Capture of Singlet Oxygen Modulates Host-Guest Behavior of Coordination Cages.

The anthracene panels of two tetrahedral M II 4 L 6 cages, where M II =Co II or Fe II , were found to react with photogenerated singlet oxygen ( 1 O 2 ) in a hetero-Diels-Alder reaction. ESI-MS analysis showed the cobalt(II) cages to undergo complete transformation of all anthracene panels into endoperoxides, whereas the iron(II) congeners underwent incomplete conversion. The reaction was found to be partially reversible in the case of the 1-Fe II cage. The dioxygen-cage cycloadducts were found to bind a set of guest molecules more weakly than the parent cages, with affinity dropping by more than two orders of magnitude in some cases. The light-driven cycloaddition reaction between cage and 1 O 2 thus served as a stimulus for guest release and reuptake.