Catalysis by Dynamically Formed Defects in a Metal-Organic Framework Structure: Knoevenagel Reaction Catalyzed by Copper Benzene-1,3,5-tricarboxylate
Abstrakt
The high catalytic activity and selectivity of the metal-organic framework (MOF) copper benzene-1,3,5-tricarboxylate (CuBTC) that are observed experimentally in the Knoevenagel reaction are explained on the basis of computational investigations by employing a periodic model and density functional theory. Three factors are responsible for the unusually high activity of CuBTC: One, CuBTC can act as a base, and the active methylene reactant is deprotonated, whereas a temporary defect in the framework is formed; two, the thus-formed defect, a Bronsted acid site, simultaneously activates the aldehyde; three, the reaction takes place on two adjacent Cu2+ sites (Lewis acid sites) that are separated by 8.2 Å.
The results reported herein show the great versatility of the CuBTC MOF catalyst, including its amphiphilic character and the concerted effect of nearby framework metal cations.