Plumbacyclopentadienylidenes, in which the lead atoms have divalent states and are coordinated by THF, pyridine and N-heterocyclic carbene, were synthesized and characterized. The THF- and pyridine-stabilized compounds can be regarded as rare examples of hypervalent 10-X-4 species. The equilibrium between the THF adduct and the free plumbacyclopentadienylidene was evidenced by spectroscopic analysis and theoretical calculations. The THF adduct in benzene converted into a plumbylene dimer, where one of the lead centers is coordinated by THF and the other lead atom is coordinated by a divalent lead atom, the dimer gradually decomposing into spiroplumbole. The THF adduct unexpectedly reacted with trifluoroborane and trichlorogallane to afford fluoroborole and chlorogallole, which are the first examples of non-annulated fluoroborole and gallole, respectively.

Plumbacyclopentadienylidenes  in which the lead atom is coordinated to a variety of Lewis bases, including THF, exhibit interesting behavior and reactivity. In their Full Paper on , M. Saito et al. show that the THF adduct, which is a rare example of a 10‐X‐4 species, reacts with trifluoroborane or trichlorogallane to afford fluoroborole and chlorogallole, respectively.