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PPh3 Propeller Diastereomers: Bonding Motif PhPPh3 Face-On π‑Ar in Half-Sandwich Compounds [(π-Ar)LL′MPPh3]

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posted on 2018-01-25, 10:03 authored by Henri Brunner, Gábor Balázs, Takashi Tsuno, Haruka Iwabe
Chiral-at-metal compounds (RRu,SC)/(SRu,SC)-[CyRu­(1O-2N)­PPh3]­PF6 and (RRu,SC)/(SRu,SC)-[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 (RRu,SC)-diastereomers were obtained by crystallization. In the unit cell of (RRu,SC)-[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/π interactions and a new bonding motif PhPPh3 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.