Double ligand activation in silyl-substituted rare-earth cyclobutadienyl complexes

The sodium cyclobutadienyl (Cb) reagent [Na2{η4-C4(SiMe3)4}(THF)]2 (2) reacts with rare-earth halides [MCl3(THF)x], where M = Y, Dy (x = 3.5) and Lu (x = 3), giving the sandwich coordination polymers [M{η3-C4(SiMe3)4H}{η4-C4(SiMe3)3-κ-(CH2SiMe2}Na]∞ (3M, M = Y, Dy, Lu). The coordination environments of the rare-earth metals in 3M feature an η4-cyclobutadienyl ligand, with additional coordination by a tuck-in trimethylsilyl group and an η3-cyclobutenyl ligand. The ligand activation is thought to be a consequence of deprotonation of the Cb ligand by 2. The axial nature of the crystal field in 3M is reflected in the single-molecule magnet properties of 3Dy, which has an anisotropy barrier of 309 cm–1 in zero applied magnetic field.