Ring expansion addition - reactivity of a -P complex towards pnictogenium cations.

A systematic study on the reactivity of the -P complexes [CpTa(CO)(η-P)] towards pnictogenium cations results in the formation of functionalised interpnictogen cations. Phosphenium ions insert into one of the P-P bonds to give ring-expanded -PR products. In contrast, an arsenium-functionalised PAsCy ligand displays an interesting borderline case between ring expansion and coordination, while stibenium cations afford addition products. Tuning of the steric and electronic properties of the stibenium ion shows a drastic influence on the reaction outcome.