Reactions of ferrocenyl-stabilised carbocations with water: substituent, medium, salt, and solvent isotope effects on rates and equilibria

Abstract

Rates and equilibrium constants have been measured for reactions of ferrocenylalkyl cations FcC(R)Ar,FcCAr₂, and FcCH(CHCH)_nFc (R = H, Bu^t, and 1 -adamantyl; Ar = Ph and p-methoxyphenyl; n= 0 and 1) with water in H₂O and in H₂O–MeCN in the absence and presence of mineral acid (HCl or H₂SO₄), and a H_R ^Fc acidity function has been constructed for reactions in H₂O–MeCN (H₂SO₄). The rates of water addition to the cations and of acid-promoted heterolysis of ferrocenylalkanols are sensitive to structural, steric, and conformational effects. Medium, salt, and solvent isotope effects on rates and equilibria are consistent with a carbocation-like transition state.