- Pyridine- A nd Quinoline-Derived Imines as N, N-Bidentate Directing Groups in Palladium versus Platinum C-H Bond Activation Reactions
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The C-H activation by Pd(II) and Pt(II) compounds of a wide range of imines related to 2-pyridinecarboxaldehyde, ArCHaNCH2(CH2)nPh (Ar = 2-pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1), which can be useful for bond functionalization assisted by bidentate directing groups, has been studied. The results indicate that the presence of two methyl groups at the α-carbon, relative to the imine nitrogen atom, facilitates the metalation. The heterocyclic fragment of the chelating ligand also shows a relevant influence on the full process, the cyclometalated compounds being more easily formed for the 2-picolinyl than for the 2-quinolinyl derivatives, while for the 2-pyridinyl derivatives the reaction is less favored. These effects have been found to be determinant for both palladium and platinum compounds. The preparative results can be explained by a steric enhancement of the metalation process, the reaction being strongly favored when bulky substituents are located in the proximity (α-carbon) of the coordinating nitrogen atoms (with both palladium and platinum). Furthermore, surprisingly the formation of six-membered platinacycles is especially favored. The kinetico-mechanistic studies of the C-H activation reaction, on some equivalent Pd(II) and Pt(II) coordination complexes of the family, have shown that the nature of the d8 metal center plays a determinant role in the reactivity observed. In this respect, the Pt(II) square-planar center has been found to be much more involved in the energetics of the reaction than the Pd(II) equivalent. The full process can be seen as a mechanistic continuum that goes from an electrophilic substitution (Pd(II) centers) to an oxidative addition/reductive elimination sequence (Pt(II) centers). The observation is directly associated with the fact that the Pt(II) center is prone to the existence of oxidatively added Pt(IV) hydrido complexes.
- Torralvo, Héctor,Albert, Joan,Ariza, Xavier,Font-Bardia, Mercè,Garcia, Jordi,Granell, Jaume,Martinez, Manuel
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- Structural elucidation of chiral (imino)pyridine/phosphine palladium(II) complexes and their applications as catalysts in methoxycarbonylation of styrene
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Treatment of ligands (S)-1-phenyl-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L1), (R)-1-phenyl-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L2), (S)-1-phenyl-N-((pyridin-2-yl)methylene)ethanamine (L3), (R)-1-phenyl-N-((pyridin-2-yl)methylene)ethanamine (L4), (S)-N-(2-(diphenylphosphino)benzylidene)-1-phenylethanamine (L5), and (R)-N-(2-(diphenylphosphino)benzylidene)-1-phenylethanamine (L6) with [Pd(COD)Cl2] afforded the respective palladium complexes [Pd(L1)Cl2] (1), [Pd(L2)Cl2] (2), [Pd(L3)Cl2] (3), [Pd(L4)Cl2] (4), [Pd(L5)Cl2] (5) and [Pd(L6)Cl2] (6) in high yields. Solid-state structures of the complexes established N^N and N^P bidentate coordination mode of the ligands to give distorted square planar geometries. Complexes 1–6 displayed moderate catalytic activities in the methoxycarbonylation of styrene, to give predominantly branched esters of up to 95%. NMR spectroscopy studies pointed to possible decomposition of the active species, via ligand dissociation.
- Akiri, Saphan O.,Ngcobo, Nondumiso L.,Ogweno, Aloice O.,Ojwach, Stephen O.
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- Structural, kinetics and mechanistic studies of transfer hydrogenation of ketones catalyzed by chiral (pyridyl)imine nickel(ii) complexes
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The chiral synthons (S-)-1-phenyl-N-(pyridine-2-yl)ethylidine)ethanamine (L1), (R-)-1phenyl-N-(pyridine-2-yl)ethylidine))ethanamine (L2) (S)-1-phenyl-N-(pyridine-2-yl methylene) ethanamine (L3), and (R)-1-phenyl-N-(pyridine-2-yl methylene) ethanamine (L4) were synthesized in good yields. Treatments of L1-L4 with NiBr2(DME) and NiCl2 precursor afforded dinuclear complexes [Ni2(L1)4-μ-Br2]NiBr4 (Ni1), [Ni2(L2)4-μ-Br2]NiBr4 (Ni2), [Ni2(L3)4-μBr2]Br2 (Ni3), [Ni2(L4)4-μ-Br2]NiBr4 (Ni4) and [Ni(L4)2Cl2] (Ni5). The identities of the compounds were established using NMR, FT-IR and EPR spectroscopy, mass spectrometry, magnetic moments, elemental analysis and single crystal X-ray crystallography. The dinuclear dibromide nickel complexes dissociate into mononuclear species in the presence of strongly coordinating solvents. Compounds Ni1-Ni5 displayed moderate catalytic activities in the asymmetric transfer hydrogenation (ATH) of ketones, but with low enantiomeric excess (ee%). Both mercury and substoichiometric poisoning tests pointed to the homogeneous nature of the active species with the partial formation of catalytically active Ni(0) nanoparticles. Low resolution mass spectrometry analyses of the intermediates supported a dihydride mechanistic pathway for the transfer of hydrogenation reactions.
- Kumah, Robert T.,Tsaulwayo, Nokwanda,Xulu, Bheki A.,Ojwach, Stephen O.
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supporting information
p. 13630 - 13640
(2019/09/30)
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- Deciphering preferred geometries of pyridylmethylamines-based complexes: A robust strategy combining NMR, DFT and X-ray
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The preparation of pyridylmethylamines (pma)-ZnBr2 and -CoBr2 complexes is described. Accurate structural informations in both solution and solid state have been obtained using an approach combining advanced NMR such as pure shift gr
- Large, Benjamin,Meddeb, Maissa,Pucheta, José Enrique Herbert,Gaucher, Anne,Cordier, Marie,Gosmini, Corinne,Farjon, Jonathan,Auffrant, Audrey,Prim, Damien
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supporting information
(2019/09/09)
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- Synthesis and application of new iminopyridine ligands in the enantioselective palladium-catalyzed allylic alkylation
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A variety of iminopyridines were obtained by condensation of chiral amines with pyridine-2-carboxaldehyde and quinoline-8-carbaldehyde, or of aminoalkylpyridine derivatives with chiral ketones. These ligands were assessed in the enantioselective palladium
- Solinas, Maurizio,Sechi, Barbara,Chelucci, Giorgio,Baldino, Salvatore,Pedro, José R.,Blay, Gonzalo
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- Synthesis and application of new iminopyridine ligands to enantioselective copper(II)-catalyzed Henry reaction
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Chiral iminopyridines obtained by reaction between a variety of chiral amines and pyridyl aldehydes or ketones were assessed as catalysts in the enantioselective Henry reaction between nitromethane and 2-methoxybenzaldehyde in the presence of copper(II) a
- Solinas, Maurizio,Sechi, Barbara,Baldino, Salvatore,Chelucci, Giorgio
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p. 206 - 212
(2013/08/15)
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- Fluorescent OFF-ON polymer chemosensor bonded alternatively with 1,4-dioctyloxybenzene and (R,R)-salen for cascade Zn2+ and chiral recognition
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The synthesis of the chiral main chain polymers 1a-b bonded alternatively with (R,R)-salen and 1,4-dioctyloxybenzene has been described employing a palladium-catalyzed C-C cross-coupling reaction as the key step. They are soluble in common organic solvent
- Sakthivel, Sekarpandi,Punniyamurthy, Tharmalingam
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experimental part
p. 570 - 576
(2012/08/28)
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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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- 1D and 2D Nuclear magnetic resonance of new silver(I) complexes with achiral and chiral bases as ligands: Crystal structure of [Ag{(S)-(6-CH3)C5H3N-CHN-CH(α-CH 3)C6H5}(PPh3)2](O 3SCF3)
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Treatment of equimolar amounts of substituted aniline or amine with substituted benzaldehyde leads to the corresponding achiral or chiral Schiff bases (L). The reaction of the bases with [Ag(O3SCF 3)(PPh3)] leads to the preparation of three or four coordinated cationic complexes, [Ag(k1-L)(PPh3) n]+ (n = 1 or 2) which have been characterized by IR, 1D and 2D NMR spectroscopy. The crystal structure of [Ag{(S)-(6-CH3)C5H3N-CHN-CH(α-CH 3)C6H5}(PPh3)2](O 3SCF3) is reported.
- Cifuentes, Olga,Contreras, Raul,Laguna, Antonio,Crespo, Olga
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experimental part
p. 81 - 89
(2012/02/02)
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- A facile circular dichroism protocol for rapid determination of enantiomeric excess and concentration of chiral primary amines
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A protocol for the rapid determination of the absolute configuration and enantiomeric excess (ee) of α-chiral primary amines with potential applications in asymmetric reaction discovery has been developed. The protocol requires derivatization of α-chiral primary amines through condensation with pyridine carboxaldehyde to quantitatively yield the corresponding imine. The Cu1 complex with 2,2′-bis (diphenylphosphino)-l,l'- dinaphthyl (BINAP-Cu1) with the imine yields a metal-to-ligand charge-transfer (MLCT) band in the visible region of the circular dichroism (CD) spectrum upon binding. Diastereomeric hostguest complexes give CD signals of the same signs but different amplitudes, allowing for differentiation of enantiomers. Processing the primary optical data from the CD spectrum with linear discriminant analysis (LDA) allows for the determination of the absolute configuration and identification of the amines, and processing with a super-vised multilayer perceptron artificial neural network (MLP-ANN) allows for the simultaneous determination of the ee and concentration. The primary optical data necessary to determine the ee of unknown samples is obtained in two minutes per sample. To demonstrate the utility of the protocol in asymmetric reaction discovery, the ee values and concentrations for an asymmetric metal-catalyzed reaction are determined. The potential of the application of this protocol in high-throughput screening (HTS) of ee is discussed.
- Nieto, Sonia,Dragna, Justin M.,Anslyn, Eric V.
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experimental part
p. 227 - 232
(2010/03/05)
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- Aminophosphinic acids in a pyridine series, Part 2: Synthesis of 2-, 3-, and 4-pyridyl derivatives of 1-(Benzylamino)-methyl-H-phosphinic Acids
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New 2-pyridyl, 3-pyridyl, and 4-pyridyl derivatives of 1-[N-(benzyl)amino]- methyl-H-phosphinic acid were prepared by the addition of bis(trimethylsilyl) phosphonite to the corresponding imines and subsequent methanolysis of the addition products. Treatment of the 2-pyridyl- and 1-(4-pyridyl)-1-(benzylamino) -methyl-H-phosphinic acids with aqueous mineral acids leads to cleavage and formation of the corresponding secondary amines and phosphorous acid (H3PO3).
- Goldeman, Waldemar,Boduszek, Bogdan
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experimental part
p. 1413 - 1425
(2010/03/24)
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- Novel N,N-bidentate ligands for enantioselective copper(I)-catalyzed allylic oxidation of cyclic olefins
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New N,N-bidentate Schiff base ligands containing the 2-quinolyl moiety proved to be effective in conferring high reactivity and moderate to high enantioselectivity (up to 84% ee) to the copper(I)-catalyzed asymmetric allylic oxidation of various cylic ole
- Tan, Qitao,Hayashi, Masahiko
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supporting information; experimental part
p. 2639 - 2644
(2009/09/07)
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- Chiral oxaziridines in the enantioselective synthesis of isoxazolidines
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The stereoselective synthesis of oxaziridines with three stereogenic centres is presented in this paper. The chirality is provided by asymmetric induction, and a possible mechanism for the induced stereoselectivity is also discussed. These small heterocyc
- Troisi, Luigino,De Lorenzis, Sara,Fabio, Marilena,Rosato, Francesca,Granito, Catia
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experimental part
p. 2246 - 2251
(2009/04/11)
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- Synthesis of enantiopure 2-aminoalkylphenols by stereoselective addition of Grignard reagents to chiral 2-imidoylphenols
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The stereoselective addition of Grignard reagents to chiral 2-imidoylphenols affords enantiopure 2-aminoalkylphenols, a class of ligands useful in stereoselective synthesis. Unusually benzyl- and allyl-magnesium chlorides add to ketimines derived from enolizable o-acylphenols with high yields and stereoselectivities. In this way a stereogenic quaternary C-1 carbon atom is introduced, which could not be obtained by other methods available till now. The mechanism and the asymmetric induction have been explained in agreement with previously obtained results.
- Cimarelli, Cristina,Palmieri, Gianni,Volpini, Emanuela
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p. 2011 - 2018
(2007/10/03)
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- Atom Transfer Polymerisation of methyl methacrylate: Use of chiral aryl/alkyl pyridylmethanimine ligands; with copper(I) bromide and as structurally characterised chiral copper(I) complexes
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The use of chiral catalysts in the living radical polymerisation of methyl methacrylate via atom transfer polymerisation (ATP) has been investigated in an effort to control the stereochemistry of the polymer backbone. Two enantiomerically pure chiral cata
- Haddleton, David M.,Duncalf, David J.,Kukulj, Dax,Heming, Alex M.,Shooter, Andrew J.,Clark, Andrew J.
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p. 1525 - 1532
(2007/10/03)
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- Molybdenum-95 nuclear magnetic resonance studies on molybdenum carbonyl complexes of isonitriles and amines
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The 95Mo NMR spectra of 28 molybdenum carbonyl complexes of isonitriles and amines are reported.Within similar classes of complexes excellent correlation is found between 95Mo chemical shifts and ligand ?-acceptor ability and, more importantly, complex structures.Application to the analysis of diastereomeric complexes is reported.From analysis of linewidths and relaxation behavior, the surprising result is found that 95Mo linewidths in isonitrile complexes are not due to coupling to the electric field gradient, but to scalar coupling between the 95Mo and 14N nucleiwhich, in turn, is inversely proportional to the substitution number n in complexes Mo(CO)6-n(CNR)n.A dependence of chemical shift on temperature of 0.3 ppm/deg C is found for Mo(CO)6.
- Merlic, Craig A.,Adams, Bruce
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p. 313 - 325
(2007/10/02)
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- ASYMMETRISCHE KATALYSEN. XXIV. CROSS-COUPLING VON 1-PHENYLETHYLGRIGNARD UND VINYLBROMID MIT Ni-KATALYSATOREN OPTISCH AKTIVER P/N-LIGANDEN
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Sixteen new N/N, P/N, and P/P chelate ligands, together with NiCl2, were used as in-situ catalysts for the enantioselective cross-coupling of 1-phenylethylgrignard and vinylbromide.The N/N ligands give no optical yield in the formation of the product 3-ph
- Brunner, H.,Li, Weichang,Weber, H.
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p. 359 - 364
(2007/10/02)
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