Lithium Salts of 2,4,6‐Triaryl‐λ 4 ‐phosphinine Anions – A Comparison Study

The λ 3 ‐phosphinine derivatives 2,6‐diphenyl‐4‐( p ‐tolyl)phosphinine and 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine were quantitatively converted into the corresponding λ 4 ‐phosphinine anions by reaction with phenyllithium. Systematic hydrolysis experiments with H 2 O and MeOH show that a subtle interplay between the p K a values of the generated 1,2‐dihydrophosphinine derivatives and the p K b value of the formed bases, LiOH and LiOCH 3 , respectively, leads either to the kinetic or thermodynamic product. The coordination chemistry of the λ 4 ‐phosphinine anions towards Rh I 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 η 5 fashion towards the Rh I atom, the latter acts as a bidentate chelating ligand with an η 1 coordination to the metal center through the phosphorus lone pair.