Electrochemical preparation of stable nickel(III) complexes with tetradentate macrocyclic ligands in aqueous solutions

The kinetics of the oxidation of a nickel(II) oxime complex by a series of iron(III) phenanthroline and bipyridine cations, Fe(LL)33+, have been investigated. The overall reaction[Formula: see text]is considered to take place via two one-electron steps, the first (rate-determining) process yielding Ni(III)(H2L)3+ being followed by very rapid oxidation to the nickel(IV) product. The second order rate constants at 25 °C in 0.50 M p-toluenesulphonic acid are: Fe(dmbpy)33+, 1.32 × 103 M−1 s−1; Fe(dmphen)33+, 3.73 × 103 M−1 s−1; Fe(bpy)33+, 3.20 × 104 M−1 s−1; Fe(mphen)33+, 6.83 × 104 M−1 s−1; Fe(phen)33+, 9.16 × 104 M−1 s−1; and Fe(cphen)33+, 5.6 × 105 M−1 s−1. The reactions are outer-sphere in character. The rate of the corresponding cross reaction of nickel(II) species with Ru(bipy)33+ (k12 = 1.1 × 106 M−1 s−1) has also been measured. Activation parameters have been incorporated in a Marcus theory correlation to yield information (k11 ~ 3 × 103 M−1 s−1) for the NiII(H2L)2+/NiIII(H2L)3+ electron exchange reaction. This value is compared with exchange parameters for NiII/NiIII tetraaza-macrocycle and other similar systems.

mentioning

confidence: 99%

The oxidation of a nickel(II) oxime complex by polypyridine iron(III) ions in acidic aqueous media. Formation of a Ni(IV) species

Macartney¹,

McAuley²

1983

“…In many instances (1)(2)(3)(4), tetraazamacrocyclic ligands have been used to stabilize this higher oxidation state of the metal and although considerable stability is shown in acetonitrile (9, only when the macrocycle is saturated are these species stable with respect to intramolecular reduction in aqueous media (2,4,(6)(7)(8). A feature of many of these studies has been the interpretation of esr spectra (1,9) where, owing to the localization of the unpaired electron in the dZ2 orbital of these low spin d7 complexes, differing g values are observed for the gll and g. parameters.…”

mentioning

confidence: 99%

Nickel(III)–tris(di-imine) complexes: a series of strong one-electron oxidants

Brodovitch¹,

Haines²,

McAuley³

1981

The complexes [Ni(III)(LL)3](ClO4)3 (LL = phen, bipy, and substituted derivatives) have been isolated as products of the electrolysis in acetonitrile of the corresponding nickel(II) species. Electron spin resonance measurements for all nickel(III) species in frozen anhydrous CH3CN and in frozen 4.0 M HClO4 solutions (77 K) show a single near symmetric line shape (g ≈ 2.10) with fine structures appearing only in the presence of mixed solvent systems. In a CH3CN/5% H2O glass (77 K) quintets in the [Formula: see text] and [Formula: see text] regions are observed [Formula: see text]consistent with Jahn–Teller distortion expected for a low-spin d7 system. Ultraviolet–visible spectra are also reported. Electrode potentials for the Ni(LL)33+/2+ couples in CH3CN (0.1 M NaClO4) lie in the range 1.51 V (Ni(4,4′-Me2bipy)33+) to 1.82 V (Ni(5-NO2-phen)33+) and the powerful oxidizing nature of these species has been confirmed in reaction with both organic and inorganic substrates.

“…The rates in the presence of trifluoroacetate, shown in Table 3, are, as expected, lower than in the presence of acid alone because of change of redox potential by ligation (15,17,18 radical by a mechanism similar to that previously proposed for coordinated bromide (17).…”

Section: Organic Productsmentioning

confidence: 71%

“…It is possible that the acid itself is merely a source of trifluoroacetate ion which is coordinating to the Ni(II1) and slowing the rate by lowering the redox potential (15,17,18). Thus the changes in spectra shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Kinetics and mechanism of the oxidation of cyclohexanone by a nickel(III) macrocyclic ligand complex in CH₃CN

Welsh¹,

Otutakowski²,

Henry³

1981

. Can. J. Chem. 59,697 (1981). CF3C02H is not due to complexation of trifluoroacetate but is a real acid inhibition term. The isotope effect, kHlkD using 2,2,6,6-tetradeuterocyclohexanone as substrate, was 3.2. The main product found in greater than 100% yield based on Ni(II1) was the non-oxidative product, 2(cyclohexen-1-yl)cyclohexanone, which must have been formed in a radical chain reaction. A mechanism involving deprotonation of one of the coordinated nitrogens followed by rearrangement to a Ni(I1) ligand rad~cal intermediate is proposed. The ligand radical extracts a hydrogen from cyclohexanone to give [Ni(II)meso- [14]ane] and a cyclohexanone radical which initiates a radical chain reaction to give the observed dimeric product. Support for the mechanism is provided by recent stud~es of the base catalyzed decomposition of Ni(II1) complexes in aqueous and non-aqueous solvents.In the presence of CF3C02Na, the Ni(II1) complex decomposes rap~dly even in the absence of cyclohexanone. This is believed to occur via trifluoroacetoxy radicals, a mechanism which has analogy in other systems. que le facteur d'inhibition dans le CF3C02H n'est pas dii a la complexation du trifluoroacetate, mais qu'il est un facteur reel d'inhibition acide. L'effet isotopique kH/kD mesurC sur la tetradeutiro-2,2,6,6 cyclohexanone est de 3,2. Le produit principal obtenu avec un rendement superieur a 100% si I'on se base sur le Ni(II1) est un produit qui ne provient pas d'une oxydation, soit la (cyclohexene-1 y1)-2 cyclohexanone, qui a dii se former au cours d'une reaction radicalaire en chaine. On propose un mecanisme qui fait intervenir la deprotonation d'un des atomes d'azote coordonnes suivie de la transposition en un intermediaire ligand radicalaire du Ni(I1). Le ligand radicalaire arrache un atome d'hydrogkne de la cyclohexanone et conduit au [Ni(II)mCsoane [l4]] et au radical cyclohexanone qui initie la reaction radicalaire en chaine conduisant aux produits dimeres. Ce mecanisme est confirme par des etudes recentes sur la decomposition catalysie par une base de complexes de Ni(II1) dans des solvants aqueux et non aqueux.En presence de CF3C02Na, le complexe de Ni(II1) se decompose rapidement mime en I'absence de cyclohexanone. On pense que cette decomposition a lieu par I'intermtdiaire de radicaux fluoroacttoxy, un mecanisme que I'on retrouve dans d'autres systemes.[Traduit par le journal]