REACTION OF 3-COORDINATE PHOSPHORUS-COMPOUNDS WITH ORGANOPHOSPHORUS PSEUDOHALOGENS .3. PHOSPHONIUM AND PHOSPHORANE INTERMEDIATES IN THE DESULFURIZATION AND DEOXYGENATION OF BIS(PHOSPHINOYL) DISULFIDES - INFLUENCE OF LEWIS-ACIDS ON THE REACTION CHEMOSELECTIVITY

The reactions of bis(phosphinoyl) disulfides RR(1)P(O)S-S-P(O)RR(1) 1 with P-III compounds have been investigated and various mechanistic fe atures have been elucidated by variable-temperature P-31 NMR spectrosc opy. These studies show that in most cases phosphonium intermediates [ drop P(O)-S-P(+)drop(-)O-P(S)drop] 5 and [drop P(S)-O-P(+)drop(-)O-P(S )drop] 6 are involved. In cases where ligands on P-III increase the st ability of the five-coordinate structures phosphorane intermediates ar e observed. In the isomerization 5 --> 6, the mode of decomposition (d esulfurization, deoxygenation or dealkylation) to give stable end prod ucts is influenced by electronic and steric factors. The presence of t he Lewis acid BF3 influences considerably the stability of the transie nt species 5 and 6 and the chemoselectivity of the reaction.