Ring expansion vs. addition – reactivity of a cyclo-P4 complex towards pnictogenium cations

Abstract

A systematic study on the reactivity of the cyclo-P₄ complexes [Cp^RTa(CO)₂(η⁴-P₄)] 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 cyclo-P₅R₂ products. In contrast, an arsenium-functionalised P₄AsCy₂ 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.