A novel N-hetero-Rh-I-metallacyclic silanone2has been synthesized. The silanone2, showing an extremely large dimerization energy (Delta G=+86.2 kcal mol(-1)), displays considerable stability and persists in solution up to 60 degrees C. Above 120 degrees C, an intramolecular C-sp3-H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol5. The exceptional stability of2, related to the unusual electronic and steric effects of Rh-I-substituent, should allow for a more profound study and understanding of these new species. Furthermore, the metallacyclic silanone2presents two reactive centers (Si=O and Rh), which can be involved depending upon the nature of reagents. Of particular interest, the reaction with H(2)starts with the hydrogenation of Rh(I)center leading to the corresponding Rh-III-dihydride complex7and it undergoes acis/trans-isomerization via a particular mechanism, demonstrating that addition-elimination processes can also happen for silanones just like for their carbon analogues!