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[AS(2) (Ph2)] (1)) and 4,5-bis(phenylselenido)-2,7,9,9-tetramethylacridan (H[ASe(2) (Ph2)] (2)), were deprotonated with one equiv of (BuLi)-Bu- n to afford dimeric lithium complexes [Li(AE(2) (Ph2))](2) (E = S (3), Se (4)) or with one equiv of KCH2Ph to afford the previously reported potassium complexes [K(AS(2) (Ph2))(dme)]( x ) (5) and [K(ASe(2) (Ph2))(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[ASe(2) (Tripp2)] (7)) and 4,5-bis(2,4,6-triisopropylphenyltellurido)-2,7,9,9-tetramethylacridan (H[ATe(2) (Tripp2)] (8)) were accessed via the reaction of 4,5-dibromo-2,7,9,9-tetramethylacridan with three equiv of (BuLi)-Bu- n , 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(AE(2) (Tripp2))(dme)(2)] (E = Se (9), Te (10)). Compounds 1-10 were characterized by H-1, C-13{H-1}, Se-77{H-1}, Te-125{H-1}, and Li-7 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. A family of rigid monoanionic pincer ligands featuring flanking neutral chalcogenoether (SR2, SeR2, TeR2) donors and a central amido donor has been used to prepare a series of lithium and potassium complexes. The complexes were characterized crystallographically, spectroscopically, and computationally and feature rare or unprecedented examples of M-ER2 interactions (M = Li or K; E = S, Se, Te), allowing for a systematic investigation of hard alkali metal cation-soft chalcogenoether interactions.