A tetrakis(amido)phosphonium cation containing 2-pyridyl (2Py) substituents,[P(NH2Py)4]+ and its reactivity studies with Ag(I) salts

Abstract

Poly-imido analogues of various phosphorus oxo anions have gained recent attention in inorganic chemistry. Current methods to obtain these anions require strong organometallic deprotonating agents in reaction with phosphonium salt like [(NHPh)4P]Cl or phosphoramides such as [(RNH)3P=E] (E = NSiMe3, O, S or Se) in non-polar solvents. Recently, employing salts of soft and reactive transition metal ions, we have developed methods to obtain these anions in polar and protic solvents. Herein, we have described a facile anion exchange route that stabilizes the highly labile tetrakis(2-pyridylamino)phosphonium cation as its nitrate salt, [P(NH2Py)4]NO3. This molecule exhibits a double chain structure mediated by H-bonding interactions of the pyridylamino segments (N-H...N). The phosphonium salt upon reaction with excess silver triflate results in a pentanuclear Ag(I) complex, {Ag5[P(N 2Py)2(NH 2Py)2]} ⋅(F3 CSO 3)3, stabilized by two imido-phosphinate [P(N2Py)2(NH 2Py)2]− ligands. Formation of a similar penta-nuclear cluster has been observed before when AgClO4 was used as a base. Our previous results with the related phosphate precursor, [PO(NH2Py)3], in reaction with various Ag(I) salts have shown to yield complexes of the corresponding neutral, mono- and dianionic ligands. However, the stability of the Ag5-cluster within the mono-anionic casing of the [P(N2Py)2(NH2Py)2]− ligand have seemingly overwhelmed the subtle reactivity changes offered by various Ag(I) salts. Employing an anion exchange route, synthesis of a stable tetrakis(2-pyridylamino)phosphonium cation as its nitrate salt, [P(NH2Py)4]NO3 has been described. The precursor phosphonium salt upon reaction with excess silver triflate results in a pentanuclear Ag(I) complex, {Ag5[P(N2Py)2(NH2Py)2]}•(F3CSO3)3, stabilized by two imido-phosphinate [P(N2Py)2(NH2Py)2]− ligands.