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(XC<sub>3</sub>H<sub>3</sub>)­(PH<sub>3</sub>)<sub>2</sub>, where M = OsH<sub>3</sub>, OsCl<sub>3</sub>, OsCl<sub>2</sub>, RuCl<sub>2</sub>, RhCl<sub>2</sub> or IrCl<sub>2</sub> and X = NH, O, S, CH<sup>–</sup>, or CH<sup>+</sup>. 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<sup>–</sup> have a low aromatic character denoted by nonintense diatropic behavior and low MCI values. Five-membered rings in complexes with X = CH<sup>+</sup> are clearly paratropic and antiaromatic according to MCI values with the exception of M = OsCl<sub>3</sub>. The reason for this exception is discussed.