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.

本研究首次报道了六核μ-氧桥钛(IV)配合物向四核配合物的结构转化过程。单晶X射线衍射研究表明，在[Ti(OtBu)4]与支链羧酸R'COOH（R'=C(Me)2Et、CH2tBu、tBu）的反应初始阶段，会生成亚稳态六核μ-氧桥配合物[Ti6O6(OtBu)(O2CR')6]。在后续反应阶段，该配合物会转化为通式为[Ti4O4(OtBu)4(O2CR')4]的四核μ-氧桥钛(IV)配合物。光谱学研究（包括13C核磁共振波谱、红外光谱及质谱）证实，六核簇的转化过程依赖于较小单元（如[Ti3O(OtBu)8(O2CR')2]或[Ti4O2(OtBu)6(O2CR')6]）的结合以及中间物种的生成（例如[Ti9O8(OtBu)14(O2CR')6]）。中间体系在后续反应阶段发生分解，最终生成四核簇合物。合成多核氧桥钛(IV)配合物时所使用的溶剂类型，是影响所生成簇合物种类的重要因素。