Evaluation of the Stereoelectronic Parameters of Fluorinated Phosphorus(III) Ligands. The Quantitative Analysis of Ligand Effects (QALE)

Abstract

Using the QALE model, we determined the QALE stereoelectronic parameters for the following ligands: P(CF3)3 (χd = 33 ± 2, θ = 137 ± 13°, Ear = 0, πp = 11.1 ± 0.6), P(CH2CH2C6F13)3 (χd = 9 ± 3, θ = 137 ± 2°, Ear = 0, πp = 2.5 ± 0.4), P[p-(F13C6)C6H4]3 (χd = 23 ± 1, θ = 145°, Ear = 2.7, πp = 0), and P(C6F5)3 (χd = 34 ± 2, θ = 191 ± 13°, Ear = 4.3 ± 0.5, πp = 0). In addition, we evaluated the parameters for P[Pyr-3,4-(CO2Et)2]3 (Pyr = pyrrolyl; χd = 43 ± 2, θ = 145°, Ear = 3.3, πp = 2 ± 1). Revised parameters for PF3 are also presented: χd = 33 ± 2, θ = 110 ± 24°, Ear = 0, πp = 13.2 ± 0.5. The absence of an indicated error means that these values were assigned initially to the particular parameters in the analyses or that the parameters are statistically indistinguishable from zero. Where a comparison can be made, we find that our calculated values of θ are indistinguishable from those of Tolman; therefore, we suggest the continued use of Tolman's values. It is observed that the perfluoroalkyl groups are highly π acidifying and that this effect is transmitted through intervening CH2 groups.