Pyrrolyl-Bridged Metallocene Complexes: From Synthesis, Electronic Structure, to Single-Molecule Magnetism.

The π- and σ-basicity of the pyrrolyl ligand affords several coordination modes. A sterically encumbering coordination sphere around metal centers may foster new coordination modes for the pyrrolyl ligand. Here, we present three dinuclear rare earth complexes [Cp*RE(μ-pyr)], [RE = Y (), La (), Dy (); Cp* = pentamethylcyclopentadienyl, pyr = pyrrolyl], which were synthesized through a protonolysis reaction between allyl complexes and H-pyrrole. Each metal is ligated by two Cp* ligands and the N atom of the pyrrolyl ring while interacting with the π-system of the other pyrrolyl ligand, yielding an unprecedented coordination mode for pyrrolyl best described as [((η-Cp*)RE)(μ-1η-pyr-2κN)(μ-2η-pyr-1κN)]. The steric congestion implemented by the Cp* ligands forces this asymmetric coordination of the pyrrolyl ligand. - were characterized by crystallography, electrochemistry, and spectroscopy. Density functional theory calculations on uncovered the bonding situation between the pyrrolyl ligand and the yttrium(III) ion. Excitingly, displays slow magnetic relaxation under zero dc field with = 98.9(7) cm and τ = 6.7(1) × 10 s, placing it among coveted dinuclear metallocene single-molecule magnets. CASSCF calculations provided the energy of the crystal field states of Dy and confirmed the barrier height.