Reactions of [Aryloxy(phenyl)carbene]pentacarbonylchromium(0) Complexes with Thiolate Ions. Decreasing Reactivity with Increasing Basicity of the Nucleophile

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• 作者：Claude F. Bernasconi ; Mois&eacute ; s P&eacute ; rez-Lorenzo ; Sara J. Codding
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：December 7, 2007
• 年：2007
• 卷：72
• 期：25
• 页码：9456 - 9463
• 全文大小：217K
• 年卷期：v.72,no.25(December 7, 2007)
• ISSN：1520-6904

文摘

A kinetic study of the reactions of thiolate ions with three Fischer-type [aryloxy(phenyl)carbene]pentacarbonyl chromium(0) complexes in 50% MeCN-50% water (v/v) is reported. Brnsted plots ofthe second-order rate constants are biphasic with an initial steep rise for weakly basic thiolate ions (_nuc 1.0) followed by a slightly descending leg with a negative slope (_nuc -0.2) for strongly basicthiolate ions. This indicates a change from rate-limiting leaving group departure at low p to rate-limiting nucleophilic attachment at high p. The negative _nuc values result from a combination ofminimal progress of C-S bond formation at the transition state and the requirement for partial desolvationof the nucleophile before it enters the transition state. Possible factors that may affect the degree of bondformation in reactions of Fischer carbene complexes as well as reactions of other unsaturated electrophileswith thiolate ions are discussed.