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

Reduction of a permethylpentalene zirconium( iv ) chloride complex [η 8 -Pn*Zr(μ-Cl) 3/2 ] 2 (μ-Cl) 2 Li·THF x with KC 8 in benzene results in activation of the aromatic solvent to yield an "inverted sandwich" complex, [η 8 -Pn*Zr] 2 (μ-η 6 :η 6 -C 6 H 6 ) ( 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. Reduction of a permethylpentalene zirconium( iv ) chloride complex [η 8 -Pn*Zr(μ-Cl) 3/2 ] 2 (μ-Cl) 2 Li·THF x with KC 8 in benzene results in activation of the aromatic solvent to yield an "inverted sandwich" complex, [η 8 -Pn*Zr] 2 (μ-η 6 :η 6 -C 6 H 6 ) ( 1 ).