Preparation, crystal structure and mechanism of formation of a novel dinuclear carbopentazane complex, [Rh-2(PPh(3))(4){(NH2NH)(2)CH2}][NO3](2)

The reaction of Rh(NO3)(3) . 2H(2)O with PPh(3) and N2H4 . H2O in MeOH gave the dinuclear carbopentazane complex [Rh-2(PPh(3))(4){(NH2NH)(2)CH2}](2+) 1, which has been characterised by multinuclear NMR measurements and X-ray diffraction. It is a dipositive, dinuclear cation in which the two bis(triphenylphosphine)rhodium units are bridged by the tetradentate carbopentazane ligand. The rhodium atoms have the expected square-planar geometry, with Rh-P and Rh-N distances of 2.225(3)-2.253(3) and 2.130(6)-2.166(6) Angstrom respectively. A series of experiments, aimed at elucidating the mechanism of formation of 1, indicated that the formation of the NCH2N linkage occurs via acid-catalysed nucleophilic addition of free N2H4 to the CH2 group of an NH2N=CH2 ligand co-ordinated to Rh-1, and unambiguous multinuclear NMR (C-13,N-15 and P-31) and mass spectrometric evidence has been obtained for the monomeric complex [Rh(PPh(3))(2)(NH2NHCH2NHNH2)](+), which readily rearranges to form 1. Related experiments have also provided evidence for the formation of [Rh(PPh(3))(2)(NH(2)NHCHMeNHNH(2))](+), which also rearranges to give a dinuclear complex,[Rh-2(PPh(3))(4){(NH2NH)(2)CHMe}](2+).