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.