Oximes, nickel oxidation

There is no evidence that oxidation of [Nim(bpy)3]3+ to give a nickel(IV) species can be effected. Likewise, when one of the pyridine rings is replaced by a benzoyl oxime as in syn-2-benzoylpyridine oxime (bpoH), oxidation, using persulfate in basic solution, is limited to... 

Holm and coworkers found that thiolates, amidates and oximates were most effective at making higher nickel oxidation states accessible (25), However, the studies noted in the previous section showed that in O2 reactions of their Ni(II) complexes, amidates and thiolates were themselves readily oxidized in a manner that precludes catalysis. Oximates have been shown to support stable nickel complexes in both the Ni(III) and Ni(IV) oxidation states (26-28), They also lack the a- and P-hydrogen atoms that are most prone to oxidative abstraction by high valent metals, thereby additionally satisfying the second design criterion. 

The nickel(IV) oxime, bis(6-amino-3-methyl-4-azahexa-3-ene-2-one oxime)nickel(IV), and the nickel(III) oxime, (15-amino-3-methyl-4,7,10,13-tetraazapentadeca-3-ene-2-one oxime)nickel(III), complexes react with hydro-quinone. Proton-related equilibria for both the nickel complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the Ni(III) complex there is evidence of an inner-sphere process. The [NiL(TCCat)] complex (TCCatH2 = tetrachlorocatechol L = 2,4,4-trimethyl-1,5,9-triazacyclododec-l-ene) forms a 1 1 adduct with tetrachloro-1,2-benzoquinone. Spectroscopic evidence suggests that this compound can be described formally as a quinone adduct of a Ni(I)-semiquinone moiety arising from inner-sphere ligand oxidation. The crystallographically determined structure (11) is shown below. Several copper complexes of a vareity of semiquinones also exist in solution in equilibrium with the corresponding catechol complexes. ... 

Oxidation of organic substrates by nickel oxide has been known for more than a century. The substrate scope of the nickd oxide hydroxide oxidation method is quite broad, and includes alcohols, aldehydes, phenols, amines, and oximes. However, an extensive review covering the major part of these reactions demonstrates the requirement of stoichiometric amounts of nickel oxide hydroxide [28]. Recent findings have led to a new oxidation method utilizing catalytic amounts of nickel(II) salts and excess of bleach (5% aqueous sodium hypochlorite) under ambient... 

The preparation of s-caprolactam via the Beckman rearrangement of cyclohexanone oxime was first described by Wallach in 1900. In the I.G. Faiben process, phenol was hydrogenated to cyclohexanol, at 140°-160°C and 15 bar, with a nickel oxide/silica catalyst. The cyclohexanol was del drogenated to cyclohexanone using a zinc/iron catalyst at 400°C, and the cyclohexanone oxime was formed by reaction with hydroxylamine monosidfonate. Conversion to cyclohexanone oxime was maximized at pH 7 by neutralizing the solution with ammonia. The organic layer of cmde oxime was crystallized and then isomerized to s-caprolactam with 20% oleum at 120°C. e-Caprolactam was purified and the ammonium sulfate recovered. 

The base was being prepared by distilling a mixture of hydroxylamine hydrochloride and sodium hydroxide in methanol under reduced pressure, and a violent explosion occurred towards the end of distillation [1], probably owing to an increase in pressure above 53 mbar. It explodes when heated under atmospheric pressure [2], Traces of hydroxylamine remaining after reaction with acetonitrile to form acetamide oxime caused an explosion during evaporation of solvent. Traces can be removed by treatment with diacetyl monoxime and ammoniacal nickel sulfate, forming nickel dimethylglyoxime [3], An account of an extremely violent explosion towards the end of vacuum distillation had been published previously [4], Anhydrous hydroxylamine is usually stored at 10°C to prevent internal oxidation-reduction reactions which occur at ambient temperature [5], See other REDOX REACTIONS... 

Oxime-type ligands (9) and (10) have been found to stabilize authentic Ni111 and NiIV complexes, respectively, when the nickel(II) complexes are oxidized by K2S2Og in alkaline solution. 

Oximes have long been known to stabilize higher oxidation states of nickel.3021 Selected examples of nickel(III) and nickel(lV) complexes with oximes for which X-ray crystal data are available are shown in Table 116. 

Comparisons can be drawn between the chemistry of [Ni,v(dmg)3]2-and that of the sexidentate bis oxime imine complex [Ni,vMezL]2+, which is much better characterized from a thermodynamic point of view (45, 56). It can be optically resolved (54) and shows no indications of protonation above pH 0. The isostructural nickel(III) and nickel(II) complexes are subject to protonation and are much more labile to substitution. Protonation of the oxime-imine chromophore destabilizes the higher oxidation states. 

The oxidation of Ni(N03)2 and benzamide oxime by H202 in ethanolic solution has been reported to yield red diamagnetic needles of Ni(benzamidoximate)4, in which nickel and the ligand have been presumed to be tetra- and mono-valent respectively on the basis of IR data.79... 

Nitrile oxide 75, generated in situ from oxime 74, gives intramolecular 1,3-dipolar cycloaddition affording a mixture of inseparable oxocane 76 and oxonane 77 in a ratio of 1 1.4 (Scheme 11). Hydrogenation of these isoxazolines with Raney nickel leads to keto alcohols 78 and 79, which can be separated by chromatography <2006SL1205>. 

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