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-HNC6H 4NH)(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 Ï€-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)(P iPr3)2]PF6 (3) and [OsH 3(κ-N,N-o-HNC6H4NH)(PiPr 3)2]PF6 (4), containing bicycles that also appear to be aromatic. © 2011 American Chemical Society.Financial support from the MICINN of Spain (Projects CTQ2008-00810 and Consolider Ingenio 2010CSD2007-00006) and Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón (E35) and the European Social Fund is acknowledged. M.B. thanks the Spanish MICINN/Universidad de Zaragoza for funding through the “Ramón y Cajal” Program.Peer Reviewe