The Structural Conversion of Multinuclear Titanium(IV) μ-Oxo-complexes

For the first time we report the structural conversion processes of hexanuclear μ-oxo-Ti­(IV) complexes into tetranuclear ones. Single-crystal X-ray diffraction studies reveal that metastable hexanuclear μ-oxo complexes ([Ti<sub>6</sub>O<sub>6</sub>(O<sup><i>t</i></sup>Bu)­(O<sub>2</sub>CR′)<sub>6</sub>]) are formed in the first stage of reactions between [Ti­(O<sup><i>t</i></sup>Bu)<sub>4</sub>] and branched carboxylic acids R′COOH (R′ = C­(Me)<sub>2</sub>Et, CH<sub>2</sub><sup><i>t</i></sup>Bu, <sup><i>t</i></sup>Bu). In the next stage they convert into tetranuclear μ-oxo-Ti­(IV) complexes of the formula [Ti<sub>4</sub>O<sub>4</sub>(O<sup><i>t</i></sup>Bu)<sub>4</sub>(O<sub>2</sub>CR′)<sub>4</sub>]. Spectroscopic investigations (<sup>13</sup>C NMR, IR, and MS) proved that the conversion of hexanuclear clusters relies on the attachment of smaller units (e.g., [Ti<sub>3</sub>O­(O<sup><i>t</i></sup>Bu)<sub>8</sub>(O<sub>2</sub>CR′)<sub>2</sub>] or [Ti<sub>4</sub>O<sub>2</sub>(O<sup><i>t</i></sup>Bu)<sub>6</sub>(O<sub>2</sub>CR′)<sub>6</sub>]) and intermediate species formation (e.g., [Ti<sub>9</sub>O<sub>8</sub>(O<sup><i>t</i></sup>Bu)<sub>14</sub>(O<sub>2</sub>CR′)<sub>6</sub>]). The decomposition of intermediate systems in the next reaction stage leads to the formation of tetranuclear clusters. The type of solvent used in the synthesis of multinuclear oxo-Ti­(IV) complexes is an important factor, which influences the kind of clusters formed.