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).