New half-sandwich chromium(III) complexes bearing phenoxy-phosphine (oxide) [O,P(i =O)] Ligands: Synthesis, structures, and catalytic properties for ethylene (Co)polymerization

Article abstract of DOI:10.1021/om400517t

A series of novel half-sandwich-type chromium complexes bearing phenoxy-phosphine [O,P] ligands (3a-3f) or phenoxy-phosphine oxide [O,Pi =O] ligands (4b-4e) were synthesized in high yields from CpCrCl₂(thf) with corresponding ligands in THF. X-

Full text of DOI:10.1021/om400517t

Article
pubs.acs.org/Organometallics
New Half-Sandwich Chromium(III) Complexes Bearing Phenoxy-
Phosphine (Oxide) [O,P(O)] Ligands: Synthesis, Structures, and
Catalytic Properties for Ethylene (Co)Polymerization
Ping Tao,†,‡ Hong-Liang Mu,† Jing-Yu Liu,*,† and Yue-Sheng Li†
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, China
‡University of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, China
S
* Supporting Information
ABSTRACT: A series of novel half-sandwich-type chromium complexes
bearing phenoxy-phosphine [O,P] ligands (3a−3f) or phenoxy-
phosphine oxide [O,PO] ligands (4b−4e) were synthesized in high
yields from CpCrCl2(thf) with corresponding ligands in THF. X-ray
structure analyses for 3b, 3c, 3e, and 4c revealed that these complexes
adopt a three-legged piano stool geometry. When activated by modified
methylaluminoxane, complexes 3a−3f exhibited moderate to high
activities toward ethylene polymerization, giving high molecular weight
polymers with unimodal molecular weight distributions. Excitingly,
complex 3c could efficiently promote ethylene/NBE copolymerization,
therefore, high molecular weight copolymers with high NBE content
could easily be obtained under optimized conditions. The [O,PO]
complexes showed higher catalytic activities than [O,P] analogues but
produced much lower molecular weight polymers. The difference in polymerization behavior might be caused by the change of
both the steric bulk and the electronic effect around the metal center.
mol) with high catalytic activities (ca. 4.0 × 106 g/molCr h)
INTRODUCTION
■
upon activation with only a small amount of AlR3 (Al/Cr =
The design and synthesis of novel transition metal catalysts for
olefin polymerization has been one of the most attractive
25).23 Jin et al. found that the half-sandwich chromium(III)
complexes bearing β-ketoiminato, β-diketiminato, and hydrox-
subjects in the field of chemistry.1 Chromium is the key
yindanimine ligands exhibited good catalytic activities (ca. 1.5 ×
element in the silica-supported Phillips and Union Carbide
105 g/molCr h) for ethylene polymerization in the presence of a
catalytic systems commercially used for olefin polymer-
small amount of triethylaluminium.24
ization.2,3 The ill-defined nature of these systems led to certain
Recent search on transition metal catalysts indicated that
introducing soft second-row donors, such as sulfur or
heterogeneities in the produced polymers. Therefore, more
recent studies have focused on developing well-defined
homogeneous chromium catalysts for improving catalytic
phosphine, in the ligands could offer beneficial stabilization of
the highly reactive metal center.25−30 However, the examples
activities and polymer properties.4−6 Research in this area
on half-sandwich chromium(III) complexes containing soft
frequently involves the design of new ancillary ligands to
support and activate the metal center toward olefin polymer-
donors ligands are limited so far. The phenoxy-phosphine
[O,P] ligands were very attractive and widely employed in
ization. Among the homogeneous chromium-based catalysts
transition metal polymerization catalysis.25,29b−d Moreover,
with various ligands, monocyclopentadienyl chromium(III)
these ligands could be easily transformed to phenoxy-
complexes have been extensively studied for ethylene (co)-
polymerization.7−23 For instance, [Cp*CrL2R]+A− complexes
(L = py, 1/2dppe, MeCN, THF; R = Me, Et; A = PF6, BPh4;
Cp* = η5-pentamethylcyclopentadienyl), discovered by Theo-
pold et al., were first reported to promote ethylene polymer-
ization in the absence of any cocatalyst.7 Jolly et al. found the
Cp*Cr(acac)Cl/Et3Al (Al/Cr = 300) system, showing a
catalytic activity of 4.2 × 104 g/molCr h under 50 atm of
ethylene at room temperature.8 Mu et al. reported that
Cp*Cr[2,4-tBu2-6-(CHNR)-C6H2O]Cl can produce linear
high molecular weight polyethylenes (Mn = 1.0−1.5 × 106 g/
phosphine oxide [O,PO] ligands by adding a spot of H2O2
in the solution. Herein, we thus synthesized and characterized
some novel half-sandwich chromium complexes containing
phenoxy-phosphine (oxide) [O,P(O)] chelating ligands, and
explored the effect of ligand structure toward catalytic activity
for ethylene (co)polymerization in the presence of modified
methylaluminoxane (MMAO).
Received: June 5, 2013
Published: August 16, 2013
© 2013 American Chemical Society
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(−30 °C). These complexes were identified by IR and UV−vis
spectroscopy, mass spectra, and elemental analyses. Moreover,
complexes 3e, 3f, and 4e were further characterized by 19F
NMR spectra. H NMR spectra indicated the paramagnetic
character of these chromium complexes.
RESULTS AND DISCUSSION
■
Synthesis and Structural Analysis of Half-Sandwich
Chromium(III) Complexes. A series of new chromium
complexes, adopted in this study, bearing phenoxy-phosphine
[O,P] ligands and phenoxy-phosphine oxide [O, PO]
ligands, Cp[O-2R1-4R2-6(Ph2P)C6H2]CrCl (3a: R1 = R2 = H;
3b: R1 = Ph, R2 = H; 3c: R1 = tBu, R2 = H; 3d: R1 = R2 = tBu;
3e: R1 = F, R2 = H; 3f: R1 = C6F5, R2 = H) and Cp[O-2R1-4R2-
6(Ph2PO)C6H2]CrCl; 4b: R1 = Ph, R2 = H; 4c: R1 = tBu, R2
1
The IR spectra of the precatalysts were obviously different
from those of the corresponding ligands. The disappearance of
the band related to the O−H stretching at about 3350 cm−1
indicated the formation of the σ bond between the oxygen
atom in the phenoxy group and the chromium atom. For
complexes 3a−3f, the strong band of ν(P−Ph) at around 1182
cm−1 shifted to low frequency around 1100 cm−1 due to the
phosphorus atom coordinating with chromium metal. The spin
state of the complexes was confirmed by magnetic susceptibility
measurements. The results indicated the presence of three
unpaired electrons on the chromium center. In addition, the
proposed structures were in line with the elemental analyses.
Crystals of 3b, 3c, 3e, and 4c suitable for crystallographic
analysis were grown from the chilled CH2Cl2−hexane mixture
solution. The crystallographic data together with the collection
and refinement parameters are summarized in Table S1 of the
Supporting Information. Selected bond distances and angles for
complexes 3b, 3c, 3e, and 4c are listed in Table 1.
t
= H; 4d: R1 = R2 = Bu; and 4e: R1 = F, R2 = H), were
synthesized in high yields (66−79%) via the reaction of in situ
produced CpCrCl2(thf) with 1.0 equiv of lithium salts of 2R1-
4R2-6(Ph2P)C6H2OH (1a−1f) or 2R1-4R2-6(Ph2PO)-
C6H2OH (2b−2e) in THF, as shown in Scheme 1. Pure
Scheme 1. Synthesis of New Half-Sandwich Chromium(III)
Complexes
Structures for 3b, 3c, and 3e are shown in Figures 1−3.
These complexes have a pseudo-octahedral coordination
Figure 1. Molecular structure of complex 3b with thermal ellipsoids at
the 30% probability level. Hydrogen atoms are omitted for clarity.
samples were collected from the chilled concentrated mixture
of dichloromethane and hexane solution placed in the freezer
Table 1. Selected Bond Distances (Å) and Angles (deg) for Complexes 3b, 3c, 3e, and 4c
3b (A)
3b (B)
3c
3e
4c
bond distances (Å)
1.939(4)
Cr(1)−O(1)
Cr(1)−P(1)
1.929(4)
1.910(2)
1.9388(15)
2.4274(7)
1.920(3)
2.4127(18)
2.4295(17)
2.4720(12)
Cr(1)−O(2)
Cr(1)−Cl(1)
Cr(1)−Cp(centroid)
Cr(1)−Cav
1.968(3)
2.2879(14)
1.884
2.2908(17)
1.881
2.2965(18)
1.881
2.2771(12)
1.882
2.2862(7)
1.874
2.225
2.231
2.229
2.217
2.225
bond angles (deg)
97.61(13)
96.92(6)
O(1)−Cr(1)−Cl(1)
P(1)−Cr(1)−Cl(1)
O(1)−Cr(1)−P(1)
97.68(3)
95.51(6)
79.85(12)
98.20(9)
96.09(4)
77.95(8)
94.95(6)
96.89(2)
80.94(5)
98.37(9)
80.45(12)
O(2)−Cr(1)−Cl(1)
O(1)−Cr(1)−O(2)
93.80(9)
92.23(12)
122.95
Cp(centroid)−Cr(1)−Cl(1)
Cp(centroid)−Cr(1)−P(1)
Cp(centroid)−Cr(1)−O(1)
Cp(centroid)−Cr(1)−O(2)
Cp−phenyl ring
123.85
123.65
123.76
123.85
123.65
123.76
124.82
126.57
121.38
123.80
128.01
126.34
119.57
122.74
70.27
45.63
67.44
45.84
74.36
45.48
72.10
48.05
Cp−[O−Cr−P]
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with the O, O, Cl atoms being the three legs and the Cp ring
being the seat. As shown in Figure 4, the phenoxy-phosphine
Figure 2. Molecular structure of complex 3c with thermal ellipsoids at
30% probability level. Hydrogen atoms are omitted for clarity.
Figure 4. Molecular structure of complex 4c with thermal ellipsoids at
the 30% probability level. Hydrogen atoms are omitted for clarity.
oxide ligand coordinating with the chromium atom formed a
six-membered ring structure (O1−Cr−O2−P1−C2−C1).
Therefore, the Cr(1)−O(1) and Cr(1)−Cl(1) bond distances
in 4c [1.920(3) and 2.2879(14) Å] are longer than those of 3c.
Moreover, the C(1)−C(2)−P bond angle in 4c (115.9°) is
larger than that in 3c (112.8°). The observed difference in the
molecular structures between 3c and 4c may have a great
influence on the behaviors for polymerization catalysis.
Figure 3. Molecular structure of complex 3e with thermal ellipsoids at
the 30% probability level. Hydrogen atoms are omitted for clarity.
Ethylene Polymerization by the New Half-Sandwich
Chromium Complexes. Ethylene polymerization by novel
half-sandwich chromium complexes 3a−3f and 4b−4e in the
presence of MMAO were explored (3 μmol catalyst, 25 °C, in
toluene, Vtotal = 70 mL), and typical results are summarized in
Table 2. Complex 3a, without any substituent in the aryloxy
moiety of the ligand, showed only low catalytic activity for
ethylene polymerization (entry 1). Introducing a conjugated
phenyl group in the R1 position (3b) clearly increased the
catalytic activity (3a, 40 kg/molCr h; 3b, 340 kg/molCr h). Note
environment in the solid state and adopt a three-legged piano
stool geometry with the O, P, Cl atoms being the three legs and
the Cp ring being the seat. Crystals of 3b consist of two
crystallographically independent molecules in the unit cell, with
only minor differences from each other [e.g., bond angles
Cl(1)−Cr(1)−P(1) and Cl(2)−Cr(2)−P(2) are 95.51(6)° and
96.92(6)°, respectively]. The Cr−P(1) bond distances in these
complexes are in the range of 2.4127(18)−2.4720(12),
indicating the significant coordination of the phosphorus
atom to the metal center. It should be noted that the complex
3e with a F atom in the R1 position of the phenoxy-phosphine
ligand has shorter Cr(1)−Cp(centroid) and Cr(1)−C(average)
distances than do 3b or 3c, which might be caused by the
strong electron withdrawing effect of the F atom. In addition,
the Cr−Cl(1) bond lengths in 3b, 3c, and 3e change slightly
with the variation of the R1 group in the ligands [3b:
2.2908(17) and 2.2965(18) Å, 3c: 2.2771(12) Å, and 3e:
2.2862(7) Å]. However, the Cr−O(1) [3b: 1.929(4) and
1.939(4) Å, 3c: 1.910(2) Å, and 3e: 1.9388(15) Å] and Cr−
P(1) [3b: 2.4127(18) and 2.4295(17) Å, 3c: 2.4720(12) Å, and
3e: 2.4274(7) Å] bond lengths are obviously affected by the R1
group. The O−Cr−P, O−Cr−Cl, and P−Cr−Cl bond angles
in these complexes occur in the ranges of 77.95−80.94°,
94.95−98.20°, and 95.51−96.89°, respectively. A bulkier
substituent in the R1 position would lead to a larger O−Cr−
Cl bond angle and a smaller O−Cr−P bond angle. Moreover,
these complexes have similar dihedral angles between the Cp
ring and the plane through Cr, O, and P atoms in the range of
45.48−48.05°. The impact of the R1 group on the dihedral
angle between the Cp ring and the phenyl ring in the aryloxy
moiety of the ligand is also slight, which makes the Cp−phenyl
ring dihedral angle change in a small range from 67.44 to
74.36°.
Table 2. Ethylene Polymerization by Half-Sandwich
a
Chromium(III) Complexes 3a−3f and 4b−4e
b
pressure
(atm)
time
(min)
yield
(g)
activity
Mw
M /
wb
entry catalyst
(kg/molCr h) (10−4
)
Mn
1
3a
3b
3c
3d
3e
3f
5
5
5
5
5
5
5
5
5
5
2
5
5
5
5
10
10
10
10
10
10
10
10
10
10
10
5
0.02
0.17
1.71
0.59
0.23
0.39
0.43
1.85
1.98
0.61
0.66
0.95
2.04
1.01
2.11
40
340
17
24
53
31
27
25
2.1
2.3
1.8
2.9
2.4
2.6
2.5
2.9
2.5
2.6
2.9
2.4
2.8
2.9
2.8
2
3
3420
1180
460
4
5
6
780
7
4b
4c
4d
4e
3c
3c
3c
4c
4c
860
0.6
8
3700
3960
1220
1320
3800
1360
2020
4220
1.2
0.7
0.4
9
10
11
12
13
14
15
21
35
60
30
5
0.5
1.7
30
a
Reaction conditions: 3 μmol catalyst, Al/Cr = 1000, MMAO as
b
cocatalyst, 25 °C, in toluene, Vtotal = 70 mL. Weight-average
molecular weights and polydispersity indexes determined by high
temperature GPC at 150 °C in 1,2,4-C6Cl3H3 versus narrow
polystyrene standards.
Complex 4c also has a pseudo-octahedral coordination
environment and adopts a three-legged piano stool geometry
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that replacement of H at the R1 position in complex 3a with a
tert-butyl group (3c and 3d) brought about dramatic
improvement in the catalytic performance. Complex 3c showed
the highest catalytic activity (3420 kg/molCr h) among these
complexes. It was assumed that a bulky R1 in the ortho-position
of the oxygen atom in the phenoxy-phosphine ligands could
prevent the coordinated oxygen atom from further coordinating
to AlR3 or another chromium complex and, therefore, keep the
active catalyst molecule from inactivation by forming inactive
binuclear species.23c Moreover, the R2 group also had a
significant effect on the polymerization behaviors. Complex 3d,
bearing tert-butyl groups in both the R1 and R2 positions,
exhibited lower activity than 3c under similar conditions (3c,
3420 kg/molCr h; 3d, 1180 kg/molCr h) and produced relatively
lower molecular weight polymers. Complexes 3e (R1 = F) and
3f (R1 = C6F5) were also synthesized in order to clarify the
electronic effect of the R1 group on the catalytic performance. It
was found that 3e displayed higher activity than 3a (3e, 460 kg/
molCr h), while the activity could be further increased if
complex 3f was used (3f, 780 kg/molCr h) under similar
conditions. Taking these results into account, it is therefore
clear that the steric bulk effect in the R1 position played a key
role in the enhanced catalytic activity for complexes 3a−3f.
The [O,PO] half-sandwich chromium(III) complexes
exhibited higher catalytic activities than the [O,P] analogues.
For instance, complex 4e with an electron withdrawing −F
group at the R1 position was found to display a relatively high
catalytic activity of 1220 kg/molCr h at 25 °C, which was ca. 3
times larger than 3e (460 kg/molCr h). In addition, complex 4d
showed higher activity than 4c. The observed result was an
interesting contrast to that found by 3c and 3d, in which 3c
showed higher activity than 3d. However, the molecular
weights of the resultant polymers produced by complexes 4b−
4e were much lower than those by 3b−3e under similar
conditions, suggesting that a reduced congestion degree around
the metal center might be not only favored for chain
propagation but also for chain transfer. The difference in
polymerization behaviors might be caused by the change of
both the steric bulk and electronic effect around the metal
center.
molecular weights of the resultant polymers obtained by 3c/
MMAO system changed slightly with the Al/Cr molar ratio,
suggesting that the dominant chain-transfer pathway is not
chain transfer to aluminum alkyls but seems to be β-hydrogen
transfer under these conditions. Moreover, the molecular
weight values sharply decreased when the polymerization was
conducted at a low ethylene pressure (entry 11 in Table 2).
This result also supported the above suggestion that the
dominant chain transfer would be the β-hydrogen transfer from
propagating metal alkyl species. In contrast, the molecular
weights of the resultant polyethylenes obtained by complex 4c
decreased with increasing cocatalyst dosage, suggesting that the
dominant chain-transfer pathway is chain transfer to aluminum
in this case. The typical sample obtained by 4c (entry 8 in
Table 2) was further characterized by high temperature 13C
NMR spectra (Figure 6). Two kinds of terminal groups, methyl
Figure 6. 13C NMR (100 MHz, o-C6D6Cl2, 135 °C) spectra of the
polymer sample obtained by catalyst 4c/MMAO (entry 8 in Table 2).
and isopropyl, were detected for the polyethylenes, which
further conformed the occurrence of chain transfer to
aluminum. However, it is very difficult to observe the
unsaturated chain ends of the polymers which are produced
with precatalyst 3c by 13C NMR due to a high molecular
weight. IR spectra were also employed to assess the chain end
groups. The IR spectrum of the sample obtained by 3c showed
resonances at 1643 (CC) cm−1 and 922 and 910 (CH2)
cm−1. The signals for ν(CC) and ν(CH2) were seldom
detected in IR spectrum of the sample obtained by 4c.
The effect of reaction condition on ethylene polymerization
was also investigated by using precatalysts 3c and 4c. For these
two systems, the catalytic activities were somewhat dependent
upon the Al/Cr molar ratio, as shown in Figure 5. The
In order to further evaluate the catalytic performance of these
new half-sandwich chromium complexes, the relationship
between the catalytic activity and the time represented by 3c
and 4c was also studied. Note that the catalytic activities by 3c
and 4c did not significantly decrease, at least for 30 min (entries
12−15, Table 2). These results indicated that either phenoxy-
phosphine ligands or phenoxy-phosphine oxide ligands can
efficiently stabilize active species and maintain single-site
catalytic behaviors of the chromium catalyst for ethylene
polymerization. All the polymers prepared by the different
complexes were linear polyethylenes confirmed by 13C NMR
spectra, which are similar to those by β-enaminoketonato or
salicylaldiminato chromium catalysts.23,24
Ethylene/Norbornene (NBE) Copolymerization. The
copolymerization of ethylene/NBE by some complexes bearing
phenoxy-phosphine ligands (3c, 3d, and 3f) was also studied,
and the representative results were summarized in Table 3. In
the presence of MMAO, these complexes showed low to high
activities toward ethylene/NBE copolymerization and pro-
Figure 5. Plot of catalytic activities and molecular weights of the
resultant polyethylenes vs Al/Cr (molar ratio). Reaction conditions: 3
μmol of catalyst, ethylene at 5 atm, 10 min, 25 °C.
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a
Table 3. Copolymerization of Ethylene with NBE Using Chromium Complexes
b
b
c
entry
catalyst
Al/Cr (molar ratio)
NBE (mol/L)
yield (mg)
activity (kg/molCr h)
Mw (10−4
)
Mw/Mn
incorporation (mol %)
1
2
3
4
5
6
7
8
9
10
3c
3d
3f
1000
1000
1000
1000
1000
1000
500
0.50
0.50
0.50
0.25
0.75
1.00
0.50
0.50
0.50
0.50
260
85
1560
510
75
43
33
54
45
36
88
61
1.1
0.8
2.1
2.7
2.6
2.1
2.1
1.7
1.9
2.8
2.0
2.3
33.8
27.9
35.4
19.7
36.7
40.1
32.1
34.1
36.9
35.4
40
240
3c
3c
3c
3c
3c
4c
4d
385
185
60
2310
1110
360
140
575
490
505
840
2000
1000
1000
3450
2940
3030
a
b
Reaction conditions: 2 μmol catalysts, 5 atm of ethylene, MMAO as cocatalyst, 5 min, 25 °C, in toluene, Vtotal = 50 mL. Weight-average molecular
c
weights and polydispersity indexes determined by high temperature GPC at 150 °C in 1,2,4-C6Cl3H3 versus narrow polystyrene standards. NBE
content (mol %) estimated by 13C NMR spectra.
duced copolymers with high molecular weights and unimodal
molecular weight distributions.
It was revealed that 3c exhibited both high catalytic activity
and efficient NBE incorporation. The catalytic activity
decreased upon increasing the NBE concentration (entries 1
and 4−6). However, the molecular weights of the resultant
copolymers remarkably increased upon increasing the NBE
feed from 0.25 to 0.50 mol/L (entry 12 in Table 2 and entries 1
and 4 in Table 3). The maximum molecular weight value of the
resultant copolymer could reach 750000. The efficient synthesis
of high molecular weight copolymer with high NBE content
could thus be accomplished under the optimized conditions.
Interestingly, the molecular weights for the resultant copoly-
mers by 3c were highly dependent on the Al/Cr molar ratio.
The observed results were an interesting contrast to those
found in ethylene homopolymerization, in which the molecular
weight values changed slightly with the Al/Cr molar ratio.
Complexes 3d and 3f showed somewhat low catalytic activities
for ethylene and norbornene copolymerization under similar
conditions. The resultant copolymers possessed unimodal
molecular weight distributions, suggesting that the copoly-
merization took place with single catalytically active species.
Complexes 4c and 4d were chosen for comparison. The results
in the presence of MMAO were also summarized in Table 3.
Compared with [O,P] analogues 3c and 3d, complexes 4c and
4d showed high catalytic activities and relatively efficient NBE
incorporations, affording low molecular weight copolymers
with unimodal molecular weight distributions (entries 1−2 vs
10−11 in Table 3).
Figure 7. 13C NMR spectra of E/NBE copolymer with different NBE
incorporations produced by 3c (a: 33.8%, entry 1 and b: 19.7%, entry
4 in Table 3, respectively).
structure analyses showed that these complexes adopt a pseudo
octahedral coordination environment with a three-legged piano
stool geometry. Using MMAO as a cocatalyst, complexes 3a−3f
exhibited moderate to high catalytic activities for ethylene
polymerization, depending on ligand structure, and produced
high molecular weight polyethylenes. Introducing additional
oxygen atom in phenoxy-phosphine ligands resulted in
significant change on the aspect of the steric and electronic
effects around the metal center, which has an impact on the
polymerization behavior. Generally speaking, the [O,PO]
half-sandwich chromium(III) complexes displayed higher
catalytic activities than the [O,P] analogues, but they produced
much lower molecular weight polymers under similar
conditions. It should be noted that complex 3c could efficiently
promote ethylene/NBE copolymerization. To the best of our
knowledge, this is the rare example of a half-sandwich
chromium catalyst for ethylene/NBE copolymerization, which
produced high molecular weight poly(ethylene-co-NBE) with
high catalytic activity and efficient NBE incorporation.
13C NMR spectra for poly(ethylene-co-NBE)s showed that
the microstructures formed by 3c possessed isolated NBE units.
The peaks at 47.7, 42.2, and 33.5 ppm are assigned to C2/C3,
C1/C4, and C7, respectively. The signals stemming from C5/
C6 and short polyethylene sequences appeared at 30.1−30.7
ppm. E/NBE alternating sequence could be found for the
copolymers with high NBE incorporation (Figure 7a). No
resonances ascribed to repeated NBE insertion was observed.
The DSC thermograms for the resultant copolymers possessed
single Tg, and Tg values increased linearly upon increasing the
NBE content, strongly suggesting that the resultant copolymer
possessed uniform NBE incorporation.
EXPERIMENTAL SECTION
■
General Procedures and Materials. All manipulation of air-
and/or moisture-sensitive compounds was carried out under a dry
argon atmosphere by using standard Schlenk techniques or under a
dry argon atmosphere in a MBraun glovebox, unless otherwise noted.
All solvents were purified from a MBraun SPS system. The NMR data
of the ligands used were obtained on a Bruker-300 MHz spectrometer
at ambient temperature, with CDCl3 as the solvent (dried by MS 4 Å).
The NMR data of the copolymers were obtained on a Bruker-400
CONCLUSIONS
■
We prepared and characterized a series of novel half-sandwich
chromium(III) complexes bearing phenoxy-phosphine [O,P]
ligands or phenoxy-phosphine oxide [O,PO] ligands. X-ray
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MHz spectrometer at 135 °C, with o-C6D4Cl2 as a solvent. Mass
spectra were obtained using electron impact (EI-MS). The 19F NMR
spectra of the complexes were recorded on a Bruker 400 MHz
spectrometer. 19F NMR spectra of the complexes were recorded with
fluorobenzene as the internal standard (δF = −112.6 ppm). UV−vis
spectra were taken on a Shimadzu UV-2450 UV−vis spectropho-
tometer. Magnetic susceptibilities were measured with a SQUID
magnetometer (Quantum Design, MPMS-LS). Elemental analyses
were recorded on an elemental Vario EL spectrometer. The IR spectra
of complexes were recorded on a Bio-Rad FTS-135 spectropho-
tometer. The weight-average molecular weights (Mw) and the
polydispersity indices (PDIs) of 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.). The 2.20 M n-butyllithium solution in hexane
was purchased from Acros. Modified methylaluminoxane (MMAO, 7%
aluminum in heptane solution) was purchased from Akzo Nobel
Chemical Inc. Commercial ethylene was directly used for polymer-
ization without further purification.
= 484 [M+]. Anal. Calcd for C27H27ClCrOP: C, 66.74; H, 5.60. Found:
C, 66.61; H, 5.65. UV−vis (hexane): 265, 306 nm. Magnetic
measurement: μeff (300 K) = 3.24 μB.
Synthesis of Chromium Complex 3d Cp[O-2,4-tBu2-6-(Ph2P)-
C6H2]CrCl. The complex was carried out according to the same
procedure as that of 3a, except that 2,4-tBu2-6-(Ph2P)C6H2OH (0.78
g, 2.0 mmol) was used in place of 6-(Ph2P)C6H4OH. Pure products
were obtained as dark green crystals (0.76 g, 70%). FT-IR (KBr,
cm−1): 3055, 2951, 2867, 1954, 1480, 1463, 1436, 1427, 1385, 1361,
1298, 1251, 1203, 1138, 1111, 1096, 1020, 1008, 998, 916, 879, 835,
814, 771, 744, 698, 654. EI-MS (70 eV): m/z = 541 [M+]. Anal. Calcd
for C31H35ClCrOP: C, 68.69; H, 6.51. Found: C, 68.54; H, 6.55. UV−
vis (hexane): 265, 306 nm. Magnetic measurement: μeff (300 K) = 3.28
μB.
Synthesis of Chromium Complex 3e Cp[O-2-F-6-(Ph2P)C6H3]CrCl.
The complex was carried out according to the same procedure as that
of 3a, except that 2-F-6-(Ph2P)C6H3OH (0.59 g, 2.0 mmol) was used
in place of 6-(Ph2P)C6H4OH. Pure products were obtained as green
crystals (0.72 g, 75%). 19F NMR (376.5 MHz, CDCl3): δ −138.6. FT-
IR (KBr, cm−1): 3055, 1596, 1464, 1438, 1315, 1296, 1256, 1232,
1179, 1095, 1063, 1020, 899, 844, 827, 776, 745, 737, 691. EI-MS (70
eV): m/z = 446 [M+]. Anal. Calcd for C23H18ClCrFOP: C, 61.69; H,
4.05. Found: C, 61.81; H, 4.01. UV−vis (hexane): 259, 349 nm.
Magnetic measurement: μeff (300 K) = 3.18 μB.
Synthesis of Chromium Complex 3f Cp[O-2-C6F5-6-(Ph2P)C6H3]-
CrCl. The complex was carried out according to the same procedure as
that of 3a, except that 2-C6F5-6-(Ph2P)C6H3OH (0.89 g, 2.0 mmol)
was used in place of 6-(Ph2P)C6H4OH. Pure products were obtained
as blue crystals (0.91 g, 76%). 19F NMR (376.5 MHz, CDCl3): δ
−162.2, −153.8. FT-IR (KBr, cm−1): 3087, 1582, 1557, 1518, 1493,
1468, 1436, 1413, 1323, 1281, 1263, 1228, 1181, 1098, 1069, 1019,
988, 904, 850, 822, 767, 755, 749, 739, 694, 654. EI-MS (70 eV): m/z
= 594 [M+]. Anal. Calcd for C29H18ClCrF5OP: C, 58.45; H, 3.04.
Found: C, 58.62; H, 2.98. UV−vis (hexane): 268, 304 nm. Magnetic
measurement: μeff (300 K) = 3.22 μB.
Synthesis of Chromium Complex 4b Cp[O-2-Ph-6-(Ph2PO)-
C6H3]CrCl. The complex was carried out according to the same
procedure as that of 3a, except that 2-Ph-6-(Ph2PO)C6H3OH (0.74
g, 2.0 mmol) was used in place of 6-(Ph2P)C6H4OH. Pure products
were obtained as blue crystals (0.76 g, 73%). FT-IR (KBr, cm−1):
3054, 2956, 1768, 1581, 1554, 1494, 1484, 1447, 1438, 1411, 1313,
1297, 1261, 1204, 1123, 1065, 1050, 1022, 998, 861, 814, 752, 726,
696. EI-MS (70 eV): m/z = 520 [M+]. Anal. Calcd for
C29H23ClCrO2P: C, 66.74; H, 4.44. Found: C, 66.91; H, 4.49. UV−
vis (hexane): 265, 334 nm. Magnetic measurement: μeff (300 K) = 3.27
μB.
Synthesis of Compounds 1a−1f and 2b−2e. Various phenoxy-
phosphine [O,P] ligands and phenoxy-phosphine oxide [O,PO]
ligands bearing different substituents on R1 and R2 positions, 2-R1-4-
R2-6-(Ph2P)C6H2OH (3a: R1 = R2 = H; 3b: R1 = Ph, R2 = H; 3c: R1 =
tBu, R2 = H; 3d: R1 = R2 = tBu; 3e: R1 = F, R2 = H; 3f: R1 = C6F5, R2 =
H) and 2-R1-4-R2-6-(Ph2PO)C6H2OH (4b: R1 = Ph, R2 = H; 4c: R1
= tBu, R2 = H; 4d: R1 = R2 = tBu; 4e: R1 = F, R2 = H) were prepared
according to literature procedures.31
Synthesis of Complexes 3a−3f and 4b−4c. Synthesis of
Chromium Complex 3a Cp[O-6-(Ph2P)C6H4]CrCl. A suspension of
CpLi (0.15 g, 2.00 mmol) in THF (10 mL) was slowly added to a
purple suspension of CrCl3(THF)3 (0.75 g, 2.00 mmol) in THF (20
mL) at 0 °C. The mixture was warmed to room temperature and
stirred overnight to get a blue solution. In another flask, a solution of
n-BuLi (2.20 M, 2.00 mmol) in hexane was added to a solution of 1a
(0.56 g, 2.00 mmol) in dried THF (20 mL) at −78 °C. The reaction
mixture was allowed to warm to room temperature and stirred for 2.5
h and then added slowly to the above reaction mixture at −78 °C. The
obtained reaction mixture was allowed to warm to room temperature
and was stirred overnight. During the reaction, the color of the
reaction mixture changes from blue to green. Next, the reaction
mixture was filtered by cannula filtration, and the filtrate was
concentrated in vacuo to about 5 mL. Then, hexane (20 mL) was
added into the system at room temperature. Green solids were
precipitated from the solution, which were isolated via filtration and
washed several times by cold hexane to yield 0.57g (66%) of complex
3a. Compounds 3b−3f and 4b−4c were prepared in similar methods.
FT-IR (KBr, cm−1): 3050, 1582, 1548, 1480, 1453, 1440, 1303, 1263,
1243, 1185, 1155, 1125, 1096, 1058, 1026, 850, 813, 744, 693. EI-MS
(70 eV): m/z = 428 [M+]. Anal. Calcd for C23H19ClCrOP: C, 64.27;
H, 4.46. Found: C, 64.13; H, 4.50. UV−vis (hexane): 267, 298 nm.
Magnetic measurement: μeff (300 K) = 3.15 μB.
Synthesis of Chromium Complex 3b Cp[O-2-Ph-6-(Ph2P)C6H3]-
CrCl. The complex was carried out according to the same procedure as
that of 3a, except that 2-Ph-6-(Ph2P)C6H3OH (0.71 g, 2.0 mmol) was
used in place of 6-(Ph2P)C6H4OH. Pure products were obtained as
dark green crystals (0.74 g, 73%). FT-IR (KBr, cm−1): 3055, 1577,
1553, 1496, 1480, 1448, 1434, 1400, 1290, 1251, 1201, 1182, 1159,
1095, 1021, 1007, 851, 822, 749, 694, 627. EI-MS (70 eV): m/z = 504
[M+]. Anal. Calcd for C29H23ClCrOP: C, 68.85; H, 4.58. Found: C,
68.98; H, 4.54. UV−vis (hexane): 253, 291 nm. Magnetic measure-
ment: μeff (300 K) = 3.12 μB.
Synthesis of Chromium Complex 4c Cp[O-2-tBu-6-(Ph2P
O)C6H3]CrCl. The complex was carried out according to the same
procedure as that for 3a, except that 2-tBu-6(Ph2PO)C6H3OH (0.70
g, 2.0 mmol) was use in place of 6-(Ph2P)C6H4OH. Pure products
were obtained as dark blue crystals (0.75 g, 75%). FT-IR (KBr, cm−1):
3088, 3058, 2978, 2939, 2897, 1575, 1552, 1483, 1460, 1437, 1407,
1386, 1350, 1291, 1264, 1198, 1185, 1166, 1121, 1051, 1022, 1010,
997, 876, 854, 813, 799, 766, 755, 730, 693. EI-MS (70 eV): m/z =
500 [M+]. Anal. Calcd for C27H27ClCrO2P: C, 64.61; H, 5.42. Found:
C, 64.77; H, 5.48. UV−vis (hexane): 266, 294 nm. Magnetic
measurement: μeff (300 K) = 3.18 μB.
Synthesis of Chromium Complex 4d Cp[O-2,4-tBu2-6-(Ph2P
O)C6H2]CrCl. The complex carried out according to the same
procedure as that for 3a, except that 2,4-tBu2-6(Ph2PO)C6H3OH
(0.81 g, 2.0 mmol) was used in place of 6(Ph2PO)C6H4OH. Pure
products were obtained as blue solids (0.88 g, 79%). FT-IR (KBr,
cm−1): 3078, 3058, 2954, 2904, 2867, 1770, 1594, 1536, 1406, 1438,
1426, 1385, 1361, 1301, 1253, 1202, 1120, 1059, 1021, 1011, 998, 916,
884, 871, 839, 807, 787, 775, 755, 726, 692. EI-MS (70 eV): m/z =
557 [M+]. Anal. Calcd for C31H35ClCrO2P: C, 66.72; H, 6.32. Found:
C, 66.54; H, 6.27. UV−vis (hexane): 266, 306 nm. Magnetic
measurement: μeff (300 K) = 3.21 μB.
Synthesis of Chromium Complex 3c Cp[O-2-tBu-6-(Ph2P)C6H3]-
CrCl. The complex was carried out according to the same procedure as
that of 3a, except that 2-tBu-6-(Ph2P)C6H3OH (0.67 g, 2.0 mmol) was
used in place of 6-(Ph2P)C6H4OH. Pure products were obtained as
dark green crystals (0.66 g, 68%). FT-IR (KBr, cm−1): 3050, 2952,
1577, 1549, 1483, 1457, 1436, 1402, 1382, 1353, 1294, 1260, 1251,
1191, 1110, 1096, 1081, 871, 844, 755, 741, 693. EI-MS (70 eV): m/z
Synthesis of Chromium Complex 4e Cp[O-2-F-6-(Ph2PO)C6H3]-
CrCl. The complex was carried out according to the same procedure as
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Organometallics
Article
that of 3a, except that 2-F-6-(Ph2P)C6H3OH (0.62 g, 2.0 mmol) was
used in place of 6-(Ph2P−O)C6H4OH. Pure products were obtained
as blue solids (0.68 g, 75%). 19F NMR (376.5 MHz, CDCl3): δ
−134.8. FT-IR (KBr, cm−1): 3057, 2961, 1599, 1465, 1441, 1309,
1264, 1234, 1191, 1120, 1068, 1014, 998, 855, 811, 743, 725, 704, 695.
EI-MS (70 eV): m/z = 462 [M+]. Anal. Calcd for C23H18ClCrFO2P:
C, 59.56; H, 3.91. Found: C, 59.68; H, 4.01. UV−vis (hexane): 265,
317 nm. Magnetic measurement: μeff (300 K) = 3.26 μB.
X-ray Crystallography. Single crystal of complexes 3b, 3c, 3e, and
4c suitable for X-ray structure determination were grown from hexane
solution at −20 °C in a glovebox, thus maintaining a dry, O2-free
environment. 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 = 0.71073 Å). Lorentz, polarization factors
were made for the intensity data, and absorption corrections were
performed using SADABS. 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.
Ethylene (Co)polymerization. A typical procedure was per-
formed as follows: the prescribed amounts of toluene and MMAO and
NBE if necessary were added into the autoclave (200 mL, stainless
steel), and the apparatus was then purged with ethylene. The reaction
mixture was then pressurized to the prescribed ethylene pressure soon
after the addition of a toluene solution containing metal complex. The
polymerization was terminated with the addition of EtOH, and the
resultant polymer was adequately washed with EtOH containing HCl
and then dried under vacuum for several hours.
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ASSOCIATED CONTENT
* Supporting Information
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23, 5681−5688.
■
S
(19) Ogata, K.; Nakayama, Y.; Yasuda, H. J. Polym. Sci., Part A 2002,
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Crystal data and structure refinements of complexes 3b, 3c, 3e,
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and PDF files). This material is available free of charge via the
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AUTHOR INFORMATION
Corresponding Author
*E-mail: ljy@ciac.jl.cn.
(22) Randoll, S.; Jones, P. G.; Tamm, M. Organometallics 2008, 27,
3232−3239.
■
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Am. Chem. Soc. 2007, 129, 2236−2237. (b) Sun, M. T.; Xu, T. Q.;
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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The authors are grateful for financial support by the National
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21234006).
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