s-Block metallabenzene: aromaticity and hydrogen adsorption

Second group metal dimers can replace the carbon atom in benzene to form metallabenzene (C(5)H(6)M(2)) compounds. These complexes possess some aromatic character and promising hydrogen adsorption properties. In this study, we investigated the aromatic character of these compounds using aromaticity indices and molecular orbital analysis. To determine the nature of interactions between hydrogen and the metallic center, variation-perturbational decomposition of interaction energy was applied together with ETS-NOCV analysis. The results obtained suggest that the aromatic character comes from three π orbitals located mainly on the C(5)H(5) (−) fragment. The high hydrogen adsorption energy (up to 6.5 kcal mol(−1)) results from two types of interaction. In C(5)H(6)Be(2), adsorption is controlled by interactions between the empty metal orbital and the σ orbital of the hydrogen molecule (Kubas interaction) together with corresponding back-donation interactions. Other C(5)H(6)M(2) compounds adsorb H(2) due to Kubas interactions enhanced by H(2)–π interactions. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00894-014-2552-6) contains supplementary material, which is available to authorized users.