Studies on phosphorus-chalcogen bond systems stabilized by bulky substituents

Reactions of sterically hindered primary phosphines with elemental sulfur or selenium are reviewed. (2,4,6-Tri-t-butylphenyl) phosphine reacted with an excess amount of elemental sulfur in the presence of a catalytic amount of base to give the corresponding dithioxophosphorane via the phosphine sulfide. Dithioxophosphoranes and diselenoxophosphoranes bearing the 2,4-di-t-butyl-6-(dialkylamino)phenyl group were prepared by a similar method. These compounds are more stable than the corresponding 2,4,6-tri-t-butylphenyl derivatives. Deselection reaction of stabilized (selenoxo)(thioxo)phosphoranes and diselenoxophosphoranes afforded thioxophosphines and selenoxophosphines, respectively. On the other hand, reaction of (2,4-di-t-butyl-6-methoxyphenyl) phosphine with sulfur gave trans- and cis-1,3,2,4-dithiadiphosphetane-2,4-disulfides via dithioxophosphorane. The monomeric form of dithioxophosphorane, which can be generated from dithiadiphosphetane disulfides by heating, reacted with benzophenone to give thiobenzophenone. (2,4-Di-t-butyl-6-methoxyphenyl) phosphine reacted with selenium to give 1,2,3,5,7-pentaselena-4,6,8-triphosphocane, which was used to convert amides into thioamides.