Palladium-Catalyzed Addition of Tetragermetanes to Alkynes

1,1,2,2,3,3,4,4-Octaisopropyltetragermetane (iPr2Ge)4 reacted with various alkynes in the presence of palladium complexes at 120 C to afford 1,2,3,4-tetrahydro1,2,3,4-tetragermins, (delta)^4-1,2,3-trigemolene, and 1H-germoles, depending on the kind of alkyne and the palladium complex employed. Terminal alkynes are more reactive than internal ones. Pd(dba)2-ETBP and Pd(acac)2-ETBP systems were found to serve as efficient catalysts. The mechanism of alkyne insertion reactions into the germanium-germanium bonds of (iPr2Ge)4 is discussed.