Thorium(IV) and Uranium(IV) Thioether and Selenoether Complexes: Synthesis and An–ER2 (E = S, Se) Bonding Comparison

Reactions of the rigid thioether- and selenoether-containing ligand salts [{Li(AE₂^Ph2)}₂] (E = S or Se; AE₂^Ph2 = 4,5-bis(phenylchalcogenido)-2,7,9,9-tetramethylacridanide) with ThCl₄(dme)₂ or UCl₄ (for E = Se) afforded the actinide chalcogenoether complexes [(AE₂^Ph2)₂ThCl₂] (E = S (1), Se (2)), and [(ASe₂^Ph2)₂UCl₂] (3). X-ray crystal structures of 1-3 revealed tetravalent actinide cations complexed to two κ³-coordinated AE₂^Ph2 ligands, with Th-ER₂ and U-ER₂ distances below the sum of the covalent radii. Complexes 1-3 provide extremely rare examples of thorium-thioether, thorium-selenoether, and uranium-selenoether bonds, and 1 and 2 contain the shortest known Th-SR₂ and Th-SeR₂ distances. DFT and QTAIM calculations confirm the presence of significant An(IV)-ER₂ interactions in 1-3 and provide insight into the extent of covalency in the An-ER₂ bonds.