A Facile Modular Addition Approach to Size Control in the Synthesis of Oxo Bridged Phosphazane Macrocycles

Inorganic macrocycles remain largely underdeveloped compared with their organic counterparts due to the challenges involved in their synthesis. Among them, cyclodiphosphazane macrocycles have shown to be promising candidates for supramolecular chemistry applications. However, further developments have been handicapped by the lack of synthetic routes to high-order cyclodiphosphazane macrocycles. Here we report the synthesis of high-order oxygen-bridged phosphazane macrocycles via a “3+n” (n= 1 and 3) condensation reaction synthetic strategy using novel trimeric building blocks. Using this method, the first-ever all-PIII high-order hexameric cyclodiphosphazane macrocycle was isolated, displaying a larger macrocyclic cavity than comparable organic crown-ether counterparts. Our approach demonstrates that increasing building block complexity enables unprecedented rational control over macrocycle size.