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

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 chi, theta and E-ar. We use this method to interpret new E degrees/T values of the eta-Cp(CO)(L)Fe(COMe)(+/0) couple (Cp = cyclopentadienyl, L = PPhiR3-i) and established way to calculate chi and E-ar values for PPhiR3-i. In support of the validity of the method, we find that these calculated chi values agree well, except for PPh2Pri, with the values previously reported by Bartik. We also calculated a value for chi equal to 0.4 for P(NC4H8)(3) for which a chi value had not been reported previously.