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Elevated Catalytic Activity of Ruthenium(II)–Porphyrin‐Catalyzed Carbene/Nitrene Transfer and Insertion Reactions with N‐Heterocyclic Carbene Ligands 下载免费PDF全文
Ka‐Ho Chan Dr. Xiangguo Guan Dr. Vanessa Kar‐Yan Lo Prof. Dr. Chi‐Ming Che 《Angewandte Chemie (International ed. in English)》2014,53(11):2982-2987
Bis(NHC)ruthenium(II)–porphyrin complexes were designed, synthesized, and characterized. Owing to the strong donor strength of axial NHC ligands in stabilizing the trans M?CRR′/M?NR moiety, these complexes showed unprecedently high catalytic activity towards alkene cyclopropanation, carbene C? H, N? H, S? H, and O? H insertion, alkene aziridination, and nitrene C? H insertion with turnover frequencies up to 1950 min?1. The use of chiral [Ru(D4‐Por)(BIMe)2] ( 1 g ) as a catalyst led to highly enantioselective carbene/nitrene transfer and insertion reactions with up to 98 % ee. Carbene modification of the N terminus of peptides at 37 °C was possible. DFT calculations revealed that the trans axial NHC ligand facilitates the decomposition of diazo compounds by stabilizing the metal–carbene reaction intermediate. 相似文献
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Siti Nurhanna Riduan Yugen Zhang Dr. Jackie Y. Ying Prof. 《Angewandte Chemie (International ed. in English)》2009,48(18):3322-3325
Activate and reduce : Carbon dioxide was reduced with silane using a stable N‐heterocyclic carbene organocatalyst to provide methanol under very mild conditions. Dry air can serve as the feedstock, and the organocatalyst is much more efficient than transition‐metal catalysts for this reaction. This approach offers a very promising protocol for chemical CO2 activation and fixation.
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Proton‐Transfer Polymerization (HTP): Converting Methacrylates to Polyesters by an N‐Heterocyclic Carbene 下载免费PDF全文
Dr. Miao Hong Prof. Dr. Eugene Y.‐X. Chen 《Angewandte Chemie (International ed. in English)》2014,53(44):11900-11906
A new polymerization termed proton (H)‐transfer polymerization (HTP) has been developed to convert dimethacrylates to unsaturated polyesters. HTP is catalyzed by a selective N‐heterocyclic carbene capable of promoting intermolecular Umpolung condensation through proton transfer and proceeds through the step‐growth propagation cycles via enamine intermediates. The role of the added suitable phenol, which is critical for achieving an effective HTP, is twofold: shutting down the radically induced chain‐growth addition polymerization under HTP conditions (typically at 80–120 °C) and facilitating proton transfer after each monomer enchainment. The resulting unsaturated polyesters have a high thermal stability and can be readily cross‐linked to robust polyester materials. 相似文献
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Water‐Soluble Luminescent Cyclometalated Gold(III) Complexes with cis‐Chelating Bis(N‐Heterocyclic Carbene) Ligands: Synthesis and Photophysical Properties 下载免费PDF全文
Faan‐Fung Hung Dr. Wai‐Pong To Dr. Jing‐Jing Zhang Dr. Chensheng Ma Prof. Dr. Wai‐Yeung Wong Prof. Dr. Chi‐Ming Che 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(28):8604-8614
A new class of cyclometalated AuIII complexes containing various bidentate C‐deprotonated C^N and cis‐chelating bis(N‐heterocyclic carbene) (bis‐NHC) ligands has been synthesized and characterized. These are the first examples of AuIII complexes supported by cis‐chelating bis‐NHC ligands. [Au(C^N)(bis‐NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (λmax) at 498–633 nm and emission quantum yields of up to 10.1 %. The emissions are assigned to triplet intraligand (IL) π→π* transitions of C^N ligands. The AuIII complex containing a C^N (C‐deprotonated naphthalene‐substituted quinoline) ligand with extended π‐conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with λmax at 454 and 611 nm respectively. With sulfonate‐functionalized bis‐NHC ligand, four water‐soluble luminescent AuIII complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water‐soluble AuIII complex with C‐deprotonated naphthalene‐substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water‐soluble AuIII complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC50 value of 0.15 μM . 相似文献
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Luciano Oehninger Laura Nadine Küster Claudia Schmidt Prof. Dr. Alvaro Muñoz‐Castro Dr. med. habil. Dr. rer. nat. Aram Prokop Prof. Dr. Ingo Ott 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17871-17880
Rhodium(I) complexes bearing N‐heterocyclic carbene (NHC) ligands have been widely used in catalytic chemistry, but there are very few reports of biological properties of these organometallics. A series of RhI‐NHC derivatives with 1,5‐cyclooctadiene and CO as secondary ligands were synthesized, characterized, and biologically investigated as prospective antitumor drug candidates. Pronounced antiproliferative effects were noted for all complexes, along with moderate inhibitory activity of thioredoxin reductase (TrxR) and efficient binding to biomolecules (DNA, albumin). Biodistribution studies showed that the presence of albumin lowered the cellular uptake and confirmed the transport of rhodium into the nuclei. Changes in the mitochondrial membrane potential (MMP) were observed as well as DNA fragmentation in wild‐type and daunorubicin‐ or vincristine‐resistant Nalm‐6 leukemia cells. Overall, these studies indicated that RhI‐NHC fragments could be used as partial structures of new antitumor agents, in particular in those drugs designed to address resistant malignant tissues. 相似文献
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N‐Heterocyclic Carbene,High Oxidation State Molybdenum Alkylidene Complexes: Functional‐Group‐Tolerant Cationic Metathesis Catalysts 下载免费PDF全文
Prof. Michael R. Buchmeiser M. Sc. Suman Sen Dr. Jörg Unold Dr. Wolfgang Frey 《Angewandte Chemie (International ed. in English)》2014,53(35):9384-9388
We synthesized the first N‐heterocyclic carbene (NHC) complexes of Schrock’s molybdenum imido alkylidene bis(triflate) complexes. Unlike existing bis(triflate) complexes, the novel 16‐electron complexes represent metathesis active, functional‐group‐tolerant catalysts. Single‐crystal X‐ray structures of two representatives of this novel class of Schrock catalysts are presented and reactivity is discussed in view of their structural peculiarities. In the presence of monomer (substrate), these catalysts form cationic species and can be employed in ring‐closing metathesis (RCM), ring‐opening metathesis polymerization (ROMP), as well as in the cyclopolymerization of α,ω‐diynes. Monomers containing functional groups, which are not tolerated by the existing variations of Schrock’s catalyst, e.g., sec‐amine, hydroxy, and carboxylic acid moieties, can be used. These catalysts therefore hold great promise in both organic and polymer chemistry, where they allow for the use of protic monomers. 相似文献
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Gregory A. Chass Dr. Christopher J. O'Brien Dr. Niloufar Hadei Dr. Eric Assen B. Kantchev Dr. Wei‐Hua Mu De‐Cai Fang Prof. Alan C. Hopkinson Prof. Imre G. Csizmadia Prof. Michael G. Organ Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(17):4281-4288
Why bigger is better : A “steric wall” created by the N‐(2,6‐diisopropylphenyl) substituent on the bulky NHC ligand IPr (1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) guides the reactants to and from the Pd center through weak, fleeting (IPr)H–Pd interactions that help the oxidative addition intermediate escape “the anti‐trap”. The alternative “side” approach leads to transmetalation (the rate‐limiting step) for which a novel Pd–Zn interaction was identified.
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Oxidative Enantioselective α‐Fluorination of Aliphatic Aldehydes Enabled by N‐Heterocyclic Carbene Catalysis 下载免费PDF全文
Fangyi Li Zijun Wu Prof. Dr. Jian Wang 《Angewandte Chemie (International ed. in English)》2015,54(2):656-659
Described is the first study on oxidative enantioselective α‐fluorination of simple aliphatic aldehydes enabled by N‐heterocyclic carbene catalysis. N‐fluorobis(phenyl)sulfonimide serves as a an oxidant and as an “F” source. The C? F bond formation occurs directly at the α position of simple aliphatic aldehydes, thus overcoming nontrivial challenges, such as competitive difluorination and nonfluorination, and proceeds with high to excellent enantioselectivities. 相似文献
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DFT calculations at the BP86/TZ2P level were carried out to analyze quantitatively the metal–ligand bonding in transition‐metal complexes that contain imidazole (IMID), imidazol‐2‐ylidene (nNHC), or imidazol‐4‐ylidene (aNHC). The calculated complexes are [Cl4TM(L)] (TM=Ti, Zr, Hf), [(CO)5TM(L)] (TM=Cr, Mo, W), [(CO)4TM(L)] (TM=Fe, Ru, Os), and [ClTM(L)] (TM=Cu, Ag, Au). The relative energies of the free ligands increase in the order IMID<nNHC<aNHC. The energy levels of the carbon σ lone‐pair orbitals suggest the trend aNHC>nNHC>IMID for the donor strength, which is in agreement with the progression of the metal–ligand bond‐dissociation energy (BDE) for the three ligands for all metals of Groups 4, 6, 8, and 10. The electrostatic attraction can also be decisive in determining trends in ligand–metal bond strength. The comparison of the results of energy decomposition analysis for the Group 6 complexes [(CO)5TM(L)] (L=nNHC, aNHC, IMID) with phosphine complexes (L=PMe3 and PCl3) shows that the phosphine ligands are weaker σ donors and better π acceptors than the NHC tautomers nNHC, aNHC, and IMID. 相似文献
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Rhodium(III)‐Catalyzed Selective ortho‐Olefinations of N‐Acyl and N‐Aroyl Sulfoximines by CH Bond Activation 下载免费PDF全文
Dr. Kanniyappan Parthasarathy Prof. Dr. Carsten Bolm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4896-4900
Two new rhodium‐catalyzed oxidative couplings between sulfoximine derivatives and alkenes by regioselective C?H activation, affording ortho‐olefinated (Heck‐type) products, are reported. A synthetic application of the ortho‐alkenylated products into the corresponding cyclic derivatives has been demonstrated, and a mechanistic rational for the rhodium catalysis is presented. 相似文献
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