Carbene Copper Research Articles

Divergent Synthesis of Disulfanes and Benzenesulfonothioates Bearing 2-Aminofurans From N-Tosylhydrazone-Bearing Thiocarbamates.

An efficient and convenient synthesis of valuable disulfanes and benzenesulfonothioates, having a 2-aminofuran framework, has been developed by employing a copper-catalyzed transformation of readily available N-tosylhydrazone-bearing thiocarbamates. This method features an inexpensive metal catalyst, mild reaction conditions, good functional-group tolerance, short reaction times, and delivers valuable and complex products. A copper carbene generated from an N-tosylhydrazone-bearing thiocarbamate is proposed as the key intermediate for the transformation and it triggers the subsequent cascade. Remarkably, the Ts anion released from N-tosylhydrazone further serves as a nucleophile, thus rendering the formation of benzenesulfonothioates under controlled conditions.

Synthesis of [2.2]paracyclophane-based bidentate oxazoline–carbene ligands for the asymmetric 1,2-silylation of N-tosylaldimines

A series of novel oxazoline-substituted imidazolium salts with planar and central chirality has been successfully synthesized and applied to copper-catalyzed enantioselective 1,2-silylation of N-tosylaldimines. The oxazoline–carbene copper complex generated in situ by the reaction of the oxazoline-substituted imidazolium and Cu2O demonstrated an exceptionally high catalytic activity in the asymmetric 1,2-silylation of N-tosylaldimines, affording chiral α-amino silanes with excellent yields and enantioselectivities.

Synthesis, Reactivity, and Catalytic Applications of Isolable (NHC)Cu(CHF2) Complexes

Difluoromethyl copper complexes have been proposed as key intermediates in a variety of Cu-catalyzed difluoromethylation reactions. However, studies of these putative intermediates have been impeded by the low stability of these [Cu(CHF2)] species. This report describes the synthesis of isolable N-heterocyclic carbene ligated copper(I) difluoromethyl complexes. The stoichiometric reactions of these complexes with aryl electrophiles (i.e., diaryliodonium salts, aryl iodides, and aryl bromides) are described. In addition, N-heterocyclic carbene copper(I) species are demonstrated to serve as catalysts for the cross-coupling of aryl iodides with (difluoromethyl)trimethylsilane to afford difluoromethyl arene products.

Synthesis and structures of gold and copper carbene intermediates in catalytic amination of alkynes

Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I)-catalysed cyclization of N-alkynyl formamidines through five-exo-dig cyclization. X-ray diffraction, 13C NMR spectra data and computational analyses provide evidence for the formation of a gold carbene intermediate with a carbocation-like electronic character. Using the intrinsic bond orbital (IBO) approach, we also evaluate the π-stabilizing effects of organic substituents at the carbene carbon atom in the gold carbene intermediate. Another rare six-membered copper carbene complex is also obtained through 6-endo-dig cyclization. These metal carbenes have proven reactive toward oxidation. The metal-promoted cyclization of N-alkynyl formamidine provides a facile approach to synthesize metal carbene species.

Copper-Catalyzed P-H Insertions of α-Imino Carbenes for the Preparation of 3-Phosphinoylindoles.

A highly efficient P-H insertion of α-imino copper carbene into H-phosphine oxides, leading to 3-phosphinoylindoles with a broad substrate diversity and good chemoselectivity, is established. This methodology provides a rapid and efficient approach for the C (sp2)-P bond formation via the P-H insertion strategy. The stereoselective P-H insertion of α-imino copper carbene represents a unique example of asymmetric P-H insertion, affording P-stereogenic 3-phosphinoylindoles with high stereoselectivities.

Four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with brightly luminescence properties

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Py-Im)(POP)](PF6) (P1), [Cu(Py-BenIm)(POP)](PF6) (P2), and [Cu(Py-c-BenIm)(POP)](PF6) (P3) (Py-Im = 3-methyl-1-(pyridin-2-yl)-1H-imidazolylidene, Py-BenIm = 3-methyl-1-(pyridin-2-yl)-1H-benzo[d]imidazolylidene, Py-c-BenIm = 3-methyl-1-(pyridin-2-ylmethyl)-1H-benzo[d]imidazolylidene, POP = bis([2-diphenylphosphino]-phenyl)ether), have been synthesized without transmetalation of the NHC–Ag(I) complex for the first time. The photophysical properties of the resultant NHC–Cu(I) complexes have been systematically investigated via spectroscopic methods. All complexes exhibit good photoluminescence properties with long excited-state lifetimes and moderate quantum yields. Density functional theory and time dependent density functional theory calculations were employed to rationalize the photophysical properties of the NHC–Cu(I) complexes.

Synthetic control of coincidental formation of an N-heterocyclic carbene–copper(i) complex and imidazolium cations within metal–organic frameworks

By changing the concentration of copper salt (Cu(ClO4)2), a two-dimensional (2D) copper paddle-wheel-based metal–organic framework (MOF) containing an imidazolium unit (Im-MOF-1 with a framework formula of [CuII(L)(NMP)](ClO4), L = 1,3-bis(4-carboxyphenyl)imidazolium and NMP = N-methyl-2-pyrrolidone) and a 3D MOF (Im-MOF-2, CuII(L)(H2O)) with aqua-bridged Cu ions as inorganic infinite secondary building units were respectively prepared. With CuCl as a copper source, another square-grid 2D MOF (Im-MOF-3, CuII(LNHC–CuICl)(NMP), LNHC = a carbene form of L) was obtained; Im-MOF-3 is isostructural with Im-MOF-1 except that its organic linker has an N-heterocyclic carbene (NHC) copper(I) complex (LNHC–CuICl). Density functional theory modeling calculations show that the NHC–CuCl complex in the organic linker of Im-MOF-3 retains the electronic properties of its molecular form, as evidenced by molecular orbital analysis.

Copper carbenes alkylate guanine chemoselectively through a substrate directed reaction.

Cu(i) carbenes derived from α-diazocarbonyl compounds lead to selective alkylation of the O6 position in guanine (O6-G) in mono- and oligonucleotides. Only purine-type lactam oxygens are targeted - other types of amides or lactams are poorly reactive under conditions that give smooth alkylation of guanine. Mechanistic studies point to N7G as a directing group that controls selectivity. Given the importance of O6-G adducts in biology and biotechnology we expect that Cu(i)-catalyzed O6-G alkylation will be a broadly used synthetic tool. While the propensity for transition metals to increase redox damage is well-appreciated, our results suggest that transition metals might also increase the vulnerability of nucleic acids to alkylation damage.

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.

ChemInform Abstract: Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene—Copper Complex.

AbstractThe reaction of allenamides with dialkylzinc reagents and CO2 proceeds smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)‐α,β‐dehydro‐β‐amino acid esters in good yields.

Dinuclear thiazolylidene copper complex as highly active catalyst for azid-alkyne cycloadditions.

A dinuclear N-heterocyclic carbene (NHC) copper complex efficiently catalyzes azide–alkyne cycloaddition (CuAAC) “click” reactions. The ancillary ligand comprises two 4,5-dimethyl-1,3-thiazol-2-ylidene units and an ethylene linker. The three-step preparation of the complex from commercially available starting compounds is more straightforward and cost-efficient than that of the previously described 1,2,4-triazol-5-ylidene derivatives. Kinetic experiments revealed its high catalytic CuAAC activity in organic solvents at room temperature. The activity increases upon addition of acetic acid, particularly for more acidic alkyne substrates. The modular catalyst design renders possible the exchange of N-heterocyclic carbene, linker, sacrificial ligand, and counter ion.

ChemInform Abstract: Extremely Efficient Hydroboration of Ketones and Aldehydes by Copper Carbene Catalysis.

A readily available copper carbene complex, (IPr)CuOtBu, catalyses the hydroboration of ketones and aldehydes even at very low catalyst loadings (0.1 mol%), in some cases with turnover frequencies exceeding 6000 h(-1). Carbonyl reduction occurs selectivitily in the presence of other reducible functional groups including alkenes, nitriles, esters, and alkyl chlorides.

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex.

The alkylative carboxylation of allenamide catalyzed by an N-heterocyclic carbene (NHC)-copper(I) complex [(IPr)CuCl] with CO2 and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO2 (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)-α,β-dehydro-β-amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ-carbon, and the carboxyl group introduced onto the β-carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2 . A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β-hydrogen atoms, such as Et2 Zn or Bu2 Zn, also gave the corresponding alkylative carboxylation products without β-hydride elimination. The present methodology provides an easy route to alkyl-substituted α,β-dehydro-β-amino acid ester derivatives under mild reaction conditions with high regio- and stereoselectivtiy.

Cu(I)-Catalyzed Tandem Reaction of Carbene Coupling and Horner-Wadsworth-Emmons Type Olefination: Access toward Enynes.

A novel strategy to synthesize 1,3-enynes has been successfully developed based on Cu(I)-catalyzed cross-coupling of α-diazo phosphonates and alkynes with a subsequent Horner-Wadsworth-Emmons (HWE) type reaction. This method provides straightforward access to conjugated enynes with high efficiency, good stereoselectivity and excellent functional group compatibility. Copper(I) carbene migratory insertion plays a crucial role in this transformation.

ChemInform Abstract: Copper(I) Complexes Bearing Carbenes Beyond Classical N‐Heterocyclic Carbenes: Synthesis and Catalytic Activity in “Click Chemistry”.

The synthesis and characterization of abnormal N-heterocyclic carbene, cyclic (alkyl)(amino)carbene, and mesoionic carbene copper(I) complexes are reported. These organometallic species are obtained via a versatile and inexpensive synthetic pathway using readily available reactants, namely copper oxide and iminium salts. The catalytic activity of this series of complexes was evaluated in the [3+2] cycloaddition of alkynes with azides (CuAAC). Outstanding catalytic properties were observed for the abnormal NHC- and triazolylidene-based copper(I) complexes.

Csp(3)-P versus Csp(2)-P Bond Formation: Catalyst-Controlled Highly Regioselective Tandem Reaction of Ene-Yne-Ketones with H-Phosphonates.

Under copper-catalyzed or base-promoted conditions, a wide range of ene-yne-ketones react with H-phosphonates to afford various phosphorylated furans in good yields. A copper carbene generation or a Michael addition is proposed as the key step in the selective construction of the Csp(3)-P or Csp(2)-P bond, which is supported by carbene capture reactions and interval (31)P NMR experiments. Furthermore, this method features inexpensive metal catalysts, no usage of oxidant, and high atom economy, which make it attractive and practical.

Extremely efficient hydroboration of ketones and aldehydes by copper carbene catalysis.

A readily available copper carbene complex, (IPr)CuOtBu, catalyses the hydroboration of ketones and aldehydes even at very low catalyst loadings (0.1 mol%), in some cases with turnover frequencies exceeding 6000 h(-1). Carbonyl reduction occurs selectivitily in the presence of other reducible functional groups including alkenes, nitriles, esters, and alkyl chlorides.

Copper complexes bearing an NHC–calixarene unit: synthesis and application in click chemistry

Novel N-heterocyclic carbene (NHC) copper complexes supported by calix[4]arene were synthesized and showed good catalytic activity when applied in click chemistry.

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.