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

Abstract

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.

Outer-sphere electron transfer reactions of aqua(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(II) and (III).

“…A g // feature is discernable, and values of g // and g were measured at 2.031 and 2.182, respectively. Similarly, slight deviations from octahedral geometry have been seen previously for nickel(III) centres, for the family of trisbidentate chelate complexes, [Ni(LL) 3 ] 3+ , where LL is 2,2′-bipy, phen, and their derivatives (12).…”

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The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,4,8, [NiL 1 (OH 2 )] + by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn) 2 ] 3+ has been studied in aqueous perchlorate media. The reaction displays reversible secondorder behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction:

The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex.

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The oxidation of hydrogen peroxide by tris(polypyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel(III) in aqueous media

“…The tris(2,2'-bipyridine) and tris(4,4'-dimethyl-2,2'-bipyridine) complexes of osmium(I1) (17), iron(1I) (1 8), ruthenium(I1) (1 8), and nickel(I1) (19) were prepared as perchlorate salts by reported procedures. The corresponding rnetal(II1) complexes for Os, Fe, and Ru were synthesized by Pb02 oxidation in 1 M H2SO4 followed by precipitation with excess sodium perchlorate.…”

“…The corresponding rnetal(II1) complexes for Os, Fe, and Ru were synthesized by Pb02 oxidation in 1 M H2SO4 followed by precipitation with excess sodium perchlorate. The nickel(II1) complexes were prepared by electrochemical oxidation of the correspond- ing nickel(I1) salts in anhydrous acetonitrile (19,20). The reactions of ~( b~~)~~+ and ~( 4 , 4 ' -( C H~)~b p~)~~+ with H202 were studied in 0.50 M CF3S03H and in the pH range of 6.0 to 8.5.…”

Synthesis and crystal structure of an octahedral nickel(II) complex derived from pentaerythrityl tetraamine

“…The hyperfine coupling constant All (=20 G) is similar to that observed where secondary amine coordination is involved. For Ni(9-aneN3):+ (30, 3 1) All = 23.7 G and with Ni(bipy):+, the corresponding value is 18.6G (32). There appears to be little difference between primary and secondary amines on the residence time of the electron on the N-donor atom.…”