Uncovering Alternative Reaction Pathways Taken by Group 4 Metallocene Cations:  Facile Intramolecular CH Activation of Cp−(Dimethylamino)alkyl Substituents by a Methylzirconocene Cation

• Published in: Organometallics Vol. 16; no. 13; pp. 2891 - 2899
• Main Authors: Bertuleit, Axel, Fritze, Cornelia, Erker, Gerhard, Fröhlich, Roland
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 24.06.1997; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; OLEFIN POLYMERIZATION CATALYSTS; TRANSITION-METAL COMPLEXES; AMINO GROUP COORDINATION; CRYSTAL-STRUCTURE; ZIRCONIUM-MEDIATED FUNCTIONALIZATION; X-RAY STRUCTURE; ZIEGLER-NATTA POLYMERIZATION; CONSTRAINED-GEOMETRY CATALYSTS; GAS-PHASE REACTIONS; ETHYLENE POLYMERIZATION
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om970164x

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−CR1R2NMe2]. Subsequent treatment with ZrCl4·2THF gives the corresponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium to give the (C5H4CR1R2NMe2)2Zr(CH3)2 complexes 11a (R1 = R1 = CH3) and 11b (R1 = CH3, R2 = 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 °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.