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 (iq0) complex, (dippiq)UO2(OTf)2THF (1-iq), the iminosemiquinone (isq1-) complex, (dippisq)2UO2THF (2-isq), and the amidophenolate (ap2-) complex, [(dippap)2UO2THF][K(18-crown-6)(THF)2]2(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-Ouranyl bond scission and reduction of U(VI) to U(IV) concomitant with ligand oxidation along with organic byproducts. 18O 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-Ouranyl bond activation.