- Gold complexes with tridentate cyclometalating and NHC ligands: A search for new photoluminescent gold(III) compounds
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Many square-planar Pt(II) complexes are strongly photoluminescent, particularly when they contain cyclometalating and/or NHC ligands which produce strong ligand fields. In this work we investigated the possibility of obtaining isoelectronic Au(III) complexes with favorable luminescence properties. Toward this end, the coordination chemistry of gold with three different (potentially) tridentate ligands was explored: 1,3-bis(1-hexyl-2′-benzimidazoyl)benzene (L1H), 2,6-bis(3-butylimidazol-1-ium)pyridine (L2H 22+), and 2,6-bis(3-hexylbenzimidazol-1-ium)pyridine (L3H22+). Pt(II) or Pd(II) complexes are known for all of these ligands or closely related analogues, and hence we anticipated that similar Au(III) complexes would be synthetically accessible as well. This turned out to be the case only for L1, despite exploration of different synthetic routes including (i) direct complexation of Au(III), (ii) transmetalation from Ag(I) precursor complexes, and (iii) transmetalation from suitable Hg(II) precursors. Only the mercury procedure was successful (at least in the case of L1); transmetalation from silver or direct complexation yields other reaction products containing Au(I) in most cases. Likewise, with ligands L2 and L3 mainly complexes of Au(I) were obtained: i.e., the propensity of gold for low oxidation states is a major obstacle to obtaining the desired Au(III) compounds. Several new complexes of Au(I) and Au(III) were characterized crystallographically. Our results provide insight into the differences between the coordination chemistry of isoelectronic Pt(II) and Au(III) with tridentate cyclometalating and NHC ligands.
- Herbst, Annika,Bronner, Catherine,Dechambenoit, Pierre,Wenger, Oliver S.
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- Determining the Catalyst Properties That Lead to High Activity and Selectivity for Catalytic Hydrodeoxygenation with Ruthenium Pincer Complexes
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Ten ruthenium pincer complexes were evaluated as catalysts for the hydrodeoxygenation (HDO) reaction on a lignin monomer surrogate, vanillyl alcohol. Four of these complexes are reported herein with the synthesis and full characterization data for all and single-crystal X-ray diffraction data for three complexes bearing OH/O-, NMe2, and Me substituents on the pincer. A systematic study of these CNC pincer complexes revealed that the π-donor substituent on the pyridine ring plays a key role in enhancing the yield of the desired deoxygenated product. While OMe, OH, and NMe2 are all effective as π-donor substituents on the central pyridine ring in the pincer, the highest conversion to products and the best selectivity was observed with OH substituents and added sodium carbonate as a base. Base serves to deprotonate the OH group and form 1O- as observed spectroscopically. Furthermore, efforts to use other catalysts have revealed that free or labile sites are needed on the ruthenium center and an electronically rich and nonbulky CNC pincer is optimal. At low catalyst loadings (0.01 mol %), the OH-substituted catalyst 1OH in the presence of base serves as a homogeneous catalyst and is able to achieve quantitative and selective conversion of vanillyl alcohol to desired the HDO product, creosol, with up to 10000 turnovers. With this knowledge in hand, we can design the next generation of homogeneous catalysts with increased reactivity toward all of the oxygenated sites on lignin-derived monomers.
- Boudreaux, Chance M.,Das, Sanjit,Delucia, Nicholas A.,Papish, Elizabeth T.,Qu, Fengrui,Vannucci, Aaron K.,Yao, Wenzhi
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- Strong antibacterial properties of anion transporters: A result of depolarization and weakening of the bacterial membrane
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The development of low molecular weight anionophores is an emerging topic in chemistry, as the need for these compounds increases with the continuous discovery of pathologies involving anomalies in anion transport processes. Development of new concepts to initiate anion imbalance in living cells while fighting multidrug-resistant bacteria is a paramount topic. In this study, three series of compounds including N,N'-diphenylethynylbenzyl benzimidazolium salts (1 and 2), 1,1'-(pyridine-2,6-diyl)bis(3-(4-(phenylethynyl)benzyl)-1H-benzo[d]imidazol-3-ium) salts (3-5), and 1,1'-(pyridine-2,6-diylbis(methylene))bis(3-(4-(phenyl ethynyl)benzyl)-1H-benzo[d]imidazol-3-ium) salts (6-8) displaying high antimicrobial activity and low toxicity against human cells were designed, synthesized, and studied. The most potent compound displayed micromolar minimal inhibitory concentrations in different Gram-negative and Gram-positive bacteria, while its hemolytic activity remained around 10% or less, even after a prolonged period of exposure. The mechanism of action of these benzimidazolium salts on bacterial membrane was assessed by bioanalytical techniques including assays in model membrane liposomes, membrane depolarization studies, and scanning electron microscopy (SEM) in living bacteria.
- Elie, Claude R.,David, Guillaume,Schmitzer, Andreea R.
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- Copper(II) complex with tridentate N donor ligand: Synthesis, crystal structure, reactivity and DNA binding study
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Penta-coordinated mononuclear copper(II) complex of tridentate 2,6-bis-(benzimidazolyl)pyridine (L) formulated as [Cu(L)(H2O)2](NO3)2, 1 was synthesized and isolated in pure form. The complex was characterized b
- Dey, Sourav,Sarkar, Sandipan,Paul, Hena,Zangrando, Ennio,Chattopadhyay, Pabitra
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- Electrocatalytic reduction of CO2 with palladium bis-N-heterocyclic carbene pincer complexes
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A series of pyridine- and lutidine-linked bis-N-heterocyclic carbene (NHC) palladium pincer complexes were electrochemically characterized and screened for CO2 reduction capability with 2,2,2-trifluoroethanol, acetic acid, or 2,2,2-trifluoroacetic acid (TFA) as proton sources. The lutidine-linked pincer complexes electrocatalytically reduce CO2 to CO at potentials as low as -1.6 V versus Ag/AgNO3 in the presence of TFA. The one-electron reduction of these complexes is shown to be chemically reversible, yielding a monometallic species, with density functional theory studies indicating charge storage on the redox-active ligand, thus addressing a major source of deactivation in earlier triphosphine electrocatalysts.
- Therrien, Jeffrey A.,Wolf, Michael O.,Patrick, Brian O.
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- Pyridine-bridged benzimidazolium salts: Synthesis, aggregation, and application as phase-transfer catalysts
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(Chemical Equation Presented) Simply structured benzimidazolium salts efficiently gelate a variety of polar organic solvents. π-Stacking, hydrogen bonding, and van der Waals interactions are responsible for the self-assembly process. A packing model is deduced from the single crystal structure of gelator 1. Fiber aggregates of benzimidazolium salts in acetonitrile are efficient phase-transfer catalysts (PTCs) for N-alkylation.
- Tu, Tao,Assenmacher, Wilfried,Peterlik, Herwig,Schnakenburg, Gregor,Doetz, Karl Heinz
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- Efficient air-stable organometallic low-molecular-mass gelators for ionic liquids: synthesis, aggregation and application of pyridine-bridged bis(benzimidazolylidene)-palladium complexes
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Novel pincer-type, pyridine-bridged bis(benzimidazolylidene)-palladium complexes 5-7 were synthesised from cheap commercial precursors under microwave assistance. Although simple in structure, carbene complexes 5a,b are efficient low-molecular-mass metall
- Tu, Tao,Bao, Xiaoling,Assenmacher, Wilfried,Peterlik, Herwig,Daniels, Joerg,Doetz, Karl Heinz
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- Solvent-free selective oxidation of primary and secondary alcohols catalyzed by ruthenium-bis(benzimidazole)pyridinedicarboxylate complex using hydrogen peroxide as an oxidant
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A convenient and selective oxidation of alcohols with aqueous hydrogen peroxide to give the corresponding carbonyl compounds under solvent-free conditions has been developed. By applying ruthenium-bis(benzimidazole) pyridinedicarboxylate complex [Ru(bbp)(pydic)] as catalyst, primary, and secondary alcohols were oxidized to aldehydes and ketones in good yield and excellent selectivity under mild conditions.
- Zhou, Xian-Tai,Ji, Hong-Bing,Liu, Sheng-Gui
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- Orchestrated catalytic double rollover annulation: Rapid access to N-enriched cationic and neutral PAHs
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Disclosed herein is a rhodium(iii)-catalyzed novel one-step back-To-back double rollover annulation on pyridine and pyrazine backbones leading to a structurally and optoelectronically diverse class of nicely decorated multi-ring-fused, extensively π-conjugated, N-enriched PAH molecules by virtue of orchestrated quadruple C-H activation events. Selected N-PAHs have been utilized as potential mitochondria and lysosome markers.
- Karak, Pirudhan,Dutta, Champak,Dutta, Tanoy,Koner, Apurba Lal,Choudhury, Joyanta
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- A novel pyridine-bridged bis-benzimidazolylidene pincer palladium complex: Synthesis and catalytic properties
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A novel pyridine-bridged bis-benzimidazolylidene CNC pincer complex 1 was synthesized from cheap, commercially available precursors under microwave assistance in moderate yield. It catalyzes cross-coupling reactions of aryl halides with alkyl acrylates (Heck reaction) and phenylboronic acid (Suzuki reaction) under aerobic conditions with extremely high turn-over numbers (frequencies) indicating that a planar extension of the π-system by benzannelation significantly increases the catalytic activity even with trace amounts of catalyst loading.
- Tu, Tao,Malineni, Jagadeesh,Doetz, Karl Heinz
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- SELECTIVE HYDRODEOXYGENATION OF AROMATIC COMPOUNDS
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Disclosed are methods of selective hydrodeoxygenation of aromatic compounds by using catalyst systems comprising N-heterocyclic carbene (NHC) and 4-pyridinol-derived pincer ligands and metal complexes containing these ligands.
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Paragraph 0238-0240
(2021/07/02)
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- A new record excited state 3MLCT lifetime for metalorganic iron(II) complexes
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Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record 3MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest 3MC state lies higher in energy than the lowest 3MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels.
- Liu, Li,Duchanois, Thibaut,Etienne, Thibaud,Monari, Antonio,Beley, Marc,Assfeld, Xavier,Haacke, Stefan,Gros, Philippe C.
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p. 12550 - 12556
(2016/07/06)
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- Metal-free site-selective C-N bond-forming reaction of polyhalogenated pyridines and pyrimidines
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This paper presents a metal-free method for highly site-selective C-N bond-forming reaction of polyhalogenated pyridines and pyrimidines. The preferred coupling site can be tuned from the fluorine group bearing the N-heterocyclic ring to the chlorine group when changing from the pyridine ring to the pyrimidine ring. A wide array of halogenated pyridines preferentially reacted with amines at the fluorine group of the pyridine ring to generate monosubstituted halogenated pyridines with high selectivities. Different halogen atoms at various positions were produced by the pyridine ring that performed well under mild conditions. Halogenated pyrimidines underwent highly selective coupling at the chloride group with a wide range of amines having broad substrate applicability and moderate to good yields. The selectivity of the polyfluoropyridines in the developed reaction system was also tested, and the result indicated that the reaction occurred site-selectively at the ortho-position of the nitrogen ring. This reaction accommodated a wide range of halogenated groups. Thus, a wide range of chloro-, bromo-, iodo-, and fluoropyridines were generated, which have a wide utility for organic synthesis.
- Wang, Lei,Liu, Ning,Dai, Bin
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p. 82097 - 82111
(2015/10/12)
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- CuI/L (L=pyridine-functionalized 1,3-diketones) catalyzed C-N coupling reactions of aryl halides with NH-containing heterocycles
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An efficient copper-catalyzed N-arylation and N-heteroarylation reactions of imidazole, pyrrole, indole, pyrazole, and perimidine with aryl or heteroaryl halides using pyridine-functionalized 1,3-diketone as ligands have been investigated. The ligands bearing pyridyl and 1,3-diketone moieties, which may form chelated Cu(I) species, are inexpensive and readily available. The combination of CuI and 1,3-di(pyridin-2-yl)propane-1,3-dione is very efficient for C-N coupling reactions to afford various N-arylated products in good to excellent yields.
- Xi, Zhenxing,Liu, Fenghui,Zhou, Yongbo,Chen, Wanzhi
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p. 4254 - 4259
(2008/09/20)
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