Highly Regiospecific Zirconocene Catalysts for the Isospecific

Maurizio Galimberti , Fabrizio Piemontesi , Laura Alagia , Simona Losio , Luca ... Matthias Johannsen , Robert Haschick , Hartmut Komber , Albena Lede...
7 downloads 0 Views 248KB Size
Download PDF
2308

J. Am. Chem. Soc. 1998, 120, 2308-2321

Highly Regiospecific Zirconocene Catalysts for the Isospecific Polymerization of Propene Luigi Resconi,*,† Fabrizio Piemontesi,† Isabella Camurati,† Olof Sudmeijer,‡ Ilya E. Nifant’ev,*,§ Pavel V. Ivchenko,§ and Lyudmila G. Kuz’mina| Contribution from the Montell Polyolefins, Centro Ricerche G. Natta, 44100 Ferrara, Italy, Shell Research and Technology Centre, 1031 CM Amsterdam, The Netherlands, Department of Chemistry, Moscow UniVersity, 119899 Moscow, Russia, and Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russia ReceiVed September 9, 1997

Abstract: A new class of isospecific and highly regiospecific C2-symmetric ansa-zirconocenes, characterized by a bisindenyl ansa ligand with bulky substituents in the 3 position of indene and a single carbon bridge is disclosed: variation of the size of the substituent in C(3) has a strong effect on the extent of chain transfer and isospecificity in propene polymerization. In fact, while rac-[Me2C(1-indenyl)2]ZrCl2 produces low molecular weight and moderately isotactic polypropene (iPP) also containing some regioirregularities (M h n ) 6500, mmmm ca. 81% and 2,1tot ) 0.4% at 50 °C in liquid monomer), rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 produces iPP with molecular weights between 25 000 (Tp ) 70 °C) and 410 000 (Tp ) 20 °C) and a fairly high isotacticity (mmmm ca. 95% at 50 °C), with no detectable 2,1 units. The influence of polymerization temperature on the catalyst performance has been investigated by polymerizing liquid propene in the temperature range of 20-70 °C: the experimental ∆∆Eq values for enantioface selectivity have been estimated for two members of the new class (rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 ∆∆Eqenant ) 4.6 kcal/mol; rac-[Me2C(3-(trimethylsilyl)1-indenyl)2]ZrCl2 ∆∆Eqenant ) 2.6 kcal/mol). For comparison, Brintzinger’s moderately isospecific, benchmark catalyst rac-[ethylene(1-indenyl)2]ZrCl2 (∆∆Eqenant ) 3.3 kcal/mol), the single carbon bridged, unsubstituted rac-[Me2C(1-indenyl)2]ZrCl2 (∆∆Eqenant ) 2.8 kcal/mol), and the C2-symmetric, practically aspecific, rac[ethylene(3-methyl-1-indenyl)2]ZrCl2 (∆∆Eqenant ) 1.9 kcal/mol) are also reported. The molecular structures of rac-[Me2C(3-tert-butyl-1-indenyl)2]ZrCl2 and rac-[Me2C(3-(trimethylsilyl)-1-indenyl)2]ZrCl2 have been determined.

Introduction The molecular architecture of polypropenes obtained from ansa-zirconocenes is strongly dependent on the biscyclopentadienyl ligand structure.1 Since the early C2-symmetric, racemic ansa-metallocenes for the isospecific polymerization of olefins, several different classes of such catalysts have been developed. The prototypal class based on C2-symmetric racemic zirconocenes with ansa-bis(3-alkyl-cyclopentadienyl) or ansa-bis(indenyl) ligands (I in Chart 1) produce isotactic polypropenes (iPP) with isotacticities ranging from very low to quite high, but invariably with low molecular weights,1,2 the best known example being Brintzinger’s rac-[ethylene(1-indenyl)2]ZrCl2.3 The introduction of an alkyl substituent in the 2 position (R to †

Montell Polyolefins. Shell Research and Technology Centre. § Moscow University. | Russian Academy of Sciences. (1) (a) 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, 1988; p 281. (b) Ewen, J. A.; Elder, M. J.; Jones, R. L.; Haspeslagh, L.; Atwood, J. L.; Bott, S. G.; Robinson, K. Makromol. Chem., Macromol. Symp. 1991, 48/49, 253. (c) Spaleck, W.; Antberg, M.; Dolle, V.; Klein, R.; Rohrmann, J.; Winter, A. New J. Chem. 1990, 14, 499. (d) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (2) Collins, S.; Gauthier, W. J.; Holden, D. A.; Kuntz, B. A.; Taylor, N. J.; Ward, D. G. Organometallics 1991, 10, 2061. ‡

the bridge) of either an ansa-bis(3-alkylcyclopentadienyl)4 or ansa-bis(indenyl)5 zirconium complex (II in Chart 1) increases both the stereoregularity and the molecular weight of the produced polyolefin, and reduces the amount of regioirregularities, in comparison with the unsubstituted analogue. Wellknown examples are Me2Si(2,4-dimethylcyclopentadienyl)2ZrCl2,4 Me2Si(2-methylindenyl)2ZrCl2,5 which led to the recent important development of the first zirconocenes able to compete with the performance of industrial Ti-based catalysts,6 and Me2Si(2-methylbenz[e]indenyl)2ZrCl2.7 The above racemic catalysts are almost invariably generated along with their meso forms which produce unwanted low molecular weight atactic polypropene with nonnegligible po(3) (a) Wild, F.; Wasiucionek, M.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1985, 288, 63. (b) Collins, S.; Kuntz, B.; Taylor, N.; Ward, D. J. Organomet. Chem. 1988, 342, 21. (c) Lee, J.; Gauthier, W.; Ball, J.; Iyengar, B.; Collins, S. Organometallics 1992, 11, 2115. (d) Piemontesi, F.; Camurati, I.; Resconi, L.; Balboni, D.; Sironi, A.; Moret, M.; Zeigler, R.; Piccolrovazzi, N. Organometallics 1995, 14, 1256. (4) Mise, T.; Miya, S.; Yamazaki, H. Chem. Lett. 1989, 1853. Roll, W.; Brintzinger, H. H.; Rieger, B.; Zolk, R. Angew. Chem., Int. Ed. Engl. 1990, 29, 279. (5) Spaleck, W.; Antberg, M.; Rohrmann, J.; Winter, A.; Bachmann, B.; Kiprof, P.; Behm, J.; Herrmann, W. Angew. Chem., Int. Ed. Engl. 1992, 31, 1347-1350. (6) Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.; Antberg, M.; Dolle, V.; Paulus, E. Organometallics 1994, 13, 954. (7) (a) Stehling, U.; Diebold, J.; Kirsten, R.; Ro¨ll, W.; Brintzinger, H.H.; Ju¨ngling, S.; Mu¨lhaupt, R.; Langhauser, F. Organometallics 1994, 13, 964. (b) Ju¨ngling, S.; Mu¨lhaupt, R.; Stehling, U.; Brintzinger, H. H.; Fischer, D.; Langhauser, F. J. Polym. Sci., Part A: Polym. Chem. 1995, 33, 1305.

S0002-7863(97)03160-0 CCC: $15.00 © 1998 American Chemical Society Published on Web 03/03/1998

Highly Regiospecific Zirconocene Catalysts

J. Am. Chem. Soc., Vol. 120, No. 10, 1998 2309

Chart 1

Scheme 1

lymerization activity and are difficult to remove from the catalyst mixture (Scheme 1, A). In addition, all of these modified C2symmetric systems require multistep, low overall yield synthetic routes.6,7 Miyake has developed a class of C1-symmetric systems8 (III in Chart 1) which are highly isospecific (e.g., threo-Me2C(3tert-butylcyclopentadienyl)(3-tert-butylindenyl)ZrCl2) but again produce low molecular weight iPP. In this case, the meso-like (erythro) isomer (less active than the racemic one) is partially isospecific. Marks9 and Ewen10 have designed a notable class of C1-symmetric systems (IV in Chart 1) for which a meso form does not exist (Scheme 1, B). Ewen’s elegant catalyst design, Me2C(3-tert-butyl-1-cyclopentadienyl)(9-fluorenyl)ZrCl2, also includes an easy ligand synthesis. This catalyst, however, has a relatively low stereoselectivity (mmmm ) 78% at 40 °C)11 and, again, produces iPP with modest molecular weights. Its Me2Si-bridged analogue shows a better performance.10 Ewen has also proposed a novel type (V in Chart 1) of C2symmetric systems, constituted of metallocenes having two strapped indenyls with a bulky substituent in the 3 position of indene.12 The prototype of this class, rac-Me2Si(3-tert-butyl1-indenyl)2ZrCl2, which reintroduces the problem of meso isomer formation (Scheme 1, C), was reported by Miyake8 to have a very poor performance, both in terms of stereospecificity and molecular weights (mmmm ) 75.5 and Mw ) 5000 only, (8) Miyake, S.; Okumura, Y.; Inazawa, S. Macromolecules 1995, 28, 3074. (9) Giardello, M.; Eisen, M.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 12114. (10) Ewen, J. A.; Elder, M. J. In Ziegler Catalysts; Fink, G., Mu¨lhaupt, R., Brintzinger, H. H., Eds.; Springer-Verlag: Berlin, 1995; p 99. (11) Razavi, A.; Vereecke, D.; Peters, L.; Den Dauw, K.; Nafpliotis, L.; Atwood, J. L. In Ziegler Catalysts; Fink, G., Mu¨lhaupt, R., Brintzinger, H. H., Eds.; Springer-Verlag: Berlin, 1995; p 111. (12) Ewen, J. A. Macromol. Symp. 1995, 89, 181.

Scheme 2

even at the low Tp of 1 °C), even if compared to that of the early C2-symmetric zirconocenes. At the same time, we were also investigating the effect of the alkyl substituent in zirconocenes of the latter type. Some of us had developed a simple, inexpensive, and general synthesis of single carbon bridged ligands, from acetone and indene (Scheme 2).13 The ligand dianions of this class generate zirconocenes in high yield, and the synthesis can be made diastereoselective by the use of stannylated ligands.14 We have investigated the performance of two members of the above class of zirconocene catalysts,15 namely rac-[isopropylidenebis(3-tert-butyl-1-indenyl)]zirconium dichloride (racMe2C(3-tBu-Ind)2ZrCl2, 4) and rac-[isopropylidenebis(3-(trimethylsilyl)-1-indenyl)]zirconium dichloride (rac-Me2C(3-Me3Si-1-Ind)2ZrCl2 5), and report here their synthesis, characterization, and evaluation in the methylalumoxane (MAO)-cocatalyzed polymerization of propene. To put the performance of 4 and 5 in the proper perspective, the C2-symmetric, moderately isospecific rac-[ethylenebis(1-indenyl)]ZrCl2 (1)3 and rac-[isopro(13) Nifant’ev, I. E.; Ivchenko, P. V. Eur. Pat. Appl. 722 949 (to Montell). Nifant′ev, I. E.; Ivchenko, P. V.; Kuz’mina, L. G.; Luzikov, Yu., N.; Sitnikov, A. A.; Sizan, O. E. Synthesis 1997, 469. (14) Nifant′ev, I. E.; Ivchenko, P. V.; Resconi, L. Eur. Pat. Appl. 722,950 (to Montell); Chem. Abstr. 1996, 125, 196000. Nifant’ev, I. E.; Ivchenko, P. V. Organometallics 1997, 16, 713. (15) Resconi, L.; Piemontesi, F.; Nifant’ev, I. E.; Ivchenko, P. V. PCT Int. Appl. WO 96 22, 995 (to Montell); Chem. Abstr. 1996, 125, 222171.

2310 J. Am. Chem. Soc., Vol. 120, No. 10, 1998 Chart 2

pylidenebis(1-indenyl)]ZrCl2 (2),1c and the aspecific rac[ethylenebis(3-methyl-1-indenyl)]ZrCl2 (3)1a (Chart 2) are used as benchmarks. Results 1. Synthesis of the Zirconocenes. Compounds 1-3 were synthesized as described in the literature. 2,2-bis(indenyl)propane and 2,2-bis(3-tert-butyl-1-indenyl)propane ligand precursors were synthesized according to the procedure developed by one of us13 by direct condensation of indene or 3-tertbutylindene and acetone. For the purpose of their purification, the crude products were converted into their dilithium salts.13 2,2-Bis(1-(trimethylsilyl)-3-indenyl)propane was prepared by silylation of the dilithium salt of bis-indenyldimethylmethane according to the procedure described in ref 14. Compounds 4 and 5 were prepared by transmetalation between the bis-trialkyltin derivative of the ligands and ZrCl4 in noncoordinating solvents (Scheme 3).14 In a one-pot synthesis, the dilithium salts of 2,2-bis(alkylindenyl)propanes (alkyl ) tBu, Me3Si) were treated with Me3SnCl in Et2O to give quantitatively 2,2-bis(1-(trimethylstannyl)-1-alkyl-3-indenyl)propanes which were then (after removing Et2O) reacted with ZrCl4 in toluene to give 4 and 5 (Scheme 3). The intermediate distannyl derivatives 6 and 7 consist of rac/meso mixtures that can be easily identified by 1H NMR: the isopropylidene bridge serves as a stereochemical Scheme 3

Resconi et al. probe for identifying the meso (diastereotopic methyls) and racemic (identical methyls) isomers. Surprisingly, 6 and 7 do not consist of equal amounts of rac and meso forms as we had observed in the synthesis of the related 1,2-bis(1-(trimethylsilyl)-4,7-dimethyl-3-indenyl)ethane, for which the dilithium or dipotassium salt, generated in THF, was quenched directly with Me3SiCl without the need of prior isolation.16 On the contrary, rac-6 and rac-7 were found to be the major isomers in their reaction mixtures. It is remarkable that the rac/meso distributions of distannyl derivatives depend on the crystallization method of the initial dilithium salts. In general, the rac-6/meso-6 ratio varies in the range 1.5-2.0:1 and rac-7/meso-7 in the range 1.0-1.2:1. This effect is probably caused by the existence of nonionic interactions between Li atoms and indenyl fragments in the crystalline salts. Cases of such structures-metallocene-like lithium salts-have been recently reported.17 Yields of 4 and 5 are close to 90%. Evidently, the rac/meso ratio for the zirconocenes reproduces that of the starting distannyl derivatives. Therefore, the real chemical yield (from the ligand) of rac-4 is considerably more than 50%. Unfortunately, the similarity of physical properties for rac and meso isomers of 4 and 5 makes their separation rather difficult; rac and meso forms of 4 and 5 were recrystallized from DME, in which the racemic isomers were slightly less soluble. We found that the stabilities of 4 and 5 depend strongly on their purity. Chemically pure samples could be exposed to air for 10 h without noticeable decomposition, while the samples contaminated with even small amounts of tin-containing impurities underwent extensive decomposition in just a few minutes. Complexes 4 and 5 could be prepared directly from the corresponding dilithium salts as well. Although the yields of zirconocenes were quite high (70-80%), 1:1 rac/meso mixtures of 4 and 5 were obtained. The major advantage of these novel systems resides in the very easy, high-yield synthetic procedure, especially the 2,2bis(3-alkyl-1-indenyl)propane ligand precursors. In addition, an added advantage of these compounds is the presence of an isopropylidene bridge which, as mentioned above for the distannyl derivatives, represents a builtin, very convenient stereochemical probe for identifying the meso (diastereotopic methyls) and racemic (identical methyls) zirconocene isomers.

Highly Regiospecific Zirconocene Catalysts

J. Am. Chem. Soc., Vol. 120, No. 10, 1998 2311

Figure 1. (a) Molecular structure and labeling scheme for rac-Me2C(3-tBu-Ind)2ZrCl2 (4). (b) Molecular structure and labeling scheme for racMe2C(3-Me3Si-Ind)2ZrCl2 (5).

This stereochemical probe is obviously present also in the Me2Si-bridged zirconocenes but is lacking in the related ethylene bridged zirconocenes such as 1 and 3. 2. X-ray Analysis of 4 and 5. The racemic structures of 4 and 5 were confirmed by X-ray analysis. Two views of each are shown in Figure 1. The zirconium atom is coordinated to the η5 cyclopentadienyl fragments of the two indenyls of the ansa ligand and two chlorine atoms. Mutual arrangement of the indenyl fragments corresponds to C2 symmetry, which is geometrically rigorous for 5. The molecules show noticeable distortions due to the short isopropylidene bridge. The most relevant geometrical parameters for 4 and 5 and a series of bis(cyclopentadienyl) zirconium complexes are compared in Table 1. In 4 and 5, the inner angle (φ, see Chart 3) at the bridging carbon atom (100.1(5)° for 4 and 99.4(2)° for 5) lies within the range 99.0-100.3° characteristic of other ansa-biscyclopentadienyl complexes with a single carbon bridge (2, 2m, and b-d). The angles γ between each CCp-Cbr bond and the plane of the corresponding cyclopentadienyl fragment are equal to 13.6° and 11.4° in 4 and 13.2° (both) in 5. These values are close to those (12.6-15.1°) in 2, 2m, and b-d. It is of interest that the (16) Resconi, L.; Piemontesi, F.; Camurati, I.; Balboni, D.; Sironi, A.; Moret, M.; Rychlicki, H.; Zeigler, R. Organometallics 1996, 15, 5046.

angle φ at the bridging atom ranges within 94.3° and 95.2°, and the displacement angle γ from the Cp planes varies from 16.0° to 18.1° in ansa complexes with a Si bridge such as a. In a (and other Si-bridged complexes), a smaller ansa φ angle and a larger γ angle compared to those in 4 and 2, 2m, and b-d, result in less significant distortion of other geometrical parameters. The R angle cp-Zr-cp′ (cp, cp′ ) centroids of the Cp rings) of 118.3° for 4 and 117.4° for 5 is close to those in 2 and 2m (117.9-118.3°) and somewhat larger than in b-d (115.6117.1°). It should be noted that, in bis(cyclopentadienyl)zirconium compounds without a bridge between the two Cp rings (e-g), this parameter ranges from 129.0° to 132.5°. An important descriptor of bent metallocene structures is the angle between the Cp plane and the cp-Zr bond, δ (Chart 3), which gives an idea (together with the value of the β angle) of the accessibility of the metal atom: the lower the values are from 90°, the more the metal is tucked in the ligand envelope. The main geometrical distinction of 4 from 2, 2m, and b-d is associated with the angle β and the range of Zr-CCp bond distances. In 4, β (75.2°) is increased compared to those of 2, 2m, and b-d (70.9-71.8°). On the contrary, 5 has a dihedral angle β that falls closer to the range of the other complexes. The range of Zr-CCp bond distances (∆r ) 0.25 Å) is wider

2312 J. Am. Chem. Soc., Vol. 120, No. 10, 1998

Resconi et al.

Table 1. Relevant Geometrical Parameters (deg or Å) of Selected Cp′2ZrX2 Complexes (see Chart 3 for angle labels)

Chart 3

than in 5 and 2, 2m, and b-d (∆r ) 0.11-0.20 Å). For unbridged molecules, ∆r ) 0.04-0.07 Å. These differences are, likely, caused by the bulky tBu substituents at C(3) of both indenyl fragments. This conclusion is supported by significant displacements of the C(3)-CtBu bonds from the planes of the parent cyclopentadienyl rings

(10.0° and 8.2°) opposite to Zr. Moreover, the Zr-C(3) and Zr-C(3′) bond distances are among the longest. The distinction between 4 and 5 are, apparently, associated with the different spatial location of the SiMe3 and tBu substituents. The C(3)-CtBu bond distance (1.55 Å) is significantly shorter than the C(3)-Si distance (1.87 Å). Hence, the tBu substituents are situated closer to the coordination sphere of the Zr atom than the SiMe3 and affect its catalytic behavior more significantly. The displacement of the C(3)-Si bond in 5 (8.0°) is similar to that of the C(3)-CtBu bond in 4. It should be noted that the X-Zr-X angle is little sensitive to the steric hindrance of the ligands. Little correlation is observed between this geometrical parameter and the type of geometry distortions for the groups of molecules selected in Table 1. This parameter varies within 98.7-100.8 (4, 5, 2, 2m, and b-d), 96.8-99.3 (a and related Si-bridged complexes), and 95.5-97.1° (e-g). 3. Influence of Ligand Structure. In Table 2 we compare

Highly Regiospecific Zirconocene Catalysts

J. Am. Chem. Soc., Vol. 120, No. 10, 1998 2313

Table 2. Propene Polymerization with Racemic Zirconocene/MAO Catalystsa tacticityb zirconocene

bobsdd

% mmmm

total regioinversions (%)c

Tm (°C)

Mve

Me2C(Ind)2ZrCl2 C2H4(Ind)2ZrCl2f C2H4(4,7-Me2-Ind)2ZrCl2f Me2Si(Ind)2ZrCl2 Me2Si(2-Me-Ind)2ZrCl2 C2H4(3-Me-Ind)2ZrCl2 Me2C(3-tBu-Ind)2ZrCl2 Me2C(3-SiMe3-Ind)2ZrCl2

0.9580 0.9737 0.9831 0.9798 0.9882 0.7233 0.9894 0.9733

80.69 87.47 91.84 90.30 94.25 19.96 94.80 87.36

0.38 0.55 2.80g 0.48 0.33 0 0 0

127 134f 131f 144 148 amorphous 152 138f

11 100 33 600f 6 700f 56 000 231 500 15 800h 88 700f 69 700f

a Polymerization conditions: 1 L stainless-steel autoclave, propene (0.4 L), 50 °C, 1 h, zirconocene/MAO aged 10 min. b Determined assuming the enantiomorphic site model, see ref 37. c Total regioirregular units (2,1 erythro + 2,1 threo + 3,1) determined as described in ref 37; end groups not included. d In liquid monomer, bobsd f b. e Determined from experimental intrinsic viscosity (THN, 135 °C) according to the [η] ) K (M h v)a with K ) 1.93 × 10-4 and R ) 0.74.48 f Average values. g End groups included. h Calculated from [η] according to the [η] ) K(M h v)a with K ) 1.85 × 10-4 and R ) 0.737.49

the molecular characterization of iPP from a series of different zirconocenes in which the bridge length and indene substitution are varied. The type of bridge (Me2C 2σ(I)] R1 ) 0.0533, wR2 ) 0.1230 R1 ) 0.0236, wR2 ) 0.0537 R indices (all data) R1 ) 0.1087, wR2 ) 0.1415 R1 ) 0.0298, wR2 ) 0.0599 extinct coeff 0.0000(8) 0.0008(2) largest diff. peak and hole, e A-3 0.507 and -0.468 0.356 and -0.425 residual solid was recrystallized from ether, and 2.72 g (25%) of pure meso-isopropylidenebis(3-tert-butylindenyl)zirconium dichloride was isolated. 1H NMR (CD Cl , 30 °C, δ, ppm). rac-4: 7.74 (“t”, 4H), 7.25 (dd, 2 2 2H), 6.97 (dd, 2H, C6 ring), 5.97 (s, 2H, C5 ring), 2.33 (s, 6H, >CMe2), 1.37 (s, 18H, -CMe3). meso-4: 7.95 (“d”, 2H), 7.70 (“d”, 2H), 7.04 (dd, 2H), 6.80 (dd, 2H, C6 ring), 5.81 (s, 2H, C5 ring), 2.67 (s, 3H, >CMe2), 2.09 (s, 3H, >CMe2), 1.47 (s, 18H, -CMe3). Anal. Calcd for C29H34ZrCl2: C, 63.94; H, 6.29. Found: C, 63.70; H, 6.21. Synthesis of Isopropylidenebis(3-(trimethylsilyl)indenyl)zirconium Dichloride (5). 2,2-bis(1-(trimethylsilyl)inden-3-yl)propane (8.34 g, 20 mmol) was dissolved in 100 mL of ether. The solution thus obtained was cooled to -20 °C, and 22 mL of a 2.0 M solution of n-BuLi in pentane was added to give a suspension of dilithium 2,2bis(3-(trimethylsilyl)inden-1-yl)propane. To this suspension, which was first allowed to rise to room temperature and was then cooled to -40 °C, 5.0 g (42 mmol) of trimethyltin chloride was added. The organic layer was separated off, and evaporated to give a mixture of rac-/mesoisopropylidenebis(1-(trimethylsilyl)-1-(trimethylstannyl)-3-indene) as yellow oil that crystallizes upon standing. The product is contaminated with a small amount of Me3SnCl. The rac/meso ratio usually averages 1.0-1.2:1. 1H NMR (C D , 30 °C, δ, ppm). rac-7: 7.71-6.98 (some groups 6 6 of multiplets, 8H), 6.65 (s, 2H), 1.96 (3, 6H), 0.07 (s, 18H), -0.07 (s, 18H). meso-7: 7.71-6.98 (some groups of multiplets, 8H), 6.62 (s,

2H), 2.01(s, 3H), 1.95(s, 3H), 0.04(s, 18H), -0.03 (s, 18H). Anal. Calcd for C33H52Si2Sn2: C, 53.39; H, 7.06. Found: C, 52.96; H, 6.81. The distannylated derivative thus obtained was dissolved in 50 mL of toluene, 4.66 g (20 mmol) of ZrCl4 was added, and the resulting mixture was heated to 80 °C and stirred for an additional 6 h. The red solution was then separated off and the toluene and Me3SnCl were removed under reduced pressure (10-2 Torr) to give 10.0 g (87%) of red crystalline solid representing rac-5/meso-5 (by NMR). The product was then recrystallized from DME. Pure rac-isopropylidenebis(3(trimethylsilyl)-1-indenyl)zirconium dichloride (3.69 g, 36%) was thus obtained. The mother liquor was collected and evaporated. The residual solid was recrystallized from ether, and 2.17 g (21%) of pure meso-isopropylidenebis(3-(trimethylsilyl)indenyl)zirconium dichloride was isolated. 1H NMR (CD Cl , 30 °C, δ, ppm). rac-5: 7.80 (“d”, 2H), 7.55 2 2 (“d”, 2H), 7.30 (t, 2H), 7.06 (t, 2H, C6 ring), 6.08 (s, 2H, C5 ring), 2.37 (s, 6H, >CMe2), 0.26 (s, 18H, -SiMe3). meso-5: 7.92 (“d”, 2H), 7.49 (“d”, 2H), 7.10 (t, 2H), 6.88 (t, 2H, C6 ring), 6.00 (s, 2H, C5 ring), 2.68 (s, 3H, >CMe2), 2.19 (s, 3H, >CMe2), 0.35 (s, 18H, -SiMe3). Anal. Calcd for C27H34Si2ZrCl2: C, 56.21; H, 5.94. Found: C, 56.04; H, 5.88. Synthesis of Isopropylidenebis(4,5,6,7-tetrahydro-3-tert-butylindenyl)zirconium Dichloride (4-H4). rac-Me2C(3-tBu-Ind)2ZrCl2 (0.66 g) was dissolved in 50 mL of CH2Cl2 (red solution) and hydrogenated with H2 (5 atm)/PtO2 (40 mg) for 4 h. The mixture turned yellow

Highly Regiospecific Zirconocene Catalysts

J. Am. Chem. Soc., Vol. 120, No. 10, 1998 2321

Table 12. Selected Bond Lengths (Å) and Angles (deg) for 4 Zr(1)-Cl(1) Zr(1)-C(1) Zr(1)-C(2) Zr(1)-C(3) Zr(1)-C(4) Zr(1)-C(9) C(1)-C(14) C(1)-C(2) C(1)-C(9) C(2)-C(3) C(3)-C(4) C(4)-C(9) C(3)-C(10) C(14)-C(15) C(1)-C(2)-C(3) C(2)-C(3)-C(4) C(2)-C(3)-C(10) C(4)-C(3)-C(10) C(3)-C(4)-C(9) C(1)-C(9)-C(4) C(9)-C(1)-C(2) C(2′)-C(1′)-C(14) C(9′)-C(1′)-C(14) C(1′)-C(14)-C(1) C(1)-C(14)-C(15) C(1)-C(14)-C(15′) Cl(1)-Zr(1)-Cl(2)

Bonds 2.405(2) Zr(1)-Cl(2) 2.439(6) Zr(1)-C(1′) 2.446(6) Zr(1)-C(2′) 2.615(5) Zr(1)-C(3′) 2.660(6) Zr(1)-C(4′) 2.539(7) Zr(1)-C(9′) 1.560(8) C(1′)-C(14) 1.431(9) C(1′)-C(2′) 1.408(9) C(1′)-C(9′) 1.411(9) C(2′)-C(3′) 1.424(8) C(3′)-C(4′) 1.446(8) C(4′)-C(9′) 1.552(8) C(3′)-C(10′) 1.51(1) C(14)-C(15′) 109.6(6) 107.5(5) 124.6(5) 126.9(5) 107.4(6) 108.6(5) 106.9(5) 123.3(6) 129.2(5) 100.1(5) 111.0(5) 113.5(6) 98.69(9)

Angles C(1′)-C(2′)-C(3′) C(2′)-C(3′)-C(4′) C(2′)-C(3′)-C(10′) C(4′)-C(3′)-C(10′) C(3′)-C(4′)-C(9′) C(1′)-C(9′)-C(4′) C(9′)-C(1′)-C(2′) C(2′)-C(1′)-C(14) C(9′)-C(1′)-C(14) C(15)-C(14)-C(15′) C(1′)-C(14)-C(15′) C(1′)-C(14)-C(15)

2.416(2) 2.425(6) 2.462(5) 2.634(5) 2.675(6) 2.510(7) 1.519(9) 1.435(8) 1.426(9) 1.416(10) 1.418(9) 1.441(10) 1.541(9) 1.53(1) 111.1(6) 106.2(6) 125.4(6) 127.3(7) 108.6(6) 108.7(6) 105.3(5) 123.3(6) 129.2(5) 107.2(6) 111.1(5) 114.0(6)

after 3 h. After filtration, the solution was brought to dryness under reduced pressure, and the solid was washed with Et2O (2 × 5 mL) and hexane (5 mL) to yield, after drying in vacuo, 0.22 g of pure (by 1H NMR) rac-Me2C(4,5,6,7-tetrahydro-3-tBu-Ind)2ZrCl2. X-ray Structure Determination and Refinements. Crystals suitable for X-ray diffraction of both compounds were grown from Et2O. The details of the X-ray experiment and crystallographic parameters are given in Table 11. Both structures were solved by direct methods and refined by fullmatrix least-squares on F2. For 4, difference Fourier synthesis shows several electron density peaks in the vicinity of the symmetry center. These peaks corresponds to disordered (C2H5)O solvate molecule. A pattern of disordering is rather complicated. For this reason, we considered as carbon atoms only three highest peaks that were well refined and gave relatively low isotropic thermal parameters. The final least-squares refinement was performed in the anisotropic approximation for the non-hydrogen atom of the complex molecule and in the isotropic approximation for three atoms of the solvate molecule. The hydrogen atoms were refined using the ridding model with Uiso equal to 1.5 of the parent carbon atom. In crystals of 5, the molecule occupies a special position at a 2-fold axis, which passes through the Zr and Cbr atoms. In this structure, all of the hydrogen atoms were found from the difference Fourier synthesis. They were included in the final structure refinement in the isotropic approximation. For both structures, the highest electron density residual peaks are located in the vicinity of Zr; for 4, they are also located in the area of the solvate molecule. All of the calculations were performed using SHELXS8645 and SHELX9346 software. The ORTEP program47 (probability 0.5) was used for drawing the molecule. Non-hydrogen atom atomic coordinates and equivalent isotropic displacements are given in the Supporting Information; Tables 12 and 13 give selected bond lengths and bond angles. Polymerizations. Polymerization grade propene and hexane were received directly from the Montell Ferrara plant. MAO was a commercial product (Witco, 30% w/w in toluene) treated in vacuo to (45) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467. (46) Sheldrick, G. M. SHELXL93, Program for the Refinement of Crystal Structures; University of Go¨ttingen, Germany. (47) Johnson, C. K. ORTEP, Report ORNL-3794, 2nd revision; Oak Ridge National Laboratory, TN, 1970.

Table 13. Selected Bond Lengths (Å) and Angles (deg) for 5 Zr(1)-Cl(1) Zr(1)-C(1) Zr(1)-C(2) Zr(1)-C(3) Zr(1)-C(4) Zr(1)-C(9) C(1)-C(10) C(1)-C(2) C(1)-C(9) C(1)-C(2)-C(3) C(2)-C(3)-C(4) C(2)-C(3)-Si(1) C(4)-C(3)-Si(1) C(3)-C(4)-C(9) C(1)-C(9)-C(4) C(9)-C(1)-C(2)

Bonds 2.4205(4) C(2)-C(3) 2.452(2) C(3)-C(4) 2.451(2) C(4)-C(9) 2.582(2) C(10)-C(11) 2.646(1) C(3)-Si(1) 2.556(1) Si(1)-C(12) 1.537(2) Si(1)-C(13) 1.423(2) Si(1)-C(14) 1.441(2) 111.8(1) 105.1(1) 127.4(1) 126.2(1) 109.5(1) 107.5(1) 106.0(1)

Angles C(2)-C(1)-C(10) C(9)-C(1)-C(10) C(1)-C(10)-C(1A) C(1)-C(10)-C(11) C(1)-C(10)-C(11A) Cl(1)-Zr-Cl(2)

1.422(2) 1.432(2) 1.443(2) 1.537(3) 1.874(2) 1.872(2) 1.863(2) 1.865(2)

123.3(1) 128.4(1) 99.4(2) 114.2(1) 110.8(1) 100.69(2)

remove most of the unreacted TMA, or modified MAO (Albemarle) was used as received. The polymerization experiments were carried out in a 1 or 2 L stainless steel autoclave with 0.4 or 1 L liquid propene for 1 h. Stirring was kept at 800 rpm by means of a three-blade propeller. Metallocene and MAO were precontacted for 10 min in toluene solution (10 mL) and then added to the monomer at 2-5 °C below the polymerization temperature, which was reached in 1-5 min. The polymerizations were quenched with CO; the polymers were isolated by venting unreacted monomer and drying in an oven under vacuum at 60 °C. Polymer Analysis. The 1H NMR spectra were acquired on a Bruker DPX-400 spectrometer operating in the Fourier transform mode at 120 °C at 400.13 MHz, with a 45° pulse and 5 s of delay between pulses; 256 or 512 transients were stored for each spectrum. The 13C NMR spectra were acquired on a Bruker DPX-400 (100.61 MHz, 90° pulse, 12 s delay between pulses) or DRX-500 (125.76 MHz, 90° pulse, 16 s delay between pulses) spectrometers; about 3000 transients were stored for each spectrum. The samples were prepared by dissolving 50-100 mg of the polymer under nitrogen in 0.5 mL of degassed C2D2Cl4. As a reference, the residual peak of C2DHCl4 in the 1H spectra (5.95 ppm) and the peak of the mmmm pentad in the 13C spectra (21.8 ppm) were used. The microstructure analysis (pentad distribution, type and amount of regioirregular units, and end group analysis) was carried out as previously described.37 The average viscosity molecular weights were obtained from the experimental intrinsic viscosities using the correlations reported in the literature for iPP48 and aPP.49

Acknowledgment. We are indebted to all of the Montell people who, over several years, provided the excellent data for this work: M. Colonnesi and S. Tartarini for the polymerization experiments, D. Balboni for the synthesis of rac-Me2C(4,5,6,7tetrahydro-3-tBu-Ind)2ZrCl2, A. Marzo and L. Rimessi for the viscosity measurements, and I. Giulianelli for the DSC analysis. We thank Dr. E. Albizzati for his continual encouragement and stimulus. I.E.N. acknowledges receipt of grant 96-15-96997 from the President of Russia and Montell for support of this work. Supporting Information Available: A listing of bond distances and bond angles, anisotropic thermal parameters, hydrogen-atom coordinates for 4 and 5 (16 pages). See any current masthead page for ordering and Internet access instructions. JA973160S (48) Moraglio, G.; Gianotti, G.; Bonicelli, U. Eur. Polym. J. 1973, 9, 693. (49) Pearson, D.; Fetters, L.; Younghouse, L.; Mays, J. Macromolecules 1988, 21, 478.