Comparison of reactivity of phosphagermaallene Tip(t-Bu)GeCPMes* towards sulfur ylides

Phosphagermaallene 1, Tip(t-Bu)GeCPMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl), reacts with diphenylsulfoniumylide (Ph2SCH2) leading to adduct 2, through a nucleophilic attack of the negatively charged carbon atom of the ylide on the positively charged germanium atom followed by a migration of one of the phenyl groups. By contrast, dimethyloxosulfoniummethylide (Me2S(O)CH2) appears much less reactive towards 1: it preferentially undergoes an in-situ oxidation of THF leading to a γ-butyrolactone intermediate which gives a [2+2] cycloaddition by the CO group with the GeC double bond to form 3. The new compounds 2 and 3 were completely characterized by multinuclear NMR spectroscopy and by single crystal X-ray structural analysis.