The first evidence for a transient stibaallene ArSbCCR2

Dechlorofluorination of ArSb(F)-C(Cl)CR2 (CR2 = fluorenylidene, Ar = 2,4,6-tri-tert-butylphenyl) by tert-butyllithium afforded a 3,4-bis(fluorenylidene)-1,2-distibacyclobutane. The formation of the latter probably involves the transient stibaallene ArSbCCR2 followed by a head-to-head dimerization via two SbC double bonds. Molecular orbital calculations at the ab initio and DFT levels support the head-to-head dimerization of ArSbCCR2 with the formation of a 1,2-distibacyclobutane.