TITANIUM COMPLEXES OF OXACALIX[3]ARENES - SYNTHESIS AND MECHANISTIC STUDIES OF THEIR DYNAMIC ISOMERIZATION

The coordination chemistry of oxacalix[3]arenes with Ti(IV) has been examined. Several Ti(L)X complexes have been prepared and characterized where L represents the trianion of the oxacalix[3]arene macrocycle and X is an isopropoxide or acetylacetonate (acac) ligand. The Ti(L)(acac) complex exhibits a dynamic interconversion on the H-1 NMR time scale. At room temperature, the macrocycle ligand in the complex exhibits C-3v symmetry and the acac methyls are equivalent. In contrast, at low temperatures, the macrocycle possesses C-s symmetry and the acac methyls are inequivalent. Computer simulation of variable temperature NMR experiments have provided rate constants and activation parameters for the interconversion process. Rapid isomerization of trigonal bipyramidal isomers via turnstile rotation or Berry pseudorotation processes is proposed to explain the dynamic behavior of this complex.