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 ([Ti6O6(OtBu)­(O2CR′)6]) are formed in the first stage of reactions between [Ti­(OtBu)4] and branched carboxylic acids R′COOH (R′ = C­(Me)2Et, CH2tBu, tBu). In the next stage they convert into tetranuclear μ-oxo-Ti­(IV) complexes of the formula [Ti4O4(OtBu)4(O2CR′)4]. Spectroscopic investigations (13C NMR, IR, and MS) proved that the conversion of hexanuclear clusters relies on the attachment of smaller units (e.g., [Ti3O­(OtBu)8(O2CR′)2] or [Ti4O2(OtBu)6(O2CR′)6]) and intermediate species formation (e.g., [Ti9O8(OtBu)14(O2CR′)6]). 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.