Uncovering alternative reaction pathways taken by group 4 metallocene cations: Facile intramolecular CH activation of Cp-(dimethylamino)alkyl substituents by a methylzirconocene cation

Alkyl- and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,N-dimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium systems Li[C5H4-(CRRNMe2)-R-1-N-2], Subsequent treatment with ZrCl4 . 2THF gives the corresponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium to give the ((C5H4CRRNMe2)-R-1-N-2)(2)Zr(CH3)(2) complexes 11a (R-1 = R-1 = CH3) and 11b (R-1 = CH3, R-2 = Ph), respectively. Treatment of 11 with tris(pentafluorophenyl)borane was carried out to generate the corresponding alkylmetallocene cations (12), which turned out to be unstable under the reaction conditions applied (-20 degrees C) with regard to Liberation of 1 equiv of methane by CH activation at a methyl group adjacent to nitrogen and formation of the spiro-metallocene complex systems 13. CH activation may be a major reaction pathway open to alkylzirconocene cation systems under suitable reaction conditions.