Water-Soluble Metallo-Supramolecular Nanoreactors for Mediating Visible-Light-Promoted Cross-Dehydrogenative Coupling Reactions

Water-soluble metallo-supramolecular cages with well-defined nanosized cavities have a wide range of functions and applications. Herein, we design and synthesize two series of metallo-supramolecular octahedral cages based on the self-assembly of two congeneric truxene-derived tripyridyl ligands modified with two polyethylene glycol (PEG) chains, i.e., monodispersed tetraethylene glycol (TEG) and polydispersed PEG-1000, with four divalent transition metals (i.e., Pd, Cu, Ni, and Zn). The resulting monodispersed cages C1–C4 are fully characterized by electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffraction. The polydispersed cages C5–C8 display good water solubilities and can act as nanoreactors to mediate visible-light-promoted C­(sp³)–C­(sp²) cross-dehydrogenative coupling reactions in an aqueous phase. In particular, the most robust Pd­(II)-linked water-soluble polydispersed nanoreactor C5 is characterized by ESI-MS and capable of mediating the reactions with the highest efficiencies. Detailed host–guest binding studies in conjunction with control studies suggest that these cages could encapsulate the substrates simultaneously inside its hydrophobic cavity while interacting with the photosensitizer (i.e., eosin Y).