Structural engineering in pre-functionalized, imine-based covalent organic framework via anchoring active Ru(II)-complex for visible-light triggered and aerobic cross-coupling of α-amino esters with indoles

Synopsis: Anchoring active homogeneous complex over N-functionalized imine-based 2D COF leads to devise band-gap engineered Ru-COF that acts as visible light mediated photocatalyst for atom-economic α-arylation of glycine derivative with indoles under aerobic condition with high reusability and wide substrate scope. • Anchoring of homogeneous Ru(II)-complex over N-functionalized 2D COF leads devising Ru-COF. • Ru-COF acts as photocatalyst in direct α-arylation of glycine derivative with indole for rapid access to indolylglycine. • Post-modified COF works under visible-light, using O 2 , and shows superior activity to Ru(Bpy) 3 Cl 2 . • High recyclability of catalyst, wide substrate scope, and atom-economic C(sp 3 )–H activation is realized. • Experimental and computational results reveal band-gap modulation in Ru-COF, and validates SET governed pathway. Site-specific functionalization of sp 3 C H bonds adjacent to a nitrogen atom is one of the unexplored heterogeneous transformations. Aiming at α-arylation of glycine derivative for rapid access to indolylglycines without the aid of bases, a chemically robust and two-dimensional COF is prepared. Integration of [2,2′]bipyridyl (Bpy) unit benefits active homogeneous complex Ru(Bpy) 2 2+ to anchor over the framework backbone to devise Ru-COF that acts as unprecedented visible light photocatalyst towards cross-dehydrogenative coupling of secondary amines with indoles in excellent yield at room temperature, under aerobic condition. Ru-COF shows admirable reusability and superior activity to that of Ru(Bpy) 3 Cl 2 , while substrate variation studies delineate wide ranges of functional group tolerance. To the best of Ru-COF, atom-economic C H functionalization is realized as iminium ion is in situ generated. The photocatalytic route is detailed from astute modulation of optical band-gap in light of density-functional theory studies and experimental results, which validates single-electron-transfer pathway.