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Title: Experimental and DFT computational study of β-Me and β-H elimination coupled with proton transfer: From amides to enamides in Cp* 2MX (M = La, Ce)

The thermal rearrangement of the f-block metallocene amides Cp* 2MNR 1R 2, where R 1 is CHMe 2, R 2 is either CHMe 2 or CMe 3, and M is either La or Ce, to the corresponding enamides Cp* 2MNR 1[C(Me)=CH 2] and H 2 or CH 4, respectively, occurs when the solid amides are heated in sealed evacuated ampules at 160–180 °C for 1–2 weeks. The net reaction is a β-H or β-Me elimination followed by a γ-abstraction of a proton at the group from which the β-elimination occurs. When R 1 is either SiMe 3 or SiMe 2CMe 3 and R 2 is CMe 3, the enamide Cp* 2MNR 1[C(Me)=CH 2] is isolated, the result of β-Me elimination, but when R 2 is CHMe 2, the enamides Cp* 2MNR 1[C(Me)=CH 2] and Cp* 2NR 1[C(H)=CH 2] are isolated, the result of β-H and β-Me elimination. In the latter cases, both enamides are formed in similar amounts and the rates of the β-H and β-Me elimination steps must be similar. A two-step mechanism is developed from DFT calculations. The first step is migration of a hydride or a methyl anion to the Cp* 2M fragment, forming M–H or M–Memore » bonds as the N=C bond in the intermediate imine forms. Furthermore, the enamide evolves from the metal-coordinated imine by abstraction of a proton from the γ-carbon of the intermediate imine. The two elementary steps involve significant geometrical changes within the N αC βC γ set of atoms during the two-step elimination process that are in large part responsible for the relatively high activation barriers for the net reaction, which may be classified as a proton-coupled hydride or methyl anion transfer reaction.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1]
  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. Lyon, Villeurbanne (France)
  3. Univ. de Montpellier, Montpellier (France)
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AC02- 05CH11231
Type:
Published Article
Journal Name:
Organometallics
Additional Journal Information:
Journal Volume: 36; Journal Issue: 1; Journal ID: ISSN 0276-7333
Publisher:
American Chemical Society
Research Org:
Univ. of California, Berkeley, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1330108
Alternate Identifier(s):
OSTI ID: 1339954