Analysis of the Aromaticity of Osmabicycles Analogous to the Benzimidazolium Cation

Complex OsH(2)Cl(2)(P(i)Pr(3))(2) (1) reacts with 1,2-phenyl-enediamine in the presence of triethylamine to give OsH(2)(kappa-N,N-o-HNC(6)H(4)NH)(P(i)Pr(3))(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 pi-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 [FeCp(2)]PF(6) to give a 1:1 mixture of [OsH(kappa-N,N-o-HNC(6)H(4)NH)(NCCH(3))(P(i)Pr(3))(2)]PF(6) (3) and [OsH(3)(kappa-N,N-o-HNC(6)H(4)NH)(P(i)Pr(3))(2)]PF(6) (4), containing bicycles that also appear to be aromatic.