Zirconium arene triple-decker sandwich complexes: synthesis, electronic structure and bonding.

Reduction of a permethylpentalene zirconium(iv) chloride complex η-Pn*Zr(μ-Cl)Li·THF with KC in benzene results in activation of the aromatic solvent to yield an "inverted sandwich" complex, η-Pn*Zr (1). The reactions in toluene, cumene, o-xylene and m-xylene also yield analogous solvent activated triple-decker sandwich complexes, which have been structurally characterised by single-crystal X-ray diffraction. Edge energies in the Zr K-edge XANES spectra are not distinguishable between 1 and formally Zr(ii) and Zr(iv) reference compounds, suggesting a broad edge structure. DFT calculations best describe the bonding in 1 as highly covalent with frontier molecular orbitals showing almost equal contributions from benzene and the Zr-permethylpentalene fragments.