Heterodimetall‐Halblanthanoidocencluster: neuartige Tetramethylaluminato‐Chloro‐Koordinationen

Abstract

Die Metallionengröße macht den Unterschied: Bei Umsetzung mit Me2AlCl laufen in den hervorragend löslichen Bis(aluminat)komplexen [Cp*Ln(AlMe4)2] (Ln=Y, La, Nd; Cp*=C5Me5) LnIII‐spezifische Alkyl/Chlorid‐Ligandenaustauschreaktionen ab. Die reproduzierbare Bildung von Y2Al2‐, La6Al4‐ und Nd5Al‐Heterodimetall‐Alkyl‐Clustern führt zu neuartigen AlMe4‐Bindungsmodi (Bild: La6Al4‐Cluster).

Half‐Sandwich Bis(tetramethylaluminate) Complexes of the Rare‐Earth Metals: Synthesis, Structural Chemistry, and Performance in Isoprene Polymerization

“…Contrary to the cluster formation observed for reactions of [Ln(AlMe 4 ) 2 (C 5 Me 5 )] ( 5 ) (Ln=Nd, La) with Me 2 AlCl,14 well‐defined dimeric compounds [{Ln(AlMe 4 )(μ‐Cl)(Cp R )} 2 ] were exclusively found for Cp R =[1,3‐(Me 3 Si) 2 C 5 H 3 ], [C 5 Me 4 SiMe 3 ], and [1,2,4‐(Me 3 C) 3 C 5 H 2 ], even for the large neodymium metal center in 9 . Such dinuclear compounds are formed in mixtures of 2 – 4 with Et 2 AlCl as sterically and electronically saturated systems without catalytic activity toward isoprene polymerization.…”

“…Contrary to the reported high activities of binary catalyst mixtures containing the above‐mentioned non‐cyclopentadienyl Ln/Al heterobimetallic complexes and Et 2 AlCl, mixtures of 2 – 5 and Et 2 AlCl did not provide active catalysts for the polymerization of isoprene. Treatment of [Ln(AlMe 4 ) 2 (C 5 Me 5 )] ( 5 ) (Ln=Y, Nd, La) with varying amounts of Me 2 AlCl has recently been reported to yield mixed tetramethylaluminate/chloride compounds 14. The extent of the [AlMe 4 ] → [Cl] exchange and the nuclearity of the resulting rare‐earth metal complexes was found to be significantly affected by subtle changes in the rare‐earth metal cation size.…”

“…2.794 Å ( 9 )) are comparable to the corresponding bond lengths of the bridging chloro ligands in dimeric [{Y(AlMe 4 )(μ‐Cl)(C 5 Me 5 )} 2 ] (av. 2.6752 Å) and the [μ 2 ‐Cl] bridges in the pentanuclear neodymium cluster [Nd 5 (μ 4 ‐Cl)(μ 3 ‐Cl) 2 (μ 2 ‐Cl) 6 (C 5 Me 5 ) 5 {(μ‐Me) 3 AlMe}] (2.775 Å) 14…”

“…8 The reactivity pattern of such alkylaluminate complexes is consistent with their formulation as “alkyls in disguise”, that is, [Ln III (AlMe 3 ) 2 Me 2 ( L )]. Their most striking features are: a) availability for the entire Ln III cation size range;9 b) accessibility by versatile synthesis protocols comprising both protonolysis and salt metathesis approaches;7, 8, 10 c) enhanced thermal stability (e.g., [Ln(AlMe 4 ) 2 (C 5 Me 5 )] may be sublimed) and hence suitability for storage;11 d) coordinational flexibility of the [AlMe 4 ] ligands, as evidenced by η 1/2/3 coordination modes;9, 12–14 e) an absence of coordinating donor molecules (Do);15 and f) the presence of AlMe 3 as an internal solvent scavenger 16. Moreover, our previous work highlighted the pivotal role of heterobimetallic [Ln(μ‐R) n Al] moieties in the activation of rare‐earth metal‐based Ziegler‐type catalysts 17–20.…”

Rare‐Earth Metal Mixed Chloro/Methyl Compounds: Heterogeneous–Homogeneous Borderline Catalysts in 1,3‐Diene Polymerization

“…[16] The NdÀm 3 -Cl separations (av 2.8868 ) are longer than the NdÀm 2 -Cl ones (av 2.8009 ) and fall in the range of those observed for [Nd 5 Cp* 5 {(m-Me) 3 AlMe}(m 4 -Cl)(m 3 -Cl) 2 (m-Cl) 6 ] (2.731(4)-3.000(4) ; Cp* = C 5 Me 5 ). [17] In the solid state, all silylamido ligands are agostically distorted, each forming one acute angle a(Nd-N-Si) (e.g. a(Nd2-N1-Si) = 94.1(2); Nd2···Si1 3.227(1) ).…”