Disilenes reductive coupling

The first disilene with an endocyclic double bond, the tetrasilacyclobutene 141b, was prepared by Kira and coworkers through reductive coupling and debromination of the oligosilanes 147 and 148 however, the yield of the pure, isolated product was merely 1.5% (equation 33)136. 

As the reaction conditions for the preparation of the masked disilenes are as harsh as those of the Wurtz-type reductive coupling reaction, the introduction of functional groups is not trivial. An elegant way to introduce at least some diversity is via the transformation of amine-functionalized polysilanes [39] to the chloro substituted derivatives. These can be converted to alkyl and aryl groups using the corresponding Grignard compounds (Fig. 9) [35]. 

The remarkable electronic behavior of these materids has stimulated considerable effort to develop selective syntheses of polysilanes with well-defined structure. Typical synthetic procedures include the Wurtz coupling of dichlorosilanes,(5-5) anionic polymerization of masked disilenes, (9-72) anionic ring-opening polymerization of strained cyclosilanes,(i5-i7) electrochemical reduction of chlorosilanes,(75-27) and transition metal catalyzed dehydrogenative coupling of phenylsilanes (eq. l).(22-55)... 

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