The reactions of 1,3,5-trimethylbiuret with dicyclohexylaminodichlorophosphine and with pyrrolidinodichlorophosphine furnished the triazaphosphinane-diones 1 and 2. Oxidation reactions of the 2-diorganoam ino-1,3,5-triorgano-1,3,5-triaza-2 λ3-phosphinane-4,6-diones 1, 2, and 4-9, as well as 2-fluoro-1,3,5-trimethyl-1,3,5-triaza-2λ3-phosphinane-4,6-dione 10 with hydrogen peroxide, elemental sulphur, phenyl azide, 1-adamantyl azide,p-nitrobenzoyl azide, tetrachloro-orthobenzoquinone, tetrabromo-orthobenzoquinone, 3,5-di-t-butyl-orthobenzoquinone, and hexafluoroacetone led to the respective oxidation products, 12-32, involving either λ4P or λ5P. In the reaction o f the P(III)C1 derivative 11 with 3-m ethyl-l,5-diphenyl-l,5- bis(trimethylsilyl)biuret the bifunctional compound 33 was produced. The new com pounds 1,2 and 12-33 were characterized via their 1H, 13C and 31P and, where appropriate, 19F NMR spectra. In the case o f the four compounds, 3 (previously described in the literature [2]), 13, 31, and 33, single crystal X-ray diffraction studies were conducted. Unusually for this type of heterocycle 3 displays a 1,4-diplanar ring conformation because o f the bulky aromatic substituents. 13 shows an envelope conformation. The hydrogen peroxide solvent molecule has crystallographic inversion symmetry, but may be disordered. In 31 the coordination geometry at phosphorus is trigonal bipyramidal. The five-membered ring shows a twist conform ation associated with the bulky trifluoromethyl groups. The exocyclic P-N bonds in 33 are unusually long.