Cyclopentaphosphine

Cyclopentaphosphine is the inorganic compound with the formula. It is prepared by the hydrolysis of cyclo-. Although only of theoretical interest, 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 _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., ₃.
The cyclophosphines can be prepared by several methods, one involves reductive coupling of dichlorophosphines:

The structures are complicated by the slow pyramidal inversion at phosphorus. In principle, many isomers are possible for cyclo-, but usually only one is observed. All phenyl substituents are equatorial in cyclo-.