Stereodiscrimination in Phosphanylthiolato Nickel(II) Complexes

AbstractThe presence of a stereogenic carbon centre (R or S) in the racemic ligand 1‐(diphenylphosphanyl)propane‐2‐thiol induces a conformational preference (λ or δ) in the five‐membered chelate ring of its 2:1 and 2:2 coordination compounds with NiII: the mononuclear trans‐[Ni{SCH(CH3)CH2PPh2‐P,S}2] (1) and the binuclear trans‐[Ni{μ‐SCH(CH3)CH2PPh2‐P,S}(Cl)]2 (2). Both complexes exist as mixtures of two diastereomers: racemic‐trans (Rλ, Rλ and Sδ, Sδ) and meso‐trans (Rλ, Sδ), in an equilibrium displaced towards the more stable isomer, the meso‐trans for 1 (calculated ΔE = < −0.1 kcal·mol−1) and the racemic‐trans for 2 (calculated ΔE = −5.1 kcal·mol−1). This phenomenon is especially evident for complex 2, in which an efficient chiral recognition between the two enantiomeric forms of the racemic ligand was observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)