PPh3 Propeller Diastereomers: Bonding Motif PhPPh3 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 hydroxynaphthalde-hydes 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 (MPPh3)configuration and molecule [3] has (PPPh3)-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/pi interactions and a new bonding motif Ph-PPh3 face-on pi-Ar, both characteristic features of [(pi-Ar) LL'MPPh3] compounds. The propeller diastereomers interconvert via a low-energy pathway and a high-energy pathway, corroborated by density functional theory calculations