Direct evidence for a rate–determining chelate ring closure mechanism during the reaction of 2,2′-bipyridine with the hexakis(dimethyl sulphoxide)-aluminium(III) ion in nitromethane solution

Abstract

Stopped-flow Fourier-transform n.m.r. experiments reveal two distinct stages in the reaction between the [Al(Me₂SO)₆]³⁺ ion and 2,2′-bipyridine in [²H₃]-nitromethane solution, substitution of the first solvent molecule (at 298·2 K, 10^–3k₁= 2·0 dm³ mol^–1 s^–1, ΔH‡= 75·9 ± 4·3 kJ mol^–1, ΔS‡=+ 73 ± 16 J K^–1 mol^–1) being much faster than the rate of displacement of the second solvent molecule (at 298·2 K, 10²k₂= 3·9 s^–1, ΔH‡= 92·0 ± 1·7 kJ mol^–1ΔS‡= 36·6 ± 6·3 J K^–1 mol^–1).