A linear, O-coordinated η1-CO2 bound to uranium

The electron-rich, six-coordinate tris-aryloxide uranium(III) complex [(((ArO)-Ar-Ad)(3)tacn)U-III] [where ((ArOH)-Ar-Ad)(3)tacn = 1,4,7-tris(3-adamantyl-5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane] reacts rapidly with CO, to yield [(((ArO)-Ar-Ad)(3)tacn)U-IV(CO2)], a complex in which the CO2 ligand is linearly coordinated to the metal through its oxygen atom (eta(1)-OCO). The latter complex has been crystallographically and spectroscopically characterized. The inequivalent O-C-O bond lengths [1.122 angstroms (Angstrom) for the O-C bond adjacent to uranium and 1.277 Angstrom for the other], considered together with magnetization data and electronic and vibrational-spectra, support the following bonding model: U-IV=O=C-.-O- H <----> U-IV-O=C-O-. In these charge-separated resonance structures, the uranium center is oxidized to uranium(IV) and the CO2 ligand reduced by one electron.