The reactivity of the iminodiphosphane C6H4(o-CN)N= PPh2-PPh2, which contains an N=P-P unit, has been investigated. Reaction with small molecules, [viz. H2O/O-2, H2O2, CH3OH, C6H4(o-CN)NH2] and elemental sulfur result in cleavage of the P-P bond to give aminophosphane-derivatised compounds. The products from these reactions have been characterized spectroscopically, including two by single-crystal X-ray diffraction. The reactivity of the iminodiphosphane towards the transition metal complexes [M(cod)Cl-2] (M = Pd or Pt) has also been investigated. In the reactions, the immodiphosphane rearranges to form the more common diphosphonylamine (P-N-P) unit which chelates to the metal centres, Three different compounds were isolated from these reactions and they have all been fully characterised by spectroscopy and single-crystal X-ray diffraction. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.