Determination of the Stereoelectronic Parameters of PF₃, PCl₃, PH₃, and P(CH₂CH₂CN)₃. The Quantitative Analysis of Ligand Effects (QALE)

Abstract

Using the QALE model, we determined the electronic parameters for PF3 (χd = 44 ± 4, Ear = 0, πp = 14 ± 1), PCl3 (χd = 42 ± 1, Ear = 4.1 ± 0.3, πp = 5.3 ± 0.5), PH3 (χd = 17 ± 1, Ear = 0, πp = 3.7 ± 0.7), and P(CH2CH2CN)3 (χd = 17.0 ± 0.6, Ear = 0, πp = 1.2 ± 0.2). These values indicate that PF3 and PCl3 are comparable in σ donor ability and are the poorest σ donor ligands we have studied. Both PH3 and P(CH2CH2CN)3 are reasonably good σ donors, comparable in strength to P(p-ClC6H4)3. PF3 is by far the best π acid. The π acidity of PCl3 is comparable to that of P[(OCH2)3]CEt, whereas the π acidity of PH3 is intermediate between P(O-p-XC6H4)3 and P(OR)3. The analysis of data sets containing PZ3-iHi sometimes requires the inclusion of “i” as a parameter, which we connect with changes in hybridization of these ligands. There are good correlations of χd and πp with the theoretical results of Gonzalez-Blanco and Branchadell and those of Fantucci. The stereoelectronic parameters for 107 PZ3 species are listed.