Multivariate Metal–Organic Frameworks as Multifunctional Heterogeneous Asymmetric Catalysts for Sequential Reactions

The search for versatile
heterogeneous catalysts with multiple
active sites for broad asymmetric transformations has long been of
great interest, but it remains a formidable synthetic challenge. Here
we demonstrate that multivariate metal–organic frameworks (MTV-MOFs)
can be used as an excellent platform to engineer heterogeneous catalysts
featuring multiple and cooperative active sites. An isostructural
series of 2-fold interpenetrated MTV-MOFs that contain up to three
different chiral metallosalen catalysts was constructed and used as
efficient and recyclable heterogeneous catalysts for a variety of
asymmetric sequential alkene epoxidation/epoxide ring-opening reactions.
Interpenetration of the frameworks brings metallosalen units adjacent
to each other, allowing cooperative activation, which results in improved
efficiency and enantioselectivity over the sum of the individual parts.
The fact that manipulation of molecular catalysts in MTV-MOFs can
control the activities and selectivities would facilitate the design
of novel multifunctional materials for enantioselective processes.