Past synthetic routes to cyclopolyphosphines ((PR)<sub>n</sub>, n = 3-6) have predominantly involved the use of mercury/magnesium/alkaline earth metals alongside dihalophosphines in Wurtz-type salt metathesis reactions (Scheme 1a), or dehydrochlorination reactions between a dichlorophosphine and a primary phosphine (Scheme 1b). The need for stoichiometric amounts of metal reagents alongside formation of metal halide waste or the necessity for both primary phosphine and dichlorophosphine moieties limit the attractiveness of both these pathways significantly. Whilst catalytic dehydrocoupling of primary phosphines offers a cleaner route to cyclopolyphosphines (Scheme 1c), reactions require forcing conditions or stoichiometric amounts of a hydrogen acceptor.<br/><br/>Utilizing the hydrogen-halogen exchange of phosphines, a 'sacrificial proton donor' phosphine is able to mediate the in-situ formation of a primary phosphine from a dichlorophosphine. A simple dehydrochlorination reaction can then occur between the dichlorophosphine and the newly formed primary phosphine to yield a cyclopolyphosphine product (Scheme 1d). This provides a mild, rapid route to these cyclic species, enabling a broad scope of examples to be synthesized with ease.

Hydrogen-halogen exchange of phosphines for the rapid formation of cyclopolyphosphines

ACS Spring 2022

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