Preparation and Characterization of the First Organoactinide Polysulfide (η⁵-C₅Me₅)₂ThS₅. A Unique Example of the Twist-Boat Conformation of the MS₅ Ring

Polysulfide chelates (S_x^2-) are an emerging class of inorganic ligands whose reactions are of interest to transition-metal and main-group specialists alike. Stable derivatives have been synthesized for most of the d-block elements, and a wide range of MS_xring sizes (x = 2–7, 9) and bonding modes have been established via X-ray crystallography.² The reaction chemistry of these transition-metal derivatives is frequently complex,³ but there are a number of useful synthetic applications such as the high-yield preparations of cyclo-S₆ and -S₇ from Cp₂TiS₅ (Cp = η5-C5H5)and SXC12 (x = 1, 2).⁴ To date, polysulfido chelates have not been introduced into the coordination spheres of f elements, but this is an obvious extension for the area and an opportunity to study the effects of the larger ionic radii and higher Lewis acidities of f elements on MS_xring sizes, conformations, and reactivity patterns. We report here the synthesis, properties, and structure of the first actinide polysulfido complex, bis(pentamethylcyclo-pentadienyl)thorium pentasulfide, and provide some theoretical insight on the nature of the Th(IV)-S₅^2-interactions.