DOI: 10.1002/chem.201201558 Conversions of Osmabenzyne and Isoosmabenzene Qianyi Zhao, Jun Zhu, Zi-Ao Huang, Xiao-Yu Cao,* and Haiping Xia* [a] Introduction Metalla-aromatics [1] are derived from the replacement of a (hydro)carbon unit in aromatic hydrocarbons with a metal fragment. Considerable effort has been devoted to the study of metallabenzenes I, and these metal-containing analogues of benzene (I’) have been found to be isolable, stable, and aromatic. [2] Synthetic methods and the reactivity of metalla- benzenes have now been established, [3–5] including some re- actions that directly relate to classic benzene chemistry. [6–8] The isolation of stable metallabenzynes II [9] and isometal- labenzenes III [10] challenged the usual notions of highly strained rings. In comparison, benzyne (II’) [11, 12] and isoben- zene (III’) [13] are too reactive and short-lived to be isolated. Among the reactions of metallabenzynes, [9e–h] the intercon- version of metallabenzyne and metallabenzene is particular- ly interesting [9g, 14] because it resembles the mutual transfor- mation of benzyne and benzene. On the other hand, isomet- ACHTUNGTRENNUNGallabenzenes remain rare, [10] thus restricting the in-depth studies of their chemistry. Herein, we show for the first time that isometallabenzene can transform into metallabenzyne, and metallabenzyne can undergo nucleophilic addition reac- tions to “restore” isometallabenzenes, or to go further and open the metallacycle. Results and Discussion Conversion of isoosmabenzene to osmabenzyne : Treatment of the osmium hydride vinylidene 1 with HC CCHACHTUNGTRENNUNG(OEt) 2 in chloroform produced osmabenzyne 3 through a formal [3+3] cycloaddition reaction [10a] via the key intermediate iso- osmabenzene 2 (Scheme 1). The reaction took 8 h to com- plete at room temperature (RT; Scheme 1, reaction condi- tions i), or 2 h if heated at reflux. The structure of osmabenzyne 3 in the solid state has been verified by X-ray diffraction. As shown in Figure 1, the six-membered metallacycle in 3 is essentially planar. The maximum deviation from the least-squares plane through Os1 and C1–C5 is 0.028  for C5. The Os1-C1-C2 angle is Keywords: isoosmabenzene · met- allacycles · nucleophilic addition · osmabenzyne · osmium Abstract: We report herein the first example of the conversion of metallabenzyne II and isometallabenzene III. The osmium hydride vinylidene complex 1 reacts with HC CCHACHTUNGTRENNUNG(OEt) 2 to give osmabenzyne 3 via isoosmabenzene 2. Compound 3 exhibits high thermal stability in air. Nonetheless, nucleophilic attack at 3 provides isoosmabenzenes 4a and 4b, or opens the ring to produce 5a and 5b. We propose mechanisms to disclose the intrinsic connection between the six-membered metal- lacycles, and carry out DFT calculations to rationalize the regioselectivity of the nucleophilic addition reactions. [a] Q. Zhao, J. Zhu, Z.-A. Huang, Dr. X.-Y. Cao, Prof.Dr. H. Xia State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical Engineering Xiamen University, Xiamen, 361005 (P.R. China) Fax: (+ 86) 592-2186628 E-mail : xcao@xmu.edu.cn hpxia@xmu.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201201558. Scheme 1. Preparation of osmabenzyne 3 via isoosmabenzene 2. Chem. Eur. J. 2012, 00,0–0  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& FULL PAPER