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 ß-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 % ß-pinene conversion) even upon decreasing the amount of catalyst from 100 to 25 mg (0.025 and 0.0063 gcatalyst mmolsubstrate -1 , 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.

Metal-Organic Frameworks M-MOF-74 and M-MIL-100: Comparison of Textural, Acidic, and Catalytic Properties.

The impact of the metal nature and framework type on the textural, acidic, and catalytic properties of M-MOF-74 (M=Co, Cu, Mg, Ni) and M-MIL-100 (M=Al, Cr, Sc, V) materials was evaluated. Both metal-organic framework (MOF) families showed 100 % selectivity to the tetrahydropyranyl ether for all alcohols (methanol, 1-propanol, 1-octanol, 2-adamantanol, 1-octadecanol) applied. Independently of the metal employed in the synthesis of M-MOF-74, the conversions were lower than those obtained with M-MIL-100. This result can be attributed to the combination of superior textural properties, accessibility, and strength of open metal sites in M-MIL-100 that improve the accessibility/diffusion of reactant and products. The variation of the size and shape of the alcohols on the activity and selectivity showed that the yield of tetrahydropyranyl ether decreased with increase of the alcohol size (methanol<1-propanol<1-octanol<2-adamantanol<1-octadecanol). The best catalytic results were achieved with V-MIL-100, and were even maintained after several cycles; this could be related to the superior polarizing power of V-containing units, which enhanced the activation of 3,4-dihydro-2H-pyran and, consequently, the yield of the target ether.