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1.
Selective Alcohol Oxidation by a Copper TEMPO Catalyst: Mechanistic Insights by Simultaneously Coupled Operando EPR/UV‐Vis/ATR‐IR Spectroscopy
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Dr. Jabor Rabeah Dr. Ursula Bentrup Prof. Dr. Reinhard Stößer Prof. Dr. Angelika Brückner 《Angewandte Chemie (International ed. in English)》2015,54(40):11791-11794
The first coupled operando EPR/UV‐Vis/ATR‐IR spectroscopy setup for mechanistic studies of gas‐liquid phase reactions is presented and exemplarily applied to the well‐known copper/TEMPO‐catalyzed (TEMPO=(2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl) oxidation of benzyl alcohol. In contrast to previous proposals, no direct redox reaction between TEMPO and CuI/CuII has been detected. Instead, the role of TEMPO is postulated to be the stabilization of a (bpy)(NMI)CuII‐O2??‐TEMPO (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole) intermediate formed by electron transfer from CuI to molecular O2. 相似文献
2.
Christian Schumacher Jos G. Hernndez Carsten Bolm 《Angewandte Chemie (International ed. in English)》2020,59(38):16357-16360
The formation and regeneration of active CuI species is a fundamental mechanistic step in copper‐catalyzed atom transfer radical cyclizations (ATRC). Typically, the presence of the catalytically active CuI species in the reaction mixture is secured by using high CuI catalyst loadings or the addition of complementary reducing agents. In this study it is demonstrated how the piezoelectric properties of barium titanate (BaTiO3) can be harnessed by mechanical ball milling to induce electrical polarization in the strained piezomaterial. This strategy enables the conversion of mechanical energy into electrical energy, leading to the reduction of a CuII precatalyst into the active CuI species in copper‐catalyzed mechanochemical solvent‐free ATRC reactions. 相似文献
3.
The Development of Copper‐Catalyzed Aerobic Oxidative Coupling of H‐Tetrazoles with Boronic Acids and an Insight into the Reaction Mechanism
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Chao‐You Liu Yu Li Jin‐Ying Ding Prof. Dr. De‐Wen Dong Prof. Dr. Fu‐She Han 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(8):2373-2381
The development of a highly efficient and practical protocol for the direct C?N coupling of H‐tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different CuI or CuII salts with only 5 mol % loading in DMSO at 100 °C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5‐disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the CuI catalyst could be oxidized to CuII by oxygen to form a [CuT2D] complex (T=tetrazole anion; D=DMSO) through an oxidative copper amination reaction. The CuII complex thus formed was confirmed to be the real catalytically active copper species. Namely, the CuII complex disproportionates to aryl CuIII and CuI in the presence of boronic acid. Facile elimination of the CuIII species delivers the C?N‐coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5‐disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu‐catalyzed coupling reactions. 相似文献
4.
《化学:亚洲杂志》2017,12(15):1865-1868
A facile synthesis of 2‐amino‐1,3‐oxazoles via CuI‐catalyzed oxidative cyclization of enamines and N ,N ‐dialkyl formamides has been developed. The reaction proceeds through an oxidative C−N bond formation, followed by an intramolecular C(sp2)−H bond functionalization/C−O cyclization in one pot. This protocol provides direct access to useful 2‐amino‐1,3‐oxazoles and features protecting‐group‐free nitrogen sources, readily available starting materials, a broad substrate scope and mild reaction conditions. 相似文献
5.
Harnessing the Dual Properties of Thiol‐Grafted Cellulose Paper for Click Reactions: A Powerful Reducing Agent and Adsorbent for Cu
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Dr. Jordi Rull‐Barrull Martin d'Halluin Dr. Erwan Le Grognec Prof. Dr. François‐Xavier Felpin 《Angewandte Chemie (International ed. in English)》2016,55(43):13549-13552
A new approach exploiting the dual properties of thiol‐grafted cellulose paper for promoting copper‐catalyzed [3+2]‐cycloadditions of organic azides with alkynes and adsorbing residual copper species in solution was developed. The thiol‐grafted cellulose paper, used as a paper strip, effects the reduction of CuII to catalytically active CuI and acts as a powerful adsorbent for copper, thereby facilitating the work‐up process and leaving the crude mixture almost free of copper residues after a single filtration. 相似文献
6.
Dr. Lydie Harmand Romain Lambert Dr. Luca Scarpantonio Dr. Nathan D. McClenaghan Dr. Dominique Lastécouères Dr. Jean‐Marc Vincent 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16231-16239
A detailed study on the photoreduction of the copper(II) precatalyst 1 to generate a highly reactive cuprous species for the copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) click reaction is presented. For the photoactive catalyst described herein, the activation is driven by a photoinduced electron transfer (PET) process harnessing a benzophenone‐like ketoprofenate chromophore as a photosensitizer, which is equally the counterion. The solvent is shown to play a major role in the CuII to CuI reduction process as the final electron source, and the influence of the solvent nature on the photoreduction efficiency has been studied. Particular attention was paid to the use of water as a potential solvent, aqueous media being particularly appealing for CuAAC processes. The ability to solubilize the copper‐tren complexes in water through the formation of inclusion complexes with β‐CDs is demonstrated. Data is also provided on the fate of the copper(I)‐tren catalytic species when reacting with O2, O2 being used to switch off the catalysis. These data show that partial oxidation of the secondary benzylamine groups of the ligand to benzylimines occurs. Preliminary results show that when prolonged irradiation times are employed a CuI to Cu0 over‐reduction process takes place, leading to the formation of copper nanoparticles (NPs). Finally, the main objective of this work being the development of photoactivable catalysts of practical value for the CuAAC, the catalytic, photolatent, and recycling properties of 1 in water and organic solvents are reported. 相似文献
7.
Quan‐Guo Zhai Shu‐Ni Li Yu‐Cheng Jiang Man‐Cheng Hu 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(9):m249-m252
In the tetranuclear copper complex tetrakis[μ‐3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]bis[3,5‐bis(2‐pyridyl)‐1,2,4‐triazolido]dicopper(I)dicopper(II) dihydrate, [CuI2CuII2(C12H8N5)6]·2H2O, the asymmetric unit is composed of one CuI center, one CuII center, three anionic 3,5‐bis(2‐pyridyl)‐1,2,4‐triazole (2‐BPT) ligands and one solvent water molecule. The CuI and CuII centers exhibit [CuIN4] tetrahedral and [CuIIN6] octahedral coordination environments, respectively. The three independent 2‐BPT ligands adopt different chelating modes, which link the copper centers to generate a chair‐like tetranuclear metallomacrocycle with metal–metal distances of about 4.4 × 6.2 Å disposed about a crystallographic inversion center. Furthermore, strong π–π stacking interactions and O—H...N hydrogen‐bonding systems link the tetracopper clusters into a two‐dimensional supramolecular network. 相似文献
8.
Copper Complexes of New Redox‐Active 4,5‐Bisguanidino‐Substituted Benzodioxole Ligands: Control of the Electronic Structure by Counter‐Ligands,Solvent, and Temperature
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David Fridolin Schrempp Dr. Elisabeth Kaifer Prof. Hubert Wadepohl Prof. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(45):16187-16199
9.
Christopher Paolucci Anuj A. Verma Shane A. Bates Vincent F. Kispersky Jeffrey T. Miller Rajamani Gounder W. Nicholas Delgass Fabio H. Ribeiro William F. Schneider 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(44):12022-12027
Operando X‐ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu‐exchanged SSZ‐13. Catalysts prepared to contain only isolated, exchanged CuII ions evidence both CuII and CuI ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for CuII reduction to CuI. DFT calculations show that NO‐assisted NH3 dissociation is both energetically favorable and accounts for the observed CuII reduction. The calculations predict in situ generation of Brønsted sites proximal to CuI upon reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of CuI to CuII, which DFT suggests to occur by a NO2 intermediate. Reaction of Cu‐bound NO2 with proximal NH4+ completes the catalytic cycle. N2 is produced in both reduction and oxidation half‐cycles. 相似文献
10.
Axel Rodenstein Jan Griebel Rainer Richter Reinhard Kirmse Prof. Dr. 《无机化学与普通化学杂志》2008,634(5):867-874
Synthesis, Structure and EPR Investigations of binuclear Bis(N,N,N?,N?‐tetraisobutyl‐N′,N″‐isophthaloylbis(thioureato)) Complexes of CuII, NiII, ZnII, CdII and PdII The synthesis of binuclear CuII‐, NiII‐, ZnII‐, CdII‐ and PdII‐complexes of the quadridentate ligand N,N,N?,N?‐tetraisobutyl‐N′,N″‐isophthaloylbis(thiourea) and the crystal structures of the CuII‐ and NiII‐complexes are reported. The CuII‐complex crystallizes in two polymorphic modifications: triclinic, (Z = 1) and monoclinic, P21/c (Z = 2). The NiII‐complex was found to be isostructural with the triclinic modification of the copper complex. The also prepared PdII‐, ZnII‐ and CdII‐complexes could not be characterized by X‐ray analysis. However, EPR studies of diamagnetically diluted CuII/PdII‐ and CuII/ZnII‐powders show axially‐symmetric g and A Cu tensors suggesting a nearly planar co‐ordination within the binuclear host complexes. Diamagnetically diluted CuII/CdII powder samples could not be prepared. In the EPR spectra of the pure binuclear CuII‐complex exchange‐coupled CuII‐CuII pairs were observed. According to the large CuII‐CuII distance of about 7,50Å a small fine structure parameter D = 26·10?4 cm?1 is observed; T‐dependent EPR measurements down to 5 K reveal small antiferromagnetic interactions for the CuII‐CuII dimer. Besides of the dimer in the EPR spectra the signals of a mononuclear CuII species are observed whose concentration is T‐dependent. This observation can be explained assuming an equilibrium between the binuclear CuII‐complex (CuII‐CuII pairs) and oligomeric complexes with “isolated” CuII ions. 相似文献
11.
《Angewandte Chemie (International ed. in English)》2017,56(35):10438-10442
Copper‐mediated coupling between alkynes to generate a structurally rigid, linear 1,3‐diyne linkage has been known for over a century. However, the mechanistic requirement to simultaneously maintain CuI and an oxidant has limited its practical utility, especially for complex functional molecules in aqueous solution. We find that addition of a specific bpy‐diol ligand protects unprotected peptides from CuII‐mediated oxidative damage through the formation of an insoluble CuII gel which solves the critical challenge of applying Glaser coupling to substrates that are degraded by CuII. The generality of this method is illustrated through the conjugation of a series of polar and nonpolar labels onto a fully unprotected GLP‐1R agonist through a linear 7 Å diynyl linker. 相似文献
12.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(35):10574-10578
Copper‐mediated coupling between alkynes to generate a structurally rigid, linear 1,3‐diyne linkage has been known for over a century. However, the mechanistic requirement to simultaneously maintain CuI and an oxidant has limited its practical utility, especially for complex functional molecules in aqueous solution. We find that addition of a specific bpy‐diol ligand protects unprotected peptides from CuII‐mediated oxidative damage through the formation of an insoluble CuII gel which solves the critical challenge of applying Glaser coupling to substrates that are degraded by CuII. The generality of this method is illustrated through the conjugation of a series of polar and nonpolar labels onto a fully unprotected GLP‐1R agonist through a linear 7 Å diynyl linker. 相似文献
13.
Visible‐Light‐Accelerated Copper(II)‐Catalyzed Regio‐ and Chemoselective Oxo‐Azidation of Vinyl Arenes
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M. Sc. Asik Hossain Dr. Adiyala Vidyasagar M. Sc. Christian Eichinger Dr. Christian Lankes M. Sc. Jenny Phan Prof. Dr. Julia Rehbein Prof. Dr. Oliver Reiser 《Angewandte Chemie (International ed. in English)》2018,57(27):8288-8292
The visible‐light‐accelerated oxo‐azidation of vinyl arenes with trimethylsilylazide and molecular oxygen as stoichiometric oxidant was achieved. In contrast to photocatalysts based on iridium, ruthenium, or organic dyes, [Cu(dap)2]Cl or [Cu(dap)Cl2] were found to be unique for this transformation, which is attributed to their ability to interact with the substrates through ligand exchange and rebound mechanisms. CuII is proposed as the catalytically active species, which upon coordinating azide will undergo light‐accelerated homolysis to form CuI and azide radicals. This activation principle (CuII‐X→CuI+X.) opens up new avenues for copper‐based photocatalysis. 相似文献
14.
Copper‐Catalyzed Oxidative Reaction of β‐Keto Sulfones with Alcohols via C−S Bond Cleavage: Reaction Development and Mechanism Study
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Yang Wang Zhenghang Qi Jiaqi Tian Dr. Jie Zhou Xiaochen Wang Prof. Dr. Jianlin Han Prof. Dr. Jing Ma Prof. Dr. Yi Pan 《化学:亚洲杂志》2018,13(4):404-408
A Cu‐catalyzed cascade oxidative radical process of β‐keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β‐keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C?S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four‐coordinated CuII intermediate, O?O bond homolysis induced C?S bond cleavage and Cu‐catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C?S bond cleavage and transformations. 相似文献
15.
Transfer of Copper from an Amyloid to a Natural Copper‐Carrier Peptide with a Specific Mediating Ligand
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Dr. Michel Nguyen Dr. Christian Bijani Nathalie Martins Prof. Dr. Bernard Meunier Dr. Anne Robert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):17085-17090
The oxidative stress that arises from the catalytic reduction of dioxygen by CuII/I‐loaded amyloids is the major pathway for neuron death that occurs in Alzheimer’s disease. In this work, we show that bis‐8(aminoquinoline) ligands, copper(II) specific chelators, are able to catalytically extract CuII from Cu–Aβ1–16 and then completely release CuI in the presence of glutathione to provide a CuI–glutathione complex, a biological intermediate that is able to deliver copper to apo forms of copper–protein complexes. These data demonstrate that bis‐8(aminoquinolines) can perform the transfer of copper ions from the pathological Cu–amyloid complexes to regular copper–protein complexes. These copper‐specific ligands assist GSH to recycle CuI in an AD brain and consequently slow down oxidative damage that is due to copper dysregulation in Alzheimer’s disease. Under the same conditions, we have shown that the copper complex of PBT2, a mono(8‐hydroxyquinoline) previously used as a drug candidate, does not efficiently release copper in the presence of GSH. In addition, we report that GSH itself was unable to fully abstract copper ions from Cu–β‐amyloid complexes. 相似文献
16.
Nathan J. Oldenhuis K. Peter Qin Shu Wang Hong‐Zhou Ye Eric A. Alt Adam P. Willard Troy Van Voorhis Stephen L. Craig Jeremiah A. Johnson 《Angewandte Chemie (International ed. in English)》2020,59(7):2784-2792
Photoresponsive materials that change in response to light have been studied for a range of applications. These materials are often metastable during irradiation, returning to their pre‐irradiated state after removal of the light source. Herein, we report a polymer gel comprising poly(ethylene glycol) star polymers linked by Cu24L24 metal–organic cages/polyhedra (MOCs) with coumarin ligands. In the presence of UV light, a photosensitizer, and a hydrogen donor, this “polyMOC” material can be reversibly switched between CuII, CuI, and Cu0. The instability of the MOC junctions in the CuI and Cu0 states leads to network disassembly, forming CuI/Cu0 solutions, respectively, that are stable until re‐oxidation to CuII and supramolecular gelation. This reversible disassembly of the polyMOC network can occur in the presence of a fixed covalent second network generated in situ by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC), providing interpenetrating supramolecular and covalent networks. 相似文献
17.
Divergent Synthesis of CF3‐Substituted Allenyl Nitriles by Ligand‐Controlled Radical 1,2‐ and 1,4‐Addition to 1,3‐Enynes
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Fei Wang Dinghai Wang Yu Zhou Ling Liang Ronghua Lu Dr. Pinhong Chen Prof. Dr. Zhenyang Lin Prof. Dr. Guosheng Liu 《Angewandte Chemie (International ed. in English)》2018,57(24):7140-7145
A ligand‐controlled system that enables regioselective trifluoromethylcyanation of 1,3‐enynes has been identified, which provides access to a variety of CF3‐containing tri‐ and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)CuII cyanide, while the tautomerized allenyl radicals are trapped by (phen)CuII cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity‐tunable functionalization of 1,3‐enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry. 相似文献
18.
Alice Santoro Jenifer S. Calvo Manuel David Peris‐Díaz Artur Krel Gabriele Meloni Peter Faller 《Angewandte Chemie (International ed. in English)》2020,59(20):7830-7835
Copper complexes are of medicinal and biological interest, including as anticancer drugs designed to cleave intracellular biomolecules by O2 activation. To exhibit such activity, the copper complex must be redox active and resistant to dissociation. Metallothioneins (MTs) and glutathione (GSH) are abundant in the cytosol and nucleus. Because they are thiol‐rich reducing molecules with high CuI affinity, they are potential competitors for a copper ion bound in a copper drug. Herein, we report the investigation of a panel of CuI/CuII complexes often used as drugs, with diverse coordination chemistries and redox potentials. We evaluated their catalytic activity in ascorbate oxidation based on redox cycling between CuI and CuII, as well as their resistance to dissociation or inactivation under cytosolically relevant concentrations of GSH and MT. O2‐activating CuI/CuII complexes for cytosolic/nuclear targets are generally not stable against the GSH/MT system, which creates a challenge for their future design. 相似文献
19.
Dr. Tamaz Guliashvili Patrícia V. Mendonça Dr. Arménio C. Serra Dr. Anatoliy V. Popov Dr. Jorge F. J. Coelho 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(15):4607-4612
The field of transition‐metal‐mediated controlled/“living” radical polymerization (CLRP) has become the subject of intense discussion regarding the mechanism of this widely‐used and versatile process. Most mechanistic analyses (atom transfer radical polymerization (ATRP) vs. single‐electron transfer living radical polymerization (SET‐LRP)) have been based on model experiments, which cannot correctly mimic the true reaction conditions. We present, for the first time, a determination of the [CuIBr]/[L] (L=nitrogen‐based chelating ligand) ratio and the extent of CuIBr/L disproportionation during CLRP of methyl acrylate (MA) in dimethylsulfoxide (DMSO) with Cu0 wire as a transition‐metal catalyst source. The results suggest that Cu0 acts as a supplemental activator and reducing agent of CuIIBr2/L to CuIBr/L. More importantly, the CuIBr/L species seem to be responsible for the activation of SET‐LRP. 相似文献
20.
The synthesis and the structures of (i) the ligand N,N‐Diethyl‐N′‐3,5‐di(trifluoromethyl)benzoylthiourea HEt2dtfmbtu and (ii) the NiII and PdII complexes of HEt2dtfmbtu are reported. The ligand coordinates bidendate forming bis chelates. The NiII and the PdII complexes are isostructural. The also prepared CuII complex could not be characterized by X‐ray analysis. However, the preparation of diamagnetically diluted powders Cu/Ni(Et2dtfmbtu)2 and Cu/Pd(Et2dtfmbtu)2 suitable for EPR studies was successful. The EPR spectra of the Cu/Ni and Cu/Pd systems show noticeable differences for the symmetry of the CuS2O2 unit in both complexes: the Cu/Pd system is characterized by axially‐symmetric g< and A cu tensors; for the Cu/Ni system g and A Cu have rhombic symmetry. EPR studies on frozen solutions of the CuII complex show the presence of a CuII‐CuII dimer which is the first observed for CuII acylthioureato complexes up to now. The parameters of the fine structure tensor were used for the estimation of the CuII‐CuII distance. 相似文献