Reactivity of Trimethylaluminum with Lanthanide Aryloxides: Adduct and Tetramethylaluminate Formation

The reaction of various highly substituted lanthanide(III) and -(II) aryloxide complexes with trimethylaluminum (TMA) was investigated. The solvent-free, π-arene-bridged dimers [Ln(OAriPr,H)3]2, derived from the ortho-iPr2-substituted aryloxide ligand OC6H3iPr2-2,6, form bis-TMA adduct complexes, Ln(OAriPr,H)3(AlMe3)2, for the metal centers yttrium, samarium, and lanthanum. Homoleptic monomeric Ln(OAr)3, featuring a large La center and sterically bulkier ortho-tBu2-substituted aryloxide ligands, afford the mono-TMA adducts La(OArtBu,R)3(AlMe3) (R = H, Me). The hetero-bridged moieties “Ln(μ-OAr)(μ-Me)Al” of these adduct complexes are rigid in solution, while at ambient temperature the exchange of bridging and terminal aluminum methyl groups is fast on the NMR time scale. Monomeric Ln(OArtBu,R)3 (R = H, Me, tBu) of the smaller rare-earth-metal centers yttrium and lutetium react with TMA to give mono(tetramethylaluminate) complexes of the type (ArtBu,RO)2Ln[(μ-Me)2AlMe2]. The heteroleptic Cp*-supported compl...