Conversions of Osmabenzyne and Isoosmabenzene

We report herein the first example of the conversion of metallabenzyne II and isometallabenzene III. The osmium hydride vinylidene complex 1 reacts with HCCCH(OEt)2 to give osmabenzyne 3 via isoosmabenzene 2. Compound 3 exhibits high thermal stability in air. Nonetheless, nucleophilic attack at 3 provides isoosmabenzenes 4 a and 4 b, or opens the ring to produce 5 a and 5 b. We propose mechanisms to disclose the intrinsic connection between the six‐membered metallacycles, and carry out DFT calculations to rationalize the regioselectivity of the nucleophilic addition reactions. Metallacycles under attack: The first formal interconversion of metallabenzyne and isometallabenzene is achieved. The osmabenzyne (left) is formed via an isoosmabenzene (middle) intermediate, and nucleophilic attack at osmabenzyne restores the isoosmabenzenes or provides ring‐opened products (right). The regioselectivity of nucleophilic additions is rationalized by DFT calculations.