Monochloro non-bridged half-metallocene-type zirconium complexes containing phosphine oxide-(thio)phenolate chelating ligands as efficient ethylene polymerization catalysts

Article abstract of DOI:10.1039/c2dt31445b

A series of novel monochloro half-zirconocene complexes containing phosphine oxide-(thio)phenolate chelating ligands of the type, ClCp′Zr[X-2-R¹-4-R²-6-(Ph₂PO)C ₆H₂]₂ (Cp′ = C₅H₅, 2a: X = O, R¹ = Ph, R² = H; 2b: X = O, R¹ = F, R² = H; 2c: X = O, R¹ = ^tBu, R² = H; 2d: X = O, R¹ = R² = ^tBu; 2e: X = O, R ¹ = SiMe₃, R² = H; 2f: X = S, R¹ = SiMe₃, R² = H; Cp′ = C₅Me₅, 2g: X = O, R¹ = SiMe₃, R² = H), have been synthesized in high yields. These complexes were identified by ¹H {¹³C} NMR and elemental analyses. Structures for 2b, 2c and 2f were further confirmed by X-ray crystallography. Structural characterization of these complexes reveals crowded environments around the zirconium. Complexes 2b and 2c adopt six-coordinate, distorted octahedral geometry around the zirconium center, in which the equatorial positions are occupied by three oxygen atoms of two chelating phosphine oxide-bridged phenolate ligands and a chlorine atom. The cyclopentadienyl ring and one oxygen atom of the ligand are coordinated on the axial position. Complex 2f also folds a six-coordinate, distorted octahedral geometry around the Zr center, consisting of a Cp-Zr-O (in PO) axis [177.16°] and a distorted plane of two sulfur atoms and one oxygen atom of two chelating phosphine oxide-bridged thiophenolate ligands as well as a chlorine atom. When activated by modified methylaluminoxane (MMAO), all the complexes exhibited high activities towards ethylene polymerization at high temperature (75 °C), giving high molecular weight polymers with unimodal molecular weight distribution. The formation of 14-electron, cationic metal alkyl species might come from the Zr-O (in phenol ring) bond cleavage based on the DFT calculations study.

Full text of DOI:10.1039/c2dt31445b

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Monochloro non-bridged half-metallocene-type
zirconium complexes containing phosphine oxide-
(thio)phenolate chelating ligands as efficient ethylene
polymerization catalysts†
Cite this: Dalton Trans., 2013, 42, 499
Xiao-Yan Tang,a,b Yong-Xia Wang,a San-Rong Liu,a Jing-Yu Liu*a and Yue-Sheng Lia
A series of novel monochloro half-zirconocene complexes containing phosphine oxide-(thio)phenolate
chelating ligands of the type, ClCp’Zr[X-2-R1-4-R2-6-(Ph2PvO)C6H2]2 (Cp’ = C5H5, 2a: X = O, R1 = Ph, R2
=
H; 2b: X = O, R1 = F, R2 = H; 2c: X = O, R1 = tBu, R2 = H; 2d: X = O, R1 = R2 = tBu; 2e: X = O, R1 = SiMe3, R2 =
H; 2f: X = S, R1 = SiMe3, R2 = H; Cp’ = C5Me5, 2g: X = O, R1 = SiMe3, R2 = H), have been synthesized in
high yields. These complexes were identified by 1H {13C} NMR and elemental analyses. Structures for 2b,
2c and 2f were further confirmed by X-ray crystallography. Structural characterization of these complexes
reveals crowded environments around the zirconium. Complexes 2b and 2c adopt six-coordinate, dis-
torted octahedral geometry around the zirconium center, in which the equatorial positions are occupied
by three oxygen atoms of two chelating phosphine oxide-bridged phenolate ligands and a chlorine
atom. The cyclopentadienyl ring and one oxygen atom of the ligand are coordinated on the axial posi-
tion. Complex 2f also folds a six-coordinate, distorted octahedral geometry around the Zr center, consist-
ing of a Cp–Zr–O (in PvO) axis [177.16°] and a distorted plane of two sulfur atoms and one oxygen
atom of two chelating phosphine oxide-bridged thiophenolate ligands as well as a chlorine atom. When
activated by modified methylaluminoxane (MMAO), all the complexes exhibited high activities towards
ethylene polymerization at high temperature (75 °C), giving high molecular weight polymers with un-
imodal molecular weight distribution. The formation of 14-electron, cationic metal alkyl species might
come from the Zr–O (in phenol ring) bond cleavage based on the DFT calculations study.
Received 3rd July 2012,
Accepted 14th September 2012
DOI: 10.1039/c2dt31445b
www.rsc.org/dalton
which is active for ethylene polymerization when activated
Introduction
with methylaluminoxane (MAO).19 Chen et al. reported a class
Group IV transition metal complexes bearing one or two cyclo- of monoalkyl or monochloro, chiral-at-metal constrained geo-
pentadienyl ligands are an important class of the new gen- metry complexes as efficient catalysts not only for olefin
eration of polymerization catalysts.1 The remarkable success of polymerization, but also for methyl methacrylate polymeri-
half-sandwich titanium amide (“constrained geometry”) cata- sation.20 Bochmann et al. found that monocyclopentadienyl
lysts (CGC) has spurred the expansion of mono-cyclopentadie- complexes containing two phenoxo-imino ligands exhibited
nyl complexes. Many examples of Cp′M(L)X2 compounds appreciable catalytic activities for olefin polymerization in con-
containing monodentate or bidentate anionic ligands have junction with methylaluminoxane (MAO).22 These reports
been reported.2–14 In addition, some new types of monochloro prompted us to extend our studies in d0 transition-metal
or monoalkyl group
4 complexes also appeared in the chemistry by synthesizing and characterizing new monochloro
literature.15–22 For instance, Royo et al. prepared a doubly silyl- group IV complexes.
amido-bridged cyclopentadienyl zirconium benzyl complex
Phosphine oxide-bridged phenolate ligands appeared
attractive due to the fact that the neutral PvO donor in phen-
oxide ligands plays an important role in stabilizing the active
species.22 In this contribution, we thus reported a new type of
monochloro non-bridged half-metallocene-type zirconium
complex by combining two phosphine oxide-phenolate chela-
ting ligands and Cp′ZrCl3 in tetrahydrofuran (Scheme 1). As
expected, these complexes exhibited high activities towards
aState Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China.
E-mail: ljy@ciac.jl.cn; Fax: +86-431-85262039
bGraduate School of the Chinese Academy of Sciences, Changchun Branch, China
†CCDC 888633–888635. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt31445b
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ethylene polymerization simply by treatment with modified for X-ray crystallographic analysis were grown from the chilled
methylaluminoxane (MMAO) and produced high molecular concentrated THF–hexane solution mixtures. The crystallo-
weight polymers at high temperature.
graphic data together with the collection and refinement para-
meters are summarized in Table 1.
Structures for 2b, 2c and 2f are shown in Fig. 1–3 and the
selected bond distances and angles for 2b, 2c and 2f are sum-
marized in Table 2. If the centroid of the cyclopentadienyl ring
is considered as a single coordination site, both 2b and 2c
exhibit a pseudo-octahedral geometry around the zirconium
center, in which the equatorial positions are occupied by three
oxygen atoms of two chelating phosphine oxide-bridged
phenolate ligands and a chlorine atom. The cyclopentadienyl
ring and the O-donor of the phosphine oxide of the second
bidentate ligand are nearly trans as indicated by the Cp (cen-
troid)–Zr–O(4) angle of 179.69° and 173.43° in 2b and 2c,
respectively. In the solid state of 2b, an intramolecular π–π
stacking interaction exists between a phenyl ring of the PPh2
Results and discussion
Synthesis of the monochloro half-metallocene-type zirconium
complexes
The reaction of Cp′ZrCl3 with 2.0 equiv. of sodium salt of 2-R1-
4-R2-6-(Ph2PvO)C6H2XH in tetrahydrofuran (THF) provided
direct access to the monochloro group IV complexes ClCp′Zr-
[X-2-R1-4-R2-6-(Ph2PvO)C6H2]2 (Cp′ = C5H5, 2a: X = O, R1 = Ph,
R2 = H; 2b: X = O, R1 = F, R2 = H; 2c: X = O, R1 = Bu, R2 = H;
t
2d: X = O, R1 = R2 = tBu; 2e: X = O, R1 = SiMe3, R2 = H; 2f: X = S,
R1 = SiMe3, R2 = H; Cp′ = C5Me5, 2g: X = O, R1 = SiMe3, R2 = H)
(Scheme 1). These complexes were identified by 1H and 13C
1
NMR spectra and elemental analyses. The H NMR spectra of
complexes 2a–f displayed a sharp single resonance assigned to
the C5H5(Cp) protons. The resonance corresponding to the
–CH3 in the Cp* group showed a doublet in 2g. Integration of
1
the H NMR spectra of complexes confirms a 1 : 2 ratio of the
Cp′ group to the phosphine oxide-(thio)phenolate chelating
ligand. Colorless block microcrystals of 2b, 2c and 2f suitable
Fig. 1 Molecular structure of complex 2b with thermal ellipsoids at the 30%
probability level. Hydrogen atoms and the solvent molecule (THF) are omitted
for clarity.
Scheme 1 Synthesis of complexes 2a–g.
Table 1 Crystal data and structure refinements of complexes 2b, 2c and 2f
2b
2c
2f
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C45H39ClF2O5P2Zr
886.37
Orthorhombic
P212121
12.9957(8)
15.2366(9)
20.3856(12)
90.00
90.00
90.00
4036.6(4), 4
1.459
0.473
C49H49ClO4P2Zr
890.49
C47H49ClO2P2S2Si2Zr + 2(C4H8O)
1098.98
Monoclinic
P21/n
10.782(2)
27.167(5)
18.915(3)
90.00
97.846(3)
90.00
Triclinic
ˉ
P1
11.3191(6)
12.4318(7)
17.7473(10)
73.078(10)
80.582(10)
63.648(10)
2139.2(2), 2
1.382
α (°)
β (°)
γ (°)
V (Å3), Z
5488.5(17), 4
1.330
0.470
Densitycalcd (Mg m−3
)
Absorption coefficient (mm−1
F (000)
)
0.439
924
1816
2296
Crystal size (mm)
0.28 × 0.22 × 0.14
1.67 to 25.04
22 739
7142 (Rint = 0.0781)
7142/0/505
1.004
0.27 × 0.14 × 0.09
1.89 to 26.04
11 172
8233 (Rint = 0.0234)
8233/0/514
1.036
0.30 × 0.22 × 0.16
1.32 to 25.07
32 047
9699 (Rint = 0.1018)
9699/7/514
1.055
θ range for data collection (°)
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]: R1, wR2
0.0514, 0.0990
0.562 and −0.302
0.0609, 0.1643
2.281 and −0.553
0.1062, 0.3065
1.988 and −0.935
Largest diff. peak and hole (e Å−3
)
500 | Dalton Trans., 2013, 42, 499–506
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Table 2 Selected bond distances (Å) and angles (°) for complexes 2b, 2c and
2f
2b
2c
2f
Bond distances in Å
Zr–O(1)/S(1)
Zr–O(2)
Zr–O(3)/S(3)
Zr–O(4)
Zr–Cl(1)
Zr–Cp (centroid)
P(1)–O(2)
2.076(3)
2.173(3)
2.088(3)
2.198(3)
2.5180(13)
2.258
2.056(3)
2.157(3)
2.090(3)
2.212(3)
2.5216(13)
2.292
2.616(3)
2.197(6)
2.636(3)
2.185(6)
2.490(3)
2.247
1.517(3)
1.510(3)
1.518(3)
1.484(3)
1.513(7)
1.509(6)
P(2)–O(4)
Bond angles in °
S(1)/O(1)–Zr–O(2)
S(3)/O(3)–Zr–O(4)
Cl(1)–Zr–O(1)/S(1)
Cl(1)–Zr–O(2)
Cl(1)–Zr–O(3)/S(3)
Cl(1)–Zr–O(4)
Zr–O(2)–P(1)
81.30(13)
78.98(12)
156.24(11)
86.40(9)
93.70(11)
78.34(9)
131.66(18)
132.2(2)
90.55(14)
15.44
82.58(11)
79.27(11)
159.60(9)
87.31(8)
87.98(9)
80.95(9)
130.13(17)
135.14(18)
93.23(12)
27.24
80.65(18)
80.27(17)
90.94(9)
156.30(19)
96.82(9)
78.92(17)
133.9(4)
134.2(4)
161.17(8)
48.67
Fig. 2 Molecular structure of complex 2c with thermal ellipsoids at the 30%
probability level. Hydrogen atoms are omitted for clarity.
Zr–O(4)–P(2)
S(1)/O(1)–Zr–O(3)/S(3)
O(2)–P(1)–C(6)–C(1)
O(4)–P(2)–C(24)–C(19)
29.90
12.13
56.19
Zr–O(4) bond lengths are obviously affected by the R1 group in
the ligand. The Zr–O(2) and Zr–O(4) bond distances in 2b, 2c
and 2f change in the range of 2.1573–2.212 Å, indicative of sig-
nificant coordination of an oxygen atom in the phenylphosphi-
nyl moiety to the metal center in the solid state. The bond
angles for O(4)–Zr–Cl(1) in 2b and 2f (2b, 78.34(9)°; 2f, 78.92
(17)°) are similar to each other, but smaller than that in 2c
(80.95(9)°). The two oxygen atoms in phenol for complexes 2b
and 2c are in the cis position to each other as evident from the
O(1)–Zr–O(3) bond angles (2b, 90.55(14)°; 2c, 93.23(12)°,
respectively). The trans orientation of the two S donors of 2f is
indicated by the S(1)–Zr–S(3) bond angle of 161.17(8)°. We
simply estimated the energy difference of cis and trans orien-
tations for complexes 2b, 2c and 2f based on density func-
tional theory (DFT). For 2b and 2c, the energies corresponding
to the formation of the trans configurations of two oxygen
atoms in phenol were much higher than those of the cis con-
Fig. 3 Molecular structure of complex 2f with thermal ellipsoids at the 30%
probability level. Hydrogen atoms and two solvent molecules are omitted for
clarity. (The solvent molecules were THF not only because THF was used for the
preparation of 2f, but also because the protons of the free THF appeared in the
1H NMR spectrum. These solvent molecules cannot be refined due to the dis-
order of the molecules and the poor data quality and were removed by the
SQUEEZE method.).
unit of one bidentate ligand with the phenol ring of the other
bidentate ligand. The geometrical parameters of the stacking figurations (2b, 8.74; 2c, 6.29 kcal mol−1), whereas the trans
contacts are as follows: the centroid–centroid distance (dc–c) is configuration of two S atoms in 2f is 4.24 kcal mol−1 more
4.017 Å; the dihedral angle between ring planes is 3.43° in the
stable than the cis configuration. The theoretical investigation
crystal structures. Complex 2f also folds a six-coordinate, dis- result was in high agreement with the experimental evidence.
torted octahedral geometry around the Zr center, consisting of Moreover, an obvious difference of torsion angles in the two
a Cp–Zr–O(2) (in PvO) axis [177.16°] and a distorted plane of
ligands was seen because the two segments are asymmetric.
two sulfur atoms and one oxygen atom of two chelating For instance, the O(3), PvO(4)-chelating ligand in 2c forms a
phosphine oxide-bridged thiophenolate ligands as well as a plane which includes a phenoxide ring, a –PvO group and
chlorine atom.
An inspection of Fig. 1–3 indicates that steric environments other two methyl groups lie on either side of the plane. There-
two carbon atoms from tert-butyl groups (C(46) and C(49)); the
around Cl-bound sites (i.e., potential polymerization sites) are
somewhat different. The Zr–Cl bond distances in 2b, 2c and 2f
fore, this segment displays a much smaller torsion angle (the
torsion angle is the angle in O(4)–P(2)–C(24)–C(19), 12.13°)
decreased in the order 2c (2.5216(13) Å) > 2b (2.5180(13) Å) > than the other fragment (the torsion angle is the angle in
2f (2.490(3) Å), in line with the order of Zr–Cp (centroid) dis-
tances in 2b, 2c and 2f (2c, 2.292 > 2b, 2.258 > 2f, 2.247 Å).
O(2)–P(1)–C(6)–C(1), 27.24°) due to the O(2) in the PvO group
deviating from the phenoxide ring. The torsion angles for
These bond distances might be related to the catalytic activity O(2)–P(1)–C(6)–C(1) and O(4)–P(2)–C(24)–C(19) in 2f (48.67°,
of these catalysts for ethylene polymerization. The Zr–O(2) and
56.19°) are larger than those in 2b and 2c (2b, 15.44°, 29.90°;
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2c, 27.24°, 12.13°, respectively), which might be a consequence possessed relatively high molecular weights (MWs) with un-
of the substantially longer Zr–S bond distances in 2f compared imodal molecular weight distributions (MWDs). Both the MW
to the corresponding Zr–O distances in 2b and 2c. These and the MWD values for the resultant PEs prepared by 2a were
results showed that the ligands employed could readily modu- comparable with those by 3a. As summarized in Table 3, a
late the spatial and the electronic properties of the active site certain excessive amount of MMAO was required for exhibiting
for polymerization and thus tune the activity of a catalyst. high catalytic activity in this catalyst system. The observed
Attempts to synthesize the ClCpZr[6-(Ph2PvO)–C6H4O]2 result was an interesting contrast to that found by 3a, in which
complex were unsuccessful.
high activity was observed even at low MMAO concentrations.
The dominant chain-transfer pathway in the 2a–MMAO catalyst
system seems to be β-hydrogen elimination due to the fact that
Ethylene polymerization by 2a–g
Because the aim of this work was to evaluate the potential of the MWs for the resultant polymers changed slightly with the
monochloro half-metallocene Zr complexes in olefin polymeri- Al/Zr molar ratio (entry 2 vs. 4). The fluorine analogue (2b)
−1
zation, the use of these complexes in ethylene polymerization afforded a high activity of 3920 kg molZr h at 75 °C with an
was thus examined in the presence of MMAO. The polymeri- MW value of 16.3 × 104 (entry 6). Complex 2b showed much
zation results are depicted in Table 3.
higher activities than 2a if the polymerizations were conducted
Complex 2a containing a conjugated phenyl group in the R1 under lower MMAO concentrations (Al/Zr = 500) and/or at
position displayed moderate catalytic activity for ethylene higher temperature (100 °C). The MW decreased upon increas-
−1
polymerization at 50 °C (250 kg molZr h) and consistently ing the Al/Zr molar ratio, suggesting that chain-transfer to
showed higher activity as the temperature was increased to aluminum alkyls rather than β-hydrogen elimination is the
−1
75 °C (4200 kg molZr
h). However, the catalytic activity dominant chain-transfer pathway in 2b/MMAO. The same
−1
noticeably decreased at 100 °C (2090 kg molZr
h). The chain-transfer pathway was seen if the polymerization was per-
observed catalytic activities were lower than those observed in formed by analogues 2c and 2d. Replacement of a phenyl
the polymerization using CpZrCl2[O-2-Ph-6-(Ph2PvO)C6H3] group at the R1 position in complex 2a with a tert-butyl group
−1
(3a) under the same conditions (1740 kg molZr h at 50 °C, (2c) led to higher activity (entries 9–11), and the activity at
4940 kg molZr−1 h at 75 °C, 3420 kg molZr−1 h at 100 °C).24 The 75 °C was the highest among these Cp analogues (4640 kg
−1
steric bulk effect around the metal center might make ethylene molZr h). The MWs decreased upon increasing Al/Zr molar
coordination more difficult and reduce catalytic activity. The ratio, in contrast to the results by CpZrCl2[O-2-tBu-6-(Ph2PvO)-
resultant polymers prepared by the 2a/MMAO catalyst C6H3] (3c) in which the MWs were independent of the amount
Table 3 Ethylene polymerization by 2a–f/MMAO catalytic systemsa
b
Entry
Catalyst (μmol)
Al/Zr (molar ratio)
Temp. (°C)
Yield (mg)
Activity (kg molZr−1 h)
Mw b (10−4
)
Mw/Mn
1
2
3
4
5
6
7
8
2a (5)
2a (5)
2a (5)
2a (5)
2b (5)
2b (5)
2b (5)
2b (5)
2c (5)
2c (5)
2c (5)
2c (5)
2d (5)
2d (5)
2d (5)
2d (5)
2e (5)
2e (5)
2e (5)
2e (5)
2f (5)
2f (5)
2f (5)
2f (5)
2g (5)
2g (5)
2g (5)
2g (5)
1000
1000
1000
500
1000
1000
1000
500
1000
1000
1000
500
1000
1000
1000
500
1000
1000
1000
500
1000
1000
1000
500
1000
1000
1000
500
50
75
100
75
50
75
100
75
50
75
100
75
50
75
100
75
50
75
100
75
50
210
250
19.7
11.3
6.2
10.7
21.3
16.3
8.5
23.8
16.5
8.3
3.0
2.1
2.2
2.6
3.0
2.4
2.0
2.7
2.4
1.9
1.9
1.9
2.8
2.0
2.2
2.4
3.2
2.6
2.5
2.8
3.1
2.8
2.5
3.3
—
3500
1740
790
4200
2090
950
610
730
3270
2430
1480
800
3870
2110
3100
480
2830
1420
1410
720
2770
2110
1020
1620
1950
1480
910
3920
2920
1780
960
4640
2530
3720
580
3400
1700
1690
860
3320
2530
1220
1940
2340
1780
1090
—
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
5.2
14.7
25.9
10.8
5.1
13.7
28.5
16.6
6.6
18.0
26.0
20.2
8.2
20.9
—
75
100
75
50
75
100
75
Trace
980
1530
Trace
1180
1840
—
44.1
17.7
—
2.2
2.1
—
a Conditions: MMAO as a 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.
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of the cocatalyst.24 Moreover, the substituent in the R2 moiety
also affected the polymerization behaviors. For the sterically
more protected system 2d, comparatively lower activities have
been observed (entries 13–15), in line with the results by
CpZrCl2[O-2,4-tBu2-6(Ph2PvO)C6H2] (3d) in which complex
with ortho- and para-substituted groups in the phenol ring dis-
played the lowest catalytic activities for ethylene polymeri-
zation under the same conditions.24 Note that 2d exhibited
Fig. 4 The optimized structures of 1–3.
−1
complex 1 with AlMe3 led to the formation of the product 2
(Fig. 4) that contains a AlMe3 unit and weak (aryl)O–Al(CH3)2–
CH3⋯Zr+ interaction. As the olefin approaches the metal center,
the Zr–Me bond will give way to allow the formation of π-com-
plexation of the monomer to the metal center (3). This process
is associated with the overcoming of a high energy barrier
because the required stretching of the Zr+⋯H3CAl(CH3)2 bond
and the rotation of the Zr–Me bond cannot be energetically
compensated by the weaker ethylene complexation.
higher activity than 3d under Al/Zr = 500 (2d, 1690 kg molZr
h; 3d, 1260 kg molZr−1 h).
Compared with complex 2c, 2e showed relatively low cataly-
tic activity at 75 °C. However, the molecular weight of the resul-
tant polymer by 2e was almost twice as large as that by 2c
(entry 10 vs. 18). It should be noted that the influence of temp-
erature on the activity exhibited by the catalyst generated from
2f, which contains a pair of phosphine oxide thiophenolate
ligands, is relatively slight over the temperature range of
50–100 °C. The dominant chain-transfer pathway in 2e and 2f
is β-hydrogen elimination. The activities by 2g were lower than
those by 2e under the similar conditions, however, the activi-
ties for 2g remained increasing over a temperature range of
50 to 100 °C (entries 25–28), which is different from the results
by Cp analogues. In addition, the MW values using the Cp*
analogue were higher than those obtained by the Cp ana-
logues. As a result, complex 2g was found to display a high
Another assumption that the detachment of one ligand
from the Zr center to generate coordinative unsaturation
seems impossible in terms of experimental results. The data in
Table 3 indicate that monochloro complexes and dichloro
complexes possessed different active species since they dis-
played different polymerization behaviors (like catalytic activity
and chain transfer pathway) under the similar conditions. For
example, the chain-transfer to aluminum alkyls is the domi-
nant chain-transfer pathway in 2c/MMAO, whereas β-hydrogen
transfer is the main chain-transfer pathway in 3c/MMAO;
complex 2d exhibited higher activity than 3d under Al/Zr = 500
−1
activity of 1840 kg molZr h with a weight average molecular
weight value of 17.7 × 104 at 100 °C. We assumed that this
might be due to the steric bulk of Cp* compared to Cp. These
results suggest that both the cyclopentadienyl ligand and the
anionic donor ligand could affect the polymerization beha-
viors. The MWDs of the polymers obtained from 2a–g were
ca. 2.5, indicating that the polymer is produced by a single
active species. Attempts to alkylate 2a–g did not give isolable
products.
−1
−1
(2d, 1690 kg molZr h; 3d, 1260 kg molZr h), whereas the
other monochloro complexes showed lower activities than rela-
tive dichloro complexes. Moreover, the polymerizations by 2a–g
took place with single catalytically active species. Taking into
account these results, the Zr–O (in phenol ring) bond cleavage
is the most possible approach to generate cationic metal alkyl
species.
Mechanism study by DFT calculations
Activation with excess MMAO leads generally to high activities,
indicating that the propagating centers are cationic alkyls
rather than neutral. The assumption of possible cleavage of
Conclusions
the Zr–O bond of the ligand by the AlMe3 component of MAO We introduce a new family of monochloro half-zirconocene
to give way for the monomer incorporation was already complex ClZrCp′(L)2, where L is the phosphine oxide-(thio)
reported by Bochmann for ethylene polymerization using a phenolate chelating ligand. These half-metallocenes of the
CpZr[CH3CH2NvCH{(3-tBuC6H3-2-O)}]2Cl catalyst.22 We sup- type ClCp′Zr[2-R1-4-R2-6-P(vO)Ph2–C6H2X]2 can be easily syn-
posed that one of the [O, PvO] ligands dissociates and creates thesized by the reaction of Cp′ZrCl3 with 2.0 equiv. of the cor-
the required vacant space for the monomer to coordinate in responding sodium salts of the ligands. Molecular structures
our case.
show that zirconium complexes adopt six-coordinate distorted
In order to seek some possible answers for the mechanism octahedral geometry. We also demonstrated that these novel
of polymerization, DFT calculations were performed to predict monochloro zirconium complexes possess very high catalytic
the structures of catalytically active species prior to the exper- activities for ethylene polymerization at high temperature in
imental proof. Our discussion has been built around the very the presence of MMAO. Based on DFT calculations, the struc-
first insertion step by modeling the growing chain end with a tures of cationic active species were predicted. The formation
methyl group, and CpZrMe[O-2-F-6-(Ph2PvO)C6H4]2 (1) was of 14-electron, cationic metal alkyl species might come from
used as a model. Due to aluminoxane globule with an the Zr–O (in phenol ring) bond cleavage in our case. We
unknown structure of stoichiometric composition (AlOMe)n, believe that these results could shed some light on the poten-
we simplified the simulation of polymerization, that is, to con- tial olefin polymerization pathways that operate under such
sider only the interaction of AlMe3 with 1. Reaction of the originally monoalkyl catalyst systems.
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102.9 Hz), −0.97. Anal. calc. for C21H23O2PSi: C, 68.83; H, 6.33.
Found: C, 68.79; H, 6.32.
Experimental
General procedures and materials
All manipulation of air- and/or moisture-sensitive compounds
was carried out under a dry argon atmosphere by using stan-
dard Schlenk techniques or under a dry argon atmosphere in
Synthesis of monochloro zirconium complexes 2a–g
Synthesis of zirconium complex 2a (CpZrCl[O-2-Ph-6-
an MBraun glove box unless otherwise noted. All solvents were (Ph2PvO)C6H3]2). The solution of CpZrCl3 (0.265 g,
purified from an MBraun SPS system. The NMR data of the 1.0 mmol) in dried tetrahydrofuran (20 mL) was added slowly
ligands and complexes used were obtained on a Bruker to a solution of 2-Ph-6-(Ph2PvO)C6H3ONa (0.74 g, 2.0 mmol)
300 MHz or 400 MHz spectrometer at ambient temperature, in tetrahydrofuran (20 mL), which was obtained by treating
with CDCl3 as the solvent (dried by MS 4 Å). The NMR data of 2-Ph-6-(Ph2PvO)C6H3OH (0.74 g, 2.0 mmol) with NaH
the copolymers were obtained on a Varian Unity-400 MHz (0.144 g, 6.0 mmol) in tetrahydrofuran (20 mL) for 6 h at room
spectrometer at 135 °C, with o-C6D4Cl2 as a solvent. Elemental temperature. The reaction mixture was stirred overnight and
analyses were recorded on an elemental Vario EL spectrometer. then the solvent removed by vacuum. The resultant mixture
The weight-average molecular weights (Mw) and the polydisper- was dissolved in CH2Cl2, and then the mixture was filtered to
sity indices (PDIs) of polymer samples were determined at remove NaCl. Recrystallization by diffusion of n-hexane
150 °C by a PL-GPC 220 type high-temperature chromatograph (20 mL) into the clear solution yielded colorless block crystals
1
equipped with three Plgel 10 μm Mixed-B LS type columns. of 2a (0.67 g, 72%). H NMR (300 MHz, CDCl3): δ 7.75 (td, J =
1,2,4-Trichlorobenzene (TCB) was employed as the solvent at a 13.5, 7.8 Hz, 4H, Ar-H), 7.62–7.29 (m, 16H, Ar-H), 7.22–7.11
flow rate of 1.0 mL min−1. The calibration was made by poly- (m, 6H, Ar-H), 7.04–6.92 (m, 4H, Ar-H), 6.88–6.61 (m, 6H,
styrene standard EasiCal PS-1 (PL Ltd). CpZrCl3 and Cp*ZrCl3 Ar-H), 5.76 (s, 5H, C5H5). 13C NMR (101 MHz, CDCl3): δ 140.2,
were purchased from Aldrich. Modified methylaluminoxane 138.5, 135.5, 134.2, 134.0, 133.3, 133.2, 132.8, 132.7, 132.5,
(MMAO, 7% aluminum in heptane solution) was purchased 132.4, 132.2, 132.1, 132.0, 131.8, 130.5, 129.7, 129.3, 129.2,
from Akzo Nobel Chemical Inc. Commercial ethylene was 128.7, 128.6, 128.4, 128.3, 128.2, 127.6, 127.2, 126.6, 117.5,
directly used for polymerization without further purification. 117.3, 116.2, 115.9. Anal. calc. for C53H41ClO4P2Zr: C, 68.41; H,
The other reagents and solvents were commercially available.
4.44. Found: C, 68.48; H, 4.39.
Synthesis of zirconium complex 2b (CpZrCl[O-2-F-6-
(Ph2PvO)C6H3]2). The synthesis of the complex was carried
out according to the same procedure as that of 2a, except that
Synthesis of monochloro half-metallocene complexes
Synthesis of compounds 1a–f. Various phosphine oxide- 2-F-6-(Ph2PvO)C6H3OH (0.62 g, 2.0 mmol) was used in place
(thio)phenol ([O, PvO] or [S, PvO]) ligands bearing different of 2-Ph-6-(Ph2PvO)C6H3OH. Yield: 0.53 g (65%). 1H NMR
substituents on R1 and R2 positions, 2-R1-4-R2-6-(Ph2PvO) (300 MHz, CDCl3): δ 7.88–7.56 (m, 12H, Ar-H), 7.55–7.28 (m,
C6H2XH (1a: X = O, R1 = Ph, R2 = H; 1c: X = O, R1 = tBu, R2 = H; 4H, Ar-H), 7.22–7.02 (m, 4H, Ar-H), 6.88–6.68 (m, 4H, Ar-H),
1d: X = O, R1 = R2 = tBu; 1f: X = S, R1 = SiMe3, R2 = H) were pre- 6.60–6.49 (m, 2H, Ar-H), 6.42 (s, 4H, C5H5), 6.26 (s, 1H, C5H5).
pared according to literature procedures.23–25 Compounds 1b 13C NMR (101 MHz, CDCl3): δ 155.7, 152.4, 134.0, 133.9, 133.6,
(X = O, R1 = F, R2 = H) and 1e (X = O, R1 = SiMe3, R2 = H) were 132.9, 132.5, 132.1, 131.2, 130.9, 129.3, 129.1, 128.8, 128.7,
prepared via a procedure similar to that for 1a and the charac- 128.5, 127.8, 127.3, 127.2, 127.0, 120.6, 120.4, 120.3, 120.2,
terizations of these two compounds are followed:
119.4, 119.2, 117.4, 117.3, 117.2, 116.7, 115.7, 114.8, 114.4,
2-F-6-Diphenylphosphinoyl-phenol (1b). Yield: 78%. 1H 112.0. Anal. calc. for C41H31ClF2O4P2Zr: C, 60.47; H, 3.84.
NMR (400 MHz, CDCl3): δ 11.39 (s, 1H, –OH), 7.76–7.65 (m, Found: C, 60.40; H, 3.88.
4H, Ar-H), 7.65–7.57 (m, 2H, Ar-H), 7.56–7.47 (m, 4H, Ar-H),
Synthesis of zirconium complex 2c (CpZrCl[O-2-tBu-6-
7.26–7.17 (m, 1H, Ar-H), 6.83–6.74 (m, 2H, Ar-H). 13C NMR (Ph2PvO)C6H3]2). The synthesis of the complex was carried
(101 MHz, CDCl3): δ 152.45 (dd, J = 12.5, 3.4 Hz), 151.98 (dd, out according to the same procedure as that of 2a, except that
J = 249.0, 12.6 Hz), 132.88 (d, J = 2.7 Hz), 131.99 (d, J = 2tBu-6(Ph2PvO)C6H3OH (0.7 g, 2.0 mmol) was used in place
10.5 Hz), 131.19 (d, J = 105.9 Hz), 128.87 (d, J = 12.6 Hz), of 2-Ph-6-(Ph2PvO)C6H3OH. Yield: 0.62 g (78%). 1H NMR
127.00 (dd, J = 9.3, 4.2 Hz), 120.28 (dd, J = 17.9, 1.9 Hz), 118.97 (300 MHz, CDCl3): δ 7.81–7.73 (m, 2H, Ar-H), 7.70–7.50 (m,
(dd, J = 14.6, 6.3 Hz), 113.85 (d, J = 102.7 Hz). Anal. calc. for 8H, Ar-H), 7.46–7.27 (m, 5H, Ar-H), 7.15–7.10 (m, 1H, Ar-H),
C18H14FO2P: C, 69.23; H, 4.52. Found: C, 69.28; H, 4.49.
6.95 (dt, J = 11.1, 3.7 Hz, 4H, Ar-H), 6.83–6.74 (m, 1H, Ar-H),
2-Trimethylsilyl-6-diphenylphosphinoyl-phenol (1e). Yield: 6.69–6.55 (m, 5H, Ar-H), 6.45 (s, 5H, C5H5), 1.56 (s, 9H, tBu-H),
84%. 1H NMR (400 MHz, CDCl3): δ 11.19 (s, 1H, –OH), 0.91 (s, 9H, tBu-H). 13C NMR (101 MHz, CDCl3): δ 168.5, 167.6,
7.77–7.64 (m, 4H, Ar-H), 7.63–7.42 (m, 7H, Ar-H), 6.99 (ddd, J = 141.4, 141.3, 141.0, 140.9, 134.5, 134.4, 133.4, 133.2, 132.9,
13.3, 7.6, 1.7 Hz, 1H, Ar-H), 6.81 (td, J = 7.4, 2.6 Hz, 1H, Ar-H), 132.7, 132.5, 132.2, 132.1, 131.9, 131.7, 131.5, 131.2, 131.1,
0.31 (s, 9H, SiMe3). 13C NMR (101 MHz, CDCl3): δ 168.62, 130.6, 130.4, 130.2, 130.1, 129.4, 129.2, 128.6, 128.4, 116.9,
140.04, 133.30 (d, J = 10.5 Hz), 132.53 (d, J = 2.4 Hz), 132.12 (d, 116.7, 115.7, 115.4, 111.1, 109.8, 109.7, 109.6, 108.2, 35.7, 35.1,
J = 10.4 Hz), 132.11 (d, J = 104.4 Hz), 129.45 (d, J = 4.7 Hz), 30.1, 29.7. Anal. calc. for C49H49ClO4P2Zr: C, 66.09; H, 5.55.
128.76 (d, J = 12.4 Hz), 118.67 (d, J = 11.8 Hz), 109.65 (d, J = Found: C, 66.17; H, 5.50.
504 | Dalton Trans., 2013, 42, 499–506
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Synthesis of zirconium complex 2d (CpZrCl[O-2,4-tBu2-6- 133.26–133.05 (m), 132.98–132.51 (m), 132.44–131.79 (m), 131.23
(Ph2PvO)C6H2]2). The synthesis of the complex was carried (d, J = 20.0 Hz), 130.41, 130.28, 129.88, 129.20, 128.69–128.36
out according to the same procedure as that of 2a, except that (m), 128.32–127.96 (m), 127.36 (dd, J = 12.8, 5.2 Hz), 122.18,
2,4-tBu2-6-(Ph2PvO)C6H2OH (0.81 g, 2.0 mmol) was used in 119.90, 115.53 (d, J = 14.1 Hz), 114.61 (d, J = 14.1 Hz), 113.88 (d,
place of 2-Ph-6-(Ph2PvO)C6H3OH. Yield: 0.75 g (75%). 1H J = 14.2 Hz), 113.38 (d, J = 14.0 Hz), 108.34, 107.38 (d, J = 22.8
NMR (300 MHz, CDCl3): δ 7.75–7.65 (m, 4H, Ar-H), 7.63–7.34 Hz), 106.28 (d, J = 28.0 Hz), 105.70, 105.05, 104.62, 12.26 (d, J =
(m, 10H, Ar-H), 7.25–7.15 (m, 2H, Ar-H), 6.95–6.81 (m, 5H, 64.1 Hz), 1.88 (d, J = 24.2 Hz), −0.16 (d, J = 8.9 Hz). Calc. for
Ar-H), 6.70–6.50 (m, 3H, Ar-H), 6.45 (s, 5H, C5H5), 1.60 (s, 9H, C52H59ClO4P2Si2Zr: C, 62.91; H, 5.99. Found: C, 62.79; H, 6.05.
tBu-H), 1.22 (s, 9H, tBu-H), 1.11 (s, 9H, tBu-H), 0.95 (s, 9H,
tBu-H). 13C NMR (101 MHz, CDCl3): δ 165.8, 164.9, 139.7,
Ethylene polymerization
138.0, 137.9, 136.7, 136.6, 133.9, 133.8, 132.7, 132.6, 132.5,
132.3, 132.2, 131.8, 131.7, 131.5, 130.9, 130.4, 129.0, 128.8,
128.7, 128.2, 128.0, 127.9, 127.8, 127.7, 126.7, 126.6, 126.0,
125.8, 125.3, 115.0, 109.4, 108.3, 107.1, 106.0, 35.4, 35.0, 31.6,
31.2, 29.8, 29.4. Anal. calc. for C57H65ClO4P2Zr: C, 68.27; H,
6.53. Found: C, 68.18; H, 6.48.
A typical procedure was performed as follows: the prescribed
amounts of toluene and MMAO were added into the autoclave
(100 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 polymeri-
zation was terminated with the addition of EtOH, and the
resultant polymer was adequately washed with EtOH contain-
ing HCl and then dried under vacuum for several hours.
Synthesis of zirconium complex 2e (CpZrCl[O-2-SiMe3-6-
(Ph2PvO)C6H3]2). The synthesis of the complex was carried
out according to the same procedure as that of 2a, except that
2-SiMe3-6-(Ph2PvO)C6H3OH (0.73 g, 2.0 mmol) was used in
place of 2-Ph-6-(Ph2PvO)C6H3OH. Yield: 0.70 g (76%). 1H
NMR (400 MHz, CDCl3) δ 7.85–7.79 (m, 2H, Ar-H), 7.71–7.49
(m, 10H, Ar-H), 7.45–7.35 (m, 2H, Ar-H), 7.22 (m, 2H, Ar-H),
7.03–6.84 (m, 6H, Ar-H), 6.74–6.55 (m, 4H, Ar-H), 6.39 (s, 5H,
C5H5), 0.50 (s, 9H, SiMe3), −0.11 (s, 9H, SiMe3). 13C NMR
(101 MHz, CDCl3) δ 173.46, 172.96, 140.83, 134.43, 134.30,
134.23, 134.12, 133.67, 133.53, 132.90, 132.80, 132.47, 132.36,
132.21, 131.99, 131.88, 131.42–131.21 (m), 130.92, 130.31,
129.81, 129.2, 129.09, 128.96, 128.23 (dd, J = 12.8, 5.8 Hz),
115.71, 0.11, −0.84. Calc. for C47H49ClO4P2Si2Zr: C, 61.18; H,
5.35. Found: C, 61.10; H, 5.39.
Synthesis of zirconium complex 2f (CpZrCl[S-2-SiMe3-6-
(Ph2PvO)C6H3]2). The synthesis of the complex was carried
out according to the same procedure as that of 2a, except that
2-SiMe3-6-(Ph2PvO)C6H3SH (0.77 g, 2.0 mmol) was used in
place of 2-Ph-6-(Ph2PvO)C6H3OH. Yield: 0.67 g (70%). 1H
NMR (400 MHz, CDCl3) δ 7.76 (d, J = 6.1 Hz, 2H, Ar-H),
7.65–7.33 (m, 12H, Ar-H), 7.14–6.98 (m, 6H, Ar-H), 6.66 (dt, J =
13.9, 7.0 Hz, 2H), 6.50–6.31 (m, 4H, Ar-H), 6.20 (s, 5H, C5H5),
0.46 (s, 9H, SiMe3), 0.38 (s, 9H, SiMe3). 13C NMR (101 MHz,
CDCl3) δ 163.76, 160.45, 147.71, 145.47, 139.38, 138.92, 134.92,
134.48, 134.30, 133.95, 133.79, 133.48–132.77 (m), 132.33,
132.11, 131.82, 128.89, 128.52–128.20 (m), 127.40, 122.34,
121.93, 116.75, 0.72, 0.32. Calc. for C47H49ClO2P2S2Si2Zr: C,
59.12; H, 5.17. Found: C, 59.21; H, 5.12.
X-Ray crystallography
Single crystals of complexes 2b, 2c and 2f suitable for X-ray
structure determination were grown from a concentrated THF–
hexane mixture solution at −30 °C in a glove box, thus main-
taining a dry, O2-free environment. The intensity data were col-
lected with the ω scan mode (186 K) on a Bruker Smart APEX
diffractometer with a 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 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.
Density functional theory (DFT) calculations
Density functional theory (DFT) calculations were employed
for the mechanism of ethylene polymerization with complex
2b by using the Amsterdam Density Functional (ADF) program
package.26a Geometry optimizations and energy calculations
were performed using the local density approximation aug-
mented with Becke’s nonlocal exchange corrections26b and
Perdew’s nonlocal correction.26c A triple STO basis set was
employed for Zr, while all other atoms were described by a
double-ζ plus polarization STO basis. The 1s electrons of the
C, P and O atoms, as well as the 1s–2p electrons of the Zr
atom, were treated as the frozen core. Finally, first-order scalar
relativistic corrections were added to the total energy of the
system.
Synthesis of zirconium complex 2g (Cp*ZrCl[O-2-SiMe3-6-
(Ph2PvO)C6H3]2). The synthesis of the complex was carried out
according to the same procedure as that of 2e, except that
Cp*ZrCl3 (0.332 g, 1.0 mmol) was used in place of CpZrCl3.
1
Yield: 0.72 g (73%). H NMR (400 MHz, CDCl3): δ 7.78–7.29 (m,
19H, Ar-H), 7.18–7.06 (m, 1H, Ar-H), 6.92–6.65 (m, 4H, Ar-H),
6.60–6.39 (m, 2H, Ar-H), 1.72 (d, J = 6.7 Hz, 15H, Cp*), 0.42 (s,
9H, SiMe3), −0.26 (d, J = 34.5 Hz, 9H, SiMe3). 13C NMR
Acknowledgements
(101 MHz, CDCl3): δ 176.77 (d, J = 36.2 Hz), 175.00, 173.94, The authors are grateful for subsidy provided by the National
141.51 (dd, J = 25.9, 10.3 Hz), 134.87–134.17 (m), 133.98 (d, J = Natural Science Foundation of China (nos. 21074128 and
14.4 Hz), 133.76 (d, J = 11.1 Hz), 133.43 (d, J = 10.8 Hz), 20923003).
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