Triphenylamine-based cadmium coordination polymer as a heterogeneous photocatalyst for visible-light-driven α-alkylation of aldehydes

The ingenious design of photoredox ligand is crucial to regulate the photoabsorption and redox potential of coordination polymer-based photocatalysts. Herein, by suitable modifying the photoactive triphenylamine, a propeller-like ligand tris(3′-carboxybiphenyl)amine (H3TCBA) was synthesized and used to construct a photofunctional Cd(II)-based coordination polymer, Cd-TCBA, with visible-light absorption band and negative enough excited state redox potential of −2.24 ​V. The good photoelectric performances promote Cd-TCBA to work as heterogeneous photocatalyst for photocatalytic α-alkylation of aldehydes with a high catalytic yield up to 89%. The high stability makes Cd-TCBA readily be recycled and reused at least five times without significant performance loss. The partially deprotonated HTCBA2− in Cd-TCBA not only creates suitable acidic/basic environment but also forms effective hydrogen bond interactions towards diethyl-2-bromomalonate substrate as donor, accelerating the electron transfer from excited state Cd-TCBA∗ to substrate and the formation of enamine intermediates, finally achieving efficient coupling of photoredox and organocatalytic cycles. In addition, the possible catalytic mechanisms were also investigated.