A HOMOLEPTIC URANIUM THIOLATE - SYNTHESIS, STRUCTURE, AND FLUXIONAL BEHAVIOR OF [LI(DME)]4[U(SCH2CH2S)4] AND REACTION WITH CS2

We have synthesized and fully characterized a tetrakis(ethane-1,2-dithiolato)uranate(IV), [Li(dme)]4[U(edt)4] (1), the first homoleptic dithiolate complex of an f element. The complex crystallizes with an additional DME solvent molecule, and its structure was determined by an X-ray study. The coordination geometry about the uranium center is dodecahedral, and four lithium cations surround the [U(cdt)4]4− anion. Each lithium bridges two sulfur atoms and is further coordinated by a dme molecule. We have analyzed the nature of the U-S bonds, using the enxtended Hiickel method, to find that U 6d, 7s, and 7p orbitals are responsible for interactions with sulfur orbitals, thus, no significant U 5f participation in bonding is discernible, and that U-S π interactions are weak. The low-temperature 1H NMR spectra in THF-d8 exhibit four resonances associated with the edt protons. The relative size of their paramagnetic isotropic shifts can be interpreted on the basis of the pseudocontact (dipolar) term, the analysis of which suggests the solid-state dodecahedral structure to be retained in solution. According to the temperature dependence of the edt proton resonances, there are two fluxional processes. (1) a conformational change of the USCCS chelate rings and (2) an exchange of the A and B sites in the dodecahedral US8 frame. The free energies of activation, ΔG*, are 9.3–9.6 kcal/mol and 12.9 kcal/mol, respectively, which are rather high probably due to coordination of lithium ions to sulfurs. The complex 1 reacts with CS2 to give [Li(dine)2]2(S2CSCH2CH2SCS2) (2) as an isolable product. The crystal structure analysis of 2 reveals a zigzag form of the ethane-1,2-diyl bis(trithiocarbonate) skeleton and 1 coordination of each trithiocarbonate to a lithium. Crystal data: 1, solvated by DME. monoclinic space group P21/n with a = 11.330 (3) Å, b = 38.454 (8) Å, r = 11.047 (2) Å, β = 95.31 (2)°, Z = 4, R = 0.0538 for 3047 independent reflections; 2, monoclinic space group P21/n with a = 8.827 (3) Å, b = 15.191 (8) Å, c = 13.304 (8) Å, ß = 107.13 (4) °, Z = 2, R = 0.0503 for 1581 independent reflections. © 1990, American Chemical Society. All rights reserved.