Synthesis and Application of Ring‐Substituted Analogues of the [4‐(η‐Cyclopentadienylidene)‐4,7,7‐trimethyl‐4,5,6,7‐tetrahydro‐η5‐indenyl]‐ZrCl2 Ansa‐Metallocene System

Reaction of the 2,5-hexanedione-derived bisfulvene 1 with RLi reagents (R = phenyl or n-butyl) yields the ring-closed [4-(cyclopentadienylidene)-7-R-4,7-dimethyl-4,5,6,7-tetrahydroindenyl]dilithium reagents 3. Their reaction with MCl4 (M = Ti, Zr, Hf) gives the corresponding ansa-group-4-metallocene dichloride complexes 4, 6, or 7. In a similar way the [7-allyl-4-(η-cyclopentadienylidene)-4,7-dimethyl-4,5,6,7-tetrahydro-η5-indenyl]metal dihalides (M = Ti, Zr) (6d, 4d) are prepared. Two diastereomers are formed in most cases, some of which could be separated. The five representative examples cis- and trans-4c, trans-4d, cis-6c, and trans-7c of these complexes were characterized by X-ray diffraction. All these six-membered ring-annulated C1-bridged ansa-metallocene dichlorides exhibit extremely small D1ZrD2 angles (D1 and D2 denote the centroids of the cyclopentadienyl rings) of 116.5°, i.e., they are characterized by a very open bite of the bent metallocene wedge. The homogeneous Ziegler-type catalysts derived from these ansa-zirconocenes by activation with methylalumoxane have high activities and all produce low-molecular mass atactic polypropylenes or propene oligomers.