2-Aminophenolate ligands for phosphorus(v): a lithium salt featuring the chiral [P(OC6H4NR)3]− anion

Abstract

Phosphoranes P(OC₆H₄NR)₂(OC₆H₄NHR) [R = Me (2a), Ph (2b), C₆F₅ (2c)] were synthesized by treating PCl₅ with the respective 2-aminophenol derivative (1a–c, 3.1 equiv.). In one instance, an intermediate species, P(OC₆H₄NR)₂Cl [R = Me (3a)], was isolated and structurally characterized. Deprotonation of the amine moieties (–NR) in phosphoranes 2a and 2b with a strong alkali–metal base (e.g. n-BuLi) in the presence of a strong-donor solvent (e.g. THF) afforded salts composed of the hexacoordinate P(V)-anions [P(OC₆H₄NR)₃]⁻ (R = Me, [4a]⁻; Ph, [4b]⁻). Employing precursor 2a, the salt Li(THF)₃fac-[4a]⁻ was isolated. The X-ray crystal of each enantiomer of [4a]⁻ was determined and, to our knowledge, represents the first structurally characterized example of a salt containing a hexacoordinate P(V)N₃O₃ anion featuring P(V)–N bonds.