Organopolysilanes

Polysilane Dendrimers

“…[44] Most remarkable, however, are the extreme down-field shifts upon going from T [3][4][5][6] and T [3][4][5][6][7] silicon nuclei (−57 ppm to −66 ppm) to T [3][4][5][6][7][8][9] silicon nuclei with values ranging from −30 ppm to −37 ppm [83,84]. These drastic changes in chemical shift seem to originate from dramatic changes in critical bond parameters such Si-Si distances and Si-Si-Si angles around the central core units, which are only observed for polysilane dendrimers with exclusively three-fold branches (core = T [3][4][5][6][7][8][9] ). As mentioned before, the strain in these molecules is released by an extreme flattening of the Si-Si-Si angles (core-spacer-branch ~130°) emanating from the central T [3][4][5][6][7][8][9] core and an elongation of the spacer-branch Si-Si distances (239-240 pm).…”

“…These drastic changes in chemical shift seem to originate from dramatic changes in critical bond parameters such Si-Si distances and Si-Si-Si angles around the central core units, which are only observed for polysilane dendrimers with exclusively three-fold branches (core = T [3][4][5][6][7][8][9] ). As mentioned before, the strain in these molecules is released by an extreme flattening of the Si-Si-Si angles (core-spacer-branch ~130°) emanating from the central T [3][4][5][6][7][8][9] core and an elongation of the spacer-branch Si-Si distances (239-240 pm). Therefore, it is reasonable to assume that these drastic chemical shift changes are a result of both electronic (increased number of electropositive silicon nuclei) and steric effects (changes in the overall geometry).…”

“…Reductive coupling of mixtures of SiCl 4 and Me 3 SiCl with elemental lithium in THF (Tetrahydrofuran) gives access to 7 in yields of 60-80% [59]. Reductive coupling of mixtures of MeSiCl 3 and Me 3 SiCl with elemental lithium in THF produces 10 as the major product in ca. 60-75% yields and 11 as the byproduct in ca.…”

“…The chemistry of well-defined polysilane dendrimers dates back to 1995, when Lambert et al [18] and Suzuki et al [19] independently reported the synthesis and structure of the first polysilane 3 . Soon after the synthesis and structural characterization of further dendritic polysilanes including the first polysilane dendrimer of second generation reported by Sekiguchi et al [20], the field developed rapidly, in part driven by the belief that polysilane dendrimers have the potential of being useful as optoelectronic materials.…”

“…Interest in this class of compounds primarily arises from their unique optical, photoelectric, and other excited state dependent properties, which result from σ-conjugation along the silicon main chain [1][2][3]. Despite their promising photo-physical properties, commercial applications have been limited by the chemical and photochemical sensitivity of the silicon-silicon bond in oligo-and polysilanes.…”