Abstract N-silylated aminoiminophosphines react with aluminium trihalides to give acyclic zwitterions having two-coordinated phosphorus. At about room temperature these adducts decompose by elimination of silylhalide and formation of 1,3,2λ2,4-diazaphosphonia-aluminatacyclobutanes. Reaction of halogens and alkyl halides with the cyclic zwitterions results in formation of the corresponding 1,1-addition products. With alkyl-azides one obtains bicyclic phosphorus nitrogen heterocycles whilst in the reaction with trimethyl-silylazide the isomeric monocyclic azide derivative is formed. The IR and NMR spectra of the cyclic zwitterions are briefly discussed.