Size-control in the synthesis of oxo-bridged phosphazane macrocycles via a modular addition approach

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 due to their ability to encapsulate small molecules or ions within their cavities. However, further developments have been handicapped by the lack of synthetic routes to high-order cyclodiphosphazane macrocycles. Moreover, current approaches allow little control over the size of the macrocycles formed. Here we report the synthesis of high-order oxygen-bridged phosphazane macrocycles via a “3 + n cyclisation” (n = 1 and 3). Using this method, an all-PIII high-order hexameric cyclodiphosphazane macrocycle was isolated, displaying a larger macrocyclic cavity than comparable organic crown-ethers. Our approach demonstrates that increasing building block complexity enables precise control over macrocycle size, which will not only generate future developments in both the phosphazane and main group chemistry but also in the fields of supramolecular chemistry.