The addition reactions of tetramesitylgermasilene with methyl vinyl ke
tone (MVK), crotonaldehyde, and acrylonitrile were studied. When tetra
mesitylgermasilene was allowed to react with MVK, [2 + 4] cycloadditio
n and nonregioselective carbonyl [2 + 2] cycloaddition products were i
solated. When tetramesitylgermasilene was allowed to react with croton
aldehyde, the carbonyl [2 + 2] adduct was produced exclusively. The re
giochemistry was not determined. The addition of acrylonitrile to tetr
amesitylgermasilene yielded a germasilacyclobutane, which is the forma
l [2 + 2] cycloadduct between the germasilene and the C-C double bond
of acrylonitrile. Tetramesityldisilene was also found to yield a forma
l [2 + 2] adduct with acrylonitrile. However, tetramesityldigermene re
arranges to a germylgermylene at a faster rate than acrylonitrile addi
tion.