A Visible-Light-Responsive Octahedral Cage for Efficient and Selective Cross-[2 + 2] Cycloadditions

Host-guest complexation enhances or even alters photoreaction selectivity by preorganizing substrates within the host's confined cavities. Since most previous hosts exhibited no visible-light absorption, at least one of the reactants needed to be an aromatic compound with UV-light absorption. Here, we developed a visible-light-responsive M₆L₄ octahedral cage that retains the encapsulation ability of standard M₆L₄ cages by simply replacing the photoinert metal unit at every vertex with a photoactive cyclometalated Pt(II) unit. This design enabled efficient visible-light-induced cross-[2 + 2] cycloadditions of inert substrates, demonstrating perfect stereo- and site-selectivity via confinement. The selective cross-[2 + 2] cycloaddition was achieved even catalytically, which was impossible with previous M₆L₄ cages.