Nanoscale Organolanthanum Clusters: Nuclearity‐Directing Role of Cyclopentadienyl and Halogenido Ligands

Abstract

Tetramethylaluminato/halogenido(X) ligand exchange reactions in half‐sandwich complexes [CpRLa(AlMe4)2] are feasible in non‐coordinating solvents and provide access to large coordination clusters of the type [CpRLaX2]x. Incomplete exchange reactions generate the hexalanthanum clusters [CpR6La6X8(AlMe4)4] (CpR=Cp*=C5Me5, X=I; CpR=Cp′=C5H4SiMe3, X=Br, I). Treatment of [Cp*La(AlMe4)2] with two equivalents Me3SiI gave the nonalanthanum cluster [Cp*LaI2]9, while the exhaustive reaction of [Cp′La(AlMe4)2] with the halogenido transfer reagents Me3GeX and Me3SiX (X=I, Br, Cl) produced a series of monocyclopentadienyl rare‐earth‐metal clusters with distinct nuclearity. Depending on the halogenido ion size the homometallic clusters [Cp′LaCl2]10 and [Cp′LaX2]12 (X=Br, I) could be isolated, whereas different crystallization techniques led to the aggregation of clusters of distinct structural motifs, including the desilylated cyclopentadienyl‐bridged cluster [(μ‐Cp)2Cp′8La8I14] and the heteroaluminato derivative [Cp′10La10Br18(AlBr2Me2)2]. The use of the Cp′ ancillary ligand facilitates cluster characterization by means of NMR spectroscopy.

Half‐Sandwich Complexes [Cp′4Ln4I8]4 (Ln=Ce, Pr):Emergence of Donor‐Free Organolanthanide Nanowheels

“…An X-ray diffraction (XRD) analysis revealed that 2 (Figure S12) is isostructural to the respective dodecalanthanum cluster [Cp'LaI 2 ] 12 . [35] The 1 H NMR spectrum of both compounds shows a mixture of products, ruling out any conclusive signal assignment and further detailed characterization.…”

“…Recently we found that the formation of half-sandwich organolanthanum clusters is crucially affected by the steric demand of the ancillary cyclopentadienyl ligand, the size of the bridging halogenido ligand, and the crystallization technique. [35] Consequently, we were interested in the effects of the Ln III ion size using otherwise identical reaction conditions.…”

“…On the one hand, the cyclopentadienylbridged octanuclear cerium cluster [Cp' 4 Ce 4 I 7 (μ 2 -Cp)] 2 (3) could be identified (Scheme 1). Partly desilylated 3 is isostructural (Figure S13 and Figure S14) to the corresponding lanthanum cluster [Cp' 4 La 4 (μ 2 -I) 4 (μ 3 -I) 2 (μ 4 -I)(μ 2 -Cp)] 2 [35] formed under the same synthesis conditions, using [Cp'La(AlMe 4 ) 2 ]/Me 3 SiI. Surprisingly, the diffusion method resulted in a second batch of crystals, which were again identified as the hexadecanuclear cluster 4 a (Scheme 1).…”

“…[29][30][31][32][33] Until now, the size of such half-sandwich-based clusters is restricted to Ln 12 entities (dodecanuclear structures) of the general composition [Cp R LnX 2 ] 12 (Cp R =C 5 H 5 , Ln=Sm, X=Cl; Cp R =C 5 H 4 SiMe 3 , Ln=La, X=I, Br). [34,35] Herein, we report an extension of the previously discovered halogenation protocol applying half-sandwich lanthanide bis(tetramethylaluminato) complexes [Cp'Ln(AlMe 4 ) 2 ] (Cp'=C 5 H 4 SiMe 3 ) as cluster precursors. [35] Special consideration is given to the Ln III ion size and the type of halogenido ligand as well as the formation of nano-sized {Ln 16 } ring-cluster hybrids.…”

“…[34,35] Herein, we report an extension of the previously discovered halogenation protocol applying half-sandwich lanthanide bis(tetramethylaluminato) complexes [Cp'Ln(AlMe 4 ) 2 ] (Cp'=C 5 H 4 SiMe 3 ) as cluster precursors. [35] Special consideration is given to the Ln III ion size and the type of halogenido ligand as well as the formation of nano-sized {Ln 16 } ring-cluster hybrids.…”