First C2 symmetrical siloles:: Synthetic, structural, and photophysical studies of 7-Sila-7H-dibenzo [c,g]fluorenes

The syntheses of 7-sila-7H-dibenzo[c,g]fluorenes 1 were effected via dilithiation of 2,2'-dibromo-1,1'-binaphthyl (2) followed by cyclization of the resulting dianion with dihalosilanes: Me2SiCl2, Ph2SiCl2, and Ph2SiF2. The X-ray structural analysis of 7-sila-7, 7-diphenyl-7N-dibenzo[c,g]fluorene (1b) provided the first geometrical parameters of the 7-sila-7H-dibenzo[c,g]fluorene derivative in which the silole skeleton was found to be twisted in the C-2 symmetrical conformation due to the significant steric repulsion of the binaphthyl group fixed within the van der Waals radii. The photophysical study and semiempirical PM3 calculation suggested the presence of significant sigma*-pi* conjugation in the LUMO of the 7-sila-7N-dibenzo[c,g]fluorene 1 like a silole.