A Linear, O-Coordinated η 1 -CO 2 Bound to Uranium

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