Synthesis of a Stable N‐Hetero ‐ Rh I ‐Metallacyclic Silanone

A novel N-hetero-Rh ^I-metallacyclic silanone 2 has been synthesized. The silanone 2, showing an extremely large dimerization energy (ΔG=+86.2 kcal mol ⁻¹), displays considerable stability and persists in solution up to 60 °C. Above 120 °C, an intramolecular C _sp3−H insertion occurs slowly over a period of two weeks leading to the bicyclic silanol 5. The exceptional stability of 2, 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 silanone 2 presents 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 complex 7 and it undergoes a cis/trans-isomerization via a particular mechanism, demonstrating that addition-elimination processes can also happen for silanones just like for their carbon analogues!.