Homoleptic Tris(dithiolene) and Tetrakis(dithiolene) Complexes of Uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded
the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4]∞ (1). The red crystals of 1 are
composed of infinite zigzag chains in which Na2(μ-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties;
the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of
Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6),
only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3]·2py
(2·2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few
red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3)
were also obtained along with orange crystals of 2·2py. All the tris(dithiolene) compounds exhibit large folding of
the dddt ligand and significant interaction between the CC double bond and the metal center.