A Convenient Preparative Method for Cyclic Triphosphenium Bromide and Chloride Salts

Analytically pure chloride and bromide salts of two different cyclic triphosphenium cations are prepared by the
reaction of PX3 (X = Cl, Br) in the presence of the halogen-scavenging reagent cyclohexene. For the brominated
species, the neutral, volatile 1,2-dibromocyclohexane byproduct is readily removed under reduced pressure, and
the desired salts are obtained in high yield. Reactions involving phosphorus trichloride are complicated by the
formation of salts containing both chloride and hydrogen dichloride anions. Reactivity experiments on potential
undesired halogenated diphosphine byproducts suggest that the formation of such species can be prevented by
increasing the concentration of cyclohexene employed in the reaction.