The role of oligomers in the synthesis of polysilanes by the Wurtz reductive coupling reaction

Size exclusion chromatography and 29Si-NMR spectroscopy have been used to investigate the evolution of low-molecular weight molecules during the synthesis of poly(methylphenylsilane) by alkali metal-mediated reductive coupling in diethyl ether, tetrahydrofuran and toluene, revealing clear evidence for the important role played by a dimer. In addition, the distinct origins of the stable cyclic oligomers that are ubiquitous side products of these reactions have been established, cyclopentamers being formed through endbiting during chain growth and cyclohexamers by a degradative backbiting reaction.