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Structural and chirooptical properties of acyclic and macrocyclic 1, 4-bisoxazoline ligands and their copper (I) and silver (I) complexes

C2 Symmetric acyclic ligands 1a-1e, macrocyclic ligands 2a-2d and 3, and their copper(I) and silver(I) complexes were studied by UV, NMR and CD spectroscopy. The stability constants of the metal-1a and -1b complexes with 1:1 and 1:2 stoichiometries in acetonitrile were determined by spectrometric titrations. Evidence of tetrahedral coordination for complex [Ag(1a)2]+ was obtained from the complexation induced shifts (CIS) and NOE effects, and corroborated by molecular modelling. Ligands with phenyl rings on the stereogenic centers (1a, c and 2) exhibit strong Cotton effect (CE) in the region of 1Bb band, which is absent in the ligands with benzyl groups on the stereogenic center (1b, 3). This effect is ascribed to the exciton coupling (EC) of two aromatic chromophores on the stereogenic center. For the ligands 1a and 2a EC changes the sign on complexation to Cu+, revealing opposite helicity of the free and complexed ligand.

circular dichroism ; conformation analysis ; copper and silver complexes ; bisoxazoline ligands ; macrocyclic ligands

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