Group 4 transition metal-benzene adducts: carbon ring deformation upon complexation.

Benzene is reacted with titanium, zirconium, and hafnium metal atoms, which are produced by laser-ablation. The M(C(6)H(6)), M(C(6)H(6))(2), and M(2)(C(6)H(6))(3) complexes are formed, isolated in solid argon, and identified by infrared spectroscopy using isotopic substitution of the benzene precursor. Density functional theory (DFT) calculations are used to confirm molecular assignments. Based on computed energies and the observed vibrational spectra and isotopic shifts, electronic ground states and geometries are predicted. Observed splitting of formerly degenerate modes provides the first experimental evidence for deformation of the planar carbon skeleton of benzene upon complexation with early transition metal atoms.