Superior Activity of Isomorphously Substituted MOFs with MIL-100(M=Al, Cr, Fe, In, Sc, V) Structure in the Prins Reaction: Impact of Metal Type.

The catalytic behavior of isomorphously substituted MIL-100(M) (M=Al, Cr, Fe, In, Sc, V) is investigated for the synthesis of nopol through the Prins condensation of β-pinene with paraformaldehyde. The large mesoporous cages of the metal-organic frameworks provide a sustainable confinement for the formation of the target product (100 % selectivity for nopol over all materials studied). MIL-100(Sc) and MIL-100(V) exhibit the highest yields (up to 90 %) of nopol after just 20 min from the beginning of the reaction, owing to their high concentrations of accessible Lewis sites possessing intermediate acidity. The high catalytic activity (reaching almost 90 % β-pinene conversion) even upon decreasing the amount of catalyst from 100 to 25 mg (0.025 and 0.0063 g  mmol , respectively), the stability of its structure, and the possibility to use it several times, make MIL-100(V) a promising material for applications in acid-catalyzed reactions under mild reaction conditions.