Myung-Jong Jin

A Practical Heterogeneous Catalyst for the Suzuki, Sonogashira, and Stille Coupling Reactions of Unreactive Aryl Chlorides†

Transition-metal-catalyzed coupling reactions have contributed greatly to the straightforward and facile construction of carbon–carbon bonds. Significant progress in this area has been achieved with a variety of homogeneous palladium catalysts. However, homogeneous catalysis suffers from the problematic separation of the expensive catalyst from the product for re-use. Moreover, the homogeneous palladium catalysts tend to lose their catalytic activity because of palladium metal aggregation and precipitation. These problems are of particular environmental and economic concern in large-scale syntheses. Heterogenization of the existing homogeneous palladium catalysts could be an attractive solution to this problem. There has been considerable interest in the development of heterogeneous catalytic systems that can be efficiently re-used whilst keeping the inherent activity of the catalytic center. Aryl iodides and bromides have been widely employed as substrates in heterogeneous coupling reactions. From a practical point of view, the use of aryl chlorides is highly desirable because they are readily available and inexpensive. However, they are much more difficult to activate than aryl iodides and bromides. The activation of aryl halides is particularly challenging for heterogeneous catalysts, and although there have been many reports of heterogeneous reactions in the literature, successful examples using deactivated aryl chlorides are quite rare. Therefore, the development of high-performance catalysts for practical catalytic coupling reactions is of ongoing interest. Magnetite Fe3O4 nanoparticles have recently emerged as promising supports for immobilization because Fe3O4-supported catalysts can be separated from the reaction medium by an external permanent magnet. This circumvents time-consuming and laborious separation steps, and allows for practical continuous catalysis. In particular, Fe3O4 nanoparticles coated with a thin layer of silica have beneficial properties, such as invariant catalytic activity and stability. We have previously reported the use of a (b-oxoiminato)(phosphanyl)palladium complex as an efficient catalyst in coupling reactions. In this context, we have prepared triethoxysilyl-functionalized palladium complex 2, which can be anchored easily onto the surface of the silica. Commercially available Fe3O4 nanoparticles, with an average diameter of 20 nm, were coated with a thin layer of silica using a sol-gel process to give silica-coated Fe3O4 (3 ; SiO2@Fe3O4). [13] The silica shell has plenty of hydroxyl groups for potential derivatization with different functional groups, and also protects the magnetite core from abrasion under harsh shaking conditions. The silylated palladium complex 2 was successfully immobilized on the surface of robust SiO2@Fe3O4 (3) (Scheme 1). Schiff-base condensation of 2,4-pentanedione with (3-aminopropyl)triethoxysilane under microwave heating afforded 1 in only 3 min in quantitative yield. Deprotonation of 1 with EtOTl in tetrahydrofuran, followed by treatment with [Pd2(m-Cl)2Me2(PPh3)2], [14] led to the formation of 2. Magnetic-nanoparticle-supported (b-oxoiminato)(phosphanyl)palladium complex 4 was obtained by reaction

Highly effective silica gel-supported N-heterocyclic carbene–Pd catalyst for Suzuki–Miyaura coupling reaction

The immobilized N-heterocyclic carbene–Pd complex was readily prepared by reaction of silica gel-supported imidazolium chloride with Pd(OAc)2. The Pd complex exhibited excellent catalytic activity in the coupling reaction of aryl halides with arylboronic acid. The heterogeneous Pd catalyst was reusable as well as air-stable to allow easy use.

Palladium acetate immobilized in a hierarchical MFI zeolite-supported ionic liquid: a highly active and recyclable catalyst for Suzuki reaction in water

Palladium acetate was immobilized in thin ionic liquid layers on the mesopore wall of hierarchical MFI zeolite, and tested as a catalyst for Suzuki coupling reaction in water. The catalyst exhibited very high activity in the coupling of various aryl bromides with arylboronic acids. Moreover, the catalyst could be recycled without a significant loss of catalytic activity.

An extremely active and general catalyst for Suzuki coupling reaction of unreactive aryl chlorides.

β-Diketiminatophosphane Pd complex 2a acted as a powerful catalyst which allows easy access to the Suzuki coupling reaction of less reactive aryl chlorides under mild conditions. A wide range of sterically hindered and deactivated aryl chlorides could be efficiently coupled at a low catalyst loading of 0.1 mol %. Furthermore, this catalytic system also proved to be highly effective in one-pot multiple couplings.

Highly active and recyclable silica gel-supported palladium catalyst for mild cross-coupling reactions of unactivated heteroaryl chlorides

Silica gel-supported β-ketoiminatophosphane-Pd complex (Pd@SiO2) was shown to be a highly active and long-lived catalyst for aqueous Suzuki, Stille and Sonogashira coupling reactions of heteroaryl chlorides. A wide range of heteroaryl chlorides could be efficiently coupled with different nucleophilic partners in the presence of only 0.5 mol% catalyst and under mild conditions. This is one of the most powerful heterogeneous catalysts for the couplings of diverse heteroaryl chlorides. Furthermore, the catalyst could be reused with almost consistent activity.

An Efficient and General Method for the Heck and Buchwald–Hartwig Coupling Reactions of Aryl Chlorides

The β-diketiminatophosphane Pd complex acted as a powerful catalyst for the Heck coupling of aryl chlorides with alkenes. Various aryl and heteroaryl chlorides were coupled efficiently under relatively mild conditions. Furthermore, this catalytic system also proved to be highly active in the Buchwald-Hartwig coupling of deactivated and sterically hindered aryl chlorides at room temperature.

Highly enantioselective aryl transfer to aldehydes: a remarkable effect of sulfur substitution in amino thioacetate ligands.

Chiral amino thioacetate ligands were prepared from the corresponding amino alcohols and used as catalysts for enantioselective aryl transfer reaction. The amino thioacetates were remarkably superior to the corresponding amino alcohols. Low catalyst loadings of only 1-2.5 mol % were sufficient to achieve excellent enantioselectivity as well as high conversion in short reaction time. The results reveal that the thioacetoxy moiety of the amino thioacetates has a surprisingly beneficial effect in enhancing the asymmetric induction.

NEW CHIRAL CATALYSTS FOR THE HIGHLY ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO ALDEHYDES

Abstract Optically active amino thioacetate derivatives of (+)-norephedrine were found to act as effective catalysts for enantioselective addition of diethylzinc to aldehydes. This reaction provided optically active secondary alcohols with e.e. of up to > 99%.

New chiral phosphinooxazolidine ligands for palladium-catalyzed asymmetric allylic substitution

Abstract New chiral phosphinooxazolidines were prepared and examined as chiral ligands in Pd-catalyzed asymmetric allylic substitution reaction of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate or benzylamine. Enantioselectivity up to 98% was observed.

Amino-functionalized SBA-15 type mesoporous silica having nanostructured hexagonal platelet morphology

Amino-functionalized SBA-15 type mesoporous silicas having unique hexagonal platelet morphologies with short channels (100-300 nm) running parallel to the thickness of the nanostructured hexagonal platelet type morphologies have been directly synthesized by co-condensation of aminopropyltriethoxysilane (APTES) and sodium metasilicate as a silica source in the presence of Pluronic P123 triblock copolymer as a structure directing agent.