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Ring opening polymerization (ROP) of hexachlorocyclotriphosphazene ([PCl2N]3) produces the phosphazene polymer that can later be functionalized for a variety of applications. However, the ROP process is irreproducible, and its mechanism is not well-understood. It had been proposed that Lewis acid catalysts might abstract a chloride from [PCl2N]3 and promote the bond breakage in the initial step of the ROP. In this research, the interactions of Group 13 Lewis acids with [PCl2N]3 were investigated. Adducts of [PCl2N]3 with AlCl3, AlBr3, and GaCl3 were successfully synthesized and characterized by X-ray crystallography and 31P and 1H VT NMR. Contrary to the previous reports, the Lewis acids did not remove the chloride from [PCl2N]3. Instead, they formed dative bonds with the nitrogen atom on [PCl2N]3. The adduct formation weakened the two P-N bonds on [PCl2N]3 that involved the nitrogen atom participating in the dative bond and its phosphorous neighbors on the ring.