5489-72-5Relevant academic research and scientific papers
Oxygen-Oxygen Bond Cleavage and Formation in Co(II)-Mediated Stoichiometric O2 Reduction via the Potential Intermediacy of a Co(IV) Oxyl Radical
Nurdin, Lucie,Spasyuk, Denis M.,Fairburn, Laura,Piers, Warren E.,Maron, Laurent
supporting information, p. 16094 - 16105 (2018/11/27)
In reactions of significance to alternative energy schemes, metal catalysts are needed to overcome kinetically and thermodynamically difficult processes. Often, high-oxidation-state, high-energy metal oxo intermediates are proposed as mediators in elementary steps involving O-O bond cleavage and formation, but the mechanisms of these steps are difficult to study because of the fleeting nature of these species. Here we utilized a novel dianionic pentadentate ligand system that enabled a detailed mechanistic investigation of the protonation of a cobalt(III)-cobalt(III) peroxo dimer, a known intermediate in oxygen reduction catalysis to hydrogen peroxide. It was shown that double protonation occurs rapidly and leads to a low-energy O-O bond cleavage step that generates a Co(III) aquo complex and a highly reactive Co(IV) oxyl cation. The latter was probed computationally and experimentally implicated through chemical interception and isotope labeling experiments. In the absence of competing chemical reagents, it dimerizes and eliminates dioxygen in a step highly relevant to O-O bond formation in the oxygen evolution step in water oxidation. Thus, the study demonstrates both facile O-O bond cleavage and formation in the stoichiometric reduction of O2 to H2O with 2 equiv of Co(II) and suggests a new pathway for selective reduction of O2 to water via Co(III)-O-O-Co(III) peroxo intermediates.
Mechanistic criteria for cation radical reactions: Aminium salt-catalyzed cyclopropanation
Yueh, Wang,Bauld, Nathan L.
, p. 5671 - 5676 (2007/10/02)
Mechanistic studies of the cyclopropanation of a series of trans-stilbenes by ethyl diazoacetate catalyzed by two different triarylaminium salts decisively confirm a cation radical mechanism and rule out a hypothetical electrophilic mechanism. The elucidation of key aspects of these cation radical mechanisms, including kinetic vs equilibrium control of ionization and chain vs catalytic mechanisms, has also been achieved for these systems. New mechanistic criteria for the positive identification of cation radical mechanisms are proposed.
Organic Electron Transfer Agents, I. Electrochemical and Spectroscopical Study of Bromo-substituted Triarylamine Redox Systems
Schmidt, Werner,Steckhan, Eberhard
, p. 577 - 585 (2007/10/02)
The redox behaviour of the bromo-substituted triarylamines 2-7 has been studied by cyclic voltammetry.The oxidation potentials of the redox pair amine/cation radical strongly depend on the degree of substitution in ortho-position showing a smaller sterical influence in addition to a strong electronic effect.The second oxidation potential, cation radical/dication, is influenced by substitution to a much smaller degree.The UV/VIS spectra of the corresponding cation radicals are shifted bathochromically with increasing ortho-substitution.A linear relationship between redox potentials of the amines and long wave-length absorbance maxima of the cation radicals is observed.Redox potentials and UV/VIS spectra allow partial analysis of the term schemes of the amines and the corresponding cation radicals.ESR spectra of the cation radicals show broad and unresolved signals.
