Group 1 complexes of rigid monoanionic ENE-donor ligands (E = Se, Te): Synthesis, structure, and computational study of metal–chalcogenoether bonding

Ether donors are ubiquitous in alkali metal chemistry, with nearly 40 % of all reported group 1 complexes in the CSD containing M–OR₂ (M = Li-Cs) bonds. The favorability of these interactions is attributed to the hard-hard pairing between electropositive group 1 cations and electronegative oxygen donors; interactions which are primarily electrostatic in nature, in accordance with hard soft acid base (HSAB) principles. By contrast, alkali metal complexes featuring heavier (and softer) chalcogenoether donors are scarce, with almost all examples confined to thioethers.

Interactions between s-block metals and selenoether and telluroether ligands push the boundaries of hard-soft mismatch, and s-block–telluroether interactions have remained elusive (outside of this work). For example, the [18]aneO₄Te₂ (1,4,10,13-tetraoxa-7,16-ditelluracyclooctadecane) macrocycle failed to react with MI₂ (M = Ca or Sr), whereas analogous reactions with [18]aneO₄Se₂ afforded [MI₂([18]aneO₄Se₂)] (M = Ca and Sr). Furthermore, while the selenoether-ligated alkaline earth dications [M([18]aneO₄Se₂)(MeCN)₂][BAr^F₄]₂ (M = Mg, Ca, Sr), [Ba([18]aneO₄Se₂)(acacH)(MeCN)][BAr^F₄]₂, [Sr(H₂O)₃([18]aneO₄Se₂)]I₂ and [Mg(κ³-[18]aneO₄Se₂)(H₂O)₂(MeCN)][BAr^F₄]₂ and the group 1 selenoether complexes [M([18]ane-O₄Se₂)][B{C₆H₃(CF₃)₂-3,5}₄] (M = Na and K) have been reported, telluroether analogues are unknown.

This talk will present the synthesis of a series of rigid monoanionic thioether-, selenoether- and telluroether-containing ligands, ‘AE₂^Ar2’ (4,5-bis(arylchalcogenido)-2,7,9,9-tetramethylacridanide; E = S, Se or Te; Ar = phenyl or 2,4,6-triisopropylphenyl), and the preparation of their lithium and potassium salts. These complexes feature rare or unprecedented alkali metal–chalcogenoether linkages, including the first Li–SeR₂, Li–TeR₂ and K–TeR₂ interactions. The new compounds were characterized using a combination of multinuclear NMR spectroscopy and X-ray crystallography, and quantum chemical calculations were employed to gain insight into the nature of alkali metal–chalcogenoether bonding. The group 1 complexes were also applied towards the installation of the AE₂^Ar2 ligands onto thorium and uranium, accessing complexes bearing uncommon or unique actinide–chalcogenoether linkages.