Phosphinoselenothioic Acids and Their Salts: Synthesis, Characterization, and Reaction with Electrophiles

Phosphinoselenothioic acid ammonium salts were synthesized in good yields by reacting phosphinoselenothioic acid S-[2-(trimethylsilyl)ethyl] esters with ammonium fluorides. Phosphinoselenothioic acid alkali metal salts were obtained as 18-crown-6 ether complexes with high efficiency
by treating the esters with alkali metal fluorides and 18-crown-6 ether. The salts were stable under
air and soluble in water. The structures of the phosphinoselenothioic acid tetramethylammonium
salt and P-methylseleno-P-methylthiophosphonium triflate were determined by X-ray molecular
structure analyses. These salts exhibited monomeric structures, and the central phosphorus atoms
adopted tetrahedral structures. Alkylation of the ammonium salts selectively gave phosphinoselenothioic acid Se-alkyl esters, whereas acylation of the salts preferentially gave S-acyl products.
Protonation of the salts selectively gave the phosphinoselenothioic S-acid. The S-acid generated in
situ was reacted with α,β-unsaturated carbonyl compounds and cyclohexene oxide to give the
adducts. Molecular orbital calculations were carried out for the model compound H2P(Se)S- to
elucidate the electronic structure.