2 research outputs found
Synthesis and Properties of Bridgehead-Functionalized Permethylbicyclo[2.2.2]octasilanes
A series
of previously unknown bridgehead-functionalized bicyclo[2.2.2]Âoctasilanes,
Me<sub>3</sub>Si-Si<sub>8</sub>Me<sub>12</sub>-X, X-Si<sub>8</sub>Me<sub>12</sub>-X, and X-Si<sub>8</sub>Me<sub>12</sub>-Y [X, Y =
−SiMe<sub><i>n</i></sub>Ph<sub>3–<i>n</i></sub> (<i>n</i> = 1, 2) (<b>2</b>, <b>3</b>, <b>10</b>), −SiMe<sub>2</sub>Fc (Fc = ferrocenyl)
(<b>4</b>, <b>11</b>, <b>13</b>, <b>14</b>), −COR (R = Me, <i>t</i>Bu) (<b>6</b>, <b>7</b>, <b>12</b>), COOMe (<b>8</b>), COOH (<b>9</b>)], have been prepared by the reaction of the silanides Me<sub>3</sub>Si-Si<sub>8</sub>Me<sub>12</sub><sup>–</sup>K<sup>+</sup> or
K<sup>+–</sup>Si<sub>8</sub>Me<sub>12</sub><sup>–</sup>K<sup>+</sup> with proper electrophiles and fully characterized.
The molecular structures of <b>2</b>, <b>3</b>, <b>4</b>, <b>6</b>, <b>8</b>, <b>9</b>, <b>10</b>, and <b>13</b> as determined by single-crystal X-ray diffraction
analysis exhibit a slightly twisted structure of the bicyclooctasilane
cage. Endocyclic bond lengths, bond angles, and dihedral angles are
not influenced considerably by the substituents attached to the bridgehead
silicon atoms. Due to σÂ(SiSi)/Ï€Â(aryl) conjugation, a 20–30
nm bathochromic shift of the longest wavelength UV absorption band
relative to Me<sub>3</sub>Si-Si<sub>8</sub>Me<sub>12</sub>-SiMe<sub>3</sub> (<b>1</b>) is evident in the UV absorption spectra
of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption
data do not support the assumption of aryl/aryl or aryl/Cî—»O
interaction via the σÂ(SiSi) bicyclooctasilane framework