Analysis of the Aromaticity of Osmabicycles Analogous to the Benzimidazolium Cation

Complex OsH2Cl2(PiPr3)2 (1) reacts with 1,2-phenylenediamine in the presence of triethylamine to give OsH2(κ-N,N-o-HNC6H4NH)(PiPr3)2 (2), containing an osmabenzimidazolium core. The planarity and length equalization of the bicycle, along with the negative NICS values calculated for both rings and the aromatic MO delocalization, suggest that, as the organic counterpart, the osmabenzimidazolium moiety of 2 is aromatic. The electron π-delocalization through the bicycle has a marked influence on the chemical behavior of the metal center. Thus, in contrast to 1, complex 2 is stable in acetonitrile and reacts with [FeCp2]PF6 to give a 1:1 mixture of [OsH(κ-N,N-o-HNC6H4NH)(NCCH3)(PiPr3)2]PF6 (3) and [OsH3(κ-N,N-o-HNC6H4NH)(PiPr3)2]PF6 (4), containing bicycles that also appear to be aromatic.