Yan Liu

A key challenge in heterogeneous catalysis is the design and synthesis of heterogeneous catalysts featuring high catalytic activity, selectivity, and recyclability. Here we demonstrate that high-performance heterogeneous asymmetric catalysts can be engineered from a metal–organic framework (MOF) platform by using a ligand design strategy. Three porous chiral MOFs with the framework formula [Mn2L(H2O)2] are prepared from enantiopure phosphono-carboxylate ligands of 1,1′-biphenol that are functionalized with 3,5-bis(trifluoromethyl)-, bismethyl-, and bisfluoro-phenyl substituents at the 3,3′-position. For the first time, we show that not only chemical stability but also catalytic activity and stereoselectivity of the MOFs can be tuned by modifying the ligand structures. Particularly, the MOF incorporated with −CF3 groups on the pore walls exhibits enhanced tolerance to water, weak acid, and base compared with the MOFs with −F and −Me groups. Under both batch and flow reaction systems, the CF3-containing MOF demonstrated excellent reactivity, selectivity, and recyclability, affording high yields and enantioselectivities for alkylations of indoles and pyrrole with a range of ketoesters or nitroalkenes. In contrast, the corresponding homogeneous catalysts gave low enantioselectivity in catalyzing the tested reactions.

Chiral Covalent Organic Frameworks with High Chemical Stability for Heterogeneous Asymmetric Catalysis

Co-reporter:Xing Han, Qingchun Xia, Jinjing Huang, Yan Liu, Chunxia Tan, and Yong Cui

Journal of the American Chemical Society June 28, 2017 Volume 139(Issue 25) pp:8693-8693

Publication Date(Web):June 8, 2017

DOI:10.1021/jacs.7b04008

Covalent organic frameworks (COFs) featuring chirality, stability, and function are of both fundamental and practical interest, but are yet challenging to achieve. Here we reported the metal-directed synthesis of two chiral COFs (CCOFs) by imine-condensations of enantiopure 1,2-diaminocyclohexane with C3-symmetric trisalicylaldehydes having one or zero 3-tert-butyl group. Powder X-ray diffraction and modeling studies, together with pore size distribution analysis demonstrate that the Zn(salen)-based CCOFs possess a two-dimensional hexagonal grid network with AA stacking. Dramatic enhancement in the chemical stability toward acidic (1 M HCl) and basic (9 M NaOH) conditions was observed for the COF incorporated with tert-butyl groups on the pore walls compared to the nonalkylated analog. The Zn(salen) modules in the CCOFs allow for installing multivariate metals into the frameworks by postsynthetic metal exchange. The exchanged CCOFs maintain high crystallinity and porosity and can serve as efficient and recyclable heterogeneous catalysts for asymmetric cyanation of aldehydes, Diels–Alder reaction, alkene epoxidation, epoxide ring-opening, and related sequential reactions with up to 97% ee.

Multivariate Chiral Covalent Organic Frameworks with Controlled Crystallinity and Stability for Asymmetric Catalysis

Co-reporter:Jie Zhang, Xing Han, Xiaowei Wu, Yan Liu, and Yong Cui

Journal of the American Chemical Society June 21, 2017 Volume 139(Issue 24) pp:8277-8277

Publication Date(Web):May 24, 2017

DOI:10.1021/jacs.7b03352

The modular construction of covalent organic frameworks (COFs) provides a convenient platform for designing high-performance functional materials, but the synthetic control over their chirality has been relatively barely studied. Here we report a multivariate strategy to prepare chiral COFs (CCOFs) with controlled crystallinity and stability for asymmetric catalysis. By crystallizing mixtures of triamines with and without chiral organocatalysts and with a dialdehyde, a family of two- and three-component 2D porous CCOFs that adopt two different stacking modes is prepared. The organocatalysts are periodically appended on the channel walls, and their contents, which can be synthetically tuned using a three-component condensation system, greatly affect the chemical stability and crystallinity of CCOFs. Specially, the ternary CCOFs displayed relatively high crystallinity and stability compared with the binary CCOFs. Under harsh conditions, the ternary CCOFs can serve as efficient heterogeneous catalysts for an asymmetric aminooxylation reaction, an aldol reaction, and the Diels–Alder reaction, with the stereoselectivity and diastereoselectivity rivaling or surpassing the homogeneous analogues. This work not only opens up a new synthetic route toward CCOFs, but also provides tunable control of COF crystallintity and stability and, in turn, the properties.

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

Co-reporter:Qingchun Xia, Zijian Li, Chunxia Tan, Yan Liu, Wei Gong, and Yong Cui

Journal of the American Chemical Society June 21, 2017 Volume 139(Issue 24) pp:8259-8259

Publication Date(Web):May 24, 2017

DOI:10.1021/jacs.7b03113

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.

Chiral NH-Controlled Supramolecular Metallacycles

Co-reporter:Jinqiao Dong, Chunxia Tan, Kang Zhang, Yan Liu, Paul J. LowJianwen Jiang, Yong Cui

Journal of the American Chemical Society 2017 Volume 139(Issue 4) pp:1554-1564

Publication Date(Web):January 6, 2017

DOI:10.1021/jacs.6b11422

Chiral NH functionalities-based discrimination is a key feature of Nature’s chemical armory, yet selective binding of biologically active molecules in synthetic systems with high enantioselectivity poses significant challenges. Here we report the assembly of three chiral fluorescent Zn6L6 metallacycles from pyridyl-functionalized Zn(salalen) or Zn(salen) complexes. Each of these metallacycles has a nanoscale hydrophobic cavity decorated with six, three, or zero chiral NH functionalities and packs into a three-dimensional supramolecular porous framework. The binding affinity and enantioselectivity of the metallacycles toward α-hydroxycarboxylic acids, amino acids, small molecule pharamaceuticals (l-dopa, d-penicillamine), and chiral amines increase with the number of chiral NH moieties in the cyclic structure. From single-crystal X-ray diffraction, molecular simulations, and quantum chemical calculations, the chiral recognition and discrimination are attributed to the specific binding of enantiomers in the chiral pockets of the metallacycles. The parent metallacycles are fluorescent with the intensity of emission being linearly related to the enantiomeric composition of the chiral biorelevant guests, which allow them to be utilized in chiral sensing. The fact that manipulation of chiral NH functionalities in metallacycles can control the enantiorecognition of biomolecular complexes would facilitate the design of more effective supramolecular assemblies for enantioselective processes.

Chiral binary metal–organic frameworks for asymmetric sequential reactions

Co-reporter:Zijian Li;Qingchun Xia;Yong Cui

Chemical Communications 2017 vol. 53(Issue 91) pp:12313-12316

Publication Date(Web):2017/11/14

DOI:10.1039/C7CC06979K

Two chiral porous MOFs with precise and appropriate spatial arrangements of different metallosalen active sites are synthesized and used as efficient heterogeneous catalysts for asymmetric sequential alkene epoxidation/epoxide ring-opening reactions with enantioselectivity of up to 99%.

Homochiral 2D Porous Covalent Organic Frameworks for Heterogeneous Asymmetric Catalysis

Co-reporter:Xiuren Wang, Xing Han, Jie Zhang, Xiaowei Wu, Yan Liu, and Yong Cui

Journal of the American Chemical Society 2016 Volume 138(Issue 38) pp:12332-12335

Publication Date(Web):September 13, 2016

DOI:10.1021/jacs.6b07714

There have been breakthroughs in the development of covalent organic frameworks (COFs) with tunability of composition, structure, and function, but the synthesis of chiral COFs remains a great challenge. Here we report the construction of two-dimensional COFs with chiral functionalities embedded into the frameworks by imine condensations of enantiopure TADDOL-derived tetraaldehydes with 4,4′-diaminodiphenylmethane. Powder X-ray diffraction and computer modeling together with pore size distribution analysis show that one COF has a twofold-interpenetrated grid-type network and the other has a non-interpenetrated grid network. After postsynthetic modification of the chiral dihydroxy groups of TADDOL units with Ti(OiPr)4, the materials are efficient and recyclable heterogeneous catalysts for asymmetric addition of diethylzinc to aldehydes with high enantioselectivity. The results reported here will greatly expand the scope of materials design and engineering for the creation of new types of functional porous materials.

Chiral Metal–Organic Framework as a Platform for Cooperative Catalysis in Asymmetric Cyanosilylation of Aldehydes

Co-reporter:Chengfeng Zhu, Qingchun Xia, Xu Chen, Yan Liu, Xia Du, and Yong Cui

ACS Catalysis 2016 Volume 6(Issue 11) pp:7590

Publication Date(Web):October 2, 2016

DOI:10.1021/acscatal.6b02359

In this work, we demonstrate cooperative asymmetric catalysis by a metal–organic framework (MOF) as exemplified in the context of catalyzing cyanation of aldehydes with a VO(salen)-MOF, which after oxidation affords remarkably increased stereoselectivity (up to >99% ee) compared to the homogeneous VO(salen) counterpart as a result of the pairs of VO(salen) units in close proximity within its open channels. The cooperative asymmetric catalysis has been evidenced by the significantly decreased stereoselectivity and activity when one VO(salen) in such pairs of VO(salen) units is replaced with one Cu(salen), which results in blocking the VO–VO synergistic pathway while prompting unimolecular activation of substrates. The heterogeneous nature of VO(salen)-MOF has been verified by the fact that it can be easily recycled and reused without significant loss of catalytic activity and enantioselectivity, and its practical utility as asymmetric cyanation catalysist has been illustrated in the gram-scale synthesis of the antiviral natural products (R)- and (S)-enantiomers of tembamide. Our work therefore advances chiral MOF as an attractive platform for cooperative asymmetric catalysis in a variety of syntheses.Keywords: asymmetric catalysis; chiral material; heterogeneoous catalysis; metal−organic framework; porous material

Chiral Cu(salen)-Based Metal–Organic Framework for Heterogeneously Catalyzed Aziridination and Amination of Olefins

Co-reporter:Yan Liu, Zijian Li, Guozan Yuan, Qingchun Xia, Chen Yuan, and Yong Cui

Inorganic Chemistry 2016 Volume 55(Issue 24) pp:12500-12503

Publication Date(Web):December 6, 2016

DOI:10.1021/acs.inorgchem.6b02151

A homochiral 3D porous metal–organic framework was assembled from a chiral dicarboxylic acid-functionalized Cu(salen)-based catalyst and could serve as an efficient heterogeneous catalyst for aziridination and allylic amination of olefins. Besides easy separation and reuse of the catalyst, the chiral framework confinement could impart substrate size selectivity, enhance catalyst activity, and induce product enantioselectivity.

Triple-Stranded Cluster Helicates for the Selective Catalytic Oxidation of C–H Bonds

Co-reporter:Yu Fang, Wei Gong, Lujia Liu, Yan Liu, and Yong Cui

Inorganic Chemistry 2016 Volume 55(Issue 20) pp:10102-10105

Publication Date(Web):September 27, 2016

DOI:10.1021/acs.inorgchem.6b01828

Triple-stranded cluster helicates with heptametallic dicubane cores are synthesized by entrapping metals in the cavities of linear triple helicates based on a C2-symmetrical hexadentate Schiff-base ligand of ortho-substitued biphenol. The helicates are stable in both the solution and solid states, and the copper species could selectively catalyze the oxidation of C–H bonds of alkanes to ketones.

Chiral DHIP-Based Metal–Organic Frameworks for Enantioselective Recognition and Separation

Co-reporter:Jie Zhang, Zijian Li, Wei Gong, Xing Han, Yan Liu, and Yong Cui

Inorganic Chemistry 2016 Volume 55(Issue 15) pp:7229

Publication Date(Web):May 26, 2016

DOI:10.1021/acs.inorgchem.6b00894

Two chiral porous 2,3-dihydroimidazo[1,2-a]pyridine (DHIP)-based metal–organic frameworks (MOFs) are assembled from an enantiopure dipyridyl-functionalized DHIP bridging ligand. The Zn-DHIP MOF shows a good enantioseparation performance toward aromatic sulfoxides, and the heterogeneous adsorbent can be readily recovered and reused without significant degradation of the separation performance.

Chiral porous metal–organic frameworks containing μ-oxo-bis[Ti(salan)] units for asymmetric cyanation of aldehydes

Co-reporter:Xia Du, Zijian Li, Yan Liu, Shiping Yang and Yong Cui

Dalton Transactions 2015 vol. 44(Issue 29) pp:12999-13002

Publication Date(Web):24 Jun 2015

DOI:10.1039/C5DT01682G

Two chiral porous Ti(salan)-based metal–organic frameworks are constructed and are shown to be efficient and recyclable heterogeneous catalysts for asymmetric cyanation reaction of aldehydes, displaying significantly higher enantioselectivity than their homogeneous counterpart.

Direct and Post-Synthesis Incorporation of Chiral Metallosalen Catalysts into MetalOrganic Frameworks for Asymmetric Organic Transformations

Co-reporter:Weiqin Xi;Dr. Yan Liu;Qingchun Xia;Zijian Li;Dr. Yong Cui

Chemistry - A European Journal 2015 Volume 21( Issue 36) pp:12581-12585

Publication Date(Web):

DOI:10.1002/chem.201501486

Abstract

Two chiral porous metal–organic frameworks (MOFs) were constructed from [VO(salen)]-derived dicarboxylate and dipyridine bridging ligands. After oxidation of V^IV to V^V, they were found to be highly effective, recyclable, and reusable heterogeneous catalysts for the asymmetric cyanosilylation of aldehydes with up to 95 % ee. Solvent-assisted linker exchange (SALE) treatment of the pillared-layer MOF with [Cr(salen)Cl]- or [Al(salen)Cl]-derived dipyridine ligands led to the formation of mixed-linker metallosalen-based frameworks and incorporation of [Cr(salen)] enabled its use as a heterogeneous catalyst in the asymmetric epoxide ring-opening reaction.

Chiral porous organic frameworks for asymmetric heterogeneous catalysis and gas chromatographic separation

Co-reporter:Jinqiao Dong, Yan Liu and Yong Cui

Chemical Communications 2014 vol. 50(Issue 95) pp:14949-14952

Publication Date(Web):13 Oct 2014

DOI:10.1039/C4CC07648F

Three chiral robust diene-based porous organic frameworks (POFs) are prepared. POF-1 is shown to be an efficient heterogeneous catalyst after metallation for asymmetric conjugation addition with up to 93% ee, and it can also function as a new chiral stationary phase for gas chromatographic separation of racemates.

Engineering chiral Fe(salen)-based metal–organic frameworks for asymmetric sulfide oxidation

Co-reporter:Zhiwei Yang, Chengfeng Zhu, Zijian Li, Yan Liu, Guohua Liu and Yong Cui

Chemical Communications 2014 vol. 50(Issue 63) pp:8775-8778

Publication Date(Web):18 Jun 2014

DOI:10.1039/C4CC03308F

Two chiral porous Fe(salen)-based metal–organic frameworks are constructed and are shown to be efficient and recyclable heterogeneous catalysts for asymmetric oxidation of sulfides to sulfoxides with an enantioselectivity of up to 96%.

Homochiral Silver-Based Coordination Polymers Exhibiting Temperature-Dependent Photoluminescence Behavior

Co-reporter:Xiaobing Xi, Yan Liu, and Yong Cui

Inorganic Chemistry 2014 Volume 53(Issue 5) pp:2352-2354

Publication Date(Web):February 10, 2014

DOI:10.1021/ic4027865

Homochiral coordination polymers based on zigzag or helical polymers are assembled from a semiflexible fluorescent bipyridyl ligand and linear coordinated AgI ions; they exhibit unusual temperature-dependent photoluminescence behavior, including multistep changes in energy and intensity upon cooling.

Chiral MetalOrganic Frameworks Bearing Free Carboxylic Acids for Organocatalyst Encapsulation

Co-reporter: Yan Liu;Dr. Xiaobing Xi;Chengcheng Ye;Tengfei Gong;Zhiwei Yang; Yong Cui

Angewandte Chemie International Edition 2014 Volume 53( Issue 50) pp:13821-13825

Publication Date(Web):

DOI:10.1002/anie.201408896

Abstract

Two chiral carboxylic acid functionalized micro- and mesoporous metal–organic frameworks (MOFs) are constructed by the stepwise assembly of triple-stranded heptametallic helicates with six carboxylic acid groups. The mesoporous MOF with permanent porosity functions as a host for encapsulation of an enantiopure organic amine catalyst by combining carboxylic acids and chiral amines in situ through acid–base interactions. The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organocatalyst.

Chiral MetalOrganic Frameworks Bearing Free Carboxylic Acids for Organocatalyst Encapsulation

Co-reporter: Yan Liu;Dr. Xiaobing Xi;Chengcheng Ye;Tengfei Gong;Zhiwei Yang; Yong Cui

Angewandte Chemie 2014 Volume 126( Issue 50) pp:14041-14045

Publication Date(Web):

DOI:10.1002/ange.201408896