Chiral Benzamidinate Ligands in Rare-Earth-Metal Coordination Chemistry

Authors

  • Dr. Paul Benndorf,

    1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854
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  • Dipl.-Chem. Jochen Kratsch,

    1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854
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  • Larissa Hartenstein,

    1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854
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  • Dipl.-Chem. Corinna M. Preuss,

    1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854
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  • Prof. Dr. Peter W. Roesky

    Corresponding author
    1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854
    • Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstrasse 15, 76131 Karlsruhe (Germany), Fax: (+49) 721-608-44854===

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Abstract

The treatment of the recently reported potassium salt (S)-N,N′-bis-(1-phenylethyl)benzamidinate ((S)-KPEBA) and its racemic isomer (rac-KPEBA) with anhydrous lanthanide trichlorides (Ln=Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)-PEBA}3Sm], bis(amidinate) complexes [{Ln(PEBA)2(μ-Cl)}2] (Ln=Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)2(thf)n] (Ln=Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)–amido complexes [{(S)-PEBA}2Ln{N(SiMe3)2}] (Ln=Y, Lu) were synthesized by an amine-elimination reaction and salt metathesis. All of these chiral bis- and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac-PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)-PEBA}2Ln{N(SiMe3)2}] (Ln=Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.

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