Ammonium and Potassium Salts of a Hexacoordinate Phosphorus(V) Anion Featuring P-O and P-C Bonds

Ammonium and potassium salts featuring the chiral mer-[P(C₆H₄CO₂)₃]^-, mer-[1]^-, have been isolated. Specifically, treating phosphorane P(C₆H₄CO₂)₂(C₆H₄CO₂H), 2, with N-containing bases [N_base = PhNMe₂, PhNH₂, pyridine (py), isoquinoline, (-)-brucine, N( n-C₈H₁₇)₃] afforded ammonium salts [N_baseH]⁺- mer-[1]^-. Each compound was fully characterized spectroscopically, and four were subjected to X-ray crystallographic analysis. Salts were isolated with the racemic mixture of the mer-[1]^- anion except in the case of [(-)-brucineH]-Λ- mer-[1], for which the crystal analyzed was enantiomerically pure. The potassium salt, K- mer-[1], was synthesized by treating 2 with KH. The solid-state structure of K- mer-[1] is a coordination polymer consisting of seven- and eight-coordinate K⁺ ions that are weakly bound by oxygen of either the racemic anion or the methanol solvent. Preliminary NMR and MS data for the formation of the Brønsted acid, H(DMF) _n[1], has also been obtained. An estimate of the basicity of anion mer-[1]^- was obtained from IR measurements of the N-H stretching frequency for [( n-C₈H₁₇)₃NH]- mer-[1]. On the basis of these measurements, anion mer-[1]^- was ranked similar to the classical weakly coordinating anion, [ClO₄]^-, in terms of its coordinating ability.