Evidence for Alkane Coordination to an Electron-Rich Uranium Center

A series of five uranium−alkane complexes of the general formula [(ArO)3tacn)U(alkane)]·(cy-alkane) has been synthesized and crystallographically characterized. In all cases, X-ray diffraction studies revealed a pseudo-six-coordinate trivalent uranium core structure, [(ArO)3tacn)U], with a coordinated alkane ligand at the axial position. The average U−C bond distance to the bound alkane was determined to be 3.798 Å, which is considerably shorter than the sum of the van der Waals radii of the U atom and a CH2 or CH3 unit (3.9 Å). In all complexes, the alkane is coordinated in an η2-H,C fashion.