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

Abstract

A series of uranyl compounds with the redoxactive 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 0 ) complex, ( dipp iq)UO 2 (OTf) 2 THF (1-iq), the iminosemiquinone (isq 1− ) complex, ( dipp isq) 2 UO 2 THF (2i s q ) , a n d t h e a m i d o p h e n o l a t e ( a p 2 − ) complex, [( dipp ap) 2 UO 2 THF][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−O uranyl bond scission and reduction of U(VI) to U(IV) concomitant with ligand oxidation along with organic byproducts. 18 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 uranyl bond activation.

The Effect of Guest Metal Ions on the Reduction Potentials of Uranium(VI) Complexes: Experimental and Theoretical Investigations

“…[21][22][23][24][25][26][27] The studies of these properties of uranium are helpful for waste managementi nn uclear reactors to prevent water and soil pollution.Uranium forms stable com-plexes with multidentate organic ligands, af act that is exploited in the detection and separation of uranium from nuclear slag, ground water,a nd seawater. [32][33][34][35][36][37][38][39] Ac onvenient method for the synthesis of U V compounds is to reduce the corresponding U VI speciese lectrochemically. [32][33][34][35][36][37][38][39] Ac onvenient method for the synthesis of U V compounds is to reduce the corresponding U VI speciese lectrochemically.…”

“…[28][29][30][31] It shows multiple oxidation states, varying from + III to + VI;h owever,i na erobic conditions the commono xidation state is + VI, which is stabilized as the uranyl dication (UO 2 2 + ). [32][33][34][35][36][37][38][39] Ac onvenient method for the synthesis of U V compounds is to reduce the corresponding U VI speciese lectrochemically. [40][41][42][43] Severalc omplexes of U V with N 2 O 2 donor salen-type Schiff bases have been prepared by this method.…”

UO22+-mediated ring contraction of pyrihexaphyrin: synthesis of a contracted expanded porphyrin-uranyl complex

“…However, the alternative formation of a ligand-based radical-U( v ) intermediate cannot be excluded. Bart, Schelter, and co-workers have recently reported the ability of redox-active iminoquinone ligands to facilitate oxo-activation and reduction of U( vi ) to U( iv ) 54. Furthermore, in the presence of a reductant and proton source, the reduction of U( vi )O 2 2+ under anaerobic conditions to yield U( vi ) and water can occur 54,55…”

Uranyl‐Bound Tetra‐Dentate Non‐Innocent Ligands: Prediction of Structure and Redox Behaviour Using Density Functional Theory

“…As a consequence, the oxidation state of the U‐atom remains (VI) and no reduction is observed at the U‐atom . In addition, uranyl compounds containing iminoquinone ligands in the coordination sphere have been reported to exhibit redox‐active character and during the course of the redox events the U‐center remains unaffected in its ‘VI’ oxidation state . Pankhurst et al .…”

“…[7] In addition, uranyl compounds containing iminoquinone ligands in the coordination sphere have been reported to exhibit redox-active character and during the course of the redox events the Ucenter remains unaffected in its 'VI' oxidation state. [24] Pankhurst et al [25] have investigated the reduction mechanism of a uranyldipyrrin complex into U(IV) with inner-sphere and outer-sphere reductants. The redox-active nature of the dipyrrin ligand was probed by DFT and experiments.…”