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

Abstract

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 ...