Polysilane first generation

Independently of each other, Lambert et al. [69] and Suzuki et al. [70] both gained access to low-generation silane dendrimers (Gl, G2) in 1995. The latter prepared a first-generation polysilane dendrimer 3 by a stepped growth polymerisation technique. Coupling of methyl[tris(chlorodimethylsilyl)]silane (1) to tris-(trimethylsilyl)silyllithiurn (2) led to the first-generation branched dendrimer 3 (Fig. 4.38). 

Fig. 4.38 Preparation of a first-generation polysilane dendrimers (according to Suzuki et al.)...

Summary Functional first generation dendrimers were synthesized starting from methyltrichlorosilane. Successive treatment with the lithium derivatives of dimethyl-phenylsilane and methyldiphenylsilane and conversion of the phenyl groups into bromides gave a stepwise construction of a branched polysilane. 

Reaction of compound 4 with dimethylphenylsilyllithium leads to the first generation polysilane dendrimer 6, which has been synthesized already by Sakurai et al [lb]. Again, treatment with HBr under the described conditions gives hexabromide 7, also in a clean reaction as a crystalline compound. Reaction of 7 with lithium aluminum hydride finally gives hydrosilane 8. 

Scheme 1. Synthesis of first generation dendritic polysilanes.

Lambert JB, Pflug JL, Denari JM (1996) First-generation dendritic polysilanes. 

Nanjo M, Sunaga T, Sekiguchi A, Horn E (1999) Crystal stmctures of the first generation of phenyl-substimted and permethyl-substituted dendritic polysilanes. Inorg Chem Commun 2 203... 

Doubtless, in these reactions unstable intermediate silylmercury compounds such as [H2(CH3)Si]2Hg and [H(CH3)2Si]2Hg are first produced which then undergo decomposition. The formation of the trisilane and higher polysilanes from the reaction of (CH3)2SiHBr with Na/Hg may be rationalized by the insertion into [H(CH3)2Si]2Hg of dimethylsilylene, (CH3)2Si , which is probably produced during the reaction through decomposition of an unstable intermediate species (CH3)2SiHg, followed by decomposition of the adducts. The generation of dimethylsilylene and its insertion into the... 

Photochemical behavior of monosilanes has been investigated by mercury-sensitized photolysis (15-19), flash photolysis (20, 21), vacuum ultraviolet photolysis (22-27), and matrix photolysis (28-30). The first examples of the photolysis of permethylated polysilanes were published in 1970 (14). All of the cyclic and acyclic permethylpolysilanes with the exception of hexamethyldisilane readily undergo photolysis on irradiation with ultraviolet light to give shorter chain compounds with the concurrent generation of the divalent silicon intermediate, dimethylsilylene (8). 

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