Formation of separated versus contact ion pairs in alkali metal thiolates and selenolates

Abstract

The solvation and ligation tendencies of alkali metal thiolates and selenolates in relation to metal and donors were investigated by synthesizing a family of target compounds, and analysing their structural features in solution and the solid state. The target compounds were synthesized utilizing hydrogen elimination, involving treatment of the chalcogenol with either sodium or potassium hydride in the presence of various donors. The separated ions were [Na(18-crown-6)(THF)₂][SMes*] 1, (Mes* = 2,4,6-tBu₃C₆H₂), [K(18-crown-6)(THF)₂][SMes*] 3, and [K(18-crown-6)(THF)₂][SeMes*] 4, and K(dibenzo-18-crown-6)(SMes*)·THF 2, displayed potassium–sulfur contacts. Compounds 1–4 were characterized using X-ray crystallography, NMR and IR spectroscopy. Cyclic voltammetry studies were carried out on 1–3, Na(dibenzo-18-crown-6)(SMes*) 5 and K(dibenzo-18-crown-6)(STrip)· THF 6 (Trip = 2,4,6-iPr₃C₆H₂). A concentration dependent equilibrium reaction, which leads to an increase in free thiolate at higher concentrations, was observed for all complexes. NMR experiments using solutions of 5 (8.5 and 0.085 mM, THF-d₈) and trimethyl phosphate confirmed the presence of free thiolate at higher concentration.