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

Abstract

The nature of bonding and aromaticity of Ti₃(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. Ti₃(CO)₃ is an example of a metal-carbonyl complex with prominent metal to carbonyl donation. Moreover, it is proven that not only is Ti₃(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 Ti₃(CO)₃ is the first synthesized species of an unknown family.