First Isolation and Full Characterization of 2,2‘-Bishalosilyl-Substituted 1,1‘-Binaphthyls:  Synthesis of 2,2‘-Bis(fluorodimethylsilyl)-1,1‘-binaphthyl and X-ray Structural Analysis of Highly Strained Disilanylene-Bridged Precursors

Brominative Si−Si cleavage of 3,4-disila-3,3,4,4-tetramethyl-3,4-dihydrodibenzo[c,g]phenanthrene (<BO>3a</BO>), LiAlH<INF>4</INF> reduction of the resulting dibromide, and fluorination of the dihydride <BO>14a</BO> thus gave 2,2‘-bis(fluorodimethylsilyl)-1,1‘-binaphthyl (<BO>7a</BO>) 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 (<BO>3b</BO>) also gave the corresponding bishydrosilane<BO> 14b</BO>. However, subsequent fluorination did not give the desired bisfluorosilane <BO>7b</BO> but rather the hydrolyzed siloxane <BO>6b</BO>. The syntheses of the disilanylene-bridged precursors <BO>3</BO> were effected via bis-silylation reactions of 2,2‘-dibromo-1,1‘-binaphthyl (DBBN, <BO>2</BO>) with dihalodisilanes ClMe<INF>2</INF>SiSiMe<INF>2</INF>Cl, ClMe<INF>2</INF>SiSiPh<INF>2</INF>Cl, FMe<INF>2</INF>SiSiPh<INF>2</INF>F, and FPh<INF>2</INF>SiSiPh<INF>2</INF>F. Although ClMe<INF>2</INF>SiSiMe<INF>2</INF>Cl predominately gave the disilanylene-bridged product <BO>3a</BO>, XMe<INF>2</INF>SiSiPh<INF>2</INF>X (X = F, Cl) produced not only the disilanylene-bridged product <BO>3b</BO> but also the dimethylsilylene-bridged product <BO>8a</BO>. FMe<INF>2</INF>SiSiPh<INF>2</INF>F served better in preparation of the desired <BO>3b</BO> than ClMe<INF>2</INF>SiSiPh<INF>2</INF>Cl. The sterically hindered FPh<INF>2</INF>SiSiPh<INF>2</INF>F did not give silylation products. The X-ray structural analyses of <BO>3a</BO> and <BO>3b</BO> 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 ((±)-<BO>1a</BO>), (R)-(−)-2,2‘-bis(dimethylphenylsilyl)-1,1‘-binaphthyl ((R)-(−)-<BO>1b</BO>), dibenzo-1,1,2,2-tetramethyl-1,2-disilacyclohexa-3,5-diene (<BO>12</BO>), and dithienodisilacyclohexadiene <BO>13</BO> the disilanylene-bridged binaphthyls <BO>3</BO> were found to be highly strained due to the steric repulsion of the binaphthyl groups fixed in a narrow angle.