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(AE2Ph2)}2] (E = S or Se; AE2Ph2 = 4,5-bis(phenylchalcogenido)-2,7,9,9-tetramethylacridanide) with ThCl4(dme)2 or UCl4 (for E = Se) afforded the actinide chalcogenoether complexes [(AE2Ph2)2ThCl2] (E = S (1), Se (2)), and [(ASe2Ph2)2UCl2] (3). X-ray crystal structures of 1-3 revealed tetravalent actinide cations complexed to two κ3-coordinated AE2Ph2 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.

A Synthetic, Structural, Spectroscopic, and Computational Study of Alkali Metal-Thioether, -Selenoether, and -Telluroether Interactions.

The rigid thioether- and selenoether-containing pro-ligands, 4,5-bis(phenylsulfido)-2,7,9,9-tetramethylacridan (H[AS2Ph2] (1)) and 4,5-bis(phenylselenido)-2,7,9,9-tetramethylacridan (H[ASe2Ph2] (2)), were deprotonated with one equiv of nBuLi to afford dimeric lithium complexes [Li(AE2Ph2)]2 (E = S (3), Se (4)) or with one equiv of KCH2Ph to afford the previously reported potassium complexes [K(AS2Ph2)(dme)]x (5) and [K(ASe2Ph2)(dme)2] (6). Attempts to prepare a direct telluroether analogue of compounds 1-2 were unsuccessful. However, the bulky selenoether- and telluroether-containing pro-ligands 4,5-bis(2,4,6-triisopropylphenylselenido)-2,7,9,9-tetramethylacridan (H[ASe2Tripp2] (7)) and 4,5-bis(2,4,6-triisopropylphenyltellurido)-2,7,9,9-tetramethylacridan (H[ATe2Tripp2] (8)) were accessed via the reaction of 4,5-dibromo-2,7,9,9-tetramethylacridan with three equiv of nBuLi, followed by the addition of two equiv of the corresponding diaryl dichalcogenide and quenching with dilute HCl(aq). The new selenoether- and telluroether-containing pro-ligands were subsequently deprotonated using KCH2Ph to afford [K(AE2Tripp2)(dme)2] (E = Se (9), Te (10)). Compounds 1-10 were characterized by 1H, 13C{1H}, 77Se{1H}, 125Te{1H}, and 7Li NMR spectroscopy, where applicable, and single-crystal X-ray structures were obtained for all lithium and potassium complexes (3-6 and 9-10). DFT calculations were also performed to assess the nature of bonding between the hard group 1 cations and the soft chalcogenoethers.

Uranium(IV) Thio- and Selenoether Complexes: Syntheses, Structures, and Computational Investigation of U-ER2 Interactions.

Rigid thioether- and selenoether-containing pincer proligands H[AS2 Ph 2 ] (1) and H[ASe2 Ph 2 ] (2) were synthesized, and deprotonation provided the potassium salts [K(AS2 Ph 2 )(dme)] (3) and [K(ASe2 Ph 2 )(dme)2 ] (4). Reaction of two equivalents of 3 or 4 with [UI4 (dioxane)2 ] afforded the uranium thioether complex [(AS2 Ph 2 )2 UI2 ] (5) and the first example of a uranium-selenoether complex, [(ASe2 Ph 2 )2 UI2 ] (6). X-ray structures revealed distorted square antiprismatic geometries in which the AE2 Ph 2 ligands are κ3 -coordinated. The nature of the U-ER2 bonding in 5 and 6, as well as methyl-free analogues of 5 and 6 and a hypothetical ether analogue, was investigated computationally (including NBO, AIM, and ELF calculations) illustrating increasing covalency from O to S to Se.

Group 3 dialkyl complexes of a rigid monoanionic NNN-donor pincer ligand: synthesis, structures, unexpected reactivity with CPh3+, and hydroamination catalysis.

Palladium-catalyzed coupling of 4,5-dibromo-2,7,9,9-tetramethylacridan with two equivalents of 1,3-diisopropylimidazolin-2-imine afforded 4,5-bis(1,3-diisopropylimidazolin-2-imino)-2,7,9,9-tetramethylacridan, H[AII2]. Reaction of the H[AII2] pro-ligand with one equivalent of [M(CH2SiMe3)3(THF)2] (M = Y or Sc) yielded the base-free neutral dialkyl complexes [(AII2)M(CH2SiMe3)2] {M = Y (1) and Sc (2)}. The rigid AII2 pincer ligand affords a similar steric profile to the previously reported XA2 pincer ligand, but is monoanionic rather than dianionic. Reaction of 1 with one equiv. of [CPh3][B(C6F5)4] in C6D5Br generated a highly active catalyst for intramolecular alkene hydroamination. However, rather than forming the expected monoalkyl cation, this reaction afforded a diamagnetic product which was identified as [(AII2-CH2SiMe3)Y(CH2SiMe3)2][B(C6F5)4] (3; AII2-CH2SiMe3 is a neutral tridentate ligand with a central amine donor flanked by imidazolin-2-imine groups) in approx. 20% yield, accompanied by HCPh3 (∼2 equiv. relative to 3), an unidentified paramagnetic product (detected by EPR spectroscopy), and a small amount of colourless precipitate. The unexpected reactivity of 1 with CPh3+ is thought to involve initial AII2 ligand backbone oxidation, given that the zwitterionic form of the ligand contains a phenylene ring with two adjacent anionic nitrogen donors, similar to a redox-non-innocent, dianionic ortho-phenylenediamido ligand.