Two-Dimensional Imine-Linked Covalent Organic Frameworks as a Platform for Selective Oxidation of Olefins.

Two-dimensional imine-linked covalent organic frameworks with hydroxyl groups, TAPT-DHTA-COFHX and TAPT-DHTA-COFDMF, were respectively constructed by the condensation of 1,3,5-tris-(4-aminophenyl)triazine and 2,5-dihydroxyl-terephthalaldehyde under solvothermal and reflux conditions. Both COFs possess excellent thermal stability and a similar eclipsed stacking structure verified by XRD patterns. However, TAPT-DHTA-COFHX presented a larger surface area (2238 m2/g) and higher crystallinity than TAPT-DHTA-COFDMF. Significantly, copper ions are efficiently incorporated into the pores of these two COFs via the coordination interaction with hydroxyl groups and imine linkers. The obtained copper-containing COFs (Cu-COFHX and Cu-COFDMF) were employed in the selective oxidation of styrene to benzaldehyde. Cu-COFHX with superior surface area (1886 m2/g) and pore volume (1.11 cm3/g) exhibited excellent catalytic performance and recyclability. This strategy not only provides a convenient approach to design imine-linked 2D COFs with hydroxyl groups, but also develops their novel application for catalysis.