THERMOLYSIS OF HEXAMESITYLSILADIGERMIRANE OR HEXAMESITYLCYCLOTRIGERMANE IN THE PRESENCE OF 2,3-DIMETHYLBUTADIENE OR WATER

The thermolysis of hexwnesitylsiladigermirane and hexamesitylcyclotrigermane in the presence of 2,3-dimethylbutadiene (DMB) or water has been investigated. Thermolysis of hexamesitylsiladigermirane (1) in the presence of DMB results in the formation of two major compounds: 1,1-dimesityl-3,4-dimethyl-1-germacyclopent-3-ene (3) and 1-mesityl-1-(trimesitylsilyl)-3,4-dimethyl-1-germacyclopent-3-ene (4). Compounds 3 and 4 are most probably formed by initial thermal regioselective cleavage of the siladigermirane to give tetramesitylgermasilene and dimesitylgermylene, which is immediately trapped by the diene. The germasilene does not appear to react with DMB but rather, under the reaction conditions, undergoes a 1,2-mesityl shift at a faster rate to give a silylgermylene, which is subsequently trapped by the diene. Similarly, thermolysis of hexamesitylcyclotrigermane (5) in the presence of DMB yields compounds 3 and 1-mesityl-1-(trimesitylgermyl)-3,4-dimethyl-1-germacyclopent-3-ene (6), in contrast to an earlier report. Again, the intermediate digermenere arranges to a germylgermylene, which is the species trapped, at a faster rate than reaction with DMB. Thermolysis of 1 or 5, in the presence of water, results in the formation of products clearly derived from the addition of water across the double bond of the intermediate germasilene or digermene. Unlike the addition of methanol, the addition of water across the germasilene is not completely regioselective. The synthetic utility and mechanistic implications of this reaction are discussed.