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An endohedrally functionalized self-assembled Fe4 L6 cage complex can catalyze oxa-Pictet-Spengler cyclizations of tryptophols and various aldehyde derivatives, showing strong rate accelerations and size-selectivity. Selective molecular recognition of substrates controls the reactivity, and the cage is capable of binding and activating multiple different species along the multistep reaction pathway. The combination of a functionalized active site, size-selective reactivity, and multistep activation, all from a single host molecule, illustrates the biomimetic nature of the catalysis.
Ngai et al. (Sun,) studied this question.