The synthesis, characterization, and some reactions of phosphonium thiolates and selenolates: the X-ray crystal structure of tetraphenylphosphonium 2,4,6-trimethy lbenzenethiolate

Synthetic methods for the preparation of PPh4[SAr], PPN[SAr], and PPh4 [SeAr] (Ar = aryl; PPN = bis(triphenylphos-phine)iminium) salts are described, and 1H NMR, infrared, and 77Se NMR spectroscopic characterization is given. The X-ray crystal structure of [PPh4]Smes] (mes = 2,4,6-trimefhylbenzene) was carried out: space group [Formula: see text] a = 9.946(3) Å, b = 10.100(2) Å, c = 14.874(3) Å, α = 70.19(2)°, β = 69.13(2)°, γ = 82.54(2)°, Z = 2, R = 0.100, Rw = 0.074. The structure establishes the ionic nature of this compound in the solid state, and conductance measurements in acetonitrile are consistent with 1:1 electrolyte behaviour. It is shown, however, that solutions of the thiolates are quite sensitive to hydrolysis to the thiol, and also the strong nucleophilicity of the thiolate and selenolate anions enables them to react with halocarbon solvents. The selenolate solutions are extremely sensitive to oxidation to the diselenide, which limited their study. Cyclic voltammetry on selected thiolate salts shows that impurities quickly develop even in acetonitrile solvent, but comparisons with the voltammograms of thiols and disulphides confirm the assignment of an irreversible oxidation wave at ca. −0.3 V (vs. Ag/AgNO3, 0.01 M) to the process: 2SR− → R2S2 + 2e−. The potential at which this reaction occurs is related to the degree of substitution of the phenyl ring of the SAr− ion. Keywords: phosphonium thiolates, phosphonium selenolates, tetraphenylphosphonium 2,4,6-trimefhylbenzene thiolate.