The synthesis of eight new cyclobutadiene or ferrocene-fused organometallic dehydroannulenes is reported. Cadiot-type coupling of a 1-bromoethynyl-2-silylethynylbenzene derivative to an organometallic diyne (1,2-diethynyl-3,4-bis(trimethylsilyl)cyclobutadiene(cyclopentadienyl)cobalt or 1,2-diethynylferrocene) is followed by deprotection and Cu(OAC)(2)-promoted ring closure. Five of the organometallic dehydroannulenes were structurally characterized. Three of the novel cycles explode at temperatures from 196 to 293 degreesC and form insoluble carbon materials. The soot produced from 13a shows a high abundance of onion-like carbon nanostructures. The nanostructures were characterized by high-resolution transmission electron microscopy.