Dilithioplumbole: A Lead-Bearing Aromatic Cyclopentadienyl Analog

Aromatic Lead The bond stabilization, or aromaticity, observed in cyclic carbon molecules, such as benzene, relies on delocalization of electrons around the ring. Although electron distributions in heavier elements can complicate this arrangement, Saito et al. (p. 339) show that even lead, one of the heaviest metals, is able to participate in an otherwise carbon-based aromatic network. In an analog of the well-studied cyclopentadienyl anion, one carbon atom was replaced with lead, and the framework stabilized by appending phenyl groups to the other four carbons. Crystallography revealed a planar structure, which together with spectroscopic data and theoretical calculations confirmed the aromatic character of the product. Lead can participate in the delocalized electron network of an aromatic carbon ring. Although the concept of aromaticity has long played an important role in carbon chemistry, it has been unclear how applicable the stabilizing framework is to the heaviest elements. Here we report the synthesis of dilithiotetraphenylplumbole by reduction of hexaphenylplumbole. X-ray crystallography revealed a planar structure with no alternation of carbon–carbon bond lengths in the five-membered ring core. Nuclear magnetic resonance spectra and relativistic theoretical calculations show considerable aromatic character in the molecule, thus extending aromaticity to carbon’s heaviest congener.