Uranyl Functionalization Mediated by Redox-Active Ligands: Generation of O-C Bonds via Acylation.

A series of uranyl compounds with the redox-active iminoquinone ligand have been synthesized, and their electronic structures elucidated using multinuclear NMR, EPR, electronic absorption spectroscopies, SQUID magnetometry, and X-ray crystallography. Characterization and analysis of the iminoquinone (iq) complex, (iq)UO(OTf)THF (1-iq), the iminosemiquinone (isq) complex, (isq)UOTHF (2-isq), and the amidophenolate (ap) complex, [(ap)UOTHF][K(18-crown-6)(THF)](3-ap crown) show that reduction events are ligand-based, with the uranium center remaining in the hexavalent state. Reactivity of 2-isq with B-chlorocatecholborane or pivaloyl chloride leads to U-O bond scission and reduction of U(VI) to U(IV) concomitant with ligand oxidation along with organic byproducts. O isotopic labeling experiments along with IR spectroscopy, mass spectrometry, and multinuclear NMR spectroscopy confirm that the organic byproducts contain oxygen atoms which originate from U-O bond activation.