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The low-temperature (<-35 °C) reduction of the trivalent uranium monoarene complex ( (Ad, Me) ArO) 3 mesU (1), with potassium spheres in the presence of a slight excess of 2. 2. 2-cryptand, affords the quantitative conversion of 1 into the uranium (II) monoarene complex K (2. 2. 2-crypt) ( ( (Ad, Me) ArO) 3 mes) U (1-K). The molecular and electronic structure of 1-K was established experimentally by single-crystal X-ray diffraction, variable-temperature (1) H NMR and X-band EPR spectroscopy, solution-state and solid-state magnetism studies, and optical absorption spectroscopy. The electronic structure of the complex was further investigated by DFT calculations. The complete body of evidence confirms that 1-K is a uranium (II) monoarene complex with a 5f (4) electronic configuration supported by δ backbonding and that the nearly reversible, room-temperature reduction observed for 1 at -2. 495 V vs. Fc/Fc (+) is principally metal-centered.
Pierre et al. (2014) studied this question.