Remote Impacts of Methyl Substituents on the Guest-Binding Ability of Self-Assembled Cages

We synthesized self‐assembled coordination cages in which 1,10‐phenanthroline derivatives serve as capping ligands. Substituents at the 2,9‐positions of the phenanthroline ligand covered the outside of the cage but had an impact on the guest binding inside the cage. Introduction of methyl groups at the 2,9‐positions allowed the cage to accommodate tetraphenylsilane. Bulky mesityl groups overhanging the cage framework significantly shrunk the cage cavity through π–π interactions with the aromatic panels of the cage. The p‐methyl group of the mesityl substituent was a determinant of the restricted motion of 4,4′‐dimethoxybenzil inside the cage at high temperature. Thus, the presence or absence of one methyl group, which is far from the guest‐binding site, makes a significant difference in the guest species and motions inside the cage. A butterfly effect: The guest‐binding ability of a self‐assembled cage was remotely and subtly tuned by the pendant substituent groups (see figure) on the metal corners of the cage. Bulky aromatic substituents push the cage framework inward to shrink the cage cavity. A single methyl group difference at the remote site makes a significant difference in guest species and motions within the cages.