Half-sandwich halolanthanacarboranes of the “carbons adjacent” C2B4-carborane ligand systems: important synthons for new polyhedral cage constructs

The reaction of LnX3 (Ln = Ce, X = Br; Ln = Gd, Lu, X = Cl) with the “carbons adjacent” carborane monoanion, [2,3-(SiMe3)2-2,3-C2B4H5]− in 1:2 molar ratio in anhydrous tetrahydrofuran (THF) produced the dimeric half-sandwich halolanthanacarboranes, [closo-1-(X)-1,1-(THF)2-2,3-(SiMe3)2-1-Ln(η5-C2B4H4)]2, in 72–92% yields along with one equivalent of the neutral nido-carborane precursor, 2,3-(SiMe3)2-2,3-C2B4H6. This reliable synthetic route avoided complications such as solvent degradation and oxide ion incorporation that give rise to large multi-lanthanacarborane clusters. This method produced the first isolated halolanthanacarborane half-sandwich in the C2B4-cage systems.