Visible-Light-Induced Amination of Quinoline at the C8 Position via a Postcoordinated Interligand-Coupling Strategy under Mild Conditions.

The postcoordinated interligand-coupling strategy provides a useful and complementary protocol for synthesizing polydentate ligands. Herein, diastereoselective photoreactions of Λ-[Ir(pq)2(d-AA)] (Λ-d) and Λ-[Ir(pq)2(l-AA)] (Λ-l, where pq is 2-phenylquinoline and AA is an amino acid) are reported in the presence of O2 under mild conditions. Diastereomer Λ-d is dehydrogenatively oxidized into an imino acid complex, while diastereomer Λ-l mainly occurs via interligand C-N cross-dehydrogenative coupling between quinoline at the C8 position and AA ligands at room temperature, affording Λ-[Ir(pq)(l-pq-AA)]. Furthermore, the photoreaction of diastereomer Λ-l is temperature-dependent. Mechanistic experiments reveal the ligand-radical intermediates may be involved in the reaction. Density functional theory calculations were used to eluciate the origin of diastereoselectivity and temperature dependence. This will provide a new protocol for the amination of quinoline at the C8 position via the postcoordinated interligand C-N cross-coupling strategy under mild conditions.

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, iPr, 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.