N-heterocyclic Carbene Copper Complexes Research Articles

Highly Diastereoselective Synthesis of C-Glycosides from Glycal Anomers.

This Letter presents a highly diastereoselective synthesis of C-hydroxymethine glycosides from glycal anomers using a chiral N-heterocyclic carbene-copper catalyst. The high diastereoselectivity was synergistically controlled by the stereocenter of the substrate and chirality of the N-heterocyclic carbene-copper complex without being interrupted by the stereochemistry of C5 and the anomeric position. This approach enables the production of a diverse array of C-hydroxymethine glycosides using synthetically versatile glycals and various functionalized aldehydes.

N-Heterocyclic carbene copper complex catalyzed Chan-Evans-Lam reactions of arylboronic acids with azoles and amines

An efficient protocol of Chan-Evans-Lam reactions involving arylboronic acids and azole and amine derivatives was developed based on a series of N-heterocyclic carbene copper (Cu-NHC) complexes as the precatalysts. The relationship between the catalyst structure and catalytic properties was investigated in detail. The results demonstrated that the modification of NHC backbone with acenaphthyl group exhibited significant beneficial effect on the coupling efficiencies. Nonetheless, it appeared that more bulk on the N-aryl moieties of NHC ligands impeded the reactions. The protocol also features mild reaction conditions, such as low catalyst loading (0.1–1 mol%), non-toxic solvent and air as the sole oxidant, which highlights the usefulness of Cu-NHC as the precatalyst for this reaction.

Immobilization of vitamin B1 on the magnetic dialdehyde starch as an efficient carbene-type support for the copper complexation and its catalytic activity examination

Since the starch biopolymer is an available and inexpensive matrix with modifiable functionality and stabilization capability for metal ions, in this report, we oxidized it to dialdehyde form for the further functionalization with vitamin B1 as a green σ-donor and π-acceptor carbene type ligand. Immobilization of vitamin B1 on this biopolymer was done through imine bond formation between NH2 groups of aminopyrimidine segment of vitamin B1 and aldehyde functional groups of starch oxide. Thiazolium heterocycle part in this biomolecule provided a carbene type precursor for the metal complexation. After the magnetization process by using of Fe3O4 nanoparticles that lead to quick and facile magnetic separation and metal catalyst recycling, copper ions immobilized on the magnetic support (5.9 wt% Cu, 0.93 mmol/g). The prepared copper N-heterocyclic carbene complex (Fe3O4@DAS@VB1@CuCl nanocomposite) was characterized by FT-IR, SEM, EDX, XRD, VSM, TGA and ICP-OES analysis and then its catalytic activity investigated in azidonation of arylboronic acids and also one-pot coupling reaction of the synthesized aryl azides with phenylacetylene. 1,4-Diaryl 1,2,3-triazoles were obtained in excellent yields (≥90%) at proper reaction times (30–200 min). The magnetic catalyst was recovered by a magnetic field and reused in azidation reaction up to 7 cycle.

Highly ordered mesoporous hybrid silica functionalized with ionic liquid framework supported copper and its application in the oxidation of alcohols

A highly ordered organic-inorganic hybrid nanomaterial containing copper N-heterocyclic carbene complex (Cu-NHC@Pyrm-OMS) was synthesized and characterized using various techniques including FTIR, MAS NMR, XRD, TGA, SEM, and TEM. Cu-NHC@Pyrm-OMS nanomaterial is highly efficient heterogeneous system towards the selective oxidation of primary and secondary alcohols to corresponding aldehydes and ketones under mild conditions. Moreover, the supported copper nanocatalyst exhibited outstanding stability and could be reused at least ten times, remaining almost unchanged from initial activity. This work has focused on sustainable and green chemistry that use recoverable nanocatalyst, clean oxidant and aqueous media.

Correction to Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex

Correction to Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex

Markovnikov-Selective Hydroboration of Olefins Catalyzed by a Copper N-Heterocyclic Carbene Complex

The efficient and atom-economical hydroboration of alkenes and alkynes using an N-heterocyclic carbene (NHC) copper hydroxide catalyst has been developed. An equimolar combination of substrate and ...

Ultrasound assisted dispersive solid phase extraction of triazole fungicides by using an N-heterocyclic carbene copper complex supported on ionic liquid-modified graphene oxide as a sorbent.

An ultrasound-assisted method is described for dispersive solid phase extraction of trace levels of triazole fungicides. A sorbent was prepared from an N-heterocyclic carbene copper complex that was supported on ionic liquid-modified graphene oxide. The sorbent was characterized by scanning electron microscopy, transmission electron microscopy, Raman and FT-IR spectroscopy, energy-dispersive X-ray spectroscopy and elemental mapping. The capability of sorption and extraction is mainly based on complexation with Cu (I) ions. The variables affecting extraction were optimized. Following desorption with ethanol, the fungicides were quantified by corona discharge ion mobility spectrometry. Under optimized conditions (solution pH value: 7.0; amount of sorbent: 10mg; extraction time: 3min; desorption agent: ethanol), the technique provides good linearity (>0.994), repeatability (RSD < 4.1%), low limits of detection (0.18ng.mL-1), excellent preconcentration factors (468-476) and high recoveries from spiked environmental water samples (92-94%). The sorbent can be reused over five cycles without significant loss of its activity. Graphical abstract Schematic presentation of design and synthesis of the N-heterocyclic carbene copper complex supported on ionic liquid-modified graphene oxide as a sorbent for triazole fungicides and its application in ultrasound-assisted dispersive solid phase extraction with ion mobility spectrometric detection.

Synthesis, spectroscopic properties and biological activity of new Cu(I) N-Heterocyclic carbene complexes

New benzimidazolium salts (2) and their copper N-heterocyclic carbene complexes (3–4) were designed, synthesized and structurally characterized by NMR (1H and 13C), IR, HRMS and elemental analysis. All obtained complexes especially compounds 3d and 3e, presented significant inhibitory activity against the tested food-borne pathogens and clinical microorganisms. The compound 3b presents against S. aureus a MIC value of 0.0195 mg/ml quite similar to that of ampicillin (0.0195 mg/ml) used as standard. Compounds 3a and 3b, from a concentration of 0.5 mg/ml, present an identical scavenging activity to that of the two used controls butylated hydroxytoluene (BHT) and gallic acid (GA). Concerning acetylcholinesterase inhibition activity (AChEI), compound 3e presents an interesting AChEI activity with 32.80% of inhibition.

Chemical Fixation of CO2 by Using Carbon Material-Grafted N-Heterocyclic Carbene Silver and Copper Complexes

Chemical fixation of CO2 is investigated by using heterogeneous catalysts (CNT-NHC-M and GN-NHC-M; M = Ag, Cu) of N-heterocyclic carbene (NHC)–silver complex and NHC–copper complex grafted on carbon materials such as multiwalled carbon nanotubes (CNTs) and graphene (GN). These carbon-based versatile catalysts efficiently promote carboxylative cycloaddition of CO2 into propargylic alcohols to produce cyclic carbonates; catalyze three-component coupling of CO2, propargyl alcohols, and amines to afford carbamates and oxazolidinones; and contribute cycloaddition of CO2 with epoxides to yield cyclic carbonates. Under optimized reactions, CNT-NHC-Ag efficiently promotes the cycloaddition of CO2 with propargyl alcohol under atmospheric pressure of CO2 by affording cyclic carbonate yield of 99%, while the CNT-NHC-Cu efficiently catalyzes three-component coupling of CO2, propargyl alcohol, and amines by giving β-oxopropylcarbamate in 99% yield and oxazolidinone with 96% yield, respectively. In the case of cycloadd...

Copper-Catalyzed Propargylic Reduction with Diisobutylaluminum Hydride.

A mild and efficient method for the synthesis of allenes through selective copper-catalyzed hydride addition to propargylic chlorides using commercially available diisobutylaluminum hydride has been developed. This transformation, which is promoted by a readily accessible N-heterocyclic carbene-copper complex, provides a wide range of new and versatile functionalized allenes in good to excellent yields with high regio- and stereoselectivities.

N-Heterocyclic carbene–copper complex supported on ionic liquid-modified graphene oxide: versatile catalyst for synthesis of (i) 1,2,3-triazole and (ii) propargylamine derivatives

A N-heterocyclic carbene–copper complex grafted on graphene oxide with an ionic liquid framework was prepared. The synthesis of (i) 1,2,3-triazole derivatives by ‘Click reaction’ and (ii) propargylamine derivatives by ‘A3 coupling reaction’ in aqueous media by this new catalyst were all successfully accomplished. The catalyst is characterized using infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, thermogravimetric analysis and energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and elemental analysis. The catalyst is reused in the ten reaction cycles without considerable loss of catalytic activity.

A new water soluble copper N-heterocyclic carbene complex delivers mild O6G-selective RNA alkylation.

We show here that copper carbenes generated from diazo acetamides alkylate single RNAs, mRNAs, or pools of total transcriptome RNA, delivering exclusively alkylation at the O6 position in guanine (O6G). Although the reaction is effective with free copper some RNA fragmentation occurs, a problem we resolve by developing a novel water-stable copper N-heterocyclic carbene complex. Carboxymethyl adducts at O6G are known mutagenic lesions in DNA but their relevance in RNA biochemistry is unknown. As a case-in-point we re-examine an old controversy regarding whether O6G damage in RNA is susceptible to direct RNA repair.

Three-component synthesis of N-sulfonylformamidines in the presence of magnetic cellulose supported N-heterocyclic carbene-copper complex, as an efficient heterogeneous nanocatalyst

A cellulose based magnetic nanocomposite possessing NHC-Cu Complex has been synthesized and characterized. It was then applied as a highly active catalyst in one-pot three-component reaction of sulfonyl azides, secondary amines and triethylamine to afford N-sulfonylformamidines. Copper catalyzed oxidative transformation of C-N bond of triethylamine is a key step to give desired products. In contrast with the good reactivity of the conventional secondary amines, aromatic amines and NH containing heteroaromatics had no activity in these reactions. Moreover, the used nanocatalyst which could be recovered by external magnet, showed reasonable catalytic activity for several times.

Direct Synthesis of a Copper(II) N-Heterocyclic Carbene Complex in Air

Copper N-heterocyclic carbene complexes (Cu-NHCs) are prevalent in the literature, and their stability and catalytic activity have been well characterized and established. In an overwhelming majority of the reported examples, copper is present as Cu(I), owing to the favorable soft–soft interaction. In contrast, there are very few reports of Cu-NHCs containing Cu(II). This can be explained by the unfavorable intermediate/hard–soft interaction between carbon and Cu(II). The syntheses of examples reported thus far require the exclusion of air and moisture and involve the use of NHC transfer reagents or the use of free NHCs. This results in tedious, multistep procedures, making their preparation more time consuming and costly. Herein we report the synthesis and characterization of two air- and moisture-stable Cu(II)-NHC complexes by direct combination of 1,3-bis(pyridin-2-ylmethyl)-1H-imidazolium chloride with copper(II) hexafluorosilicate. Analysis by single-crystal X-ray diffraction revealed that the specie...

Synthesis and Photophysical Properties of New Three-Coordinate N-Heterocyclic Carbene Copper Complex

A three-coordinateopper (I) complex supported by N-heterocyclic carbene (NHC) ligand and bis [2-(diphenylphosphino) phenyl] ether (POP) ligand were successfully reported and characterized. The corresponding photophysical properties were investigated using UV-vis and emission spectrometry. The lowest-energy absorption band at 343 nm was assigned to metal-to-ligand charge transfer (MLCT) transtion. The emission maximum located at 470 nm upon excitation at 290 nm in PMMA films at room temperature originates from the typical 3MLCT excited state.

Designing NHC-Copper(I) Dipyridylamine Complexes for Blue Light-Emitting Electrochemical Cells.

This study presents the influence of various substituents on the photophysical features of heteroleptic copper(I) complexes bearing both N-heterocyclic carbene (NHC) and dipyridylamine (dpa = dipyridylamine skeleton corresponding to ligand L1) ligands. The luminescent properties have been compared to our recently reported archetypal blue emitting [Cu(IPr)(dpa)][PF6] complex. The choice of the substituents on both ligands has been guided to explore the effect of the electron donor/acceptor and "push-pull" on the emission wavelengths and photoluminescence quantum yields. A selection of the best candidates in terms of their photophysical features were applied for developing the first blue light-emitting electrochemical cells (LECs) based on copper(I) complexes. The device analysis suggests that the main concern is the moderate redox stability of the complexes under high applied driving currents, leading to devices with moderate stabilities pointing to a proof-of-concept for further development. Nevertheless, under low applied driving currents the blue emission is stable, showing performance levels competitive to those reported for blue LECs based on iridium(III) complexes. Overall, this work provides valuable guidelines to tackle the design of enhanced NHC copper complexes for lighting applications in the near future.

Functionalized hypercrosslinked polymers with knitted N-heterocyclic carbene–copper complexes as efficient and recyclable catalysts for organic transformations

An N-heterocyclic carbene–copper complex supported on hypercrosslinked polymers was synthesized and characterized by spectroscopic methods, displaying very good catalytic activity in many organic reactions.

Synthesis and catalytic application of N-heterocyclic carbene copper complex functionalized conjugated microporous polymer

The first example of IPr(CuCl) functionalized conjugated microporous polymer has been synthesized and applied for the hydrosilylation of terminal alkynes and hydrosilylation of CO2. Good catalytic activities and catalytic stability have been achieved.

A theophylline based copper N-heterocyclic carbene complex: synthesis and activity studies in green media

The synthesis of an easily accessible theophylline-derived copper complex with additional ammonium functionalization has been developed.

Copper N-Heterocyclic Carbene: A Catalyst for Aerobic Oxidation or Reduction Reactions.

Copper N-heterocyclic carbene complexes can be readily used as catalysts for both aerobic oxidation of alcohols to aldehydes and reduction of imines to amines. Our methodology is universal for aromatic substrates and shows versatile tolerance to potential cascade reactions. A one-pot tandem synthetic strategy could afford useful imines and secondary amines via an oxidation-reduction strategy.