Reactions of the hydrido-butenylcarbyne complex [OsHCl₂(≡CC(PPh₃)=CHEt)(PPh₃)₂]BF₄ (1) with nitriles RC≡N (R=2-cyclopropyl-2-oxopropyl, 3-amino-2-oxobutyl) lead to six-membered cyclic vinylidene complexes 3 and azavinylidene complexes 4, that is, iso-osmapyridiniums. Treatment of 1 with excess 2-formylbenzonitrile at reflux temperature in CHCl₃ in the presence of air produces a fused osmapyridinium 8, which is first oxidized to the tricyclic iso-osmapyridinium derivative 7, then to iso-osmapyridinium 9, which contains a fused naphthalenone fragment. The conversion of iso-osmapyridinium 9 (with a vinylidene segment) to the iso-osmapyridinium compounds 10 and 11 (with azavinylidene segments) was achieved in the presence of a hydrogen halide, such as HCl or HI. The molecular structures of the complexes synthesized were confirmed by X-ray studies. Moreover, the aromatic stabilization energy and nucleus-independent chemical-shift values of the osmapyridiniums and the strain in the iso-osmapyridinium rings were investigated by DFT calculations.

The transformations of metallabenzene to substituted benzenes have been achieved by reactions of osmabenzenes with silver/copper acetylides. In this investigation, novel tetraphenylphosphonium salts containing two phosphonium substituents on the same benzene ring are generated.

Invited for the cover of this issue is the group of Haiping Xia at the University of Xiamen. The image depicts their recent work on the chemistry of transition-metal-containing metallaaromatics, organometallic compounds derived from formal replacement of a (hydro)carbon segment in an organic aromatic ring by an isolobal transition-metal fragment. Read the full text of the article at 10.1002/chem.201304957.

Treatment of the osmium complex [Os{CHC-(PPh₃)CH(OH)-η²-C≡CH}(PPh₃)₂(NCS)₂] (1) with excess triethylamine produces the first m-metallaphenol complex [Os{CHC(PPh₃)CHC(OH)CH}(PPh₃)₂(NCS)₂] (2). The NMR spectroscopic and structural data as well as the nucleus-independent chemical-shift (NICS) values suggest that osmaphenol 2 has aromatic character. The reactivity studies demonstrate that 2 can react with different isocyanates to form the annulation reaction products [Os{CHC(PPh₃)CHC(OCONR)C}(PPh₃)₂(NCS)₂] (R=Ph (3), iPr (7), Bn (8)) via the carbamate intermediates [Os{CHC(PPh₃)CHC(O-CONHR)CH}(PPh₃)₂(NCS)₂] (R=Ph (4), iPr (5), Bn (6)). In addition, the similar annulation reactions can be extended to other unsaturated compounds containing N–C multiple bonds, for example, isothiocyanates, pyridine, and sodium thiocyanate, which can produce the corresponding fused osmabenzene complexes. In contrast, the reactions of 2 with common electrophiles, such as NOBF₄, NO₂BF₄, N-bromosuccinimide, and N-chlorosuccinimide only led to the decomposition of the metallaphenol ring. The experimental results suggest that 2 is very electrophilic and readily reacts with nucleophiles, which is mainly due to the metal center and the strong electron-withdrawing phosphonium group.