Chemie der schweren Carben-Analogen R2M, M=Si, Ge, Sn XIII. Reaktionen von thermisch und photolytisch erzeugtem Dimethylgermylen mit Alkinyl, Propargyl- und Allenyl- halogeniden, sowie Aktivierungsparameter der Germylenbildung

Article abstract of DOI:10.1016/0022-328X(89)85019-3

Free Me2Ge (1) inserts efficiently into C-Cl and C-Br bonds of alkynyl halides (3) and propargyl halides (6) under thermal or under photolytica conditions and prefers a concerted mechanism.In addition to the expected propargyl germyl derivatives (7), the rearranged allenyl derivatives (8) are also found.With other propargyl halides (9), the rearranged products 1-(halogenodimethylgermyl)allenes (10) are formed almost exclusively.Allenyl bromides (12) quantitatively yield the expected insertion products, 1-(bromodimethylgermyl)allenes (13).The mechanisms are discussed.The rates of all the thermal reactions equivalent to the spontaneous first order decay of the Me2Ge precursor, 7-dimethylgerma-2,3-benzonorbornadiene (2).E_A of the thermolysis is 28.1+/-1.0, ΔH^<*>=27.4+/-1.0, ΔG^<*>=26.7+/-1.6 kcal/mol, ΔS^<*>=6.1+/-1.6 e.u. (58-80 degC, 0.05-0.21 M solutions), in benzene or in Ph2O.Addition of excess CCl4, CCl3Br, and tBuCCCN, all of which react rapidly with 1, have no influence on these values.The intermediate adduct of 1 to alkyne, V12., the germirene (15), was not detected; 1,4-digermacyclohexadiene (16) is the first, and only product to be observed.