Hydrazido(2–)-complexes as intermediates in the conversion of ligating dinitrogen into ammonia and hydrazine

Abstract

The formation of hydrazido(2–)-complex intermediates in solution during the reaction of cis-[M(N₂)₂(PMe₂Ph)₄](1)(M = Mo or W) with H₂SO₄ in tetrahydrofuran (thf) has been established by ¹⁵N n.m.r. spectroscopy and the hydrazido(2–)-complexes [M(NNH₂)(HSO₄)₂(PMe₂Ph)₃](2) isolated from these solutions. When treated with H₂SO₄ in methanol, the complexes [MX₂(NNH₂)(PMe₂Ph)₃](3), [MX(NNH₂)(PMe₂Ph)₃L]⁺(4)(X = Cl, Br, or I; L = tertiary phosphine or substituted pyridine), and [M(NNH₂)(quin)(PMe₂Ph)₃]X (5)(quin = quinolin-8-olate) give ammonia or hydrazine in varying yields depending upon the complex. Ammonia is also obtained by treating [MX₂(NNH₂)(PMe₂Ph)₃] with Na[BH₄] in thf or methanol, hydrides of the type MH_n(PMe₂Ph)₃(M = W, n= 6; M = Mo, n unknown) which did not react with dinitrogen, being the metallic products. The tungsten hydrazido-(2–)-complexes, but not those of molybdenum, also give ammonia on treatment with aqueous K[OH]. The preparation and characterisation of the new hydrazido(2–)-complexes [WBr(NNH₂)(NC₉H₇)(PMe₂Ph)₃]⁺ and [W(NNH₂)L¹(PMe₂Ph)₃]⁺(L¹= NC₅H₄CO₂-2 or NC₉H₆CO₂-2) are also described.