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, 0, 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.