Heterogeneous photosensitizers based on iridium polypyridine complexes immobilized on periodic mesoporous organosilica for aza–Henry reaction and CO2 reduction

Iridium bis(phenylpyridine)(bipyridine) complex, Ir(ppy)₂(bpy)⁺, which exhibits outstanding photophysical and photochemical properties as a photosensitizer, was immobilized on 2,2′-bipyridine-bridged mesoporous organosilica (BPyPMO) to afford Ir-BPyPMO. Successful immobilization of the iridium complex within the PMO framework was confirmed by X-ray absorption fine structure analysis. Ir-BPyPMO exhibited a characteristic UV–vis diffuse-reflectance spectrum with a metal-to-ligand charge-transfer (MLCT) band at a wavelength comparable to that of the corresponding MLCT band of the homogeneous Ir(ppy)₂(bpy)⁺ complex, indicating that the photophysical properties of the iridium complex were retained after immobilization. Under visible-light irradiation, Ir-BPyPMO functioned as an efficient heterogeneous photosensitizer for the aza–Henry reaction through C–H functionalization of 2-phenyl-1,2,3,4-tetrahydroisoquinoline. Furthermore, co-immobilization of a rhenium tricarbonyl complex on Ir-BPyPMO afforded Re-Ir-BPyPMO, which efficiently catalyzed CO₂ reduction in the presence of a sacrificial electron donor. These results demonstrate that the immobilized iridium complex functions effectively as a heterogeneous photosensitizer and highlight the potential of BPyPMO as a versatile platform for constructing photocatalytic systems.