethylene. Electron-deficient ligands were found to increase the catalytic activity, decrease the MW, and enhance the branching content of the polyethylene. In addition, phosphine Ni^II-Ph complexes 4a-d proved to be more active than the corresponding pyridine Ni^II-Me complexes 3a-d, probably due to the easier dissociation of PPh₃ relative to a pyridine from a nickel center.

Full text of DOI:10.1021/om2010194

Article
pubs.acs.org/Organometallics
Ligand Steric and Electronic Effects on β-Ketiminato Neutral Nickel(II)
Olefin Polymerization Catalysts
Dong-Po Song,†,‡ Xin-Cui Shi, Yong-Xia Wang, Ji-Xing Yang, 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
‡
Graduate School of the Chinese Academy of Sciences, Changchun Branch, Changchun 130023, People's Republic of China
*
S Supporting Information
ABSTRACT: A series of novel neutral nickel complexes 3a−g
i
and 4a−d bearing the β-ketiminato ligands [(2,6- Pr C H )N
2
6
3
CHCHC(R)O]Ni(R′)(L) (for 3a−g, R′ = Me, L = Py, and R =
Bu (3a), Ph (3b), 1-naphthyl (3c), 9-anthryl (3d), PhNMe (p)
t
2
(
3e), PhOMe(p) (3f), PhCF (p) (3g); for 4a−d, R′ = Ph, L =
3
t
PPh , and Bu (4a), Ph (4b), 1-naphthyl (4c), 9-anthryl (4d))
3
have been synthesized and characterized. The molecular
structures of 3b−d,f,g and 4a,c were further confirmed by
X-ray crystallographic analysis. These complexes were employed in ethylene polymerization to systematically investigate ligand
steric and electronic effects on the catalytic properties, including activity, molecular weight (MW), and branching number of the
polyethylene obtained. The complexes bearing more bulky ligands showed higher activities and produced more branched
polyethylene. Electron-deficient ligands were found to increase the catalytic activity, decrease the MW, and enhance the
II
branching content of the polyethylene. In addition, phosphine Ni −Ph complexes 4a−d proved to be more active than the
II
corresponding pyridine Ni −Me complexes 3a−d, probably due to the easier dissociation of PPh relative to a pyridine from a
3
nickel center.
INTRODUCTION
The discovery of cationic Ni(II) and Pd(II) catalysts by
Brookhart triggered a true exploration of the late-transition-
Scheme 1. Modifications on the α-Diimine Ligand Backbone
■
1
−7
metal catalysts for olefin polymerization.
The key feature of
these catalysts lies in the bulky α-diimine ligand that has steric
hindrance in the axial direction of the metal coordination plane
1b
to suppress the associative chain transfer. As a result, they
showed outstanding performances in catalyzing ethylene poly-
merization and the copolymerization of olefin with polar
2
monomers for production of functional polymers. In the
following years, more and more investigations have focused on
the improvement of the catalytic properties through modifica-
3
−7
tion of the catalyst structure.
For example, Guan et al.
reported the ligand electronic and steric effects on late-metal
olefin polymerization catalysts A and B (see Scheme 1), which
showed greatly improved catalytic performances in olefin
3
(
co)polymerization. Recently, a series of C -symmetric late-
2
metal catalysts C and D based on α-diimine ligands (see
Scheme 1) were successfully prepared and employed in the
living polymerization of ethylene, propylene, higher α-olefins,
neutral nickel catalysts for the oligomerization of ethylene as
practiced in Shell’s higher olefin process (SHOP). However,
there was no significant progress in neutral nickel catalysts
during the following two decades. At the beginning of the
century, another breakthrough facilitating forays into neutral
6
4-alkylcyclopentene, etc. Moreover, neutral palladium catalysts
10
with phosphine−sulfonate ligands proved to be a success in the
coordination−insertion copolymerization of ethylene with
8a
polar monomers after the first report by Drent et al. The
sulfonate group, being a rather poor electron donor, was
9
thought to be mainly responsible for the result.
2
As early as the 1970s, the κ -[P,O]Ni catalysts E (see
Received: October 21, 2011
Published: January 20, 2012
Scheme 2) discovered by Keim were the first examples of
©
2012 American Chemical Society
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Article
Scheme 2. Typical Neutral Nickel Complexes Reported
Previously
Scheme 3. General Synthetic Route of Nickel Complexes
3a−h
Scheme 4. General Synthetic Route of Nickel Complexes
4a−d
nickel catalysts came from Grubbs’ research work with the
11
discovery of salicylaldiminato catalysts F (see Scheme 2). As a
result, a majority of the investigations on neutral nickel catalysts
have focused on salicylaldiminato ligand based species because
of the facility for introducing various substituents on the
backbone to enhance the activity and control the microstruc-
activity, molecular weight, and branching content of the poly-
mer obtained.
12−16
RESULTS AND DISCUSSION
ture of the polymer.
For instance, the nickel salicylaldi-
■
minato methyl pyridine catalysts G (see Scheme 2) reported by
Mecking’s group, bearing substituted aryls at the 2,6-positions
of the N-aryl moiety, displayed high efficiency for ethylene
Synthesis and Characterization of β-Ketiminato
Ligand Compounds. Scheme 3 illustrates the general
synthetic route for β-ketiminato ligand compounds 2a−h
used in this study. First, β-diketones were prepared via the
reaction between ethyl formate and the corresponding ketones
with the help of a strong base such as potassium tert-butoxide.
At the end of the reaction, a large amount of solid suspension
was formed and was separated by filtration. Next, formic acid in
ethanol was added to the solid until pH <7, affording the
corresponding β-diketones. Finally, the β-diketones were used
directly in the preparation of β-ketimines 2a,c−g in good yields
by the condensation reaction with 2,6-diisopropylaniline in
ethanol containing a small amount of formic acid as a catalyst.
The facile synthesis of compound 2b has been reported in our
(
co)polymerization in common solvents or unconventional
1
2,13
media such as water and supercritical carbon dioxide.
Our
group developed a series of nickel salicylaldiminato catalysts
14
highly active toward olefin polymerization. Marks et al.
reported a bimetallic neutral nickel complex that showed a
visible bimetallic association effect in ethylene polymerization
15
and copolymerization with polar monomers.
In addition to the neutral nickel salicylaldiminato complexes,
complexes based on other ligand backbones were also
developed by many research groups. As shown in Scheme 2,
Bazan’s group investigated various α-iminocarboxamide nickel
catalysts H, which exhibited excellent performance in
20d
previous publication. However, compound 2h was synthe-
17
sized in low yield, probably due to the strongly electron-
promoting olefin polymerization. Brookhart et al. reported a
series of neutral nickel catalysts containing five-membered
nickel chelates (complexes I in Scheme 2) that exhibited high
withdrawing properties of the NO group in a para position.
2
1
Compounds 2a−h have been clearly characterized by H and
C NMR spectra. The chemical shifts from 11.4 to 11.9 ppm in
1
1
3
18
activities toward ethylene polymerization. Brookhart and
Mecking demonstrated that electron-poor neutral nickel
enolatoimine catalysts were highly active for ethylene polymer-
H NMR are the characteristic signals for the N−H of the
ligand compound, and the chemical shifts in the downfield
region of C NMR spectra (187−191 ppm) are the
19
13
ization under nonaqueous or aqueous conditions. All the
modifications, namely ligand steric or electronic effects, on
various ligand backbones have showed great influences on the
catalytic performances of the olefin polymerization catalysts.
Recently, our group found the β-ketiminato ligand backbone
promising for development of high-performance neutral nickel
corresponding peaks for the carbons connected to nitrogens
(NC). For compounds 2e−h, variation of the substituent at
the para position leads to visible electronic effects on the ligand
backbone. As shown in Figure 1, the chemical shift for N−H
increases in the sequence NMe < OMe < H < CF < NO ,
2
3
2
20
catalysts for olefin polymerization. Modifications of the ligand
structure (complexes J in Scheme 2), such as conjugation
degree adjustment and geometric fixation, proved to be
which correlates strongly with the para Hammett substituent
21
constant σ of these substituted groups on the ligands. This
p
can be explained by the fact that electron-withdrawing groups,
20c,d
effective strategies to improve catalytic properties.
How-
such as CF and NO , would reduce the electron density of the
3
2
ever, the most important ligand-designing parameters, steric
and electronic factors, were not completely involved in our
previous reports. In this work, we aim to present a systematic
investigation of both the steric and electronic effects of the β-
ketiminato ligand on nickel(II) olefin polymerization catalysts.
Interestingly, variation of the substituted R group (see Schemes
ligand backbone, resulting in a more reactive hydrogen on the
1
3
nitrogen atom. In addition, the NC signals in C NMR for
compounds 2g,h with electron-withdrawing groups (CF , NO )
3
2
shift to the upfield region relative to compounds 2e,f with
electron-donating substituents (OMe, NMe ), which provides
2
further evidence for the electronic effects. Such modulation of
electronic density on the ligand backbone would subsequently
3
and 4) could greatly affect the catalytic properties, including
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Article
Too great an NPA charge on the nickel center of our target
complex 3h may be the major reason for the instability of the
complex, which makes it difficult to synthesize.
II
The synthesis of phosphine Ni −Ph complexes 4a,c,d is
shown in Scheme 4. The deprotonation of free ligands 2a,c,d
readily proceeded with excess sodium hydride in anhydrous
THF for 4 h at room temperature, and the isolated sodium salts
then reacted with an equivalent amount of trans-PhNi-
(
PPh ) Cl for 12 h in toluene to afford the neutral nickel
3 2
complexes 4a,c,d, respectively. The synthesis of complex 4b has
20b
been reported in our previous publication.
Neutral nickel complexes 3a−g and 4a−d bearing β-
1
ketiminato ligands have been clearly characterized by H and
C NMR spectra as well as elemental analysis. To further
1
13
Figure 1. Chemical shifts (ppm) for N−H in H NMR (left) and
13
NC in C NMR (right) of compounds 2b and 2e−h versus the
confirm the structures of these complexes, single crystals of
3b−d,f,g and 4a,c suitable for X-ray crystallographic analysis
were grown from a toluene−hexane solution. The data
collection and refinement data of the analysis are summarized
in Table 1, and the ORTEP diagrams are shown in Figures 3−7.
In the solid state, these complexes adopt a nearly square planar
coordination geometry, and the pyridine group or the phosphine
group is trans to the N-aryl group, just as for the neutral nickel
21
para Hammett substituent constant σ .
p
influence the electron environment of the nickel(II) centers of
our target complexes and thus their catalytic performances
(vide infra).
Synthesis and Characterization of Neutral β-Ketimi-
nato Nickel Complexes. According to the literature, β-
ketiminato pyridine Ni −Me complexes 3a,c−g were success-
fully prepared in high yields (more than 90%) by adding
12c
II
20c,d
complexes reported previously.
The selected bond distances and angles are summarized in
Table 2. For complexes 3b−d, variation of the R group from
the small phenyl through 1-naphthyl to the bulky 9-anthryl
exhibits an obvious influence on the molecular structure
obtained (see Figures 3 and 4). It is noteworthy that complex
(
pyridine) NiMe to toluene solutions of ligands 5a−c with
2
2
vigorous stirring (Scheme 3). At first, the reaction systems were
cooled to about −30 °C and then warmed to room
temperature. The facile synthesis of complex 3b has been
20d
reported in our previous publication.
Unfortunately, our
attempt to synthesize complex 3h was a complete failure,
probably due to the strongly electron-withdrawing group
NO ) at the para position. In order to confirm the possible
influence of the electronic substituent, natural population
analysis (NPA) was subsequently performed to evaluate the
substituted effects on the electron environment of the
nickel(II) centers for complexes 3b,e−h with electron-donating
or electron-withdrawing groups, and the calculated results are
shown in Figure 2. Although the synthesis of complex 3h was
3d exhibits a shorter Ni−C(1) and a longer Ni−O bond
distance in comparison to those of complexes 3b,c, though
they display similar Ni−N bond distances. There are no significant
differences in O−C(8), N−C(10), and C(8)−C(9) bond
distances for the three complexes, except that the C(9)−C(10)
length for complex 3d is much longer than those of complexes
(
2
3b,c (see Table 2). Analogously, the angles around the nickel
center of the three complexes are almost the same (see Table 2).
However, the intriguing differences concerning the N(1)−Ni−
N(2) and O−Ni−C(1) angles should not be ignored. As shown in
Table 2, complex 3b exhibits larger angles relative to complexes
22
3c,d, indicating that 3b has the least distortion in the nickel(II)
coordination plane (see Figure 4). In contrast, such distortion is
enhanced with regard to complexes 3c,d due to the increased
steric hindrance of the R group. The molecular structures of
complexes 3b−d from a view perpendicular to the nickel
coordination plane are shown in Figure 4, indicating a great steric
effect of the R group definitely confirmed by the increasing torsion
angle O−C(8)−C(7)−C(6) for complexes 3b−d from 2.83°
through 35.77° to 69.36°.
Complexes 3f,g were also synthesized to investigate the
electronic effects of the substituted electron-donating or
electron-withdrawing groups at the para positions. The
electronic effects have showed a remarkable influence on the
bond distances or angles of the complexes. Complex 3g with a
Figure 2. NPA charge on nickel(II) centers for catalysts 3e (NMe ), 3f
2
(
OMe), 3b (H), 3g (CF ), and 3h (NO ) versus the para Hammett
3 2
21
CF group has Ni−O, Ni−C(1), and C(8)−C(9) bonds much
3
substituent constant σp.
shorter than those of the mother complex 3b (see Table 2).
More interestingly, both complexes 3f (OMe) (see Figure 5)
not successful, we carried out the calculation to find out the
large difference between this complex and the other complexes.
From the figure, we found more NPA charges on nickels of the
complexes bearing more electron-deficient ligands, which is in
line with the tendency demonstrated in Figure 1. Moreover,
electron-withdrawing groups, such as CF and NO , seem to
and 3g (CF ) exhibit larger O−C(8)−C(7)−C(6) torsion
3
angles (19.33 and 13.19°) relative to complex 3b (2.83°). In
addition, in contrast to an electron-withdrawing group such as
CF , an electron-donating group such as OMe would enlarge
3
the O−C(8)−C(9)−C(10) torsion angle and decrease the
C(8)−C(9)−C(10)−N(1) torsion angle, which may be caused
by the influence of electron density on the nickel chelate ring.
3
2
show more influence on the NPA charges of the nickel centers.
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Table 1. Crystal Data and Structure Refinement Details for Complexes 3b−d,f,g and 4a,c
3
b
3c
3d
3f
3g
4a
4c
empirical formula
formula wt
temp (K)
cryst syst
space group
a (Å)
C H N NiO
C H N NiO
C H N NiO
C H N NiO
C H F N NiO
C H NNiOP
C H NNiOP
2
7
32
2
31 34
2
42 43
2
28 34
2
2
28 31
3
2
43 48
49 46
459.26
185(2)
509.31
651.50
489.28
527.26
684.50
754.55
185(2)
triclinic
185(2)
triclinic
185(2)
185(2)
185(2)
185(2)
monoclinic
monoclinic
C2/c
monoclinic
monoclinic
monoclinic
P2 /c
1
P1
̅
P1
̅
C2/c
P2 /n
1
P2 /c
1
12.6963(10)
20.8476(16)
9.6062(8)
90.00
9.7228(6)
9.7228(6)
13.013(8)
60.7090(10)
85.7880(10)
69.6070(10)
2
10.8870(6)
13.3072(8)
13.5337(8)
70.6830(10)
74.1560(10)
71.1360(10)
2
20.7171(17)
14.5516(12)
17.5100(15)
90.00
20.8591(17)
15.3042(12)
34.431(3)
90.00
10.4168(7)
24.7978(18)
14.4080(10)
90.00
13.5194(5)
11.3647(4)
25.5163(9)
90.00
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
106.66(10)
90.00
97.5690(10)
90.00
102.402(2)
90.00
96.6200(10)
90.00
89.9240(10)
90.00
Z
4
8
16
4
4
3
V (Å )
2435.9(3)
1.252
1320.62(14)
1.281
1720.40(17)
1.258
5232.7(8)
1.242
10735.0(15)
1.305
3697.0(4)
1.230
3920.4(2)
1.278
−
3
ρcalcd (Mg m )
−
1
abs coeff, (mm )
F(000)
0.816
0.760
0.599
0.767
0.766
0.601
0.574
976
540
692
2080
4416
1456
1592
θ range (deg)
no. of measd/indep rflns
Rint
1.67−26.03
14 519/4796
0.0379
1.81−26.02
7219/5059
0.0116
1.62−26.04
9418/6626
0.0130
1.72−26.05
16 479/5170
0.0283
1.66−25.05
31 220/9493
0.0710
1.64−25.70
20 076/7017
0.0603
1.51−26.05
21 308/7727
0.0212
abs cor
multiscan
0.929, 0.838
280
multiscan
0.9347, 0.7875
316
multiscan
0.953, 0.917
415
multiscan
0.933, 0.863
298
multiscan
0.8496, 0.7862
641
multiscan
0.9535, 0.7993
431
multiscan
0.950, 0.908
482
max, min transmissn
no. of params
final R indices (I > 2σ(I))
R1
0.0425
0.1010
1.009
0.0342
0.0402
0.0405
0.0620
0.0491
0.0321
wR2
0.0884
0.1070
0.1033
0.1301
0.0925
0.0837
goodness of fit on F2
1.032
1.030
1.034
1.018
0.968
1.035
−3
largest diff peak, hole (e Å ) 0.459, −0.374
0.372, −0.353
0.543, −0.421
0.342, −0.357
0.627, −0.353
0.459, −0.236
0.543, −0.241
Figure 3. Molecular structure of complex 3d. Thermal ellipsoids are
drawn at the 30% probability level, and H atoms as well as a toluene
molecule are omitted for clarity.
Figure 5. Molecular structure of complex 3f. Thermal ellipsoids are
drawn at the 30% probability level, and H atoms are omitted for
clarity.
bond distances and angles as well as torsion angles in com-
II
parison with the pyridine Ni −Me complexes, probably due to
the influence of the ancillary ligands (PPh vs Py). As shown in
3
Table 2, complex 4c exhibits bond distances around the nickel
centers very different from those of its analogue 3c bearing
the same ligand. Complex 4c exhibits a Ni−O bond distance
shorter than that of complex 3c, and such a difference is more
remarkable for the distance of Ni−C(1) indicating the large
difference between a methyl group and a phenyl group
connected to a nickel(II). In contrast, the Ni−N(1) bond
length of complex 4c is much longer that of complex 3c (see
Table 2) due to the distortion of the nickel chelate ring caused
Figure 4. Molecular structures of complexes 3b−d. Views are
perpendicular to the nickel coordination plane.
by the bulky PPh group. In addition, the Ni−P bond (complex 4c)
3
II
The molecular structures of phosphine Ni −Ph complexes
is much longer than the Ni−N(2) bond (complex 3c), which
4
a,c are shown in Figures 6 and 7. They display very different
would have a great effect on the polymerization behavior.
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Organometallics
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coordination plane (see Figure 7). Moreover, there are visible
differences in the angles around the nickel centers of complexes
4c and 3c. As can be seen from Table 2, a much broader O−
Ni−P angle of complex 4c is observed relative to the O−Ni−
N(2) angle of 3c, compensated by the narrower angles of O−
Ni−N(1), C(1)−Ni−N(1), and C(1)−Ni−P because of the
steric congestion between the PPh3 and R groups. The
influence of the ancillary ligands (Py vs PPh ) can also be
3
confirmed by the much different torsion angles between
complexes 4c and 3c. A much larger O−C(8)−C(7)−C(6)
torsion angle (50.33°) for complex 4c relative to complex 3c
(
35.77°) is observed due to steric hindrance from the PPh3
group. More interestingly, complex 4c exhibits much larger
torsion angles of O−C(8)−C(7)−C(6) and C(8)−C(9)−
C(10)−N(1) (10.73 and 10.25°) relative to complex 3c (0.58
and 3.05°). In a word, all the differences between the
Figure 6. Molecular structure of complex 4a. Thermal ellipsoids are
drawn at the 30% probability level, and H atoms are omitted for
clarity.
II
II
phosphine Ni −Ph complex and the pyridine Ni −Me complex
may greatly influence the olefin polymerization behaviors.
II
Ethylene Polymerization with Pyridine Ni −Me Com-
plexes 3a−g. Neutral nickel complexes 3a−g were inves-
tigated as catalysts for ethylene polymerization in toluene.
Typical results are summarized in Table 3. The data indicate
that ligand structure can greatly affect the catalytic activity and
polymer microstructure along with the properties. Complexes
3
a−d were synthesized to explore the steric effects of R groups
on catalytic properties. Without a cocatalyst, catalyst 3a (R =
t
Bu) showed a moderate activity of 36 (kg of PE)/((mol of Ni)
h atm) (entry 3-1) under the typical conditions (70 °C,
ethylene pressure 30 atm). In comparison, catalyst 3d (R = 9-
anthryl) exhibited a similar activity of 38 (kg of PE)/((mol of
Ni) h atm) (entry 3-7) under the same conditions. However,
lower activities (29 and 26 (kg of PE)/((mol of Ni) h atm),
entries 3-3 and 3-5) of catalysts 3b,c were observed because of
their less bulky substituents relative to the 9-anthryl group. This
is consistent with the notion that the neutral nickel
salicylaldiminato catalyst also needs a bulky 9-anthryl group
at the ortho position of the phenoxy group to achieve a high
Figure 7. Molecular structure of complex 4c. Thermal ellipsoids are
drawn at the 30% probability level, and H atoms are omitted for
clarity.
Complex 4c exhibits larger angles of N(1)−Ni−P and O−
Ni−C(1) relative to the corresponding angles of complex 3c,
indicating that 4c has less distortion in the nickel(II)
11
catalytic activity. Herein, steric hindrance must have played an
important role in stabilizing the active centers and enhancing
Table 2. Selected Bond Distances (Å) and Angles (deg)
3
b
3c
3d
3f
3g
4a
4c
Bond Distances
1.922(13)
1.894(15)
1.911(16)
1.913(2)
1.280(2)
1.316(2)
1.377(3)
1.413(3)
Bond Angles
172.95(7)
166.29(9)
94.61(6)
84.39(6)
93.76(8)
88.60(8)
Torsion Angles
69.36
Ni−O
Ni−N(1)
Ni−(N(2) or P)
Ni−C(1)
O−C(8)
N(1)−C(10)
C(8)−C(9)
C(9)−C(10)
1.916(18)
1.893(2)
1.914(2)
1.929(3)
1.275(3)
1.314(3)
1.386(4)
1.393(4)
1.912(13)
1.880(15)
1.912(15)
1.924(2)
1.277(2)
1.326(2)
1.394(3)
1.390(3)
1.918(15)
1.894(18)
1.919(18)
1.924(2)
1.280(3)
1.317(3)
1.384(3)
1.398(3)
1.897(3)
1.889(3)
1.916(3)
1.911(4)
1.283(5)
1.317(5)
1.371(5)
1.396(6)
1.912(17)
1.915(2)
2.176(8)
1.884(3)
1.283(3)
1.306(3)
1.376(4)
1.403(4)
1.897(11)
1.929(13)
2.202(4)
1.886(17)
1.282(19)
1.318(2)
1.386(2)
1.399(2)
N(1)−Ni−(N(2) or P)
O−Ni−C(1)
O−Ni−N(1)
O−Ni−-(N(2) or P)
C(1)−Ni−N(1)
C(1)−Ni−(N(2) or P)
176.00(8)
172.12(10)
93.72(8)
170.92(7)
170.37(8)
93.89(6)
83.31(6)
94.07(8)
89.62(8)
172.93(8)
172.15(9)
93.37(7)
84.22(7)
93.08(9)
89.88(9)
172.80(15)
172.53(16)
93.22(13)
83.72(13)
93.32(16)
90.22(16)
163.23(7)
158.84(10)
93.93(9)
88.59(6)
95.33(11)
88.00(9)
175.71(4)
174.45(6)
91.56(5)
85.55(4)
93.90(6)
88.95(5)
84.23(8)
93.20(11)
89.08(11)
O−C(8)−C(7)−C(6)
O−C(8)−C(9)−C(10)
C(8)−C(9)−C(10)−N(1)
2.83
2.38
2.96
35.77
0.58
3.05
19.33
4.26
0.12
13.19
0.31
3.08
50.33
10.73
10.25
1.47
0.71
7.65
6.75
9
70
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Organometallics
Article
a
Table 3. Results of Ethylene Polymerization Reactions for Complexes 3a−g
b
c
d
entry
complex (amt (μmol))
T (°C)
pressure (atm) amt of polymer (g) activity
Tm (°C)
Mw (kg/mol)
.
branches /1000C
3
3
3
3
3
3
3
3
3
3
3
3
-1
-2
-3
-4
-5
-6
-7
-8
-9
3a (20)
3a (20)
3b (20)
3c (20)
3c (20)
3c (20)
3d (20)
3d (20)
3e (20)
3f (20)
3f (10)
3g (20)
70
30
20
30
30
30
30
30
20
20
20
20
20
7.2
2.5
5.7
1.1
5.1
1.5
7.5
36
19
29
106
105
99
26.2
24.9
25.2
28.5
21.9
10.8
18.6
20.9
33.2
18.5
31.9
22.8
1.8
1.8
1.9
2.0
1.9
2.0
1.9
1.9
2.0
1.8
1.8
27
nd
32
37
46
66
49
nd
35
nd
37
40
e
60
70
60
5.5
26
7.5
38
105
8.3
101
94
70
80
82
70
94
e
e
70
14
94
70
1.1
5.3
106
87
-10
-11
-12
70
40
33
96
e
e
70
2.2
103
96
70−77
12.8
1.8
c
a
b
Reaction conditions: 100 mL of toluene, polymerization for 20 min. In units of (kg of PE)/((mol of Ni) h atm). Determined by GPC.
Calculated from H NMR. Two equivalents of B(C F ) added.
d
1
e
6
5 3
the catalytic activities of the neutral nickel β-ketiminato
catalysts. In addition, catalyst 3d exhibited a high activity of
up to 105 (kg of PE)/((mol of Ni) h atm) (entry 8) upon the
addition of B(C F ) .
can be attributed to the accelerated chain-walking reaction
caused by the electronic perturbation of the nickel(II) centers.
A similar effect of the electron-withdrawing substituents
strongly enhancing chain termination over chain propagation
was also found in ethylene oligomerization with the SHOP
6
5 3
The steric hindrance can also greatly affect the molecular
weight (MW) as well as the branching content of the polymers
obtained. As shown in Table 3, with regard to catalysts 3b−d,
23
catalyst.
Reaction conditions, such as reaction temperature and
ethylene pressure, also dramatically influence the catalytic
activity as well as the MW and branching number. For 3c, the
catalytic activity was greatly enhanced from 5.5 to 26 (kg of
PE)/((mol of Ni) h atm) via increasing the reaction
temperature from 60 to 70 °C (entries 3-4 and 3-5). However,
further elevating the temperature to 80 °C caused a lower
catalytic activity of 7.5 (kg of PE)/((mol of Ni) h atm) (entry
3-6). The lower equilibrium concentration of ethylene in
solution as well as the catalyst instability at 80 °C relative to
70 °C may be mainly responsible for the difference. As shown
in Table 3, the amount of polymer produced by catalysts 3a is
greatly influenced by ethylene pressure. A much lower
productivity (entries 3-1 and 3-2) was observed by decreasing
the ethylene pressure from 30 to 20 atm. Additionally, the
MWs of the polyethylenes produced by catalyst 3c decreased
from 28.5 to 10.8 kg/mol by increasing the reaction
temperature from 60 to 80 °C, and the branch contents were
enhanced from 37 to 66 branches per 1000 carbon atoms
(entries 3-4−3-6). A similar phenomenon has also been
reported concerning α-diimine cationic nickel catalysts as well
the weight-average molecular weight (M ) decreases from 25.2
w
through 21.9 to 18.6 kg/mol (entries 3-3, 3-5, and 3-7), with
the steric hindrance increasing from a phenyl through a 1-
naphthyl to a 9-anthryl group. Nevertheless, an enhancement of
the branching content from 32 to 49 branches per 1000 carbon
atoms (entries 3-3, 3-5, and 3-7) was observed. As we know,
there is a competitive relationship between the ethylene
insertion reaction and the chain transfer reaction, which
determines the molecular weight of the polyethylene produced.
For the neutral nickel β-ketiminato catalysts, bulky ligands
would not only suppress the chain transfer reaction but also
decrease the ethylene insertion rate according to the DFT
20d
results in our previous report. The decreased MW can be
best explained by the reduced value of (chain propagation
rate)/(chain walking rate) due to the steric effects.
As shown in Table 3, complex 3e with a strongly electron-
donating NMe group in the para position showed a much
2
lower activity of 8.3 (kg of PE)/((mol of Ni) h atm) (entry 3-9)
relative to that of mother catalyst 3b (29 (kg of PE)/((mol of Ni)
h atm)), although B(C F ) was added as the cocatalyst. In
6
5 3
1a,11
contrast, a higher activity of 40 (kg of PE)/((mol of Ni) h atm)
entry 3-10) was observed using catalyst 3f with an OMe
as the neutral nickel salicylaldiminato systems,
demonstrat-
(
ing that the rate of chain migration and termination in our
systems also increased at elevated temperature, yielding more
highly branched and lower MW polymer.
group. Therefore, we can not simply ascribe the greatly
decreased activity of 3e to the electronic effect of the NMe2
group; the possibly direct interaction between NMe groups
and nickel(II) centers may be partly responsible for the issue.
The microstructure of the typical polyethylene obtained has
2
1
13
been definitely characterized using H and C NMR, as shown
1
In addition, complex 3g with a p-CF showed an activity of
in Figure 8. In Figure 8a ( H NMR), the signal at about
3
9
6 (kg of PE)/((mol of Ni) h atm) (entry 3-12), higher than
0.8 ppm can be assigned to methyl branches that are the
predominant branching style in the polymers produced under
that for the mother complex 3b.
24a
13
The electronic factors can also greatly influence the MW as
well as the branching content of the polyethylene obtained. It
can be generally observed from the data (Table 3) that
polymers with higher MWs have been produced by catalysts
bearing more electron-donating ligands. The MW of the
polymer produced by 3e with an NMe group is higher than
that of catalyst 3g with a CF group (entry 3-9 vs 3-12). In
contrast, catalysts with more electron deficient ligands prefer to
produce the polyethylene with more branching content, which
30 atm (entry 3-1). Moreover, as shown in Figure 8b ( C
NMR), methyl branches are the only type of branches in the
24b
polymer chain produced by 3a (entry 3-1).
The melting
points of polymers decrease with an increase of branching
number (Table 3), because branches can restrain the
crystallization of the polymers. The low PDI (M /M = 1.8−
2
w
n
2.0) of the obtained polyethylene indicates that these neutral
nickel complexes are favorable homogeneous single-site
catalysts.
3
9
71
dx.doi.org/10.1021/om2010194 | Organometallics 2012, 31, 966−975

Organometallics
Article
4
a−d bearing different ligands. Different R groups with variable
steric effects should be the determining factor for the MW of
polyethylene, which has also been supported by the polymer-
ization results for catalysts 3b−d (see Table 3).
Similar to the case for catalysts 3b−d, the reaction
temperature can greatly influence the catalytic properties of
catalysts 4a−d. For 4c, a great increase of the activity from 14
to 65 (kg of PE)/((mol of Ni) h atm) (entries 4-3 and 4-4) was
observed by elevating the reaction temperature from 50 to
6
0 °C, but higher temperature (70 °C) leads to a decrease of
the activity. This is different from the case for catalyst 3c, which
showed the highest activity at 70 °C, suggesting that the
pyridine complexes need more energy than the phosphine
complexes to be efficiently activated for the ethylene polymer-
ization in our systems. In addition, polyethylenes with lower
molecular weights (MWs) were produced by catalyst 4c upon
increasing the reaction temperature because of the accelerated
chain-walking reaction, which is the same as that for the
pyridine catalyst 3c.
1
Figure 8. (a) H and (b) 13C NMR spectra of polyethylene produced
24
by 3a (entry 1), assigned according to the literature.
II
Ethylene Polymerization with Phosphine Ni −Ph
II
Complexes 4a−d. Phosphine Ni −Ph complexes 4a−d
were also investigated as catalysts for ethylene polymerization
II
CONCLUSIONS
to find out their differences from pyridine Ni −Me complexes
■
3
a−d in catalytic performance. The typical polymerization data
We have proved that a family of newly designed neutral nickel
complexes 3a−g and 4a−d based on various β-ketiminato
ligands is highly active for ethylene polymerization. Ligand
steric and electronic effects have been confirmed to greatly
influence the catalytic behavior. Complexes with more bulky
ligands were found to be more active, producing polyethylene
with lower molecular weight and higher branching number.
Catalyst 3g, with a strongly electron-withdrawing group (CF3),
showed an activity much higher than the value for the mother
catalyst 3b. In contrast, a much lower activity of catalyst 3e was
observed due to the strongly electron-donating group (NMe2)
on the ligand. Moreover, electron-deficient ligands were found
to decrease the molecular weight and enhance the branching
content of the polyethylene obtained. In addition, phosphine
in Table 4 indicate that the variation of the R group can also be
Table 4. Results of Ethylene Polymerization Reactions for
a
Complexes 4a−d
c
T
amt of
Tm
Mw
M /
w
c
b
entry complex (°C) polymer (g) activity
(°C) (kg/mol) Mn
d
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4a
4b
4c
4c
4c
4c
4d
4d
60
60
50
60
70
60
60
60
9.7
10
42
75
105
103
99
28.4
26.9
27.3
18.2
10.6
30.8
15.0
17.9
1.9
1.8
1.9
2.0
1.9
2.0
1.9
2.2
1.9
8.6
6.0
14
65
88
45
82
d
d
11
47
101
86
14
15
105
64
II
Ni −Ph complexes 4a−d showed higher activities relative to
95
II
pyridine Ni −Me complexes 3a−d because of the different
a
Reaction conditions: 100 mL of toluene, 20 μmol of catalyst, ethylene
ancillary ligands (PPh vs Py) on the nickel centers.
3
b
pressure of 20 atm, polymerization for 20 min. In units of (kg of PE)/
c
d
(
(mol of Ni) h atm). Determined by GPC. The ethylene pressure is
EXPERIMENTAL SECTION
35 atm.
■
General Procedures and Materials. All work involving air- and/
or moisture-sensitive compounds was carried out under a dry nitrogen
atmosphere by using standard Schlenk techniques or under a dry
argon atmosphere in an MBraun glovebox unless otherwise noted. All
solvents used were purified from an MBraun SPS system. The NMR
data of ligands and complexes were obtained on a Bruker 300 MHz
spectrometer at ambient temperature with CDCl or C D as the
effective for the modulation of catalytic properties. At a reaction
t
temperature of 60 °C, catalyst 4a (R = Bu) showed a moderate
activity of 42 (kg of PE)/((mol of Ni) h atm) (entry 4-1),
which is much higher than that of catalyst 3a (19 (kg of PE)/
(
(mol of Ni) h atm), entry 3-2, Table 3). In the absence of a
cocatalyst, complex 4d (R = 9-anthryl) showed an activity (105
kg of PE)/((mol of Ni) h atm), entry 4-7) higher than those
3
6
6
solvent. The NMR analyses of polymers were performed on a Varian
Unity 400 MHz spectrometer at 135 °C, using o-C Cl as the
(
6
D
4
2
solvent. The differential scanning calorimetric (DSC) measurements
were performed with a PerkinElmer Pyris 1 DSC differential scanning
calorimeter at a rate of 10 °C/min. The molecular weights and the
polydispersities of the polymer samples were determined at 150 °C by
a PL-GPC 220 type high-temperature chromatograph equipped with
three PLgel 10 μm Mixed-B LS type columns. 1,2,4-Trichlorobenzene
(TCB) was employed as the solvent at a flow rate of 1.0 mL/min. The
calibration was made by polystyrene standard EasiCal PS-1 (PL Ltd.).
Pinacolone, 1-acetonaphthone, and 9-anthracenone were purchased
from Aldrich Chemicals and directly used without purification. 2,6-
Diisopropylaniline and NaH were obtained from Acros. Potassium
tert-butoxide was purchased from Aldrich Chemicals. Py Ni(CH )
of complexes 4b,c (75 and 65 (kg of PE)/((mol of Ni) h atm),
entries 4-2 and 4-4) under the typical polymerization
conditions (60 °C, 20 atm). In comparison with 4d, the
II
pyridine Ni −Me complex 3d exhibited the same activity but in
the presence of B(C F ) at a higher reaction temperature of
6
5 3
7
0 °C. A possible reason is that the dissociation of PPh from
3
the nickel center seems to be easier than that of a pyridine
because of more steric congestion of the bulky PPh with the R
3
group (see the single-crystal structure). As shown in Table 4,
the variation of the ligand structure is an efficient methodology
to control the molecular weight (MW) of the polyethylene
obtained. Polyethylenes with different MWs ranging from 28.4
to 15.0 kg/mol (see entries 4-1, 4-2, 4-4, and 4-7) were
prepared under the same reaction conditions using catalysts
2
3 2
25
and trans-PhNi(PPh ) Cl were prepared according to the literature.
3
2
Commercial ethylene was used without further purification.
Synthesis of Ligands 2a−h. To a slurry of 3.3 g of potassium tert-
butoxide (1.5 equiv) in anhydrous diethyl ether (40 mL) were added
9
72
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Organometallics
Article
i
i
2
.0 g of pinacolone (20 mmol) and 2.9 g of ethyl formate (2.0 equiv)
125.74, 124.26, (Ar), 91.85 (C), 28.79 ( Pr CH), 24.17 ( Pr CH ).
3
at 0 °C. Immediately a large amount of white solid appeared in the
reaction bottle, and the mixture was stirred for 30 min at 0 °C. Then
the resulting suspension was warmed to room temperature and stirred
for about 10 h. The white solid was separated by filtration and dried
under reduced pressure. Formic acid in ethanol was added to the solid
until the pH <7, affording the corresponding β-diketone, which was
used directly in the preparation of ligand 2a. Subsequently, 3.5 g of
Anal. Calcd for C H F NO: C, 70.38; H, 6.44; N, 3.73. Found: C,
22
24 3
70.45; H, 6.38; N, 3.78.
i
1
(2,6-Pr
C
H
)NCHCHC(p-O
NPh)OH (2h). Yield: 21%. H NMR
2
): δ 11.82 (d, J = 12.6 Hz, 1H, N−H), 8.31 (d, J =
2
6
3
(300 MHz, CDCl
3
8.7 Hz, 2H, Ar H), 8.11 (d, J = 8.7 Hz, 2H, Ar H), 7.34−7.21 (m, 3H,
Ar H), 7.04 (dd, J = 12.6, 7.2 Hz, 1H, NCH), 5.96 (d, J = 7.2 Hz,
3
i
3
1H, CCH), 3.21 (sept, J = 6.9 Hz, 2H, Pr CH), 1.24 (d, J = 6.9
i
13
2,6-diisopropylaniline (1.0 equiv) was added to the obtained β-
Hz, 12H, Pr CH
3
). C NMR (300 MHz, CDCl
3
): δ 187.90 (NC),
(Ar), 91.69 (C), 28.44 ( Pr CH), 23.79 ( Pr CH ). Anal. Calcd for
diketone in ethanol and the condensation reaction was carried out for
about 24 h, yielding 3.3 g of ligand 2a (58%). Ligands 2b−h were
prepared according to the same method as for 2a.
155.46, 149.26, 144.78, 144.53, 135.69, 128.21, 128.11, 123.93, 126.63
i
i
3
C H N O : C, 71.57; H, 6.86; N, 7.95. Found: C, 71.51; H, 6.81;
21 24 2 3
(
2,6- Pr C H )NCHCHC( Bu)OH (2a). 1H NMR (300 MHz,
i
t
N, 7.90.
Synthesis of Complexes 3a−g. To (pyridine) NiMe (0.27 g,
2 2
2
6 3
3
CDCl ): δ 11.10 (d, J = 12.0 Hz, 1H, N−H), 7.25−7.14 (m,
3
HH
3
3
H, Ar H), 6.69 (dd, J = 12.6, 7.8 Hz, 1H, NC−H), 5.38 (d,
1.1 mmol) and the ligand 2a (0.29 g, 1.0 mmol) in a 100 mL septum-
capped Schlenk bottle was added toluene (15 mL) at 25 °C.
Immediate methane evolution was observed, which ceased within 5−
HH
3
3
i
JHH = 7.8 Hz, 1H, CCH), 3.19 (sept, J = 6.9 Hz, 2H, Pr CH),
HH
t
3
i
13
1
.22 (s, 9H, Bu H), 1.20 (d, J = 6.9 Hz, 12H, Pr CH ). C NMR
HH 3
1
0 min. The resulting red solution was stirred for an additional 4 h at
(
1
300 MHz, CDCl ): δ 207.49 (NC), 153.22, 144.93, 136.88, 127.66,
3
i
t
i
25 °C, during which time excess (pyridine) NiMe decomposed to
24.11, (Ar), 90.91 (C), 28.61 ( Pr CH), 28.08 ( Bu), 24.21 ( Pr
2 2
nickel black. The resulting mixture was filtrated to remove nickel black,
the residue was extracted with toluene, and all volatiles were removed
under reduced pressure to yield pure samples of pyridine complex 3a
as a red powder in high yield (89%). The other neutral nickel(II)
complexes 3b−g were prepared by the same procedure with similar
yields.
CH ). Anal. Calcd for C H NO: C, 79.39; H, 10.17; N, 4.87. Found:
C, 73.32; H, 10.12; N, 4.93.
3
19 29
i
(
2,6- Pr C H )NCHCHC(Ph)OH (2b). The synthesis of the ligand
2
6 3
20d
has been reported in our previous work.
2,6- Pr C H )NCHCHC(1-naphthyl)OH (2c). Yield: 65%. 1H
i
(
2
6 3
NMR (300 MHz, CDCl ): δ 11.73 (d, J = 12.0 Hz, 1H, N−H),
3
i
t
1
3
[(2,6-Pr C H )NCHCHC( Bu)O]Ni(Py)(CH ) (3a). H NMR (300
2
6
3
3
8
7
7
.58 (d, J = 8.1 Hz, 1H, Ar H), 7.93−7.77 (m, 3H, Ar H), 7.60−
HH
3
3
MHz, C D ): δ 8.68 (d, J = 5.1 Hz, 2H, o-H Py), 7.09−6.89 (m,
6 6 HH
.47 (m, 3H, Ar H), 7.32−7.20 (m, 3H, Ar H), 6.94 (dd, J = 12.6,
HH
3
3
3
3H, Ar H), 6.61 (t, J = 7.8 Hz, 1H, p-H Py), 6.22 (t, J = 6.9 Hz,
HH HH
.5 Hz, 1H, NCH), 5.75 (d, J = 7.5 Hz, 1H, CCH), 3.33
HH
3
3
3
i
3
i
m-H Py), 5.31 (d, JHH = 6.3 Hz, 1H, CCH), 4.36 (sept, JHH = 6.9
Hz, 2H, Pr CH), 1.53, 1.23, (d, JHH = 6.9 Hz, 12H, Pr CH
3
(
sept, J = 6.9 Hz, 2H, Pr CH), 1.28 (d, J = 6.9 Hz, 12H, Pr
HH
HH
i
3
i
1
3
), 1.11 (s,
H, Bu H), −0.60 (s, 3H, NiCH ). C NMR (600 MHz, C D ): δ
CH3). C NMR (300 MHz, CDCl ): δ 195.42 (NC), 154.17,
3
t
13
9
3
6
6
1
1
44.95, 139.68, 136.63, 134.31, 130.82, 128.70, 127.15, 126.51, 126.42,
i
i
187.97 (NC), 151.69, 142.28, 135.28, 125.48, 123.14, 122.66, (Ar, Py),
26.38, 125.20, 124.28, (Ar), 96.71 (C), 28.85 ( Pr CH), 24.27 ( Pr
t
t
i
8
2
9.73 (C), 38.88 ( Bu C), 28.41 ( Bu CH ), 28.03 ( Pr CH), 24.91,
3
CH ). Anal. Calcd for C H NO: C, 83.99; H, 7.61; N, 3.92. Found:
C, 83.87; H, 7.66; N, 3.97.
3
25 27
i
3.11, ( Pr CH ), −7.14 (NiCH ). Anal. Calcd for C H NNiO: C,
3
3
25 36
i
1
68.36; H, 8.26; N, 6.38. Found: C, 68.30; H, 8.21; N, 6.39.
(
2,6- Pr C H )NCHCHC(9-anthryl)OH (2d). Yield: 62%. H NMR
2
6
3
i
[
(2,6-Pr C H )NCHCHC(Ph)O]Ni(Py)(CH ) (3b). The synthesis of
2
6
3
3
(
300 MHz, CDCl ): δ 11.94 (d, J = 12.3 Hz, 1H, N−H), 8.47 (s, 1H,
20d
3
the complex has been reported in our previous work.
Ar H), 8.23−8.01 (m, 4H, Ar H), 7.53−7.24 (m, 7H, Ar H), 6.97 (dd,
i
3
3
[(2,6- Pr
2
C
H
6
3
)NCHCHC(1-naphthyl)O]Ni(Py)(CH
3
) (3c). Yield:
J
= 12.6, 7.2 Hz, 1H, NCH), 5.67 (d, J = 7.2 Hz, 1H, C
1
3
HH
HH
9
1%. H NMR (300 MHz, C D ): δ 8.68 (d, J = 5.1 Hz, 2H, o-
3
i
3
6
6
HH
CH), 3.43 (sept, J = 6.6 Hz, 2H, Pr CH), 1.35 (d, J = 6.9 Hz,
3
HH
HH
H Py), 7.09−6.89 (m, 3H, Ar H), 6.61 (t, J = 7.8 Hz, 1H, p-H Py),
i
13
HH
1
1
1
2
3
2H, Pr CH ). C NMR (300 MHz, CDCl ): δ 196.94 (NC),
3
3
3
3
6
4
1
.22 (t, J = 6.9 Hz, m-H Py), 5.31 (d, J = 6.3 Hz, 1H, CCH),
.36 (sept, J = 6.9 Hz, 2H, Pr CH), 1.53, 1.23, (d, J = 6.9 Hz,
HH HH
HH
HH
53.82, 144.84, 137.84, 136.53, 131.67, 128.88, 128.23, 128.10, 127.90,
3
i
3
i
26.39, 126.20, 125.69, 124.35, (Ar), 99.72 (C), 28.98 ( Pr CH),
i
t
13
2H, Pr CH ), 1.11 (s, 9H, Bu H), −0.60 (s, 3H, NiCH ). C NMR
600 MHz, C D ): δ 177.04 (NC), 160.13, 151.57, 150.91, 142.07,
39.85, 135.26, 134.20, 131.12, 128.90, 127.04, 125.70, 125.41, 124.96,
i
3
3
4.25 ( Pr CH ). Anal. Calcd for C H NO: C, 85.47; H, 7.17; N,
3
29 29
(
6 6
.44. Found: C, 85.39; H, 7.13; N, 3.39.
1
1
(
(
2,6- Pr C H )NCHCHC(p-Me NPh)OH (2e). Yield: 55%. 1H
i
i
2
6
3
2
23.25, 122.88 (Ar, Py), 96.95 (C), 28.24 ( Pr CH), 24.93, 23.19
NMR (300 MHz, CDCl ): δ 11.51 (d, J = 12.0 Hz, 1H, N−H),
i
3
Pr CH ), −6.79 (NiCH ). Anal. Calcd for C H N NiO: C, 73.11;
3
3
3
31 34
2
7
.92 (d, J = 6.0 Hz, 2H, Ar H), 7.26−7.17 (m, 3H, Ar H), 6.83 (dd,
HH
H, 6.73; N, 5.50. Found: C, 73.18; H, 6.70; N, 5.54.
3
3
JHH = 12.3, 7.8 Hz, 1H, NCH), 6.71 (d, J = 9.0 Hz, 2H, Ar H),
i
HH
[(2,6- Pr C H )NCHCHC(9-anthryl)O]Ni(Py)(CH ) (3d). Yield:
2
6
3
3
3
3
5
.91 (d, J = 7.8 Hz, 1H, CCH), 3.29 (sept, J = 6.9 Hz, 2H,
1
3
HH
HH
93%. H NMR (300 MHz, C D ): δ 8.69 (d, J = 8.7 Hz, 2H, Ar
6 6 HH
i
3
i
3
Pr CH), 3.06 (s, 3H, NCH ), 1.22 (d, J = 6.9 Hz, 12H, Pr CH ).
3
HH
3
H), 8.62 (d, J = 5.1 Hz, 2H, o-H Py), 8.05 (s, 1H, Ar H), 7.72 (d,
JHH = 7.8 Hz, 2H, Ar H), 7.31−7.00 (m, 6H, Ar H), 6.25 (t, J
7.8 Hz, 1H, p-H Py), 5.87 (t, J = 6.9 Hz, m-H Py), 5.56 (d, J
HH
1
3
3
3
C NMR (300 MHz, CDCl ): δ 190.34 (NC), 152.92, 145.05,
=
=
3
HH
3
3
1
37.11, 129.56, 127.65, 124.14, 111.40, (Ar), 91.49 (C), 40.55
HH
HH
i
i
3
i
(
NMe), 28.71 ( Pr CH), 24.28 ( Pr CH ). Anal. Calcd for C H N O:
6.0 Hz, 1H, CC−H), 4.71 (sept, J = 6.9 Hz, 2H, Pr CH), 1.66,
3
23 30
2
HH
3
i
13
C, 78.82; H, 8.63; N, 7.99. Found: C, 78.92; H, 8.57; N, 7.96.
1.38 (d, J = 6.9 Hz, 12H, Pr CH ), −0.45 (s, 3H, NiCH ).
C
HH
3
3
i
1
(
2,6- Pr C H )NCHCHC(p-MeOPh)OH (2f). Yield: 60%. H NMR
NMR (600 MHz, C D ): δ 176.26 (NC), 159.71, 151.45, 150.97,
2
6
3
6 6
(
300 MHz, CDCl ): δ 11.58 (d, J = 12.3 Hz, 1H, N−H), 7.96 (m, 2H,
141.99, 138.36, 135.12, 131.63, 129.03, 128.64, 128.29, 128.04, 127.01,
3
Ar H), 7.30−7.18 (m, 3H, Ar H), 6.97−6.86 (m, 3H, Ar H), 5.92 (d,
126.73, 125.74, 125.36, 125.01, 123.31, 122.82 (Ar, Py), 100.04 (C),
3
3
i
i
J
= 7.5 Hz, 1H, CCH), 3.88 (s, 3H, OCH ), 3.26 (sept, J
=
28.47 ( Pr CH), 24.95, 23.23 ( Pr CH ), −6.49 (NiCH ). Anal. Calcd
HH
3
HH
3
3
i
3
i
13
6
.9 Hz, 2H, Pr CH), 1.23 (d, J = 6.9 Hz, 12H, Pr CH ). C NMR
for C35
H N NiO: C, 75.15; H, 6.49; N, 5.01. Found: C, 75.08; H,
36 2
HH
3
(
1
300 MHz, CDCl ): δ 190.22 (NC), 162.64, 153.92, 145.04, 136.78,
6.51; N, 5.06.
3
i
32.57, 129.67, 127.93, 124.19, 113.97 (Ar), 91.53 (C), 55.75
[(2,6- Pr
2
C
6
H
3
)NCHCHC(p-Me
NPh)O]Ni(Py)(CH ) (3e). Yield:
2 3
89%. H NMR (300 MHz, C ): δ 8.82 (d, JHH = 5.1 Hz, 2H, o-
H Py), 7.88 (d, 2H, J = 8.7 Hz, Ar H), 7.29−7.15 (m, 3H, Ar H), 6.74
(t, JHH = 7.8 Hz, 1H, p-H Py), 6.52 (d, 2H, J = 8.7 Hz, Ar H), 6.37 (t,
i
i
1
3
(
OMe), 28.75 ( Pr CH), 24.24 ( Pr CH ). Anal. Calcd for C H NO :
D
6 6
3
22 27
2
C, 78.30; H, 8.06; N, 4.15. Found: C, 78.38; H, 8.02; N, 4.12.
i
1
3
(
2,6- Pr C H )NCHCHC(p-F CPh)OH (2g). Yield: 63%. H NMR
2
6
3
3
3
3
(
300 MHz, CDCl ): δ 11.75 (d, J = 12.3 Hz, 1H, N−H), 8.06 (m, 2H,
J
HH = 6.9 Hz, m-H Py), 6.06 (d, JHH = 6.6 Hz, 1H, CCH), 4.59
3
3
i
Ar H), 7.72 (m, 2H, Ar H), 7.72 (m, 3H, Ar H), 7.0 (m, 3H, Ar H),
(sept, JHH = 6.9 Hz, 2H, Pr CH), 2.49 (s, 6H, NCH ), 1.71, 1.38, (d,
3
3
i
3
i
13
5
(
.95 (m, 1H, CCH), 3.22 (sept, J = 6.9 Hz, 2H, Pr CH), 1.24
d, J = 6.9 Hz, 12H, Pr CH ). C NMR (300 MHz, CDCl ): δ
HH 3 3
J
HH = 6.9 Hz, 12H, Pr CH
3
), −0.46 (s, 3H, NiCH ). C NMR (600
3
MHz, C D ): δ 173.28 (NC), 159.48, 151.85, 151.40, 151.17, 142.47,
HH
3
i
13
6
6
189.40 (NC), 155.33, 144.96, 142.88, 136.29, 128.31, 127.97,
135.15, 125.43, 123.13, 122.74, 111.36 (Ar, Py), 90.74 (C), 39.44
9
73
dx.doi.org/10.1021/om2010194 | Organometallics 2012, 31, 966−975

Organometallics
Article
i
i
H), 7.99 (s, 1H, Ar H), 7.71 (d, 3JHH = 8.1 Hz, 2H, Ar H), 7.53−7.19
(
NCH ), 28.13 ( Pr CH), 24.95, 23.23 ( Pr CH ), −6.97 (NiCH ).
3
3
3
Anal. Calcd for C H N NiO: C, 69.34; H, 7.42; N, 8.37. Found: C,
(m, 11H, Ar H), 7.13−6.89 (m, 5H, Ar H), 6.81−6.70 (m, 9H, Ar H),
2
9
37
3
3
6
9.24; H, 7.45; N, 8.32.
6.44−6.35 (m, 3H, Ar H), 5.55 (d, J = 6.3 Hz, 1H, CC−H), 4.51
HH
i
3
i
3
[
(2,6- Pr C H )NCHCHC(p-MeOPh)O]Ni(Py)(CH ) (3f). Yield:
(sept, J = 6.9 Hz, 2H, Pr CH), 1.39, 1.32 (d, J = 6.9 Hz, 12H,
2
6
3
3
HH
HH
1
3
i
13
8
7%. H NMR (300 MHz, C D ): δ 8.75 (d, J = 5.1 Hz, 2H, o-
Pr CH3). C NMR (300 MHz, C D ): δ 175.64 (NC), 160.44,
6
6
HH
6 6
H Py), 7.79 (d, 2H, J = 8.4 Hz, Ar H), 7.26−7.13 (m, 3H, Ar H), 6.74
150.99, 147.03, 146.71, 141.55, 139.62, 137.82, 134.34, 134.27, 131.71,
131.43, 129.30, 128.62, 126.71, 125.59, 125.38, 125.20, 125.16, 124.69,
3
(
d, 2H, J = 8.4 Hz, Ar H), 6.68 (t, J = 7.8 Hz, 1H, p-H Py), 6.30 (t,
HH
3
3
i
i
JHH = 6.9 Hz, m-H Py), 5.93 (d, J = 6.6 Hz, 1H, CCH), 4.53
122.49, 121.26 (Ar), 97.30 (C), 28.77 ( Pr CH), 25.83, 22.74 ( Pr
HH
i
(
sept, 3J = 6.9 Hz, 2H, Pr CH), 3.26 (s, 3H, OCH ), 1.68, 1.35, (d,
CH ). Anal. Calcd for C53 48NNiOP: C, 79.11; H, 6.01; N, 1.74.
3
H
HH
3
3
i
13
JHH = 6.9 Hz, 12H, Pr CH ), −0.47 (s, 3H, NiCH ). C NMR (600
MHz, C D ): δ 172.45 (NC), 160.92, 159.93, 151.72, 151.13, 142.24,
Found: C, 79.13; H, 5.98; N, 1.71.
3
3
Ethylene Polymerization. A 200 mL autoclave was heated under
vacuum up to 130 °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 or 20 μmol amount of cocatalyst
dissolved in 10 mL of toluene was added into the autoclave by syringe
if necessary, followed by the same amount of catalyst. The total
volume of the reaction medium was fixed at 100 mL. The reactor was
then sealed and pressurized to the desired level, and the stirring motor
was engaged. Temperature control was maintained 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. The solid polyethylene was filtered, washed with acetone
several times, and dried at 60 °C for more than 10 h under vacuum.
Crystallographic Studies. Crystals for X-ray analysis were
obtained as described in the preparations. The crystallographic data,
collection parameters, and refinement parameters are given in Table 1.
The crystals were manipulated in a glovebox. The intensity data were
collected with the ω scan mode (186 K) on a Bruker Smart APEX
diffractometer with CCD detector using Mo Kα radiation (λ = 0.710
6
6
1
35.28, 132.40, 128.07, 125.58, 123.18, 122.81, 113.39, (Ar, Py), 91.31
i
i
(
−
5
C), 54.40 (O−CH ), 28.15 ( Pr CH), 24.91, 23.18, ( Pr CH ),
3
3
6.82 (NiCH ). Anal. Calcd for C H N NiO : C, 68.73; H, 7.00; N,
3 28 34 2 2
.73. Found: C, 68.71; H, 7.04; N, 5.68.
i
[
(2,6-Pr C H )NCHCHC(p-F CPh)O]Ni(Py)(CH ) (3g). Yield: 91%.
2
6
3
3
3
1
3
H NMR (300 MHz, C D ): δ 8.67 (d, J = 5.1 Hz, 2H, o-H Py),
6 6 HH
7
.59, 7.31 (d, 2H, J = 8.1 Hz, Ar H), 7.25−7.14 (m, 3H, Ar H), 6.69 (t,
3
J
= 7.8 Hz, 1H, p-H Py), 6.31 (d, 2H, J = 8.7 Hz, Ar H), 6.31 (t,
HH
3J
3
= 6.9 Hz, m-H Py), 5.76 (d, J = 6.3 Hz, 1H, CC−H), 4.44
HH
HH
3
i
3
(
sept, J = 6.9 Hz, 2H, Pr CH), 1.65, 1.33, (d, J = 6.9 Hz, 12H,
HH HH
i
13
Pr CH ), −0.46 (s, 3H, NiCH ). C NMR (600 MHz, C D ): δ
3
3
6
6
1
1
(
70.50 (NC), 160.47, 151.57, 141.83, 135.51, 128.04, 126.59, 125.88,
24.91, 124.45, 124.05, 123.28, 122.95 (Ar, Py), 92.79 (C), 28.18
i
i
Pr CH), 24.84, 23.09 ( Pr CH ), −6.47 (NiCH ). Anal. Calcd for
3
3
C H F N NiO: C, 63.78; H, 5.93; N, 5.31. Found: C, 63.73; H, 5.96;
28
31
3
2
N, 5.33.
Synthesis of Complexes 4a−d. A solution of ligand 2a (0.29 g,
.0 mmol) in THF (15 mL) was added to sodium hydride (48 mg, 2.0
1
mmol). Immediately a large amount of bubbles were emitted from the
mixture and a yellow solution formed. Then the solution was stirred at
room temperature for 4 h, filtered, and evaporated. The solid residue
was washed with hexane (20 mL) and dried under vacuum, affording a
light yellow sodium salt. The sodium salt was dissolved in toluene at
room temperature and transferred to a toluene solution of trans-
7
3 Å). Lorentz−polarization factors were used for the intensity data,
and absorption corrections were performed using the SADABS
program. The crystal structures were solved using the SHELXTL
program and refined using full-matrix least squares. The positions of
hydrogen atoms were calculated theoretically and included in the final
cycles of refinement in a riding model along with attached carbons.
PhNi(PPh ) Cl (0.7 g, 1.0 mmol) in a Schlenk flask with stirring at
3
2
room temperature for 12 h, forming a red solution. Then the reaction
mixture was filtered by cannula filtration and the filtrate was
concentrated in vacuo to about 4 mL, to which hexane (15 mL)
was added. Subsequently, yellow crystals precipitated from the
solution, which were isolated via filtration and washed several times
with cold hexane to yield 0.41 g (60%) of complex 4a. The other
neutral nickel(II) complexes 4b−d were prepared by the same
procedure in similar yields.
ASSOCIATED CONTENT
■
*
S
Supporting Information
CIF files giving X-ray data for the crystal structure
determinations. This material is available free of charge via
the Internet at http://pubs.acs.org.
i
t
1
[
(2,6-Pr C H )NCHCHC( Bu)O]Ni(Ph)(PPh ) (4a). H NMR (300
2
6
3
3
MHz, C D ): δ 7.79−7.65 (m, 6H, Ar H), 7.05−6.89 (m, 15H, Ar H),
6 6
AUTHOR INFORMATION
3
■
6
.36−6.25 (m, 3H, Ar H), 5.35 (d, J = 6.6 Hz, 1H, CCH), 4.26
HH
3
i
3
(
sept, J = 6.9 Hz, 2H, Pr CH), 1.32, 1.21 (d, J = 6.9 Hz, 12H,
Corresponding Author
*Fax: +86-431-85262039. E-mail: ysli@ciac.jl.cn.
HH
HH
i
t
13
Pr CH ), 0.80 (9H, Bu H). C NMR (300 MHz, C D ): δ 187.32
3
6
6
(
NC), 160.46, 151.07, 141.77, 137.37, 134.84, 134.47, 134.40, 132.15,
1
3
29.50, 129.33, 125.21, 125.08, 122.44, 120.99 (Ar), 89.62 (C),
9.12 ( Bu C), 28.66 ( Bu CH ), 28.19 ( Pr CH), 25.73, 22.72 ( Pr
3
t
t
i
i
ACKNOWLEDGMENTS
■
CH ). Anal. Calcd for C H NNiOP: C, 75.45; H, 7.07; N, 2.05.
Found: C, 75.42; H, 7.10; N, 2.08.
We are grateful for a subsidy provided by the National Natural
Science Foundation of China (No. 20923003).
3
43 48
i
[
(2,6-Pr C H )NCHCHC(Ph)O]Ni(Ph)(PPh ) (4b). The synthesis
2
6
3
3
2
0c
of the complex has been reported in our previous work.
i
REFERENCES
[
(2,6-Pr C H )NCHCHC(1-naphthyl)O]Ni(Ph)(PPh ) (4c). Yield:
■
2
6
3
3
1
3
6
3%. H NMR (300 MHz, C D ): δ 8.34 (d, J = 8.4 Hz, 1H, N
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6
HH
CH), 7.63−7.39 (m, 9H, Ar H), 7.17−6.79 (m, 18H, Ar H), 6.40−
3
6
.30 (m, 3H, Ar H), 5.69 (d, J = 6.3 Hz, 1H, CCH), 4.36 (sept,
HH
3
i
3
i
JHH = 6.9 Hz, 2H, Pr CH), 1.39, 1.27 (d, J = 6.9 Hz, 12H, Pr
HH
CH3). 13C NMR (300 MHz, C D ): δ 175.53 (NC), 160.31, 150.87,
6
6
1
1
1
2
1
46.89, 146.57, 141.43, 139.50, 137.70, 134.22, 134.15, 133.65, 131.59,
31.31, 130.42, 129.18, 128.50, 126.59, 125.47, 125.26, 125.08, 125.04,
i
24.57, 122.37, 121.14 (Ar), 97.18 (C), 28.65 ( Pr CH), 25.71,
i
2.62 ( Pr CH ). Anal. Calcd for C H NNiOP: C, 78.00; H, 6.14; N,
3
49 46
.86. Found: C, 78.02; H, 6.11; N, 1.85.
i
[
(2,6- Pr C H )NCHCHC(9-anthryl)O]Ni(Ph)(PPh ) (4d). Yield:
2
6
3
3
1
3
5
8%. H NMR (300 MHz, C D ): δ 8.33 (d, J = 8.7 Hz, 2H, Ar
6 6 HH
9
74
dx.doi.org/10.1021/om2010194 | Organometallics 2012, 31, 966−975

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(
(
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22) We employed density functional theory (DFT) calculations by
26
using the Amsterdam Density Functional (ADF) program package.
A triple-STO basis set was employed for Ni, while all other atoms were
described by a double-ζ plus polarization STO basis. The 1s electrons
of the C, N and O atoms, as well as the 1s−2p electrons of the Ni
atom, were treated as a frozen core.
3
(
903−3914.
8) (a) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R.
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