Structural and chiroptical properties of acyclic and macrocyclic 1,5-bis(oxazoline) ligands and their copper(I) and silver(I) complexes

C-2-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 NOEs, and corroborated by molecular modeling. Ligands with phenyl rings on the stereogenic centers (1a,c and 2) exhibit a strong Cotton effect (CE) in the region of the B-1(b) 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 ligands la and 2a the EC changes the sign on complexation to Cu+, revealing opposite helicity of the free and complexed ligand.