The Gomberg-type dimerization of bifluorenylidene radicals: an X-ray crystallographic investigation

The reaction of phenylethynyllithium with 9-bromofluorene yields 9,9′-bifluorenylidene, 8, 9,9′-bifluorenyl, 9, and a molecule 10, of formula C52H32, in which coupling has occurred between a 9,9′-bifluorenyl fragment and a 9,9′-bifluorenylidene moiety such that a C(9) position of the former is attached to a C(3) site of the latter. This parallels the unsymmetrical radical coupling of triphenylmethyl radicals, which leads to the Gomberg dimer, rather than hexaphenylethane. The structure of 10 has been elucidated by X-ray crystallography, and a mechanistic rationale is offered.