Hydrogen/Halogen Exchange of Phosphines for the Rapid Formation of Cyclopolyphosphines

The hydrogen/halogen exchange of phosphines has been exploited to establish a truly useable substrate scope and straightforward methodology for the formation of cyclopolyphosphines. Starting from a single dichlorophosphine, a sacrificial proton donor phosphine makes the rapid, mild synthesis of cyclopolyphosphines possible: reactions are complete within 10 min at room temperature. Novel (aryl)cyclopentaphosphines (ArP)(5) have been formed in good conversion, with the crystal structures presented. The use of catalytic quantities of iron(III) acetylacetonate provides significant improvements in conversion in the context of diphosphine (Ar2P)(2) and alkyl-substituted cyclotetra- or cyclopentaphosphine ((AlkylP)(n), where n = 4 or 5) formation. Both iron-free and iron-mediated reactions show high levels of selectivity for one specific ring size. Finally, investigations into the reactivity of Fe(acac)(3) suggest that the iron species is acting as a sink for the hydrochloric acid byproduct of the reaction.

Automated summary

The hydrogen/halogen exchange of phosphines has been utilized to establish a method for the synthesis of cyclopolyphosphines. The use of catalytic quantities of iron(III) acetylacetonate significantly improves conversion and selectivity for specific ring sizes. Investigation into the reactivity of Fe(acac)(3) suggests that the iron species acts as a sink for the hydrochloric acid byproduct of the reaction.