Synthesis and Properties of a Strained Germacycle Having a Ge−Ge Bond, 3,4-Benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene

A new strained germacycle, 3,4-benzo-1,1,2,2-tetraethyl-1,2-digermacyclobut-3-ene (1), was prepared by treatment of 1,2-bis(chlorodiethylgermyl)benzene with sodium in toluene. At ambient temperature, 1 was gradually oxidized in air to give 3,4-benzo-1,3-digerma-2-oxacyclopent-4-ene (2), and in the presence of sulfur, 1 was converted to 3,4-benzo-1,3-digerma-2-thiacyclopent-4-ene (3), quantitatively under similar thermal conditions. The digermacyclobutene 1 was thermally labile and readily underwent ring-opening polymerization in toluene to give the corresponding polymer 4 (M n = 4.4 × 105, M w = 7.4 × 105, M w/M n = 1.7). On thermolysis at 160 °C for 20 h, 1 gave two products, 4,5-benzo-1,2,3-trigermacyclopent-4-ene (5) and 3,4:6,7-dibenzo-1,2,5-trigermacyclohepta-3,6-diene (6), in reasonable yields. On the other hand, the thermolysis of 1 in the presence of phenylacetylene gave 2,3-benzo-1,4-digerma-5-phenyl-cyclohexa-2,5-diene (7), quantitatively. Further, 1 was thermolyzed in CCl4 to give two chlorinated products, 1,2-bis(chlorodiethylgermyl)benzene (9) and 1-(chlorodiethylgermyl)-2-(diethyl(trichloromethyl)germyl)benzene (10), in reasonable yields. The reaction mechanisms for the polymerization and the thermolysis are discussed.