Reactivity of Trimethylaluminum with Lanthanide Aryloxides:  Adduct and Tetramethylaluminate Formation

Abstract

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(OAr i Pr,H)3]2, derived from the ortho-iPr2-substituted aryloxide ligand OC6H3 i Pr2-2,6, form bis-TMA adduct complexes, Ln(OAr i Pr,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(OAr t Bu,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(OAr t Bu,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 (Ar t Bu,RO)2Ln[(μ-Me)2AlMe2]. The heteroleptic Cp*-supported complex (C5Me5)Y(OAr t Bu,H)2 also produced a tetramethylaluminate complex, namely (C5Me5)Y(OAr t Bu,H)[(μ-Me)2AlMe2], in the TMA reaction. The solvated 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-OAr t Bu,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 the metal center (Yb ≫ Sm), the amount of TMA, the reaction period, and the substituents of the aryloxide ligand (OAr i Pr,H ≫ OAr t Bu,H > OAr t Bu,Me ≫ OAr t Bu, t Bu). For the Ln(III) aryloxide complexes, peralkylated complexes Ln(AlMe4)3 were detected only in the presence of the least bulky ligand, OAr i Pr,H. Various mechanistic scenarios are depicted on the basis of the rare-earth-metal species identified, including byproducts such as [Me2Al(μ-OAr)]2, and of the interactivity of rare-earth alkoxide complexes with trialkylaluminum compounds known from the literature. The complexes Y(OC6H3 i Pr2-2,6)[(μ-OC6H3 i Pr2-2,6)(μ-Me)AlMe2]2 and Ln(OC6H3 t Bu2-2,6)2[(μ-Me)2AlMe2] (Ln = Y, Lu) have been characterized by X-ray diffraction structure determinations.

Crystal structure of bis(μ2-methanolato-κO:κO)hexamethylbis(μ2-triphenylacetato-κO:κO′)bis(μ2-triphenylacetato-κ2 O,O′:κO)dialuminiumdilanthanum toluene tetrasolvate

“…Cg1, Cg2, Cg3 and Cg4 are the centroids of the C33-C38, C39-C44, C52-C57 and C19-C24 rings, respectively. Occhipinti et al, 2011;GEQMOF, GEQMUL, Fischbach et al, 2006b) Biagini et al, 1994;WAPYIV, WAPYOB, Evans et al, 1993a;WEHHAS, Evans et al, 1993b) Fischbach et al, 2003;MIMPED, Giesbrecht et al, 2002;MOQYOG, Gordon et al, 2002;PETMUX, Fischbach et al, 2006c) Giesbrecht et al, 2002;ROCHOH, Sommerfeldt et al, 2008) Evans et al, 1998). MIMPED is the only La structure among them.…”

Surface Organobarium and Organomagnesium Chemistry on Periodic Mesoporous Silica MCM‐41: Convergent and Sequential Approaches Traced by Molecular Models

“…[9] In addition to strained siloxane bridges [SiOSi ], Brønsted acidic Q 3 functionalities feature reactive surface sites on silica supports that are predominantly available after partial dehydration at elevated temperatures. [3,4] More recently, Gauvin et al reported on the equimolar reaction of www.chemeurj.org 3 ] 2 , due to the Schlenk equilibrium prevailing in solution.…”

“…[4][5][6] The synthesis of molecular complexes mimicking such surface species is a viable/popular approach to obtain more insight into the nature of a given immobilization scenario. [7] In the meantime, sterically demanding monovalent silanols, such as triphenylsilanol [8] or tris(tert-butoxy)silanol, [9] and multivalent, incompletely condensed oligosilsesquioxanes [10] or calixarenes [11] are routinely employed to assess the local environment of silica-grafted organometallics.…”

In situ X-ray absorption fine structure study on the polymerization of isoprene assisted by Nd-based ternary catalysts

“…The aluminum cocatalyst was speculated to have an activating effect by either increasing the concentration of active Nd or by increasing the number of active sites per Nd. Anwander et al 3,[22][23][24][25][26] focused on the precise structure of Nd-Al compounds. Elaborated crystal samples were used for X-ray structure determination.…”