Breaking the C[sbnd]C bond of glucose on tungsten oxide-based catalysts in aqueous phase

In chemistry, selective activation of C[sbnd]C bonds enables the direct production of valuable chemicals from widely available and inexpensive natural materials but remains a fundamental challenge due to their kinetic inertness. The selective cleavage of C[sbnd]C bond in glucose by tungsten oxide-based catalysts in aqueous phase pioneers a path for converting cellulose biomass into valuable ethylene glycol. However, debates regarding the active phase and how it selectively breaks the C₆ into C₂ fragments have persisted for over a decade. In this study, we present a comprehensive mechanistic investigation by modeling three potential active phases, i.e. the reduced WO_3-x surface, the dissolved tungstic acid, and tungsten bronze, in explicit solvent waters. By constrained molecular dynamics simulations, we have demonstrated that the low-coordinated W center can chelate with glucose, forming a metallacyclic complex with a 5-membered ring after the protonation of carbonyl group. The formation of 5-membered ring serves as the premise for the selectivity to C₂ fragments via homolytic cleavage of C[sbnd]C bond. Furthermore, the reduced W⁵⁺ center is suggested to be crucial in facilitating the cleavage process by stabilizing the dissociated C₄ intermediates via a redox process. In conclusion, we propose that the surface decoration of reduced and low-coordinated W sites can act as active heterogeneous catalysts for the selective conversion of cellulose in aqueous phase. These recent findings have the potential to provide valuable insights and strategies for C[sbnd]C bond activation in both biomass conversion and organic synthesis.