Gas-Phase Reactions of Bis(5-cyclopentadienyl)methylzirconium Cations with Ketones and Aldehydes
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- 作者：Alexander A. Aksenov ; Cesar S. Contreras ; David E. Richardson ; John R. Eyler
- 刊名：Organometallics
- 出版年：2007
- 出版时间：January 29, 2007
- 年：2007
- 卷：26
- 期：3
- 页码：478 - 488
- 全文大小：262K
- 年卷期：v.26,no.3(January 29, 2007)
- ISSN：1520-6041
文摘
The reactions of the bis(
5-cyclopentadienyl)methylzirconium cation (1) with ketones and aldehydesin the gas phase have been studied by Fourier transform ion cyclotron resonance mass spectrometry.Reactions of 1 with a majority of the ketones studied resulted in consecutive addition of one and twosubstrate molecules and/or elimination of alkanes. Deuterium-labeled substrates and methylzirconocenewere used to investigate the mechanistic details. On the basis of DFT calculations, the key products ofthe elimination reaction(s) were identified as 3-enolate complexes formed via an insertion/eliminationmechanism. Similar product ion structures are postulated for the reaction of 1 with aldehydes in caseswhere these complexes are either the only or the major reaction product. A multiple-step mechanism isproposed, which involves migratory insertion of an aldehyde molecule into the methylzirconocene cation,followed by 
-H elimination, and, via a six-membered cyclic transition state, formation of the resultingenolate complex. When a -H elimination pathway is not available for ketones, the reaction is insteadproposed to proceed via direct nucleophilic attack of the metal-bound alkyl preceded by a fast migratoryinsertion equilibrium.
5-cyclopentadienyl)methylzirconium cation (1) with ketones and aldehydesin the gas phase have been studied by Fourier transform ion cyclotron resonance mass spectrometry.Reactions of 1 with a majority of the ketones studied resulted in consecutive addition of one and twosubstrate molecules and/or elimination of alkanes. Deuterium-labeled substrates and methylzirconocenewere used to investigate the mechanistic details. On the basis of DFT calculations, the key products ofthe elimination reaction(s) were identified as 3-enolate complexes formed via an insertion/eliminationmechanism. Similar product ion structures are postulated for the reaction of 1 with aldehydes in caseswhere these complexes are either the only or the major reaction product. A multiple-step mechanism isproposed, which involves migratory insertion of an aldehyde molecule into the methylzirconocene cation,followed by -H elimination, and, via a six-membered cyclic transition state, formation of the resultingenolate complex. When a -H elimination pathway is not available for ketones, the reaction is insteadproposed to proceed via direct nucleophilic attack of the metal-bound alkyl preceded by a fast migratoryinsertion equilibrium.