256394-29-3Relevant academic research and scientific papers
Reactivity of trimethylaluminum with lanthanide aryloxides: Adduct and tetramethylaluminate formation
Fischbach, Andreas,Herdtweck, Eberhardt,Anwander, Reiner,Eickerling, Georg,Scherer, Wolfgang
, p. 499 - 509 (2008/10/08)
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 complex (C5Me5)Y(OArtBu,H)2 also produced a tetramethyl-aluminate complex, namely (C5Me5)Y(OArtBu,H)[(μ-Me)2 AlMe2], 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-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 the metal center (Yb ? Sm), the amount of TMA, the reaction period, and the substituents of the aryloxide ligand (OAriPr,H ? OArtBu,H > OArtBu,Me ? OArtBu,tBu). For the Ln(III) aryloxide complexes, peralkylated complexes Ln(AlMe4)3 were detected only in the presence of the least bulky ligand, OAriPr,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(OC6H3iPr2-2,6) [(μ-OC6H3iPr2-2,6)(μ-Me) AlMe2]2 and Ln(OC6H3tBu2-2,6)2[(μ- Me)2AlMe2] (Ln = Y, Lu) have been characterized by X-ray diffraction structure determinations.
Interactions of remote alkyl groups with lanthanide metal centers: Synthesis, characterization and ligand redistribution reactions of heterobimetallic species containing trialkylaluminum fragments
Giesbrecht, Garth R.,Gordon, John C.,Brady, John T.,Clark, David L.,Keogh, D. Webster,Michalczyk, Ryszard,Scott, Brian L.,Watkin, John G.
, p. 723 - 731 (2007/10/03)
The reaction of [Ln(OAr)3]2 with four equivalents of trialkylaluminum leads to the formation of the bis-trialkylaluminum adducts (ArO)Ln[(μ-OAr)(μ-R)AlR2]2 [Ln = La, R = Me (1); Ln = La, R = Et (3); Ln = Sm, R = Et (4)]. The X-ray crystal structure of 1 reveals short La-C(bridging) distances of 2.800(5) and 2.759(5) A. A reduced 1JC-H coupling constant of 110 Hz and a low energy v(C-H) stretch in the solution and solid state IR spectra are consistent with a strong agostic La···H-C interaction in solution. Crystal data for 1: a = 11.708(2) A; b = 18.416(4) A; c = 20.949(4) A; α = 90°; β = 90°; γ = 90°; V = 4516.8(15) A3; Z = 4; R1 = 4.69%. The solid-state structure of the samarium ethyl derivative 4 reveals close contacts of 2.627(4) and 2.649(4) A between the samarium center and the methylene carbons of the triethylaluminum groups. The room temperature 13C NMR spectrum of 4 exhibits a 1JC-H coupling constant of 102 Hz; additionally, the fluxional process that exchanges methyl groups in 1 and 2 is slow enough on the NMR time scale to allow distinct methylene groups in 4 to be observed. Crystal data for 4: a = 19.318(1) A; b = 20.150(1) A; c = 26.280(1) A; α = 90°; β = 90°; γ = 90°; V = 10229.8(9) A3 Z = 8; R1 = 3.53%. Thermolysis of 1-4 results in ligand redistribution to form [R2Al(OAr)]2 [R = Me, Et (5)] and other unidentified species. Crystal data for 5: a = 9.496(4) A; b = 10.183(4) A; c = 18.794(7) A; α = 90.06(1)°; β = 92.394(7)°; γ = 114.976(6)°; V = 1645.6(11) A3; Z = 2; R1 = 10.13%.
Ancillary aryloxide ligands in ethylene polymerization catalyst precursors
Firth, Andrea V.,Stewart, Jeffrey C.,Hoskin, Aaron J.,Stephan, Douglas W.
, p. 185 - 193 (2007/10/03)
The compounds CpTiCl2(OC6H3-i-Pr2) (1), CpTiCl(OC6H3-i-Pr2)2 (2), CpTi(R)(OC6H3-i-Pr2)2 (R=t-Bu 3, s-Bu 4, n-Bu 5, Me 6) have been prepared and characterized. Compounds 1 or 2 in the presence of 500 equivalents of methylaluminoxane (MAO) act as catalyst precursors for ethylene polymerization. While the catalysts derived from the monocyclopentadienyl complexes are much less active that the metallocenes, there is a clear enhancement in the activity of about 40% as a result of the inclusion of a second aryloxide ligand. Reactions of 1 with AlMe3 revealed stepwise formation of CpTi(Me)Cl(OC6H3-i-Pr2) 7 and CpTi(Me)2(OC6H3-i-Pr2) 8, while subsequent addition of AlMe3 afforded complete conversion to 8, with formation of the aluminum species [AlMe2(OC6H3-i-Pr2)]n 9. In contrast, the catecholate complex CpTi(O2C6H4)Cl 10 reacts with AlMe3 yielding the paramagnetic species [CpTi(O2(C6H4))·AlClMe2] 2 11. Incorporation of aryloxide ligands in modified metallocenes was readily accomplished with the preparation of Cp2ZrCl(OC6H3-i-Pr2) 12, Cp2ZrCl(OC6H5) 13, Cp2ZrMe(OC6H5) 14 and Cp2TiCl(OC6H3-i-Pr2) 15. In combination with MAO, 12, 14 and 15 effect the polymerization of ethylene with an 11% increase in activity over the parent metallocenedichlorides. The implications of the increased activity are considered. Crystallographic data are reported for 2, 3, 6, 9, 11, 12 and 13.
