Geometrical structures of phosphorus-containing heterocyclic compounds

Structural and electronic influences on phosphite basicity and its application to heterogeneous and homogeneous catalysis

“…However, the approximate equivalence of the lEp values under assignment a) with that of Me2NP(0Me)2 may be due to greater sp^ character in the ring oxygens of ^ and ^ which would tend to reduce lone-pair interactions between phosphorus and oxygen.The photoelectron assignments given in a) would seem best since they remove all five objections to assignment b). At the same time the values in assignment a) for _20 and_21_ are in agreement with those found for Me2NP(0Me)2(162) and(163). However, it would appear that the lEg for the a',a" interactions of the p AO's on the oxygens in20 and 21 are quite low compared to those for Me2NP(0Me)2.…”

“…The arrangement of lone-pairs in this conformation should cause a higher lEp than for the conformation of _20 and(as illustrated by the conformations of lone-pairs in similar compounds (Fig. 24)(163)). This is due to lack of interaction between the lone-pairs on oxygen and phosphorus in the acyclic compounds, which would normally tend to raise the energy of the phosphorus lone-pair.…”

Stereoselective PCO/POC-Rearrangement of P–C-Cage Phosphorane in the Reaction of 4,5-Dimethyl-2-(2-oxo-1,2-diphenyl)ethoxy-1,3,2-dioxaphospholane with Hexafluoroacetone

“…Methyl groups are situated in the axial positions of this five-membered cycle. Disagreement with the X-ray data for molecule 9 , where diequatorial arrangement of these groups is observed, may be caused by two reasons: first, the calculations were performed in the gas phase; second, five-membered phosphorus cycles show a certain conformational flexibility, , and the forms with diaxial and diequatorial arrangement of methyl groups possess similar energies. The concerned geometry is more favorable than an analogous geometry with different relative disposition of phenyl groups at atoms C 3 and C 4 (P 1 R C 3 S C 4 S C 7 S C 8 S /P 1 S C 3 R C 4 R C 7 R C 8 R -diastereoisomer d 3 ) (see Figure ).…”

“…On the whole, structural parameters of the 1,3,2-dioxaphospholane cycle are close to the experimental ones, which were obtained by X-ray analysis of 2,2′-dioxybinaphthyl derivative of 4,5-dimethyl-1,3,2-dioxaphospholane. 52 Optimized geometry for phospholane 9 calculated by the DFT method is presented in , where diequatorial arrangement of these groups is observed, may be caused by two reasons: first, the calculations were performed in the gas phase; second, fivemembered phosphorus cycles show a certain conformational flexibility, 53,54 and the forms with diaxial and diequatorial arrangement of methyl groups possess similar energies. The concerned geometry is more favorable than an analogous geometry with different relative disposition of phenyl groups at atoms C 3 and 5).…”