Theoretical insights into the structure of the η5-(Cp∗)C+ cation

Using both ab initio and density functional theory (DFT) calculations in combination with basis sets of triple- and quadruple-ξ quality we investigate the molecular and electronic structure of the half-sandwich η5-(Cp∗)C+ cation. The results indicate that the lowest-energy rotamer is a C5-symmetric ground state singlet while the triplet state is Cs-symmetric and ∼68 kcal/mol higher in energy. A topological analysis of the theoretical electron density based on the quantum theory of atoms in molecules (QTAIM) indicates that the η5-type bonding between the apical carbon atom and Cp∗ comprises five bond paths each bearing a bond critical point of type (3,−1).