Cyclopentaphosphine Explained

Cyclopentaphosphine is the inorganic compound with the formula (PH)₅. It is prepared by the hydrolysis of cyclo-[PSiMe₃]₄ (Me = methyl). Although only of theoretical interest, (PH)₅ is parent of many related cyclic polyphosphines that are the subject of research.

Organic cyclophosphines

Organic cyclophosphanes are a family of organophosphorus compounds with the formula (RP)_n where R is an organic substituent. Many examples are known. They are white, air-sensitive solids which have good solubility in organic solvents. Well-characterized examples are known for ring sizes 3–6. The three-membered rings feature bulky substituents, e.g., [''tert''-BuP]₃.

The cyclophosphines can be prepared by several methods, one involves reductive coupling of dichlorophosphines:^[1]

5PhPCl₂ + 5 Mg → [PhP]₅ + 5MgCl₂

Isomerism

The structures are complicated by the slow pyramidal inversion at phosphorus(III). In principle, many isomers are possible for cyclo-P₅R₅, but usually only one is observed.^[2] All phenyl substituents are equatorial in cyclo-P₆(C₆H₅)₆.^[3]

References

1. Marianne Baudler, Klaus Glinka . Monocyclic and Polycyclic Phosphines . . 1993 . 93 . 1623–1667 . 10.1021/cr00020a010.
2. 10.1021/ic50150a051. Conformational Stability and Ring-Size Integrity of Cyclic Polyphosphines . 1975 . Hoffman . P. R. . Caulton . K. G. . Inorganic Chemistry . 14 . 8 . 1997–1999 .
3. 10.1080/10426509308034357. Transformations of Difluorophosphines: The Influence of Solvent on the Reaction Pathway and Ring Size in Cyclopolyphosphines . 1993 . Schmutzler . Reinhard . Heuer . Lutz . Schomburg . Dietmar . Phosphorus, Sulfur, and Silicon and the Related Elements . 83 . 1–4 . 149–156 .