Clarification of the Reduction Behaver of Photoexcited Samarium Species and its Application to the Development of New Synthetic Processes

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It has been revealed that the irradiation with visible light enhances the reducing ability of samarium diiodide. While the reduction of organic fluorides with SmI_2 alone is difficult, irradiation with visible light causes the efficient reduction of organic fluorides to the corresponding hydrocarbons. Next we examined the application of this system to the reductive cleavage of Si-Cl bonds. After lots of effort, the reductive coupling of chlorosilanes is found to take place effectively by using samarium diiodide, samarium metal, and magnesium metal, giving the corresponding disilanes in good yields. Even in the absence of magnesium metal, the reductive dimerization of silyl chlorides proceeds to give the corresponding disilanes in relatively lower yields, whereas the presence of both samarium diiodide and samarium metal is essential. A catalytic amount of samarium diiodide is found to cause reductive coupling of organic tin chlorides and organic germyl chlorides with magnesium metal as a co-reductant efficiently even in the absence of samarium metal. The reduction system of chlorosilanes is successfully applied to the formation of polysilanes. Phenylmethyldichlorosilane is reductively polymerized to produce the polysilane with narrow and normal molecular weight distributon. The UV-visible spectra of polysilanes indicate the absorption based on the σ-conjugation of Si-Si at 340 nm, suggesthg the high purity of polysilanes synthesized by this samarium method. This finding indicates that this polymerization method is of potential for polysilnae synthesis.