A new class of chiral bridged metallocene: Synthesis, structure, and olefin (Co)polymerization behavior of rac- and meso-1,2-CH2CH2{4-(7-me- indenyl)}2ZrCl2 [3]

Full text of DOI:10.1021/ja9811290

J. Am. Chem. Soc. 1998, 120, 9945-9946
A New Class of Chiral Bridged Metallocene:
9945
Synthesis, Structure, and Olefin (Co)polymerization
Behavior of rac- and
meso-1,2-CH2CH2{4-(7-Me-indenyl)}2ZrCl2
Colin J. Schaverien,* Rene´ Ernst, Peter Schut, and
W. Mason Skiff
Shell Research and Technology Centre Amsterdam
Postbus 38000, 1030 BN Amsterdam, The Netherlands
Luigi Resconi,* Elisabetta Barbassa, Davide Balboni, and
Yuri A. Dubitsky
Montell Polyolefins, Centro Ricerche G. Natta
P. le G. Donegani 12, 44100 Ferrara, Italy
A. Guy Orpen
School of Chemistry, UniVersity of Bristol
Bristol BS8 1TS, U.K.
Pierluigi Mercandelli, Massimo Moret, and Angelo Sironi
Dipartimento di Chimica Strutturale e
Stereochimica Inorganica, UniVersita´ di Milano
Via Venezian 21, 20133 Milano, Italy
ReceiVed April 6, 1998
Figure 1. Synthesis of 1,2-CH2CH2{4-(7-Me-indenyl)}2ZrCl2.
Chiral bridged metallocenes1 exercise stereocontrol in the
polymerization of propylene.2,3 Extensive investigation of sub-
stituent effects has resulted in highly active, highly isospecific
homogeneous catalysts.4 These contain two indenyl groups with
a bridge (-CH2CH2- or -SiMe2-) linking the 1,1′-positions.
We report here a new class of chiral bridged metallocenes which
are efficient catalysts, after activation with MAO, for the
polymerization of ethylene and propylene, and are very active
for their copolymerization. They have an ethylene bridge between
the 4,4′-positions, i.e., linking the two phenyl rings,5 rather than
the cyclopentadienyl rings, as is the case with all hitherto known
bridged bis(indenyl) ligands.3
conventional 1,1′-bridged metallocenes, its synthesis requires the
stepwise assembly of the cyclopentadienyl ring.
Friedel-Crafts addition of ClCH2CH2COCl to para-substituted
bis(aryl)ethanes affords the skeleton of the cyclopentadienyl-ring
fragment in only one position relative to the ultimate 4,4′-CH2-
CH2- bridge in the metallocene. Because Friedel-Crafts acylation
is not regiospecific, three isomers of 2 are formed.7 Subsequent
ring closure of 2 with concentrated H2SO4 afforded three isomers
of 3.7 Reduction with NaBH4 and dehydration with dilute HCl
gave two (double bond) isomers of 4.7 Reaction of [4]2- with
ZrCl4 in ether gave two (diastereo)isomers of 1 in a ca. 4:1 ratio
(1H/13C NMR) which could be separated by extraction with
toluene.
The synthesis6 of rac- and meso-1,2-CH2CH2{4-(7-Me-
indenyl)}2ZrCl2 (1) is shown in Figure 1. In contrast to
(1) Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H.-H. J.
Organomet. Chem. 1982, 232, 233. Wild, F. R. W. P.; Wasiuconek, M.;
Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1985, 288, 63.
(2) Ewen, J. A. J. Am. Chem. Soc. 1984, 106, 6355. Kaminsky, W.; Ku¨lper,
K.; Brintzinger, H. H.; Wild, F. R. W. P. Angew. Chem., Int. Ed. Engl. 1985,
24, 507.
(3) Horton, A. D. Trends Polym. Sci. 1994, 2, 158. Brintzinger, H. H.;
Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1143.
(4) Ewen, J. A.; Haspeslagh, L.; Elder, M. J.; Atwood, J. L.; Zhang, H.;
Cheng, H. N. In Transition Metals and Organometallics as Catalysts for Olefin
Polymerization; Kaminsky, W., Sinn, H., Eds.; Springer-Verlag: Berlin,
Heidelberg, 1987; p 381. Kaminsky, W.; Rabe, O.; Schauwienold, A.-M.;
Schupfner, G. U.; Hanss, J.; Kopf, J. J. Organomet. Chem. 1995, 497, 181.
Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.; Antberg,
M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954. Diebold, J.;
Kirsten, R.; Ro¨ll, W.; Brintzinger, H. H.; Ju¨ngling, S.; Mu¨lhaupt, R.;
Langhauser, F. Organometallics 1994, 13, 964.
(5) A bridged metallocene in which the bridge is part of an η-fused bis-
(tetrahydroindenyl) ligand has been reported. Ko¨nemaan, M.; Erker, G.;
Fro¨hlich, R.; Kotila, K. Organometallics 1997, 16, 2900. Resconi, L.;
Nifant’ev, I. E.; Dubitsky, Y. A.; Barbassa, E.; Schaverien, C. J.; Ernst, R.
WO 96/38458 to Montell Technology Company. Uchino, H.; Endo, J.;
Takahama, T.; Sugano, T.; Katoh, K.; Iwama, N.; Taniyama, E. Eur. Pat.
Appl. 693502 to Mitsubishi Chemical Corporation. There was no mention of
rac and meso isomers. Okamoto, T.; Uemura, M.; Watanabe, M.; Ohtani, T.
WO 96/04317 (in Japanese) to Idemitsu Kosan.
As well as different 7-Me 1H NMR chemical shifts (δ2.60 ppm
for 1r;8 δ2.33 ppm for 1m9), the 4,4′-CH2CH2 bridge of 1r gave
a deceptively simple aa′bb′ pattern (δ3.04, 3.35 ppm; aa′ ) 5.04,
ab ) a′b′ ) -13.1, ab′ ) a′b ) 4.35, bb′ ) 13.97 Hz, simulated),
while 1m gave a more complex pattern (δ3.29, 3.47 ppm; aa′ )
8.85, ab ) -14.4, ab′ ) 3.77, a′b ) 8.51, a′b′ ) -14.5, bb′ )
9.26 Hz, simulated).
To confirm that the two isomers were indeed the rac and meso
isomers as expected by UFF molecular modeling (vide infra) and
to understand the geometric consequences of a 4,4′-bridge, the
X-ray crystal structures7 of both 1r and 1m were determined.
Their molecular structures are given in Figures 2 and 3.
Molecules of 1m/1r consist of a Zr(IV) center coordinated by
two chloride ligands and a bis(indenyl) ligand so as to form the
meso(rac) isomer of 1. The local geometry at zirconium is of
(7) See the Supporting Information.
(8) 1H NMR (CD2Cl2): δ 7.08-7.21 (dd, J ) 6.9 Hz, 4H), 6.72 (t, J )
3.5 Hz, 2H, 5 ring), 6.67 (t, J ) 3.5 Hz, 2H, 5 ring), 4.48 (dd, 2H, 5 ring),
3.35 (m, 2H, bridge), 3.04 (m, 2H, bridge), 2.60 (s, 6H, Me) ppm. 13C NMR
(CD2Cl2): δ 19.90 (CH3), 36.58 (CH2), 102.18 (CH, 5 ring), 108.48 (CH, 5
ring), 125.13 (CH, 6 ring), 126.48 (C), 126.55 (CH, 6 ring), 126.95 (C), 130.59
(CH), 135.08 (C), 137.08 (C) ppm.
(6) (i) 100 g (0.71 mol) of p-MeC6H4CH2Cl and 0.39 mol of Mg in 650
mL of THF gave 70 g of bis(tolyl)ethane, 93%. (ii) ClCH2CH2COCl, 1 equiv
of AlCl3 in CH2Cl2 at 0 °C gave 2 (3 isomers), 86%. (iii) Concentrated H2-
SO4, reflux 4 h, 94%. (iv) NaBH4 added to 3 in THF/MeOH at 0 °C; then
dehydration with HCl in ether gave 4, 46%. (v) 82.5 mL of 1.6 M n-BuLi
added to 18 g of 4 in ether at -78 °C, warmed to 20 °C; ZrCl4 added at -40
°C and warmed to 20 °C. See the Supporting Information for full details.
(9) 1H NMR (CD2Cl2): δ 7.14 (dd, J ) 3.45 Hz, 2H, 5 ring), 6.67 (m, 4H,
6 ring), 6.60 (t, J ) 3.45 Hz, 2H, 5 ring), 6.51 (dd, J ) 3.45 Hz, 2H, 5 ring),
3.47 (m, 2H, bridge), 3.29 (m, 2H, bridge), 2.33 (s, 6H, Me) ppm. 13C NMR
(CD2Cl2): δ 19.62 (CH3), 30.83 (CH2), 99.30 (CH, 5 ring), 106.09 (CH, 5
ring), 121.52 (C), 122.76 (CH, 5 ring), 125.47 (CH, 6 ring), 125.75 (CH, 6
ring), 130.75 (C), 132.96 (C), 134.81 (C) ppm.
S0002-7863(98)01129-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/11/1998

9946 J. Am. Chem. Soc., Vol. 120, No. 38, 1998
Communications to the Editor
was found with a strain energy 18 kcal mol-1 higher than the
first.7 These two rac-gauche conformations are separated by a
transition barrier of 21 kcal mol-1 in which the hydrogen atoms
in the -CH2-CH2- bridge are approximately eclipsed. These
UFF results were within 1-2 kcal mol-1, with and without,
Coulombic interactions. The strain energy of the meso isomer
(also gauche) is 10 kcal mol-1 higher in energy than the lowest
energy rac-gauche isomer with Coulombic interactions, and 4 kcal
mol-1 higher without Coulombic interactions.7 On the basis of
these calculations, the isolation of both rac-gauche and meso
metallocenes was to be expected.
Compound 1r, after activation with excess MMAO, polymer-
izes14,15 ethylene with an activity of 138 kg/g of Zr h to give
high molecular weight polyethylene (Mv ) 390 00016). The
complex of 1m/MMAO is more active (375 kg/g of Zr h) and
gives polyethylene with lower molecular weight (Mv ) 32 500).
The complex of 1r/MAO, polymerizes17 propylene with an
activity of only 10 kg/g of Zr h. The polymer has Mv ) 122 000
and is highly regioregular with 99.7 mol % 1,2- and 0.3 mol %
3,1-insertions. No 2,1-units were observed. The polymer has
low isotacticity (mm ) 77%; mmmm ) 65%). The complex of
1m/MAO is appreciably more active (204 kg/g of Zr h) and
affords atactic-PP (mm ) 28%, mr ) 49%, rr ) 23 mol %) with
a molecular weight Mv ) 29 000. There were no regioerrors.
These catalysts were significantly more active for the copo-
lymerization18 of ethylene and propylene; 1r/MAO afforded a high
molecular weight (Mv ) 335 000) copolymer with an activity of
230 kg copolymer/g of Zr h. The copolymer contained 60 mol
% ethylene and 40 mol % propylene (13C NMR). Under the same
conditions, 1m/MAO was much more active and afforded a high
molecular weight (Mv ) 224 000) copolymer with very high
activity (5350 kg/g of Zr h; ) 490 tons copolymer/mol of 1m
h!). 13C NMR analysis indicated 75 mol % ethylene incorpora-
tion.
Figure 2. X-ray crystal structure of rac-1,2-CH2CH2{4-(7-Me-indenyl)}2-
ZrCl2 (1r). Thermal ellipsoids are drawn at the 30% probability level.
Hydrogen atoms are given arbitrary radii.
Figure 3. X-ray crystal structure of meso-1,2-CH2CH2{4-(7-Me-indenyl)}2-
ZrCl2 (1m). Non-hydrogen atoms are represented as ellipsoids enclosing
50% probability density.
the usual distorted pseudo tetrahedral sort typical of group 4
metallocene dichlorides1 (data for 1m; 1r in {}) (i.e., bond angles
(°) Cl(1)-Zr(1)-Cl(2) 96.38 (3) {94.50(3)}, Cl(1)-Zr(1)-cp1
106.1 {106.12(2)}, Cl(2)-Zr(1)-cp1 105.1 {107.64(2)}, Cl(1)-
Zr(1)-cp2 106.9 {107.09(1)}, Cl(2)-Zr(1)-cp2 105.7 {105.43-
(2)}, cp1-Zr(1)-cp2 131.3 {130.31(1)}). The zirconium-
chloride bond lengths are approximately equal at Zr-Cl(1) )
2.4330(7) Å and Zr-Cl(2) ) 2.4464(7) {2.4358(8), 2.4277(4)}
Å. The Zr-Cp centroid distances are effectively equal at Zr-
Cp1 ) 2.228 Å and Zr-Cp2 ) 2.231 {2.222, 2.226} Å. The
Zr-Cp bond lengths lie in the range of 2.458-2.634 Å {2.466-
2.586} (av 2.535 {2.527} Å) indicating that the indenyl rings
are η5-coordinated to the zirconium. These parameters are quite
normal for zirconium metallocenes.1
To gain insight into the geometry and strain energy of the
isomers, 110 was modeled using the Universal Force Field.11,12
Two sets of calculations were performed: with and without
Coulombic interactions. In the former case, the atomic charges
were calculated using the charge equilibration method.13 The
range of validity of these methods has been previously describ-
ed.11-13 The lowest-energy isomer was the rac isomer in a gauche
conformation.7 The structure is in good agreement with that of
1r as found by X-ray diffraction. The rac-anti bridge conforma-
tion was found not to be an equilibrium structure and was found
by constraining the dihedral angle Cipso-CH2-CH2Cipso to 180°.
This led to an unstable rac-anti conformation with a very high
strain energy (nonplanar indenyl rings) of 124 kcal mol-1. Upon
relaxation of this constraint, a second rac-gauche conformation
Further research will focus on gaining understanding into the
potential of this new class of chiral metallocene and to improve
polymer properties.
Acknowledgment. This research was sponsored by Montell Technol-
ogy Company, Hoofddorp, The Netherlands. We thank Olof Sudmeijer
(SRTCA) for running the NMR spectra of the (co)polymers and Tiziano
Dall’Occo (Montell, Ferrara) for the ethylene polymerizations.
Note Added in Proof. Similar 4,4′-bridged metallocenes
have just been published. Halterman, R. L.; Combs, D.; Khan,
M. A. Organometallics 1998, 17, 3900-3707.
Supporting Information Available: Synthetic methods, polymeri-
zation details and results of UFF calculations, as well as tables of data
collection parameters, atom coordinates, bond distances and angles for
1m and 1r (25 pages, print/PDF). See any current masthead page for
ordering information and Web access instructions.
JA9811290
(14) Ethylene polymerizations at 80 °C under 9.6 bar in hexane using
“modified” MAO with Al:Zr ratio ) 1000.
(15) Under identical conditions, CH2CH2(4,7-dimethylindenyl)2ZrCl2/MAO,
as reference compound, gave polyethylene (molecular weight 205 000) with
an activity of 420 kg/g of Zr h. See: Resconi, L.; Piemontesi, F.; Camurati,
I.; Balboni, D.; Sironi, A.; Moret, M.; Rychlicki, H.; Zeigler, R. Organome-
tallics 1996, 15, 5046 and references therein.
(16) Polyethylene and atactic and isotactic polypropylene viscosity-averaged
molecular weights (Mv) were obtained from the experimentally determined
intrinsic viscosities using the correlations reported in the literature. For PE,
[η] ) (3.8 × 10-4) Mv0.725; for a-PP, [η] ) (1.85 × 10-4) Mv0.74; for i-PP, [η]
) (1.93 × 10-4) Mv0.74. Moraglio, G.; Gianotti, G.; Bonicello, U. Eur. Polym.
J. 1973, 9, 623. Pearson, D. S.; Fetters, L. J.; Younghouse, L. B.; Mays, J.
W. Macromolecules 1988, 21, 478.
(17) Propylene polymerizations were performed at 50 °C with 4 µmol of
metallocene; Al:Zr ratio ) 5000 in a 5 L reactor containing 1.6 kg of liquid
propylene for 1 h.
(18) Copolymerizations at 50 °C with 0.49 µmol of metallocene, Al:Zr
ratio ) 40 000, in a 25 L reactor containing 7.5 kg liquid propylene and 6
mol % C2H4. The very large Al:Zr ratio is a consequence of the high catalyst
activity. From experience, 20 mmol MAO is necessary for efficient and
effective scavenging of 7.5 kg of liquid propylene in a 25 L autoclave. The
very small amount of metallocene added therefore necessarily implies a very
large Al:Zr ratio.
(10) The 7-Me group was omitted in the UFF calculations. This should
have little effect on the strain energy.
(11) Rappe´, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A., III;
Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024. The UFF calculations
were performed using the Molecular Classical Mechanics (MCM) software
written by Rappe´ and Skiff.
(12) A pseudoatom was used to attach each cyclopentadienyl ring to the
metal center. Castonguay, L. A.; Rappe´, A. K. J. Am. Chem. Soc. 1992, 114,
5832.
(13) Rappe´, A. K.; Goddard, W. A., III J. Phys. Chem. 1991, 95, 3358.