The 2-phosphaethynolate has received particular attention and displayed various reaction patterns due to its ambident property. In this work, the reactivity of monoanionic bidentate anilidophosphine PN ligand (PN: N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethyl anilide) supported (PNMe3)2PrIIICl (2A) and (PNMe3)2TbIIICl (2B) with NaOCP(dioxane)2.5 by salt elimination reaction is described. The reactions yield corresponding praseodymium and terbium phosphaethynolate complexes: (PNMe3)2PrIIIOCP (3A) and (PNMe3)2TbIIIOCP (3B), respectively. These two complexes feature a preferential O-bound terminal adduct. Magnetic data analysis reveals that praseodymium and terbium chloride and phosphaethynolate complexes showed a strong temperature dependence. All the complexes have been characterized by various measurement means, including NMR, UV spectroscopies, FT-IR spectrum as well as X-ray single crystal crystallography. For comparison, bond analyses of all the complexes collected from experimental and computational approaches are conducted in detail.