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

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Zirconium complexes are crucial in catalysis and materials science.
• Aromatic solvent activation presents a pathway for novel complex synthesis.
• Understanding bonding in multi-decker complexes is key to their application.

Purpose of the Study:

• To synthesize and characterize novel "inverted sandwich" and triple-decker complexes.
• To investigate the role of aromatic solvents in complex formation.
• To elucidate the electronic structure and bonding in the synthesized complexes.

Main Methods:

• Reduction of a permethylpentalene zirconium(IV) chloride complex using KC8.
• Reactions in various aromatic solvents (benzene, toluene, xylenes).
• Structural characterization via single-crystal X-ray diffraction.
• Spectroscopic analysis using Zr K-edge X-ray absorption near edge structure (XANES).
• Computational analysis using Density Functional Theory (DFT).

Main Results:

• Successful synthesis of an "inverted sandwich" complex, [η8-Pn*Zr]2(μ-η6:η6-C6H6) (1), via benzene activation.
• Formation of analogous solvent-activated triple-decker sandwich complexes in toluene, cumene, and xylenes.
• XANES spectra indicated broad edge structures, making differentiation between Zr oxidation states challenging.
• DFT calculations revealed highly covalent bonding in complex 1, with significant contributions from both benzene and zirconium-permethylpentalene fragments.

Conclusions:

• Aromatic solvents can be activated to form novel organometallic complexes.
• The synthesized triple-decker complexes exhibit unique "inverted sandwich" structures.
• Bonding in these complexes is predominantly covalent, with delocalized electronic contributions.