Theoretical study, NBO analysis, HOMO/LUMO and first static hyperpolarizability for the structural prediction of new 1X-tri-R-σ3λ3-phosphacyclohexadienyl anion ligands using DFT calculations

Abstract

Phosphacyclohexadienyl anions derived from phosphinine can be distinguished from related carbon-containing cyclohexadienyls by their ambidentate donor properties and versatile coordination behavior. These species are applied in materials science serving as ligands stabilizing metal complexes. It is well established that nucleophilic (X–) attacks at the phosphorus hetero­atom in λ3-phosphinine form the corresponding σ3λ3-phosphacyclohexadienyl anion containing a covalent P—X bond (X = halogen, halide). Starting from this assumption, a theoretical investigation is presented for predicting the structural behavior and relative stability of six new ligands (1X-tri-R-σ3λ3-phosphacyclohexadienyl anion), resulting from such a nucleophilic attack in 2,4,6-trisubstituted-λ3-phosphinine. The DFT calculations have been carried out. The geometry optimization and the search for normal vibrational mode, the NBO population analysis, and the HOMO/LUMO analysis are reported and discussed. In addition, solvent and counterion effects are briefly discussed, and the first static hyperpolarizability (βtot) is calculated in order to predict the nonlinear optic (NLO) behavior of these anions. The results confirm the existence of real minima on PES in all structures studied. The predicted geometric parameters for these species are, approximately, in good agreement with those found in the literature for similar compounds. The heteroatom is confirmed to be σ3λ3-P coordinated. The NBO analysis predicts the main charge transfers which stabilize the systems. The hyperpolarizability values predicted suggest that these species have good NLO behavior. The six anions studied are relatively stable and the cis-isomers are slightly more stable than their trans-forms. The latter exhibit high βtot values compared to those of their cis-isomers.