Stabilized well-dispersed Pd(0) nanoparticles for aminocarbonylation of aryl halides

Well-dispersed palladium (0) nanoparticles stabilized with phosphonium based ionic liquid were synthesized conveniently and fully characterized. A catalyst system comprising of the Pd(0) nanoparticles and a base was found to be recyclable and efficient for the aminocarbonylation reaction of aryl iodide in ionic liquid media. In the presence of potassium tert-butyloxide, for the relatively stable aryl chloride and bromide substrates, medium activities were achieved for the catalyst. The catalyst composites can be recycled at least five times with sustained activity.     

Polyethylene glycol (PEG) promoted hydrodehalogenation of aryl halides

Transition-metal-free hydrodehalogenation of aryl halides (eg. bromides) can take place efficiently in the presence of green polyethylene glycol (PEG-800) and t-BuOK without adding any extra solvents and additives. A radical mechanism is proposed for this transition-metal-free dehalogenation of aryl halides and the role of polyethylene glycol is both reaction promotor and activated alkyl CH donor.     

Cobalt-catalyzed electrochemical vinylation of aryl halides using vinylic acetates

The electroreduction of aryl halides (bromides or chlorides) allows the coupling reaction with vinylic acetates, in the presence of 2,2-bipyridine and catalytic amounts of cobalt bromide, leading to styrene derivatives in good yields.     

Room temperature dehalogenation of (hetero)aryl halides with magnesium/methanol

Magnesium in methanol was found to be an effective and inexpensive reagent for the dehalogenation of (hetero)aryl chlorides, bromides and iodides under mild conditions. The halogen/hydrogen exchange proceeded at room temperature and tolerated functional groups such as esters, nitriles, alcohols, and alkenes.     

Solvent-free palladium-catalyzed CO cross-coupling of (hetero)aryl halides with primary alcohols

A new efficient solvent-free procedure for the CO cross-coupling between (hetero)aryl halides with phenols, primary alkanols, or (hetero)arylmethanols using Pd₂(dba)₃/Bu^tBrettPhos catalytic system is proposed using 23 examples.     

Cross-coupling of alkynylsilanols with aryl halides promoted by potassium trimethylsilanolate

The palladium-catalyzed cross-coupling of aliphatic alkynylsilanols with aryl iodides has been demonstrated with potassium trimethylsilanolate as the coupling promoter and copper(I) iodide as a cocatalyst. The cross-coupling proceeds at room temperature in good to excellent yield with a range of aryl iodides. A comparison of the reactivity of alkynylsilanols, trimethylsilylalkynes, and terminal alkynes under fluoride and fluoride-free conditions was performed to elucidate the role of silicon in the Sonogashira reaction.     

Cobalt-catalyzed low pressure double carbonylation of aryl and secondary benzyl halides

α-Ketoacids can be easily synthesized with satisfactory yields and selectivities by carbonylation of aryl halides and secondary benzyl halides under very mild conditions. The reactions are catalyzed by Co₂(CO)₈ in alcoholic solvents; the presence of a methyl source (dimethyl sulfate or methyl iodide) is necessary for the carbonylation of the aryl halides. Base, temperature and solvent have large effects on the course of the reaction.     

Porous polymeric ligand promoted copper-catalyzed C-N coupling of(hetero)aryl chlorides under visible-light irradiation

A porous polymeric ligand(PPL)has been synthesized and complexed with copper to generate a heterogeneous catalyst(Cu@PPL)that has facilitated the efficient C-N coupling with various(hetero)aryl chlorides under mild conditions of visiblelight irradiation at 80°C(58 examples,up to 99%yields).This method could be applied to both aqueous ammonia and substituted amines,and is compatible to a variety of functional groups and heterocycles,as well as allows tandem C-N couplings with conjunctive dihalides.Furthermore,the heterogeneous characteristic of Cu@PPL has enabled a straightforward catalyst separation in multiple times of recycling with negligible catalytic efficiency loss by simple filtration,affording reaction mixtures containing less than 1 ppm of Cu residue.     

Synthesis of aryl azides from aryl halides promoted by Cu2O/tetraethylammonium prolinate

An efficient approach to aryl azides, in short reaction times and good to excellent yields, has been developed via the reaction of aryl halides with sodium azide under Cu₂O/tetraethylammonium prolinate catalysis.     

Synthesis of primary aromatic amides by aminocarbonylation of aryl halides using formamide as an ammonia synthon

Primary aromatic amides were prepared by a palladium-catalyzed aminocarbonylation reaction of aryl halides in high yields (70-90%) using formamide as the amine source. The reactions require a palladium catalyst in combination with a nucleophilic Lewis base such as imidazole or 4-(dimethylamino)pyridine (DMAP). Aryl, heteroaryl, and vinyl bromides and chlorides were converted to the primary amides under mild conditions (5 bar, 120 degrees C) using 1 mol % of a palladium-phosphine complex. Best results were obtained in dioxane using triphenylphosphine as the ligand and DMAP as the base. For activated aryl bromides, a phosphine-to-palladium ratio of 2:1 was sufficient, but less reactive aryl bromides or aryl chlorides required ligand-to-palladium ratios up to 8:1 in order to stabilize the catalyst and achieve full conversion. The influence of catalyst, base, solvent, pressure, and temperature was studied in detail. The mechanism of the reaction could be clarified by isolating and identifying the reaction intermediates. In addition, methylamides and dimethylamides were prepared by the same method using N-methylformamide and N,N-dimethylformamide as the amine source.     

Mild and efficient Pd(PtBu3)2‐catalyzed aminocarbonylation of aryl halides to aryl amides with high selectivity

This work describes a mild and efficient approach for the synthesis of aryl amides via catalytic aminocarbonylation of aryl halides with alicyclic amines using a Pd(P^t Bu₃)₂/NH₄Cl catalyst system. Under mild reaction temperature of 60°C and balloon pressure of CO, 5 mol% Pd(P^t Bu₃)₂ with a cheap NH₄Cl promoter is sufficient for high yields of aryl amides. The influence of reaction parameters such as reaction temperature, ligand type and promoter on catalytic activity was investigated. This work also discusses the catalytic intermediates in detail, and provides a plausible mechanism based on an acid chloride intermediate.     

Cobalt-catalyzed chemoselective dehydrogenation through radical translocation under visible light

The transformations that allow the direct removal of hydrogen from their corresponding saturated counterparts by the dehydrogenative strategy are a dream reaction that has remained largely underexplored. In this report, a straightforward and robust cobaloxime-catalyzed photochemical dehydrogenation strategy via intramolecular HAT is described for the first time. The reaction proceeds through an intramolecular radical translocation followed by the cobalt assisted dehydrogenation without needing any other external photosensitizers, noble-metals or oxidants. With this approach, a series of valuable unsaturated compounds such as α,β-unsaturated amides, enamides and allylic and homoallylic sulfonamides were obtained in moderate to excellent yields with good chemo- and regioselectivities, and the synthetic versatility was demonstrated by a range of transformations. And mechanistic studies of the method are discussed.

The dehydrogenative reactions proceeded through selective 1,n-hydrogen atom transfer (n = 5–7) for remote C–H activation by cobaloxime catalysis.     

Palladium-catalyzed carbon-monoxide-free aminocarbonylation of aryl halides using N-substituted formamides as an amide source

A carbon-monoxide-free aminocarbonylation of various N-substituted formamides with aryl iodides and aryl bromides using palladium acetate and Xantphos is described. The developed methodology is applicable for a wide range of formamides and aryl halides containing different functional groups furnishing good to excellent yield of the corresponding products. N-substituted formamides are used as an amide source wherein a Vilsmeier-type intermediate plays a major role, thus eliminating the need of toxic carbon monoxide gas.     

Water oxidation reaction promoted by MIL-101(Fe) photoanode under visible light irradiation

This work spotlights the recently discovered photoelectrocatalytic properties of iron-based metal–organic frameworks (MOFs) for water oxidation reaction (WOR) under visible light irradiation. The low efficiency of WOR is one of the biggest difficulties faced by photoelectrochemical solar energy conversion; the development of new photoanodes for WOR is greatly desired. In view of the fact that a higher efficiency for WOR was forecast thanks to the peculiar properties of MOFs, such as a highly ordered framework and homogenous porous structure, the photoelectrodes based on MIL-101(Fe) containing photo-active iron(III) clusters have been fabricated by using a drop-casting method and applied to photoelectrochemical water oxidation as photoanodes. XRD measurements revealed the successful formation of MIL-101(Fe) electrodes while retaining their framework structures. From the results of photoelectrochemical measurements, the optimal thickness of the MIL-101(Fe) electrodes was determined to be ca. 60 μm, and the optimized MIL-101(Fe) electrode was found to promote photoelectrochemical WOR under visible light irradiation more efficiently than conventional α-Fe₂O₃ electrodes. Moreover, electrochemical impedance spectroscopy measurements demonstrated a lower resistance of charge transfer at the interface between the MOF surface and the electrolyte, resulting in better photoelectrochemical performance of the MIL-101(Fe) electrode.     

Cs2CO3 in pyrrolidinone promoted hydration of functionalized (hetero)aryl nitriles under metal-free conditions

An efficient hydration reaction of various (hetero)aryl nitriles using Cs₂CO₃ in pyrrolidinone is described. This new metal-free protocol proved to be highly effective and general to synthesize a variety of (hetero)aryl amides.     

Nickel‐catalyzed aminocarbonylation of aryl halides with carbamoylsilanes: efficient synthesis of secondary (primary) aromatic amides

A nickel‐catalyzed aminocarbonylation of aryl halides using carbamoylsilane as an amide source leading to corresponding secondary or primary aromatic amides has been developed, in which the methoxymethyl and benzyl were used as amino protecting group. The protocol tolerates a broad range of aryl halides bearing different functional groups to afford good yields of aryl amides under mild reaction conditions. The types and the relative positions of substituents on the aryl ring make a notable impact on the coupling efficiency. The plausible mechanism of nickel‐catalyzed aminocarbonylation has been suggested.     

Palladium-catalyzed decarboxylative coupling of quinolinone-3-carboxylic acids and related heterocyclic carboxylic acids with (hetero)aryl halides

An efficient and practical decarboxylative cross-coupling reaction of quinolin-4(1H)-one 3-carboxylic acids with (hetero)aryl halides has been established. Under a bimetallic system of PdBr(2) and silver carbonate, the protocol proved to be general, and a variety of 3-(hetero)aryl 4-quinolinones and related heterocycles, such as 3-aryl-1,8-naphthyridin-4(1H)-ones, 3-arylcoumarins, 3-arylquinolin-2(1H)-ones, and 2-arylchromones, can be prepared in good to excellent yields.     

Ethanol‐promoted reductive homocoupling reactions of aryl halides catalyzed by palladium on carbon (Pd/C)

Homocoupling reactions of aryl bromides or iodides proceeded smoothly with palladium on carbon (Pd/C) catalyst, ethanol and base in dimethyl sulfoxide (DMSO) to afford exclusively symmetric biaryls in good to excellent yields. Ethanol was first used as a reducing agent in situ to reduce the Pd²⁺/C species into Pd⁰/C active species to complete the catalytic redox cycle. It was found that ethanol can promote the Pd/C‐catalyzed reductive homocoupling of aryl iodides and bromides efficiently in the presence of base. A reaction mechanism has been put forward and discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Cobalt-catalyzed direct electrochemical cross-coupling between aryl or heteroaryl halides and allylic acetates or carbonates

The electroreduction of a mixture of functionalized aromatic or heteroaromatic bromides or chlorides and allylic compounds such as acetates or carbonates in an electrochemical cell fitted with a sacrificial iron anode affords, in the presence of cobalt halide associated with pyridine as ligand in acetonitrile or DMF, the corresponding coupling product in good yields.