Chiral metal-organic frameworks bearing free carboxylic acids for organocatalyst encapsulation

Angew Chem Int Ed Engl. 2014 Dec 8;53(50):13821-5. doi: 10.1002/anie.201408896. Epub 2014 Nov 7.


Two chiral carboxylic acid functionalized micro- and mesoporous metal-organic frameworks (MOFs) are constructed by the stepwise assembly of triple-stranded heptametallic helicates with six carboxylic acid groups. The mesoporous MOF with permanent porosity functions as a host for encapsulation of an enantiopure organic amine catalyst by combining carboxylic acids and chiral amines in situ through acid-base interactions. The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organocatalyst.

Keywords: aldol reactions; heterogeneous catalysis; metal-organic frameworks; organocatalysis; porous materials.