Synthesis and Characterization of Ti Complexes Using 4‐tert‐Butyl‐2,6‐bis(hydroxymethyl)phenol: X‐ray Structures of a Confacial Bioctahedron with Terminal Nucleophilic Phenylmethoxide Ligands, and a Ti4O16 Core Protected by Two Hydrophobic Binding Pockets

Abstract

AbstractTreatment 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[L2(HL)4Ti4O2] 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)3TiIV(μ2‐OPh)3TiIV(OBz)3]− core. The phenylmethoxide ligands (BzO−), and the phenolato ligands are bound to the strong Lewis acid TiIV. The bond lengths are for Ti−OBz ca. 1.83 Å and for Ti−μ2‐OPh ca. 2.11 Å. Despite the highly covalent Ti−OBz bond, the phenylmethoxide ligands exhibit nucleophilic character, and a tendency to bridge two TiIV 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 μ3‐O2− ligands of the Ti4O16 core. In the crystal structure of 2·2CH3CN, two Et4N+ cations occupy these two binding pockets. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)