245659-79-4Relevant academic research and scientific papers
Evidence for α-Nitrogen Participation in the Internal C-H Activation Reaction at ((Dimethylamino)methyl)cyclopentadienyl-Derived Methylzirconocene Cations
Pflug, J?rg,Bertuleit, Axel,Kehr, Gerald,Fr?hlich, Roland,Erker, Gerhard
, p. 3818 - 3826 (2008/10/08)
Treatment of 6-(dimethylamino)-6-methylfulvene (1) with methyllithium followed by the reaction of the resulting [C5H4-CMe2NMe2]Li reagent with CpZrCl3 gave the complex [(η5-C5H4-CMe2NMe 2)CpZrCl2] (2). Its treatment with 2 molar equiv of methyllithium furnished [(η5-C5H4-CMe2NMe 2)CpZr(CH3)2] (3). Complex 3 reacted with B(C6F5)3 by methyl group transfer. The in situ [Zr]+-CH3 cation system generated in this manner proved to be unstable under the reaction conditions and instantaneously eliminated methane with formation of 4. In the course of this reaction a N-CH3 hydrogen atom was abstracted. Complex 4 was stabilized by the addition of 1 equiv of the alkyl isocyanide RN≡C (R = CMe3, n-C4H9, -CMe2-CH2CMe3) to yield the respective adducts 5. The complex [(η5:η2(C,N)-C5H 4-CMe2N(=CH2)-CH3)CpZr(κC-C≡N-CMe 3)]+[CH3B(C6F5) 3]- (5a) was characterized by an X-ray crystal structure analysis. It exhibits an η2-coordination of the pendant formaldiminium moiety to zirconium (d(Zr-N) = 2.318(7) A?, d(Zr-C) = 2.272(7) A?). The (η-R2NCH2)Zr moiety shows a characteristic 15N NMR chemical shift (δ-376 ppm), deshielded by ca. Δδ ≈ -40 ppm relative to the 15NMe2 NMR resonance found for 3. Complex 4 reacts with butadiene or isoprene by insertion into the Zr-CH2 bond of the (η2-formaldiminium)Zr moiety to form the metallacyclic (π-allyl)metallocene complexes 6a,b The X-ray crystal structure analysis of 6b shows a close Zr-N contact at 2.491(4) A?. A corresponding 15N NMR feature was found at δ -357 ppm. The complex [(η5-C5H4-CMe2NMe 2)2Zr(CH3)2] reacts analogously: upon treatment with B(C6F5)3 in a 1:1 ratio, CH3 is transferred from zirconium to boron, and 1 equiv of methane is liberated to give complex 8 (15N NMR signals at δ -357 and -372 ppm). Complex 8 was also characterized by X-ray diffraction. It shows coordination of both nitrogen atoms to zirconium: i.e., the presence of a (η2-R2NCH2)Zr+ three-membered-ring system, formed by C-H activation, and a κN-coordinated intact pendant -CMe2-NMe2 group. The latter is displaced upon the addition of tert-butyl isocyanide to yield the (κC-isonitrile)(η2-formaldiminium)metallocene cation complex 9.
Uncovering alternative reaction pathways taken by group 4 metallocene cations: Facile intramolecular CH activation of Cp-(dimethylamino)alkyl substituents by a methylzirconocene cation
Bertuleit, Axel,Fritze, Cornelia,Erker, Gerhard,Fr?hlich, Roland
, p. 2891 - 2899 (2008/10/08)
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.
