The mechanism of formation of hydrazido(2—)- and hydrido-complexes by the reaction of dinitrogen complexes with acids in tetrahydrofuran

Abstract

The kinetics of the reactions of trans-[M(N₂)₂(Ph₂PCH₂CH₂PPh₂)₂] or trans-[M(N₂)₂(Et₂PCH₂CH₂PEt₂)₂](M = Mo or W) with acids, HX (X = Cl, Br, or HSO₄), in tetrahydrofuran, to yield the corresponding hydrazido(2–)-complexes, trans-[M(NNH₂)X(diphos)₂]⁺(diphos = bidentate diphosphine), have been investigated. The mechanism proposed involves the initial rapid formation of an adduct between HX and the substrate, and protonation of a co-ordinated dinitrogen by another molecule of acid, prior to the rate-limiting dissociation of dinitrogen. The reaction between HCl and trans-[M(N₂)₂(Ph₂PCH₂CH₂PPh₂)₂] yields the hydrido-complexes [WH(N₂)₂(Ph₂-PCH₂CH₂PPh₂)₂]⁺ and [MoH₂Cl₂(Ph₂PCH₂CH₂PPh₂)₂]. The kinetics of formation of these hydrides have also been studied and a rationalisation for their formation, rather than the hydrazido(2–)-complexes, is presented.