Unprecedented Catalysis of Cs⁺ Single Sites Confined in Y Zeolite Pores for Selective C_sp3–H Bond Ammoxidation: Transformation of Inactive Cs⁺ Ions with a Noble Gas Electronic Structure to Active Cs⁺ Single Sites

We report the transformation of Cs⁺ ions with an inactive noble gas electronic structure to active Cs⁺ single sites chemically confined in Y zeolite pores (Cs⁺/Y), which provides an unprecedented catalysis for oxidative cyanation (ammoxidation) of C_sp3–H bonds with O₂ and NH₃, although in general, alkali and alkaline earth metal ions without a moderate redox property cannot activate C_sp3–H bonds. The Cs⁺/Y catalyst was proved to be highly efficient in the synthesis of aromatic nitriles with yields >90% in the selective ammoxidation of toluene and its derivatives as test reactions. The mechanisms for the genesis of active Cs⁺ single sites and the ammoxidation pathway of C_sp3–H bonds were rationalized by density functional theory (DFT) simulations. The chemical confinement of large-sized Cs⁺ ions with the pore architecture of a Y zeolite supercage rendered the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap reduction, HOMO component change, and preferable coordination arrangement for the selective reaction promotion, which provides a trimolecular assembly platform to enable the coordination-promoted concerted ammoxidation pathway working closely on each Cs⁺ single site. The new reaction pathway without involvement of O₂-dissociated O atom and lattice oxygen differs from the traditional redox catalysis mechanisms for the selective ammoxidation.