NMR-Spectroscopic and Solid-State Investigations of Cometal-Free Asymmetric Conjugate Addition: A Dinuclear Paracyclophaneimine Zinc Methyl Complex

Ay, Sefer; Ziegert, Robert E.; Zhang, H.; Nieger, Martin; Rissanen, Kari; Fink, Karin; Kubas, Adam; Gschwind, Ruth M.; Bräse, Stefan

doi:10.1021/ja1032502

Cited by 28 publications

(9 citation statements)

References 53 publications

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“…When using different molar mixtures of the two salts with d - and l -prolinate, a complex nonlinear effect was observed ( Figure 6 b, Table S2 ). Such relationships have been often observed in diastereomeric systems and are associated to a complex aggregation behavior with the participation of homo- and/or heteroaggregates [ 56 , 57 ]. Interestingly, a 10% ee ( S ) was obtained for the equimolecular mixture, while for the region where ( S , S )- trans -Cy6-OH-Im-Bu- l -Pro was the major component, the enantioselectivity remained essentially constant (ca.…”

Section: Resultsmentioning

confidence: 99%

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

et al. 2021

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Chiral imidazolium l-prolinate salts, providing a complex network of supramolecular interaction in a chiral environment, have been studied as synzymatic catalytic systems. They are demonstrated to be green and efficient chiral organocatalysts for direct asymmetric aldol reactions at room temperature. The corresponding aldol products were obtained with moderate to good enantioselectivities. The influence of the presence of chirality in both the imidazolium cation and the prolinate anion on the transfer of chirality from the organocatalyst to the aldol product has been studied. Moreover, interesting match/mismatch situations have been observed regarding configuration of chirality of the two components through the analysis of results for organocatalysts derived from both enantiomers of prolinate (R/S) and the trans/cis isomers for the chiral fragment of the cation. This is associated with differences in the corresponding reaction rates but also to the different tendencies for the formation of aggregates, as evidenced by nonlinear effects studies (NLE). Excellent activities, selectivities, and enantioselectivities could be achieved by an appropriate selection of the structural elements at the cation and anion.

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Section: Resultsmentioning

confidence: 99%

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

et al. 2021

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“…Typical processes that induce ligation changes in copper(I) and other d 10 species are solvent coordination, intermolecular ligand exchange and/or aggregation. [42,45,[56][57][58][59][60][61] For reference purposes, the ligand of each complex was synthesized by adapting previously reported procedures for Schiff base ligands. [62] Based on literature reports for similar ML 2 -type complexes, [60,63,64] it seems likely that complexes 2, 4 and 6 are in equilibrium with an ML complex and the free ligand.…”

Section: Nmr Studies Of Dynamic Solution Behaviour: Ligand Exchange and Aggregationmentioning

confidence: 99%

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N‐Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X‐ray Spectroscopic and Crystallographic Investigation

et al. 2021

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A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole-and pyridine-based ligands were examined by 1 H, 13 C and 15 N NMR spectroscopy. The magnitude of the 15 N imine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained CuÀ N imine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperaturedependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.

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“…While SpiroBOX IV (Figure 1) combines axial chirality from the spiro backbone with the central chirality of the 2-substituted BOX moiety, [2.2]paracyclophane (PCP) exhibits planar chirality, which has previously demonstrated remarkable performance as planar chiral ligand or chiral catalyst in asymmetric catalysis [9]. Notable examples include the addition of alkyl, aryl, alkynyl, and alkenyl zinc reagents to aromatic and aliphatic aldehydes and imines that are catalyzed by PCP ligands[10,11,12,13,14]. The PCP core allows different substituents to be positioned regioselectively using carefully chosen reaction parameters [15].…”

Section: Introductionmentioning

confidence: 99%

Planar Chiral [2.2]Paracyclophane-Based Bisoxazoline Ligands and Their Applications in Cu-Mediated N–H Insertion Reaction

Knoll

Hassan

et al. 2019

Molecules

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New catalysts for important C–N bond formation are highly sought after. In this work, we demonstrate the synthesis and viability of a new class of planar chiral [2.2]paracyclophane-based bisoxazoline (BOX) ligands for the copper-catalyzed N–H insertion of α-diazocarbonyls into anilines. The reaction features a wide substrate scope and moderate to excellent yields, and delivers the valuable products at ambient conditions.

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NMR-Spectroscopic and Solid-State Investigations of Cometal-Free Asymmetric Conjugate Addition: A Dinuclear Paracyclophaneimine Zinc Methyl Complex

Cited by 28 publications

References 53 publications

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N‐Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X‐ray Spectroscopic and Crystallographic Investigation

Planar Chiral [2.2]Paracyclophane-Based Bisoxazoline Ligands and Their Applications in Cu-Mediated N–H Insertion Reaction

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