The λ3‐phosphinine derivatives 2,6‐diphenyl‐4‐(p‐tolyl)phosphinine and 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine were quantitatively converted into the corresponding λ4‐phosphinine anions by reaction with phenyllithium. Systematic hydrolysis experiments with H2O and MeOH show that a subtle interplay between the pKa values of the generated 1,2‐dihydrophosphinine derivatives and the pKb value of the formed bases, LiOH and LiOCH3, respectively, leads either to the kinetic or thermodynamic product. The coordination chemistry of the λ4‐phosphinine anions towards RhI was further investigated, and the anions based on 2,6‐diphenyl‐4‐(p‐tolyl)‐phosphinine and 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine demonstrate different coordination modes. Whereas the former coordinates in an η5 fashion towards the RhI atom, the latter acts as a bidentate chelating ligand with an η1 coordination to the metal center through the phosphorus lone pair. The λ4‐phosphinine anions of 2,6‐diphenyl‐4‐(p‐tolyl)phosphinine and the structurally related 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine show a remarkable difference in selectivity towards hydrolysis with water and methanol. Moreover, the presence or absence of an additional nitrogen atom within the ligand framework influences the coordination chemistry of the phosphinine derivatives towards RhI.