chong

Organometallic multi-decker sandwich complexes containing f-elements remain rare, despite their attractive magnetic and electronic properties. The reduction of the Ce^III siloxide complex, [KCeL₄] (1; L=OSi(OtBu)₃), with excess potassium in a THF/toluene mixture afforded a quadruple-decker arene-bridged complex, [K(2.2.2-crypt)]₂[{(KL₃Ce)(μ-η⁶:η⁶-C₇H₈)}₂Ce] (3). The structure of 3 features a [Ce(C₇H₈)₂] sandwich capped by [KL₃Ce] moieties with a linear arrangement of the Ce ions. Structural parameters, UV/Vis/NIR data, and DFT studies indicate the presence of Ce^II ions involved in δ bonding between the Ce cations and toluene dianions. Complex 3 is a rare lanthanide multi-decker complex and the first containing non-classical divalent lanthanide ions. Moreover, oxidation of 1 by AgOTf (OTf=O₃SCF₃) yielded the Ce^IV complex, [CeL₄] (2), showing that siloxide ligands can stabilize Ce in three oxidation states.

Ce^II in the sandwich: A quadruple-decker sandwich of divalent cerium was assembled from siloxide-supported Ce^III and toluene under strongly reducing conditions. The siloxide ligands and the δ-bonds between the Ce centers and the toluene dianion are key in the assembly.