Synthesis and Reductive Complexation Properties of a Cone-Configurated Tetra[p-(tert-butyl)]calix[4]arene incorporating bipyridyl and pyridine subunits. NMR characterization and crystal structure of its chiral copper(I) complex

The hetero-armed p(tert-butyl)calix4]arene 1 was synthesized by a stepwise procedure. This ligand presented a very strong complexing behavior towards Cu¹, giving the chiral complex 2 and parent species when reacted with Cu^II salts. High-resolution NMR techniques were employed for the characterization of 2 , demonstrating notably exchange processes between its two enantiomeric forms. The racemic nature of 2 was confirmed by X-ray crystal-structure analysis.