Uranium(IV) terminal hydrosulfido and sulfido complexes: insights into the nature of the uranium–sulfur bond

Herein, we report the synthesis and characterization of a series of terminal uranium(IV) hydrosulfido and sulfido complexes, supported by the hexadentate, tacn-based ligand framework (Ad,MeArO)3tacn3− (= trianion of 1,4,7-tris(3-(1-adamantyl)-5-methyl-2-hydroxybenzyl)-1,4,7-triazacyclononane). The hydrosulfido complex [((Ad,MeArO)3tacn)U–SH] (2) is obtained from the reaction of H2S with the uranium(III) starting material [((Ad,MeArO)3tacn)U] (1) in THF. Subsequent deprotonation with potassium bis(trimethylsilyl)amide yields the mononuclear uranium(IV) sulfido species in good yields. With the aid of dibenzo-18-crown-6 and 2.2.2-cryptand, it was possible to isolate a terminal sulfido species, capped by the potassium counter ion, and a “free” terminal sulfido species with a well separated cation/anion pair. Spectroscopic and computational analyses provided insights into the nature of the uranium–sulfur bond in these complexes