The Reaction of bis(1,2,4-tri-t-butylcyclopentadienyl)ceriumbenzyl, Cp'2CeCH2Ph with Methylhalides: a Metathesis Reaction that does not proceed by a Metathesis Transition State

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The experimental reaction between [1,2,4-(Me3C)3C5H2]2CeCH2Ph and CH3X, X = F, Cl, Br, and I, yields the metathetical exchange products, [1,2,4-(Me3C)3C5H2]2CeX and CH3CH2Ph. The reaction is complicated by the equilibrium between the benzyl derivative and the metallacycle [[1,2,4-(Me3C)3C5H2] [(Me3C)2C5H2C(CH3)2CH2]Ce, plus toluene since the metallacycle reacts with CH3X. Labelling studies show that the methyl group of the methylhalide is transferred intact to the benzyl group. The mechanism, as revealed by DFT calculations on (C5H5)2CeCH2Ph and CH3F, does not proceed by way of a four-center mechanism, (sigma-bond metathesis) but a lower barrier process involves a haptotropic shift of the Cp2Ce fragment so that ... continued below

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Werkema, Evan; Andersen, Richard; Maron, Laurent & Eisenstein, Odile September 2, 2009.

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The experimental reaction between [1,2,4-(Me3C)3C5H2]2CeCH2Ph and CH3X, X = F, Cl, Br, and I, yields the metathetical exchange products, [1,2,4-(Me3C)3C5H2]2CeX and CH3CH2Ph. The reaction is complicated by the equilibrium between the benzyl derivative and the metallacycle [[1,2,4-(Me3C)3C5H2] [(Me3C)2C5H2C(CH3)2CH2]Ce, plus toluene since the metallacycle reacts with CH3X. Labelling studies show that the methyl group of the methylhalide is transferred intact to the benzyl group. The mechanism, as revealed by DFT calculations on (C5H5)2CeCH2Ph and CH3F, does not proceed by way of a four-center mechanism, (sigma-bond metathesis) but a lower barrier process involves a haptotropic shift of the Cp2Ce fragment so that at the transition state the para-carbon of the benzene ring is attached to the Cp2Ce fragment while the CH2 fragment of the benzyl group attacks CH3F that is activated by coordination to the metal ion. As a result the mechanism is classified as an associative interchange process.

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44

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  • Journal Name: Dalton Transactions; Journal Volume: 39; Journal Issue: 29; Related Information: Journal Publication Date: 8/7/2010

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  • Report No.: LBNL-4236E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 1004700
  • Archival Resource Key: ark:/67531/metadc845418

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  • September 2, 2009

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  • May 19, 2016, 3:16 p.m.

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  • July 26, 2016, 5:46 p.m.

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Werkema, Evan; Andersen, Richard; Maron, Laurent & Eisenstein, Odile. The Reaction of bis(1,2,4-tri-t-butylcyclopentadienyl)ceriumbenzyl, Cp'2CeCH2Ph with Methylhalides: a Metathesis Reaction that does not proceed by a Metathesis Transition State, article, September 2, 2009; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc845418/: accessed April 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.