Low-Valent Chemistry: An Alternative Approach to Phosphorus-Containing Oligomers

A convenient preparative approach to low-valent phosphorus-rich oligomers is presented. Ligand substitution reactions involving anionic diphosphine ligands of the form [(PR₂)₂N]⁻ and [(PPh₂)₂C₅H₃]⁻ and a triphosphenium bromide P^I precursor result in the formation of phosphorus­(I)-containing heterocycles, several of which are of types that have never been prepared before. The methodology described also allows for the preparation of the known heterocycle cyclo-[P­(PPh₂)­N­(PPh₂)]₂ in better yields and purity than the synthetic approach reported previously. Preliminary reactivity studies demonstrate the viability of such zwitterionic oligomers as multidentate ligands for transition metals.