Si3C2-Rings: From a Nonconjugated Trisilacyclopentadiene to an Aromatic Trisilacyclopentadienide and Cyclic Disilenide

1,2,3-Trisitacyclopenta-1,4-diene 2, featuring three skeletal Si atoms in the five-membered ring, was synthesized by the thermolysis of the 1,2,3-trisilabicyclo[1.1.0]butane derivative 1 at 130 degrees C in the presence of hex-3-yne. Possessing the properties of nonconjugated cyclopentadiene, 2 readily underwent reduction with KC8, which was followed by treatment with LiBr to form the lithium salt of 1,2,3-trisitacyclopentadienide 3(-)center dot[Li+(thf)], from which the ketone-coordinated derivative 3(-)center dot[Li+(O=(CBu2)-Bu-t)] was prepared. Both 3(-)center dot[Li+(L)] (L = thf, O=(CBu2)-Bu-t) are classified as novel. 6 pi-electron aromatic systems based on their characteristic X-ray crystal and NMR spectral. data. Addition of 12-crown-4 to 3(-)center dot[Li+(thf)] resulted in the unexpected formation of 4(-)center dot[Li+(12-crown-4)(2)], featuring the unprecedented cyclic disilenide ion 4(-).