Lithium Salts of 2,4,6-Triaryl-λ4-phosphinine Anions – A Comparison Study


  • Dedicated to Professor Dr. Lothar Weber on the occasion of his 70th birthday


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.