Hetero-Diels-Alder Reaction between Singlet Oxygen and Anthracene Drives Integrative Cage Self-Sorting

A (Zn8L6)-L-II pseudocube containing anthracene-centered ligands, a (Zn4L4)-L-II' tetrahedron with a similar side length as the cube, and a trigonal prism (Zn6L3L2)-L-II' were formed in equilibrium from a common set of subcomponents. Hetero-Diels-Alder reaction with photogenerated singlet oxygen transformed the anthracene-containing "L" ligands into endoperoxide "L-O" ones and ultimately drove the integrative self-sorting to form the trigonal prismatic cage (Zn6L3L2)-L-II-L-O' exclusively. This (Zn6L3L2)-L-II-L-O' structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial (Zn8L6)-L-II + (Zn4L4)-L-II' (sic) 2 x (Zn6L3L2)-L-II-L-O' equilibrating system. Whereas the (Zn8L6)-L-II pseudocube had a cavity too small for guest encapsulation, the (Zn6L3L2)-L-II' and (Zn6L3L2)-L-II-L-O' trigonal prisms possessed peanut-shaped internal cavities with two isolated compartments divided by bulky anthracene panels. Guest binding was also observed to drive the equilibrating system toward exclusive formation of the (Zn6L3L2)-L-II' structure, even in the absence of reaction with singlet oxygen.