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

Abstract

Alkyl-and aryllithium reagents add cleanly to the electrophilic carbon center C6 of 6-(N,Ndimethylamino)fulvenes to yield the corresponding substituted cyclopentadienyllithium systems Li[C 5 H 4 -CR 1 R 2 NMe 2 ]. Subsequent treatment with ZrCl 4 ‚2THF gives the corresponding Cp-functionalized zirconocene dichlorides. These were reacted with methyllithium to give the (C 5 H 4 CR 1 R 2 NMe 2 ) 2 Zr(CH 3 ) 2 complexes 11a (R 1 ) R 1 ) CH 3 ) and 11b (R 1 ) CH 3 , 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°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.

Novel sandwich complexes of zirconium [C9H5(SiMe3)2](C5Me4R)ZrCl2 (R=CH3, CH2CH2NMe2): Synthesis and reduction behavior

“…Recently, we reported the synthesis of closely related complex (g 5 -C 5 Me 5 )[g 5 :g 2 (C,N)-C 5 Me 4 CH 2 CH 2 N(Me)CH 2 ]-ZrH (8) (Scheme 6) [17]. The similar cyclic products of the intramolecular CH-activation of NCH 2 -H bonds have been obtained by Erker and coworkers [18,19] via d 0 Zr(IV) cationic intermediates. In contrast we observed the reaction proceeds via d 2 Zr(II) intermediate.…”

Ion pair symmetrization in metallocenium cations partnered with diborane derived borate counteranions

“…The samples of [2-A] examined were found to be stable over several hours at room temperature and up to a week at low temperature (À40°C). The decomposition products that resulted have not been identified but appear to be derived only from the cation [1,17], since the anions remain intact as monitored by 19 F NMR spectroscopy.…”

Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring Systems

“…The starting materials for the preparation of the related [(dimethylamino)alkyl−C 5 H 4 ]zirconium complexes ( 6a , b and 10 ) were also prepared by a fulvene route,22 as described previously by us 14−16. The synthesis started from 6‐(dimethylamino)‐6‐methylfulvene 23.…”