A Rigid Cj-Bridged Ansa-Zirconocene-Derived Catalyst System Suited for Stereoselective Low Molecular Weight Polypropylene Formation Gerhard Erker*, Christian Psiorz, Roland Fröhlich Organisch-Chemisches Institut der Universität Münster, Corrensstraße 40, D-48149 Münster Dedicated to Prof. Dr. Dr. h.c. mult. Günther Wilke on the occasion o f his 70th birthday Z. Naturforsch. 50b, 469-475 (1995); received September 20, 1994 Homogeneous Ziegler Catalyst, Isotactic Polypropylene, Ansa-Metallocene, Fulvene 2,5-Hexanedione was converted into the bisfulvene 2, then treated with two molar equiva­ lents of methyllithium to yield the [4-cyclopentadienylidene-4,7,7-trimethyl-4,5,6,7-tetra- hydroindenyl]dilithio compound 4. Hydrolysis, followed by treatment with acetone/pyrroli­ dine, gave the corresponding fulvene system 5. Reaction of 5 with methyllithium followed by treatment with ZrCl4 furnished the ring-annulated Cr bridged ansa-metallocene 8, bearing a tert-butyl substituent at the Cp ring, as a 1:1 mixture of two diastereoisomers. Treatment of the fulvene 5 with LiAlH4 followed by ZrCl4 yielded the respective isopropyl-substituted ansa-metallocene diastereomers 9a and 9 b. Com plex 9 b was separated by fractional crys­ tallization and characterized by X-ray diffraction. Complexes 8 and 9 provide active homo­ geneous Ziegler-type catalyst systems upon activation with excess methylalumoxane produc­ ing low molecular weight isotactic polypropylene with high catalyst activities.

Introduction Homogeneous group 4 bent metallocene methylalumoxane-derived Ziegler-type catalyst systems have become of enormous importance for the development of a-olefin polymerization [ 1], Most of the catalyst systems of practical impor­ tance are derived from ansa-metallocene precur­ I sors [2]. Developing ansa-metallocene derivatives and novel ansa-metallocene structural types has been very rewarding as this has turned out to be knowledge this is the smallest D -Z r -D angle in of prime importance for significantly changing and a bent metallocene so far [4]. Decreasing the controlling the catalyst properties. D -Z r -D angle results in a pronounced change We have recently developed a new ansa-metal­ of the electronic features of the bent metallocene locene system which is characterized by a very system and thus of the catalyst behavior [5], high backbone rigidity [3]. The Cp ring systems Homogeneous Ziegler-catalyst systems derived are connected by a one-carbon atom bridge which from 1 by MAO activation have rather specific at the same time is part of a Cp-annulated six- properties [3]: they are very active; they produce membered ring system. Binding a large zirconium rather low molecular weight polypropylene or pro- center into this specially fused bis-cyclopenta- pene oligomers at higher temperatures, respec­ dienyl system creates a very rigid ansa-metallo­ tively, and the polypropylene obtained is slightly cene system which is characterized by a very open syndiotactic (a ~ 0.30-0.35; chain end control bite of the bent metallocene wedge. [6]). Such catalyst features are potentially useful The ansa-zirconocene dichloride 1 exhibits a for practical applications. Among these is the pos­ D l- Z r - D 2 angle (D 1 and D2 denote the cen­ sible use in catalytic organic synthesis, i.e. catalytic troids of the Cp ring systems) of 116.2°. To our olefin coupling reactions to give new organic monomers. The zirconium complex 1 is chiral. However, the * Reprint requests to Prof. Dr. G. Erker. 1/MAO catalyst system does not produce polypro-

0932-0776/95/0300-0469 $06.00 © 1995 Verlag der Zeitschrift für Naturforschung. All rights reserved. 470 G. Erker et al. ■ A Rigid Cr Bridged Ansa-Zirconocene-Derived Catalyst System pylene by enantiomorphic site control. The lack of The dilithio compound 4 provides the basis for any chirality transfer from the bent metallocene a synthetic entry to derivatives bearing alkyl sub­ backbone to the final C-C-coupling product is a stituents at the Cp ring systems. It was hydrolyzed distinct disadvantage for a variety of potential to give a mixture of double bond shift isomers of applications of such a very active catalyst system. the neutral ligand system. This was directly sub­ Therefore, we have searched for ways to achieve jected to the fulvene synthesis (treatment with an effective influence of the bent metallocene’s acetone in methanol solution in the presence of stereochemical properties in the catalytic process. pyrrolidine) to yield a 1:1 mixture of two double As it turned out, attaching alkyl substituents at the bond shift isomers of the mono-fulvene system 5. Cp rings oriented toward the front side of the bent metallocene wedge leads to a drastic change in the stereochemical characteristics of the propene polymerization process. We here describe a typi­ cal example. 2CH ,Li

Results and Discussion

The synthesis of the parent compound 1 exhibit­ 1) h 2o h 3c ing the rigid annulated [4-(//5-cyclopentadienyl- 2 ~> h 3c c h 3 idene)-4,7,7-trimethyl-(?75-4,5,6,7-tetrahydro- 113 V-, 3 0 Li indenyl)]ligand system is outlined in Scheme 1. 1) LiAlH4 Reaction of the bis-fulvene 2 [7], readily available o (mixture of isomers) reflux h 3c 2) H20 0 Li by treatment of 2,5-hexanedione with cyclopenta- 3) 2 CHjLi diene in the presence of pyrrolidine [ 8 ], with two h 3c / CH , molar equivalents of methyllithium gives 4. In this H 3 Schem e 2. reaction sequence one equivalent of CH3Li acts as 7 a nucleophile, the other as a base. Treatment of 4 Reaction of the fulvene 5 with two molar equiv­ with ZrCl4 gives the ansa-zirconocene dichloride alents of methyllithium in ether proceeded with in low but reproducible yield (10-15% ). methylanion addition at the exocyclic fulvene sp2- carbon center [9] to give a tert-butyl group at the Cp ring system and deprotonation at the tetra- hydroindene moiety to yield the dilithiated ligand system 6. Subsequent reaction of this reagent with C H 3 C H 3L i ZrCl4 furnished the /m-butyl-substituted ansa- H,C metallocene complex as a mixture of two dia- stereoisomers 8 a and 8 b in a 1:1 ratio. Treatment of the fulvene 5 with LiAlH 4 in refluxing ether followed by hydrolysis gave the isopropyl-substituted ligand system. Subsequent CH 3Li lithiation with methyllithium and treatment with zirconium tetrachloride produced a 1:1 mixture of the isopropyl-substituted ansa-zirconocene dichlo­ H3C / CH 3 ride diastereoisomers 9 a and b. Crystallization ZrCI, gave one of these (9 b) isomerically pure. Accord­ H,C ing to an X-ray crystal structure analysis this dia­ stereomer is characterized by the stereochemical descriptor (4R*, p-R*, p -R*). In the crystal complex 9 b exhibits an ansa- Scheme 1. metallocene framework very similar to the one ob- G. Erker et al. • A Rigid C]-Bridged Ansa-Zirconocene-Derived Catalyst System 471

H,C. CH H?C ß H3

H,C H,C

6 [R = C(CH3)3] 8b 7 [R = CH(CH3)2] 9a 9b Schem e 3.

Fig. 1. Two projections of complex 9b (4R *, p-R*. p-R*-diastereoisomer). served for the parent compound 1 (see Table I). planes is 72.3°, which is very similar to that in 1 The C(sp2)-C (sp 3)-C (sp 2) angle at the ligand- (71.4°). The electronic features of the ansa-zir- bridging carbon center in 9 b is 99.6(2)° (1: conocene complexes 9 b and 1 are probably closely 99.9(2)°). The angle between the cyclopentadienyl related as expressed by their almost identical D 1 -Z r -D 2 angles (9b: 116.6°; 1: 116.3°). In 9b the Cl 1-Z r-C 12 angle is 98.47(3)° [1: 98.3(1)°]. Table I. Selected bond lengths (A), angles (°), and tor­ sion angles (°) of complex 9 b. An inspection of the molecular geometry of complex 9 b (see Fig. 1) reveals that the newly in­ Z r-C l 2.599(2) C 7 -C 8 -C 9 123.1(2) Z r-C 2 2.530(2) C 8 -C 9 -C 4 122.0(2) troduced isopropyl substituent may very effec­ Zr-C3 2.421(2) C9-C4-C13 99.6(2) tively shield one quadrand (i.e. the “south-west” Z r-C 8 2.555(2) Cl 1 -Zr-C 12 98.47(3) Z r-C 9 2.444(2) D 1 -Z r -D 2 116.6 sector) at the front of the bent metallocene unit. Z r-C 13 2.434(2) Cp(A)-Cp(B) 72.3 There may be some additional shielding in the Z r-C 14 2.454(2) C 2 -C 1-C 8 -C 7 166.5(2) “north-east” sector envisaged potentially being Z r-C 15 2.561(2) C3-C9-C8-C7 -168.0(2) Zr-C 16 2.601(2) C 2 -C 3 -C 9 -C 4 161.9(2) caused by some unfavourable steric interaction be­ Z r-C 17 2.469(2) C 1-C 8 -C 9 -C 4 -162.4(2) tween the C ll methyl group and substituents of Zr-Cl 1 2.4459(9) C16-C17-C13-C4 -164.0(2) Zr-C12 2.4287(7) C 15-C 14-C 13-C 4 162.4(2) incoming prochiral a-olefin substrates. Thus from C 4-C 9 1.525(3) C 14-C 15-C 16-C 18 173.4(2) the X-ray crystal structure analysis of complex 9 b C 4-C 13 1.537(3) C 13-C 17-C 16-C 18 -172.2(2) one might expect that transfer of the metallocene 472 G. Erker et al. • A Rigid Cr Bridged Ansa-Zirconocene-Derived Catalyst System

Table II. A tom ic coordinates o f 9b. stantial amounts of low molecular weight prod­ ucts, which were not separated from the toluene A tom X z y solvent. The product obtained at ambient tem­ Zr -0.0160(1) 0.3033(1) 0.3087(1) perature had a seizable amount of dimers along C l(l) 0.1765(1) 0.1510(1) 0.4330(1) with trimers to hexamers (as judged from a quali­ Cl(2) 0.1066(1) 0.4974(1) 0.2203(1) C (l) -0.1705(2) 0.4708(2) 0.4545(2) tative GC/MS analysis). C(2) -0 .1 4 0 6 (2 ) 0.3323(2) 0.5225(2) The stereochemical outcome of the propene C(3) -0.2048(2) 0.2450(2) 0.4682(2) C-C-coupling reaction at the 9b/methylalum- C(4) -0.3277(2) 0.2848(3) 0.2577(2) C(5) -0.4237(3) 0.4146(4) 0.1802(3) oxane catalyst was strikingly different from that C(6) -0.3769(3) 0.5580(3) 0.1592(3) obtained with the 1/MAO system. Isotactic poly­ C(7) -0.3413(3) 0.6010(3) 0.2759(2) propylene was obtained at all three temperatures C(8) -0.2565(2) 0.4726(2) 0.3573(2) (see Table IV) with a pronounced percentage (co) C(9) -0.2781(2) 0.3329(2) 0.3659(2) C(10) -0.4087(3) 0.1630(4) 0.3018(3) of enantiomorphic site control [11]. The marked C(11) -0 .2 5 9 8 (4 ) 0.7233(5) 0.2413(3) difference of the stereocontrol exerted by the in­ C(12) -0.4844(3) 0.6514(3) 0.3554(3) troduction of the single isopropyl substituent is C( 13) -0 .1 7 8 4 (2 ) 0.2314(3) 0.1905(2) C(14) -0 .0 9 4 5 (3 ) 0.3139(3) 0.1021(2) visualized by comparing the appearance of the 13C C(15) 0.0500(2) 0.2358(2) 0.0921(2) NMR methyl pentade spectra of the polypro­ C( 16) 0.0608(2) 0.1052(2) 0.1728(2) pylenes obtained at the 1/MAO and 9b/MAO C (17) -0 .0 7 9 5 (2 ) 0.1039(2) 0.2365(2) C(18) 0.1913(2) -0.0172(2) 0.1832(2) catalysts (polymerizations carried out at -5 °C C(19) 0.3313(3) 0.0302(3) 0.1275(3) and 0 °C, respectively). The former polypropylene C (20) 0.1645(4) -0.1340(3) 0.1212(3) (PP7) is slightly syndiotactic (only chain end con­ trol) with the isotactic mmmm signal completely missing [3], whereas the latter polypropylene backbone stereochemical information is greatly (PP4) exhibits a 45% mmmm resonance. It is iso­ enhanced by the presence of the additional isopro­ tactic and was formed by a substantial transfer of pyl substituent at the Cp ring as compared to the the ansa-metallocene chirality onto the carbon- unsubstituted parent system 1. This was indeed ob­ carbon-coupled product. served when 9 b was converted to an active cata­ The diastereomer 9 a was employed as a catalyst lyst system. component for comparison. At -2 0 °C the 9a/ Treatment of 9 b with an excess of methylalum- MAO catalyst system polymerizes propene. The oxane in toluene gave an active homogeneous catalyst activity is almost identical to that of the Ziegler-type catalyst for propene polymerization. diastereomeric 9b/MAO catalyst, and the polypro- The catalyst activities are similar as observed for the complex 1 derived catalyst system, only the * Further details of the crystal structure investigation average molecular weights of the propene poly­ are available on request from Fachinformationszen- mers and oligomers are even lower. The product trum Karlsruhe, Gesellschaft für wissenschaftlich- technische Information mbH, D-76344 Eggenstein- mixtures obtained from the reactions at 0 °C and Leopoldshafen, on quoting the depository number 25 °C with the 9b/MAO catalyst contained sub­ CSD 401245 and the journal citation.

Table III. Details of the X-ray crys­ Formula C2()H 26Cl2Zr Formula weight 428.53 me m 3 tal structure analysis of 9 b*. a 9.460(3) A a 78.48(1)° b 9.805(1) A ß 82.68(2)° c 10.994(2) A y 76.21(2)° V 968.9(4) A3 z 2 Space group PI bar (No. 2) T 223(2) K A 0.71073 Ä (MoKa) 0.84 m m “1 Reflections 3926 (R ml = 0.021) Parameters 213 R (all data) 0.031 wR2 (all data) 0.084 GOF 1.128 Diffractometer Enraf-Nonius C A D 4 Programs used SHELX-86. SHELX-93. SCHAKAL-92 G. Erker et al. ■ A Rigid Q-Bridged Ansa-Zirconocene-Derived Catalyst System 473

Table IV. A comparison of characteristic data concerning the propene polymerization at the homogeneous Ziegler- type catalyst systems derived from the ansa-metallocene complexes 9b, 9a, 8a/b, and 1 [10].

Polymer Complex T [°C] A l: Zr A ctivity3 M„ %mmmm cob a b <7b Ref.

PP1 8a, b -15 770 200 700 38.5 0.64 0.70 0.94 C P P2 9a -2 0 745 165 750 45.4 0.84 0.76 0.88 C PP3 9b -20 711 130 860 30.7 0.66 0.79 0.93 c P P4 9b 0 745 1700 770 44.8 0.59 0.79 0.90 c d c PP5 9b + 25 711 >3300 ---- P P6 1 - 3 0 706 340 12700 e -- 0.30 [3] P P7 1 - 5 706 1500 1900 e - - 0.34 [3]

a In g polymer/g[Zr] • h; b for definitions of the statistical parameters see text and ref. [10]; c this work; d n < 11 as judged from GC-MS and 13C NMR end group analysis; e no intensity of the mmmm 13C NMR methyl pentade signal observed. pylene obtained is also of a low molecular weight. polypropylenes. This may be due to a dominating The overall isotacticity at the 9 a and 9 b derived electronic control of the ktermination/kpropagation catalyst systems is similar, only the proportion of ratio which is due to the rather large bite angle enantiomorphic site control is higher employing of the bent metallocene wedge observed in these 9a/MAO (see Table IV). The /err-butyl-substituted extremely rigid six-membered ring-annulated Cr ansa-metallocene diastereoisomers could not be bridged ansa-zirconocenes. The alkyl-substituted separated in this study. Therefore, the 1:1 mixture derivatives 8 /MAO and 9/MAO exert a pro­ of stereoisomers was employed as the catalyst pre­ nounced enantiomorphic site stereocontrol in con­ cursor. The 8 a, b/MAO catalyst gave a very similar trast to the parent system 1/MAO where transfer polypropylene as obtained with the 9 a and 9 b/ of stereochemical information from the bent MAO homogeneous Ziegler-type catalyst systems metallocene backbone to the product is comple­ (see Table IV). tely absent. These observations make us optimistic that these rigid ansa-metallocenes may provide a Conclusions suitable basis for further development of such This study has shown that substituted deriva­ homogeneous Ziegler-type catalyst systems to be tives of our novel ansa-metallocene system ( 1) employed in organic synthesis. Studies aimed at bearing alkyl groups at the Cp moiety can readily converting active homogeneous a-olefin polymeri­ be prepared via a fulvene route. The homogeneous zation catalysts into systems effecting organic metallocene/methylalumoxane Ziegler-type cata­ monomer formation by selective catalytic olefin lyst systems derived from the substituted ansa- coupling are actively pursued in our laboratory. metallocene systems ( 8 , 9) exhibit similar propene polymerization activities as the parent compounds Experimental Section (1). The alkyl-substituted 8 /MAO and 9/MAO For general information, including a list of spec­ catalysts also produce very low molecular weight trometers used, see ref. [10]. All reactions with

Fig. 2. 13C NMR methyl pentade reso­ nances of polypropylenes PP7 and PP4 formed at the 1/MAO and 9b/MAO catalyst systems, respectively 474 G. Erker et al. • A Rigid Q-Bridged Ansa-Zirconocene-Derived Catalyst System organometallic compounds and reagents were car­ fied by vigorous stirring in pentane to give 23% ried out in an inert atmosphere (argon) using (787 mg) of the crude 8 a, b mixture. Continuous Schlenk-type glassware or in a glove box. All sol­ extraction with pentane gave 370 mg (11%) of the vents were dried and distilled under argon prior pure 1:1 mixture of 8 a and 8 b, m.p. >300 °C to use. Propene polymerization reactions were car­ (decomp. DSC). ried out in a thermostated glass autoclave (Biichi) Analysis for C2IH28Cl2Zr (442.6) as previously described in detail [10]. The iso­ lation, physical and spectroscopic characterization Calcd C 56.99“ H 6.38%, Found C 57.21 H 6.56%. of the polypropylenes PP1 to PP5 were performed analogously as described previously [3, 10]. For 'H NMR (CDC13): ö 6.74, 6.67, 6.52 (double details see Table IV. intensity), 6.37, 6.33, 5.98, 5.85 (double intensity), 5.67 (threefold intensity) (m. 12 H. CH), 2.35, 1.98, [4-( rf-3-tert- Bntylcyclopentadienylidene) - 1.69 (m. 8 H, 5-H, 6-H), 1.82, 1.81 (s, each 3H. 4,7,7-trimethyl-(r/5-4,5,6,7-tetrahydroindenyl)]- 4-CH3 of 8 a and 8b), 1.33 (double intensity), 1.12, dichlorozirconium 8 1.09 (s. each 3H, 7-CH 3 of the diastereomers), 1.31, 1.25 (s, each 9H, tert-butyl). 13C NMR The dilithio compound 4 [3] (7.35 g, 23.5 mmol) (CDCU): (3 151.1, 143.3, 137.8, 137.2,120.3 (double was dissolved in 50 ml of ether and treated with intensity), 115.4. 112.8 (C), 124.3, 123.3, 123.1, 50 ml of degassed H20 at 0 °C. From the ether 116.2, 115.4, 114.8, 112.2, 108.9, 107.5, 105.7, 105.0. phase 5.12 g (96%) of the neutral ligand system 103.3 (CH), 36.0, 35.9, 32.2, 32.0 (CH2), 37.4, 35.8. was obtained (HRMS: calcd. for C 17H22 226.1722 33.3, 32.9, 32.8, 32.1 (C4, C7, CMe3), 35.2, 34.8. (M+), found 226.1727). The obtained bis-cyclopen- 27.7, 27.6, 27.1, 26.5 (CH3), 30.5, 29.8 (C(CH3)3). tadiene (7.70 g, 34.0 mmol) was dissolved in 70 ml IR (KBr): v (cm"1) 3102, 3092, 2959, 2928, 2883. of methanol at 0 °C. Acetone (2.96 g, 51.0 mmol) 2867, 1476, 1457, 1437, 1382, 1363, 1104, 1048. and pyrrolidine (4.83 g, 68.0 mmol) were added 1023, 852, 841, 802, 793, 747. and the mixture was stirred for 24 h at 0 °C, then for 12 h at r.t. The mixture was hydrolyzed by adding 4 ml of glacial acetic acid and then 200 ml [4-(rf-3-lsopropylcyclopentadienylidene)- of water. The yellow suspension was extracted 4,7,7-trimethyl- (rf-4,5,6,7-tetrahydroindenyl)]- with pentane (3x50 ml). The combined organic dichlorozirconium 9 extracts were repeatedly washed with brine and To a suspension of 2.17 g (57.3 mmol) of LiAlH 4 dried over anhydrous magnesium sulfate. Re­ in 100 ml of ether a solution of 6.11 g (22.9 mmol) moval of the solvent in vacuo yielded the fulvene of the fulvene 5 in 20 ml of ether was added drop- 5 (8.0 g, 88 %) as an orange colored crystalline wise. The mixture was refluxed for 3 h, then hy­ solid after crystallization from pentane at -20 °C drolyzed. Work-up analogously as described above (1:1 mixture of two double bond isomers). gave 5.63 g (92%) of the neutral ligand system as Analysis for Ciobhf. (266.4) a mixture of double bond isomers (HRMS: calcd. Caicd C 90.16 H 9.84%, for C20H28 268.2198 (M+), found 268.2191). The Found C 89.59 H9.91%. obtained bis-cyclopentadiene ligand (4.21 g. 15.7 mmol) was dissolved in 70 ml of ether. Meth­ A sample of the fulvene 5 (2.70 g, 10.1 mmol) yllithium (21.6 ml of a 1.60 M ethereal solution. was treated with 14.0 ml of a 1.60 M ethereal 34.5 mmol) was added dropwise at 0 °C. The mix­ methyllithium solution (22.3 mmol) at 0 °C. ture was stirred for 15 h at r.t. and then the re­ Within seconds a yellow precipitate was formed. sulting white precipitate collected by filtration to The mixture was stirred for 12 h at ambient tem­ give 5.20 g (93%) of 7 E t 20. The dilithio com­ perature. The precipitated product was collected pound (5.20 g, 14.7 mmol) was suspended in 200 by filtration, washed with pentane and dried ml of toluene. At -78 °C ZrCl 4 (3.40 g, 14.6 mmol) in vacuo to yield 2.50 g of 6 E t 20 ( 68 %). was added in several portions. The resulting mix­ A suspension of the dilithiated ligand system ture was stirred at r.t. for 24 h and filtered. The (6 E t20 , 2.84 g, 7.71 mmol) in 150 ml of toluene clear filtrate was concentrated in vacuo to a vol­ was charged with ZrCl4 (1.79 g, 7.71 mmol) in sev­ ume of 50 ml. ’H NMR spectroscopy of an aliquot eral portions at -78 °C. The mixture was allowed revealed that the diastereomeric products 9a and to warm to r.t. and stirred for 48 h. Some precipi­ 9b were present in a ca. 1:1 ratio. Pentane (20 ml) tate was removed by filtration. The toluene sol­ was added. Crystallization at -20 °C gave 1.42 g vent was removed in vacuo and the residue solidi­ of 9 b in ca. 90% d.e. Removal of the solvent from G. Erker et al. • A Rigid Cr Bridged Ansa-Zirconocene-Derived Catalyst System 475 the mother liquor yielded 1.62 g of 9 a (>85% 26.7, 24.9, 20.8 (CH 3 and isopropyl-CH). Diaste­ d.e.); combined yield of 9: 49%. Slow diffusion of reomer 9 b: 'H NMR (CDC13): (3 6.77, 6.43, 6.22, pentane into a methylene chloride solution of 9 b 5.97, 5.55, 5.42 (m, 6 H, CH), 2.91 (sept., 1H, gave crystals suitable for the X-ray crystal struc­ CHMe2), 2.41 (ddd, 1H, 5-Heq), 2.28 (ddd, 1 H, ture analysis, m.p. 193 °C (DSC). 5-Hax), 2.01 (ddd, 1H, 6-Hax), 1.72 (ddd, 1H, 6-Heq; coupling constants: 2J = 14.5 Hz, 3J(ax,ax) = Analysis for C2oH 26 Cl2Zr (428.6) 14.5 Hz, 3/(ax,eq) = 6.2/5.6 Hz, V(eq,eq) = 2.8 Hz), Calcd C 56.05 H 6.12%, 1.78, 1.32, 1.11 (s, each 3H, CH3), 1.24, 1.09 (s, Found C 56.00 H5.92%. each 3H, isopropyl-CH3). 13C NMR (CDC13): (3 146.6, 137.2, 119.8, 111.9 (C), 122.6, 115.7, 114.9, Diastereomer 9a: lH NMR (CDC13): (3 6.69, 110.8, 105.5, 105.3 (CH), 37.5, 32.8 (C4, C7), 35.9, 6.45, 6.38, 5.75 (threefold intensity) (m, 6 H, CH), 32.2 (CH,), 35.0, 28.2, 27.7, 26.5, 24.0, 20.9 (CH 3 3.03 (sept., 1H, CHMe2), 2.32 (ddd, 1H, 5-Heq), and isopropyl-CH). IR (KBr): v (cm -1) 3077, 2968, 2.24 (ddd, 1H, 5-Hax), 1.98 (ddd, 1H, 6-Hax), 1.70 2959, 2924, 2915, 2868, 1476, 1456, 1384, 1362, (ddd, 1 H, 6-Heq; coupling constants: 2J = 14.5 Hz, 1116, 1056, 847, 831, 806, 797, 748. V(ax,ax) = 14.5 Hz, V(ax,eq) = 5.7/5.7 Hz, 3/(eq,eq) = 2.8 Hz), 1.82, 1.32, 1.09 (s, each 3H, Acknowledgements CH3), 1.25, 1.12 (s, each 3H, isopropyl-CH3). 13C Financial support from the Fonds der Chemi­ NMR (CDCh): <3 139.7, 137.4. 119.2, 112.4 (C), schen Industrie, the Hoechst AG, and the Alfried 123.2, 121.3, 114.9, 109.8, 107.3, 105.3 (CH), 37.6, Krupp von Bohlen und Halbach-Stiftung is grate­ 32.8 (C4, C7), 35.8, 32.0 (CH7), 35.2, 28.2, 27.7, fully acknowledged.

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