Reduction of Dithiocarbonates as a Novel Route to Dithiolene Compounds of Uranium. Crystal Structure of the First Bimetallic Dithiolene Complex of an f-Element

Abstract

Reaction of [U(COT)(BH4)2(THF)] (COT = η-C8H8) with the dithiocarbonates dddtCO and dmioCO (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate; dmio = 1,3-dithiole-2-one-4,5-dithiolate) gave the neutral dithiolene compounds [U(COT)(dithiolene)]2 in good yields (dithiolene = dddt, dmio, or 1,3-dithiole-4,5-dithiolate (mdt)). The X-ray crystal structures of [U(COT)(mdt)]2 and [U(COT)(mdt)(pyridine)2] show the interaction between the CC double bond of the mdt ligand and the uranium atom, and the 1H NMR spectra reveal the facile dithiolene ring inversion process in solution.

Monocyclooctatetraenyl(dithiolene)uranium Compounds

“…[7,15,21,35] Two signals of equal intensities corresponding to the magnetically non-equivalent methylene protons of the dddt and mdt ligands in the Lewis-base adducts [U(cot)(dithiolene)(L) 2 ] are visible at 20°C, or at lower temperature in the case of 12, as already observed for 6 and 8. [19] Coalescence of these resonances occurred upon increasing the temperature, and the fast limit spectrum was obtained for complex 12.…”

“…The crystal structure of the dinuclear compound 5 (Figure 1) has already been described in a preliminary report; [19] only the main geometrical features will be recalled for comparison with its congeners. (9); the hydrogen atoms have been omitted for clarity; the displacement ellipsoids are drawn at the 30% probability level Figure 3.…”

“…[19] Upon dissolution in pyridine, those dimeric compounds could be transformed into the mononuclear complexes [U(cot)(dithiolene)(py) 2 ] [dithiolene ϭ dddt (6), dmio (7), mdt (8)]. The crystal structure of 8 revealed a significant interaction between the dithiolene ligand and the metal centre.…”

“…The crystal structure of 8 revealed a significant interaction between the dithiolene ligand and the metal centre. [19] With the aim of understanding and controlling this interaction, we have studied the complexation of 3Ϫ5 with various Lewis bases, such as triphenylphosphine oxide (tppo) or hexamethylphosphoramide (hmpa), and chelating pyridines such as bipyridine or terpyridine.…”

“…We describe the X-ray crystal structures of the complexes, paying special attention to the interaction between the dithiolene ligand and the metal centre, and we present the 1 H NMR spectra, which reveal the dynamic behaviour of the complexes in solution, related to the facile ring-inversion process of the dithiolene ligand. [17,19] …”