Conversion of Trivalent Uranium Anilido to Tetravalent Uranium Imido Species via Oxidative Deprotonation

Abstract

Two uranium(III) anilido complexes were synthesized, Tp* 2 U(NH-C 6 H 4 -p-terpyridine) (2-terpy) and Tp* 2 U(NH-C 6 H 4 -p-CH 3 ) (2-ptol), where Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, by protonation of Tp* 2 UBn (1-Bn; Bn = benzyl) with 4-[2,6-di(pyridin-2-yl)pyridin-4-yl]benzenamine or p-toluidine, respectively. Conversion to the respective uranium(IV) imido species was possible by oxidation and deprotonation, forming Tp* 2 U(N-C 6 H 4 -p-terpyridine) (3-terpy) and Tp* 2 U(N-C 6 H 4 -p-CH 3 ) (3-ptol). These compounds were characterized by multinuclear NMR spectroscopy, IR spectroscopy, electronic absorption spectroscopy, and X-ray crystallography.

Origin of Bond Elongation in a Uranium(IV) cis-Bis(imido) Complex

“…Treating 1 equiv of a thawing tetrahydrofuran (THF) solution of uranium­(VI) bis­(2,6-diisopropylphenyl)­imido, UI 2 (NDIPP) 2 (THF) 3 , with 3 equiv of KNTSA in cold THF, followed by stirring for 1 h and workup, furnished a dark-brown powder (eq ). Purification was achieved by dissolution of this material in diethyl ether and layering with pentane, which resulted in the precipitation of blocks of dark-red crystals. The 1 H NMR spectroscopic data clearly revealed several broadened and shifted peaks, consistent with a paramagnetic species.…”

“…The presence of imido ligands was supported by the absence of an N–H absorption by IR spectroscopy. The bonding of the NTSA moiety was also confirmed by a 70 cm –1 shift in the SiH band, as seen by IR spectroscopy, from 1929 cm –1 in KNTSA to 2003 cm –1 in this new product …”

The synthesis and versatile reducing power of low-valent uranium complexes

“…212 Recently, oxidative deprotonation of a uranium(III) anilido complex was demonstrated as a method to form uranium(IV) imidos. 213 Reaction of oxo-transfer reagents or organic azides with uranium(III) complexes containing benzyl or singly reduced bipy ligands has also led to uranium(IV) oxos and imidos (see section 3.2.3). 157,163,164,167,168 Uranium(III) precursors have even provided direct access to complexes containing more than one imido group.…”

Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex

“…[12] The main factors influencing the stability of a certain oxidation state and thus reactivity arise from differences of the actinides' electronic structure, which is strongly affected by for example organic ligands as complexation partners but also by the reaction conditions. In recent years, N donor ligands gained centre stage for stabilizing uranium over a wide range of oxidation states due to the quite flexible number of bonds they can form: They can thus be utilized as amide [12][13][14][15] or imine [16][17][18][19] functionalities, and even triple bonds as nitrides [12,[20][21][22][23] are possible. Interestingly, bonds from imino ligands to U(VI) are more covalent compared to their dioxo analogues and capable of inducing further electronic effects like the inverse trans influence (ITI), opening an opportunity to shed light on 5forbital involvement.…”