Redox Chemistry of tris(β-diketonate)cobalt(III) Complexes: A Molecular View

Abstract

Reduction of low spin S = 0 tris(β-diketonate)cobalt(III) complexes leads to an intermediate spin S = 3/2 anion. This electron rearrangement upon reduction could be the reason why a large peak potential difference between the reduction and re-oxidation peaks was observed during electrochemical analysis, using cyclic voltammetry. It is shown that experimental redox potentials obtained from the following methods, (i) polarography, (ii) cyclic voltammetry on a hanging Hg electrode, as well as (iii) cyclic voltammetry on a carbon fibre surface, related linearly to various empirical (Gordy scale group electronegativities, Hammett meta-substituent constants, pKa and the Lever electronic parameters) and density functional theory calculated (LUMO energy, adiabatic electron affinity, chemical potential, global electrophilicity index and molecular electrostatic potential on Co) reactivity parameters. Deviations from these linear trends were due to a resonance effect of aromatic substituent groups. The linear relationships obtained for complexes containing aliphatic substituent groups can be used to predict redox potential and the electrophilic reactivity of related tris(β-diketonate)cobalt(III) complexes.

Copper-2-Hydroxyphenone CVs

“…The influence of different electron donating and electron withdrawing groups on the reduction potential of structure benzophenones (1-9) and copper-2-hydroxyphenone complexes (10)(11)(12)(13)(14)(15)(16)(17)(18)(19) are shown in Figures 1 and 2, respectively. This trend is as expected and in agreement with the trends observed for the reduction of enolised 1,3-diketones [30], para-substituted nitrobenzenes [31], bis(cyclopentadienyl)mono(β-diketonato) titanium(IV) complexes [32,33], tris(β-diketonato)metal(III) complexes (metal = Co [34], Cr [35], Mn [36], and Fe [37]), and octahedral bis(β-diketonato)-titanium(IV) complexes [38]. The amount of shift to lower (due to electron-donating substituents) or higher (due to electron-withdrawing substituents) potentials, however, depends on the resonance and inductive electronic effects of the substituents [31,39].…”

A mononuclear cobalt(iii) carboxylate complex with a fully O-based coordination sphere: CoIII–O bond homolysis and controlled radical polymerisation from [Co(acac)2(O2CPh)]

“…The Δ V between the two waves is similar to that observed for [Co III (acac) 3 ] and other related Co III tris(β-diketonates), 55 for which this Δ V was attributed to a spin state change to 3/2 after reduction. 56…”

“…The ΔV between the two waves is similar to that observed for [Co III (acac) 3 ] and other related Co III tris(β-diketonates), 55 for which this ΔV was attributed to a spin state change to 3/2 after reduction. 56 A variable temperature 1 H NMR investigation in C 6 D 6 reveals a line broadening phenomenon between 25 and 80 °C, possibly consistent with a dynamic configuration inversion, e.g. via a Bailar twist.…”

Electrochemical and Theoretical Modelled Reduction of β‐Diketone Inspired Chalcones

“…[36] The applications of chalcones in galvanostatic electrosynthesis employing its reductive cyclodimerization and self-adaptability was recently reported by Garbini et al [37] β-diketones on the other hand are 1,3-substituted propan-1,3-diones. They form complexes with various metals e. g., Titanium, [38][39][40][41] iron, [42] cobalt, [43] copper, [44] manganese, [45] chromium, [46] rhodium, [47] nickel, palladium, and gold. [48] βdiketones and their metal complexes are reported widely as anticancer, [49][50][51][52][53] antimicrobial, [48,[54][55][56][57] and antimlarial agents.…”

“…β‐diketones on the other hand are 1,3‐substituted propan‐1,3‐diones. They form complexes with various metals e. g., Titanium, [38–41] iron, [42] cobalt, [43] copper, [44] manganese, [45] chromium, [46] rhodium, [47] nickel, palladium, and gold [48] . β‐diketones and their metal complexes are reported widely as anticancer, [49–53] antimicrobial, [48,54–57] and antimlarial agents [58] .…”