Dendritic phosphotungstate hybrids efficiently catalyze the selective oxidation of alcohols with H2O2
Keggin-type phosphotungstic acid (HPW) was incorporated into the polyamidoamine (PAMAM) matrix by partly protonating the amino groups of the PAMAM dendrimer. Characterization results suggested that the PAMAM dendrimer accommodated trivalent PW anions through ionic interactions and hydrogen bonds, resulting in novel dendritic phosphotungstate hybrids (dendri-PW hybrids). The dendritic PAMAM matrix as a countercation not only fine-tunes the redox properties of the PW anions but also has a positive “dendrimer effect” on the enhancement of the catalytic activity of the hybrids. Higher conversion of alcohols was observed over the dendri-PW hybrids in the selective oxidation of alcohols with H2O2 than over their non-dendritic counterparts. Furthermore, the dendritic ammonium cations impart reaction-controlled phase-transfer function to the dendri-PW hybrids. The catalysts precipitated from the solvent upon consumption of H2O2 and could be reused several times without loss of activity and selectivity.