Exploring the Ring–Ring Expansion and Pyrazole Substitution of Chlorophosphazenes [PCl2N]3,4 Through Mechanochemical Ball-Milling and Quantum Mechanical Computation

In this study, we are using low-energy mechanochemical ball-milling with [PCl2N]3–4 at room temperature as an alternative to high-temperature reactions that use hazardous solvents such as chlorobenzene. Our study demonstrates ring–ring expansion of chlorophosphazenes without prior linearization, showcasing the feasibility of mechanochemical approaches to possibly obtain larger cyclic chlorophosphazenes without the need to separate them from linear products. Additionally, we explored the pyrazole substitution of [PCl2N]3 through mechanochemical ball-milling. Using density functional theory (DFT), the initiation step in the substitution is investigated by quantum mechanical computation to reveal the mechanism and thermodynamic contributions at the B3LYP/6-311+G(d,p) level of theory.