The first evidence for a transient stibaallene ArSbdouble bond; length as m-dashCdouble bond; length as m-dashCR2

Dechlorofluorination of ArSb(F)–C(Cl)double bond; length as m-dashCR2 (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 ArSbdouble bond; length as m-dashCdouble bond; length as m-dashCR2 followed by a head-to-head dimerization via two Sbdouble bond; length as m-dashC double bonds. Molecular orbital calculations at the ab initio and DFT levels support the head-to-head dimerization of ArSbdouble bond; length as m-dashCdouble bond; length as m-dashCR2 with the formation of a 1,2-distibacyclobutane.