Highly Active La(III)-Based Metal-Organic Framework as a Heterogeneous Lewis Acid Catalyst for Friedel-Crafts Alkylation.

In this study, a novel La(III)-based two-dimensional (2D) metal-organic framework, [La2/3 (qptca)1/2 ] (referred to as SLX-2), from LaCl3 and 1,1' : 4',1'' : 4'',1''' : 4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H4 qptca) was synthesized by conventional solvothermal method and thoroughly characterized by using X-ray single-crystal diffraction, powder X-ray diffraction, and thermogravimetric analyses. The 2D SLX-2 features a unique lanthanum center exposed to the skeleton and was used as an efficient Lewis acid catalyst for the Friedel-Crafts alkylation of indole and pyrrole with ß-nitrostyrene along with a wide substrate scope, giving the desired products in good-to-high yields under the optimal reaction conditions. Furthermore, the catalyst was used for twenty cycles, with nearly no effect on its activity, and the reaction was heterogeneous in nature. Moreover, compared to the previous hydrogen-bond-donating MOF catalysts for such alkylation reactions, SLX-2 showed an excellent stability toward harsh acidic and basic environment, and gave comparable catalytic activities.

Size-Selective Suzuki-Miyaura Coupling Reaction over Ultrafine Pd Nanocatalysts in a Water-Stable Indium-Organic Framework.

Metal nanoparticles stabilized by crystalline metal-organic frameworks (MOFs) are highly promising for green heterogeneous catalysis. In this work, in situ formed ultrafine Pd nanocatalysts with an average size of 3.14 nm have been successfully immobilized into the mesopores or defects of a water-stable indium-based MOF by the double-solvent method and subsequent reduction. Significantly, the obtained Pd@InOF-1 displays an obvious and satisfactory size-selective effect in the Suzuki-Miyaura coupling reaction between arylboronic acids and aryl bromides. On the basis of the synergistic effect, microporous InOF-1 nanorods afford a confined space for improving the selectivity of target products while Pd nanoparticles endow abundant active sites for catalysis. Herein, choosing the smallest size reactant with only one benzene ring gives the highest isolated yield of 90%, and if the size is larger, the yield is obviously reduced or even the target product could not be collected. Looking forward, this demonstrated study not only assembles a well-designed Pd@MOF composite with unique micro-nanostructures but also delivers an impressive option for cross-coupling reaction, which has implications for the further development of MOF hybrids for sustainable applications.

Design of an antenna effect Eu(III)-based metal-organic framework for highly selective sensing of Fe3.

Highly selective sensing of Fe3+ is very important due to its great effect on biological systems. A novel ligand [1,1':4',1'':4'',1''':4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H4qptca) was designed and successfully obtained for the first time via three steps in high total yields according to the absorption spectrum of Fe3+. The europium(III)-based metal-organic framework derived from H4qptca, {[Eu(qptca)1/2(H2qptca)1/2(H2O)2]·DMF}n (referred to as SLX-1), was then synthesized and used as a water-stable and highly selective luminescent sensor for Fe3+ in aqueous solution with a comparable detection limit using Ln-MOF probes (6.45 µM) through the antenna effect of SLX-1. Furthermore, the luminescence quenching mechanism was also proposed as a competitive absorption mechanism.

An efficient glucose sensor thermally calcined from copper-organic coordination cages.

Due to the harmfulness of diabetes, a fast and efficient glucose detector is particularly important. Metal-organic polyhedron (MOP) provides a porous framework and a special matrix, which makes it an excellent precursor for electrochemical detection. Herein, we report a novel MOP as a precursor for the preparation of an electrocatalytic detector for glucose. The new metal-organic polyhedron of Cu4(TPDC)4 can be solvothermally obtained and characterized by X-ray crystallography, which can be thermally converted into nanosized copper oxides embedded into graphitic carbon layers (MOP-CO). The as-prepared MOP-CO electrode is further applied to glucose detection, which shows a fast response time (<1 s) in a wide linear range of 0-4000 µM and high sensitivity of 2720 µA mM-1 cm-2, as well as low detection limit (26 nM (S/N = 3)), good anti-interference, repeatability and stability (>3600 s).

N-Heterocyclic carbene-palladium(ii)-1-methylimidazole complex catalyzed direct C-H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides.

We herein reported the N-heterocyclic carbene-palladium(ii)-1-methylimidazole complex catalyzed direct C-H bond arylation of imidazo[1,2-a]pyridines with aryl chlorides. Under suitable conditions, all reactions between various imidazo[1,2-a]pyridines and aryl chlorides worked well to give the desired C3-H arylated products in acceptable to high yields, giving a convenient and alternative method for the direct C-H bond arylation of imidazo[1,2-a]pyridines, using economic and easily available aryl chlorides as the arylating reagents.

N-Heterocyclic Carbene-Palladium(II)-1-Methylimidazole Complex Catalyzed Direct C-H Bond Arylation of Benzo[b]furans with Aryl Chlorides.

The first example of sole direct C-H bond arylation of benzo[b]furans with aryl chlorides was achieved catalyzed by a well-defined NHC-Pd(II)-Im complex. Under the suitable conditions, all reactions involving kinds of benzo[b]furans and (hetero)aryl chlorides proceeded well to give the desired C2-arylated benzo[b]furans in sole regioselectivity in acceptable to high yields, providing an efficient and economic pathway for the direct C2-H bond arylation of benzo[b]furans.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed α-arylation reactions of tetralones with aryl chlorides and further transformation of the products.

NHC-Pd(II)-Im complex 1 has proven to be an efficient catalyst in the reaction between tetralones 2 and aryl chlorides 3, giving the α-arylated tetralones 4 in good to high yields. In addition, if the above reaction mixture was exposed to air at room temperature for another 3 h, the normal α-arylated products 4 can be fully oxidized to 2-aryl-2'-hydroxytetralones 6 in good yields in a one-pot procedure. Furthermore, if the reaction mixture containing the oxidized products 6 was treated with TsOH/toluene solution under reflux for 19 h, the final aromatized products, 2-aryl-naphthalen-1-ols 5 can be achieved in acceptable to moderate yields. All reactions can tolerate various substituents on the tetralones 2 and aryl chlorides 3, thus giving an efficient method for the α-arylation of tetralones and further transformation of the products, and also enriching the applications of NHC-Pd(II) complexes in organic synthesis.

Direct C-H bond arylation of fluorenes with aryl chlorides catalyzed by N-heterocyclic carbene-palladium(II)-1-methylimidazole complex and further transformation of the products in a one-pot procedure.

We report here the NHC-Pd(II)-Im complex 1-catalyzed direct C-H bond functionalization of the C9 position of fluorenes with aryl chlorides and further transformation of the resulting products in a one-pot procedure. Under the optimal conditions, arylated fluorenes can be obtained in moderate to almost quantitative yields using various activated and unactivated (hetero)aryl chlorides as the arylating reagents. Furthermore, if the mixture from the arylation reaction is exposed to air, the C9-oxidized products can be obtained in acceptable to good yields in a one-pot procedure. In addition, alkyl groups can also be efficiently introduced to the above mixture from the arylation reaction, producing further C9-alkylated products in good to almost quantitative yields in a one-pot procedure, thus providing an expedient, inexpensive and practical strategy for the mono- and di-functionalization of fluorenes.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex-catalyzed direct C-H bond arylation of (benz)imidazoles with aryl chlorides.

(Benz)imidazoles can be efficiently functionalized by (hetero)aryl chlorides via direct C-H bond arylation in the presence of a well-defined NHC-Pd(II)-Im complex. Under the optimal conditions, various activated, unactivated, and deactivated (hetero)aryl chlorides were successfully applied as the arylating reagents to achieve the 2-(hetero)aryl (benz)imidazoles in acceptable to high yields, giving a facile and alternative methodology for the direct C-H bond arylation of (benz)imidazoles.

Direct C-H bond arylation of (benzo)oxazoles with aryl chlorides catalyzed by N-heterocyclic carbene-palladium(II)-1-methylimidazole complex.

The direct C-H bond arylation of (benzo)oxazoles with aryl chlorides was achieved catalyzed by a well-defined NHC-Pd(II)-Im complex. Under the optimal conditions, various aryl chlorides were successfully applied as the arylating reagents to achieve the 2-aryl (benzo)oxazoles in acceptable to high yields, providing a convenient and alternative method for the direct C-H bond arylation of (benzo)oxazoles and enriching the chemistry of the NHC-Pd(II) complex in organic synthesis.

Two-component, three-molecule reactions between 2,3-dihydroinden-1-ones and aryl chlorides catalyzed by an N-heterocyclic carbene-palladium(II)-1-methylimidazole complex.

The two-component, three-molecule reactions between 2,3-dihydroinden-1-ones and aryl chlorides were achieved in the presence of an NHC-Pd(II)-Im complex. Under the optimal conditions, all reactions performed well to give the corresponding products in moderate to high yields.

Palladium-catalyzed Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids.

Readily available NHC-Pd(II)-Mp complexes 2 showed efficient catalytic activity toward the Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids or potassium phenyltrifluoroborate, giving the expected coupling products in good to high yields. It should be noted that this is the first example so far of the phosphine-free, NHC-Pd(II) complexes catalyzed Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed α-arylation of oxindoles with aryl chlorides and aerobic oxidation of the products in a one-pot procedure.

NHC-Pd(II)-Im complex 1 was found to be an effective catalyst for the α-arylation of unprotected oxindoles with aryl chlorides to give products 4 in 44-98% yields under a N2 atmosphere. Furthermore, if the reactions were first performed under conditions identical to those for the α-arylation reaction for 12 h and then exposed to air for another 3 h, 3-aryl-3-hydroxy-2-oxindoles 5 can be obtained in 49-84% yields in a one-pot procedure.

N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Mizoroki-Heck reaction of aryl chlorides with styrenes.

A well-defined N-heterocyclic carbene-palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 was found to be an effective catalyst for the Mizoroki-Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB) as the ionic liquid.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed amination between aryl chlorides and amides.

We report herein that amides are excellent N-sources in the NHC-Pd(II)-Im complex 1 catalyzed amination of aryl chlorides. In the presence of KO(t)Bu, various aryl chlorides and amides can react smoothly to give the corresponding aminated products in moderate to almost quantitative yields at room temperature within 6 h.

N-heterocyclic carbene-palladium(II)-1-methylimidazole complex-catalyzed Suzuki-Miyaura coupling of aryl sulfonates with arylboronic acids.

A well-defined NHC-Pd(II)-Im complex 1 was found to be an effective catalyst for the Suzuki-Miyaura coupling of aryl sulfonates including tosylates and phenylsulfonates with arylboronic acids, giving the desired coupling products in good to high yields. Acceptable yields can also be achieved even by using the less reactive mesylates as the substrates. It is worthy of noting here that this is the first example of NHC-Pd(II) complex-catalyzed Suzuki-Miyaura coupling of aryl sulfonates with arylboronic acids, enriching an inexpensive, convenient, and alternative method for the synthesis of biaryl compounds.

Rapid generation of molecular complexity in the Lewis or Brønsted acid-mediated reactions of methylenecyclopropanes.

Although they are highly strained, methylenecyclopropanes (MCPs) are readily accessible molecules that have served as useful building blocks in organic synthesis. MCPs can undergo a variety of ring-opening reactions because the release of cyclopropyl ring strain (40 kcal/mol) can provide a thermodynamic driving force for reactions and the π-character of the bonds within the cyclopropane can afford the kinetic opportunity to initiate the ring-opening. Since the 1970s, the chemistry of MCPs has been widely explored in the presence of transition metal catalysts, but less attention had been paid to the Lewis or Brønsted acid mediated chemistry of MCPs. During the past decade, significant developments have also been made in the Lewis or Brønsted acid mediated reactions of MCPs. This Account describes chemistry developed in our laboratory and by other researchers. Lewis and Brønsted acids can be used as catalysts or reagents in the reactions of MCPs with a variety of substrates, and substituents on the terminal methylene or on the cyclopropyl ring of MCPs significantly affect the reaction pathways. During the past decade, we and other researchers have found interesting transformations based on this chemistry. These new reactions include the ring expansion of MCPs, cycloaddition reactions of MCPs with aldehydes and imines, cycloaddition reactions of MCPs with nitriles in the presence of strong Brønsted acid, radical reactions of MCPs with 1,3-dicarbonyl compounds, intramolecular Friedel-Crafts reactions of MCPs with arenes, acylation reactions of MCPs, and the reaction of MCPs with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers. These Lewis or Brønsted acid mediated reactions of MCPs can produce a variety of new compounds such as cyclobutanones, indenes, tetrahydrofurans, and tetrahydroquinolines. Finally, we have also carried out computational studies to explain the mechanism of the Brønsted acid mediated reactions of MCPs with acetonitrile.

PdCl(2)-promoted reactions of diaryl-substituted methylenecyclopropanes.

The PdCl(2)-promoted reactions of methylenecyclopropanes (MCPs) 1 bearing diaryl substituents on the terminal double bond were carefully investigated. The solvents employed significantly affected the reaction outcomes. It was found that dimeric allylpalladium(ii) complexes 2a-2f can be obtained as the sole products in acceptable to good yields under mild reaction conditions with THF as the solvent, while dimeric allylpalladium(ii) complexes 2a-2f along with another type of dimeric allylpalladium(ii) complexes 4a-4e can be obtained in good to high total yields if N,N-dimethylacetamide (DMAc) was used as the solvent. Moreover, using N,N-dimethylformamide (DMF) as the solvent in the presence of water, it was found that water can also participate in the reaction to form another type of dimeric allylpalladium(ii) complex 6 as the minor product. All of these dimeric allylpalladium(ii) complexes reported in the paper have been characterized by X-ray crystal structure diffraction.

Silica gel triggered transformations of 3-methylenecyclopropylmethyl sulfonates to 3-methylenecyclobutyl analogues: experimental and computational studies.

Methylenecyclopropylcarbinols treated with sulfonyl chloride and Et(3)N form the sulfonated products in almost quantitative yields, which can be transformed to the corresponding 3-methylenecyclobutyl sulfonates with silica gel chromatography work-up. The rational explanation was proposed on the basis of computational studies.