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Aggregation and Solvation of Chiral N,P-Amide Ligands in Coordinating Solvents: A Computational and NMR Spectroscopic Study

Authors

  • Petra Rönnholm,

    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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  • Sten O. Nilsson Lill,

    Corresponding author
    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
    • Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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  • Jürgen Gräfenstein,

    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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  • Per-Ola Norrby,

    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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  • Mariell Pettersson,

    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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  • Göran Hilmersson

    1. Department of Chemistry and Molecular Biology, University of Gothenburg, Kemigården 4, 412 96 Gothenburg (Sweden), Fax: (+46) 31-772-1394
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Abstract

The lithium amides of a series of chiral N,P ligands were studied in solution. This ligand class had been shown previously to give good selectivities in asymmetric alkylation of benzaldehyde. These lithium amides were found to aggregate into dimers with surprisingly strong coordination of phosphorus to lithium. The equilibrium between dimeric forms was found to depend strongly on non-bonded interactions within the solute and between solute and solvent. Only if dispersion and free-energy contributions were scaled to approximately 20 % of the gas-phase values was it possible to reproduce the experimentally observed aggregation preferences. NMR spectroscopic shieldings were calculated and found to correlate well with the experimentally observed shifts. Calculated Li,P couplings were shown to be a sensitive measure of the Li[BOND]P distance.

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