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.

开发兼具高活性与选择性、稳定且多孔的负载型催化剂，对于精细化学品与医药的绿色合成而言至关重要，但同时极具挑战。本研究报道了一类具有不同拓扑结构的高稳定性手性四价锆基金属有机框架（Metal-Organic Frameworks，MOFs），用于负载铱配合物，并证实其不对称催化性能取决于网络结构。基于调控合成与同构拓展策略，我们以对映纯的1,1'-联苯酚衍生四羧酸连接配体与Zr6、Zr9或Zr12团簇为构筑基元，合成了5种具有flu或ith拓扑结构的手性Zr-MOFs。所制备的MOFs均在沸水、强酸性及弱碱性水溶液中表现出优异的化学稳定性。其中2种具有flu拓扑结构的MOFs，其联苯酚的二羟基位点位于开放大笼腔中；经先后用三(二甲氨基)膦（P(NMe2)3）与二(1,5-环辛二烯)二铱(I)二聚体（[Ir(COD)Cl]2）进行后合成修饰后，它们可作为高效可循环的非均相催化剂，用于α-脱氢氨基酸酯的加氢反应，对映体过量值（enantiomeric excess, ee）最高可达98%。而3种具有ith拓扑结构的MOFs，其二羟基位点位于小笼腔中，无法通过P(NMe2)3修饰负载铱配合物。将铱-磷基催化剂负载于Zr-MOFs中，可显著提升其化学稳定性、耐用性，甚至立体选择性。因此，本研究不仅将Zr-MOFs开发为适用于非均相不对称催化的易失活金属催化剂的稳定载体，同时也为框架拓扑结构如何调控高活性手性中心的形成提供了全新视角。