Ullmann-type Coupling Reactions Research Articles

On-Surface Synthesis within a Porphyrin Nanoring Template

On-surface synthesis provides a route for the production of 1D and 2D covalently bonded polymeric structures. Such reactions are confined to the surface of a substrate and the catalytic properties of the substrate are often utilised to initiate the reaction. Recent studies have focused on the properties of various crystallographic planes of metallic substrates, as well as native surface features such as step-edges, in an effort to provide control over the pathway of the reaction and the resultant products. An alternative approach is to template the catalytic surface with a porous molecular overlayer; giving rise to well-defined surface regions within which an on-surface reaction may be confined. Here we present a methodology where macromolecular templates are used to confine an on-surface reaction. Cyclic porphyrin polymers, nanorings - consisting of 40 porphyrin units with internal diameter 13 nm, are used to form a template on a Au(111) surface, and an on-surface Ullmann-type coupling reaction is initiated within the nanoring template. The surface confined template and covalently coupled reaction products are investigated and characterised with scanning tunnelling microscopy.

Synthesis of tri(di)fluoroethylanilines via copper-catalyzed coupling reaction of tri(di)fluoroethylamine with (hetero)aromatic bromides.

We have realized the first Ullmann type coupling reaction of tri(di)fluoroethylamine with (hetero)aromatic bromides, employing 5-20 mol% Cu2O and an oxalamide ligand [N-(2,4,6-trimethoxyphenyl)acetamide]. This efficient and practical method has the following features: (i) avoids the use of an expensive catalyst; (ii) does not require anhydrous solvent and strict air extrusion; (iii) uses bench stable and inexpensive (hetero)aromatic bromides; (iv) is suitable for the synthesis of fluoroalkylated hetero-aromatic substrates; (v) is suitable for gram-scale synthesis. This work also shows the "negative fluorine effect" for the alkylamines in the copper catalysed coupling reactions.

Copper(I)-USY as a Ligand-Free and Recyclable Catalyst for Ullmann-Type O-, N-, S-, and C-Arylation Reactions: Scope and Application to Total Synthesis.

The copper(I)-doped zeolite CuI-USY proved to be a versatile, efficient, and recyclable catalyst for various Ullmann-type coupling reactions. Easy to prepare and cheap, this catalytic material enables the arylation and heteroarylation of diverse O-, N-, S-, and C-nucleophiles under ligand-free conditions while exhibiting large functional group compatibility. The facility of this catalyst to promote C-O bond formation was further demonstrated with the total synthesis of 3-methylobovatol, a naturally occurring diaryl ether of biological relevance. From a mechanistic viewpoint, two competitive pathways depending on the nature of the nucleophile and consistent with the obtained results have been proposed.

Preparation and application of hyperbranched polymer-modified polyethersulfone membrane containing Ni–Pd–Sn-coated MWCNT for catalytic aryl halide coupling reactions

In this research, the preparation, application and optimization of catalytic membrane based on nickel–palladium–tin-coated carbon nanotubes/polyethersulfone-hyperbranched polyol (Ni–Pd–Sn@MWCNT/PES-HBAPO) were assessed. The nickel nanoparticles were coated on the carbon nanotubes by an electroless plating method. Later, Ni–Pd–Sn@MWCNT was mixed with the polyethersulfone modified with hyperbranched polymer, and membrane samples were prepared by a phase inversion process. For improvement of the membrane properties including thermal and chemical stability, an aromatic hyperbranched polymer was synthesized and was utilized in the membrane blend. For evaluation of the properties of the resultant membranes, FE-SEM, SEM-Mapping, TEM, FTIR, ICP-OES, DSC and 1H NMR tests were used. The catalytic activity of the obtained membranes in Ullmann-type coupling reaction was studied. High reaction yields were obtained with no significant catalyst leaching.

CuI catalyzed-novel one-pot synthesis of aryl alkenyl thioethers through Ullmann-type coupling reactions using carbon disulfide as a sulfur surrogate in the presence of nitroalkanes and aryl iodides

A mild, general and efficient copper-catalyzed system for C-S bond formation is developed. With CuI as catalyst and l-Proline as ligand, the S-arylation of nitroalkane-CS2 adducts with aryl iodides were performed under mild conditions to give the corresponding products in good to excellent yields.

Modular Synthesis of γ-Valerolactone-Based Ionic Liquids and Their Application as Alternative Media for Copper-Catalyzed Ullmann-type Coupling Reactions

A convenient procedure was developed for the manufacturing of partially bio-ionic liquids (ILs) from renewable γ-valerolactone (GVL) and cheap and readily available tetraalkylphosphonium bromides with excellent (>99%) yields. The novel ionic liquids were characterized by their temperature dependent vapor pressure, density, viscosity, and conductivity. We have proven that these ILs can be a useful medium for copper-catalyzed Ullmann-type coupling reactions without the use of any ligand or additive, representing an environmentally benign tool for the synthesis of various amines. Twenty cross-coupling products were isolated with good to excellent yields (50–87%).

An On-Surface Reaction Confined within a Porous Molecular Template.

On-surface reactions based on metal-catalysed Ullmann coupling have been successfully employed to synthesise a wide variety of covalently coupled structures. Substrate chemistry and topology are both known to effect the progression of an on-surface reaction; offering routes to control efficiency and selectivity. Here, we detail ultra-high vacuum scanning probe microscopy experiments showing that templating a catalytically active surface, via a supramolecular template, influences the reaction pathway of an on-surface Ullmann-type coupling reaction by inhibiting one potential intermediate structure and stabilising another.

Ullmann Coupling Reactions on Ag(111) and Ag(110); Substrate Influence on the Formation of Covalently Coupled Products and Intermediate Metal-Organic Structures

On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometallic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required.

N-Arylation of indole and aniline by a green synthesized CuO nanoparticles mediated by Thymbra spicata leaves extract as a recyclable and heterogeneous nanocatalyst

In a biological procedure where the aqueous leaves extract of Thymbra spicata was utilized as a reducing and capping agent, copper oxide (CuO) nanoparticles (NPs) were synthesized. These CuO NPs were characterized via Fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), wavelength-dispersive X-ray spectroscopy (WDX), and UV–visible spectroscopy. The as prepared nanoparticles have been employed as an appropriate nanocatalyst for ligand-free N-arylation of indole and aniline via Ullmann-type CN coupling reactions. Adequate to outstanding quantities of the N-arylated products were synthesized and the nanocatalyst was retrievable and reusable seven times without noticeable decrease in catalytic performance.

CuI mediated synthesis of heterocyclic flavone-benzofuran fused derivatives

Abstract An efficient synthetic method of heterocyclic flavone benzofuran fused derivatives is reported in good to excellent yield (75–90%) via Ullmann type coupling reaction. The protocol involves catalytic amount of CuI (10 mol%) and K 2 CO 3 base for the intramolecular C O bond formation under mild reaction conditions.

Hierarchical on-surface synthesis and electronic structure of carbonyl-functionalized one- and two-dimensional covalent nanoarchitectures

The fabrication of nanostructures in a bottom-up approach from specific molecular precursors offers the opportunity to create tailored materials for applications in nanoelectronics. However, the formation of defect-free two-dimensional (2D) covalent networks remains a challenge, which makes it difficult to unveil their electronic structure. Here we report on the hierarchical on-surface synthesis of nearly defect-free 2D covalent architectures with carbonyl-functionalized pores on Au(111), which is investigated by low-temperature scanning tunnelling microscopy in combination with density functional theory calculations. The carbonyl-bridged triphenylamine precursors form six-membered macrocycles and one-dimensional (1D) chains as intermediates in an Ullmann-type coupling reaction that are subsequently interlinked to 2D networks. The electronic band gap is narrowed when going from the monomer to 1D and 2D surface-confined π-conjugated organic polymers comprising the same building block. The significant drop of the electronic gap from the monomer to the polymer confirms an efficient conjugation along the triphenylamine units within the nanostructures.

Synthesis and structure of 4-methyl-1-N-(p-tolyl)imidazole as organic corrosion inhibitor

ABSTRACTHeterocyclic organic compounds containing nitrogen, sulfur or oxygen atoms are often used to protect metals from corrosion acting as organic corrosion inhibitors. Their inhibiting role is based on excellent ligand abilities and formation of stabile metal complex. Two requirements are essential for using selected class of organic inhibitors: (a) ligand capacity in the conditions of corrosion such as atmospheric conditions, acid or neutral corrosion, etc., and (b) nontoxicity, i.e., environmentally friendly inhibitors. Imidazole derivatives are capable to fulfil both requirements and they are, from that point of view, very promising and profound class of ligands. Synthesis and X-ray diffraction molecular and crystal structure of 4-methyl-1-N-(p-tolyl)imidazole has been reported, since it exhibits the most prominent corrosion inhibiting role. The synthesis, starting from 4-methylimidazole and 4-bromotoluene, is based on Ullmann-type coupling reaction by applying modifications of N-arylation by arylhalogenides and Cu2O as an efficient catalyst.The molecular and crystal structure of prepared N-substituted imidazole derivative reveals non-planar molecular conformation and the supramolecular assembling of the molecules via C-H···N intermolecular hydrogen bonds between Csp2-H proton donor groups and basic imidazole nitrogen atom. The molecules are related by a 21 screw axis parallel to [0 1 0] in the form of infinite C(4) zig-zag 1D chains via C-H···N intermolecular hydrogen bonds. Such alignment produces additional weak stacking interaction between imidazole and phenyl ring of related chains.

As-prepared and intercalated layered double hydroxides of the hydrocalumite type as efficient catalysts in various reactions

The activities of the research group in the synthesis, characterization and, especially catalytic applications of layered double hydroxides (LDHs) of the hydrocalumite type are reviewed placing the work in literature context. In the project, CaFe- and CaAl-LDHs and their intercalated varieties were synthesized with wet chemical, mechanochemical and ultrasonically-assisted mechanochemical methods, and their structural characterization was performed with state-of-the-art methods. Metal ion [Mn(II), Cu(II), Fe(III) or Ni(II)]-amino acid (l-tyrosine, l-histidine or l-cysteine)−CaAl-LDH composites were also prepared and characterized. The as-prepared LDHs and composites were applied in a wide range of reactions like epoxidation/oxidation of olefins with or without additional functionality, the Baeyer-Villiger oxidation, cross-aldol dimerization–condensation or the Ullmann-type coupling reactions. The activities, selectivities and recycling abilities of the catalysts were investigated.

Syntheses, characterization and catalytic activities of CaAl-layered double hydroxide intercalated Fe(III)-amino acid complexes

Synthesis of intercalated composites were carried out using CaAl-LDH (layered double hydroxide) as host and the anionic form of Fe(III)-amino acid complexes as guest materials. Intercalation was attempted with two methods either introducing the preformed complexes or constructing the complex among the layers of the LDH. After optimization of the synthesis parameters, structural characterization was performed by X-ray diffractometry, scanning electron microscopy as well as mid and far infrared spectroscopies. Quantitative data about the intercalated complexes were collected by chemical analysis and X-ray absorption spectroscopy investigating the near edge region as well as the extended fine structure. Structural models based on characterization measurements are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann-type etherification coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities.

ChemInform Abstract: Pd Immobilized on Modified Magnetic Fe3O4 Nanoparticles: Magnetically Recoverable and Reusable Pd Nanocatalyst for Suzuki—Miyaura Coupling Reactions and Ullmann‐Type N‐Arylation of Indoles.

The Pd supported on amidoxime (AO)-functionalized Fe3O4 (Fe3O4/AO/Pd) hybrid material was used as an effective and recyclable nanocatalyst in Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Suzuki-Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was excellent in most cases. The yields of the products were in the range from 7–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without a significant loss in its catalytic activity. Also, a wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)–N bond formation from the corresponding aryl iodides and indoles through Ullmann-type coupling reactions in the presence of the prepared catalyst.

Recent advancement of Ullmann-type coupling reactions in the formation of C–C bond

The present text discussed about the recent developments and applications of the Ullmann reaction in respect of the C–C bond formation. The major drawback of the Ullmann reaction, i.e., harsh reaction condition has recently been overcome with the development of various synthetic methodologies. Green synthetic methodologies such as metal-, ligand-, and additive free conditions, recyclable heterogenous catalysts, microwave- and ultrasound-assisted synthesis, etc. have got special importance in this field. This text lucidly describes all these recently developed synthetic methodologies which make the century old Ullmann reaction much efficient, effective, economical and attractive in the field of synthetic organic chemistry. On-surface Ullmann coupling for the C–C bond formation, i.e., invoking C–C coupling reactions on a reactive surface has been discussed. All such developments of the Ullmann C–C coupling facilitate its application in the synthesis of bio-active heterocycles, drug-like molecules and natural products which has also been discussed in this text.

Orthogonal Discrimination among Functional Groups in Ullmann-Type C-O and C-N Couplings.

The copper-catalyzed arylation of nucleophiles has been established as an efficient methodology for the formation of C-C and C-heteroatom bonds. Considering the advances during the last two decades, the ligand choice plays a key role in such transformations and can strongly influence the catalytic efficiency. The applicability of these Ullmann-type coupling reactions regarding the orthogonal selectivity of different functional groups constitutes a challenging subject for current synthetic strategies. Herein, we report a useful toolkit of Cu-based catalysts for the chemoselective arylation of a wide-range of nucleophiles in competitive reactions using aryl iodides and bromides. We show in this work that the arylation of all kinds of amides can be orthogonal to that of amines (aliphatic or aromatic) and phenol derivatives. This high chemoselectivity can be governed by the use of different ligands, yielding the desired coupling products under mild conditions. The selectivity trends are maintained for electronically biased iodobenzene and bromobenzene electrophiles. Radical clock experiments discard the occurrence of radical-based mechanisms.

Pd immobilized on modified magnetic Fe3O4 nanoparticles: Magnetically recoverable and reusable Pd nanocatalyst for Suzuki-Miyaura coupling reactions and Ullmann-type N-arylation of indoles

The Pd supported on amidoxime (AO)-functionalized Fe3O4 (Fe3O4/AO/Pd) hybrid material was used as an effective and recyclable nanocatalyst in Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Suzuki-Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was excellent in most cases. The yields of the products were in the range from 7–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without a significant loss in its catalytic activity. Also, a wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)–N bond formation from the corresponding aryl iodides and indoles through Ullmann-type coupling reactions in the presence of the prepared catalyst. Pd supported on amidoxime (AO)-functionalized Fe3O4NPs (Fe3O4/AO/Pd) showed high catalytic activity in Suzuki and Ullmann coupling reaction.

Superparamagnetic Copper Ferrite Nanoparticles Catalyzed One Step Regioselective Synthesis of Dibenzodiazepinones via Ligand and Base Free Ullmann Type Coupling Reaction

CuFe2O4 superparamagnetic nanoparticles were used as an efficient heterogeneous catalyst for the one-step synthesis of dibenzodiazepinones via Ullmann type coupling reaction. The catalyst was highly stable, efficient and easily synthesized from readily available starting materials. The prepared CuFe2O4 NPs was characterized using various characterization techniques such as TEM, SEM, EDX, XRD, VSM, XPS and FT-IR analysis. The thermal stability of the catalyst was also examined by TGA analysis. The present methodology eliminates the multistep procedure for the synthesis of the said compounds. The catalyst efficiently catalyzed the reaction under milder condition furnishing high yield of the product within a short reaction time with higher regioselectivity. Furthermore, the CuFe2O4 super paramagnetic nanoparticles could be easily separated by an external magnet and reused for four consecutive runs. The present protocol is devoid of any base or ligands and showed excellent result for reproducibility and gram scale reaction which addressing the issues of sustainability and environment friendliness.

Tethering of Cu(II) Schiff base metal complex on mesoporous material MCM-41: catalyst for Ullmann-type coupling reactions

The siloxane-functioned Cu(II) complex derived from 3-aminopropyltrimethoxysilane, terephthaldehyde and 2-aminophenol was anchored on hexagonal mesoporous silica MCM-41. The MCM-41 and its Schiff base MCM-41 complex was characterized by FTIR, small-angle X-ray diffraction, SEM-EDX, N2 adsorption and desorption analysis and TGA. The synthesized Cu-Schiff base MCM-41 catalyst has been successfully applied as a catalyst for Ullmann-type coupling reaction of the aryl halides with aryl halides, phenols, amines and N-heterocyclic amines. In the coupling reaction the yields of the products were good and the catalyst was recovered by simple filtration method and can be reused.