Reaction of decamethylsilicocene, (Me5C5)2Si (1), with MeSCN, 2,4-Me2C6H3OCN, Me2NCN, BrCN, and Me3SiCN is described. In all reactions, the formal oxidation state of the silicon atom changes from +2 in 1 to +4 in the products, and the hapticity of the pentamethylcyclopentadienyl ligands changes from η5 to η1. Under mild conditions (−78 °C or room temperature) 1 reacts with 2 equiv of MeSCN, 2,4-Me2C6H3OCN, and Me2NCN under C−C bond formation to the respective diazasilole derivatives 3−5. Reaction of 1 with BrCN at −78 °C affords the silyl cyanide 7; at room temperature, a mixture of the silyl cyanide 7 and of the silyl isocyanide 8 is formed. Reaction of 1 with Me3SiCN leads to the silyl cyanide 10. In the reactions described, the product formation presumably proceeds via [2 + 1] cycloaddition compounds of the azasilirene type as reactive intermediates. All products are characterized by NMR (1H, 13C, 29Si) spectroscopy, IR spectroscopy, mass spectrometry, and microanalytical data. The structures of 3, 4, and 10 were determined by X-ray crystallography.