Heterogeneous Synergistic Acceleration of Ketone α-Allylation with Allyl Alcohol by Pd/Cu Complexes on Organomodified Mesoporous Silica

This study reports the α-allylation of simple ketones and allyl alcohols. Only a few examples of this reaction have been reported to date because the low reactivity of allyl alcohols compared with other allylating agents, such as allyl halides, and the low nucleophilicity of simple ketones relative to active methylene compounds render this combination particularly challenging for allylation. We previously demonstrated that introducing multiple catalytically active species with well-defined structures onto solid surfaces can accelerate organic reactions through cooperative effects. In this study, we found that a multifunctional catalyst incorporating both Pd and Cu complexes on mesoporous silica (MS) enabled the simultaneous activation of ketones and allyl alcohols, thereby efficiently promoting the allylation reaction. The coexistence of organic functional groups, such as phenyl groups, on the MS surface further amplified catalytic activity. Compared with a catalyst bearing only immobilized Pd complexes, the overall catalytic activity of the proposed catalyst was enhanced by a factor of 15.5. This catalytic system was applicable to the allylation of various carbonyl compounds and could be easily separated and reused. Recycling tests conducted using indanone as the substrate yielded a total Pd-based turnover number of 600. Various spectroscopic analyses, isotope-labeling experiments, and density functional theory calculations indicated that the Cu complex activates the ketone to facilitate the reaction. Results further suggested that organic functional groups coexisting on the solid surface promote the reaction by optimizing the spatial arrangement of the Pd and Cu complexes. The strategy of introducing multiple structurally well-defined catalytic species onto a solid surface represents an approach to enhance catalytic activity that is distinct from conventional methods such as active-site control and ligand design.