Cyclic sulphur-nitrogen compounds and phosphorus reagents. Part 2. Reactions of tetrasulphur tetranitride with (morpholino)diphenylphosphine. First observation of the ring contraction of 1,5-[(OC<inf>4</inf>H<inf>8</inf>N)Ph<inf>2</inf>PN]<inf>2</inf>S <inf>4</inf>N<inf>4</inf> to (OC<inf>4</inf>H<inf>8</inf>N)Ph<inf>2</inf>PNS<inf>3</inf>N<inf>3</inf> in solution

(Morpholino)diphenylphosphine, unlike PPh3, gives only two new compounds, (OC4H8N)Ph2PNS3N3, (1), and 1,5-[(OC4H8N)Ph2PN]2S 4N4, (2), on reacting with S4N4. The reaction temperature, solvent, and mole ratio of the reactants are critically important in their synthesis. For the first a ring contraction of compound (2) to compound (1) in solution at room temperature has been observed and evidence for the elimination of the 'NSR' group (R = phosphinimino group) obtained.