Polysilanes with various architectures

Abstract

Copolymers and homopolymers containing silicon atoms connected to three and four other silicon atoms have been prepared and characterized. We report the first evidence of dendritic polymers with silicon backbones. Copolymers made from RSiCl3 and R1R2SiCl2 resemble hybrid materials of polysilyne and polysilanes. Polymers, which contain tetrasilyl‐substituted Si atoms, [(SiMe2)4Si]n and (Si)m(Me2Si)n, have also been synthesized. These molecules appear to be the first hyperbranched polymers, which have applications based on their electronic properties. The properties of these molecules fit into the hierarchy of 1‐D to 3‐D topologies known for Si materials.

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 .…”