Synthesis and characterization of novel half-metallocene-type group IV complexes containing phosphine oxide - Phenolate chelating ligands and their application to ethylene polymerization

Article abstract of DOI:10.1021/om200317x

A series of novel half-metallocene-type group IV metal complexes containing phosphine oxide-phenolate chelating ligands of type CpMCl₂[O-2R ₁-4R₂-6(Ph₂P=O)C₆H₂] (Cp = C₅H₅, M = Ti, 2a: R₁ = R₂ = H; 2b: R₁ = Ph, R₂ = H; 2c: R₁ = ^tBu, R₂ = H; 2d: R₁ = R₂ = ^tBu; M = Zr, 3b: R₁ = Ph, R₂ = H; 3c: R₁ = ^tBu, R₂ = H; 3d, R₁ = R₂ = ^tBu) have been synthesized in high yields (60-76%) from CpMCl₃ (M = Ti, Zr) with 1.0 equiv of 2R₁-4R₂-6(Ph₂P=O)C ₆H₂OH in THF and in the presence of triethylamine, and the complexes were identified by NMR and mass spectra as well as elemental analysis. Structures for 2a-d and 3d were further confirmed by X-ray crystallography. Complexes 2a-d adopt a five-coordinate, distorted square-pyramidal geometry around the titanium center. Complex 3d has a six-coordinate, distorted octahedral geometry around the zirconium center, in which the equatorial positions are occupied by oxygen atoms of the chelating phosphine oxide-phenolate ligand and two chlorine atoms. The cyclopentadienyl ring and the oxygen atom of the THF molecule are coordinated on the axial position. When activated by modified methylaluminoxane, all complexes exhibited moderate to high activities toward ethylene polymerization, giving high molecular weight polymer with a unimodal molecular weight distribution. The substituents on ligands and the metal center as well as the reaction conditions have a profound effect on the polymerization. It should be noted that zirconium complexes 3b-d displayed notable ethylene polymerization activity even at high temperature (75 C). Moreover, using Ph₃CB(C₆F ₅)₄/i-Bu₃Al in place of MMAO as a cocatalyst, 3b-d also generate high molecular weight polymer with high efficiency under the same conditions.

Full text of DOI:10.1021/om200317x

ARTICLE
pubs.acs.org/Organometallics
Synthesis and Characterization of Novel Half-Metallocene-Type Group
IV Complexes Containing Phosphine OxideꢀPhenolate Chelating
Ligands and Their Application to Ethylene Polymerization
Jing-Yu Liu, San-Rong Liu, Bai-Xiang Li, Yan-Guo Li, 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
S Supporting Information
b
ABSTRACT: A series of novel half-metallocene-type group IV metal complexes
containing phosphine oxideꢀphenolate chelating ligands of type CpMCl2[O-2R1-
4R2-6(Ph2PdO)C6H2] (Cp = C5H5, M = Ti, 2a: R1 = R2 = H; 2b: R1 = Ph, R2 = H;
2c: R1 = tBu, R2 = H; 2d: R1 = R2 = tBu; M = Zr, 3b: R1 = Ph, R2 = H; 3c: R1 = tBu, R2
t
= H; 3d, R1 = R2 = Bu) have been synthesized in high yields (60ꢀ76%) from
CpMCl3 (M = Ti, Zr) with 1.0 equiv of 2R1-4R2-6(Ph2PdO)C6H2OH in THF and
in the presence of triethylamine, and the complexes were identified by NMR and
mass spectra as well as elemental analysis. Structures for 2aꢀd and 3d were further
confirmed by X-ray crystallography. Complexes 2aꢀd adopt a five-coordinate, distorted square-pyramidal geometry around the
titanium center. Complex 3d has a six-coordinate, distorted octahedral geometry around the zirconium center, in which the
equatorial positions are occupied by oxygen atoms of the chelating phosphine oxideꢀphenolate ligand and two chlorine atoms. The
cyclopentadienyl ring and the oxygen atom of the THF molecule are coordinated on the axial position. When activated by modified
methylaluminoxane, all complexes exhibited moderate to high activities toward ethylene polymerization, giving high molecular
weight polymer with a unimodal molecular weight distribution. The substituents on ligands and the metal center as well as the
reaction conditions have a profound effect on the polymerization. It should be noted that zirconium complexes 3bꢀd displayed
notable ethylene polymerization activity even at high temperature (75 °C). Moreover, using Ph3CB(C6F5)4/i-Bu3Al in place of
MMAO as a cocatalyst, 3bꢀd also generate high molecular weight polymer with high efficiency under the same conditions.
’ INTRODUCTION
(Cp0Ti(NPR3)X2) and explored the effect of the substituents on
both Cp0 and NPR3 groups for the catalytic activity in ethylene
polymerization. These complexes exhibited remarkable activities
for ethylene polymerization in the presence of MAO, and the
activity improved with the combination of borate compound
[Ph3C][B(C6F5)4].3 Sita and co-workers focused on (un)sym-
metrically substituted acetamidinato ligands to prepare various
half-metallocene-type group IV metal complexes.4 They utilized
chiral metal compounds to achieve the living stereoselective poly-
merization of 1-alkenes.
We are also interested in the design and synthesis of efficient
nonbridged half-metallocene transition metal catalysts for pre-
cise, controlled olefin polymerization. We reported a series of
titanium complexes with cyclopentadienyl and β-enaminoketo-
nato ligands, which display an effective ability to copolymerize
ethylene with norbornene and produce high molecular weight
cyclic olefin copolymers.16 Our recent research indicated phos-
phine oxide-bridged phenolato ligands appeared attractive due to
the fact that the neutral PdO donor in phenoxide ligands plays
an important role in stabilizing the active species.19 We became
attracted to building on this platform to prepare a new family of
Over the past decades, a significant amount of research has
focused on the development of well-defined, single-site transition
metal catalysts for olefin polymerization. Among them, group IV
transition metal complexes bearing one or two cyclopentadienyl
ligands are an important class of the new generation of polymer-
ization catalysts.1 Half-sandwich titanium amide (“constrained
geometry”) catalysts (CGC) constitute a typical example that is
currently in commercial use. The remarkable success of CGC has
spurred the expansion of monocyclopentadienyl complexes. Re-
cently, many examples of Cp0M(L)X2 compounds containing
monodentate or bidentate anionic ligands have been reported.2ꢀ18
In conjunction with cocatalysts such as methylaluminoxane
(MAO), triphenylcarbenium tetrakis(pentafluorophenyl)borate
([Ph3C]+[B(C6F5)4]ꢀ), or tris(pentafluorophenyl)borane
(B(C6F5)3), many of these complexes exhibited appreciable
catalyticactivities for olefinpolymerization. Nomuraet al. reported
that half-titanocenes containing an aryloxo ligand of the type
Cp0TiCl2(OAr) (Cp0 = cyclopentadienyl group; OAr = aryloxo
group, O-2,6-iPr2C6H3, etc.) exhibited not only notable catalytic
activities for olefin polymerization but also efficient comonomer
incorporations for ethylene with R-olefin, styrene, and/or cyclic
olefin copolymerization.2a,b Stephan and co-workers synthesized a
series of cyclopentadienyl-phophinimide titanium(IV) complexes
Received: April 13, 2011
Published: July 13, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/om200317x Organometallics 2011, 30, 4052–4059
|

Organometallics
ARTICLE
half-metallocene-type group IV complexes containing [O,PdO]
ligands. Herein, we thus describe the synthesis and characteriza-
tion of a number of novel complexes with cyclopentadienyl and
phosphine oxideꢀphenolate chelating ligands (Scheme 1). Mod-
ification in the metal center and ligand architecture results in
changes in catalytic activity and the molecular weight of the
resultant polymer. We also report the effects observed on
variation of the reaction conditions.
dichloromethane and hexane solution placed in the freezer
1
(ꢀ20 °C). The resultant complexes were identified by H and
13C NMR spectra, mass spectra, and elemental analysis. The 1H
NMR spectra of these complexes showed no complexity; a sharp
single resonance assigned to the C5H5(Cp) protons and reso-
nances corresponding to the ligand were observed. Integration
1
of the H NMR spectra of complexes confirms a 1:1 ratio
of cyclopentadienyl to phosphine oxideꢀphenolate chelating
ligand. Crystals of 2aꢀd suitable for crystallographic analysis
were grown from the chilled, concentrated CH2Cl2ꢀhexane
mixture solution. Colorless block microcrystal of 3d suitable
for X-ray crystallographic analysis was grown from the chilled,
concentrated THFꢀhexane mixture solution. The crystallo-
graphic data together with the collection and refinement para-
meters are summarized in Table 1.
Structures for 2aꢀc are shown in Figures 1ꢀ3, and the
selected bond distances and angles for 2aꢀc are summarized
in Table 2. If the centroid of the cyclopentadienyl ring is
considered as a single coordination site, complexes 2aꢀc all
adopt five-coordinate, distorted square-pyramidal geometry
around the titanium center in which the equatorial positions
are occupied by two oxygen atoms and two chlorine atoms. The
cyclopentadienyl group is coordinated on the axial position. The
TiꢀCp (centroid) distance in 2aꢀc (2a: 2.037, 2b: 2.042, 2c:
2.043 Å) is somewhat longer than that in CpTiCl2[PhNdC-
(CF3)CHC(tBu)O] (1, 2.033 Å).16 The TiꢀO(1) bond length
is obviously affected by the R1 group in the ligand (2a:
2.0809(16), 2b: 2.066(12), 2c: 2.0509(12) Å). The TiꢀO(1)
bond distances in these complexes are in the range 2.0509ꢀ
2.0809 Å, indicative of significant coordination of the oxygen
atom in the phenylphosphinyl moiety to the metal center in the
solid state. However, the TiꢀO(2) and O(2)ꢀC(19) bond
lengths in 2aꢀc change slightly with the variation in R1 groups,
as shown in Table 2.
’ RESULTS AND DISCUSSION
Synthesis and Structural Analysis of Complexes CpMCl2-
[O-2R1-4R2-6(Ph2PdO)C6H2]. A series of titanium and zirco-
nium complexes containing phosphine oxideꢀphenolate
chelating ligands of type CpMCl2[O-2R1-4R2-6(Ph2PdO)-
C6H2] (Cp = C5H5, M = Ti, 2a: R1 = R2 = H; 2b: R1 = Ph,
R2 = H; 2c: R1 = tBu, R2 = H; 2d: R1 = R2 = tBu; M = Zr, 3b: R1 =
Ph, R2 = H; 3c: R1 = tBu, R2 = H; 3d, R1 = R2 = tBu)) have been
prepared in high yields (60ꢀ76%) from CpMCl3 with 1.0 equiv
of 2R1-4R2-6(Ph2PdO)C6H2OH in tetrahydrofuran and in the
presence of triethylamine, as shown in Scheme 1. These reactions
took place along with evolution of NH4Cl, and pure samples
were collected from the chilled, concentrated mixture of
Scheme 1. Synthesis of Half-Metallocene Complexes
Table 1. Crystal Data and Structure Refinements of Complexes 2aꢀd and 3d
2a
2b
2c
2d
3d
empirical formula
fw
C
23H19Cl2O2PTi
C29H23Cl2O2PTi
553.24
C27H27Cl2O2PTi
533.25
C31H35Cl2O2PTi
589.36
C31H35Cl2O2PZr
632.71
477.14
cryst syst
space group
a (Å)
triclinic
triclinic
triclinic
triclinic
orthorhombic
Iba2
P1
P1
P1
P1
10.6152(5)
12.100(1)
12.4094(6)
103.747(1)
108.377(1)
103.579(1)
1383.89(15), 2
1.535
9.8668(9)
10.3366(10)
17.1795(16)
73.720(1)
77.134(1)
89.696(1)
1636.6(3), 2
1.467
10.4659(4)
11.4478(5)
13.8469(6)
84.576(1)
84.480(1)
69.257(1)
1541.02(11), 2
1.348
10.5395(8)
18.0015(14)
21.3304(16)
66.943(1)
87.971(1)
73.780(1)
3562.9(5), 4
1.270
37.906(2)
10.3445(7)
19.7199(13)
90.00
b (Å)
c (Å)
R (deg)
β (deg)
90.00
γ (deg)
90.00
V (Å3), Z
densitycalcd (Mg/m3)
7732.5(9), 8
1.335
absorp coeff (mmꢀ1
)
0.969
0.828
0.533
0.466
0.501
F(000)
656
736
652
1432
3248
cryst size (mm)
0.32 ꢁ 0.28 ꢁ 0.17
2.12 to 26.12
7785
0.21 ꢁ 0.18 ꢁ 0.10
2.06 to 25.00
8524
0.29 ꢁ 0.178 ꢁ 0.09
1.91 to 26.08
8633
0.21 ꢁ 0.14 ꢁ 0.07
1.95 to 26.10
16 844
0.21 ꢁ 0.14 ꢁ 0.10
2.04 to 25.04
20 561
θ range for data collection (deg)
reflns collected
indep reflns
5439 (Rint = 0.0135)
5439/0/316
1.065
5683 (Rint = 0.0214)
5683/0/370
1.015
6027 (Rint = 0.0134)
6027/0/365
1.046
12 563 (Rint= 0.0304)
12 563/9/724
1.035
6481 (Rint = 0.0527)
6481/2/393
1.145
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]: R1, wR2
0.0366, 0.0954
1.572 and ꢀ0.790
0.0511, 0.1223
0.693 and ꢀ0.390
0.0317, 0.0798
0.377 and ꢀ0.266
0.0612, 0.1529
1.352 and ꢀ1.187
0.0682, 0.1718
3.619 and ꢀ0.967
largest diff peak and hole (e Åꢀ3
)
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Organometallics
ARTICLE
For cyclopentadienyl phosphine oxide-bridged phenolato tita-
nium dichloride 2d (Figure 4), the asymmetric unit consists of
two virtually identical molecules, which is somewhat analogous
to that in Cp{2-tBu-6-(RNCH)C6H3O}TiCl2 (2) reported by
Bochmann.14 In each, the Ti atom is five-coordinate with the Cp
ligand in the apical site of a distorted square-pyramidal geometry.
The Ti(1)ꢀO(2) and P(1)ꢀO(1) bond distance in 2d(A)
(1.855(3) and 1.509(3) Å) and the Ti(2)ꢀO(4) and P(2)ꢀO(3)
bond distances in 2d(B) (1.862(3) and 1.510(3) Å) are shorter
than those in 2aꢀc. The bond angles for Ti(1)ꢀO(1)ꢀP(1)
and Ti(1)ꢀO(2)ꢀC(19) in 2d(A) (134.83(17)°, 148.4(3)°)
and Ti(2)ꢀO(3)ꢀP(2) and Ti(2)ꢀO(4)ꢀC(50) in 2d(B)
(134.44(18)°, 146.4(3)°) are much larger than those in other
complexes. The O,PdO-chelating ligand forms a plane that
includes the phenoxide ring, the ꢀPdO group, and four carbon
atoms from two tert-butyl groups (C(24), C(26) and C(28),
C(29) in 2d(A); C(55), C(57) and C(59), C(60) in 2d(B));
the other four methyl groups are on either side of the plane.
Therefore, 2d displays a much smaller torsion angle (the torsion
angle is the angle Ti(1)ꢀO(2)ꢀC(19)ꢀC(18) in 2d(A), 12.40°;
Ti(2)ꢀO(4)ꢀC(50)ꢀC(49) in 2d(B), 18.33°) than 2c
(TiꢀO(2)ꢀC(19)ꢀC(18) in 2c, 48.19°). The observed differ-
ences between 2c and 2d may be due to the influence from the
substituent in the R2 position of the ligands (H vs tBu). The TiꢀCp
distance in 2aꢀd (2.033ꢀ2.049 Å) is normal and compares well
with values observed in Ti(IV) η-cyclopentadienyl complexes.20
The complexes 2aꢀc possess a similar spatial disposition regarding
the Ti, O, and Cl atoms and the Cp group. An inspection of
Figure 4 indicates that the steric environments around the Cl-
bound sites (i.e., potential polymerization sites) are somewhat
different among the complexes. The distances between the Cl
and its nearest C atom in the R1 group are 3.81 Å (C(29)ꢀCl(1)
in 2b), 4.05 Å (C(25)ꢀCl(1) in 2c), and 3.66 and 3.77 Å
Figure 1. Molecular structure of complex 2a with thermal ellipsoids at
Figure 3. Molecular structure of complex 2c with thermal ellipsoids at
30% probability level. Hydrogen atoms are omitted for clarity.
30% probability level. Hydrogen atoms are omitted for clarity.
Figure 2. Molecular structure of complex 2b with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity.
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Organometallics
ARTICLE
(C(27)ꢀCl(1) and C(58)ꢀCl(3) in 2d), suggesting that complex
2d provides the largest steric hindrance to the Cl atom.
The structure of 3d is shown in Figure 5. Complex 3d has a six-
coordinate, distorted octahedral geometry around Zr, in which
the equatorial positions are occupied by oxygen atoms of the
chelating phosphine oxide-bridged phenolato ligand and two
chlorine atoms. The cyclopentadienyl ring and the oxygen atom
of the THF molecule are coordinated at the axial position. The
two chlorine atoms and two oxygen atoms are in a cis position to
each other. The bond angle for Cl(1)ꢀZrꢀCl(2) (95.90(6)°) in
Zr complex 3d is larger than Cl(1)ꢀTiꢀCl(2) (85.31(5)°,
85.02(5)°) in the corresponding Ti complex. Moreover, the
torsion angle in 3d (ZrꢀO(2)ꢀC(19)ꢀC(18), 29.28°) is much
larger than that in 2d. These results are to be expected when the
atomic radii of the two metal atoms and the crystal structures are
considered. Attempts to synthesize complex CpZrCl2[6-P-
(dO)Ph2-C6H2O] (3a) were unsuccessful. Some unidentified
products were obtained when the reaction was conducted under
similar conditions.
Ethylene Polymerization Catalyzed by 2aꢀd. Ethylene
polymerizations by CpTiCl2[2-R1-4-R2-6-P(dO)Ph2-C6H2O]
(2aꢀd) in the presence of modified methylaluminoxane
(MMAO) were examined to explore the effect of the steric
environments near the polymerization center on the catalytic
activity (ethylene 4 atm, under the optimized Al/Ti molar ratio),
and typical results are summarized in Table 3. These data
demonstrate that changing the substituents at the R1 and R2
positions significantly affects the polymerization behaviors.
Complex 2a showed moderate catalytic activity for ethylene
polymerization, affording high molecular weight (MW) poly-
mers with unimodal molecular weight distributions (MWDs)
(entry 1). Introducing a conjugated phenyl group in the R1
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Complexes 2aꢀc
2a
2b
2c
Bond Distances
2.0809(16)
1.8920(16)
2.3610(7)
2.3513(7)
2.037
TiꢀO(1)
2.066(2)
1.898(2)
2.3576(11)
2.3575(11)
2.043
2.0509(12)
1.8993(12)
2.3531(5)
2.3620(5)
2.043
TiꢀO(2)
TiꢀCl(1)
TiꢀCl(2)
TiꢀCp(centroid)
PꢀO(1)
1.5237(16)
1.778(2)
1.522(2)
1.785(4)
1.344(4)
1.5217(12)
1.7782(17)
1.345(2)
PꢀC(18)
O(2)ꢀC(19)
1.346(3)
Bond Angles
82.61(6)
O(1)ꢀTiꢀO(2)
Cl(1)ꢀTiꢀCl(2)
TiꢀO(1)ꢀP
82.09(9)
85.36(4)
127.84(14)
134.6(2)
85.08(7)
134.50(8)
144.78(8)
80.69(7)
108.61(15)
114.9(3)
118.9(3)
82.67(5)
85.38(2)
84.955(19)
129.18(7)
138.44(10)
85.55(4)
126.39(9)
134.54(15)
84.72(5)
position (2b) decreased the activity (2a, 300 kg/molTi h; 2b,
3
TiꢀO(2)ꢀC(19)
O(2)ꢀTiꢀCl(1)
O(2)ꢀTiꢀCl(2)
O(1)ꢀTiꢀCl(1)
O(1)ꢀTiꢀCl(2)
O(1)ꢀPꢀC(18)
PꢀC(18)ꢀC(19)
O(2)ꢀC(19)ꢀC(18)
200 kg/molTi h). Alternatively, replacement of H at the R1
3
position in complex 2a with a tert-butyl group (2c and 2d)
enhanced catalytic activities. Complex 2d, bearing tert-butyl
groups in both the R1 and R2 position, exhibited the highest
132.54(5)
146.18(5)
80.47(5)
136.11(4)
143.23(4)
79.89(4)
activities among the four catalysts (860 kg/molTi h at 25 °C).
3
109.50(10)
114.45(17)
119.3(2)
110.51(7)
115.82(13)
118.26(15)
These data suggest that the steric bulk effect was not important,
but the electron-donating effect of the aliphatic group plays a key
role in the enhanced catalytic activity.
Figure 4. Molecular structure of complex 2d with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (deg): Ti(1)ꢀO(1) 2.059(3); Ti(1)ꢀO(2) 1.855(3); Ti(1)ꢀCl(1) 2.3841(13); Ti(1)ꢀCl(2) 2.3417(13); P(1)ꢀO(1)
1.509(3); P(1)ꢀC(18) 1.780(4); Ti(2)ꢀO(3) 2.066(3); Ti(2)ꢀO(4) 1.862(3); Ti(2)ꢀCl(3) 2.3829(14); Ti(2)ꢀCl(4) 2.3279(14); P(2)ꢀO(3)
1.510(3); P(2)ꢀC(49) 1.781(4); O(1)ꢀTi(1)ꢀO(2) 82.15(11); Cl(1)ꢀTi(1)ꢀCl(2) 85.31(5); Ti(1)ꢀO(1)ꢀP(1) 134.83(17); O(3)ꢀTi(2)ꢀO-
(4) 81.31(12); Cl(3)ꢀTi(2)ꢀCl(4) 85.02(5); Ti(2)ꢀO(3)ꢀP(2) 134.44(18).
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Organometallics
ARTICLE
Due to better performance observed by the catalyst containing
an ortho- and para-tBu substituent, catalyst 2d was investigated in
detail by changing the reaction parameters such as Al/Ti ratio,
temperature, and ethylene pressure. The polymerization results
are depicted in Table 3. The increase in Al/Ti ratio from 500 to
3000 did not change either the catalytic activity or the MWs for
the resultant polymers. This result suggests that the dominant
chain-transfer pathway is not chain transfer to aluminum alkyls
but seems to be β-hydrogen transfer under these conditions.
Complex 2d was found to display a relatively high activity of 980
above suggestion that the dominant chain transfer would be the
β-hydrogen transfer from propagating metalꢀalkyl species.
Ethylene Polymerization Catalyzed by 3bꢀd. Zirconium
complexes 3bꢀd were also investigated as ethylene polymeriza-
tion catalysts. A series of experiments were undertaken to
determine the effect of temperature variation on catalyst perfor-
mance. Table 4 shows the results of polymerizations performed
at three different temperatures (50, 75, and 100 °C), and
75 °C seems favored for 3bꢀd under these conditions. The
t
Ph analogue (3b) and Bu analogue (3c) showed remarkable
kg/mol molTi h at 0 °C, which was ca. 7 times larger than that
catalytic activities under the optimized conditions (3b, 4940 kg/
molZr h; 3c, 5860 kg/molZr h). Complex 3d showed somewhat
low catalytic activities for ethylene polymerization (3740 kg/
3
exhibited at 50 °C. Upon increasing ethylene pressure, the
polymer yield increased, but the molecular weight changed only
slightly (entry 12 in Table 3). These results also support the
3
3
molZr h). The observed results were an interesting contrast to
3
those found for 2aꢀd, in which 2d exhibited the highest catalytic
activities for ethylene polymerization. A decrease in the activity of
3bꢀd was found if the polymerization was conducted at 100 °C,
maybe due to the deactivation of catalyst. Complex 3d afforded
relatively high molecular weight polymers at 75 and 100 °C,
which suggests that increasing the steric bulk in the phosphine
oxideꢀphenolate chelating ligand can effectively restrain the
chain-transfer reaction even at high temperature. The polydis-
persity indices (PDIs) of the polymers obtained from complexes
2bꢀd were ca. 2.0, indicating that the polymer is produced by a
single active species.
Inaddition toMMAO, the catalytic performancesof3bꢀd with
Ph3CB(C6F5)4/iBu3Al as the cocatalyst were also investigated.
Typical results are summarized in Table 5. 3bꢀd/Ph3CB-
(C6F5)4/i-Bu3Al systems also exhibited high catalytic activity
toward ethylene polymerization under similar conditions. The
activities of 3bꢀd increased at 75 °C in the order 3c (6190 kg/
molZr h) > 3d (5920 kg/molZr h) > 3b (3930 kg/molZr h),
3
3
3
which is different from the results by MMAO as cocatalyst
(Figure 6). There appears no clear reason at this moment why
these complexes displayed different catalytic performance as a
result of using MMAO and Ph3CB(C6F5)4/iBu3Al as cocatalysts,
one possible explanation is that the local environment of the active
species may be somewhat different during the polymerization.
The catalytic activities in the presence of Ph3CB(C6F5)4/
iBu3Al were also influenced by reaction temperature. In the case
Figure 5. Molecular structure of complex 3d with thermal ellipsoids at
30% probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and bond angles (deg): ZrꢀO(1) 2.156(5); ZrꢀO(2)
2.066(4); ZrꢀCl(1) 2.5198(17); ZrꢀCl(2) 2.4977(19); PꢀO(1)
1.504(5); PꢀC(18) 1.789(6); O(1)ꢀZr-O(2) 80.46(15); Cl(1)ꢀZr-
Cl(2) 95.90(6); ZrꢀO(1)ꢀP134.0(3); ZrꢀO(2)ꢀC(19) 143.1(4);
O(2)ꢀZrꢀCl(1) 150.10(12); O(2)ꢀZrꢀCl(2) 92.48(12); O(1)ꢀ
ZrꢀCl(1) 79.76(12); O(1)ꢀ ZrꢀCl(2) 154.68(12); O(1)ꢀPꢀ
C(18) 113.1(3); PꢀC(18)ꢀC(19) 120.1(5); O(2)ꢀC(19)ꢀC(18)
120.8(5).
of 3b, the catalytic activity was 4060 kg/molZr h at 50 °C and
3
gradually decreased to 1880 kg/molZr h at 100 °C. In compar-
3
ison, 3c provided an activity of 4320 kg/molZr h at 50 °C. Its
3
activity increased to 6190 kg/molZr h at 75 °C. Above 75 °C, the
3
catalytic activity changed slightly. It should be noted that the
activity for 3d increased over the temperature range 50 to 100 °C
Table 3. Ethylene Polymerization by 2aꢀd/MMAO Catalytic Systemsa
b
entry
catalyst (μmol)
Al/Ti (molar ratio)
temp (°C)
E (atm)
yield (mg)
activity (kg/molTi h)
Mwb (10ꢀ4
)
Mw/Mn
3
1
2
3
4
5
6
7
8
9
2a (5)
2b (5)
2c (5)
2d (5)
2d (5)
2d (5)
2d (5)
2d (5)
2d (5)
1000
1000
1000
1000
1000
1000
500
25
25
25
25
0
4
4
4
4
4
4
4
4
8
250
170
660
720
820
120
630
670
890
300
200
790
860
980
140
760
800
1070
17.4
22.7
22.0
23.4
24.1
20.4
25.0
23.8
25.5
2.2
2.5
2.2
1.8
1.9
2.3
2.3
2.2
2.5
50
25
25
25
3000
1000
a Conditions: MMAO as cocatalyst, 10 min, Vtotal = 80 mL. b Weight-average molecular weights and polydispersity indexes determined by high
temperature GPC at 150 °C in 1,2,4-C6Cl3H3 vs narrow polystyrene standards.
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ARTICLE
Table 4. Ethylene Polymerization by 3bꢀd/MMAO Catalytic Systemsa
b
entry
catalyst (μmol)
Al/Zr (molar ratio)
temp (°C)
yield (mg)
activity (kg/molZr h)
Mwb (10ꢀ4
)
Mw/Mn
3
1
3b (5)
3b (5)
3b (5)
3b (5)
3c (5)
3c (5)
3c (5)
3c (5)
3d (5)
3d (5)
3d (5)
3d (5)
1000
1000
1000
500
50
75
1450
4120
2850
3970
1280
4880
2320
4270
610
1740
4940
3420
4760
1540
5860
2780
5120
730
18.0
10.9
5.3
2.0
2.0
1.9
2.0
2.2
2.1
2.5
2.1
2.1
2.0
2.1
2.2
2
3
100
75
4
11.3
17.0
8.5
5
1000
1000
1000
500
50
6
75
7
100
75
4.6
8
8.7
9
1000
1000
1000
500
50
11.9
14.8
7.8
10
11
12
75
3120
1800
1050
3740
2160
1260
100
75
12.1
a Conditions: MMAO as cocatalyst, 10 min, ethylene 4 atm, Vtotal = 80 mL. b Weight-average molecular weights and polydispersity indexes determined
by high-temperature GPC at 150 °C in 1,2,4-C6Cl3H3 vs narrow polystyrene standards.
Table 5. Ethylene Polymerization by 3bꢀd/Ph3CB(C6F5)4/iBu3Al Catalytic Systemsa
cocatalyst/Zr (molar ratio)
Mwb (10ꢀ4
)
Mw/Mn
b
entry
catalyst (μmol)
Ph3CB(C6F5)4
iBu3Al
temp (°C)
yield (mg)
activity (kg/molZr h)
3
1
3b (5.0)
3b (5.0)
3b (5.0)
3c (5.0)
3c (5.0)
3c (5.0)
3d (5.0)
3d (5.0)
3d (5.0)
3d (2.0)
3d (5.0)
3d (5.0)
2
2
2
2
2
2
2
2
2
2
1
2
55
55
55
55
55
55
55
55
55
55
55
30
50
75
3380
3280
1570
3600
5160
5100
2150
4930
5410
4420
trace
trace
4060
3930
1880
4320
6190
6120
2580
5920
6490
13 300
22.1
10.8
9.5
1.7
2.1
2.5
2.4
2.0
2.3
2.1
1.9
1.8
1.9
2
3
100
50
4
20.4
8.9
5
75
6
100
50
6.8
7
18.4
13.3
9.2
8
75
9
100
75
10
11
12
12.7
75
75
a Conditions: Ph3CB(C6F5)4/iBu3Al as cocatalyst, 10 min, ethylene 4 atm, Vtotal = 80 mL. b Weight-average molecular weights and polydispersity
indexes determined by high-temperature GPC at 150 °C in 1,2,4-C6Cl3H3 vs narrow polystyrene standards.
(2580 kg/molZr h at 50 °C; 5920 kg/molZr h at 50 °C; 6490 kg/
3
3
molZr h at 100 °C). Moreover, the catalytic activity significantly
3
increased when the polymerization was performed under low
catalyst concentration (entry 8 vs entry 10). The maximum
activity for 3d reached 13 300 kg/molZr h, as shown in Table 5.
3
A trace amount of polyethylene was obtained if the molar ratio of
Ph3CB(C6F5)4/AliBu3 in the system was changed. A suitable
amount of both Ph3CB(C6F5)4 and AliBu3 was thus required to
optimize the polymerization conditions (entries 8, 11, 12). In
addition, the observed polydispersities indices were relatively
narrow in all cases (Mw/Mn = 1.7ꢀ2.5, Table 5). The resultant
polymers were linear polyethylenes, confirmed by the 13C NMR
spectrum. Taking into account these results, it is thus demon-
strated that, as far as we know, the present catalyst system is a rare
example affording high molecular weight polymer with signifi-
cant catalyst efficiency at high temperature.21
Figure 6. Catalytic activities of complexes 3bꢀd toward ethylene
polymerization at different conditions. Conditions: 5 μmol of complex,
MMAO as cocatalyst (A), Ph3CB(C6F5)4/iBu3Al as cocatalyst (B),
10 min, ethylene 4 atm, Vtotal = 80 mL.
’ CONCLUSIONS
We introduce a new family of Cp(L)MX2 catalysts, where
L is a phosphine oxideꢀphenolate chelating ligand. These
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Organometallics
ARTICLE
half-metallocenes of the type CpMCl2[2-R1-4-R2-6-P(dO)Ph2-
C6H2O] can be easily synthesized by reaction of CpMCl3 with
the corresponding ligand in the presence of triethylamine.
Molecular structures show that titanium complexes adopt a
five-coordinate distorted square-pyramidal geometry, and the
Zr complex has a six-coordinate distorted octahedral geometry.
We also demonstrated that these novel zirconium complexes
possess a very high catalytic performance for ethylene polymer-
ization at high temperature whether using MMAO or Ph3CB-
(C6F5)4/iBu3Al as cocatalyst. From the aspect of industrial
applications, a high catalytic activity at high polymerization
temperature should be very important because performing a
solution polymerization at high temperature can improve the
viscosity of the reaction system, leading to better mass transpor-
tation and temperature control. Therefore, the zirconium com-
plexes introduced in this paper have high potential as a new
generation of olefin polymerization catalysts.
concentrated to about 10 mL, and then the mixture was filtered to
remove NH4Cl. Recrystallization by diffusion of n-hexane (20 mL) into
the clear solution yielded red block crystals of 3a (0.67 g, 70%). 1H NMR
(CDCl3): δ 7.74ꢀ7.65 (m, 5H, Ar-H), 7.60ꢀ7.56 (m, 5H, Ar-H),
7.05ꢀ6.9 (m, 4H, Ar-H), 6.77 (s, 5H,C5H5). 13C NMR (CDCl3):
δ 170.9, 136.4, 134.2, 132.9, 131.6, 129.7, 129.6, 124.0, 121.2, 119.0.
Anal. Calcd for C23H19Cl2O2PTi: C, 57.90; H, 4.01. Found: C, 5 7.86;
H, 4.06.
Synthesis of titanium complex 2b (CpTiCl2[O-2Ph-6(Ph2PdO)-
C6H3]) was carried out according to the same procedure as that of 2a,
except that 2Ph-6(Ph2PdO)C6H3OH (0.74 g, 2.0 mmol) was used in
place of 6(Ph2PdO)C6H4OH. Yield: 0.69 g (62%). 1H NMR (CDCl3):
δ 7.81ꢀ7.83 (d, 1H, Ar-H), 7.76ꢀ7.66 (m, 8H, Ar-H), 7.60ꢀ7.56 (m,
4H, Ar-H), 7.51ꢀ7.46 (t, 2H, Ar-H), 7.43ꢀ7.38 (t, 1H, Ar-H),
7.11ꢀ6.94 (m, 2H, Ar-H), 6.39 (s, 5H,C5H5). 13C NMR (CDCl3): δ
136.3, 134.1, 133.1, 132.9, 131.0, 130.9, 130.7, 129.7, 129.5, 128.7, 128.1,
123.9, 121.7, 121.5, 119.1. Anal. Calcd for C29H23Cl2O2PTi: C, 62.96;
H, 4.19. Found: C, 62.91; H, 4.23.
Synthesis of titanium complex 2c (CpTiCl2[O-2tBu-6(Ph2PdO)-
C6H3]) 2c was carried out according to the same procedure as that for
2a, except that 2tBu-6(Ph2PdO)C6H3OH (0.7 g, 2.0 mmol) was used
in place of 6(Ph2PdO)C6H4OH. Yield: 0.80 g (75%). 1H NMR
(CDCl3): δ 7.68ꢀ7.56 (m, 11H, Ar-H), 6.88ꢀ6.838 (m, 2H, Ar-H),
6.56 (s, 5H, C5H5), 1.45 (s, 9H, tBu-H). 13C NMR (CDCl3): δ 170.9,
140.0, 134.3, 133.7, 133.4,133.0, 129.6, 129.3, 128.4, 126.9, 123.8, 121.2,
119.0, 35.7, 30.2. Anal. Calcd for C27H27Cl2O2PTi: C, 60.81; H, 5.10.
Found: C, 60.86; H, 5.06.
’ EXPERIMENTAL SECTION
General Procedures and Materials. All manipulations of air-
and/or moisture-sensitive compounds were carried out under a dry
argon atmosphere by using standard Schlenk techniques or under a dry
argon atmosphere in an MBraun glovebox unless otherwise noted. All
solvents were purified from an MBraun SPS system. The NMR data of
the ligands and complexes used were obtained on a Bruker 300 MHz
spectrometer (300 MHz for 1H, 75.5 MHz for 13C) at ambient
temperature, with CDCl3 as the solvent (dried by MS 4 Å). The
NMR data of the copolymers were obtained on a Varian Unity-400
MHz spectrometer at 135 °C, with o-C6D4Cl2 as a solvent. Elemental
analyses were recorded on an Elemental Vario EL spectrometer. Mass
spectra were obtained using electron impact (EI-MS) and LDI-1700
(Linear Scientific Inc.). The weight-average molecular weights and
the polydispersity indices 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 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.). CpTiCl3 and CpZrCl3 were purchased from
Aldrich. Modified methylaluminoxane (MMAO, 7% aluminum in
heptane solution) was purchased from Akzo Nobel Chemical Inc.
Commercial ethylene was directly used for polymerization without
further purification. The other reagents and solvents were commer-
cially available.
Synthesis of titanium complex 2d (CpTiCl2[O-2,4tBu2-6(Ph2PdO)-
C6H2]) was carried out according to the same procedure as that of 2a,
except that 2,4tBu2-6(Ph2PdO)C6H2OH (0.81 g, 2.0 mmol) was
used in place of 6(Ph2PdO)C6H4OH. Yield: 0.90 g (76%). 1H NMR
(CDCl3): δ 7.74ꢀ7.61 (m, 10H, Ar-H), 7.50 (s, 1H, Ar-H), 6.90 (d,
1H, Ar-H), 6.74 (s, 5H,C5H5), 1.45 (s, 9H, tBu-H), 1.23 (s, 9H, tBu-
H). 13C NMR (CDCl3): δ 168.4, 143.7, 139.2, 134.3, 133.6, 132.8,
130.6, 129.5, 125.6, 123.6, 109.3, 107.8, 35.8, 34.9, 31.7, 30.3. Anal.
Calcd for C31H35Cl2O2PTi: C, 63.18; H, 5.99. Found: C, 63.
15; H, 6.02.
Synthesis of zirconium complex 3b (CpZrCl2[O-2Ph-6(Ph2PdO)-
C6H3]) was carried out according to the same procedure as that of 2b,
except that CpZrCl3 (0.53 g, 2.0 mmol) was used in place of CpTiCl3.
Yield: 0.71 g (60%). 1H NMR (CDCl3): δ 7.62ꢀ7.39 (m, 16H, Ar-H),
6.95ꢀ6.88 (m, 2H, Ar-H), 6.24 (s, 5H,C5H5). 13C NMR (CDCl3): δ
137.6, 136.4, 135.5, 133.5, 132.8, 131.5, 131.1, 130.3, 129.7, 129.5, 129.0,
128.6, 128.2, 127.9, 127.6, 119.6, 119.3, 117.4, 115.90. Anal. Calcd for
C29H23Cl2O2PZr: C, 58.38; H, 3.89. Found: C, 58.33; H, 3.93.
Synthesis of zirconium complex 3c (CpZrCl2[O-2tBu-6(Ph2PdO)-
C6H3]) was carried out according to the same procedure as that of 2c,
except that CpZrCl3 (0.53 g, 2.0 mmol) was used in place of CpTiCl3.
Yield: 0.80 g (70%). 1H NMR (CDCl3): δ 7.53ꢀ7.61 (m, 11H, Ar-H),
Synthesis of Half-Metallocene Complexes. Synthesis of
Compounds 1aꢀd. Various phosphine oxideꢀphenolate [O, PdO]
ligands bearing different substituents on the R1 and R2 positions,
2R1-4R2-6(Ph2PdO)C6H2OH (1a, R1 = R2 = H; 1b, R1 = Ph, R2 =
H; 1c, R1 = tBu, R2 = H; 1d, R1 = R2 = tBu), were prepared according
to literature procedures.19b By addition of phenols into a stirred
solution of 3,4-dihyro-2H-pyran in the presence of a catalytic
amount of hydrochloric acid in THF, the THP ethers were pre-
6.83ꢀ6.90 (m, 2H, Ar-H), 6.56 (s, 5H,C5H5), 1.45 (s, 9H, tBu-H). 13
C
NMR (CDCl3): δ 167.0, 141.4, 134.2, 133.4, 132.9, 132.8, 130.1, 129.9,
128.9, 127.5, 120.0, 119.6, 117.3, 109.9, 108.4, 35.6, 30.1. Anal. Calcd for
C31H35Cl2O2PZr: C, 56.24; H, 4.72. Found: C, 56.35; H, 4.68.
Synthesis of zirconium complex 3d (CpZrCl2[O-2,4tBu2-6-
(Ph2PdO)C6H2]) was carried out according to the same procedure
as that of 2d, except that CpZrCl3 (0.53 g, 2.0 mmol) was used in place of
n
pared and then lithiated with BuLi/TMEDA and quenched with
PPhCl2. The protective group could be removed by hydrochloric
acid. Compounds 1aꢀd were obtained in high yields after oxidation
using H2O2.
Synthesis of Titanium Complexes 2aꢀd and Zirconium Complexes
3bꢀd. Synthesis of titanium complex 2a (CpTiCl2[O-6(Ph2PdO)-
C6H4]): To a stirred solution of CpTiCl3 (0.44 g, 2.0 mmol) in dried
tetrahydrofuran (20 mL) was added slowly a solution of 6(Ph2PdO)-
C6H4OH (0.59 g, 2.0 mmol) in tetrahydrofuran (20 mL). The reaction
mixture was stirred for 10 min, and then Et3N (0.3 mL, 216 mg, 2.1 mol)
was added. After stirring for 4 h at room temperature the solution was
1
CpTiCl3. Yield: 0.91 g (72%). H NMR (CDCl3): δ 7.54ꢀ7.71 (m,
10H, Ar-H), 6.80ꢀ6.85 (d, 1H, Ar-H), 6.54 (s, 5H,C5H5), 1.45 (s, 9H,
tBu-H), 1.20 (s, 9H, tBu-H). 13C NMR (CDCl3): δ 164.8, 141.9, 141.7,
140.5, 134.0, 132.9, 132.8, 130.9, 129.6, 127.9, 126.0, 125.8, 117.2, 108.4,
106.7, 35.8, 34.7, 31.7, 30.2. Anal. Calcd for C31H35Cl2O2PZr: C, 58.85;
H, 5.58. Found: C, 58.91; H, 5.63.
Ethylene Polymerization. A typical procedure was performed as
follows: the prescribed amounts of toluene and MMAO were added into
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Organometallics
ARTICLE
the autoclave (100 mL, stainless steel) in the drybox, and the apparatus
was then purged with ethylene. The reaction mixture was then pressur-
ized to the prescribed ethylene pressure soon after the addition of a
toluene solution containing the 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.
Crystallographic Studies. Single crystal of complexes 2aꢀd and
3d 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 BrukerSmart APEXdiffractometerwithCCD detectorusing
Mo KR radiation (λ = 0.71073 Å). Lorentz, polarization factors were
made for the intensity data, and absorption corrections were performed
using 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.
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’ ASSOCIATED CONTENT
S
Supporting Information. X-ray diffraction data for 2aꢀd
b
and 3d (as CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: +86-431-85262039. E-mail: ysli@ciac.jl.cn.
’ ACKNOWLEDGMENT
The authors are grateful for a subsidy provided by the National
Natural Science Foundation of China (Nos. 20874096 and
21074128).
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