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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-7H-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 σ*−π* conjugation in the LUMO of the 7-sila-7H-dibenzo[c,g]fluorene 1 like a silole.

Brominative Si-Si cleavage of 3,4-disila-3,3,4,4-tetramethyl-3,4-dihydrodibenzo[c,g]phenanthrene (3a), LiAlH 4 reduction of the resulting dibromide, and fluorination of the dihydride 14a thus gave 2,2′-bis(fluorodimethylsilyl)-1,1′-binaphthyl (7a) in high yield as the first isolated and fully characterized 2,2′-bis(halosilyl)-1,1′-binaphthyl. Similar conversion of the more sterically hindered 3,4-disila-3,3-dimethyl-4,4-diphenyl-3,4-dihydrodibenzo[c,g]phenanthrene (3b) also gave the corresponding bishydrosilane 14b. However, subsequent fluorination did not give the desired bisfluorosilane 7b but rather the hydrolyzed siloxane 6b. The syntheses of the disilanylene-bridged precursors 3 were effected via bis-silylation reactions of 2,2′-dibromo-1,1′-binaphthyl (DBBN, 2) with dihalodisilanes ClMe 2 SiSiMe 2 Cl, ClMe 2 SiSiPh 2 Cl, FMe 2 SiSiPh 2 F, and FPh 2 SiSiPh 2 F. Although ClMe 2 SiSiMe 2 Cl predominately gave the disilanylene-bridged product 3a, XMe 2 SiSiPh 2 X (X ) F, Cl) produced not only the disilanylene-bridged product 3b but also the dimethylsilylene-bridged product 8a. FMe 2 -SiSiPh 2 F served better in preparation of the desired 3b than ClMe 2 SiSiPh 2 Cl. The sterically hindered FPh 2 SiSiPh 2 F did not give silylation products. The X-ray structural analyses of 3a and 3b provided the first geometrical parameters of the 2,2′-disilanylene-bridged 1,1′binaphthyl derivatives. In comparison with the acyclic analogues and less sterically hindered disilanylene-bridged biaryls such as 2,2′-bis(trimethylsilyl)-1,1′-binaphthyl ((()-1a), (R)-(-)-2,2′-bis(dimethylphenylsilyl)-1,1′-binaphthyl ((R)-(-)-1b), dibenzo-1,1,2,2-tetramethyl-1,2-disilacyclohexa-3,5-diene (12), and dithienodisilacyclohexadiene 13 the disilanylenebridged binaphthyls 3 were found to be highly strained due to the steric repulsion of the binaphthyl groups fixed in a narrow angle.