Thermodynamic Resolution and Enantioselective Synthesis of -Symmetric Bis-sulfoxides Based on Chiral Iridium(III) Complexes.

Enantiopure Λ-Ir(dfppy)(MeCN) and Δ-Ir(dfppy)(MeCN) (where dfppy is (4,6-difluoropheny)pyridine) were demonstrated to preferentially react with (,)-1,2-bis(arylsulfinyl)ethane and (,)-1,2-bis(arylsulfinyl)ethane, respectively, under thermodynamic equilibrium. Sequential treatment of Λ-Ir(dfppy)(MeCN) and Δ-Ir(dfppy)(MeCN) with -symmetric bis-sulfoxides led to diastereoselective formation of the corresponding diastereomers Λ-Ir(dfppy)(,)-bis-sulfoxide) in 90-92% and Δ-Ir(dfppy)(,)-bis-sulfoxide) in 88-90%, respectively. The uncoordinated (,)-bis-sulfoxides were afforded in 45% with >97% de values. Enantiopure (,)-bis-sulfoxides and (,)-bis-sulfoxides were respectively obtained by the release of sulfoxide ligands from the corresponding complexes in the presence of glycine in yields of 20-21% with 97-99% ee values. The enantioreceptors Λ-Ir(dfppy)(MeCN) and Δ-Ir(dfppy)(MeCN) can be recycled and reused in the next reaction cycle. Moreover, a protocol for asymmetric oxidation of prochiral bis-sulfide into enantiopure symmetric bis-sulfoxide was also developed in a high enantioselectivity. The absolute configurations at the metal centers and sulfur atoms were determined by X-ray crystallography.