Germylenes as monomers for polymer synthesis

Germylenes have been utilized as monomers for polymer synthesis for the first time. The construction of a repeating unit of O—Ge—O, O—Ge—Ge—O, O—Ge—C, and C—Ge—C as well as the formation of polygermane have been achieved on the basis of new concepts of “oxidation-reduction copolymerization” and “ligand substitution polymerization.” The former involves a redox process between a germylene (reductant monomer, M_red) and an oxidant monomer (M_ox). The M_ox employed are p-benzoquinone derivatives, cyclic α,β-unsaturated ketones, and substituted acetylenes. During the copolymerization, the germylene (M_red) is oxidized and the M_ox is reduced (“oxidation-reduction copolymerization”). The reaction mechanism between germylenes and p-benzoquinone derivatives has been elucidated as copolymerization proceeding via a biradical propagating species involving a germyl radical and/or a semiquinone radical. This is, to our best knowledge, the first clear-cut evidence for a biradical mechanism in polymerization chemistry. A new type of polymerization for the synthesis of polygermanes has been established by the reaction of germanium dichloride and various alkyllithium compounds (“ligand substitution polymerization”).