Displacement of Acetone from η-(C₅R₅)(CO)Fe(AC)(COMe)⁺ by Thioethers. Application of the Quantitative Analysis of Ligand Effects (QALE)

Abstract

The displacement of acetone (AC) from η-(C5R5)(CO)Fe(AC)(COMe)+ (R = H, Me) by thioethers {SMe2, SMeEt, SEt2, S(n-Bu2), SMe(t-Bu), S(i-Pr)2,S(t-Bu)2, SPh2, SMe(p-XC6H4) (X = H, Me, MeO, Cl), and SEtPh} at −41 °C was studied using square-wave voltammetry. Rate constants were extracted from the square-wave voltammograms using computer simulation methods and were found to be sensitive to the stereoelectronic properties of the nucleophiles. The Cp (C5H5) complex is more reactive toward the smaller thioethers than the Cp* (C5Me5) complex, but there is an inversion of reactivity for the large thioethers. The rate constants were analyzed in terms of the electronic parameters (χ and Ear) and one of the steric parameters θ, ER, or Ωs. The best correlation is found using χ, θ, and Ear. Of the two families of complexes, the rates of reaction of the Cp* complex with the thioethers are less dependent on the stereoelectronic properties of the nucleophiles. This leads to a model of the transition states for the Cp* complex that is more flexible than that for the Cp complex, thereby allowing the reactions with the larger thioethers.