The stereoelectronic parameters of phosphites. The quantitative analysis of ligand effects (QALE)

Abstract

Through an analysis of pKa values for HPZ3+, ionization potentials (IP) for PZ3, νCO for η-Cp(CO)(PZ3)Fe(COMe)0, and E° (229 K) and ΔH° for the η-Cp(CO)(PZ3)Fe(COMe)+/0 couple, we determined the values of the three electronic parameters, χd, Ear and πp that are needed to describe the stereoelectronic properties of phosphites. The phenomenon we call the ‘aryl effect’, which is described by the parameter Ear, is apparently not restricted to phosphines bearing pendant aryl groups but applies to the phosphites. πp is a new parameter related to the π acidity of the phosphites. The phosphites studied are listed in terms of increasing π acidity: P(OMe)3 ≈ P(OEt)3 ≈ P(OBu)3 ≈ P(O-i-Bu)3 ≈ P(O-i-Pr)3 < P(OCH2CH2Cl)3 < P(O-p-XC6H4)3 < P(OCH2)3CEt (X = MeO, Me, H, Cl, CN). Using these electronic parameters, along with Tolman’s cone angle, we have now incorporated the phosphites into the QALE (quantitative analysis of ligand effects) model and analyzed 32 sets of spectroscopic, thermodynamic, and kinetic data mostly taken from the literature. The analyses give a median r2 value of 0.982.