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Ji-Woong Lee

Bio: Ji-Woong Lee is an academic researcher from University of Copenhagen. The author has contributed to research in topics: Catalysis & Nucleophile. The author has an hindex of 21, co-authored 77 publications receiving 1737 citations. Previous affiliations of Ji-Woong Lee include University of Toronto & University of California, Berkeley.


Papers
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TL;DR: This work uses colloidal nanocrystals functionalized with light-responsive ligands that readily self-assemble and trap various molecules from the surrounding bulk solution and Illumination with visible light disassembles these nanoflasks, releasing the product in solution and thereby establishes a catalytic cycle.
Abstract: The chemical behaviour of molecules can be significantly modified by confinement to volumes comparable to the dimensions of the molecules. Although such confined spaces can be found in various nanostructured materials, such as zeolites, nanoporous organic frameworks and colloidal nanocrystal assemblies, the slow diffusion of molecules in and out of these materials has greatly hampered studying the effect of confinement on their physicochemical properties. Here, we show that this diffusion limitation can be overcome by reversibly creating and destroying confined environments by means of ultraviolet and visible light irradiation. We use colloidal nanocrystals functionalized with light-responsive ligands that readily self-assemble and trap various molecules from the surrounding bulk solution. Once trapped, these molecules can undergo chemical reactions with increased rates and with stereoselectivities significantly different from those in bulk solution. Illumination with visible light disassembles these nanoflasks, releasing the product in solution and thereby establishes a catalytic cycle. These dynamic nanoflasks can be useful for studying chemical reactivities in confined environments and for synthesizing molecules that are otherwise hard to achieve in bulk solution.

270 citations

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TL;DR: This work highlights the work in elucidating the origin of the accelerating effects of ionic liquids in a range of catalytic reactions, and develops a better understanding of these modularly tunable liquid salts that will foster new discoveries of catalyzed reactions that are accelerated by ionic liquid as solvents or additives.
Abstract: Over the past decade, ionic liquids have received a great deal of attention as a new means for catalyst immobilization. Large numbers of catalysts having polar or ionic character have been successfully immobilized in ionic liquids, thus allowing their recovery and recycling. However, catalyst immobilization is not the only benefit of ionic liquids in catalysis, of greater importance are the positive effects of ionic liquids on catalytic rates. In this Account, we highlight our work in elucidating the origin of the accelerating effects of ionic liquids in a range of catalytic reactions. Lewis acidic metal triflates often become much more reactive in ionic liquids containing noncoordinating anions as a result of "anion exchange." Consequently, the more electrophilic Lewis acidic species generated in situ accelerate the catalytic reactions dramatically. In some cases, highly reactive intermediates, such as vinyl cations, arenium cations, oxygen radical anions, and so forth, can be stabilized in the presence of ionic liquids, thus increasing the reactivity and selectivity of the reactions. Concerted processes such as S(N)2 and Diels-Alder reactions can also be accelerated through the cooperative activation of both the nucleophile and the electrophile by ionic liquids. In transition metal-catalyzed reactions, certain catalytically active oxidation states can be stabilized in ionic liquids against deactivation to catalytically inactive species. Thus it is clear that gaining an understanding of the origin of these "positive ionic liquid effects" is highly important, not only for predicting the effects of ionic liquids on other organic reactions but also for designing new catalytic reactions. Ionic liquids, by virtue of (typically) having a synthetically accessible carbon backbone, are amenable to tailoring by the organic chemist. Accordingly, their molecular structures can be subtly varied to give "tunable" properties, which can then be used to rationally examine the fundamental reasons that they accelerate catalyzed reactions. Although the origins of enhanced catalytic rates by ionic liquids have been elucidated in many areas, other undiscovered ionic liquid phenomena remain to be unearthed. Developing a better understanding of these modularly tunable liquid salts will foster new discoveries of catalytic reactions that are accelerated by ionic liquids as solvents or additives.

177 citations

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TL;DR: A thermally robust sulfonamide-based bifunctional organocatalysts I is presented, which shows unprecedented catalytic activity and excellent enantioselectivity in the methanolytic desymmetrization of meso cyclic anhydrides.
Abstract: At present, there is much interest in organocatalysts, as they tend to be less toxic and more environmentally friendly than traditional metal-based catalysts. Although much progress has been made, the development of chiral organocatalysts that are as reactive and stereoselective as some of the best transition-metal catalysts remains a considerable challenge. To attain reasonable reaction rates and stereoselectivity with organocatalysts, a large catalyst loading is often required. One way to address this difficulty is to design bifunctional or multifunctional organocatalysts with functional groups that work cooperatively to stabilize the transition state and accelerate the rate of the reaction. It has been shown that ureaor thiourea-based bifunctional organocatalysts are effective in facilitating a variety of useful organic reactions, including the methanolytic desymmetrization of cyclic anhydrides. However, we showed recently that ureaand thiourea-based organocatalysts can form hydrogen-bonded aggregates, which results in a strong dependence of reactivity and enantioselectivity on concentration and temperature. X-ray crystal structures of monofunctional and bifunctional (thio)urea derivatives show that they form aggregates through hydrogen bonding between the (thio)urea NH groups and the (thio)urea sulfur or oxygen atom in an intermolecular fashion. A recent NMR spectroscopic study also showed that the thiourea IV exists as a dimer, even in solution. Furthermore, thiourea groups tend to degrade under thermal conditions. Herein we present a thermally robust sulfonamide-based bifunctional organocatalyst I (Scheme 1), which shows unprecedented catalytic activity and excellent enantioselectivity in the methanolytic desymmetrization of meso cyclic anhydrides. A detailed mechanistic and computational approach to the design of I resulted in a catalyst that does not self-aggregate to any appreciable extent. To the best of our knowledge, I is the first quinineand sulfonamide-based bifunctional organocatalyst. The quinuclidine group of I may be able to function as a general-base catalyst to activate the nucleophile, and the sulfonamide group may be able to activate the electrophile simultaneously by hydrogen bonding. To investigate the catalytic activity and enantioselectivity of the cinchona-alkaloid-based sulfonamide catalyst I, we examined the asymmetric methanolysis of cis-1,2-cyclohexanedicarboxylic anhydride (1a) in Et2O with various amounts of I at ambient temperature. The results are summarized in Table 1, together with the results obtained with other cinchona-alkaloid-based catalysts (quinine (II), (DHQ)2AQN (III), and the quinine-based thiourea catalyst IV; Scheme 1). The desymmetrization of 1a with I (10 mol%) proceeded surprisingly fast; the reaction was complete within 1 h to Scheme 1. Structures of cinchona-alkaloid-based organocatalysts.

136 citations

Journal ArticleDOI
TL;DR: From carbon fixation, Grignard reaction, metal-catalyzed reactions and asymmetric CO2-incorporation, what would be the idealCO2-functionalization?
Abstract: This Perspective recapitulates recent developments of carbon dioxide utilization in carbon–carbon bond formation reactions, with an intention of paving a way toward sustainable CO2-functionalization and its tangible applications in synthetic chemistry. CO2 functionalization reactions possess intrinsic drawbacks: the high kinetic inertness and thermodynamic stability of CO2. Numerous procedures for CO2 utilization depend on energy-intensive processes (i.e. high pressure and/or temperature), often solely relying on reactive substrates, hampering its general applications. Recent efforts thus have been dedicated to catalytic CO2-utilization under ambient reaction conditions, however, it is still limited to a few activation modes and the use of reactive substrates. Herein, ideal CO2-functionalization with particular emphasis on sustainability will be discussed based on the following sub-categories; (1) metal-catalyzed ‘reductive’ carboxylation reaction of halides, olefins and allyl alcohols, (2) photochemical CO2-utilization, (3) redox-neutral CO2-functionalization, and (4) enantioselective catalysis incorporating CO2 to form C–CO2 bonds (excluding strain mediated reactions with epoxide- and aziridine-based substrates). Recent progress in these fields will be discussed with the proposed reaction mechanisms and selected examples, highlighting redox-neutral, umpolung, and asymmetric carboxylation to postulate ideal CO2 functionalization reactions to be developed in the near future.

116 citations

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TL;DR: Simultaneous dual activation of reacting partners by intermolecular hydrogen bonding and the enhancement of the "effective fluoride nucleophilicity", which is Nature's biocatalytic approach with the fluorinase enzyme, are the key to this unprecedentedly successful nucleophilic fluorination.
Abstract: Due to the tremendous interest in carbon–fluorine bond-forming reactions, research efforts in this area have been dedicated to the development of facile processes to synthesize small fluorine-containing organic molecules. Among others, PET (Positron Emission Tomography) is one of the most important applications of fluorine chemistry. Recognizing the specific requirements of PET processes, some groups have focused on fluorination reactions using alkali metal fluorides, particularly through SN2-type reactions. However, a common “misconception” about the role of protic solvents and hydrogen bonding interactions in this class of reactions has hampered the employment of these excellent promoters. Herein, we would like to review recent discoveries in this context, showing straightforward nucleophilic fluorination reactions using alkali metal fluorides promoted by protic solvents. Simultaneous dual activation of reacting partners by intermolecular hydrogen bonding and the enhancement of the “effective fluoride nucleophilicity”, which is Nature's biocatalytic approach with the fluorinase enzyme, are the key to this unprecedentedly successful nucleophilic fluorination.

112 citations


Cited by
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TL;DR: This review discusses efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions, and explores the unique possibilities offered by leveraging nontraditional surface chemistries and assembly environments to control superlattice structure and produce nonbulk assemblies.
Abstract: Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...

1,376 citations

Journal ArticleDOI
TL;DR: This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction.
Abstract: Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction.

751 citations

Journal ArticleDOI
TL;DR: Ionic Liquids-Based Extraction: A Promising Strategy for theAdvanced Nuclear Fuel Cycle Xiaoqi Sun, Huimin Luo, and Sheng Dai.
Abstract: Ionic Liquids-Based Extraction: A Promising Strategy for theAdvanced Nuclear Fuel Cycle Xiaoqi Sun, Huimin Luo, and Sheng Dai* Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37916, United States State Key Laboratory of Rare Earth Resource Utilization, Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China

719 citations