We have developed a simple, high yielding synthetic procedure for the compounds, Cp2U(=NR)2, (Cp = C5H5, R = tBu, Ph, mesityl, 2,6-iPr(C6H3), 2-tBu(C6H4)). These U(VI) complexes are the only unsubstituted bis-Cp complexes of uranium that do not undergo conproportionation by Cp ring exchange at room temperature. Despite being diamagnetic, they have very unusual NMR spectra in which the proton and carbon signals of the R groups display extraordinary chemical shifts, eg. the para resonances of a the aryl R groups are observed in the range of 1.0-0.1ppm. The unusual NMR properties are consistent with temperature independant paramagnetism (TIP) that arises from second order mixing of a low lying triplet excited state with the ground state of the molecule. A surprising low energy electronic transition is observed in the NIR spectum of the compounds. The electronic structure of these molecules that leads to these unusual properties will be discussed as will the novel synthesis of these compounds.

Cp2U(=NR)2: Simple organoactinde compounds with surprisingly complicated electronic structures

251st National Meeting (2016)

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