Item

Abstract

Single-crystal cryogenic X-ray diffraction at 6 K, electron paramagnetic resonance spectroscopy, and correlated electronic structure calculations are combined to shed light on the nature of the metal-tris(aryloxide) and eta(2)-H, C metal-alkane interactions in the [(((ArO)-Ar-t center dot Bu)(3)tacn)U-III((me)cy-C6)]center dot((me)cy-C6) adduct. An analysis of the ligand field experienced by the uranium center using ab initio ligand field theory in combination with the angular overlap model yields rather unusual U-O-ArO and U-N-tacn bonding parameters for the metal-tris(aryloxide) interaction. These parameters are incompatible with the concept of sigma and pi metal-ligand overlap. For that reason, it is deduced that metal-ligand bonding in the [(((ArO)-Ar-t center dot Bu)(3)tacn)U-III] moiety is predominantly ionic. The bonding interaction within the [(((ArO)-Ar-t center dot Bu)(3)tacn)-U-III] moiety is shown to be dispersive in nature and essentially supported by the upper-rim Bu-t groups of the ((ArO)-Ar-t center dot Bu)(3)tacn(3)-ligand. Our findings indicate that the axial alkane molecule is held in place by the guest-host effect rather than direct metal-alkane ionic or covalent interactions.