74707-27-0Relevant academic research and scientific papers
Formation of ammonia and hydrazine from the reactions of acids with bis(dinitrogen) complexes of molybdenum. Identification and isolation of intermediates. Possible analogy with the hydrazine-forming property of nitrogenase
Baumann, John A.,Bossard, Gerald E.,George, T. Adrian,Howell, Daniel B.,Koczon, Lenore M.,Lester, Richard K.,Noddings, Colleen M.
, p. 3568 - 3578 (2008/10/08)
The reactions of anhydrous HBr and HCl with trans-[Mo(N2)2(triphos)(PR3)], where triphos = PhP(CH2CH2PPh2)2 (PR3 = PPh3 (1), PMePh2 (2)), in tetrahydrofuran (THF) solution to produce ammonia and in benzene solution to produce hydrazine and ammonia have been examined. Complex 1 reacted with HBr in THF to produce 1.5 mol of N2/mol of 1 and routinely ca. 0.72 mol of NH3/mol of 1, respectively, and MoBr3(triphos) (≥94% yield). No more than a trace of hydrazine was detected. Total nitrogen balance was increased to 100% when amounts of HBr were added periodically during the reaction. The reaction of 1 or 2 with HBr or HCl led to the rapid loss of 1 mol of N2 and the formation of a pair of isomeric hydrazido(2-) complexes, [MoX(NNH2)(triphos)(PR3)]X (PR3 = PPh3 for 1A(X) and 1B(X), PPh2Me for 2A(X) and 2B(X); X = Br, Cl). The same mixtures were formed in the absence of solvent. The presence of two isomers was the result of the position of the phenyl group on the central phosphorus atom of the triphos ligand relative to the hydrazido(2-) ligand. Monitoring the ammonia-forming reactions by 31P[1H] NMR spectroscopy showed the rapid loss of PPh3 from the B series of hydrazido(2-) complexes. Addition of excess PMe2Ph to a 1A-1B mixture led to the rapid replacement of PPh3 in 1B(Br) by PMe2Ph to form [MoBr(NNH2)-(triphos)(PMe2Ph)]Br, 3B(Br). Addition of excess PMe2Ph to a mixture of 1A(Cl) and 1B(Cl) in toluene led to the isolation and characterization of 1A(Cl) and 3B(Cl). From the reaction of a 1A(Br)-1B(Br) mixture with HBr in benzene, a novel molybdenum(III) complex was isolated, MoBr4(Ph2PCH2CH2PPhCH 2CH2PHPh2), in which triphos was behaving as a bidentate ligand and the pendant phosphorus atom was protonated. If water was added to an ammonia-forming reaction in THF after PPh3 had been lost from 1B(Br) (or 1B(Cl)), ca. 1 h, significant quantities of hydrazine were detected. The yield of hydrazine decreased as the reaction was allowed to proceed longer before hydrolysis until eventually (> 12 h) no more than a trace of hydrazine was detected. It was shown that free hydrazine was not present before hydrolysis. It is proposed that following the loss of PPh3 from the B hydrazido(2-) complex an intermediate was formed that upon hydrolysis produced hydrazine. The behavior of this intermediate appeared analogous to that of nitrogenase during nitrogen fixation. The relationship between the chemistry of 1 and nitrogenase is discussed.
