Polyoxometalate-Based Metal-Organic Frameworks as Heterogeneous Catalysts for Selective Oxidation of Ethylbenzene

The catalytic properties of four polyoxometalate (POM)-based metal-organic frameworks, ([Cu-2(4,4'-bipy)(4)(H2O)(4)](SiW12O40)(H2O)(18)}(n) (1), {[Cu-2(4,4'-bipy)(4)(H2O)(4)](SiW12O40)(4,4'-bipy)(2)(H2O)(4)}(n) (2), {[Cu-2(4,4'-bipy)(4)(H2O)(4)](PW12O40)(H2O)(18)}(n) (3), and {[Cu-2(4,4 '-bipy)(4)(H2O)(4)](PMo12O40)(H2O)(18)}(n) (4) (bipy = bipyridine), for the oxidation of ethylbenzene were investigated. Complexes 1-4, which feature 3D frameworks formed through static incorporation between distinct Keggin POMs and the same voids in the 2D network of [Cu2(4,4'-bipy)(4)(H2O)(4)](n)(4n+), show the distinct conversion and selectivity for the oxidation of ethylbenzene. Investigation into the difference in the catalytic activity of 1-4 reveals that the oxidation of the substrate was performed in the pore of the framework and that the valence of the metal ion in the polyoxometalates significantly affects the catalytic activity of the 3D framework.