Cycloheptatrienyl-Bridged Triple-Decker Complexes

The first structurally characterized organometallic multidecker sandwich complexes featuring a cycloheptatrienyl ring (Cht, C₇H₇^3–) in the coordination sphere are presented. The synthesis of inverse sandwich complexes of the rare earth elements Y^III and Er^III with a bridging cycloheptatrienyl ligand of the type [(thf)(BH₄)₂Ln^III(μ–η⁷:η⁷-Cht)Ln^III(BH₄)(thf)₂] is described first. The subsequent introduction of the Cot^TIPS ligand (Cot^TIPS = 1,4-(ⁱPr₃Si)₂C₈H₆^2–) into the coordination sphere of the rare earth cations resulted in the isolation of unprecedented triple-decker compounds with the formula [(thf)₃K{(η⁸-Cot^TIPS)Ln^III}₂(μ–η⁷:η⁷-Cht)], bearing a seven-membered aromatic carbon ring as a middle deck. These compounds are also the first examples of rare earth triple-decker complexes not bridged by a Cot derivative, based on purely carbon-based ligands. The magnetic properties of the respective Er^III congeners were investigated in detail, leading to the observation of antiferromagnetic coupling of the Er^III cations and a blocking temperature of 13.5 K. The conversion of the Y^III compound [(thf)₃K{(η⁸-Cot^TIPS)Y^III}₂(μ–η⁷:η⁷-Cht)] with [Y^III(Cot)I(thf)₂] resulted in ligand rearrangement and the selective formation of the first triple-decker complex ([(η⁸-Cot^TIPSY^III)₂(μ–η⁸:η⁸-Cot)]) featuring two Cot ligands with different substituents in its coordination sphere.