Jiseul Chun

Nanoparticulate Iron Oxide Tubes from Microporous Organic Nanotubes as Stable Anode Materials for Lithium Ion Batteries

During the last several decades, diverse porous materials have been prepared for a wide range of applications, such as adsorbents, gas storage materials, and solid supports for catalytic materials. These materials can be classified into three groups according to their components: inorganic materials, metal–organic composites, and purely organic systems. Among these porous materials, organic porous materials have recently attracted special attention because of their low densities and robustness. The accumulated organic synthetic methods can also be easily applied for the designed synthesis of organic porous materials with tailored functionalites. Thus, in a short period, diverse microporous organic networks have been prepared through diverse C C bond-forming reactions. In the synthesis of porous organic networks, the rigid building blocks are chosen so that the connection of these building blocks through covalent bonds induces the intrinsic porosity of the materials. Related studies have focused on the inner porosity and the resultant high surface area of materials. However, porous organic systems with well-defined outer shapes are rare. In particular, the template-free synthesis of hollow organic materials is quite rare. It is noteworthy that in the synthesis of secondary target inorganic materials using porous materials, the organic templates can be easily removed by combustion in air. In these cases, the outer shapes of materials along with their inner porosity are very critical for obtaining well-defined materials. Moreover, inorganic materials with a particulate surface could be obtained from the microporosity of organic network. Recently, Cooper and others have shown that Sonogashira coupling between alkynes and arylhalides is a very efficient method for the preparation of microporous organic materials. The resultant materials themselves showed promising gas-adsorption capacities. It can be expected that more diverse functional sites can be introduced into materials by designing the organic building blocks. During our trials for introduction of viologen groups into microporous organic materials, we observed the unexpected formation of microporous organic nanotubes. Herein, we present the preparation of microporous organic nanotubes and the template synthesis of iron oxide nanotubes with particulate walls and their application as anode materials for high-performance lithium ion batteries. Figure 1a shows the synthesis of microporous organic nanotubes (MONTs). For preparation of the MONT, two building blocks, N,N’-di(4-iodophenyl)-4,4’-bipyridinium dichloride (2 equiv) and tetra(4-ethynylphenyl)methane (1 equiv) were dissolved in a 3:2:2 mixture of toluene, methanol, and triethylamine. After adding catalytic amount of bis(triphenylphosphine)palladium dichloride and copper iodide, the reaction mixture was heated at 90 8C for 72 h to form precipitates. After cooling to room temperature, the solid was retrieved by centrifugation and washed with excess dimethyl sulfoxide, methanol, dichloromethane, and diethyl ether. The resultant materials were dried under a vacuum for a day. The obtained precipitates were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As shown in typical SEM images(Figure 1b), the obtained materials have a 1D character with mild ending-parts. Interestingly, a careful investigation of the materials by TEM revealed the hollow inner space and dark-contrasted walls (Figure 1c–e; Supporting Information, Figure S1). The average diameter and thickness of the wall of MONT were (92 19) nm and (31 4) nm, respectively. Brunauer– Emmett–Teller (BET) analysis showed the microporous character of materials with type I N2 isotherm at 77 K, 765.0 mg 1 surface area, and 1.01 cmg 1 pore volume (P/P0=0.995; Figure 2a). Powder X-ray diffraction (PXRD) studies revealed the amorphous character of MONT that has been observed previously (Supporting Information, Figure S2). Thermogravimetric analysis (TGA) of the materials showed that they are stable up to 205 8C and then slowly decomposed at a higher temperature (Figure 2b). Solidstate C NMR spectroscopy showed signals at d= 62 ppm, d= 90 ppm, and d= 120–160 ppm for benzyl, alkyne, and aryl groups, respectively (Figure 2c). Elemental analysis of mate[*] N. Kang, Dr. J. H. Park, J. Choi, J. Jin, J. Chun, Dr. I. G. Jung, Prof. S. U. Son Department of Chemistry and Department of Energy Science Sungkyunkwan University, Suwon 440-746 (Korea) E-mail: sson@skku.edu

Tandem Synthesis of Photoactive Benzodifuran Moieties in the Formation of Microporous Organic Networks

Over the last decade, microporous organic materials have been extensively prepared through various coupling reactions. In the early stages, relatively simple aromatic building blocks were used to prepare microporous organic networks (MONs) and relevant studies have focused on their physisorption behavior toward gas guests. Recently, more specific functionalities were achieved by the introduction of designed active sites into MONs. Usually, the active sites could be introduced by using the predesigned building blocks or by postmodification of the porous materials. If the active sites could be concomitantly formed in the network formation process for porous materials, this synthetic process would be very efficient and ideal for functional materials. For example, we have demonstrated the successful incorporation of active N-heterocyclic carbene metal species into metal– organic frameworks (MOFs) during self-assembly processes. However, this kind of synthetic approach is relatively rare, especially in the synthesis of MONs. Benzodifurans (BDFs) are very interesting materials owing to their unique optical and electrical properties. Their electron-rich nature has enabled them to be applied as redox-active hole transfer materials in organic lightemitting devices. Moreover, very recently, anti-benzodifuran-based organic materials have attracted significant attention as photoand redox-active materials in solar cells and organic field-effect transistors. anti-Benzodifurans can be prepared in the intramolecular cyclization reaction of 1,4hydroquinone with two alkyne groups at the 2,5-positions. Generally, tandem reactions in organic synthesis can be defined as a consecutive series of intramolecular reactions. In well-designed tandem processes, the functional groups for the following successive reactions can be generated in situ as a result of the previous reaction. Through the introduction of tandem processes to organic synthesis, the synthetic strategies become more atom-economical, because the work-up and isolation processes for intermediates can be reduced. Thus, much effort has been made for the development of smart tandem processes for complicated target organic materials. The Cooper research group and others have shown that MONs can be prepared by Sonogashira coupling between multialkyne connectors and multihalo arene building blocks. 7, 8] We have continued to develop functional MONs. We speculated that the generation of benzodifuran species can be induced in a tandem manner during the formation of the MON through a Sonogashira coupling. As far as we are aware, tandem synthetic strategies for the preparation of functional MONs have not been reported. Herein, we report the preparation of photoactive MONs with benzodifuran moieties through tandem synthetic processes, and their applications to photocatalytic coupling of primary amines. Figure 1 shows the synthetic strategy for the synthesis of a MON containing benzodifuran moieties (BDF-MON).

Metal−Organic Framework@Microporous Organic Network: Hydrophobic Adsorbents with a Crystalline Inner Porosity

This work reports the synthesis and application of metal-organic framework (MOF)@microporous organic network (MON) hybrid materials. Coating a MOF, UiO-66-NH2, with MONs forms hybrid microporous materials with hydrophobic surfaces. The original UiO-66-NH2 shows good wettability in water. In comparison, the MOF@MON hybrid materials float on water and show excellent performance for adsorption of a model organic compound, toluene, in water. Chemical etching of the MOF results in the formation of hollow MON materials.

Microporous organic networks bearing metal-salen species for mild CO2 fixation to cyclic carbonates

This work shows that porous solid systems for catalytic carbon dioxide fixation can be developed by a direct assembly of metal-salen containing building blocks with organic connectors through a carbon–carbon bond formation reaction. For use as a dihalo building block, Al, Cr, Co-salen building blocks with two iodo groups were prepared. Sonogashira coupling of these building blocks with tetra(4-ethynylphenyl)methane resulted in microporous organic networks (MONs) bearing Al, Cr, and Co-salen species (Al-MON, Cr-MON, Co-MON). Scanning electron microscopy (SEM) showed that the materials had granular or spherical shapes. Brunauer–Emmett–Teller (BET) analysis revealed surface areas of up to 522–650 m2 g−1, and microporosity (<2 nm). The thermal stability of the materials was dependent on the degree of networking. Their chemical components were characterized by solid-phase 13C-nuclear magnetic resonance spectroscopy (NMR) and X-ray photoelectron spectroscopy (XPS). The materials containing metal-salen (M-MON) showed excellent chemical conversion of carbon dioxide with epoxide to cyclic carbonates under mild conditions (60 °C and 1 MPa CO2). Among the M-MONs, the Co-MON showed the best reactivity for carbon dioxide conversion to cyclic carbonates with 1400–1860 TON and 117–155 h−1 TOF. The size effect of epoxides in CO2 fixation was observed due to the microporosity of Co-MON.

Concomitant Formation of N-Heterocyclic Carbene−Copper Complexes within a Supramolecular Network in the Self-Assembly of Imidazolium Dicarboxylate with Metal Ions

A new building block containing an imidazolium salt was synthesized and used for the construction of supramolecular networks with metal ions. We discovered the concomitant formation of the N-heterocyclic carbene-copper complex (CN = 2) in the self-assembly of imidazolium dicarboxylates and copper nitrates in N,N-dimethylformamide under heating. The proton in the 2 position of the imidazolium salt was abstracted, and Cu(II) was reduced to Cu(I) during the self-assembly process.