Monomeric, oligomeric, and polymeric copper(II) complexes of calix[4]arene-derived ligands

Deprotonation of the p-tert-butylcalix[4]arene disubstituted at alternate phenolic positions with picolyl groups 2 was achieved with alkali metal hydrides LiH, NaH, and KH. The dianionic calixarene derivatives were subjected to complete substitution at the phenolic rim with allyl bromide, providing the tetraalkylated derivatives in cone 3a and partial-cone conformations 3b; both compounds were crystallographically characterized. Compound 2, as well as 3a and 3b were tested as ligands towards CuCl2, affording Cu2+ complexes in the first two cases. Polymeric [2·CuCl2] was obtained from 2 and CuCl2 in MeOH/CH2Cl2 solutions, and consists of chains of the ditopic calixarene acting as an N-donor towards Cu2+ ions outside the macrocyclic cavity. Employment of EtOH/CH2Cl2 mixtures results in the tricopper complex [(2)2Cu3Cl6(EtOH)2]. In contrast, reactions of ligand 3a with CuCl2 afforded monomeric [3a·CuCl2], while no Cu2+ complexes could be obtained when 3b was employed. The presence of intramolecular hydrogen bonds in 2 appears to control the formation of oligomeric or polymeric copper complexes, while the lack of such hydrogen bonds allows the proper alignment of N-donors to coordinate Cu2+ directly above the macrocyclic cavity.

Graphical abstractIntroduction of allyl groups to bispicolyl-calix[4]arene results in the selective preparation of cone and partial-cone tetrasubstituted conformers. The nuclearity of the corresponding CuCl2 complexes is controlled by the crystallization solvent, as well as by the presence or absence of intramolecular hydrogen bonds.Figure optionsDownload full-size imageDownload as PowerPoint slide