A Linear, O-Coordinated η1-CO2 Bound to Uranium

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Science  17 Sep 2004:
Vol. 305, Issue 5691, pp. 1757-1759
DOI: 10.1126/science.1102602

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The electron-rich, six-coordinate tris-aryloxide uranium(III) complex [((AdArO)3tacn)UIII] [where (AdArOH)3tacn = 1,4,7-tris(3-adamantyl-5-tert-butyl-2-hydroxybenzyl)1,4,7-triazacyclononane] reacts rapidly with CO2 to yield [((AdArO)3tacn)UIV(CO2)], a complex in which the CO2 ligand is linearly coordinated to the metal through its oxygen atom (η1-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: UIV=O=C⚫–O ↔ UIV–OEmbedded ImageC–O. In these charge-separated resonance structures, the uranium center is oxidized to uranium(IV) and the CO2 ligand reduced by one electron.

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