Mesocellular silica foams supported size-controlled Pd nanoparticles for racemic and asymmetric iodomethyl dihydrobenzofuran synthesis

Supported metal nanoparticles (NPs) catalysts in constructing benzene-fused cyclic framework with chirality is very challenging. Dihydrobenzofuran and its derivatives are significant heterocyclic units in biologically molecules. Herein, size-controlled Pd NPs fixed on mesoporous silica (Pd/MS-xT) SBA-15, FDU-12 and mesocellular silica foams (MCFs) were utilized to synthesize racemic and asymmetric iodomethyl dihydrobenzofuran for the first time. The size of Pd NPs was regulated by increasing NaBH4 reduction treatments times (-xT) and enlarging supports pore. Based on large mesopore of MCF-3, supported catalyst 3%Pd/MCF-3-4T possessed larger Pd size gave the excellent performance at 92% racemic yield. Under chiral phosphine modifier N–Me-Xu3, we implemented more deserving asymmetric reaction over 3%Pd/MCF-3-1T with smaller Pd NPs. TGA for organic surface coverage demonstrated that the substrate preferred larger Pd NPs, N–Me-Xu3 capped more easily on smaller ones. Besides, effects of reaction medium and N–Me-Xu3 additive quantity further revealed the coordination of chiral modifier on Pd/MCF-3 was the determinant. For broader visions, the performance dependence based on surface properties of heterogeneous catalyst would play crucial contributions towards construction of complexed organic molecules.