Probing the Impact of Metal Centers and Ligands on the Aromaticity of Metallacyclopropene in Metallabenzofurans

ABSTRACT In recent years, there has been a growing interest in the field of adaptive aromaticity, which refers to compounds that demonstrate aromaticity in both the lowest singlet and triplet states. Our previous research focused on the aromaticity of rhenacycloprop‐2‐ene units in fused rhenabenzofurans and discovered a substantial σ‐aromatic contribution in the singlet state. To explore the variations in aromaticity with different metal centers and ligands in metallacyclopropene‐containing metallabenzofurans in both the singlet and triplet states, DFT calculations were performed. The computational analysis revealed adaptive σ‐aromaticity for most of the metallacyclopropene units in metallabenzofurans M–X (M = Re, Os + , Ir 2+ /X = F − , Cl − , Br − ), except for Ir–Cl and Ir–Br , which are σ‐aromatic only in the lowest singlet state. Further computational analysis demonstrated that variations in aromaticity followed the Re, Os + , Ir 2+ metal centers. While the impact of halide ligands F − , Cl − , Br − on aromaticity did not show a clear trend, it was observed that the presence of a π acceptor ligand PF 3 weakened the aromaticity.