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Iogann Tolbatov, Cecilia Coletti, Alessandro Marrone, Nazzareno Re
Neutral N⁻heterocyclic carbene gold(I) compounds such as IMeAuCl are widely used both in homogeneous catalysis and, more recently, in medicinal chemistry as promising antitumor agents. In order to shed light on their reactivity with protein side chains, we have carried out density functional theory (DFT) calculations on the thermodynamics and kinetics of their reactions with water and various nucleophiles as a model of plausible protein binding sites such as arginine, aspartic acid, asparagine, cysteine, glutamic acid, glutamine, histidine, lysine, methionine, selenocysteine, and the N-terminal group...
February 14, 2019: International Journal of Molecular Sciences
Sang Weon Roh, Kyoungmin Choi, Chulbom Lee
With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis...
February 15, 2019: Chemical Reviews
Shuyang Shi, Moon Chul Jung, Caleb Coburn, Abegail Tadle, Daniel Sylvinson M R, Peter I Djurovich, Stephen R Forrest, Mark E Thompson
A series of six luminescent two-coordinate Cu(I) complexes were investigated bearing nonconventional N-heterocyclic carbene ligands, monoamido-aminocarbene (MAC*) and diamidocarbene (DAC*), along with carbazolyl (Cz) as well as mono- and dicyano-substituted Cz derivatives. The emission color can be systematically varied over 270 nm, from violet to red, through proper choice of the acceptor (carbene) and donor (carbazolyl) groups. The compounds exhibit photoluminescent quantum efficiencies up to 100% in fluid solution and polystyrene films with short decay lifetimes (τ ≈ 1 μs)...
February 15, 2019: Journal of the American Chemical Society
Sha Li, Ziwei Tang, Yang Wang, Dan Wang, Zhanlin Wang, Chenxia Yu, Tuanjie Li, Donghui Wei, Changsheng Yao
An N-heterocyclic carbene (NHC) catalyzed γ-specific aldol-like reaction between allenoates and isatins has been achieved under mild conditions, giving trisubstituted allene derivatives bearing isatin moiety in moderate to good yields with high diastereoselectivity and excellent atom efficiency. The DFT computations indicated that the formation of the γ-adduct was more energetically favorable than that of the α-adduct. The result reported herein opens a new route for NHC-promoted allenoate-involved reaction...
February 15, 2019: Organic Letters
Jennifer L Minnick, Doaa Domyati, Rachel Ammons, Laleh Tahsini
Over the last two decades, N-heterocyclic carbene (NHC)-copper catalysts have received considerable attention in organic synthesis. Despite the popularity of copper complexes containing monodentate NHC ligands and recent development of poly(NHC) platforms, their application in C-C and C-heteroatom cross-coupling reactions has been limited. Recently, we reported an air-assisted Sonogashira-type cross-coupling catalyzed by well-defined cationic copper-pincer bis(NHC) complexes. Herein, we report the application of these complexes in Ullmann-type C-X (X = N, O) coupling of azoles and phenols with aryl halides in a relatively short reaction time...
2019: Frontiers in Chemistry
Martin Brehm, Martin Pulst, Joerg Kressler, Daniel Sebastiani
We present first results on triazolium-based ionic liquids (ILs) as a novel class of non-derivatising solvents for cellulose. Despite their chemical similarity to imidazolium cations, the 1,2,3-triazolium cation lacks the isolated ring proton, leading to reduced formation of N-heterocyclic carbenes (NHCs), and therefore to lower reactivity and less unwanted side reactions. We synthesised six ILs based on 1,2,3-triazolium and 1,2,4-triazolium cations. The acetates are room temperature ionic liquids (RTILs) and dissolve a similar amount of cellulose as the corresponding imidazolium salt...
February 14, 2019: Journal of Physical Chemistry. B
Ana Sánchez-Grande, Bruno de la Torre, José Santos, Borja Cirera, Koen Lauwaet, Taras Chutora, Shayan Edalatmanesh, Pingo Mutombo, Johanna Rosen, Radek Zboril, Rodolfo Miranda, Jonas Björk, Pavel Jelínek, Nazario Martín, David Ecija
Engineering low band gap π-conjugated polymers is a burgeoning area in basic and applied research. The main synthetic challenge lies in the solubility of the materials during the chemical synthesis which precludes the advance of the field. Here, we report an unprecedented on-surface synthesis protocol to overcome such difficulties, being able to design poly(p-anthracene ethynylene) molecular wires on an Au(111) surface. To this aim, a quinoid anthracene precursor endowed with =CBr2 moieties is deposited and annealed to 400 K resulting in anthracene-based polymers, with a measured electronic bandgap of 1...
February 14, 2019: Angewandte Chemie
Rai-Shung Liu, Yu-Chen Hsu, Shu-An Hsieh
Gold-catalyzed annulation of N-propargyl ynamides with anthranils can proceed via two distinct mechanisms. In the case of a terminal N-propargyl ynamide, its resulting α-imino gold carbene reacts with a tethered alkyne to generate a vinyl cation to enable hydrolysis, ultimately yielding a pyrrolo[2,3-b]quinoline derivative after treatment with TsOH. For an internal alkyne, its α-imino gold carbene reacts with a tethered alkyne via either a vinyl cation or an alkenylgold carbene; both paths lead to a 4-ketone-2-aminopyrrole derivative ultimately...
February 11, 2019: Chemistry: a European Journal
Tsz-Lung Lam, Ka-Chung Tong, Chen Yang, Wai-Lun Kwong, Xiangguo Guan, Ming-De Li, Vanessa Kar-Yan Lo, Sharon Lai-Fung Chan, David Lee Phillips, Chun-Nam Lok, Chi-Ming Che
A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII (ttp)(IMe)2 ]+ ( 2a ), [IrIII (oep)(BIMe)2 ]+ ( 2d ), [IrIII (oep)(I i Pr)2 ]+ ( 2e ) and [IrIII (F20 tpp)(IMe)2 ]+ ( 2f ) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 Å and long Ir-CNHC bonds of 2.100-2.152 Å. Variable-temperature 1 H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol-1 ...
January 7, 2019: Chemical Science
Łukasz Gułajski, Andrzej Tracz, Katarzyna Urbaniak, Stefan J Czarnocki, Michał Bieniek, Tomasz K Olszewski
The influence of microwave and ultrasonic irradiation on the performance of ammonium-tagged Ru-based catalysts in olefin metathesis transformations in aqueous media was studied. Differences in the catalytic activity in correlation with the nature of the present counter ion and the size of the N -heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions.
2019: Beilstein Journal of Organic Chemistry
Lorenz J Schiegerl, Mohand Melaimi, Daniel R Tolentino, Wilhelm Klein, Guy Bertrand, Thomas F Fässler
The coordination of Ge9 Zintl clusters at (carbene)CuI moieties is explored, and the complexes [(CAAC)Cu]2 [η3 -Ge9 {Si(TMS)3 }2 ] (1), (CAAC)Cu[η3 -Ge9 {Si(TMS)3 }3 ] (2), and (MIC)Cu[η3 -Ge9 {Si(TMS)3 }3 ] (3) are compared with their known N-heterocyclic carbene (NHC) derivatives (A and B), where CAAC = cyclic (alkyl)amino carbene, MIC = mesoionic carbene, and TMS = trimethylsilane. In analogy to the NHC derivatives, the synthesis of 1-3 proceeds by single-step reactions of (CAAC)CuCl or (MIC)CuCl with the [Ge9 R2 ]2- and [Ge9 R3 ]- [R = Si(TMS)3 ] cluster ligands, respectively, and yields complexes of (carbene)CuI (carbene = CAAC, MIC) moieties exhibiting η3 -coordination modes of the Ge9 deltahedron to the Cu atom...
February 11, 2019: Inorganic Chemistry
Nguyen Nhat Thu Le, Josefine Just, Jonathan M Pankauski, Paul R Rablen, Dasan M Thamattoor
Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes-formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon-were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled...
February 7, 2019: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Alexandria Deliz Liang, Joan Serrano-Plana, Ryan L Peterson, Thomas R Ward
Artificial metalloenzymes (ArMs) result from anchoring a metal-containing moiety within a macromolecular scaffold (protein or oligonucleotide). The resulting hybrid catalyst combines attractive features of both homogeneous catalysts and enzymes. This strategy includes the possibility of optimizing the reaction by both chemical (catalyst design) and genetic means leading to achievement of a novel degree of (enantio)selectivity, broadening of the substrate scope, or increased activity, among others. In the past 20 years, the Ward group has exploited, among others, the biotin-(strept)avidin technology to localize a catalytic moiety within a well-defined protein environment...
February 8, 2019: Accounts of Chemical Research
Qian Zeng, Kuiyong Dong, Jingjing Huang, Lihua Qiu, Xinfang Xu
A copper-catalyzed selective cascade reaction of alkyne-tethered diazo compounds is reported for the direct and efficient construction of dihydrocyclohepta[b]indole skeletons under mild reaction conditions. A vinyl copper carbene is the key intermediate, which is generated in situ via carbene/alkyne metathesis (CAM) and terminated with the Buchner reaction.
February 8, 2019: Organic & Biomolecular Chemistry
Rajendra S Dhayal, Werner E van Zyl, C W Liu
Hydrogen is seen as an increasingly important clean and sustainable energy source going into the future. There are a host of materials being investigated for the storage of hydrogen. In this frontier, we provide an overview of hydride clusters derived from Earth-abundant copper being used for the storage and conversion of hydrides into hydrogen, and the reaction of CO2 with hydride sources to produce the formic acid/formate pairing, which are considered excellent hydrogen carriers. We summarize the main synthesis methods to stabilize high-nuclearity hydride clusters with phosphine, N-heterocyclic carbene, and in particular phosphor-1,1-dithiolate ligands...
February 6, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Toshiki Nishiura, Asako Takabatake, Mariko Okutsu, Jun Nakazawa, Shiro Hikichi
Exposure of O2 to a reaction mixture containing bis(acac)cobalt(ii), a facially capping tris(N-heterocyclic carbene)borate ligand and 1-methylimidazole yields a heteroleptic cobalt(iii) complex with acac, 1-methylimidazole and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this heteroleptic complex to catalytically oxidize cyclohexane at ambient temperature.
February 5, 2019: Dalton Transactions: An International Journal of Inorganic Chemistry
Syeda Tazeen Zehra, Guoxiang Zhang, Shuang Yang, Xinqiang Fang
Chiral β-ketoesters bearing fully substituted carbon centers are important building blocks in organic synthesis. Mono-substituted ketoesters have been widely used to synthesize the above compounds through asymmetric additions or substitutions. The limitations of these protocols mainly exist in the substrate scopes, and α-methyl or α-fluoro-substituted β-ketoesters or acetyl acetates are frequently used owing to their relatively higher reactivity. To break through this limitation, we employed N-heterocyclic carbene-catalyzed kinetic resolution to achieve the access to enantioenriched β-ketoesters with quaternary stereocenters...
February 5, 2019: Organic & Biomolecular Chemistry
Birte M Zimmermann, Sarah C K Kobosil, Johannes F Teichert
A simple and air-stable copper(i)/N-heterocyclic carbene complex enables the catalytic hydrogenation of enoates and enamides, hitherto unreactive substrates employing homogeneous copper catalysis and H2 as a terminal reducing agent. This atom economic transformation replaces commonly employed hydrosilanes and can also be carried out in an asymmetric fashion.
February 4, 2019: Chemical Communications: Chem Comm
Yaru Gao, Dehai Liu, Zhenqian Fu, Wei Huang
A novel strategy for the construction of 2,2-diacyl spirocyclohexanones 3 has been demonstrated on the basis of an NHC-catalyzed [3C + 3C] annulation of potassium 2-oxo-3-enoates with 2-ethylidene 1,3-indandiones. Furthermore, enantioenriched 3 was obtained in good to excellent yields with good enantioselectivities when chiral N-heterocyclic carbene (NHC) was employed. Notably, ring opening of the resulting 2,2-diacyl spirocyclohexanones 3 with hydrazine led to the formation of phthalazinones in good to excellent yields...
February 4, 2019: Organic Letters
Julia K Schuster, Dipak Kumar Roy, Carsten Lenczyk, Jan Mies, Holger Braunschweig
A range of mono- and bis-adducts of beryllium dichloride with cyclic (alkyl)(amino)carbenes (CAAC), cyclic diamidocarbene (DAC), and carbodiphosphorane (CDP) are prepared, and their reactions with nucleophiles are studied. Salt elimination with Yamashita and Nozaki's lithium diazaborolide reagent led to the isolation of an unsymmetrical beryllium diazaborolyl complex and a base-stabilized diazaborolyl beryllium chloride. From structural and spectroscopic analyses, the Be-B bonding in these compounds was determined to be polar covalent in character...
February 1, 2019: Inorganic Chemistry
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