Reactions of coordinated dinitrogen. 12. Identification of intermediates in the conversion of molybdenum-bound dinitrogen into ammonia and hydrazine. Factors affecting the ammonia-forming reaction

Abstract

When bis(dinitrogen) complexes of molybdenum and tungsten are treated with an excess of strong acid, with few exceptions, a complex containing the hydrazido(2-) ligand has been identified either as a product in the reaction or as an intermediate on the way to the formation of ammonia and hydrazine. In the case of those molybdenum complexes that produce ammonia, the stoichiometry of the reaction can be represented by eq 1 and 2: (1) )Mo/sup 0/(N/sub 2/)/sub 2/) ..-->../sup H/sup +// )Mo(NNH/sub 2/)) + N/sub 2/, (2) )Mo(NNH/sub 2/)) ..-->../sup H/sup +// 1/2N/sub 2/ + HN/sub 4//sup +/ + )Mo(III)), with a molybdenum(III) complex as the final molybdenum-containing product. Here the identification of two isomeric hydrazido(2-) complexes are reported upon, that are formed as a mixture in the reaction of excess HBr in tetrahydrofuran (THF) solution with trans-(Mo(N/sub 2/)/sub 2/(triphos)(PPh/sub 3/)), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/. From this mixture of hydrazido(2-) complexes ammonia and a trace of hydrazine are produced in THF solution, but in benzene or toluene solution more hydrazine than ammonia is produced. On the basis of data presented, reversible phosphine dissociation is the next recognizable step toward ammonia formation.