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(mu-NR)](2). The method involves the in situ generation of the key intermediate [E -(S -) P-(mu-NR)](2)(2-) (E = S, Se) dianion, which can be reacted with electrophilic [CLP(mu-NR)](2) to give P-III/P-V hexameric rings or reacted with I-2 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.