Design, synthesis and visible-light-induced non-radical reactions of dual-functional Rh catalysts

Transition metal photo-induced catalysts operating in a single catalytic cycle are preferable compared with binary catalytic systems comprising both transition metal and photoredox catalysts. Such single-catalyst systems perform the dual function of visible light absorption and chemical transformation. However, most visible-light-driven catalytic reactions proceed via radical mechanisms, limiting the reaction types to which the catalysts are applicable. Several non-radical catalytic reactions have been developed, but these reactions are substrate dependent owing to the low visible-light-harvesting ability of the catalysts. Here we report the design, synthesis and visible-light-induced non-radical reactions of dual-functional Rh catalysts, spiro-fluorene-indenoindenyl (SFI)-Rh(I) complexes. The SFI-Rh(I) complexes with non-fused but π-extended ligands reduce substrate dependence owing to high visible-light-harvesting ability, and show high stability due to resistance against protonation. Thus, the SFI-Rh(I) catalysts extend the scope of typical Rh(I)-catalysed reactions, such as the C–H borylation of arenes and [2+2+2] cycloaddition of alkynes, to challenging substrates under blue light-emitting diode irradiation at room temperature. Photoinduced catalytic systems typically consist of a transition metal catalyst and a photoredox catalyst. Now spiro-fluorene-indenoindenyl-Rh(I) complexes are reported as a single catalytic system that extends the scope of C–H borylation of arenes and [2+2+2] cycloaddition of alkynes to challenging substrates under irradiation with blue light.