Heterobimetallic Calix[4]arene Complexes: Interconversion of Dimeric (Ca, Sr or Ba)/TiIV Complexes with a Monomeric K/TiIV Complex

Abstract

AbstractReaction of calix[4]arene with alkaline earth metals (Ca/Sr/Ba) in methanol followed by the addition of various titanium(IV) sources afforded novel dimeric 1:1 alkaline earth/titanium(IV) calix[4]arene complexes. In each complex the central core of the crystallographically imposed centrosymmetric dimer consists of a rhombus of alternating alkaline earth metals and μ3‐oxo‐centres. Five terminal methanol ligands form seven‐coordinate calcium and strontium centres, while the barium centres are bridged by two additional methanol ligands, making them nine‐coordinate. Each oxo centre is the apical ligand of a square‐pyramidal titanium(IV) centre, whose basal plane ligands are the four phenolate oxygens from a calix[4]arene in the symmetrical cone‐conformation. Deprotonation of calix[4]arene with potassium metal, followed by the addition of a titanium(IV) source containing at least one acetylacetonate ligand, formed a mixed potassium/titanium complex based on one calix[4]arene. The potassium cation in this complex binds within the π‐basic calix[4]arene cavity, whilst titanium is octahedrally complexed in the exo‐position, by four phenolates and one acetylacetonate. The alkaline earth titanium dimers and potassium/titanium monomers could be interconverted merely by changing the solvent, with the appropriate cations and ligands present in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)