Eun Sung Lee

The unnatural isotope fluorine-18 ((18)F) is used as a positron emitter in molecular imaging. Currently, many potentially useful (18)F-labeled probe molecules are inaccessible for imaging because no fluorination chemistry is available to make them. The 110-minute half-life of (18)F requires rapid syntheses for which [(18)F]fluoride is the preferred source of fluorine because of its practical access and suitable isotope enrichment. However, conventional [(18)F]fluoride chemistry has been limited

Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal-organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM-1. This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a metal bindi

A one-step oxidative fluorination for carbon-fluorine bond formation from well-defined nickel complexes with oxidant and aqueous fluoride is presented, which enables a straightforward and practical (18)F late-stage fluorination of complex small molecules with potential for PET imaging.

Cucurbituril is used as the molecular “bead” for the synthesis of the first three-dimensional polyrotaxane network, which shows an inclined α-polonium topology. The novel solid-state interlocked structure is made up of binulcear Tb3+ centers and pseudorotaxane units containing cucurbituril “beads” threaded on a “string” with 3-phenylcarboxylate terminals (shown schematically).

A seven-membered molecular necklace composed of six copper ions and six pseudorotaxane units behaves as a secondary building block in the formation of a two-dimensional polyrotaxane network with large voids. This novel metal-organic framework allows size-selective anion exchange as well as the exchange of coordinated ligands. Thus a new synthetic strategy has been identified for modular porous solids which utilizes large, rigid, interlocked supermolecules as primary or secondary building blocks.

Over the past decade, numerous stable organic and main-group radicals have been synthesized from N-heterocyclic carbenes (NHCs). The structure of NHCs, in particular, offers electronic stabilization that helps to delocalize the unpaired electron over the molecule. In addition, the sterically bulky substituents of NHCs protect the radical center to prevent detrimental reactions such as dimerization. These advantages enable the straightforward synthesis and characterization of various interesting

Cucurbituril als molekulare „Perle”︁ wurde bei der Synthese eines dreidimensionalen Polyrotaxan-Netzwerks mit verzerrter α-Polonium-Struktur verwendet. Die neuartige Struktur ist aufgebaut aus zweikernigen Tb3+-Zentren und Pseudorotaxan-Einheiten, bei denen das Cucurbituril wie eine Perle auf einer Schnur aufgereiht ist. Die Schnüre tragen 3-Phenylcarboxylate in entständiger Position (siehe Bild).

Abstract Separation of acetylene from carbon dioxide and ethylene is challenging in view of their similar sizes and physical properties. Metal–organic frameworks (MOFs) in general are strong candidates for these separations owing to the presence of functional pore surfaces that can selectively capture a specific target molecule. Here, we report a novel 3D microporous cationic framework named JCM‐1 . This structure possesses imidazolium functional groups on the pore surfaces and pyrazolate as a m

Notwithstanding the notable progress in the synthesis of N-heterocyclic carbene-stabilized radicals, aminyl radicals, supported by NHCs or otherwise, have been scarcely studied due to synthetic challenges. Triazenyl radical is a particular form of aminyl radical that contains three adjacent nitrogen atoms, and offers intriguing possibilities for unique reactivity and physical properties stemming from expected delocalization of the spin density over the NNN moiety and its conjugated substituents.

Stable organic radicals have been of great academic interest not only in the context of fundamental understanding of reactive intermediates but also because of their numerous applications as functional materials. Apart from the early examples of triphenylmethyl and TEMPO derivatives, reports on air- and water-stable organic radicals are scarce, and their development remains a challenge. Herein, we present the design and synthesis of a novel organic radical based on a 1,2-dicarbonyl scaffold supp

N-Heterocyclic carbene-stabilized nitric oxide radicals were prepared by direct addition of nitric oxide to two N-heterocyclic carbenes in solution phase. The compounds were fully characterized by X-ray crystallography and EPR. The nitric oxide moiety in the solid compounds obtained can be thermally transferred to another N-heterocyclic carbene, suggesting potential applications to NO delivery.

Persistent radicals are potential building blocks of novel materials in many fields. Recently, highly stable persistent radicals are considered to be within reach, thanks to several radical stabilization strategies such as spin delocalization and steric protection. N-Heterocyclic carbene (NHC)-derived substituents can be attached to a radical center for these purposes, as illustrated by numerous NHC-stabilized radicals reported in the last two decades.This Account describes our recent work on de

A mild and practical cobalt-catalyzed defluoroborylation of fluoroarenes is presented for the first time. The method permits straightforward functionalization of fluoroarenes, with high selectivity for borylation of C-F over C-H bonds, and a tolerance for aerobic conditions. Furthermore, two-step ¹⁸F-fluorination was achieved for expanding the scope of ¹⁸F-positron emission tomography probes.

Herein we report a facile transformation of hydroxylated cucurbit[<i>n</i>]uril (CB[<i>n</i>], <i>n</i> = 6 and 7) to other functionality-conjugated CB[<i>n</i>]s by nucleophilic substitution of the hydroxyl group with a wide range of nitriles and alcohols. The reaction proceeds efficiently via generation of a superelectrophilic carbocation on the CB framework from hydroxylated CB[<i>n</i>]s under superacidic conditions. One of the resulting CB[<i>n</i>] derivatives with reactive functionality,