Mechanism of electrophilic substitution at a saturated carbon atom. Part XV. The displacement of an iron carbonyl group from saturated carbon by mercury(II) and thallium(III) species

Abstract

Mercury(II) perchlorate and thallium(III) perchlorate displace the dicarbonyl-π-cyclopentadienyliron cation from pyridiniomethyldicarbonyl-π-cyclopentadienyliron ions extremely rapidly in aqueous solution at 25 °. These reactions are believed to involve the bimolecular S_E2 reaction at saturated carbon in which there is an open unbridged transition state. The products are the corresponding pyridiniomethylmercury(II) or thallium(III) cations, though the latter are too unstable to remain as such. The influence of chloride ion on the rates of these reactions has been studied and the variation of the observed rate coefficients has been interpreted in terms of the different reactivities of the various mercury(II) and thallium(III) species in solution. Individual rate coefficients for the species Hg²⁺, HgCl⁺, HgCl₂, HgCl₃^–, HgCl₄^2–, Tl³⁺, TlOH²⁺, TlCl²⁺, TlCl₂⁺, TlCl₃, and TlCl₄^– have all been estimated, and the variations are commented on briefly.