Studies in nickel(IV) chemistry. Part 6. Kinetics of electron transfer from phenylhydrazine to tris‐(dimethylglyoximato) nickelate(IV) in aqueous medium

Abstract

The kinetics of electron transfer from phenylhydrazine(S) to tris-(dimethylglyoximato) nickelate(IV), Ni(dmg)i-(dmg2-= dimethylglyoximate dianion), have been studied in aqueous medium in the range of 6.21 I pH I 12.2. The kinetics exhibit a pseudo-first-order disappearance of Ni(dmg)g-when excess S is present. The pseudo-first-order rate constants hobs are almost linearly dependent on [S]o for varying concentrations of the reductant. At constant [S]O, the k,b,-pH profile is U shaped. The kob values register a decrease as the [H+] is increased in the pH range of -12.2-9.5, remain almost constant (minimum) in the range of -9-8, and then again linearly increase as [H+] is increased in the pH range of -7-6.21. Results are interpreted in terms of a probable mechanism involving outer-sphere electron transfer from the phenylhydrazine and phenylhydrazinium cation species to the unprotonated and one-protonated species of the Ni(IV) complex. The reduction rate appears to be dependent on the nature of the species (unprotonated and one-protonated) of the oxidant Ni(IV) complex. The phenylhydrazinium cation reduces the Ni(IV) complex at least one order of magnitude faster than does the neutral reductant species. The major product of the oxidation of phenylhydrazine by the Ni(IV) complex is 4-hydroxyazobenzene with a small amount of phenol.

Kinetic, Mechanistic and Spectral Investigation of Ruthenium(III) Catalysed Oxidation of Atenolol by Alkaline Diperiodatonickelate(IV) (Stopped Flow Technique)

“…The terms (1+ K 1 [Ni(IV)]) and (1+ K 2 [Ru(III)]) should be in the denominator of equation (2). But in view of low concentration of Ni(IV) and ruthenium(III) used, they approximate to unity.…”

“…Scheme 1 leads to rate low [2] as follows Rate Cat ¼ Rate Total À Rate Uncat where the right hand side represents the catalysed path.…”

“…The use of diperiodatonickelate(IV) (DPN) as an oxidant in alkaline medium is new and restricted to a few cases [1][2][3][4][5][6] due to the fact of its limited solubility and stability in aqueous medium. Reduction of nickel(IV) complexes have been received a considerable attention in order to understand, the nature of intermediate oxidation states of nickel such as nickel(III).…”

Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium

“…The kinetics of the Ni(1V)-Fe(CN)t-reaction were followed by monitoring the disappearance of the Ni(1V)l at 460 nm (€460 = 9.6 X 103M-lcm-l) in a Pye Unicam SP 1800 or Zeiss VSU 2-P ultraviolet visible spectrophotometer or in an Aminco stopped-flow assembly as described earlier [17,18]. The pH values of the solutions were measured by a Systronics 335 digital pH meter before and after the reactions, and the average (which did not differ by more than f0.01 unit from the measured values) was taken into record after allowing due corrections for the ionic strength effect [19].…”

“…Tris(dimethylglyoximato)nickelate(IV), Ni(dmg)!-(dmg2-= dimethylglyoximate dianion), is a two-electron oxidant [16][17][18]. As part of a study of electron transfer from various cyanoferrate(I1) compounds to this Ni( IV) complex, we have undertaken the Ni(IV)-Fe(CN);-reaction with a view to getting an insight into the mechanistic details involved, and the results are presented in this paper.…”