Preparation, crystal structure and mechanism of formation of a novel dinuclear carbopentazane complex, [Rh2(PPh3)4{(NH2NH)2CH2}][NO3]2

The reaction of Rh(NO3)3·2H2O with PPh3 and N2H4·H2O in MeOH gave the dinuclear carbopentazane complex [[graphic omitted]H)2CH2}]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)A 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 NH2NCH2 ligand co-ordinated to RhI, and unambiguous multinuclear NMR (13C, 15N and 31P) and mass spectrometric evidence has been obtained for the monomeric complex [[graphic omitted]HNH2)]+, which readily rearranges to form 1. Related experiments have also provided evidence for the formation of [[graphic omitted]HNH2)]+, which also rearranges to give a dinuclear complex, [[graphic omitted]H)2CHMe}]2+.