TiO2-Modified Montmorillonite-Supported Porous Carbon-Immobilized Pd Species Nanocomposite as an Efficient Catalyst for Sonogashira Reactions.

In this study, a combination of the porous carbon (PCN), montmorillonite (MMT), and TiO2 was synthesized into a composite immobilized Pd metal catalyst (TiO2-MMT/PCN@Pd) with effective synergism improvements in catalytic performance. The successful TiO2-pillaring modification for MMT, derivation of carbon from the biopolymer of chitosan, and immobilization of Pd species for the prepared TiO2-MMT/PCN@Pd0 nanocomposites were confirmed using a combined characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption isotherms, high-resolution transition electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was shown that the combination of PCN, MMT, and TiO2 as a composite support for the stabilization of the Pd catalysts could synergistically improve the adsorption and catalytic properties. The resultant TiO2-MMT80/PCN20@Pd0 showed a high surface area of 108.9 m2/g. Furthermore, it exhibited moderate to excellent activity (59-99% yield) and high stability (recyclable 19 times) in the liquid-solid catalytic reactions, such as the Sonogashira reactions of aryl halides (I, Br) with terminal alkynes in organic solutions. The positron annihilation lifetime spectroscopy (PALS) characterization sensitively detected the development of sub-nanoscale microdefects in the catalyst after long-term recycling service. This study provided direct evidence for the formation of some larger-sized microdefects during sequential recycling, which would act as leaching channels for loaded molecules, including active Pd species.

Cobalt(ii)-catalyzed hydroarylation of 1,3-diynes and internal alkynes with picolinamides promoted by alcohol.

The Co(ii)-catalyzed selective C-H alkenylation of picolinamides with 1,3-diynes has been developed. This protocol can be applied to a variety of 1,3-diynes. In addition, both symmetrical and unsymmetrical internal alkynes were well tolerated, affording the corresponding alkenyl arenes. Moreover, control experiments indicated that C-H bond cleavage may be involved in the rate-determining step. Furthermore, a deuterium incorporation product was achieved when deuterated alcohol was employed as the solvent, which suggested that alcohol was essential for the final protonolysis.

Selective Synthesis of Alkynylated Isoquinolines and Biisoquinolines via RhIII Catalyzed C-H Activation/1,3-Diyne Strategy.

Described herein is a convenient and highly selective synthesis of alkynylated isoquinolines and biisoquinolines from various aryl ketone O-pivaloyloxime derivatives and 1,3-diynes via rhodium-catalyzed C-H bond activation. In this transformations, alkynylated isoquinolines, 3,4'- and 3,3'-biisoquinolines could be obtained respectively through changing the reaction conditions. Mechanistic investigation revealed that the C-H activation of aryl ketone O-pivaloyloxime was the key step to this reaction.

Co-immobilization of Pd and Zn nanoparticles in chitosan/silica membranes for efficient, recyclable catalysts used in ullmann reaction.

In this study, an efficient heterogeneous catalyst including palladium (Pd) and zinc (Zn) nanoparticles supported on chitosan/silica (CS/SiO2) composite membrane is synthesized using partially etching of SiO2 technique. N2 sorption isotherm results shows that the prepared Pd-Zn@CS/SiO2 (1/1) porous membrane had a BET surface area of 26.50m2/g. High-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), characterization of the catalyst shows that the Pd0 nanoparticles (below 5nm), and Zn0 aggregates (about 10-15nm) dispersed well in the CS/SiO2 matrix. Zinc crystal was also detected by X-ray diffraction study and HR-TEM observation. The prepared Pd-Zn@CS/SiO2 membrane catalyst is highly active for Ullmann reductive homocoupling reactions of aryl iodides and aryl bromides, and can be recycled 5 times without significant loss of activities. This work supplies a successful approach to realize Pd catalysts and Zn reducing reagent co-immobilized in the same carrier material with excellent catalytic performances.

Encaging Palladium Nanoparticles in Chitosan Modified Montmorillonite for Efficient, Recyclable Catalysts.

Metal nanoparticles, once supported by a suitable scaffolding material, can be used as highly efficient heterogeneous catalysts for numerous organic reactions. The challenge, though, is to mitigate the continuous loss of metals from the supporting materials as reactions proceed, so that the catalysts can be recycled multiple times. Herein, we combine the excellent chelating property of chitosan (CS) and remarkable stability of montmorillonite (MMT) into a composite material to support metal catalysts such as palladium (Pd). The in situ reduction of Pd2+ into Pd0 in the interstices of MMT/CS composites effectively encages the Pd0 nanoparticles in the porous matrices, while still allowing for reactant and product molecules of relatively small sizes to diffuse in and out the matrices. The prepared Pd0@MMT/CS catalysts are highly active for the Heck reactions of aromatic halides and alkenes, and can be recycled 30 times without significant loss of activities. Positron annihilation lifetime analysis and other structural characterization methods are implemented to elucidate the unique compartmentalization of metal catalysts in the composite matrices. As both CS and MMT are economical and abundant materials in nature, this approach may facilitate a versatile platform for developing highly recyclable, heterogeneous catalysts containing metal nanoparticles.

N-doped mesoporous carbons supported palladium catalysts prepared from chitosan/silica/palladium gel beads.

In this study, a heterogeneous catalyst including palladium nanoparticles supported on nitrogen-doped mesoporous carbon (Pd@N-C) is synthesized from palladium salts as palladium precursor, colloidal silica as template, and chitosan as carbon source. N2 sorption isotherm results show that the prepared Pd@N-C had a high BET surface area (640m(2)g(-1)) with large porosity. The prepared Pd@N-C is high nitrogen-rich as characterized with element analysis. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy characterization of the catalyst shows that the palladium species with different chemical states are well dispersed on the nitrogen-containing mesoporous carbon. The Pd@N-C is high active and shows excellent stability as applied in Heck coupling reactions. This work supplies a successful method to prepare Pd heterogeneous catalysts with high performance from bulk biopolymer/Pd to high porous nitrogen-doped carbon supported palladium catalytic materials.

Synthesis of 2,3-dihydro-1H-indazoles by Rh(III)-catalyzed C-H cleavage of arylhydrazines.

A rhodium-catalyzed efficient method for the synthesis of 2,3-dihydro-1H-indazoles is described. The reaction of arylhydrazines with olefins results in the corresponding 2,3-dihydro 1H-indazoles with exclusive regioselectivity via C-H bond activation. The utility of the methodology is illustrated by a rapid synthesis of 1H-indazoles under mild reaction conditions in half an hour.

Free-amine directed arylation of biaryl-2-amines with aryl iodides by palladium catalysis.

A new palladium-catalyzed free-amine directed arylation of C(sp(2))-H bonds in the presence of AgOAc and TFA is described. Biaryl-2-amines react with various aryl iodides to give the corresponding mono- or diarylated products with exclusive regioselectivity.

Cu(II)-promoted palladium-catalyzed C-H ortho-arylation of N,N-dimethylbenzylamines.

A novel protocol for palladium-catalyzed arylation of the C(sp(2))-H bond directed by a N,N-dimethylaminomethyl group in the presence of AgOAc and Cu(OAc)2·H2O is described. Various aryl iodides proved to be efficient coupling partners, furnishing the corresponding ortho monoarylated or diarylated arenes in moderate to good yields. Cu(OAc)2·H2O is found to be the important additive to improve the yields in this transformation.

(E)-N'-[1-(4-Chloro-phen-yl)ethyl-idene]-2-hydroxy-benzohydrazide.

In the title compound, C(15)H(13)ClN(2)O(2), the dihedral angle between the two benzene rings is 7.0 (1)°. An intra-molecular N-H⋯O hydrogen bond is present and inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into chains along [001].

Ethyl 6-(2-chloro-phen-yl)-4-methyl-1-(3-oxobut-yl)-2-thioxo-1,2,3,6-tetra-hydro-pyrimidine-5-carboxyl-ate.

In the title mol-ecule, C(18)H(21)ClN(2)O(3)S, the pyrimidine ring exhibits a half-chair conformation. The ethyl group is disordered between two positions in a ratio 0.74:0.26. In the crystal structure, the mol-ecules are linked into chains along the a axis by N-H⋯O hydrogen bonds.