Anomalous One-Electron Processes in the Chemistry of Uranium Nitrogen Multiple Bonds
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posted on 2014-09-02, 00:00 authored by Kimberly
C. Mullane, Andrew J. Lewis, Haolin Yin, Patrick J. Carroll, Eric J. SchelterNovel reaction pathways
are illustrated in the synthesis of uranium(IV), uranium(V), and uranium(VI)
monoimido complexes. In contrast to the straightforward preparation
of UV(NSiMe3)[N(SiMe3)2]3 (1), the synthesis of a uranium(V)
tritylimido complex, UV(NCPh3)[N(SiMe3)2]3 (4), from UIII[N(SiMe3)2]3 and Ph3CN3 was found to proceed through multiple one-electron steps.
Whereas the oxidation of 1 with copper(II) salts produced
the uranium(VI) monoimido complexes UVI(NSiMe3)X[N(SiMe3)2]3 (X = Cl, Br),
the reaction of 4 with CuBr2 undergoes sterically
induced reduction to form the uranium(VI) monoimido complex UVI(NCPh3)Br2[N(SiMe3)2]2, demonstrating a striking difference in
reactivity based on imido substituent. The facile reduction of compounds 1 and 4 with KC8 allowed for the synthesis
of the uranium(IV) monoimido derivatives, K[UIV(NSiMe3)[N(SiMe3)2]3] (1-K) and K[UIV(NCPh3)[N(SiMe3)2]3] (4-K), respectively. In
contrast, an analogous uranium(IV) monoimido complex, K[UIV(NPhF)[N(SiMe3)PhF]], PhF = -pentafluorophenyl (6), was prepared through a loss of N(SiMe3)2PhF concomitant with one-electron oxidation of
a uranium(III) center. The uranium(IV) monoimido complexes were found
to be reactive toward electrophiles, demonstrating N–C and
N–Si single bond formation. One-electron reduction of nitrite
provided a route to the uranium(VI) oxo/imido complex, [Ph4P][UVIO(NSiMe3)[N(SiMe3)2]3]. The energetics and electrochemical processes
involved in the various oxidation reactions are discussed. Finally,
comparison of the UVI(NSiMe3)X[N(SiMe3)2]3, X = Cl, Br, complexes with the
previously reported UVIOX[N(SiMe3)2]3, X = Cl, Br, complexes suggested that the donor strength
of the trimethylsilylimido ligand is comparable to the oxo ligand.
