A thermodynamic method based on isoequilibrium behavior to determine the values of stereoelectronic parameters of phosphines

Abstract

Isoequilibrium behavior provides a method of determining stereoelectronic parameters, for use in linear free energy relationships. This method is based on thermodynamics and is different from the usual ways of assigning values to these parameters. Analysis of isoequilibrium behavior is done in terms of the three parameter QALE (quantitative analysis of ligand effects) model, with parameters χ, θ and E_ar. We use this method to interpret new E°/T values of the η-Cp(CO)(L)Fe(COMe)^+/0 couple (Cp = cyclopentadienyl, L = PPh_iR_3–i) and establish a way to calculate χ and E_ar values for PPh_iR_3–i. In support of the validity of the method, we find that these calculated χ values agree well, except for PPh₂Prⁱ, with the values previously reported by Bartik. We also calculated a value for χ equal to 0.4 for P(NC₄H₈)₃ for which a χ value had not been reported previously.