PPh₃ Propeller Diastereomers: Bonding Motif Ph_PPh 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 _PPh )-configuration and molecule [3] has (P _PPh )-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_PPh 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.