Analysis of the Aromaticity of Five-Membered Heterometallacycles Containing Os, Ru, Rh, and Ir

We study the molecular structure and aromaticity in a series of experimental and new in silico designed five-membered heterometallacycles with general formula M­(XC₃H₃)­(PH₃)₂, where M = OsH₃, OsCl₃, OsCl₂, RuCl₂, RhCl₂ or IrCl₂ and X = NH, O, S, CH^–, or CH⁺. The electron delocalization of the five-membered rings in these complexes is analyzed using the induced magnetic field, NICS, and MCI descriptors of aromaticity. Our results indicate that the five-membered rings in all complexes with X = NH, O, S, and CH^– have a low aromatic character denoted by nonintense diatropic behavior and low MCI values. Five-membered rings in complexes with X = CH⁺ are clearly paratropic and antiaromatic according to MCI values with the exception of M = OsCl₃. The reason for this exception is discussed.