Ab initio calculations on phosphorus compounds. II. Effects of disubstitution on ligand apicophilicity in phosphoranes

Abstract

Geometry optimizations at the HF/3-21G(*) and HF/6-31G* levels of ab initio theory have been carried out for various isomers of model disubstituted phosphoranes PH:>XY(X, Y=OH, CH3, NH2, and SH). Reasonable agreement was obtained between the optimized geometries and available crystal structure data for analogous compounds. The isomers were further characterized by frequency calculations. The MP2/6-31G*//6-31G* + ZPE energy data reveal that the interactions between the ligands are relatively small (0-4 kcal mol-') for the most stable conformations of the isomers. Hence, for these conformations the apicophilicities (based upon monosubstituted phosphoranes) are approximately additive. The less stable PHuXY conformations are in general transition states or higher-order saddle points, and their interligand interactions are larger in magnitude (up to 10 kcal mol-'); the results with these conformations suggest that apicophilicities may not be as additive for some highly substituted phosphoranes.

The Ligand‐Exchange Process of P–Hapical Phosphoranes and the Thermal Formation and Pseudorotation of Anti‐Apicophilic Spirophosphoranes

“…On the other hand, the corresponding bonds in O ‐ cis 6b were found to be different, as expected, with the apical bonds being typically longer than the corresponding equatorial bonds (P–O apical 1.773 > P–O equatorial 1.658 Å and P–C apical 1.860 > P–C equatorial 1.806 Å). The percentages of contraction of an equatorial bond compared to that of an apical bond for 6b are 6 % for P–O and 3 % for P–C, and are in good agreement with averaged (among three conformers) differences between P–O (4 %) and P–H (2 %) bonds in PH 3 (OH) apical (OH) equatorial by theoretical calculations,12 thus reflecting the larger polarity of the P–O bond compared with the P–C bond. The trends are practically the same in O ‐ cis 6c .…”

“…This is understandable considering the fact that a rather large difference in energy is expected for them [empirical estimate: ca. 8.3 kcal mol –1 ;10 theoretical values for cyclic phosphorane PH 3 (CH 2 CH 2 O): 7.7711 and 2.4 kcal mol –1 ;9c for acyclic phosphorane PH 3 CH 3 OH:12 1.6 kcal mol –1 ]. Furthermore, there is a question as to whether such species actually exist as stationary points on the pseudorotation reaction coordinate at all 12…”

Novel Synthesis, X-ray Crystal Structures, and Spectroscopic Properties of Metalated Hypervalent Phosphorus Compounds, Cp(CO)LFe{P(OC6H4Y)(OC6H4Z)} (L = CO, P(OPh)3, P(OMe)3, PMe3; Y, Z = NH, NMe, O)

“…The O1−P1−O2 bond is in the same plane as the nitrogens and the three atoms directly bonded to the nitrogens. Therefore, the nitrogen undergoes sp 2 hybridization and the lone-pair electrons are located on the equatorial plane, implying π donation of the lone-pair electrons to equatorial σ* orbitals on the phosphorus. − The observed Fe−P bond lengths (2.291 Å for 1b and 2.272 Å for 2b ) are close to that of the only precedent of iron phosphorane (2.300 Å) …”

The Potassium Ion Channel: Comparison of Linear Scaling Semiempirical and Molecular Mechanics Representations of the Electrostatic Potential

“…By contrast, to compute a single MD step requires approximately 1 s. Although several different sets of coordinates were extracted from each MD trajectory, for simplicity, only the results from a single set of coordinates are presented here; the other results were analyzed and found to be quantitatively similar. The QM calculations were performed using the Mopac2000 v.1.1 [25] program and the parametrized molecular electrostatic potential method therein . The QM results were compared with the MEP computed using partial atomic charges taken from the Amber, OPLS, Charmm19, and Charmm22 4 force-fields.…”