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

A Zn II 8 L 6 pseudocube containing anthracene-centered ligands, a Zn II 4 L' 4 tetrahedron with a similar side length as the cube, and a trigonal prism Zn II 6 L 3 L' 2 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 Zn II 6 L O 3 L' 2 exclusively. This Zn II 6 L O 3 L' 2 structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial Zn II 8 L 6 + Zn II 4 L' 4 ⇌ 2 × Zn II 6 L 3 L' 2 equilibrating system. Whereas the Zn II 8 L 6 pseudocube had a cavity too small for guest encapsulation, the Zn II 6 L 3 L' 2 and Zn II 6 L O 3 L' 2 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 Zn II 6 L 3 L' 2 structure, even in the absence of reaction with singlet oxygen.