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.配合物OsH₂Cl₂(PiPr₃)₂ (1) 与邻苯二胺在三乙胺存在下发生反应，生成OsH₂(κ-N,N-o-HNC₆H₄NH)(PiPr₃)₂ (2)，该产物含有锇苯并咪唑鎓核。该稠环的平面性与键长均等化特征，结合两个环的核独立化学位移（Nucleus-Independent Chemical Shift, NICS）负值以及芳香性分子轨道（Molecular Orbital, MO）离域现象，表明与有机对应物类似，配合物2中的锇苯并咪唑鎓单元具有芳香性。经由该稠环的π电子离域对金属中心的化学行为具有显著影响。因此，与配合物1不同，配合物2在乙腈中稳定存在，并可与[FeCp₂]PF₆反应，得到1:1比例的[OsH(κ-N,N-o-HNC₆H₄NH)(NCCH₃)(PiPr₃)₂]PF₆ (3) 与[OsH₃(κ-N,N-o-HNC₆H₄NH)(PiPr₃)₂]PF₆ (4) 的混合物，两种产物所含的稠环同样呈现芳香性。