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New Chromium Enolates

Published in Helvetica Chimica Acta. 2003, vol. 86, no. 12, p. 4169-4184
Abstract Three new (?2-acrylate)(?6-arene)dicarbonylchromium complexes are reported. They were obtained either by CO/acrylate exchange in [Cr(?6-benzene)(CO)3] (1) via the photolytically generated ?2-cyclooctene intermediate or by arene exchange in [Cr(?2-methyl acrylate)(?6-benzene)(CO)2] (3) (Scheme 1). On crystallization, [Cr(?2-methyl acrylate)(?6-o-xylene)(CO)2] (5) underwent partial resolution. The degree of this resolution was analyzed via X-ray crystal-structure determination (Fig. 1) and was correlated to the CD spectra in solution (Fig. 6), thus allowing the assignment of the absolute configuration. The reaction of [Cr(?2-acrylate)(?6-benzene)(CO)2] complexes with cyclopentad-1,3-diene or 1H-indene afforded new (?6-cyclopenta-2,4-dien-1-yl)- or (?6-1H-inden-1-yl)(?3-oxaallyl)chromium complexes (Scheme 2). A mechanism is proposed that involves arene-ligand substitution by the diene ligand, initiated by haptotropic rearrangement of the acrylate from a ?2- to a ?4-coordination mode, followed by hydride migration from the diene to the acrylate (Scheme 3). An X-ray crystal-structure determination of [Cr(CO)2(?5-1H-inden-1-yl){?3-CH(CH2CF3)C(O)OEt}] (8) reveals a metal enolate that is best described as ?3-oxaallyl species (Fig. 2). A shorter, more-efficient route to the [Cr(?5-1H-inden-1-yl)(?3-oxaallyl)] complexes was devised via the reaction of [Cr(CO)2(?2-cyclooctene)(?6-1H-indene)] with methyl acrylate (Scheme 4).
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KUNDIG, Ernst Peter et al. New Chromium Enolates. In: Helvetica Chimica Acta, 2003, vol. 86, n° 12, p. 4169-4184. doi: 10.1002/hlca.200390343 https://archive-ouverte.unige.ch/unige:7831

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Deposited on : 2010-06-21

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