Dispersion Forces Drive the Formation of Uranium-Alkane Adducts

Area of Science:

• Organometallic Chemistry
• Uranium Chemistry
• Spectroscopy

Background:

• Understanding metal-ligand interactions is crucial in organometallic chemistry.
• Uranium complexes exhibit diverse bonding behaviors.
• Alkane activation and stabilization present significant challenges.

Purpose of the Study:

• To elucidate the nature of metal-tris(aryloxide) and metal-alkane interactions in a uranium complex.
• To characterize the bonding parameters and electronic structure of the uranium center.
• To determine the mechanism of alkane stabilization within the adduct.

Main Methods:

• Single-crystal cryogenic X-ray diffraction at 6 K.
• Electron paramagnetic resonance (EPR) spectroscopy.
• Correlated electronic structure calculations, including ab initio ligand field theory and angular overlap model.

Main Results:

• Unusual U-O and U-N bonding parameters suggest predominantly ionic metal-ligand bonding, deviating from typical sigma and pi overlap models.
• Dispersive interactions, supported by tert-butyl groups of the aryloxide ligand, dominate within the uranium moiety.
• The axial alkane molecule is stabilized by a guest-host effect, not direct ionic or covalent metal-alkane bonding.

Conclusions:

• The bonding in the uranium tris(aryloxide) complex is primarily ionic.
• Dispersive forces play a significant role in stabilizing the complex.
• Alkane binding is governed by non-covalent guest-host interactions.