Carbene Copper Complexes Research Articles

N‐heterocyclic carbene copper complexes catalyze the C1 polymerization of substituted diazomethanes

AbstractThe C1 polymerization of substituted diazomethanes, including diazoethane and 2,2,2‐trifluoromethyl diazomethane, are reported. N‐heterocyclic carbene copper complexes were employed as catalysts for the polymerization reactions and afforded the corresponding persubstituted polymers containing methyl or trifluoromethyl units along the backbones of the polymer products. The polymers were characterized using size exclusion chromatography, a variety of spectroscopic and thermal techniques, and contact angle measurements. Polymers prepared using the C1 polymerization methodology described herein are more hydrophobic than related polymers that were obtained using a standard C2 polymerization method and the fluorinated polymers were determined to be more hydrophobic than their hydrogenated analogues. The relationship between fluorine content and wettability of persubstituted polymers was quantified.

Synthesis, luminescence properties and computation studies of two-coordinate N-heterocyclic carbene (NHC) copper(I) complexes bearing quinoline derivatives as ligands

Here, we report a series of two-coordinate N-heterocyclic carbene (NHC) copper(I) complexes having monodenate NHC 1,3-bis(2,6- diisopropylphenyl)imidazol-2-ylidene) (IPr) as a σ donor and quinoline and its derivatives as π-chromophore ligands, [Cu(IPr)(Quinoline)]BF4 (P1), [Cu(IPr)(Chloroquinoline)]BF4 (P2), [Cu(IPr)(Phenylquinoline)]BF4 (P3), and [Cu(IPr)(Aminoquinoline)]BF4 (P4), (Chloroquinoline = 2,4-dichloroquinoline, Phenylquinoline = 2-phenylquinoline, Aminoquinoline = 2,4-diaminequinoline). The X-ray diffraction studies of P1 and P3 revealed the linear coordination around the copper atom. P1 and P2 exhibit the typical metal-to-ligand charge transfer (1MLCT) absorption bands in the lowest-lying energy region, while P3 and P4 show the mixed characters of ligand-to-ligand charge transfer (1LLCT) and π→π* transition. The emission wavelengths of all NHCCu(I) complexes can be fine-tuned to cover the spectral range of 419–543 nm with the main 3(π-π) emission origin in the solid state. The differences for photophysical properties of NHCCu(I) complexes were rationalized using density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations.

Aminoquinoline-Based Tridentate (NNN)-Copper Catalyst for C–N Bond-Forming Reactions from Aniline and Diazo Compounds

A new tridentate Cu2+ complex based on (E)-1-(pyridin-2-yl)-N-(quinolin-8-yl)methanimine (PQM) was generated and characterized to support the activation of diazo compounds for the formation of new C–N bonds. This neutral Schiff base ligand was structurally characterized to coordinate with copper(II) in an equatorial fashion, yielding a distorted octahedral complex. Upon characterization, this copper(II) complex was used to catalyze an efficient and cost-effective protocol for C–N bond formation between N-nucleophiles and copper carbene complexes arising from the activation of diazo carbonyl compounds. A substrate scope of approximately 15 different amine-based substrates was screened, yielding 2° or 3° amine products with acceptable to good yields under mild reaction conditions. Reactivity towards phenol and thiophenol were also screened, showing relatively weak C–O or C–S bond formation under optimized conditions.

Cyclisation of Alkynyl Alcohols and Carboxylic Acids Mediated by N‐Heterocyclic Carbene Copper(I) Complexes

AbstractThe cyclisation of alkynyl alcohols and carboxylic acids in the presence of a [Cu(NHC)2]X complex is reported. The reactions were carried out in technical grade toluene in the presence of air with a catalyst that is readily accessible. N‐Heterocyclic carbenes are recognised for stabilising metal centres in a range of oxidation states, and this work further supports that NHCs can also be used as activation sites in air and moisture stable yet active catalysts.

Synthesis and photophysical properties of dinuclear N-heterocyclic carbene (NHC) copper(I) complexes and their application to photoluminescent light-emitting diodes and anti-counterfeiting

Here, a series of dinuclear N-heterocyclic carbene (NHC) copper(I) complexes having 3,3′-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-1H-imidazolylidene as bis-NHC ligand and bis[(2-diphenylphosphino)phenyl]ether (POP) as auxiliary ligand have been successfully prepared, and their photophysical properites were investigaged experimentally and theocitcally. The resulting complexes all exhibited intense green to yellow emission that originated from the thermally activated delayed fluorescence (TADF) with a high photoluminescence quantum yield of up to 0.67 and longer excited-state lifetimes on the microsecond time scale in the solid state. Green and yellow light-emitting diode (LED) devices based on Cu(I) complexes have successfully achieved good color rendering indices. Moreover, the anti-counterfeiting patterns and QR codes made of Cu(I) complexes have been applied to clothing, banknotes, books and glass plates with excellent anti-counterfeiting effects.

Luminescent four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes bearing the pyridyl-imidazolylidene ligand

The synthesis, characterization and photophysical properties of a series of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes are reported. These NHC-Cu(I) complexes contain two bidentate ligands, the R-substituted pyridyl-imidazolylidene-type ligand and diphosphine ligand bis[(2-diphenylphosphino)phenyl] ether (POP). The photophysical properties of these complexes can be adjusted depending on the nature of substituents at 4-position of the phenyl ring in the NHC ligand. The metal-to-ligand charge transfer (MLCT) absorption band can be observed for all complexes at 348–362 nm, and the emission wavelengths can be fine-tuned to cover the spectral range of 543–555 nm with the higher photoluminescence efficiency of up to 66.2% in the solid state. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to support potophysical properties of the NHC-Cu(I) complexes.

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.

Synthesis and luminescence properties of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with different bisphosphine ligands

Synthesis and luminescence properties of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with different bisphosphine ligands

A Straightforward Access to Cyclic (Alkyl)(amino)carbene Copper (I) Complexes

AbstractThe synthesis and characterization of cyclic (alkyl)(amino)carbene, bicyclic (alkyl)(amino)carbene and cyclic (amino)(barrelene)carbene copper (I) complexes is reported. These complexes are obtained via a scalable, versatile, green, and cost/user‐friendly strategy.

Synthesis and Antimicrobial Activity of Carbene Complexesof the Imidazole, Benzimidazole and 1,2,4‐Triazole Series

AbstractNew carbene complexes of copper (I), silver and palladium, including ionic carbene‐phenanthroline complexes, were synthesized on the basis of imidazole, benzimidazole, 1,2,4‐triazole systems with cetyl and aryl including fluorophenyl substituents. The study of the antimicrobial action of the synthesized compounds revealed high antibacterial and antifungal activities of fluoro‐ and phenanthroline‐containing carbene complexes.

Development of a Graphene Oxide-Supported N-Heterocyclic Carbene Copper(I) Complex as a Heterogeneous Catalyst for the Selective N-Monoalkylation of Amines

A new N-heterocyclic carbene (NHC) copper(I) complex supported on graphene oxide (GO-NHC-Cu) was synthesised and thoroughly characterised by various instrumental techniques such as FT-IR, FT-Raman, PXRD, XPS, FESEM, EDX, HRTEM, TGA and ICP-OES. The catalytic activity of the supported complex was explored in the N-alkylation of anilines with alcohols under solvent-free and aerobic conditions to afford monoalkylated products in good to excellent yields (20 products, 83–96%). All products were isolated and characterised by 1H and 13C{1H} NMR spectroscopy. The catalyst was recuperated from the reaction mixture by simple filtration and reused for up to five successive cycles with insignificant loss in the catalytic activity. The control experiments showed that the reaction proceeded in aerobic conditions. The green chemistry metrics for the reaction were found to be fairly close to the ideal values: carbon efficiency (95.9%), E-factor (0.15), atom economy (92.14%), process mass intensity (1.15) and reaction mass efficiency (86.80%). The air stability, selectivity, recyclability of the catalyst, and the high yields of the products under solvent-free conditions are some of the salient features of the reported methodology.

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.

Luminescence color tuning of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with imidazolylidene ligand functionalized by thiazole/benzoxazole moiety

Here, we report a series of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with imidazolylidene and POP ligands, [Cu(BenzThiazolyl-Im)(POP)]PF6 (P1), [Cu(BenzThiazolyl-BenIm)(POP)]PF6 (P2), [Cu(BenzBenzoxazolyl-Im)(POP)]PF6 (P3), and [Cu(BenzBenzoxazolyl-BenIm)(POP)]PF6 (P4), (BenzThiazolyl-Im=3-benzyl-1-(thiazol-2-yl)-1H-imidazolylidene, BenzThiazolyl-BenIm=3-benzyl-1-(thiazol-2-yl)-1H-Benzoimidazolylidene BenzBenzoxazolyl-Im=3-benzyl-1-(benzoxazol-2-yl)-1H-imidazolylidene, BenzBenzoxazolyl-BenIm=3-benzyl-1-(benzocazol-2-yl)-1H-imidazolylidene, POP=bis[2-diphenylphosphino]-phenyl)ether). Thiazole/benzoxazole moiety were functionalized onto imidazolylidene ligand to tune the photophysical properties of the corresponding complexes. P1 and P2 exhibit the metal-to-ligand charge transfer (MLCT) absorption band with the onset at 406–412 nm, while P3 and P4 have similar MLCT band with the onset at 380–389 nm. The emission wavelengths of all NHCCu(I) complexes can be fine-tuned to cover the spectral range of 517–551 nm with the phosphorescent origin in PMMA films. P2 show the highest photoluminescence efficiency of 40.9% with the red-shifted emission wavelength at 551 nm, whereas P4 has the lowest photoluminescence efficiency of 1.80% with the blue-shifted emission wavelength at 517 nm. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to rationalize the differences for photophysical properties of the NHCCu(I) complexes.

A new class of deep blue emitting four-coordinate NHC-Cu(I) complexes bearing nonconjugated triazolyl-imidazolylidene-type ligand: Synthesis, photophysical properties and theoretical investigations

In the present study, a series of the four-coordinate N-hetercycle carbene (NHC) copper (I) complexes [Cu(MethyIm-Meth-benzTriazole)(POP)]PF6 (P1), [Cu(BenzyIm-Meth-benzTriazole)(POP)]PF6 (P2), and [Cu(BenzyBenzoIm-Meth-benzTriazole)(Xantphos)]PF6 (P3), MethyIm-Meth-benzTriazole = 1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-3-methyl-1H-imidazolylidene, BenzyIm-Meth-benzTriazole = 1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-3-phenyl-1H-imidazolylidene, BenzyBenIm-Meth-benzTriazole = 3-benzyl-1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1H-benzo[d]imidazolylidene, POP = bis[(2-diphenylphosphino)phenyl]ether, have been synthesized and characterized. The molecular structure of P2 has been established by single-crystal X-ray diffraction study. The addition of the methylene spacer into the NHC ligand effectively breaks the π-conjugation of the ligand, resulting in a larger HOMO-LUMO energy gap. In the solid state, P1–P3 exhibit deep blue emission in the range of 452–466 nm with the excited-state lifetimes (τ) of 14.9–16.2 μs and the emission quantum yields (Φ) of 8.50–11.9 % at room temperature. Additionally, the photophysical properties are explained by using density functional theory (DFT) and time dependent DFT.

Synthesis, structures, and photophysical properties of orange-red emissive Cu(I) complexes of 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene (Xantphos) with the substituted N-hetercycle carbene (NHC) ligand

In the present study, a series of the four-coordinate N-hetercycle carbene (NHC) copper (I) complexes [Cu(Ph-Im-cyPy)(Xantphos)]PF6 (P1), [Cu(DimBenPh-Im-cyPy)(Xantphos)]PF6 (P2), and [Cu(BenDimBenIm-CNPy)(Xantphos)]PF6 (P3), Ph-Im-cyPy=3-benzyl-1-(4-cyano-pyridin-2-yl)-1H-imidazolylidene, DimBenPh-Im-cyPy=3-(3,5-dimethylbenzyl-1-(4-cyano-pyridin-2-yl)-1H-imidazolylidene, BenDimBenIm-CNPy=3-benzyl-1-(4-cyano-pyridin-2-yl)-1H-5,6-dimethylbenzimidazolylidene, Xantphos=9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene, have been synthesized and characterized. The molecular structures of P1–P3 have been established by single-crystal X-ray diffraction study. In the solid state, P1–P3 exhibit orange-red emission in the range of 621–643 nm with shorter excited-state lifetimes (τ) of 5.73–6.42 μs and the emission quantum yields (Φ) of 1.0–3.9 % at room temperature. Additionally, the photophysical properties are explained by using density functional theory (DFT) and time dependent DFT.

Mechanochemical synthesis of carbene copper complexes for CO2 hydrogenation to formate

This paper reports mechanochemical synthesis of carbene copper complexes for catalytic hydrogenation of CO2 to formate with H2. Significantly improved in catalytic activity was acquired by adding triethoxysilane activator, affording the highest TON up to 5720. Stoichiometric reactions are managed to support the rationality of the pivotal steps in proposed catalytic cycle for the cleavage of H2 and activation of CO2.

Helicenic N-heterocyclic carbene copper(I) complex displaying circularly polarized blue fluorescence.

Enantiopure copper(I) chloride complexes bearing a monodentate N-(carbo[6]helicenyl)-NHC ligand have been prepared and characterized experimentally and computationally. Their high stability enables the stereochemistry to be probed by X-ray crystallography and NMR spectroscopy. The resolved enantiomeric complexes emit circularly polarized blue fluorescence with glum ∼1.3 × 10-3 in solution. The photophysical and chiroptical properties of these systems, with their helicene-centred origin, are similar to those of the organic helicene-benzimidazole precursor proligand, although the reverse axial chirality configuration is preferentially observed for the complex compared to the ligand.

Orange-red emissive N-hetercycle carbene (NHC) Cu(I) complexes bearing benzimidazolylidene-type ligands: Synthesis, structures, and photophysical properties

Herein, three four-coordinate N-hetercycle carbene (NHC) copper (I) complexes of the types [Cu(BenDimBenIm-CHOPy)(POP)]PF6 (P1), [Cu(BenDimBenIm-CNPy)(POP)]PF6 (P2), and [Cu(DimbenDimBenIm-CNPy)(POP)]PF6 (P3) (BenDimBenIm-CHOPy = 3-benzyl-1-(5-formyl -pyridin-2-yl)-1H-5,6-dimethylbenzimidazolylidene, BenDimBenIm-CNPy = 3-benzyl-1-(5-cyano -pyridin-2-yl)-1H-5,6-dimethylbenzimidazolylidene, DimbenDimBenIm-CNPy = 3-(3,5-dimethylbenzyl-1-(5-cyano-pyridin-2-yl)-1H-5,6-dimethylbenzimidazolylidene, POP = bis[2-diphenylphosphino]-phenyl)ether) have been prepared and investigated. All complexes exhibit the lowest energy metal-to-ligand charge transfer (MLCT) characters in 320–360 nm region showing a slight blue-shift of the absorption maxima in the order P1 >P2 >P3. The emissive wavelength can be fine-tuned to cover the orange-red spectral range of 615−638 nm with higher photoluminescence quantum yields (PLQY) of 17.6–40.3 %. Additionally, the photophysical properties are also investigated theoretically using density functional theory (DFT) and time dependent DFT.

Synthetic Access to Ring-Expanded N-Heterocyclic Carbene (RE-NHC) Copper Complexes and Their Performance in Click Chemistry

The facile syntheses of ring-expanded N-heterocyclic carbene (RE-NHC) copper(I) halide complexes are reported. The method makes use of a weak inorganic base in a green solvent. The reaction times can be greatly reduced by use of this weak-base route under microwave irradiation. The easy access to these complexes permits an evaluation of the catalytic activity and reaction profiling of [Cu(RE-NHC)X] complexes in the Huisgen 1,3-cycloaddition reaction.

Copper carbene complexes. Synthesis and structural analysis of a chloro-bridged dicopper cation and the triosmium-copper carbene cluster complex HOs3(CO)11[µ-Cu(IPr)

The chloro-bridged carbene-substituted dicopper salt [{(IPr)Cu}2(µ-Cl)][PF6], 1, IPr = [N,N′-bis(2,6-diisopropylphenyl)imidazolin-2- ylidene], was synthesized by the reaction of (IPr)CuCl with Tl[PF6]. Reaction of 1 with the anion, [HOs3(CO)11]− of the salt [PPN][HOs3(CO)11], 2 yielded the Cu - Os heterometallic cluster complex, HOs3(CO)11[µ-Cu(IPr)], 3, the first example of Cu - Os bimetallic cluster complex containing a N-heterocyclic carbene ligand. Compounds 1 and 3 were characterized by IR, 1H NMR and structurally by single-crystal X-ray diffraction analysis. Compound 3 contains a triosmium carbonyl cluster with a bridging Cu(IPr) group on one edge of the cluster and a terminally-coordinated hydrido ligand on one of the Cu-bridged osmium atoms.