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Relevant academic research and scientific papers

A terphenyl phosphine as a highly efficient ligand for palladium-catalysed amination of aryl halides with 1° anilines

A terphenyl phosphine ligand (2,6-bis(2,4,6-triisopropylphenyl)phenyl-dicyclohexylphosphine, TXPhos) and its supported palladium complex [(TXPhos)(allyl)PdCl] have been developed and the catalyst system is highly efficient in amination of aryl halides with 1° anilines, especially effective for densely functionalized substrates including both partners possessing ortho-ester, acetyl, nitrile and nitro groups. With the TXPhos-supported catalyst system, many partner combinations have been unprecedentedly realized and the base scope has been even extended to KOAc, which is even the best choice in the amination of 2-nitrochlorobenzene.

Light-Promoted C–N Coupling of Aryl Halides with Nitroarenes

A photochemical C–N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step-economic extension to the widely used Buchwald–Hartwig C–N coupling reaction. The method tolerates coupling partners with steric-congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI/NiIII cycle, to a nitrosoarene intermediate.

Modified graphene supported Ag-Cu NPs with enhanced bimetallic synergistic effect in oxidation and Chan-Lam coupling reactions

Herein, well dispersed Ag-Cu NPs supported on modified graphene have been synthesized via a facile and rapid approach using sodium borohydride as a reducing agent under ambient conditions. Dicyandiamide is selected as an effective nitrogen source with TiO2 as an inorganic material to form two kinds of supports, labelled as TiO2-NGO and NTiO2-GO. Initially, the surface area analysis of these two support materials was carried out which indicated that N-doping of GO followed by anchoring with TiO2 has produced support material of larger surface area. Using both types of supports, ten nano-metal catalysts based on Ag and Cu were synthesized. Benefiting from the bimetallic synergistic effect and larger specific surface area of TiO2-NGO, Cu?Ag-TiO2-NGO is found to be a highly active and reusable catalyst out of other synthesized catalysts. It exhibits excellent catalytic activity for oxidation of alcohols and hydrocarbons as well as Chan-Lam coupling reactions. The nanocatalyst is intensively characterized by BET, SEM, HR-TEM, ICP-AES, EDX, CHN, FT-IR, TGA, XRD and XPS. This journal is

Palladate Precatalysts for the Formation of C-N and C-C Bonds

A series of imidazolium-based palladate precatalysts has been synthesized and the catalytic activity of these air- and moisture-stable complexes evaluated as a function of the nature of the imidazolium counterion. These precatalysts can be converted under

Nickel-catalyzed N-arylation of amines with arylboronic acids under open air

In this study, a well-defined, novel NHC-Ni complex was developed and used to catalyze the N-arylation of alkyl- and arylamines with arylboronic acids in a rare version of Chan-Lam coupling. Although the same coupling using copper catalysts has been widely studied, the nickel-catalyzed version is rare and normally requires 10–20 mol% catalyst loading. This novel NHC-Ni complex in combination with 4,4′-dimethyl-2,2′-bipyridine, however, proved to be an effective catalyst that lowered the required catalyst loading to only 2.0 mol%.

Diamines as interparticle linkers for silica-titania supported PdCu bimetallic nanoparticles in Chan-Lam and Suzuki cross-coupling reactions

A series of highly efficient amine functionalized SiO2-TiO2 supported bimetallic PdCu catalysts with varied metal composition have been synthesized. Ethane-1,2-diamine, butane-1,4-diamine and hexane-1,6-diamine were employed as interparticle linkers for amine functionalization of a SiO2-TiO2 support material so as to study the effect of pendant chain length on stabilization and immobilization of bimetallic nanoparticles. The shortest carbon chain length on the support provided the best results, which may be due to the trapping of metal nanoparticles more efficiently by the basic nitrogen sites. The catalytic activities of these materials were evaluated for C-N and C-C coupling reactions. The most active catalyst, Pd1Cu1@12DA-STS, was characterized by various techniques including SEM, HR-TEM, ICP-AES, XRD, FTIR, EDX, CHN analysis and TGA studies. Moreover, the synthesized catalyst was found to be recyclable for up to five runs without significant loss of activity.

Synergistic Ligand Effect between N-Heterocyclic Carbene (NHC) and Bicyclic Phosphoramidite (Briphos) Ligands in Pd-Catalyzed Amination

A synergistic ligand effect between NHC and phosphorus ligands in Pd-catalyzed Buchwald-Hartwig amination reactions was demonstrated with tunable π-acceptor bicyclic bridgehead phosphoramidite (briphos) ligands. The catalytic activity of NHC-Pd-L (L = phosphorus ligand) precatalysts depends on the electronic properties of L. A NHC-Pd-L catalyst with an N-cyclohexyl-substituted briphos ligand was found to be highly efficient. A series of C-N bond coupling reactions between primary or secondary amines and aryl chlorides were performed with high yields under mild reaction conditions.

Efficient and versatile buchwald-hartwig amination of (hetero)aryl chlorides using the Pd-PEPPSI-IPr(NMe2)2 precatalyst in the presence of carbonate base

The precatalyst Pd-PEPPSI-IPr(NMe2)2, in which the IPr ligand was modified by attachment of two dimethylamino groups on to the 4- and 5-positions of the imidazolyl heterocycle, was found to show high catalytic efficiency in the Buchwald-Hartwig amination under mild conditions using Cs2CO3 as a weak base, using a low catalyst loading of 1 mol-%. The protocol is applicable to aryl chlorides bearing base-sensitive substituents, as exemplified by the coupling of 4-chloroacetophenone with aniline. It can also be used with an unprecedentedly wide range of amines, including strongly basic secondary alkylamines, primary arylamines, and primary alkylamines. The Palladium precatalyst Pd-PEPPSI-IPr(NMe2)2, whose supporting N-heterocyclic carbene ligand was decorated with two dimethylamino groups, was found to catalyse the Buchwald-Hartwig amination of aryl halides with a wide range of amines under mild conditions using cesium carbonate as base.

Skeleton decoration of NHCs by amino groups and its sequential booster effect on the palladium-catalyzed Buchwald-Hartwig amination

A challenging synthetic modification of PEPPSI-type palladium pre-catalysts consisting of a stepwise incorporation of one and two amino groups onto the NHC skeleton was seen to exert a sequential enhancement of the electronic donor properties. This appears to be positively correlated with the catalytic performances of the corresponding complexes in the Buchwald-Hartwig amination. This is illustrated, for example, by the quantitative amination of 4-chloroanisole by morpholine within 2 h at 25°C with a 2 mol% catalyst/substrate ratio or by a significant reduction of catalytic loading (down to 0.005 mol%) for the coupling of aryl chlorides with anilines (max TON: 19600).

SYNTHESES OF N-HETEROCYCLIC CARBENES AND INTERMEDIATES THEREFOR

A method of preparing a 2,6 disubstituted anilines includes, reacting a 2-amino isophtha!ic acid diester with sufficient Grignard reagent R2CH2MgX to form the corresponding diol product, dehydrating the diol product to the corresponding dialkene; and hydrogenating the diol product to form the corresponding aniline. The 2,6 disubstituted anilines can be used to produce N-Heterocyciic Carbenes (NHCs). The NHCs can find application in various fields such as organic synthesis, catalysis and macromolecular chemistry. Palladium catalysts containing the NHCs are also described.