PUB - Publikationen an der Universität Bielefeld

Treatment of 4-tert-butyl-2,6-bis (hydroxymethyl) phenol (H3L) with [TiO(acac)(2)] in protic solvents at elevated temperatures leads to the formation of the dinuclear complex (Et4N)[L3Ti2] 1, whereas carrying out the reaction at room temperature or in aprotic solvents leads to the formation of the tetranuclear complex (Et4N)(2)[L-2(HL)(4)Ti4O2] 2. Heating 2 in protic solvents leads to the formation of 1, but 2 is stable in non-protic solvents such as THF even upon heating. Dissolving 1 in an aprotic solvent leads to the formation of 2. The anion of 1 consists of a confacial bioctahedron with a [(BzO)(3)Ti-IV(mu(2)-OPh)(3)Ti-IV(OBz)(3)](-) core. The phenylmethoxide ligands (BzO(-)), and the phenolato ligands are bound to the strong Lewis acid Ti-IV. The bond lengths are for Ti-OBz ca. 1.83 Angstrom and forTi-mu(2)-OPh ca. 2.11 Angstrom. Despite the highly covalent Ti-OBz bond, the phenylmethoxide ligands exhibit nucleophilic character, and a tendency to bridge two Ti-IV ions as demonstrated by the synthesis of the tetranuclear complex 2. The dianion in 2 consists of a Ti4O16 core with two hydrophobic half-bowl shaped pockets built from three tert-butylbenzene units each. The hydrophobic pockets allow access to the Lewis basic mu(3)-O2- ligands of the Ti4O16 core. In the crystal structure of 2(.)2CH(3)CN, two Et4N+ cations occupy these two binding pockets. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).