Unexpected Dimerization of a Bis(fluorenyl)-bis(trimethylsilyl)-diallene to a Dihydroquatercyclopentadiene, an Octacyclic C36 Fragment Corresponding to 60% of C60: Reaction of the Diallene with Fe2(CO)9

The propargylallene 3,3′-biphenylene-1-trimethylsilyl-1-(9-trimethylsilylethynyl)-9H-fluorenylallene, 12, undergoes thermal rearrangement in refluxing THF to the corresponding s-trans-bis(fluorenylidene)bis(trimethylsilyl)diallene, 13. In contrast, when thermolyzed in refluxing toluene, 12 cyclizes to form a cyclopentenylidene carbene that dimerizes to furnish the tetrabenzodihydroquatercyclopentadiene 15. Moreover, treatment of 13 with NaF yields C60H36, 17 (the “parent” analogue of 15), whose C36 backbone can be mapped onto C60 and which represents 60% of the fullerene framework. The ligands 12 and 13 both react with di-iron nonacarbonyl to produce the novel complex 21, in which an (η5-fluorenyl)Fe(CO)2 moiety is linked both directly and via a bridging carbonyl to a cyclopentadiene ring bearing two trimethylsilyl substituents and a spiro-bonded fluorenyl fragment. The proposed mechanism involves rearrangement of a coordinated trimethylsilylalkyne unit into a vinylidene complex prior to formation of the cyclopentadiene ring. However, the complex 21 is relatively unstable and undergoes oxidative decomposition with loss of iron and formation of a bicyclic lactone, 27, possessing two spiro-bonded fluorenyl groups. The X-ray crystal structures of 13, 15, 17, 21, and 27, as well as that of 1,4-bis(fluorenylidene)-2-butyne, 20, are reported.