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Fakultäten

Metallorganische Chemie

Detection of the Elusive Highly Charged Zintl Ions Si4 (4-) and Sn4 (4-) in Liquid Ammonia by NMR Spectroscopy.

M. Neumeier, F. Fendt, S. Gärtner, C. Koch, T. Gärtner, N. Korber, R.M. Gschwind

Angewandte Chemie International Edition, WILEY-VCH Verlag, 2013, 52, 4483-4486

Web-Edition

 

 It's detected! The existence of the prototypical Zintl ions Tt44− (Tt=Group?14 element), which are isoelectronic to the P4 molecule, used to be confined to the solid state. Recently, circumstantial evidence for a solution chemistry in liquid ammonia emerged. Direct spectroscopic observation of the dissolved anions has now been achieved. In the case of Si44−, this is the first solution detection of any homoatomic silicide.


The Supramolecular Balance for Transition-Metal Complexes: Assessment of Noncovalent Interactions in Phosphoramidite Palladium Complexes

Hartmann, E. & Gschwind, R.

Angewandte Chemie International Edition, WILEY-VCH Verlag, 2013, 52, 2350-2354

Web-Edition

 

 

The virtue of enantiomers: A general method has been developed for measuring the individual contributions of noncovalent interactions within transition-metal complexes and dissecting them from electronic effects. On Pd complexes with one enantiopure and two enantiomeric phosphoramidite ligands, it was experimentally shown that modulations in extended CH–π and π–π interaction interfaces provide a ΔΔG value that is significant for stereoselection. 


1H DOSY Spectra of Ligands for Highly Enantioselective Reactions: A Fast and Simple NMR Method to Optimize Catalytic Reaction Conditions

Schober, K.; Hartmann, E.; Zhang, H. & Gschwind, R.

Angewandte Chemie International Edition, WILEY-VCH Verlag, 2010, 49, 2794-2797

Web-Edition

 

 

DOSY awakening: The aggregation trends of phosphoramidite transition-metal complexes, which can catalyze highly enantioselective reactions, can be predicted by a DOSY NMR screening of the free ligands (see picture). This method is valuable for catalyst optimization as no structural knowledge of the complexes is required.


Highly diastereoselective Csp3–Csp2 Negishi cross-coupling with 1,2-, 1,3- and 1,4-substituted cycloalkylzinc compounds

T. Thaler, B. Haag, A. Gavryushin, K. Schober, E. Hartmann, R. M. Gschwind, H. Zipse, P. Mayer and P. Knochel

Nat Chem, 2010, 2, 125-130

Web-Edition

Stereoselective functionalizations of organic molecules are of great importance to modern synthesis. A stereoselective preparation of pharmaceutically active molecules is often required to ensure the appropriate biological activity. Thereby, diastereoselective methods represent valuable tools for an efficient set-up of multiple stereocentres. In this article, highly diastereoselective Csp3 Negishi cross-couplings of various cycloalkylzinc reagents with aryl halides are reported. In all cases, the thermodynamically most-stable stereoisomer was obtained. Remarkably, this diastereoselective coupling was successful not only for 1,2-substituted cyclic systems, but also for 1,3- and 1,4-substituted cyclohexylzinc reagents. The origin of this remote stereocontrol was investigated by NMR experiments and density functional theory calculations. A detailed mechanism based on these experimental and theoretical data is proposed.


Ligand exchange reactions in Cu(III) complexes: mechanistic insighty by combined NMR and DFT studies

Gärtner T., Yoshikai N., Neumeier M., Nakamura E. & Gschwind, R. M.

Chemical Communications, 2010, 46(25), 4625-4626

Web-Edition

NMR studies of 13C/12C isotopic patterns in Cu(III) intermediates and reaction products together with DFT calculations of possible reaction pathways indicate an intermolecular SN2 like substitution mechanism for ligand exchange reactions in square planar Cu(III) complexes, which is proposed to be slow compared to reductive elimination at synthetic conditions.

 


Temperature-Dependent Interconversion of Phosphoramidite-Cu Complexes Detected by Combined Diffusion Studies, 31P NMR, and Low-Temperature NMR Spectroscopy

Schober, K.; Zhang, H. & Gschwind, R. M.

Journal of the American Chemical Society, 2008, 130, 12310-12317

Web-Edition

 

For copper-catalyzed enantioselective conjugate additions, knowledge about the precatalytic and catalytic complexes has not yet been sufficiently developed to understand the strong influence of different temperatures on these famous reactions. Therefore, NMR experiments with four Cu(I) salts and two phosphoramidite ligands have been performed to elucidate the temperature dependence and the low-temperature structures of these copper complexes. The existence of the precatalytic binuclear complex with a mixed trigonal/tetrahedral coordination on copper is for the first time proven with direct NMR spectroscopic methods. Below 200 K, intermolecular interactions between free ligands and [Cu2X2L3] complexes induce binuclear [Cu2X2L4] complexes similar to the crystal structures. By combining diffusion experiments and 31P integrals at different temperatures, it is for the first time possible to follow the formation of stoichiometrically different complexes, even under experimental conditions in which the 31P signals of the complexes are spectroscopically not resolved due to exchange processes. This allows a first correlation between the complex species observed and the synthetic conditions reported. Furthermore, different preferences to build homo- or heterochiral complexes are detected for binaphthol and biphenol phosphoramidite complexes.


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

Ay, S.; Ziegert, R. E.; Zhang, H.; Nieger, M.; Rissanen, K.; Fink, K.; Kubas, A.; Gschwind, R. M. & Bräse, S.

Journal of the American Chemical Society, 2010, 132, 12899-12905 

Web-Edition

We present herein the first indications for dimeric structures in cometal-free asymmetric conjugate addition reactions of dialkylzinc reagents with aldehydes. These are revealed by nonlinear effect (NLE) studies. A monomer−dimer equilibrium can be assumed which explains the increase of the ee value in the product over time. Also, DOSY NMR spectroscopic measurements indicate the existence of the catalyst as [LZnEt]n complexes in solution. Additionally, the first X-ray structure of a zinc complex with a [2.2]paracyclophane ligand was determined. The structures of the zinc complexes are supported by DFT calculations of monomeric and dimeric species. 

 


Organocuprate Conjugate Addition: Structural Features of Diastereomeric and Supramolecular π-Intermediates

Henze, W.; Gärtner, T. & Gschwind, R. M.

Journal of the American Chemical Society, 2008, 130, 13718-13726 

Web-Edition

In the reaction pathway of conjugate additions with organocuprate reagents, Cu(I) π-complexes and Cu(III) σ-complexes have been identified as central, NMR-detectable intermediate species. However, no experimental evidence for the structures of π-intermediates with extensive chiral enones or the principal aggregation level and aggregate structure of π-complexes in diethyl ether has been available so far. Furthermore, the structural characteristics of π-complexes which are essential for their high reactivities and diastereoselectivities have not yet been rationalized experimentally. Therefore, the π-intermediates of 4,4a,5,6,7,8-hexahydro-4a-methyl-naphthalen-2(3H)-one and Me2CuLi or Me2CuLi·LiX (X = I, CN) in diethyl ether are investigated in detail. For the first time, the formation of two intermediate cuprate enone π-complexes on both sides of the double bond is observed. In addition, the conformation of the enone adopted in the major β-face π-complex rationalizes the exclusive syn addition observed in the synthetic product. For the investigation of the aggregation level and structure, a NMR screening of π-complexes with Me2CuLi·LiX (X = I, CN) and three achiral enones is performed, which simplifies the spectra by the generation of enantiotopic π-complexes. Thus, NMR diffusion experiments on cuprate intermediates and the detection of scalar couplings across copper without isotope labeling are possible for the first time. Extensive NMR studies, including those of cyclohexanone complexes, show that, in principle, salt-free dimethylcuprate is able to complex the carbonyl group. However, in the presence of salt, the carbonyl-complexing aggregates are composed of salt and cuprate moieties. These mixed aggregates cause the formation of large supramolecular π-intermediate structures which control their reactivity. The π-complexing cuprate units show a bent geometry as a general structural feature that is unaffected by the presence or kind of salt and the type of enone. Thus, the high diastereoselectivity and the reactivity of organocuprate 1,4-addition reactions are for the first time rationalized on the basis of structural characteristics of selected π-intermediates.  

 


Organocuprates and Diamagnetic Copper Complexes: Structures and NMR Spectroscopic Structure Elucidation in Solution

Gschwind, R. M.

Chemical Reviews, 2008, 108, 3029-3053

Web-Edition

  1. Introduction
  2. 63Cu and 65Cu NMR-Spectroscopy
    1. General Applicability
    2. Structural Information Available from 63/65Cu NMR Spectra
  3. Structure Determination of Organocuprates in Solution
    1. Introduction
    2. Diorganocuprates
      1. Monomer Structure
      2. Monomer/Dimer Equilibria
      3. Structure of the Dimeric Core Unit
      4. Oligomerization Trends
      5. Aggregate Structures beyond Dimers Influence Reactivity
    3. Diorganocuprate Intermediates
      1. Introduction
      2. Organocuprate π-Complexes
      3. Cu(III)-Intermediates
      4. Kinetic Isotope Effects
    4. Heteroleptic Lithium Amidocuprates
  4. Catalytic and Precatalytic Copper Complexes with Chiral Ligands
    1. Introduction
    2. Thiolate Copper Complexes
    3. Phosphoramidite Copper Complexes
    4. Ferrocene-Derived Diphosphine Copper Complexes
    5. Diimine Copper Complexes
  5. Conclusion

 

 


  1. Fakultät für Chemie und Pharmazie
  2. Institut für Organische Chemie

Arbeitskreis Prof. Gschwind

Prof. Dr.
Ruth M. Gschwind

 

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