Methyl anion abstraction from group 4 metallocene dimethyl complexes by B ACHTUNGTRENNUNG(C6F5)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. 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. 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 and 3 (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. These examples all contained the strongly electrophilic B ACHTUNGTRENNUNG(C6F5)2 group. We have now found that even systems featuring the much weaker 9-borabicycloACHTUNGTRENNUNG[3.3.1]nonane (9BBN) electrophile tethered to a Cp ring system show related reactivities. Herein we wish to describe some selected representative examples, mostly from the ZrCp3 series, that show how general such consecutive reactions take place at bifunctional alkyl group 4 metal complexes, even when a weakly Lewis acidic borane functionality is attached to a Cp ring by an oligomethylene tether. [Zr ACHTUNGTRENNUNG(allyl-Cp)ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp2)] (7) was synthesized along the pathway that we previously developed for the preparation of the parent [Zr ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp3)] complex. We have shown that it is advantageous to introduce the [Zr]-CH3 functionality at an early stage in the synthesis. Consequently, we treated the starting material [Zr ACHTUNGTRENNUNG(CH3)(Cl) ACHTUNGTRENNUNG(Cp2)] (5) with the K ACHTUNGTRENNUNG(allyl-Cp) reagent 6 (see Scheme 2). Workup of the reaction mixture from toluene eventually gave the functionalized tris(cyclopentadienyl)Zr product 7 in 55% yield. Complex 7 was characterized spectroscopically (H NMR in CD2Cl2: d=0.28/16.3 ( H/C; [Zr]-CH3), 5.64 (s, 10H; Cp), 5.25/5.66 (AA’BB’, 2H each; C5H4), 3.19 (CH2), 5.02/ 5.07 ppm (=CH2) and by X-ray crystal structure analysis (single crystals were obtained from a toluene/heptane mix[a] Dipl.-Chem. M. Emmert, Dr. G. Kehr, Dr. R. Frchlich, Prof. Dr. G. Erker Organisch-Chemisches Institut der Universit t M nster Corrensstr. 40, 48149 M nster (Germany) Fax: (+49)251-83-36503 E-mail : erker@uni-muenster.de [] This author was responsible for X-ray crystal structure analyses. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900981, and contains experimental details and characterization of the compounds 7–18. CCDC721637 (10), -721638 (7), and -721639 (12) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Scheme 1.