Thermal and photochemical reactions of phenylethynyltris-(trimethylsilyl)germane

The thermal and photochemical behavior of phenylethynyltris(trimethylsilyl)germane (1) has been reported. The thermolysis of 1 in the absence of a trapping agent in a sealed glass tube at 240 °C for 6 h gave 1,3-bis(trimethylsilyl)-1-tris(trimethylsilyl)germyl-1-germaindene (2) in 18% yield, together with phenyl(trimethylsilyl)acetylene in 60% yield. Similar thermolysis of 1 in the presence of 2,3-dimethylbutadiene afforded 3,4-dimethyl-1,1-bis(trimethylsilyl)-1-germacyclopent-3-ene (3) in 62% yield, along with phenyl(trimethylsilyl)acetylene. When 1 was irradiated with a low-pressure mercury lamp in the presence of a large excess of 2,3-dimethylbutadiene at room temperature for 10 min, compound 3 was obtained in 11% yield, in addition to 17% of phenyl(trimethylsilyl)acetylene and 31% of the starting compound 1. The photolysis of 1 in the absence of a trapping agent under the same conditions afforded phenyl(trimethylsilyl)acetylene as the sole volatile product. The DFT calculations were carried out to investigate the reaction mechanisms for the thermal reaction of 1 leading to the germaindene 2.