Direct Reaction of Silicon with α−ω Dichloroalkanes:  Direct Formation of Dichlorosilacyclopentane

The direct reaction of silicon with 1,4-dichlorobutane in the presence of a CuCl catalyst gives high selectivity for dichlorosilacyclopentane under some conditions. The effects of residence time, temperature, and promoters are explored, and the highest selectivity occurs at short residence time and in the presence of a Cd promoter. The reaction of silicon with methyl chloride is discussed as well. The methyl chloride reaction is usually promoted by Zn and not by Cd. The reaction of silicon with 1,3-dichloropropane and with 1,5-dichloropentane was also explored; however poor selectivity to any product occurred with these other dichloroalkanes. The origin of the selectivity for the silacyclopentane is discussed in terms of low activation energy for ring closure in the five-membered ring case. Other low activation options such as reaction of silylene intermediate with C−H vs C−Cl prevent good selectivity in the dichloropropane and dichloropentane reactions.