Highly isotactic polymers have been prepared from propene and longer chain a-olefins with chiral transitionmetal compounds such as (R,S)-[l ,lf-ethylenebis(4,5,6,7-tetrahydro-I-indenyl)]zirconium dichloride and methylalumoxane as cocatalysts.[1-31 If, instead of the racemate, one of the two enantiomers of the transition-metal compound is used, the resulting polyolefins should exhibit practically no optical activity in solution.r41 By contrast, measurable optical rotations are expected for oligomers. Thus, Pino et al. were able to synthesize optically active alkanes by hydrooligomerization of propene with this catalyst Of greater preparative interest are the more reactive, optically active alkenes. However, hydrogenation cannot be used to control their molecuIar weights in the asymmetric oligomerization. Instead, similarly low degrees of oligomerization have to be achieved by a method that preserves the terminal double bond. This is possible by raising the catalyst concentration and simultaneously lowering the monomer concentration, thereby increasing the rate of chain termination relative to chain growth in the polymerization.Use of (8-[I ,l'-ethylenebis(4,5,6,7-tetrahydro-l-indenyl)]-zirconium bis(O-a~etyl-(R)-mandeIate)('~ and methylalumoxane[*] (Scheme 1) thus allowed the preparation of optically active propene and I-butene oligomers. The mandelate was employed because its activity is similar to that of the corresponding dichloride and may be obtained in purer form. In the first step, an olefin molecule undergoes insertion into a transition-metal methyl bond formed by methylation with methylalumoxane (Scheme 2). Subsequent insertions lead to chain growth. Chain termination takes place by P-hydrogen transfer to the transition-metal atom or to a complex-bound olefin, resulting in formation of the hydrido or alkyl transition-metal compound in addition to

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Die erfolgreiche Synthese von 9 legt die Frage nahe, ob man auch das C,-Molekiil ,,stabilisieren" konnte. Dies sollte analog zur Stabilisierung eines C-Atoms in 1 wieder durch zwei Donormolekule moglich sein (13). Entsprechend mul3te 13 14 C, dann wieder wie C, durch ein Donor-und ein Acceptormolekiil stabilisiert werden (14). Mit Versuchen zur Synthese derartiger Systeme sind wir beschiftigt.

With the homogeneous Ziegler-Natta catalyst based on chiral metallocenes/methylalumoxane highly isotactic polypropylene could be prepared. The catalysts can be separated into the optical active enantiomers. Even longer chained α-olefins as butene-1, pentene-1, or hexene-1, give isotactic polymers. Among the polymer features molecular weight and molecular weight distribution, solubility in toluene, melting point, density, and x-ray crystallinity as well as macrotacticity have been examined. Except for polyhexene all polymers investigated arrange in a stable helical conformation. Oligomers of butene -1 and pentene-1 show an optical rotation.Among the great number of Ziegler-type catalysts, Vanden berg (1) examined at a very early stage the heterogeneous titanium trichloride system, especially for synthesizing isotactic polypropylene. Homogeneous systems have been preferentially studied in order to understand the elementary steps of the polymerization which is simpler in soluble systems than in heterogeneous ones. The situa tion has changed since in recent years a homogeneous cat alyst based on metallocene and aluminoxane was discovered which is very active and also interesting for industrial uses (2-3). In some cases special polymers could be syn thesized only with soluble catalysts (4).Breslow (5) discovered that bis(cyclopentadienyl)-titanium(IV) compounds which are well soluble in aromatic hydrocarbons, could be used instead of titanium tetra chloride as the transition metal compound together with aluminum alkyls for ethylene polymerization. Subsequent research on this and other systems with various alkyl

Highly active catalysts for the polymerization of olefins are formed b combination of metallocenes and meth laluminoxane. Both components are soluble in hydrocarbons. I n unusually wide field of syntheses of didrent polyolefins is opened up by the mere variation of the ligands coordinated to the transition metal.With simple zirconocenes propene is polymerized to a purely atactic polymer. lsotactic polypropylene is obtained when chiral ethylene(bistetrahydroindeny1)zirconiumdichloride is used. For the first time it has become possible to resolve the racemic catalyst into the enantiomers. With this catalyst an isotacticity index of more than 99% was achieved. Cyclic olefins like cyclobutene, cyclopentene, norbornene, or dimethanonaphthalene could be polymerized without any ring opening reaction using this catalyst. The polycycloalkenes have extremely high melting points ranging from 400 to 600°C. Copolymers of cycloalkenes and ethene could be used as starting materials for optical discs.If one indenyl ligand is replaced with a fluorenyl ligand, crystalline syndiotactic polypropylene will be formed. Zirconocenes with neomenthylcyclopentadienyl groups yield stereoblock polymers with isotactic lengths of 6 to 12 units.The optically active catalyst produces optically active oligomers and hydrooligomers from olefins.