Showing papers by "Jun-Chul Choi published in 2021"

One-pot catalytic synthesis of urea derivatives from alkyl ammonium carbamates using low concentrations of CO2

Abstract: To reduce anthropogenic carbon dioxide (CO2) emissions, it is desirable to develop reactions that can efficiently convert low concentrations of CO2, present in exhaust gases and ambient air, into industrially important chemicals, without involving any expensive separation, concentration, compression, and purification processes. Here, we present an efficient method for synthesizing urea derivatives from alkyl ammonium carbamates. The carbamates can be easily obtained from low concentrations of CO2 as present in ambient air or simulated exhaust gas. Reaction of alkyl ammonium carbamates with 1,3-dimethyl-2-imidazolidinone solvent in the presence of a titanium complex catalyst inside a sealed vessel produces urea derivatives in high yields. This reaction is suitable for synthesizing ethylene urea, an industrially important chemical, as well as various cyclic and acyclic urea derivatives. Using this methodology, we also show the synthesis of urea derivatives directly from low concentration of CO2 sources in a one-pot manner. Upconverting anthropogenic CO2 into valuable chemicals generally involves separation and concentration steps of the feed gas. Here, the authors report an efficient, one-pot method for synthesizing urea derivatives from alkyl ammonium carbamates obtained from atmospheric CO2 or simulated exhaust gas with low concentrations of CO2.

Sustainable Catalytic Synthesis of Diethyl Carbonate

Abstract: New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO2 and alcohols. Using tetraethyl orthosilicate (TEOS) and CO2 with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO2 -inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.

One-Pot Synthesis of Triazatriphenylene Using the Povarov Reaction.

Abstract: The Povarov reaction combines aromatic amines, aldehydes, and alkynes in a single step and is regarded as an annulative π-extension reaction of aromatic amines. In this study, the Povarov reaction was investigated as an efficient tool for the synthesis of aza-polycyclic aromatic hydrocarbons via multiple π-extensions. The double Povarov reaction of 1,4-diaminobenzene yielded the 4,7-phenanthroline derivative as the major product, regardless of the steric repulsion in the product. The site selectivity mainly depended on the HOMO distribution of the intermediate rather than the steric factor. Based on these insights, a 1,5,9-triazatriphenylene derivative was synthesized via a triple Povarov reaction. The structures of the synthesized compounds were unambiguously determined by single-crystal X-ray diffraction analysis. The triazatriphenylene derivative formed a smooth and stable thin film upon vacuum vapor deposition and served as a hole-blocking material in organic light-emitting diodes.

Immobilized Zn(OAc)2 on bipyridine-based periodic mesoporous organosilica for N-formylation of amines with CO2 and hydrosilanes

Abstract: Zinc acetate (Zn(OAc)2) was successfully immobilized on a bipyridine-based periodic mesoporous organosilica (BPy-PMO-TMS), as confirmed by solid-state NMR and energy-dispersive X-ray spectroscopies, X-ray diffractometry, and nitrogen adsorption/desorption isotherm analyses. The immobilized Zn complex, Zn(OAc)2(BPy-PMO-TMS), exhibited good catalytic activity during the N-formylations of amines and amides with CO2 and PhSiH3 to produce the corresponding formamides. Zn(OAc)2(BPy-PMO-TMS) with a lower Zn loading was found to exhibit higher catalytic activity.

Bidentate Disilicate Framework for Bis-Grafted Surface Species.

Abstract: Recent advances in surface organometallic chemistry have enabled the detailed characterization of the surface species in single-site heterogeneous catalysts. However, the selective formation of bis-grafted surface species remains challenging because of the heterogeneity of the supporting surface. Herein, we introduce a metal complex bearing bidentate disilicate ligands, -OSi(Ot Bu)2 OSi(Ot Bu)2 O-, as a molecular precursor, which has a silicate framework adjacent to the metal (Pt) center. The grafting of the precursors on silica supports (MCM-41 and CARiACT Q10) proceeded through a substitution reaction on the silicon atoms of the disilicate ligand, which was verified by the detection of isobutene and t BuOH as the elimination products, to selectively yield bis-grafted surface species. The chemical structure of the surface species was characterized by solid-state NMR, and the chemical shift values of the ancillary ligands and 195 Pt nuclei suggested that the bidentate coordination sphere was maintained following grafting.

Synthesis of diethyl carbonate from CO2 and orthoester promoted by a CeO2 catalyst and ethanol

Abstract: The combination of a CeO2 catalyst and ethanol effectively promotes the direct synthesis of diethyl carbonate (DEC) from CO2 and an orthoester. The reaction temperature, initial CO2 pressure, and the ethanol/orthoester volume ratio were found to significantly influence DEC formation and were systematically studied to determine the optimum conditions. DEC amount of 5.2 mmol was obtained at 160 °C, 5 MPa of CO2, and a reaction time of 20 h, providing high productivity (1.21 mmolDEC mmolcatalyst−1 h−1) using a CeO2 catalyst. The recovered CeO2 catalyst was recyclable at least four times without any significant loss of activity when both triethyl orthoacetate and triethyl orthovalerate were used. A series of orthoesters bearing various alkyl substituents, aromatic substituents and halide moieties were evaluated for their activities with and without ethanol. In the presence of ethanol, orthoesters bearing longer alkyl substituents led to higher DEC yields, and orthoesters bearing aromatic and halide moieties negatively impacted DEC formation. In the absence of ethanol, triethyl orthoacetate provided the highest DEC yield; in all cases, the use of ethanol resulted in a greater DEC formation than when the reaction was performed without ethanol.

Hydroxycarbonylation of alkenes with formic acid using a rhodium iodide complex and alkyl ammonium iodide

Abstract: Hydroxycarbonylation of alkenes using formic acid (HCOOH) is ideal for the synthesis of various carboxylic acids as a means to develop a sustainable reaction system with lower environmental impact. In this study, we developed a new catalytic system for hydroxycarbonylation of alkenes with HCOOH using a Vaska-type Rh complex with an iodide ligand, RhI(CO)(PPh3)2 (1), as the catalyst, and a quaternary ammonium iodide salt as the promoter for the catalyst. In comparison with similar reaction systems using Rh catalysts, our reaction system is safer and more environmentally friendly since it does not require high-pressure conditions, explosive gases, or environmentally unfriendly CH3I and extra PPh3 promoters. In addition, we also experimentally clarified that the catalytic reaction proceeds via RhHI2(CO)(PPh3)2 (2), which is formed by the reaction of 1 with a quaternary ammonium iodide salt and p-TsOH. Furthermore, the Rh(III) complex 2 can catalyze hydroxycarbonylation of alkenes with HCOOH without any promoters.

Fluoride Ion-Initiated Decarboxylation of Silyl Alkynoates to Alkynylsilanes.

Abstract: This communication describes the development of a metal-free catalytic decarboxylation of silyl alkynoates to alkynylsilanes. Treatment of a silyl alkynoate with a catalytic amount of tetrabutylamm...

Facile Synthesis of Sequence-Defined Oligo(Dimethylsiloxane-co-Diphenylsiloxane)s.

Abstract: 1,1,3,3,5,5,7,7-Octamethyltetrasiloxane (H MD2 MH ), which is reported to release Me2 SiH2 via a B(C6 F5 )3 -catalyzed redistribution, acts as a good Me2 SiH2 precursor in the B(C6 F5 )3 -catalyzed dehydrocarbonative condensation of alkoxysilanes. A series of oligo(dimethylsiloxane-co-diphenylsiloxane)s that are uniformly sized and sequence-defined at the atomic level are synthesized by a one-pot controlled iteration of a B(C6 F5 )3 -catalyzed dehydrocarbonative condensation of alkoxysilanes with H MD2 MH or Ph2 SiH2 and a B(C6 F5 )3 -catalyzed hydrosilylation of carbonyl compounds, followed by the subsequent B(C6 F5 )3 -catalyzed dehydrogenative condensation of silanols.