The critical re-evaluation of the aromatic/antiaromatic nature of Ti3(CO)3: a missed opportunity?

The nature of bonding and aromaticity of Ti(3)(CO)(3), a mill-shaped metal-carbonyl complex, is studied carefully. A unique bonding mechanism between metal and carbonyl groups is found in this species. Ti(3)(CO)(3) is an example of a metal-carbonyl complex with prominent metal to carbonyl donation. Moreover, it is proven that not only is Ti(3)(CO)(3) not an antiaromatic complex but also it is the first synthesized example of d-block, σ+π aromatic species. A quick survey among the first row of transition metals in the periodic table shows that other local minima with similar structures and aromaticity are present and Ti(3)(CO)(3) is the first synthesized species of an unknown family.