A Modular Approach to Inorganic Phosphazane Macrocycles

Inorganic macrocycles, based on non-carbon backbones, present exciting synthetic challenges in the systematic assembly of inorganic molecules, as well as new avenues in host-guest and supramolecular chemistry. Here we demonstrate a new high-yielding modular approach to a broad range of trimeric and hexameric S- and Se-bridged inorganic macrocycles based on cyclophosphazane frameworks, using the building blocks [S=(H)P(μ-NR)]₂ . The method involves the in situ generation of the key intermediate [E....._ (S....._ )P(μ-NR)]₂^2- (E=S, Se) dianion, which can be reacted with electrophilic [ClP(μ-NR)]₂ to give P^III /P^V hexameric rings or reacted with I₂ to give trimeric P^V variants. Important issues which are highlighted in this work are the competitive bridging ability of S versus Se in these systems and the synthesis of the first air-stable and chiral inorganic macrocycles.