Functionalized Metal-Organic Framework as a Biomimetic Heterogeneous Catalyst for Transfer Hydrogenation of Imines.

Mimicking a biocatalytic system has been one of the prevalent strategies for the design of novel and efficient chemical transformations. Among the enzyme-catalyzed reactions, the cooperative interplay of Lewis- and Brønsted-acidic functionalities at active sites represents a common feature in activating reactants. Employing MIL-101(Cr) as a biomimetic platform, we customize a sulfonic group (SO3H) into its hierarchical pores to generate a heterogeneous catalyst for transfer hydrogenation of imines by using Hantzsch ester as the reductant. Both aldimines and ketimines were efficiently converted to their hydrogenated counterparts in a manner similar to metal enzymes. The Cr3+ node and sulfonic acid functionality encapsulated in MOF cages worked cooperatively in promoting this transformation, resulting in an enhanced reactivity as compared to its homogeneous analogue. Furthermore, MIL-101(Cr)-SO3H could be recycled for many times without considerable loss in reactivity.