Bulking up Cp(BIG): A Penta-Terphenyl Cyclopentadienyl Ligand

[Image: see text] The modification of cyclopentadienyl ligands with carefully selected substituents is a widely used strategy for tuning their steric and electronic properties. We describe the synthesis of an extremely bulky penta-terphenyl cyclopentadienyl ligand (Cp(T5)) by arylation of cyclopentadiene. Deprotonation reactions with various group 1 metals and bases afforded a complete series of alkali metal salts MCp(T5) (M = Li–Cs). The compounds were isolated as solvate-free salts, which were characterized by multinuclear nuclear magnetic resonance spectroscopy, ultraviolet–visible spectroscopy, and elemental analysis. Single-crystal X-ray diffraction studies of LiCp(T5), NaCp(T5) (crystallized as a solvate with one tetrahydrofuran molecule per formula unit), and KCp(T5) revealed the formation of metallocene-like sandwich structures in the solid state.