Rhythmical catalysis of Au₁₀ clusters for KA oil oxidation to ε-caprolactone

Identifying active sites in heterogeneous catalysis has intrigued researches for many decades yet remains a challenge. This becomes more challenging to reveal the responsiveness of local sites on a catalyst to reactive species during a reaction. Here we utilize a flexible Au₁₀(DPPF)₄PPh₃ cluster to pinpoint active sites and untangle the communication between adjacent sites to match transient intermediates underlying the key steps from KA oil oxidation to ε-caprolactone. Our study suggests that the detachment of a triphenylphosphine ligand at the initial reaction exposes one Au atom and breaks one Au–Au bond on this cluster, thereby invoking two Au atoms to activate dioxygen and benzaldehyde to form benzoyl hydroperoxide intermediate. Sequentially, the two Au atoms spontaneously approach to adapt to the bridged adsorption of benzaldehyde over the two sites, leading to re-bonding of the two Au atoms and meanwhile stabling the cluster structure. More notably, the desorption of hydroperoxide intermediate from the active sites persuades this Au–Au bond to open again for being active sites in the next cycle. This interactive catalysis between active sites and reactants leads to benzoyl hydroperoxide affluently produced on the cluster to oxidize KA oil, eventually achieving a record-high synthesis efficiency for ε-caprolactone.