Adaptive aromaticity in osmapentalene and osmapyridinium complexes with carbone ligands

Discovery of species with adaptive aromaticity, being aromatic in both the lowest-lying singlet and triplet states (S-0 and T-1), is a significant challenge because cyclic conjugated complexes are commonly aromatic in one state only according to Huckel's and Baird's rules. On other hand, the carbone ligands containing two lone pair electrons at the carbon(0) atom have attracted considerable attention from both theoretical and experimental chemists recently. Here, we carry out density functional theory (DFT) calculations on osmapentalene and osmapyridinium complexes with carbone ligands to examine their aromaticity in both the S-0 and T-1 states. It is found that these complexes can possess adaptive aromaticity, supported by various aromaticity indices including the harmonic oscillator model of aromaticity (HOMA), nucleus-independent chemical shift (NICS), anisotropy of the induced current density (ACID), electron density of delocalized bonds (EDDB), and the change of heat of hydrogenation ( increment increment H). Our findings expand the scope of the concept of adaptive aromaticity, inviting experimental chemists' verification to enrich aromatic organometallic chemistry.

Automated summary

This study used density functional theory (DFT) calculations to discover that osmapentalene and osmapyridinium complexes can exhibit adaptive aromaticity in both the S-0 and T-1 states, supported by various aromaticity indices. This finding expands the concept of adaptive aromaticity and invites experimental chemists to verify and enrich the field of aromatic organometallic chemistry.