Homocoupling Products Research Articles

Stable Mono- and Dinuclear Organosilver Complexes

A series of mononuclear and dinuclear complexes of silver(I), supported by an N-heterocyclic carbene and bound to sp3-, sp2-, and sp-hybridized carbanions, has been synthesized. Synthetic routes include transmetalation from organozinc, organomagnesium, and organosilicon reagents, as well as the deprotonation of a terminal alkyne. These complexes exhibit greater thermal stability than typical organosilver reagents, permitting spectroscopic and structural characterization. The carbanion-bridged disilver cations feature three-center, two-electron bonding with short Ag···Ag distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO2 to form silver carboxylates.

ChemInform Abstract: Stereospecific Synthesis of Unsymmetrical (E)‐ and (Z)‐1,2‐difluorostilbenes.

AbstractThe title stilbenes are stereospecifically obtained using dioxane as solvent.

Chromium-Catalyzed Cross-Coupling Reactions of Alkylmagnesium Reagents with Halo-Quinolines and Activated Aryl Chlorides

An efficient protocol for chromium(III)-catalyzed C(sp2)–C(sp3) cross-coupling is reported. The alkylations of halo-quinoline and phenacyl derivatives proceed at room temperature within minutes using the tetrahydrofuran-soluble chromium(III) complex CrCl3·3THF. The reactions occur without the formation of homo-coupling side products, which are common for the related iron-, cobalt- or manganese-catalyzed cross-coupling reactions.

Stereospecific synthesis of unsymmetrical (E)- and (Z)-1,2-difluorostilbenes

Abstract The synthesis of 1,2-difluorostilbenes via a Susuki reaction using a benzene/ethanol/water solvent mixture required long reaction times and generated significant quantities of a homo-coupled boronic acid product, which was difficult to separate. Therefore, we attempted 1,4-dioxane as a solvent for these reactions, which showed remarkable increased reaction rates and minimized the amount of homo-coupled products to aid in purification. Both ( E )- and ( Z )-1-chloro-1,2-difluorostyrenes stereospecifically gave the 1,2-difluorostilbenes in moderate to excellent yields. We investigated 4 protocols for the reaction. Protocols 2 and 3 were recommended for scale up, since the chlorostyrene starting material can be obtained in large quantities stereospecifically as described in previous reports. This work represents the first practical synthesis of unsymmetrical ( E )- and ( Z )-1,2-difluorostilbenes from readily available starting materials.

Directly Oxidative Cross-Coupling between Alkenylzirconocene and Alkynylcopper Reagents

External oxidant-free oxidative cross-coupling between alkenylzirconocene and alkynylcopper reagents has been achieved, which provides a new method for the selective synthesis of highly substituted enynes. In this reaction, no homocoupling products were observed.

Unsaturated fatty acid esters metathesis catalyzed by silica supported WMe5

Metathesis of unsaturated fatty acid esters (FAEs) by silica supported multifunctional W-based catalyst is disclosed. This transformation represents a novel route towards unsaturated di-esters. Especially, the self-metathesis of ethyl undecylenate results almost exclusively on the homo-coupling product whereas with such catalyst, 1-decene gives ISOMET (olefinisomerization and metathesis) products. The olefin metathesis in the presence of esters is very selective without any secondary cross-metathesis products demonstrating that a high selective olefin metathesis could operate at 150°C. Additionally, a cross-metathesis of unsaturated FAEs and α-olefins allowed the synthesis of the corresponding ester with longer hydrocarbon skeleton without isomerisation.

ChemInform Abstract: Oxidative Homocoupling of Diheteroaryl‐ or Diarylmanganese Reagents Generated via Directed Manganation Using TMP2Mn.

We report an oxidative homocoupling of diheteroaryl or diarylmanganese reagents prepared by directed manganation using TMP2Mn·2MgCl2·4LiCl. The resulting diorganomanganese reagents can efficiently undergo an oxidative dimerization leading to the homocoupling products in good yields. Remarkably, a number of functional groups, as well as sensitive heterocycles are tolerated using this metalation–dimerization procedure.

Sonogashira cross-coupling on the Au(1 1 1) and Au(1 0 0) facets of gold nanorod catalysts: Experimental and computational investigation

The catalytic activity of well-defined gold nanorods enclosed by Au(111) and Au(100) surfaces is investigated for the Sonogashira cross-coupling reaction between phenylacetylene and 4-iodoanisole, which gives rise to two homo-coupling products (diphenyldiacetylene, PhCCCCPh and 4,4′-dimethoxy-1,1′-biphenyl, MeOC6H4C6H4OMe) and a cross-coupling product (1-methoxy-4-(2-phenylethynyl)benzene, PhCCC6H4OMe). This study shows that shorter nanorods (∼33nm) with a higher percentage of Au(111) surface are considerably more selective toward the cross-coupling product (57% conversion with 90% selectivity). The selectivity of longer nanorods (e.g., 42 and 50nm) with a higher percentage of Au(100) surface, as well as of corresponding shapeless gold nanoparticles (e.g., 2–4 and 20nm), is found to be less than 59%. The catalytic mechanism of the homo- and cross-coupling reactions, in particular, roles played by Au(100) and Au(111) surfaces, is examined via DFT simulation. It is found that iodobenzene adsorption, CI bond dissociation, reactant surface diffusion, and coupling reactions are more favorable on Au(111) than on Au(100). This work demonstrates the gold facet effect on catalytic coupling reactions, and the combined approach of experiment and theory permits mechanistic understanding at the molecular level.

ChemInform Abstract: Reductive Homocoupling of Benzylic Halides in Aqueous Medium Using Recyclable Alumina‐Supported Nickel Nanoparticles.

Abstract An economical aqueous protocol for the synthesis of bibenzyls has been developed using easily accessible alumina-supported nickel nanoparticles as a stable recyclable heterogeneous catalyst in the presence of hydrazine hydrate as a co-reductant. Various sensitive moieties like alkoxycarbonyl, methylenedioxy, benzyl, chloro, bromo and nitro were tolerated in the aforesaid method. Besides primary benzylic halides, secondary and tertiary benzylic halides reacted efficiently to furnish the homocoupling products without any elimination.

ChemInform Abstract: Cu‐Catalyzed Aerobic Oxidative Three‐Component Coupling Route to N‐Sulfonyl Amidines via an Ynamine Intermediate.

Cu-catalyzed aerobic oxidative three-component coupling of a terminal alkyne, secondary amine, and sulfonamide enables efficient synthesis of amidines. The use of Cu(OTf)2 (5 mol %) produces amidines selectively without Glaser–Hay alkyne homocoupling products. Preliminary studies suggest that the reaction pathway involves initial oxidative coupling of the terminal alkyne with the secondary amine, followed by hydroamidation of the ynamine intermediate with the sulfonamide.

Oxidative Homocoupling of Diheteroaryl- or Diarylmanganese Reagents Generated via Directed Manganation Using TMP2Mn

We report an oxidative homocoupling of diheteroaryl or diarylmanganese reagents prepared by directed manganation using TMP₂Mn·2MgCl₂·4LiCl. The resulting diorganomanganese reagents can efficiently undergo an oxidative dimerization leading to the homocoupling products in good yields. Remarkably, a number of functional groups, as well as sensitive heterocycles are tolerated using this metalation–dimerization procedure.

A Graphite Powder Cavity Cell as an Efficient Tool of Sustainable Chemistry: Electrocatalytic Homocoupling of 2-Halopyridines

A new electrochemical synthetic method for the transition metal-catalyzed homocoupling of 2-halopyridinic compounds into symmetrical 2,2’-bipyridines is described. Experiments were carried out in a cavity cell under various reaction conditions, using a nickel complex as catalyst, and controlled-potential or constant-current electrolyses. A graphite powder/carbon nanotube 9:1 ratio mixture proved to constitute the optimal cathode material. Excellent homocoupling product yields were observed using aqueous KCl solution as anolyte. The cathode material proved to be recyclable with possible reuse three times without notable loss of activity.

Reductive homocoupling of benzylic halides in aqueous medium using recyclable alumina-supported nickel nanoparticles

An economical aqueous protocol for the synthesis of bibenzyls has been developed using easily accessible alumina-supported nickel nanoparticles as a stable recyclable heterogeneous catalyst in the presence of hydrazine hydrate as a co-reductant. Various sensitive moieties like alkoxycarbonyl, methylenedioxy, benzyl, chloro, bromo and nitro were tolerated in the aforesaid method. Besides primary benzylic halides, secondary and tertiary benzylic halides reacted efficiently to furnish the homocoupling products without any elimination.

Ligand-promoted oxidative cross-coupling of aryl boronic acids and aryl silanes by palladium catalysis.

The first cross-coupling reaction between aryl silanes and aryl boronic acids is described. This transformation represents one of the very few examples of coupling reactions between two nucleophilic organometallic reagents and provides a new method for the formation of biaryl compounds. The successful development of this reaction was enabled by the use of commercially available 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) as the ligand. A small amount of BINAP (3 mol %) was sufficient to suppress the formation of the homocoupling products, and the reaction yielded the cross-coupling products with high selectivity under mild conditions, even when the ratio of the two coupling partners was 1:1.

Ligand‐Promoted Oxidative Cross‐Coupling of Aryl Boronic Acids and Aryl Silanes by Palladium Catalysis

AbstractThe first cross‐coupling reaction between aryl silanes and aryl boronic acids is described. This transformation represents one of the very few examples of coupling reactions between two nucleophilic organometallic reagents and provides a new method for the formation of biaryl compounds. The successful development of this reaction was enabled by the use of commercially available 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) as the ligand. A small amount of BINAP (3 mol %) was sufficient to suppress the formation of the homocoupling products, and the reaction yielded the cross‐coupling products with high selectivity under mild conditions, even when the ratio of the two coupling partners was 1:1.

Cu-catalyzed aerobic oxidative three-component coupling route to N-sulfonyl amidines via an ynamine intermediate.

Cu-catalyzed aerobic oxidative three-component coupling of a terminal alkyne, secondary amine, and sulfonamide enables efficient synthesis of amidines. The use of Cu(OTf)2 (5 mol %) produces amidines selectively without Glaser-Hay alkyne homocoupling products. Preliminary studies suggest that the reaction pathway involves initial oxidative coupling of the terminal alkyne with the secondary amine, followed by hydroamidation of the ynamine intermediate with the sulfonamide.

Amino acid derived CuII compounds as catalysts for asymmetric oxidative coupling of 2-naphthol.

We report the synthesis and characterization of several novel aminopyridine - L-amino acid derived Cu(II)-complexes. The ligands are prepared by a one-pot reductive alkylation of the L-amino acid scaffold and the respective aminopyridine Cu(II)-complexes were obtained by reaction with CuCl2 or Cu(acetato)2. All compounds were characterized by spectroscopic techniques, as well as ESI-MS. Two of the Cu(II)-complexes were characterized by single-crystal X-ray diffraction, one of them, [Cu(II)(L)(CH3COO)] (HL = (S)-3-phenyl-2-(pyridin-2-ylmethylamino)propanoic acid), being the first ever reported aminopyridine-class Cu(II) complex bearing a tridentate N,N,O donor set and a monodentate acetato ligand. The complexes are tested as catalysts in the oxidative coupling of 2-naphthol in organic solvent-water mixtures using dioxygen as the terminal oxidant. The effect of variables such as ligand denticity and substituents, as well as solvent, temperature and oxidant intake, on the overall performance is studied. In general, moderate to low conversions of 2-naphthol to 1,1'-bi-2-naphthol (BINOL) are obtained. The catalysts also showed moderate to low enantioselectivity. Some aspects of the reaction mechanism were elucidated by spectroscopy, electrochemical and theoretical studies. It was found that basic additives are important for activity, but these also increase the formation of secondary oxidation products. The addition of peroxide scavengers such as KI resulted in an increase of conversion, the yield of BINOL and enantioselectivity.

Catalytic hydrodechlorination of benzyl chloride promoted by Rh-N-heterocyclic carbene catalysts.

The rhodium(I) complexes [Rh(Cl)(COD)(R-NHC-(CH2 )3 Si(OiPr)3 )] [COD=cyclooctadiene; R=2,6-diisopropylphenyl (1 a); n-butyl (1 b)] are effective catalyst precursors for the homogeneous hydrodechlorination of benzyl chloride using HSiEt3 as hydrogen source. This reaction is selective to the formation of toluene. However, in presence of a stoichiometric amount of potassium tert-butoxide (KtBuO) the formation of mixtures containing toluene together with 17-19 mol % of the C--C homocoupling product, namely PhCH2 CH2 Ph, is observed. A mechanism proposal based on experimental insights and theoretical calculations at the DFT level that allows explanation of the experimental findings is included. Moreover, the heterogeneous catalytic system based on catalyst 1 a supported on MCM-41 has been demonstrated to be effective for the solvent-free hydrodechlorination of benzyl chloride using HSiEt3 and HSiMe(OSiMe3 )2 .

Synthesis of substituted naphthalenes by GaCl3-mediated cross-dimerization—fragmentation of 2-arylcyclopropane-1,1-dicarboxylates

Substituted naphthalenes were obtained by treatment of a mixture of two different 2-arylcyclopropane-1,1-dicarboxylates with GaCl3 at 80 ℃. The process is accompanied by removal of the malonic moieties, naphthalene fragments being mainly formed from the arylcyclopropane, which is more prone to give the similar homocoupling product.

Csp3-csp3 homocoupling reaction of benzyl halides catalyzed by rhodium.

A highly reactive alkylrhodium complex was formed from Me(2)Zn and RhCl(PPh(3))(3) and effectively catalyzed a Csp(3)-Csp(3) homocoupling reaction of benzyl halides. A Csp(3)-Csp(3) coupling reaction using Rh catalyst has not been reported up to now. The reaction proceeded under very mild conditions and gave the corresponding homocoupling products even if they had reactive substituents such as an uncovered formyl or hydroxymethyl group.