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Helicates of Chiragen‐Type Ligands and Their Aptitude for Chiral Self‐Recognition
Author(s) -
Mamula Olimpia,
von Zelewsky Alex,
Brodard Pierre,
Schläpfer CarlWilhelm,
Bernardinelli Gérald,
StoeckliEvans Helen
Publication year - 2006
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.200401109
Subject(s) - enantiopure drug , circular dichroism , chemistry , xylylene , chirality (physics) , enantiomer , ligand (biochemistry) , stereochemistry , planar chirality , enantioselective synthesis , crystallography , polymer chemistry , organic chemistry , catalysis , receptor , chiral symmetry , biochemistry , nambu–jona lasinio model , physics , quantum mechanics , quark
Two (−)‐5,6‐pinene‐bipyridine moieties connected by a para ‐xylylene bridge (so‐called chiragen‐type ligands), (−)‐L1, undergo self‐assembly upon reaction with equimolar amounts of Cu I to form enantiopure circular hexanuclear P ‐helicates. If both enantiomers of L1 are used, mixtures of P and M hexanuclear helicates are exclusively obtained through a complete chiral recognition; that is, no mixing of the (+) and (−) ligands, respectively, occurs upon complexation. This was proven by a) NMR spectroscopy where identical spectra to those for complexes with the enantiomerically pure ligands were obtained and b) circular dichroism (CD) spectroscopy. The reaction is completely changed by the use of the corresponding meso ‐L1. Instead of well‐defined species, oligomeric mixtures are observed, a result demonstrating the crucial role played by ligand chirality in self‐assembly processes. Structural variations on the chiral ligand L1, such as a meta ‐xylylene bridge instead of a para ‐xylylene one (in L4) or four pinene groups instead of two (in L5 and L6), favor nondiscrete coordination assembly.