Montmorillonite-Entrapped Sub-Nanoordered Palladium Clusters

Significance

A montmorillonite (mont)-entrapped sub-nanoordered Pd cluster as a hetero­geneous catalyst for allylic substitution reactions was developed. Thus, ion-exchange reaction of Na⁺-mont with an aqueous solution of Ca(OH)₂, followed by treatment of the resulting Ca²⁺-mont with a solution of Pd(dba)₂ gave a Pd(II)-mont. Reduction of the Pd(II)-mont with KBH₄ afforded the Pd clusters entrapped within the mont (Pd-mont) (eq. 1). The size of the Pd clusters was estimated to be 0.57-0.82 nm. The allylic substitution reaction of allyl methyl carbonate with ethyl acetoacetate was carried out in the presence of the Pd-mont catalyst to give the allylic substitution product in 93% yield (eq. 2).