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Chiral Benzamidinate Ligands in Rare‐Earth‐Metal Coordination Chemistry
Author(s) -
Benndorf Paul,
Kratsch Jochen,
Hartenstein Larissa,
Preuss Corinna M.,
Roesky Peter W.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202457
Subject(s) - rare earth , coordination complex , chemistry , metal , astrobiology , combinatorial chemistry , organic chemistry , mineralogy , physics
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} 3 Sm], 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} 2 Ln{N(SiMe 3 ) 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} 2 Ln{N(SiMe 3 ) 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.