Sequential metalation of benzene: electronic, bonding, magnetotropic and spectroscopic properties of coinage metalated benzenes studied by DFT.

A series of coinage metalated benzenes formulated as C6H6-nMn (M = Cu, Ag, Au, n = 1-5) were investigated by means of density functional theory (DFT) calculations. The structural, energetic, magnetotropic and spectroscopic properties of the coinage metalated benzenes were analyzed thoroughly and compared to the respective properties of the archetype aromatic benzene molecule. In contrast to the latter, the C6H6-nMn (M = Cu, Ag, Au, n = 1-5) molecules are predicted to be aromatic even in their excited triplet state. Excellent linear correlations between (I) the zz component of the nucleus independent chemical shift [NICSzz(1)] values and the total negative natural charge acquired by the carbocyclic ring, and (ii) the NICSzz(1) vs wavelength (λ) of the HOMO → LUMO transitions in the absorption spectra of the coinage metalated benzenes were established. The emission spectra of the coinage metalated benzenes were characterized by high [Formula: see text] values, particularly for the di-substituted - and p-isomers, with the highest [Formula: see text] value of 67 kcal mol(-1) calculated for the m-M6H4Au2 species. The bonding pattern of the coinage metalated benzenes was analyzed thoroughly by means of a multitude of electronic structure calculation methods [natural bond orbital (NBO), atoms-in-molecules (AIM), electron localization function (ELF), reduced density gradient (RDG) and Sign(λ 2(r))ρ(r) functions]. Our findings indicate whole classes of new coinage metalated benzenes (mono-, di-, tri-, four- and five-substituted) opening a new chemistry for the coinage metalated benzenes, indicating that their chemistry will be worthwhile studying both experimentally and theoretically in the future. Graphical Abstract The complete series of coinage metalated benzenes were investigated by density functional theory methods. The structural, energetic, bonding, magnetotropic and spectroscopic properties of the coinage metalated benzenes were analyzed thoroughly. In contrast to the archetype aromatic benzene molecule, the coinage metalated benzenes are predicted to be aromatic even in their excited triplet state.