Oxo Ligand Silylation in a Uranyl β-Ketoiminate Complex

摘要

The microbial reduction of the uranyl ion (UO2n2+) to U(IV) is anvital component of the environmental remediation of legacy wastensites.1,2 This process requires the functionalization and/ornsubstitution of the normally inert uranyl oxo ligands. However,nthere is little evidence available for the mechanism of reduction,3,4nand model systems are scarce.5,6 In one recent example, oxonligand silylation in uranyl was achieved by deprotonation ofnUO2(THF)(H2L) (L ) “Pacmac” polypyrrolic macrocycle),nultimately resulting in the formation of a U(V) silyloxidencomplex [UO(OSiMe3)(THF)Fe2I2L].7 During the reaction, annintermediate species, UO2(THF)(K2L), is both reduced and silylatednby HN{SiMe3}2 to generate the final product.8,9 The ability ofnHN{SiMe3}2 to act as a reducing agent in this system is surprising,ngiven the relatively small oxidation potential of the uranyl ionn(-0.35 V for UO2n2+(aq) vs Fc/Fc+).10 Herein we report thensynthesis and characterization of a novel uranyl(V) bis-silyloxidencomplex, namely U(OSiMe3)2I2(Aracnac), derived from the uranylnion and Me3SiI, and provide a redox-based rationale for why oxonligand silylation occurs concomitant with uranyl reduction. Me3SiXnreagents have long been employed for oxo ligand substitution inntransition metal synthesis,11 but only one example is previouslynknown for uranyl.12