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

Dalton Transactions : an International Journal of Inorganic Chemistry
Evan L WerkemaOdile Eisenstein

Abstract

The experimental reaction between [1,2,4-(Me(3)C)(3)C(5)H(2)](2)CeCH(2)Ph and CH(3)X, X = F, Cl, Br, and I, yields the metathetical exchange products, [1,2,4-(Me(3)C)(3)C(5)H(2)](2)CeX and CH(3)CH(2)Ph. The reaction is complicated by the equilibrium between the benzyl derivative and the metallacycle [1,2,4-(Me(3)C)(3)C(5)H(2)][(Me(3)C)(2)C(5)H(2)C(CH(3))(2)CH(2)]Ce, plus toluene since the metallacycle reacts with CH(3)X. 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 (C(5)H(5))(2)CeCH(2)Ph and CH(3)F, does not proceed by way of a four-center mechanism, a sigma-bond metathesis, but by a lower barrier process involving a haptotropic shift of the Cp(2)Ce fragment so that at the transition state the para-carbon of the benzene ring is attached to the Cp(2)Ce fragment while the CH(2) fragment of the benzyl group attacks CH(3)F that is activated by coordination to the metal ion. As a result the mechanism is classified as an associative interchange process.

Citations

Apr 22, 2017·Journal of the American Chemical Society·Nicholas S SettineriJohn Arnold
Oct 19, 2016·Dalton Transactions : an International Journal of Inorganic Chemistry·Rongala RamalakshmiSundargopal Ghosh
Mar 10, 2016·Chemical Society Reviews·Christos E KefalidisLaurent Maron
Nov 12, 2014·Angewandte Chemie·Polly L ArnoldFritz E Kühn
Sep 8, 2018·Dalton Transactions : an International Journal of Inorganic Chemistry·Jan RaederMarc D Walter
Dec 2, 2017·Science·Andrew S S WilsonLaurent Maron

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