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.