Facile Cyclometalation Reactions of Cp–Zirconium Complexes with Weakly Lewis Acidic Pendent Boron Functionalities
✍ Scribed by Marion Emmert; Gerald Kehr; Roland Fröhlich; Gerhard Erker
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 210 KB
- Volume
- 15
- Category
- Article
- ISSN
- 0947-6539
No coin nor oath required. For personal study only.
✦ Synopsis
Dedicated to Professor Helmut Quast on the occasion of his 75th birthday
Methyl anion abstraction from group 4 metallocene dimethyl complexes by BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 or functionally related maingroup element Lewis acids (e.g. MAO) represents the most important activation pathway in homogeneous metallocene Ziegler-Natta olefin polymerization catalysis. [1] It seemed tempting to search for intramolecular versions of this reaction. The simplest approach would be to attach a suitable Lewis acid functionality to the cyclopentadienyl (Cp) ring of a metallocene or related group 4 metal complex system by means of a saturated hydrocarbon tether. We and others have previously shown that such bifunctional systems are readily obtained by hydroboration of alkenyl-functionalized zirconocene dichlorides. [2] The chemistry of related complexes with active s-hydrocarbyl ligands at the group 4 metal center proved to be more challenging. Typical previously reported examples include complexes 1 [3] and 3 [2b] (see Scheme 1). The former turned out to be unstable with regard to "self attack" of the strongly electrophilic borane on the adjacent Cp ring. This electrophilic aromatic substitution sequence resulted in the clean formation of the stable zwitterionic product 2 with liberation of benzene. The bifunctional complex 3 was reported to react by a sequence of alkyl abstraction reactions to eventually form 4.