Cyclic Disilylated and Digermylated Germylenes

The
preparation of triethylphosphine adducts of cyclic disilylated
or digermylated germylenes was achieved by reaction of 1,4-dipotassio-1,1,4,4-tetrakis­(trimethylsilyl)­tetramethyltetrasilane
with GeBr2·(dioxane) and PEt3. Phosphine
abstraction with B­(C6F5)3 allowed
formation of the base-free germylenes, which undergo 1,2-trimethylsilyl
shifts to the germylene atom to form the respective silagermene or
digermene, which further dimerize in [2 + 2] cycloadditions to tricyclic
compounds. The reasons responsible for the germylenes’ completely
different reactivities in comparison to the previously studied analogous
stannylenes and plumbylenes were elucidated in a theoretical study.