Copper Co-catalyst Research Articles

Copper-free Sonogashira cross-coupling reaction catalyzed by polymer-supported N-heterocyclic carbene palladium complex

A core-shell type of polymer-supported N-heterocyclic carbene (NHC) palladium catalyst was applied to Sonogashira cross-coupling reactions without copper cocatalyst under ambient atmosphere. This supported NHC–palladium complex efficiently catalyzed the copper-free Sonogashira reaction of various aryl iodides and bromides with terminal alkynes; the reaction exhibited high dependency on the temperature and the amount of base as well as its nature. In addition, this heterogeneous catalyst exhibited good reusability for the copper-free Sonogashira reaction.

Nanocrystalline Magnesium Oxide Stabilized Palladium(0): An Efficient Heterogeneous Catalyst for Heck and Sonogashira Coupling of Aryl Halides

Nanocrystalline magnesium oxide supported palladium(0) catalyst [NAP-Mg-Pd(0)], prepared by the counter-ion stabilization of PdCl 4 2- followed by reduction with hydrazine hydrate, was effectively used in the Heck olefination of haloarenes (chloro, bromo, and iodo) to afford good to excellent yields of substituted olefins. This ligand-free heterogeneous NAP-Mg-Pd(0) catalyst was quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost no loss of activity. Moreover, NAP-Mg-Pd(0) efficiently catalyzed the Sonogashira coupling of haloarenes with terminal alkynes without any copper co-catalyst under milder conditions to afford excellent yields of substituted alkynes.

Synthesis of Pyrrolidines via Palladium(II)-Catalyzed Aerobic Oxidative Carboamination of Butyl Vinyl Ether and Styrenes with Allyl Tosylamides

[Structure: see text] Palladium(II) catalyzes the oxidative coupling of allyl tosylamides with butyl vinyl ether and various styrene derivatives to produce 2,4-substituted pyrrolidine products at room temperature. Molecular oxygen together with a copper(II) cocatalyst mediates reoxidation of the palladium catalyst. The reactions with styrene substrates can be performed in an open flask with ambient air as the source of O2. Several nontraditional cocatalysts, including catechol, cyclooctadiene, and methyl acrylate, have a beneficial effect on the reactions.

Copper‐ and Ligand‐Free Sonogashira Reaction Catalyzed by Pd(0) Nanoparticles at Ambient Conditions under Ultrasound Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Aryl alkynylation versus alkyne homocoupling: unprecedented selectivity switch in Cu, phosphine and solvent-free heterogeneous Pd-catalysed couplings

Sonogashira reaction and oxidative dimerisation of terminal alkynes are among the most relevant and attractive C–C bond forming transformations in the metallo-catalysed cross-coupling scenario. Often, the homocoupling reactions of substituted acetylenic derivatives are concomitant to the Sonogashira pathway and time-consuming optimization procedures are required in order to reach satisfactory levels of selectivity. In this paper, the potential of a class of Pd-complexes loaded to mesoporous silica gel in promoting the Sonogashira reaction between aryl acetylenes and iodoarenes is underlined. This family of heterogeneous organo-palladium systems allows the desired cross-coupled compounds to be isolated in excellent yield under very mild conditions. In fact, the absence of organic solvents, copper(I) co-catalyst and phosphane ligands, (which are easily oxidisable and whose preparation has a heavy environmental impact), in conjunction with the low catalyst loading ([Pd] 0.1–1 mol%) and its recoverability, stresses the environmental benefits of the protocol. The Sonogashira/homocoupling selectivity proved to be function of the haloarene employed. As a matter of fact, while iodoarenes bearing EWG (electron withdrawing groups) on the phenyl ring underwent smoothly the Sonogashira pathway, electron-rich iodobenzenes showed opposite behaviour by mainly furnishing the homocoupling product. The use of bromoarenes provided solely the homocoupling product in excellent yield without themselves being consumed. This is despite that fact that the catalysts used activate bromoarenes equally as well as iodoarenes in both Heck and Suzuki systems. Kinetic investigations revealed a highly temperature-dependent profile, which indicates strongly that the reaction takes place at the surface. Finally, the full heterogeneous character of the catalytically active species as well as the reusability of the immobilised Pd-complex were confirmed by hot-filtration test and by multiple reuses of the supported catalyst in subsequent Sonogashira cross-couplings.

Copper- and Ligand-Free Sonogashira Reaction Catalyzed by Pd(0) Nanoparticles at Ambient Conditions under Ultrasound Irradiation

The Sonogashira reaction proceeds at ambient temperature (30 degrees C) in acetone or room-temperature ionic liquid, 1,3-di-n-butylimidazolium tetrafluoroborate ([bbim]BF4), as solvent under ultrasound irradiation to give enhanced reaction rates, excellent chemoselectivity, and high yields in the absence of a copper cocatalyst and a phosphine ligand. TEM analysis showed the formation of stable, crystalline, and polydispersed Pd(0) nanoparticles as catalyst for the reaction.

Efficient Palladium‐Catalyzed Coupling of Aryl Chlorides and Tosylates with Terminal Alkynes: Use of a Copper Cocatalyst Inhibits the Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Copper‐Free, Recoverable Dendritic Pd Catalysts for the Sonogashira Reaction.

Three generations of bidentate phosphinated Pd(II) dendrimers are efficient catalysts in the absence of copper co-catalyst for the Sonogashira reaction and are, with two cyclohexyl substituents on the phosphorus atoms, recovered by precipitation and re-used.

Efficient Palladium‐Catalyzed Coupling of Aryl Chlorides and Tosylates with Terminal Alkynes: Use of a Copper Cocatalyst Inhibits the Reaction

Less catalyst, lower temperature, and greater generality are the advantages of the new general protocol over those previously described for the palladium-catalyzed coupling of aryl chlorides and alkynes (see scheme). Better results are obtained without a copper cocatalyst, which has been found to inhibit product formation in the coupling reaction of aryl chlorides with terminal alkynes.

Efficient Palladium‐Catalyzed Coupling of Aryl Chlorides and Tosylates with Terminal Alkynes: Use of a Copper Cocatalyst Inhibits the Reaction

Efficient Palladium‐Catalyzed Coupling of Aryl Chlorides and Tosylates with Terminal Alkynes: Use of a Copper Cocatalyst Inhibits the Reaction

Palladium-Catalyzed Carbonylation of Homoallylic Amine Derivatives in the Presence of a Copper Co-catalyst

Abstract γ-Lactams were synthesized from N-tosylhomoallylamines by a carbonylation reaction catalyzed by palladium and copper salts under the normal pressure of CO and O2 at room temperature. Monocarbonylation proceeded by the use of [PdCl2(CH3CN)2] and CuCl2 to afford 3-methyl-2-pyrrolidones, while the use of PdCl2 and CuCl switched the reaction from monocarbonylation to dicarbonylation to produce alkyl 2-oxopyrrolidine-3-acetate in good yields, respectively.

Copper-free, recoverable dendritic Pd catalysts for the Sonogashira reaction.

Three generations of bidentate phosphinated Pd(II) dendrimers are efficient catalysts in the absence of copper co-catalyst for the Sonogashira reaction and are, with two cyclohexyl substituents on the phosphorus atoms, recovered by precipitation and re-used.

Transition metal control in the reaction of alkyne-substituted phenyl iodides with terminal alkynes: Sonogashira coupling vs cyclic carbopalladation

Reaction between terminal alkynes and phenyl iodides bearing a tethered alkyne unit can be effectively controlled by the nature of a transition metal catalyst. Whereas the use of Pd(0)/Cu(I) promotes the expected Sonogashira coupling to give phenyl alkynes, the absence of the copper co-catalyst triggers a palladium-mediated cyclisation providing 1,2-dihydroacenaphthylene, 1 H,3 H-benzo[ de]isochromene, (1 Z)-1-(2-propynylidene)-2,3-dihydro-1 H-indene and (4 E)-4-(2-propynylidene)-3,4-dihydro-1 H-isochromene derivatives. In the latter Pd-catalysed two-component process, the product distribution depends on the structure of alkyne-substituted phenyl iodides, terminal alkynes and secondary amines used as solvents. The proposed reaction mechanism reflects a competitive formation of intermediary σ-(acetylide) vs π-alkyne Pd(II) complexes.

Polynaphthalene Networks from Bisphenols

Enediynes were first studied by Bergman and are known to undergo thermal intramolecular cyclization to benzene 1,4diradical or “dehydroaromatic” intermediates.1 While the primary impetus for enediyne research remains focused on their biological activity as antitumor agents,2 others have reported using enediynes in a polymerization scheme.3,4 Tour detailed the synthesis of linear poly(phenylenes) and poly(naphthalenes) by thermolysis of substituted enediynes and 1,2-dialkynylbenzenes (Scheme 1).3 This work extended earlier accounts4 and revealed the Bergman cyclization as a viable polymerization reaction in detail. Polynaphthalenes prepared by Bergman cyclopolymerization to date have been limited to linear systems of soluble, low molecular weight oligomers with fair thermal stability, or high molecular weight polymers exhibiting exceptional thermal stability yet are insoluble and not easily processed.3,4 In addition, the preparation of 1,2-dialkynyl monomers is typically accomplished by the palladium-catalyzed coupling of terminal alkynes with difficult to prepare 1,2-dibromo or -diiodo aromatics.3-5 We have found, however, that bis(o-di(phenylethynyl)phenyl) monomers 1-4 (Scheme 2) overcome both monomer synthetic obstacles and the processability/performance “tradeoff” issues common to linear polyarylenes.6 We have developed a general multi hundred gram preparation of these compounds in three steps from commodity starting materials and reagents. When heated, monomers 1-4 undergo Bergman cyclopolymerization to reactive oligomers which can be melt or solution processed and thermally cured providing a new class of polynaphthalene networks. Other polymers containing naphthalene linkages are also known.7 Our polynaphthalene networks were designed specifically to replace current dielectric materials used in integrated circuits.8 Monomer intermediates were prepared by selective o-bromination followed by quantitative trifluoromethanesulfonate (triflate) esterification of the corresponding bisphenols and gave aryl dibromide ditriflate intermediates in good yield (>75%). Sonogoshira-type9 palladium coupling with phenylacetylene produced tetraynes 1-4 in isolated yields usually >80% (Scheme 2).10 Our method does not use a copper cocatalyst, common to aryl alkyne couplings, thereby eliminating the potentially hazardous formation of copper acetylide.11 All monomers were isolated as lightly colored crystalline solids with sharp melting points (Table 1). Neat exothermic polymerizations of 1-4 are detected by differential scanning calorimetry (DSC, 10 °C/min) at 200-210 °C, giving reaction profiles consistent with known phenylsubstituted aryldiynes.4 For example, the polymerization of 1,2,4,5-tetrakis(phenylethynyl)benzene and poly(arylene-1,2-ethynylene) each containing four acetylene linkages, gave a DSCmeasured -∆H ) 29 kcal/mol alkyne, whereas the thermolysis of 1-3 gave -∆H ) 27, 29, and 27 kcal/mol alkyne, respectively. Fluorenyl monomer 4 exhibited a significantly lower -∆H ) 18 kcal/mol alkyne, due to incomplete conversion. Bergman cyclopolymerization kinetics, and thus rheological properties, are controlled by tetraphenyl substitution and provide

Oxidation of olefins to aldehydes using a palladium–copper catalyst

The oxidation of terminal olefins with palladium salts usually affords methyl ketones.1–3 However, in 1986 it was reported that aldehydes could be obtained using a catalyst comprising (CH3CN)2Pd(NO2)Cl and CuCl2 in t-butanol solvent, which was proposed to be bimetallic with the NO2 group intact.4 Our studies suggest that this catalyst is best described as a Wacker-like oxidation catalyst modified by an alkyl nitrite, and we report an improved version of this catalyst. Moreover, the application of our system to the oxidation of terminal olefins with allylic substituents has led to some insight as to the potential role of the copper co-catalyst in Wacker-like reactions.

A practical system for manganese(III)-mediated electrochemical synthesis of sorbic acid precursors

An efficient, practical, electrochemical system was developed for the synthesis of a mixture of 4-acetoxy-5-hexenoic acid and trans-6-acetoxy-4-hexenoic acid via manganese (III)-mediated oxidation of acetic acid-acetic anhydride in the presence of butadiene. Copper (II) co-catalyst enhanced the efficiency of this oxidation and copper (I) was shown to catalyze in situ conversion of the acetoxyhexenoic acids into γ-vinyl-γ- butyrolactone.

Grafting of wool with vinyl monomers by using trichloroacetic acid–bis(acetonylacetonato)‐copper(II) cocatalyst

AbstractGraft copolymerization of wool with methyl methacrylate (MMA) and acrylonitrile (AN) was effected under the catalytic influence of trichloroacetic acid (TCA) together with bis(acetonylacetonato)copper(II). Investigation of the action of the cocatalyst on wool in the absence of monomer revealed that the treated wool is completely soluble in dilute alkali. The effect of storage on the catalyzed wool was also studied. Increasing the period of storage, before adding the monomer, causes a significant decrease in the graft yields, indicating vitiation of some of the free radicals on the wool backbone. Based on these studies, a mechanism for the grafting reaction was proposed. Moreover, grafting of wool modified through its disulfide bonds and amino and hydroxyl groups suggests that the thiol, hydroxyl, and amino groups participate in the grafting reaction as sites for graft attachment. Wool—graft copolymers show excellent antifelt properties, particularly at higher levels of grafting.