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 Ear. We use this method to interpret new E°/T values of the η-Cp(CO)(L)Fe(COMe)+/0 couple (Cp = cyclopentadienyl, L = PPhiR3–i) and establish a way to calculate χ and Ear values for PPhiR3–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.