CHEMISTRY OF HEAVY CARBENE ANALOGS R2M (M = SI, GE, SN) .16. REACTIONS OF FREE DIMETHYLGERMYLENE WITH ALKYNES AND THEIR PALLADIUM CATALYSIS

Free dimethylgermylene, Me2Ge (1), reacts with alkynes RC=CR' (3) to give a multitude of four-, five-, and six-membered germaheterocycles 4-6, 8, containing one, two, or even three Ge atoms, or the acyclic 3-germapent-1-en-4-yne 7. The nature of R and R' (H, alkyl, or aryl) determines whether 1,4-digermacyclohexa-2,5-dienes 4, 1-germacyclopenta-2,4-dienes 6, or 1,2,3-trigermacyclopent-4-enes 5 are formed. Hexafluoro-2-butyne gives the corresponding 1,2-digermacyclobut-3-ene 8. The mechanisms of product formation are discussed. Germirenes 11 or, in special cases, the digermene Me2Ge=GeMe2 (10) and the cyclotrigermane (Me2Ge)3 (12) are proposed as intermediates. A number of alkynes 3 which do not form isolable products with 1 give compounds 4 or 6 when catalytic amounts of (Ph3P)4Pd are present.