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| - Reactions of [Aryloxy(phenyl)carbene]pentacarbonylchromium(0)Complexes with Thiolate Ions. Decreasing Reactivity with IncreasingBasicity of the Nucleophile
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| - 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. Brønsted plots ofthe second-order rate constants are biphasic with an initial steep rise for weakly basic thiolate ions (βnuc≈ 1.0) followed by a slightly descending leg with a negative slope (βnuc ≈ −0.2) for strongly basicthiolate ions. This indicates a change from rate-limiting leaving group departure at low pto rate-limiting nucleophilic attachment at high p. The negative βnuc 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.
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