A proton magnetic resonance study of trimethyl phosphate exchange on magnesium(II)

Abstract

A ¹H N.M.R. study of the exchange reaction Mg(tmp)₆²⁺ ↔ tmp (tmp, trimethyl phosphate) in methylene chloride and acetone diluents is reported. A complete signal shape analysis is used to derive kinetic parameters. The value for k_ex (193 K) in the rate law R = 6k_ex[Mg(tmp)₆²⁺] is 3.2±0.5 s^-1, ΔH^? = 70.7±3.8 kJ mol^-1, and ΔS? = 135.1±12.6 J mol^-1 K^-1 when the Mg²⁺ : tmp : methylene chloride mole ratio is 1.00 : 12.1 : 34.9. Values of similar magnitude are obtained under different mole ratio and diluent conditions. The tmp exchange is considered to proceed through a dissociative mechanism involving solvent structural rearrangement in the activation process.