Nanoscale Organolanthanum Clusters: Nuclearity-directing Role of Cyclopentadienyl and Halogenido Ligands.

Tetramethylaluminato/halogenido(X) ligand exchange reactions in half-sandwich complexes [Cp R La(AlMe 4 ) 2 ] are feasible in non-coordinating solvents and provide access to large coordination clusters of the type [Cp R LaX 2 ] x . Incomplete exchange reactions generate the hexalanthanum clusters [Cp R 6 La 6 X 8 (AlMe 4 ) 4 ] (Cp R = Cp* = C 5 Me 5 , X = I; Cp R = Cp' = C 5 H 4 SiMe 3 , X = Br, I). Treatment of [Cp*La(AlMe 4 ) 2 ] with exc. Me 3 SiI gave the nonalanthanum cluster [Cp*LaI 2 ] 9 , while the exhaustive reaction of [Cp'La(AlMe 4 ) 2 ] with the halogenido transfer reagents Me 3 GeX and Me 3 SiX (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'LaCl 2 ] 10 and [Cp'LaX 2 ] 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 [(micro-Cp) 2 Cp' 8 La 8 I 14 ] and the heteroaluminate derivative [Cp' 10 La 10 Br 18 (AlBr 2 Me 2 ) 2 ]. The use of the Cp' ancillary ligand facilitates cluster characterization by means of NMR spectroscopy.