Chiral Recognition and Dynamic Thermodynamic Resolution of Sulfoxides by Chiral Iridium(III) Complexes

The optically active Ir­(III) complex Λ-[Ir­(ppy)2(MeCN)2]­(PF6) (ppy is 2-phenylpyridine) with a chiral-at-metal was first demonstrated to preferentially react with (R)-configuration sulfoxides 2-(alkylsulfinyl)­phenol (HLO-R, R = Me, Et, i Pr, and Bn) rather than (S)-configuration sulfoxides under...

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Published in:Inorganic chemistry 2017-01, Vol.56 (2), p.878-885
Main Authors: Yao, Su-Yang, Chen, Xing-Yang, Ou, Yan-Ling, Ye, Bao-Hui
Format: Article
Language:English
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Summary:The optically active Ir­(III) complex Λ-[Ir­(ppy)2(MeCN)2]­(PF6) (ppy is 2-phenylpyridine) with a chiral-at-metal was first demonstrated to preferentially react with (R)-configuration sulfoxides 2-(alkylsulfinyl)­phenol (HLO-R, R = Me, Et, i Pr, and Bn) rather than (S)-configuration sulfoxides under thermodynamic equilibrium due to the hydrogen-bonding interaction and the differences in the steric interference, and thus act as a highly efficient enantioreceptor for resolution of sulfoxide enatiomers. Treatment of Λ-[Ir­(ppy)2(MeCN)2]­(PF6) with 2 equiv of rac-HLO-R offered (S)-HLO-R in yields of 46–47% with 97–99% enantiomeric excess (ee) values and Λ-[Ir­(ppy)2{(S)-LO-R}] complex in yields of 89–93% with 98% diastereomeric excess (de). The (R)-HLO-R chiral sulfoxides were obtained by the acidolysis of Λ-[Ir­(ppy)2{(S)-LO-R}] complexes with trifluoroacetic acid (TFA) in the presence of coordinated solvent MeCN in yields of 45–47% with 98–99% ee values. Moreover, the enantioreceptor Λ-[Ir­(ppy)2(MeCN)2]­(PF6) can be recycled in a yield of 86–91% with complete retention of the configuration at metal center and can be reused in a next reaction cycle without loss of reaction activity and enantioselectivity. The absolute configurations at the metal centers and sulfur atoms were determined by X-ray crystallography.
ISSN:0020-1669
1520-510X
DOI:10.1021/acs.inorgchem.6b02494