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

Abstract

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.

Asymmetric Catalysis within the Chiral Confined Space of Metal–Organic Architectures

“…Indeed, the charming strategy of incorporating different synergistic functionalities into one crystalline network for various asymmetric transformations has long been pursued but remains a formidable synthetic challenge . A noteworthy development contributed by Cui and co‐workers is the fruitful synthesis of multivariate MOFs (MTV‐MOFs), where one, two, or three different enantiopure metallosalen‐based ligands M( L 5 ‐H 2 ) (M = Cu, VO, Cr, Mn, Fe, and Co) were strategically fixed and combined into a single framework. By varying the ratios of the different metallosalen ligands, five binary and two ternary MOFs were obtained with twofold interpenetrated isostructural networks corresponding to the single‐component MOFs, M10 − Cu ( Figure ).…”

“…d) Close‐up view of two L 5 ‐Cu units brought into proximity to each other by twofold interpenetration. Reproduced with permission . Copyright 2017, American Chemical Society.…”

Controlling Metal Ion Counter Diffusion in Confined Spaces for In Situ Growth of Mixed Metal MOF Membranes for Gas Separation

“…In the meantime, the recently developed mixed component metal‐organic frameworks (MC‐MOFs) materials by integrating two or more different components into one skeleton render MOFs with different functional sites thus providing these porous materials access to various utilities . Examples of MC‐MOFs including mixed linker or multivariate, mixed metal, core‐shell, and surface modified MOFs, showed better porosity, absorption, stability, catalytic performance or other characteristics compared with the single component MOFs . Among these MC‐MOF materials, mixed metal MOFs have attracted much attention for diverse applications such as catalysis, separation, and others due to their improved properties, especially pointing to mixed metal zeolitic imidazolate frameworks (ZIFs) .…”

Promoting Frustrated Lewis Pairs for Heterogeneous Chemoselective Hydrogenation via the Tailored Pore Environment within Metal–Organic Frameworks

“…Thea bove notable new bands of MIL-101(Cr)-FLP-H 2 further suggest the existence of the FLP-H 2 inside the MOF. [12] Interestingly,f or the substrate 7a,b oth imine and alkene double bonds were reduced in the case of homogeneous FLP,and no 7b can be observed after the catalytic reaction. TheCr(2p 1/2 )and Cr (2p 3/2 )peaks of MIL-101(Cr)-FLP-H 2 are shifted by around 0.58-2 eV toward higher binding energies,c ompared to those of MIL-101(Cr).…”

“…It remains as ignificant challenge for FLP catalysts to selectively hydrogenate a,b-unsaturated organic compounds to afford the relevant olefin product especially in heterogeneous systems. [11] Thediverse yet tunable features of MOFs [12] make them an efficient platform to manipulate heterogeneous catalysts for various organic transformations that traditional porous materials simply cannot provide. [11] Thediverse yet tunable features of MOFs [12] make them an efficient platform to manipulate heterogeneous catalysts for various organic transformations that traditional porous materials simply cannot provide.…”