Supramolecular Protection of Trityl Cations †

Comprehensive Summary The triphenylmethyl (trityl) cation ( Tr + ) features pronounced Lewis acidity and broad utility in organic chemistry. Strategies that tune the balance between the stability and reactivity of Tr + continue to be actively pursued. Developing a supramolecular platform that can selectively recognize Tr + and regulate its reactivity through noncovalent interactions represents a compelling topic. Herein, we report the efficient synthesis of a family of unsymmetrical, pyrene‐embedded macrocycles, O₂,S₂‐homocorona[2]arene[2]tetrazines. Subsequent inverse‐electron‐demand Diels‐Alder (IEDDA) reactions of these macrocycles with 2,5‐norbornadiene afforded O₂,S₂‐homocorona[2]arene[2]pyridazines featuring an electron‐rich, spatially confined cavity, as confirmed by single‐crystal X‐ray diffraction. Fluorescence, UV‐vis and 1 H NMR titrations reveal a highly selective 1 : 1 complexation between the macrocycles and several Tr + species, with an association constant ( K a ) up to (6.10 ± 2.40) × 10 7 M −1 . DFT calculations indicate the synergy of multiple noncovalent interactions together with cavity confinement affords the main driving forces. In situ 1 H NMR monitoring of hydride‐transfer reactions shows that the host‐guest encapsulation provides pronounced steric shielding around the electrophilic center of Tr + , efficiently suppressing hydride abstraction (Et 3 SiH, Et 3 GeH, n ‐Bu 3 SnH). The reaction of (OMe) 1 Tr + with Et 3 SiH is slowed ≈91‐fold when the host is present. More broadly, this supramolecular protection and regulation strategy could be extended to the selective recognition of cations of heavier group 14 elements (R₃E + ; E = Si, Ge, Sn), providing a conceptual basis for the stabilization of highly reactive species. This work establishes a supramolecular strategy to recognize and stabilize organic cations, offering a conceptual platform for the recognition and potential manipulation of unstable cationic intermediates in organic chemistry.