Bulking up Cp BIG : A Penta-Terphenyl Cyclopentadienyl Ligand.

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.