In Situ Observation of Solvent‐Mediated Cyclic Intermediates during the Alkene Epoxidation/Hydration over a Ti‐Beta/H2O2 System

Abstract Solvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five‐membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)−H 2 O 2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13 C MAS NMR, two‐dimensional (2D) 1 H− 13 C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five‐membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti‐Beta/H 2 O 2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid‐phase epoxidation/hydration reactions over Ti(IV)−H 2 O 2 system.