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(mu-Me)(2)M moiety in the solid state. Complexes [CP*(2)Ln(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*La-2(AlMe4)](2) and [Cp*Y-2(GaMe4)](2) as well as monomeric CP*La-2(GaMe4) were analyzed by X-ray diffraction.