| Abstract
| - The reaction of various highly substituted lanthanide(III) and -(II) aryloxide complexeswith 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, formbis-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 stericallybulkier 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 adductcomplexes are rigid in solution, while at ambient temperature the exchange of bridging andterminal 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 withTMA to give mono(tetramethylaluminate) complexes of the type (ArtBu,RO)2Ln[(μ-Me)2AlMe2].The heteroleptic Cp*-supported complex (C5Me5)Y(OArtBu,H)2 also produced a tetramethylaluminate complex, namely (C5Me5)Y(OArtBu,H)[(μ-Me)2AlMe2], in the TMA reaction. Thesolvated aryloxide complexes Ln(OAr)2(THF)x (x = 1, 2), featuring the divalent rare-earth-metal centers ytterbium and samarium, yield the bis-TMA adduct complexes Ln[(μ-OArtBu,R)(μ-Me)AlMe2]2. However, it was found that the generation of homoleptic hexane-insoluble[Ln(AlMe4)2]n is an important reaction pathway governed by the size (oxophilicity) of themetal center (Yb ≫ Sm), the amount of TMA, the reaction period, and the substituents ofthe aryloxide ligand (OAriPr,H ≫ OArtBu,H> OArtBu,Me ≫ OArtBu,tBu). For the Ln(III) aryloxidecomplexes, peralkylated complexes Ln(AlMe4)3 were detected only in the presence of theleast bulky ligand, OAriPr,H. Various mechanistic scenarios are depicted on the basis of therare-earth-metal species identified, including byproducts such as [Me2Al(μ-OAr)]2, and ofthe interactivity of rare-earth alkoxide complexes with trialkylaluminum compounds knownfrom the literature. The complexes Y(OC6H3iPr2-2,6)[(μ-OC6H3iPr2-2,6)(μ-Me)AlMe2]2 andLn(OC6H3tBu2-2,6)2[(μ-Me)2AlMe2] (Ln = Y, Lu) have been characterized by X-ray diffractionstructure determinations.
- The principle of steric unsaturation/oversaturation and the criterion of oxophilicity are important factors governing the sequential reaction of trimethylaluminum (TMA) with aryloxide complexes of the tri- and divalent rare-earth metals. Mono- and bis-TMA adducts as well as heteroleptic and homoleptic tetramethylaluminate derivatives have been obtained as isolable products for each specific LnIII(OAr)3/TMA and LnII(OAr)2/TMA pair, with OAr representing [OC6H3iPr2-2,6], [OC6H3Ph2-2,6], and [OC6H2tBu2-2,6−4-R] (R = H, Me, tBu).
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