Trigonal bipyramidal phosphorus

Fig. 7. Itinerary for permutational isomerizations by single turnstile rotation, or by Berry pseudorotation, when the five ligands in trigonal bipyramidal phosphorus are different. Isomers are denoted by Permutational Notation.

Binding Energies (in kcal mole-1) of Trigonal Bipyramidal Phosphorus Compounds from CNDO/2 Calculations. A = Loss of Stability Among Isomers... 

Electron Densities of Isomers of Trigonal Bipyramidal Phosphorus Compounds Calculated by CNDO/2... 

Regular processes are not the only way by which trigonal bipyramidal phosphorus can undergo permutational isomerization. Irregiilar processes, involving bond ruptures and reformations, must always be considered as alternatives, and some experimental justification or reasoning-by-analogy must be provided in discussions of permutational isomerization itineraries. This is particularly important when selection... 

Cf the strong preference for axial positions found for fluorine etc. in trigonal bipyramidal phosphorus compounds R. R. Holmes, Pentacoordinated Phosphorus , ACS, Washington, DC, 1980 vol. 11. 

Configuration-dependent conformational transmission in trigonal bipyramidal phosphorus(V) compounds enhances the gauche (-) conformation population around the 6 linkage in phosphorylated... 

The pyramidal structure of phosphorus trichloride, PCI3 typifies trivalent phosphorus compounds, while tetrahedral phosphoryl chloride, POCI3, the ions PCIJ and PO together with trigonal bipyramidal phosphorus pentachloride, PCI5, typify the spatial arrangements adopted by pentavalent phosphorus compounds. The hexachloro-phosphate (hexachlorophosphoride) anion. 

Many trigonal bipyramidal phosphorus molecules exist in equilibrium with tetrahedral phospho-nium cations and octahedral anions. In some instances all forms can be isolated and characterised. Phosphorus pentachloride, for example, exists as PCI5 in the vapour state, but as an assembly of PCI4 PCI in the solid state. Dimerisation also occurs to a small extent in some solvents (3.41). 

The formation of a stable trigonal bipyramidal phosphorus compound is most likely when none of the substituents are good leaving groups as, for example, in the formation of pentaphenylphospho-rane (3.83). On the other hand, elimination seems to occur most readily when a phosphoryl group is involved (3.84). 

DIAD) with cyclic phosphites/phosphoramidites were examined in an effort to delineate the structural preferences in spirocyclic penta- and tri- cyclic hexacoordi-nate (amino)oxyphosphoranes. Thus the reaction of (38) with DEAD or DIAD leads to the chlorophosphoranes (39). Treatment of (39) with pyrazole or imidazole leads to (40) that have trigonal bipyramidal phosphorus with reversed apicophili-city . Compound (41, Y = NH/Pr) and DIAD affords the pentacoordinate... 

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