Remote impacts of methyl substituents on the guest-binding ability of self-assembled cages.

ABSTRACT

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.