Topology-Based Functionalization of Robust Chiral Zr-Based Metal–Organic Frameworks for Catalytic Enantioselective Hydrogenation

The
design and development of robust and porous supported catalysts
with high activity and selectivity is extremely significant but very
challenging for eco-friendly synthesis of fine chemicals and pharmaceuticals.
We report here the design and synthesis of highly stable chiral Zr­(IV)-based
MOFs with different topologies to support Ir complexes and demonstrate
their network structures-dependent asymmetric catalytic performance.
Guided by the modulated synthesis and isoreticular expansion strategy,
five chiral Zr-MOFs with a flu or ith topology
are constructed from enantiopure 1,1′-biphenol-derived tetracarboxylate
linkers and Zr6, Zr9, or Zr12 clusters.
The obtained MOFs all show high chemical stability in boiling water,
strongly acidic, and weakly basic aqueous solutions. The two flu MOFs featuring the dihydroxyl groups of biphenol in open
and large cages, after sequential postsynthetic modification with
P­(NMe2)3 and [Ir­(COD)­Cl]2, can be
highly efficient and recyclable heterogeneous catalysts for hydrogenation
of α-dehydroamino acid esters with up to 98% ee, whereas the
three ith MOFs featuring the dihydroxyl groups in small
cages cannot be installed with P­(NMe2)3 to support
the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs
leads to great enhancement of their chemical stability, durability,
and even stereoselectivity. This work therefore not only advances
Zr-MOFs as stable supports for labile metal catalysts for heterogeneous
asymmetric catalysis but also provides a new insight into how highly
active chiral centers can result due to the framework topology.