- Complexation of N4-tetradentate ligands with Nd(III) and Am(III)
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To improve understanding of aza-complexants in trivalent actinide-lanthanide separations, a series of tetradentate N-donor ligands have been synthesized and their complexation of americium(III) and neodymium(III) investigated by UV-visible spectrophotometry in methanolic solutions. The six pyridine/alkyl amine/imine ligands are N,N′-bis(2-methylpyridyl)-1,2- diaminoethane, N,N′-bis(2-methylpyridyl)-1,3-diaminopropane, trans-N,N-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (BPMDAC), N,N'-bis(2-pyridylmethyl)piperazine, N,N'-bis-[pyridin-2-ylmethylene]ethane-1,2- diamine, and trans-N,N-bis-([pyridin-2-ylmethylene]-cyclohexane-1,2-diamine. Each ligand has two pyridine groups and two aliphatic amine/imine N-donor atoms arranged with different degrees of preorganization and structural backbone rigidity. Conditional stability constants for the complexes of Am(III) and Nd(III) by these ligands establish the selectivity patterns. The overall selectivity of Am(III) over Nd(III) is similar to that reported for the terdentate bis(dialkyltriazinyl)pyridine molecules. The cyclohexane amine derivative (BPMDAC) is the strongest complexant and shows the highest selectivity for Am(III) over Nd(III) while the imines appear to prefer a bridging arrangement between two cations. These results suggest that this series of ligands could be employed to develop an enhanced actinide(III)- lanthanide(III) separation system.
- Ogden, Mark D.,Sinkov, Serguei I.,Meier, G. Patrick,Lumetta, Gregg J.,Nash, Kenneth L.
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- EPR spectroscopic trapping of the active species of nonheme iron-catalyzed oxidation
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(Graph Presented) The key intermediate of a bioinspired iron catalyst for selective hydrocarbon oxidation based on hydrogen peroxide and an iron complex with a tetradentate aminopyridine ligand was trapped by EPR. On the basis of EPR and reactivity data this intermediate is tentatively proposed to be an oxoiron(V) complex.
- Lyakin, Oleg Y.,Bryliakov, Konstantin P.,Britovsek, George J. P.,Talsi, Evgenii P.
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- From Mesocates to Helicates: Structural, Magnetic and Chiro-Optical Studies on Nickel(II) Supramolecular Assemblies Derived from Tetradentate Schiff Bases
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The systematic reactions of a family of tetradentate pyridyl/imine and quinolyl/imine racemic or enantiopure Schiff bases with Ni(NO3)2 or Ni(ClO4)2 in the presence of sodium azide yielded, as a function of the
- Mayans, Júlia,Font-Bardia, Mercè,Di Bari, Lorenzo,Arrico, Lorenzo,Zinna, Francesco,Pescitelli, Gennaro,Escuer, Albert
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- Synthesis and evaluation of conformationally restricted N 4-tetradentate ligands for implementation in An(III)/Ln(III) separations
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The previous literature demonstrates that donor atoms softer than oxygen are effective for separating trivalent lanthanides (Ln(III)) from trivalent actinides (An(III)) (Nash, K.L., in: Gschneider, K.A. Jr., et al. (eds.) Handbook on the Physics and Chemistry of Rare Earths, vol. 18-Lanthanides/ Actinides Chemistry, pp. 197-238. Elsevier Science, Amsterdam, 1994). It has also been shown that ligands that "restrict" their donor groups in a favorable geometry, appropriate to the steric demands of the cation, have an increased binding affinity. A series of tetradentate nitrogen containing ligands have been synthesized with increased steric "limits". The pK a values for these ligands have been determined using potentiometric titration methods and the formation of the colored copper(II) complex has been used as a method to determine ligand partitioning between the organic and aqueous phases. The results for the 2-methylpyridyl-substituted amine ligands are encouraging, but the results for the 2-methylpyridyl-substituted diimines indicate that these ligands are unsuitable for implementation in a solvent extraction system due to hydrolysis. Springer Science+Business Media, LLC 2012.
- Ogden, Mark D.,Patrick Meier,Nash, Kenneth L.
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- Rhodium(I) bisaldimine complexes in transfer hydrogenation
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The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system [Rh(cod)Cl]2–L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-, and thiophenecarboxaldehyde) were studie
- Nindakova,Badyrova,Sadykov, E. Kh.,Ushakov,Vanzarakshaeva, S. Ch.
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- Kinetic Resolution of Cyclic Secondary Azides, Using an Enantioselective Copper-Catalyzed Azide-Alkyne Cycloaddition
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An enantioselective copper-catalyzed azide-alkyne cycloaddition (E-CuAAC) is reported by kinetic resolution. Chiral triazoles were isolated in high yield with limiting alkyne (up to 97:3 enantiomeric ratio (er)). A range of substrates were tolerated (>30 examples), and the reaction was scaled to >1 g. The er of a triazole product could be enhanced by recrystallization and the recovered scalemic azide could be racemized and recycled. Recycling the azide allows efficient use of the undesired azide enantiomer.
- Alexander, Juliana R.,Ott, Amy A.,Liu, En-Chih,Topczewski, Joseph J.
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supporting information
p. 4355 - 4358
(2019/06/14)
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- Catalytic oxidation of alcohols with novel non-heme N4-tetradentate manganese(ii) complexes
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We report the preparation and characterisation of a series of novel non-heme N4-tetradentate Mn(OTf)2 complexes of the type, [(L)MnOTf2], where L = R,R and S,S enantiomers of BPMCN, its 6-methyl and 6-bromo derivatives as well as the novel ligand BMIMCN (BPMCN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-(R,R/S,S)-1,2-diaminocyclohexane, BMIMCN = N,N′-dimethyl-N,N′-bis(1-methyl-2-imidazolemethyl)-(R,R/S,S)-1,2-diaminocyclohexane). Solid state structural analysis of the BMIMCN-ligated Mn-triflate complexes (R,R-C4 and S,S-C4) revealed opposite helicity but identical metal site accessibility. This feature was exploited in the catalytic oxidation of primary and secondary alcohols, with hydrogen peroxide as oxidant and acetic acid as co-catalyst. Complexes R,R-C4 and S,S-C4 displayed the highest activity in benzyl alcohol oxidation, attributed to the electron-donating property of the BMIMCN ligand. Complex S,S-C4, displayed high activity for a variety of primary alcohol substrates, but the reaction suffered from reduced selectivity and side-reactions due to the presence of acetic acid. In contrast, secondary alcohol substrates could be oxidised to the corresponding ketone products in excellent isolated yields under mild reaction conditions and short reaction times.
- Vermaak, Vincent,Young, Desmond A.,Swarts, Andrew J.
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supporting information
p. 16534 - 16542
(2018/12/05)
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- Synthesis of N,N′-Dialkylated Cyclohexane-1,2-diamines and Their Application as Asymmetric Ligands and Organocatalysts for the Synthesis of Alcohols
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A series of N,N′-dialkylated derivatives of (1R,2R)-cyclohexane-1,2-diamine were synthesized, and a new approach to the one-pot preparation of this type of amine was demonstrated. The prepared diamines were used as organocatalysts for the two-step synthesis of α-hydroxy γ-keto esters from arenes, chlorooxoacetates, and ketones; they were also used as chiral ligands for Meervein-Ponndorf-Verley reductions and Henry reactions.
- Tsygankov, Alexey A.,Chun, Man-Seog,Samoylova, Alexandra D.,Kwon, Seongyeon,Kreschenova, Yuliya M.,Kim, Suhyeon,Shin, Euijin,Oh, Jinho,Strelkova, Tatyana V.,Kolesov, Valerii S.,Zubkov, Fedor I.,Semenov, Sergei E.,Fedyanin, Ivan V.,Chusov, Denis
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p. 615 - 619
(2017/03/11)
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- Schiff base ligands and their transition metal complexes in the mixtures of ionic liquid + organic solvent: A thermodynamic study
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Schiff bases and their metal complexes in the mixtures of ionic liquid (IL) + organic solvent have shown great potential in attractive oxidation catalytic processes. The efficiency of such a process is strongly dependent on the various molecular interactions occurring between components. Thermodynamic properties of these systems can provide valuable information about structural interactions. Therefore, in this work, the interactions of the IL 1-hexyl-3-methylimidazolium chloride ([HMIm]Cl) with Schiff bases in organic solvents were studied through the measurements of density, viscosity, and electrical conductivity. The effect of solvent on the interactions was examined by the solutions of IL + BPIC Schiff base + solvent (C2H6O-C3H8O-C4H10O). Moreover, the influence of Schiff base ligand and Schiff base complex structures was probed by the solutions of IL + DMA + ligand (salcn/salpr/salen) and IL + DMA + complex (VO(3-OMe-salen)/VO(salophen)/VO(salen)), respectively. Using the experimental data, some important thermodynamic properties, such as standard partial molar volume (Vf,IL0), experimental slope (Sv), viscosity B-coefficient, solvation number (B/Vf,IL0), and limiting molar conductivity (Λ0) were calculated and discussed in terms of solute-solvent (IL-DMF/alcohol) and solute-cosolute (IL-Schiff base) interactions.
- Shekaari, Hemayat,Kazempour, Amir,Khoshalhan, Maryam
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p. 2179 - 2191
(2015/02/19)
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- Catalytic and mechanistic studies into the epoxidation of styrenes using manganese complexes of structurally similar polyamine ligands
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Two structurally similar polyamine ligands (7 and 8) have been prepared, which differ only by the presence of either a secondary or tertiary nitrogen donor within their N5 donor set. The ligands, in combination with iron and manganese salts, have been screened for their efficacy as catalysts for the epoxidation of styrene, using both hydrogen peroxide and peracetic acid as oxidants. Clear differences in activity between the two systems were observed, with 7 proving most effective in the presence of MnSO4 with H 2O2, whereas ligand 8 proved to be effective with Mn(OTf)2, MnCl2 and Mn(ClO4)2 using peracetic acid as the oxidant. A Hammett analysis of the initial rate kinetics of the optimal systems, combined with analysis by UV-vis spectroscopy, indicates that the small structural differences in the ligands elicit profound changes in the nature of the active species formed. The Royal Society of Chemistry.
- Ilyashenko, Gennadiy,De Faveri, Giorgio,Follier, Thomas,Al-Safadi, Rawan,Motevalli, Majid,Watkinson, Michael
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p. 1124 - 1134
(2014/02/14)
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- Parallel screening of asymmetric bidentate ligands in zinc catalyzed transfer hydrogenation
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Development in the field of asymmetric catalysis is driven by the importance of stereochemically pure compounds in the field of pharmaceutical industry, agrochemicals and flavors. The unpredictable results given by new catalysts make the design of effecti
- Zaman, Tariq,Nasir, Habib,Bergin, Enda
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- Application of rapidly generated bidentate ligand libraries to zinc catalyzed reductions
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A methodology for the combinatorial synthesis of bidentate ligands - allowing direct screening of reaction products without the need for isolation or purification - has been employed in a zinc catalyzed hydrosilylation. This reaction allowed the robustness of the methodology to be examined, by employing it in a challenging case where the metal complex is not pre-formed prior to catalysis. Four different ligand families have been examined: imines, aminals, bis-imines and oxazolines and related compounds, with a small library of each type produced and directly screened in the reaction. Three ligands providing enantioselectivities of 50% or more in this very challenging reaction were identified, and ees and conversions were equivalent whether the ligand was obtained as a crude mixture from a library synthesis or as an isolated, purified compound.
- Zaman, Tariq,Frauenlob, Robin,McCarthy, Robert,Walsh, Carolyn M.,Bergin, Enda
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p. 159 - 166
(2012/11/13)
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- Rapid, in situ synthesis of bidentate ligands: Chromatography-free generation of catalyst libraries
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The parallel synthesis of chiral bidentate ligands and their subsequent use in situ for a catalytic process is described. The ligands thus prepared gave comparable results to those obtained when the ligands were synthesized and purified by conventional means. This includes oxazolines and other compounds of similar complexity, meaning that for the first time these valuable compounds have been brought into the field of combinatorial catalysis.
- Frauenlob, Robin,McCormack, Martha M.,Walsh, Carolyn M.,Bergin, Enda
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supporting information; experimental part
p. 6934 - 6937
(2011/11/04)
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- When is an imine not an imine? Unusual reactivity of a series of Cu(ii) imine-pyridine complexes and their exploitation for the Henry reaction
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In this paper we report the synthesis and solid-state structures for a series of pyridine based Cu(ii) complexes and preliminary data for the asymmetric Henry reaction. Interestingly, the solid-state structures indicate the incorporation of an alcohol into one of the imine groups of the ligand, forming a rare α-amino ether group. The complexes have been studied via single crystal X-ray diffraction, EPR spectroscopy and mass spectrometry. Intriguingly, it has been observed that the alcohol only adds to one of the imine moieties. Density functional theory (DFT) calculations have also been employed to rationalise the observed structures. The Cu(ii) complexes have been tested in the asymmetric Henry reaction (benzaldehyde + nitromethane or nitroethane) with ee's up to 84% being achieved as well as high conversions and modest diastereoselectivities. The Royal Society of Chemistry 2011.
- Cooper, Christine J.,Jones, Matthew D.,Brayshaw, Simon K.,Sonnex, Benjamin,Russell, Mark L.,Mahon, Mary F.,Allan, David R.
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p. 3677 - 3682
(2011/07/30)
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- Chiral bis-pyridinium salts as novel stereoselective catalysts for the metal-free diels-alder cycloaddition of α,β-unsaturated aldehydes
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The synthesis of enantiomerically pure C2-symmetric bis-pyridinium salts was realized through a simple condensation of 2-pyridyl-carboxyaldehydes with a chiral diamine. The catalytic properties of such novel compounds were preliminarily studied
- Genoni, Andrea,Benaglia, Maurizio,Puglisi, Alessandra,Rossi, Sergio
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supporting information; experimental part
p. 1926 - 1929
(2011/08/07)
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