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Carlos D Yamamoto, Zijie Zhang, Sabine Chantal E Stieber
The crystal structure of the title compound, [Ni(C25 H28 N4 )(C8 H12 )]·C4 H8 O or (Mes NHC2 Me)Ni(COD), which contains a bidentate N-heterocyclic carbene (NHC) ligand with mesityl aryl groups is reported. The complex at 100 K has monoclinic ( P 21 / c ) symmetry and a distorted tetra-hedral geometry around the nickel center, with the cyclo-octa-diene ligand coordinated in a κ2 ,η2 fashion. The bidentate NHC ligand is not planar, with a C(carbene)-Ni-C(carbene) angle of 91.51 (12)°, resulting in the mesityl groups being on the same side of the cyclo-octa-diene (COD) ligand...
October 1, 2018: Acta Crystallographica. Section E, Crystallographic Communications
Chin Min Wong, Marianna Fekete, Rhianna Nelson-Forde, Mark R D Gatus, Peter J Rayner, Adrian C Whitwood, Simon B Duckett, Barbara A Messerle
The catalytic signal amplification by reversible exchange process has become widely used for the hyperpolarisation of small molecules to improve their magnetic resonance detectability. It harnesses the latent polarisation of para hydrogen, and involves the formation of a labile metal complex that often contains an N-heterocyclic carbene (NHC) ligand ( e.g. [Ir(H)2 (NHC)(pyridine)3 ]Cl), which act as a polarisation transfer catalyst. Unfortunately, if the target molecule is too bulky, binding to the catalyst is poor and the hyperpolarisation yield is therefore low...
October 7, 2018: Catalysis Science & Technology
Amlan K Pal, Simonas Krotkus, Mattia Fontani, Campbell F R Mackenzie, David B Cordes, Alexandra M Z Slawin, Ifor D W Samuel, Eli Zysman-Colman
High-efficiency pure blue phosphorescent organic light-emitting diodes (OLEDs) remain one of the grand challenges, principally because the emissive complexes employed either do not possess sufficiently high photoluminescence quantum yields or exhibit unsatisfactory Commission International de l'Éclairage (CIE) coordinates. Here two deep-blue-emitting homoleptic iridium(III) complexes are reported and OLEDs are demonstrated with CIE coordinates of (0.15, 0.05) and maximum external quantum efficiency of 13.4%, which decreases slightly to 12...
October 15, 2018: Advanced Materials
Lai-Hon Chung, Chun-Yuen Wong
While the fascinating chemistry demonstrated by metalated N-heterocyclic carbene complexes highlights the significance of metalated heterocyclic chemistry, the development of other metalated heterocycles is falling behind, presumably because of the sparseness of general synthetic methodologies. In this Concept article, the strategy to prepare metalated heterocyclic complexes via metal-induced cycloisomerization of heteroatom-functionalized alkynes is presented. The isolation of and calculations on novel ruthenium complexes bearing chromene, chromone, indole, indoline, indolizine and indolizinone moieties prepared from reactions between alkynes and ruthenium complexes are discussed, with emphasis on their mechanistic insights into the ruthenium-induced alkyne transformations and applications in material design and drug discovery...
October 12, 2018: Chemistry: a European Journal
Peter J Rayner, Philip Norcott, Kate M Appleby, Wissam Iali, Richard O John, Sam J Hart, Adrian C Whitwood, Simon B Duckett
Iridium N-heterocyclic carbene (NHC) complexes catalyse the para-hydrogen-induced hyperpolarization process, Signal Amplification by Reversible Exchange (SABRE). This process transfers the latent magnetism of para-hydrogen into a substrate, without changing its chemical identity, to dramatically improve its nuclear magnetic resonance (NMR) detectability. By synthesizing and examining over 30 NHC containing complexes, here we rationalize the key characteristics of efficient SABRE catalysis prior to using appropriate catalyst-substrate combinations to quantify the substrate's NMR detectability...
October 12, 2018: Nature Communications
Wolfram Sander, Enrique Mendez-Vega, Mika Maehara, Akshay Hemant Raut, Joel Mieres-Perez, Masashi Tsuge, Yuan-Pern Lee
The hydrogenation reactions of diphenylcarbene 1, fluorenylidene 2, and dibenzocycloheptadienylidene 3 were investigated in solid H2 and D2 matrices and in H2- and D2-doped argon matrices at cryogenic temperatures. The reactivity of the carbenes towards H2 increases in the order 1 < 3 < 2. While 1 is stable in solid H2, 2 and 3 react fast under the same conditions via quantum chemical tunneling. In D2 both 1 and 3 are stable, whereas 2 slowly reacts. The different reactivity of the three carbenes is rationalized in terms of differing carbene stabilization energies...
October 12, 2018: Chemistry: a European Journal
Shahar Dery, Suhong Kim, David Haddad, Albano Cossaro, Alberto Verdini, Luca Floreano, F Dean Toste, Elad Gross
Catalytic nanoparticles are heterogeneous in their nature and even within the simplest particle various surface sites exist and influence the catalytic reactivity. Thus, detailed chemical information at the nanoscale is essential for understanding how surface properties and reaction conditions direct the reactivity of different surface sites of catalytic nanoparticles. In this work, hydroxyl-functionalized N-heterocyclic carbene molecules (NHCs) were anchored to the surface of Pt particles and utilized as chemical markers to detect reactivity variations between different surface sites under liquid and gas phase oxidizing conditions...
August 21, 2018: Chemical Science
Zhongyi Zeng, Hongming Jin, Matthias Rudolph, Frank Rominger, A Stephen K Hashmi
We herein describe a facile, site-selective and divergent approach to construct 2-aminopyrroles and quinoline-fused polyazaheterocycles enabled by a simple gold(III) catalyst from ynamides and anthranils under mild reaction conditions. This one-pot strategy uses readily available starting materials, proceeds in a highly step- and atom-economical manner, with broad substrate scope and scale-up potential. The key element for success in this tandem reaction is a catalyst-directed preferred quenching of the in-situ generated gold carbene intermediates by a nucleophilic benzyl/2-furylmethyl moiety on the ynamides as an alternative to the known C-H annulation leading to indoles...
October 11, 2018: Angewandte Chemie
Shi Jun Ang, Adrian M Mak, Ming Wah Wong
The recently developed adiabatic absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA) has proven to be useful in determining the effects of different energy components on the geometries of complexes bound by intermolecular interactions. The authors have applied it to systems such as the water dimer, water-ion complexes, metallocenes and lone-pair type halogen-bonded (XB) dimers. In this study, we have extended the second-generation ALMO-EDA method to 40 different XB complexes by benchmarking against its classical counterpart and symmetry-adapted perturbation theory (SAPT)...
October 11, 2018: Physical Chemistry Chemical Physics: PCCP
Xinqiang Fang, Laxmaiah Vasamsetty, Shuang Yang, Miao Meng, Pogula Sreekanth Reddy, Xiangwen Kong, Weici Xu
Racemic mixtures of four stereoisomers are easily formed via many fundamental organic transformations, but the direct utilities of these mixtures have been less studied and remain as big challenges to date. In this work, we introduce a new method, i.e., divergent dynamic kinetic resolution, to achieve the separation of racemic mixtures of four stereoisomers. The hypothesis was proved by N-heterocyclic carbene-catalyzed benzoin reaction, which afforded two separable diastereomeric products bearing three consecutive stereocenters with good to excellent enantioselectivties...
October 10, 2018: Chemistry, An Asian Journal
Karel Škoch, Ivana Císařová, Filip Uhlík, Petr Štěpnička
Isomeric phosphinoferrocene ligands, viz. 1'-(diphenylphosphino)-1-cyanoferrocene (1) and 1'-(diphenylphosphino)-1-isocyanoferrocene (2), show markedly different coordination behaviours. For instance, the reactions of 1 with [PdCl2(MeCN)2] and [(LNC)Pd(μ-Cl)]2 (LNC = [2-(dimethylamino-κN)methyl]phenyl-κC1) produced the "phosphine" complexes [PdCl2(1-κP)2] (7) and [(LNC)PdCl(1-κP)] (8), and the latter was converted into the coordination polymer [(LNC)Pd(μ(P,N)-1)][SbF6] (9). Conversely, the reaction of 2 with [(LNC)Pd(μ-Cl)]2 involved coordination of the phosphine moiety and simultaneous insertion of the isocyanide group into the Pd-C bond, giving rise to the P,η1-imidoyl complex [PdCl(Ph2PfcN[double bond, length as m-dash]CC6H4CH2NMe2-κ3C,N,P)] (10; fc = ferrocene-1,1'-diyl)...
October 10, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Peter V Simpson, Marco Falasca, Massimiliano Massi
Re(i) complexes bound to π-conjugated bidentate N-heterocyclic carbene ligands with formulation Re(CO)3(N^NHC)L (where N^NHC represents an imidazole or benzimidazole carbene ligand conjugated to a N-based heterocycle such as pyridine, pyrimidine, quinoline or quinoxaline) are a relatively new class of complexes belonging to the archetypal family of well known luminescent Re(CO)3(diim)X species (where diim is a conjugated diimine ligand and X is a halogen anion). The complexes Re(CO)3(N^NHC)L are characterised by blue-shifted emission compared to Re(CO)3(diim)X, but with shorter excited state lifetime decays and lower quantum yields, in contrast to trends expected by the energy gap law...
October 10, 2018: Chemical Communications: Chem Comm
F Ekkehardt Hahn
No abstract text is available yet for this article.
October 10, 2018: Chemical Reviews
Rudi Fasan, Ajay L Chandgude
A chemobiocatalytic strategy for the highly stereoselective synthesis of nitrile-substituted cyclopropanes is reported. The present approach relies on an asymmetric olefin cyclopropanation reaction catalyzed by an engineered myoglobin in the presence of ex situ generated diazoacetonitrile within a compartmentalized reaction system. This method enabled the efficient transformation of a broad range of olefin substrates at the preparative scale with up to 99.9% de and ee and up to 5,600 turnovers. The enzymatic product could be further diversified to furnish a variety of functionalized chiral cyclopropanes...
October 9, 2018: Angewandte Chemie
Yong-Heng Wang, An-An Wu, Kai Tan, Xin Lu
Gold-catalyzed intermolecular alkyne oxidation has attracted much synthetic attention, but mostly suffering undesired over-oxidation. Recent experiments demonstrated that over-oxidation could be dramatically suppressed in zinc(II)-catalyzed intermolecular alkyne oxidation/CH functionalization. By means of first-principle density functional theory calculations, we explored the mechanism of the M-catalyzed intermolecular alkyne oxidations (M = Zn(OTf)2 and Au+ PR3 ) as well as the effects of oxidants, temperature, and metal catalysts on chemoselectivity, in an effort to disclose the origin of the extraordinary chemoselectivity pertaining to zinc catalysis...
October 9, 2018: Journal of Computational Chemistry
Didier Bégué, Alain Dargelos, Curt Wentrup
The electronic structure and the rearrangements of the 2-phenylnitrene radical cation C6H5N.+ 2.+ have been investigated at DFT and CASPT2(7,9) levels of theory. The 2B2 state has the lowest energy of five identified electronic states, and it can undergo ring expansion to the 1-azacycloheptetetraene radical cation 4.+ with an activation energy of ca. 28 kcal/mol. Ring opening and recyclization provides a route to 5-cyanocyclopentadiene radical cation 8.+, which may undergo facile 1,5-hydrogen shifts. The 2-, 3-, and 4-pyridylcarbene radical cations 31...
October 9, 2018: Journal of Physical Chemistry. A
Surojit Santra, Arka Porey, Barun Jana, Joyram Guin
Highly diastereo- and enantioselective 1,6-addition of 1,3-ketoamides to p -quinone methides ( p -QMs) using chiral NHCs as Brønsted base catalysts is developed. The reaction is based on the utilization of a 1,3-ketoamide having acidic N-H that forms a chiral ion-pair consisting of the enolate and the azolium ion. Different β-ketoamides and functionalized p -QMs are applicable to the reaction. Synthetic application of the method is demonstrated via the preparation of highly enantioenriched β and γ-lactam derivatives...
August 14, 2018: Chemical Science
Qiyuan He, Naoto Chatani
The alkylation of C-H bonds with N-vinylphthalimide by a rhodium-catalyzed reaction of aromatic amides containing an 8-aminoquinoline moiety as the directing group is reported. N-Vinylphthalimide functions as a 2-aminoethylating reagent. The resulting alkylated products can be converted into 3,4-dihydroisoquinolin-1(2H)-one derivatives in a one pot transformation. Deuterium-labeling experiments suggest that the reaction proceeds through a carbene mechanism.
October 4, 2018: Journal of Organic Chemistry
Chao Pei, Guang-Wei Rong, Zhi-Xiang Yu, Xinfang Xu
Herein, a copper-catalyzed intramolecular cascade reaction of conjugated enynones to deliver substituted 1H-indenes is reported. The inexpensive and lower toxic copper salt served as the only catalyst in the transformation, affording the 3-(2-furyl)-substituted 1H-indenes in good to excellent yields under mild reaction conditions with broad functional group tolerations and making it highly appealing for synthetic organic chemistry. Notably, detailed DFT calculations have been carried out to elucidate that the reaction undergoes a copper-mediated 5-exo-dig cyclization of enynones to afford copper-(2-furyl)-carbene intermediate, followed by dienecarbene cyclization (one step but involving 6π cyclization of Cu-carbene and reductive elimination) and 1,5-hydrogen shift to provide the 1H-indenes...
October 4, 2018: Journal of Organic Chemistry
Erik Troschke, Khoa Dang Nguyen, Silvia Paasch, Johannes Schmidt, Georg Nickerl, Irena Senkovska, Eike Brunner, Stefan Kaskel
The successful incorporation of a thermally fragile imidazolium moiety into a covalent triazine framework resulted in a heterogeneous organocatalyst active in carbene-catalysed Umpolung reaction. The structural integrity of the imidazolium moiety was confirmed by combining solid state NMR and XPS experiments.
October 4, 2018: Chemistry: a European Journal
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