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 Lambda-[Ir(pq)(2)(D-AA)] (Lambda-D) and Lambda-[Ir(pq)(2)(L-AA)] (Lambda-L, where pq is 2-phenylquinoline and AA is an amino acid) are reported in the presence of O-2 under mild conditions. Diastereomer Lambda-D is dehydrogenatively oxidized into an imino acid complex, while diastereomer Lambda-L mainly occurs via interligand C-N cross-dehydrogenative coupling between quinoline at the C8 position and AA ligands at room temperature, affording Lambda-[Ir(pq)(L-pq-AA)]. Furthermore, the photoreaction of diastereomer Lambda-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.

Automated summary

The postcoordinated interligand-coupling strategy was used to synthesize polydentate ligands under mild conditions. Diastereoselective photoreactions of Lambda-[Ir(pq)(2)(D-AA)] and Lambda-[Ir(pq)(2)(L-AA)] were reported, with mechanistic experiments revealing the involvement of ligand-radical intermediates. Density functional theory calculations were used to elucidate the origin of diastereoselectivity and temperature dependence.