• Bulletin of the Korean Chemical Society
• /
• v.19 no.8
• /
• pp.825-830
• /
• 1998

The electrocatalytic reduction of dioxygen by Co(TTFP)(Y)2 {Y=H2O or HO-} is investigated by cyclic voltammetry, spectroelectrochemistry, hydrodynamic voltammetry at a glassy carbon electrode in dioxygen-saturated aqueous solutions. Electrocatalytic reduction of dioxygen by CoⅡ(TTFP)(Y)2 establishes a pathway of 2e- reduction to form hydrogen peroxide, and then the generated hydrogen peroxide is reduced to water by CoⅠ(TTFP)(Y)2 at more negative potential. CoⅡ(TTFP)(Y)2 may bind dioxygen to produce the adduct complex [CoⅡ-O2 or CoⅢ-O2] which exhibits a Soret band at 411 nm and Q band at 531 nm.

• Journal of the Korean Chemical Society
• /
• v.30 no.6
• /
• pp.516-520
• /
• 1986

This study is related to reactivity of dioxygen bridged palladium complexes having ${\pi}$-allyl ligands. In this case, new dioxygen bridged palladium complexes were prepared using superoxide ion$(O_2^-)$ as an oxygen source. Reactions of the dioxygen palladium complexes prepared in the study were examined in order to clarify the nature of the coordinated dioxygen. Treatments of a solution of the dioxygen bridged palladium complexes in benzene by water, methanol and acetic acid gave hydrogen peroxide $(H_2O_2)$ as hydroxy-, methoxy-, and acetoxybridged palladium complexes, respectively. The dioxygen bridged palladium complexes reacted also with substitution phenols of salicylaldehyde, 8-hydroxyquinoline and active methylenes of acetylacetone, dimethyl malonate to afford mononuclear complexes of palladium and hydrogen peroxide. The results suggest that dioxygen is coordinated as peroxo $(O_2^{2-})$ in the complexes and behaves as a strong base.

• Applied Chemistry for Engineering
• /
• v.3 no.3
• /
• pp.471-481
• /
• 1992

This study is related to the reactivity of dioxygen bridged palladium complexes having amine ligands. New dloxygen bridged palladium complexes were prepared using superoxide ion(${O_2}^-$) as an oxygen source. The reactions of dioxygen palladium complexes prepared in the study were examined in order to clarify the nature of the coordinated dioxygen. Treatments of a solution of the dioxygen bridged palladium complexes in benzene by water, methanol, acetic acid gave hydrogen peroxide($H_2O_2$) and hydroxy, methoxy, acetoxy-bridged palladium complexes, respectively. The dioxygen bridged palladium complexes reacted with substitution phenols of salicylaldehyde, 8-hydroxyquinoline and active mothylenes of acetylacetone, dimethyl malonate to afford mononuclear complexes of palladium and hydrogen peroxide. Furthermore, she dioxygen bridged palladium complexes changed to acetonyl bridged palladium complex and hydrogen peroxide reacting with acetone. The results suggest that dioxygen is coordinated as peroxo (${O_2}^{2-}$) in the complexes and behaves as a strong base.

• Journal of the Korean Chemical Society
• /
• v.28 no.2
• /
• pp.135-142
• /
• 1984

New type dioxygen bridged complexes of palladium were prepared by using $KO_2$ as a source of superoxide ion $(O_2^-)$. The method is completely different from the traditional one which has adopted the oxidative addition of molecular oxygen to transition metal complexes in low valency. It was suggested that the reaction to prepare the dioxygen complexes proceeded via nucleophilic displacement followed by electron transfer reaction. Five new type dioxygen complexes having ${\pi}$-allyl ligand were prepared and characterized by the application of the reaction of $O_2^-$.

• Applied Chemistry for Engineering
• /
• v.3 no.1
• /
• pp.64-71
• /
• 1992

New type dioxygen bridged complexes of palladium were prepared by using $KO_2$ as a source of superoxide ion($O_2{^-}$). The method is completely different from the traditional one which has adopted the oxidative addition of molecular oxygen to prepare the dioxygen complexes. This reaction proceeds via nucleophilic displacement followed by electron transfer reaction. Three new type dioxygen complexes of palladium having amine ligands were prepared and characterized by the application of the reaction of $O_2{^-}$.

• Analytical Science and Technology
• /
• v.8 no.4
• /
• pp.617-622
• /
• 1995

Electrocatalytic reduction of dioxygen has been investigated by cyclic voltammetry at glassy carbon electrode modified with new Co(II)-Schiff base complexes in aqueous solutions of various pH. The reduction potentials of dioxygen at chemically adsorbed electrodes show the dependence of pH between pH 4 and 14. The catalytic effect is large and the reaction occurs via two or four electron transfer in various pH solution.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.9
• /
• pp.1056-1060
• /
• 1999

New water soluble and highly electron deficient cobalt(II) tetrakis-(1,2,5,6-tertrafluoro-4-NN'N"-trimethyla-nilinium)-β-octabromoporphyrin [Co II (Br8TTFP)(Y)2] was synthesized and used for the electrocatalytic reduction of dioxygen. The first reduction of synthesized [Co II (Br8TTFP)(Y)2] involves one electron process to give metal centered [Co I (Br8TTFP)(Y)2]. The reduction of potential [E1/2 = -0.32 V] of [Co II (Br8TTFP)(Y)2] shifts positively 370 mV compared with that of [Co II (TTFP)(Y)2] due to the substituted bromide to β-pyrrole positions. The electrochemically reduced [Co I (Br8TTFP)(Y)2] binds dioxygen and catalytically reduces it to HOOH by 2e - transfer. Cyclic and hydrodynamic voltammetry at a glassy carbon electrode in dioxygen-saturated aqueous solutions are used to study the electrocatalytic pathway.

• Bulletin of the Korean Chemical Society
• /
• v.15 no.7
• /
• pp.563-567
• /
• 1994

The electroreduction of dioxygen at glassy carbon electrodes with irreversible self-assembly of N-hexadecyl-N'-methyl viologen $(C_{16}VC_1)$ proceeds at potentials more positive than those where the reduction occurs at bare electrodes. The electrocatalyzed reduction takes place at potentials well ahead of those where the catalyst is reduced in the absence of dioxygen and the limiting currents observed at rotating disk electrodes did not deviate from the thoretical Levich line up to 6400 rpm, indicating that the electrocatalysis is extremely rapid. The rate constant for the heterogeneous reaction between $C_{16}V^+C_1$ immobilized on the electrode surface and $O_2$ in solution was estimated to be ca. $10^8\;M^{-1}s^{-1}$. The half-wave potential of dioxygen reduction was independent of solution pH.

• Bulletin of the Korean Chemical Society
• /
• v.17 no.12
• /
• pp.1127-1131
• /
• 1996

[FeⅡ2(N-Et-HPTB)Cl2]BPh4(1), where N-Et-HPTB is the anion of N,N,N',N'-tetrakis(N-ethyl-2-benzimidazolylmethyl)-2-hydroxy-l,3-diaminopropane, has been synthesized to model dioxygen binding to the diferrous centers of proteins. 1 has a singly bridged structure with a μ-alkoxo of N-Et-HPTB and contains two five-coordinate iron(Ⅱ) centers with two chloride ligands as exogenous ligands. 1 exhibits an electronic spectrum with a λmax at 336 nm in acetone. 1 in acetone exhibits no EPR signal at 4 K, indicating diiron(Ⅱ) centers are antiferromagnetically coupled. Exposure of acetone solution of 1 to O2 at -90 ℃ affords an intense blue color intermediate showing a broad band at 586 nm. This absorption maximum of the dioxygen adduct(1/O2) was found in the same region of μ-l,2-peroxo diiron(Ⅲ) intermediates in the related complexes with pendant pyridine or benzimidazole ligand systems. However, this blue intermediate exhibits EPR signals at g = 1.93, 1.76, and 1.59 at 4 K. These g values are characteristic of S = 1/2 system derived from an antiferromagnetically coupled high-spin Fe(Ⅱ)Fe(Ⅲ) units. 1 is the unique example of a (μ-alkoxo)diferrous complex which can bind dioxygen and form a metastable mixed-valence intermediate. At ambient temperature, most of 1/O2 intermediate decays to form a diamagnetic species. It suggests that the dacay reaction of the intermediate might be bimolecular, implying the formation of mixed-valence tetranuclear species in transition state.

• Journal of the Korean Chemical Society
• /
• v.37 no.4
• /
• pp.462-469
• /
• 1993

The electrocatalytic reduction of dioxygen is investigated by cyclic voltammetry and chronoamperometry at glassy carbon electrode and carbon microelectrode coated with a variety of cobalt phenylporphyrins. The n value obtained at carbon microelectrode is slightly different from that determined at glassy carbon electrode. Dioxygen reduction catalyzed by the monormeric porphyrin Co(II)-TPP mainly occurs through the $2e^-$ reduction pathway resulting in the formation of hydrogen peroxide, electrocatalytic process carries out $4e^-$ reduction pathway of dioxygen to $H_2O$ at the electrodes coated with bis-cobalt phenylporphyrins. The electrocatalytic reduction of dioxygen is irreversible and diffusion controlled.