Organosilicon Polymers?Synthesis, Architecture, Reactivity and Applications

Polysilane Dendrimers

“…During the preparation of this manuscript we noticed that the 29 Si-NMR chemical shift of the central core silicon (T [3][4][5][6][7][8][9] ) of polysilane dendrimer 26, reported by Lambert and coworkers [24] to be at -66.1 ppm, did not match the expected chemical shift range for a tertiary silicon nucleus that has 3 silicon nuclei in β-position and 9 silicon nuclei in γ-position (T [3][4][5][6][7][8][9] ). Note that the central T [3][4][5][6][7][8][9] silicon nuclei of 25 and 56 appear at −37.1 ppm and −35.3 ppm, respectively. We independently prepared 26 by treating 3.5 equivalents of K-Si(SiMe 3 ) 2 SiMe 2 SiMe 2 Si(SiMe 3 ) 3 with one equivalent of MeSi(SiMe 2 Cl) 3 in hexane.…”

“…However, efficient synthetic methods to functionalized polysilane dendrimers of higher generation in high yields still need to be developed. [18] reported the tertiary silicon core (T [3][4][5][6][7][8][9] ) of polysilane dendrimer 25, to appear at -65.0 ppm in the 29 Si-NMR (measured in C 6 D 6 ). Suzuki et al [19], however, found the latter signal to be at -37.1 ppm (measured in CDCl 3 ).…”

“…[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).…”

“…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. To overcome this problem, architectures alternative to linear and cyclic polysilanes such as branched and hyperbranched polysilanes [4][5][6][7], network polysilanes (polysilyne) [8][9][10][11][12][13] ladder polysilanes [14], organosilicon nanoclusters [15][16][17] and also dendritic polysilanes have been proposed and investigated .…”