Engineering Cavity and Aperture Binding Sites Within a Metal–Organic Cage for Up‐ and Down‐Regulation of Catalysis

Engineering molecular recognition events into catalytic systems to precisely control the up‐ or down‐regulation of catalysis in a biomimetic fashion is a challenging goal in supramolecular chemistry. In this work, we report on the construction of a new metal–organic cage, Zn II 4 L 4 tetrahedron 1 , using a protonated azacalix[3](2,6)pyridine‐based ligand as the capping faces. The cage features a large cavity and wide gaps between its faces, enabling the simultaneous binding of anionic guests centrally and peripherally. Encapsulation of α‐Mo 8 O 26 4− within the T ‐symmetric tetrahedron 1 leads to a C 3 ‐symmetric inclusion complex Mo 8 O 26 4− ⊂ 1 . The apertures of Mo 8 O 26 4− ⊂ 1 act as secondary binding sites for accommodating tetraarylborate guests or for providing access to the included Mo 8 O 26 4− for catalyzing reactions. Catalytic experiments demonstrated that inclusion within 1 significantly enhances the catalytic activity of Mo 8 O 26 4− for the oxidation of sulfides into sulfoxides. In contrast, peripheral binding of the bulky tetraarylborate anion to the inclusion complex Mo 8 O 26 4− ⊂ 1 effectively inhibits its catalytic activity by obstructing access to the catalytic active sites of Mo 8 O 26 4− .