Tetramethylaluminate and Tetramethylgallate Coordination in Rare-Earth Metal Half-Sandwich and Metallocene Complexes

The synthesis of half-sandwich tetramethylaluminate complexes Cp*Y(AlMe4)2 (Cp* = C5Me5) was achieved by applying two synthesis protocols: (a) protonolysis of Y(AlMe4)3 with excess HCp* at ambient temperature; (b) alkylamide elimination using Cp*Y(NiPr2)2(THF) and trimethylaluminum at ambient temperature. The tetramethylgallate derivative Cp*Y(GaMe4)2 was obtained from the equimolar reaction of Y(GaMe4)3 with HCp* or by addition of 2 equiv of trimethylgallium to [Cp*YMe2]3. The half-sandwich complexes Cp*Y(MMe4)2 (M = Al, Ga) display similar structural chemistry featuring highly fluxional methyl groups in solution and one planar and one atypically bent Y(μ-Me)2M moiety in the solid state. Complexes [Cp*2Ln(MMe4)] (Ln = Y, La; M = Al, Ga) were synthesized from Ln(MMe4)3 with excess HCp* at elevated temperature. Such metallocene complexes show the known monomer−dimer equilibria in solution, with the entropically disfavored dimer prevailing at low temperature. Dimeric [Cp*2La(AlMe4)]2 and [Cp*2Y(GaMe4)]2 as well as monomeric Cp*2La(GaMe4) were analyzed by X-ray diffraction.

本研究通过两种合成方案实现了半夹心型四甲基铝配合物Cp*Y(AlMe₄)₂（其中Cp* = C₅Me₅，即五甲基环戊二烯基）的合成：(a) 室温下以过量HCp*对Y(AlMe₄)₃进行质子解反应；(b) 室温下以Cp*Y(NiPr₂)₂(四氢呋喃，THF)与三甲基铝发生烷基酰胺消除反应。
四甲基镓酸盐衍生物Cp*Y(GaMe₄)₂可通过两种途径制备：一是Y(GaMe₄)₃与等摩尔量的HCp*发生反应，二是向[Cp*YMe₂]₃中加入2当量三甲基镓。
半夹心型配合物Cp*Y(MMe₄)₂（M = Al、Ga）具有相似的结构化学特征：在溶液中其甲基基团呈现高度流动性，固态下则存在一个平面构型与一个非典型弯曲的Y(μ-甲基)₂M结构单元。
配合物[Cp*₂Ln(MMe₄)]（Ln = Y、La；M = Al、Ga）通过Ln(MMe₄)₃与过量HCp*在升温条件下反应合成。这类茂金属配合物在溶液中存在已被报道的单体-二聚体平衡，低温下熵不利的二聚体占主导地位。
通过X射线衍射分析对二聚体形式的[Cp*₂La(AlMe₄)]₂、[Cp*₂Y(GaMe₄)]₂以及单体形式的Cp*₂La(GaMe₄)进行了结构表征。