Synthesis, Characterization, and Interconversion of β‐Diketiminato Nickel N_xH_y Complexes

Abstract

The β-diketiminato nickel(II) hydrazido(-1) complex [L tBu Ni(η 2 -N 2 H 3 )], (IV) was investigated with respect to its deprotonation/protonation behavior. Deprotonation with KOtBu led to [L tBu Ni(μ,η 2 :η 2 -N 2 H 2 )K(solv)] (1), and this process was proven to be reversible. Spectroscopic and DFT studies revealed an electronic structure intermediate between nickel(II) hydrazido(-2) and nickel (0) diazene. On the [a]

Late Metal Scaffolds that Activate Both, Dinitrogen and Reduced Dinitrogen Species NxHy

“…Reaction of the hydrazido complex 53 with the strong base potassium tert-butoxide in the presence of 18-crown-6 (18-c-6) afforded a nickel(II) complex side-on bound diazene ligand trans- [L tBu Ni(η 2 -N 2 H 2 )K(18-c-6)] (52). [172] The trans N 2 H 2 ligand reveals a NN bond length of 1.351(3) Å and lies in the range between a single and a double bond. Based on structural and spectroscopic data, and the results of DFT calculations, the "diazene" can be described best as N 2 H 2 2-with partial double bond char- (54), binding a neutral hydrazine ligand, which was characterized by crystal diffraction analysis and spectroscopic methods.…”

“…[168] Interestingly, the same β-diketiminato nickel scaffold also accommodates a variety of other nitrogenous ligands relevant to NH 3 generation, including side-on bonded N 2 H 2 , N 2 H 3 -, N 2 H 4 , and NH 3 ligands (Scheme 13). [171,172] The reaction of a nickel(II) bromide precursor with an excess of hydrazine resulted in the formation of the mononuclear hydrazido(1-) complex [L tBu Ni(η 2 -N 2 H 3 )] (53) and the concomitant precipitation of hydrazinium bromide (N 2 H 5 Br). [171] The same complex can be obtained when the doubly reduced dinitrogen complex 51 is treated with an excess of hydrazine.…”

“…Again, the interconversion between the nickel hydrazine complex and the nickel hydrazido(1-) species by acid-base reaction was shown to be reversible. [172] Solutions of 53 decompose at elevated temperatures yielding the ammine complex [L tBu Ni(NH 3 )] (55), as a result of hydrazine disproportionation. Remarkably, the ammine ligand can be exchanged by dinitrogen: Exposure of 55 to an excess of KC 8 (51), as indicated by means of 1 H NMR spectroscopy.…”

Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

“…To the best of our knowledge, there is only one example of a nickel complex featuring a coordinated N2H2 unit, bound side-on to a single Ni center. 52 A Cu I 2(trans-N2H2) species related to 5 has also been described. 53 With the aim of regenerating the dinitrogen complex 1 with 2,4,6-tri-tert-butylphenoxyl radical, attempts to further oxidize 5 did not prove fruitful.…”

“…Free diazene bears an N-N bond length of 1.252(2) Å,54 and hence compound 5 is best described with an intact N-N double bond (HN=NH). By contrast, the aforementioned other example of a Ni-N2H2 species features an elongated N-N bond length of 1.351(3) Å and is described as an HN-NH 2ligand 52. In the absence of a radical H-atom abstractor, the hydrazine complex 4 slowly undergoes disproportionation in THF at 25 ºC to yield the ammonia adduct 2 and diazene-bridged 5 in a 2:1 molar ratio (Eq.…”