Developing a New Class of Axial Chiral Phosphorus Ligands: Preparation and Characterization of Enantiopure Atropisomeric Phosphinines

Both enantiomers of the first atropisomeric phosphinine (1) have been isolated by using analytical HPLC on a chiral stationary phase. The enrichment of one enantiomer and a subsequent investigation into its racemization kinetics revealed a barrier for internal rotation of Δ${G{{{\ne}\hfill \atop 298\hfill}}}$=(109.5±0.5) kJ mol−1, which is in excellent agreement with the theoretically predicted value of Δ${G{{{\ne}\hfill \atop 298\hfill}}}$=116 kJ mol−1. Further analysis with UV and circular dichroism spectroscopies and density functional theory calculations led to the determination and assignment of the absolute configurations of both enantiomers. These results are the basis for future investigations into this new class of axially chiral phosphinine‐based ligands and their possible applications in asymmetric homogeneous catalysis. Separated and stable: Enantiomers of the first axially chiral, racemic phosphinine (1) have been successfully separated by using analytical HPLC on a chiral stationary phase. The energy barrier for internal rotation was determined experimentally and theoretically and the absolute configurations 1‐R and 1‐S (see graphic; yellow atoms= phosphorus) were assigned from experimental and theoretical circular dichroism spectra.