PPh₃ Propeller Diastereomers: Bonding Motif Ph_PPh3 Face-On π‑Ar in Half-Sandwich Compounds [(π-Ar)LL′MPPh₃]

Chiral-at-metal compounds (R_Ru,S_C)/(S_Ru,S_C)-[CyRu­(1O-2N)­PPh₃]­PF₆ and (R_Ru,S_C)/(S_Ru,S_C)-[CyRu­(2O-1N)­PPh₃]­PF₆ were prepared using anions 1O-2N^– and 2O-1N^– of the Schiff bases, derived from the hydroxynaphthaldehydes and (S)-1-phenylethylamine. The pure (R_Ru,S_C)-diastereomers were obtained by crystallization. In the unit cell of (R_Ru,S_C)-[CyRu­(1O-2N)­PPh₃]­PF₆, there are three independent molecules, which differ in the propeller sense of the PPh₃ ligand. Molecules [1] and [2] have (M_PPh3)-configuration and molecule [3] has (P_PPh3)-PPh₃ configuration. PPh₃ diastereoisomerism is discussed including other pairs of compounds, differing only in the PPh₃ configuration. A conformational analysis reveals an internal stabilization inside the PPh₃ ligand by a system of attractive CH/π interactions and a new bonding motif Ph_PPh3 face-on π-Ar, both characteristic features of [(π-Ar)­LL′MPPh₃] compounds. The propeller diastereomers interconvert via a low-energy pathway and a high-energy pathway, corroborated by density functional theory calculations.