Kinetics of nucleophilic attack on co-ordinated organic moieties. Part I. Addition of β-diketones on cyclic dienyl complexes

Abstract

The kinetics have been studied for the nucleophilic addition of β-diketones on cyclic dienyl complexes of type (i)(n= 1, 2; M = Fe, Os; A = H, OMe; X = CO, PPh₃), yielding the substituted diene complexes (ii). For, [graphic omitted] acetylacetone and dimedone a rate law of the form –dR/dt=k_obs[R][BH] has been demonstrated (where R = dienyl salt, BH =β-diketone). A mechanism is suggested involving a rapid pre-equilibrium dissociation of the β-diketone to yield a reactive carbanion, which then reacts directly with the co-ordinated dienyl group in a rapid but rate-determining fashion. The influence of the metal and other co-ordinated ligands, and the effect of variations in the solvent and β-diketone are discussed.