Abstract In the reaction of decamethylsilicocene ( 1) with protic substrates HX, the corresponding oxidative addition products 2–9, 11, 12, and 15 of the type (σ-Me 5C 5) 2Si(H)X are formed in good yields. Reactions of the hydrogen halides HF, HCl, and HBr with 1 lead to the silanes 2, 3 and 4, respectively. The oxo acids trifluoroacetic acid and propionic acid react with 1 to give the compounds 5 and 6, respectively. Phenol and p-methylphenol add to 1 to give the compounds 7 and 8, respectively. In the reaction of 4-methyl-catechol with 1, the oxidative addition product 9 is an intermediate; 9 decomposes with catalytic amounts of water or pyridine to give the o-phenylenedioxysilane 10a. Compound 10b is obtained from 1 and catechol. Treatment of 1 with cyclohexanone-oxime and ethanal-oxime leads to the addition products 11 and 12, respectively. The six-membered heterocycles 13 and 14 are formed in the reaction of 1 with the corresponding 1,3-diketones. Oxidative addition products are postulated as intermediates; they rearrange by Cp★ migration and SiO bond formation. The silane 15 is obtained from the reaction of 1 with p-methyl-phenylthiol. The new compounds have been characterized by NMR, IR, and mass spectrometry, and in the case of 9, 10b, and 13 by an X-ray crystal structure determination as well. The mechanism of the oxidative addition processes is discussed.