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

Abstract

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)Å 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 Rh^I, 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⁺.