Bifunctional Photocatalysts\nDisplay Proximity-Enhanced\nCatalytic Activity in Metallaphotoredox C–O Coupling

Dual catalytic reactions may be made more effective through\nimproved\nintegration of the catalytic cycles achieved using bifunctional catalysts.\nHerein, we describe two bifunctional photocatalysts consisting of\na photoactive donor–acceptor cyanoarene unit linked to a bipyridine\nligand moiety that can bind transition metals. The bifunctional photocatalysts\nwere synthesized in 3–5 steps from commercially available compounds\nand fully characterized in terms of photophysical properties, which\nare strongly affected by the type of linkage used (C vs O) to connect\nthe cyanoarene core to the ligand. Catalytic tests carried out in\nthe Ni-catalyzed C–O cross-coupling of alcohols to aryl bromides\npromoted by visible light have shown that the bifunctional systems\nare more active than the corresponding “dual catalytic systems”\n(i.e., not covalently bound), taking advantage of the proximity between\nthe two catalytic moieties (Ni-complex and photocatalyst). The best\nbifunctional photocatalysts were tested with several alcohols and\naryl halides, giving good yields at low catalytic loading (0.5–2\nmol %).