[P(μ-NTer)]2: A Biradiealoid That Is Stable at High Temperature

摘要

As early as 1894 Michaelis and Schroeter isolated the first phosphorus(III)-nitrogen heterocycle from the reaction of aniline hydrochloride with an excess of PCl3 (Scheme 1). Interestingly, the authors assumed to have isolated the monomeric species, C6H5—N=P—Cl, which they called "phos-phazobenzene chloride" but already speculated on the existence of the dimer. Today we know that the dimer is the stable form, and such four-membered rings of the type [XP(μ-NR)]2, which contain alternating phosphorus(III) and nitrogen centers, are called cyclo-1,3-diphospha(III)-2,4-diazanes (X = halogen, R = organic group; old name: l,3-diaza-2,4-diphosphetidines). They play a major role in preparative phosphorus-nitrogen chemistry because such species are good starting materials for polycyclic inorganic and organo-metallic compounds.