Cyclo-oligomerization of 6,12-Diethynyl Indeno[1,2-b]fluorenes via Diradical Intermediates.

Indeno[1,2-b]fluorene derivatives with trimethylsilylethynyl substituents at the 6- and 12-positions were found to undergo cyclo-dimerization, cyclo-trimerization, and higher oligomerizations at room temperature. The cyclic dimer features a novel double-decker motif, composed of two face-to-face stacked bis(propadienylide)dihydroindeno[1,2-b]fluorenes with a short centroid-to-centroid distance of 3.50 Å. The existence of a cyclic trimer and higher oligomers was confirmed by mass spectroscopy and gel permeation chromatography. The results clearly demonstrate the diradical feature of the indeno[1,2-b]fluorene moiety.