Cobalt porphyrins electrochemical oxidation

Huang D, Lu J, li S, Luo Y, Zhao C, Hu B, Wang M, Shen Y. Fabrication of cobalt porphyrin. Electrochemically reduced graphene oxide hybrid films for electrocatalytic hydrogen evolution in aqueous solution. Langmuir 2014 30 6990-8. 

A combination of PQQ derivatives with transition metals leads to form the efficient redox systems. Dropwise addition of terminal olefin to the solution of PdCl2 (0.1 molar equiv.), trimethyl ester of PQQ, (PQQTME, 0.1 molar equiv.) and H2O in DMF under molecular oxygen results in the formation of 2-alkanone (Scheme 3.2). It should be noted that PQQTME constitutes a catalytic redox cycle. The orthoqui-none function appears to reoxidize the reduced palladium species generated in situ. Use of 1,7- or 1,10-phenanthrolinequinone gives a poor result maybe due to the coordination of paUadium(II) species towards the pyridine moiety opposite to the quinone group [5]. Mediation ofp-benzoquinone in the palladium-catalyzed oxidation reactions has been reported to require electrochemical or cobalt porphyrin catalyzed oxidation of the quinol [6-8]. The above-mentioned results provide an example for efficient redox systems of coenzyme derivatives with transition metals, which is demonstrated to be synthetically useful. 

According to [96], electrochemical methods, especially the application of cyclic voltammetry, could be a powerful tool to find suitable catalysts for NO removal from combustion products. Investigation of electrocatalytic properties of vitamin B12 toward oxidation and reduction of nitric oxide was reported in [97]. The catalytic activity of meso-tetraphenyl-porphyrin cobalt for nitric oxide oxidation in methanolic solution and in Nafion film was reported in [98]. 

Comparison with analogous investigations on [(TPP)Co] reveals that for the cobalt porphyrin complex [(T BuP)Co] the first electrochemical oxidation occurs metal-centred, leading to a Co(III) species [(T BuP)Co(III)]. The second... 

Cheng, S.-H. and Y.O. Sn (1994). Electrocatalysis of nitric oxide reduction by water-soluble cobalt porphyrin. Spectral and electrochemical studies. Inorg. Chem. 33, 5847-5854. 

One important characteristic of cobalt porphyrins is their ability to bind or react with small molecules, such as NO [27, 67, 70, 91, 93, 100], CO [36, 114, 115], O2 [314-320], or CO2 [321], and several studies have focused on the chemical and/or electrochemical reactivity of (P)Co toward these small molecules. The interaction of cobalt porphyrins with NO and the electrochemical properties of the resulting cobalt-nitrosyl porphyrins have been investigated by several research groups [7]. (TPP)Co(NO) exhibits two oxidations and three reductions at a microelectrode in CH2CI2 [90]. The NO group remains coordinated after electrooxidation and the initial electron abstraction from (TPP)Co(NO) was proposed to involve the porphyrin jr-ring system. Other electrode reactions were accompanied by a dissociation of NO from the compound and the site of electron transfer could not be determined. 

Electrocatalytic oxidations (mainly epox-idation) of alkenes by manganese porphyrins [77, 78] and a Schiff-base [79] and iron and cobalt porphyrins [78] have been achieved. Hydrogen peroxide or the superoxide ion (O ) was generated electrochem-ically by reduction of dioxygen in solvents containing an acid or acid anhydride, the metal compounds as catalysts, and olefins as substrates, in the presence or absence of an axial base. The reaction was believed to take place through the formation of a high valent metal 0x0 porphyrin, produced... 

In the field of energy production, oxidative water splitting is an appealing process, especially if it can be achieved without noble metal catalysts. Thus, cobalt porphyrin, covalently bound to MWCNTs, gave a promising catalyst, in that it resulted in active electrochemical oxidation of water at low overpotential [209]. 

Yan Y, Yao P, Mu Q, Wang L, Mu J, Li X, Kang S-Z. Electrochemical behavior of amino-modified multi-walled carbon nanotubes coordinated with cobalt porphyrin for the oxidation of nitric oxide. Appl Surf Sci 2011 258 58-63. 

Metal porphyrins act as catalysts for chain transmission in radical polymerisation [55] and for electrochemical oxidation of sulphur dioxide [64], as well as for oxidation of a wide range of organic substrates [65]. Cobalt and nickel complexes with LI5 are effective in the electrocatalytic reduction of carbon dioxide [66]. Porphyrin complexes of cobalt and tetraazamacrocyclic complexes of nickel catalyse reduction of the proton [67-71]. 

Muthukumar P. and S. A. John. Synergistic effect of gold nanoparticles and amine functionalized cobalt porphyrin on electrochemical oxidation of hydrazine. New J. Chem. 38, 2014 3473-3479. 

Metal to nitrogen migrations generally seem to occur after chemical or electrochemical " oxidation of o-bonded cobalt porphyrins. The initial sequence of steps for the electrochemically initiated conversion of TPP)Co(III)(R) to [ N-RTPP)Co II)]+ is similar to that reported for the electrochemicaly initiated conversion of (P)Fe(R) to [(N-RP)Fe(II)]+ and is illustrated in Equation 3. 

An aluminum electrode modified by a chemically deposited palladium pen-tacyanonitrosylferrate film was reported in [33]. Vitreous carbon electrode modified with cobalt phthalocyanine was used in [34]. Electrocatalytic activity of nanos-tructured polymeric tetraruthenated porphyrin film was studied in [35]. Codeposition of Pt nanoparticles and Fe(III) species on glassy-carbon electrode resulted in significant catalytic activity in nitrite oxidation [36]. It was shown that the pho-tocatalytic oxidation at a Ti02/Ti film electrode can be electrochemically promoted [37]. 

An alternative route used in organometallic chemistry is the reaction of low valent organometallic derivatives with alkyl (aryl) halides. The two electron oxidative addition of alkyl (aryl) halides or cyclopropane derivatives to metalloporphyrins such as [M (Por)] leads to metal alkyl (aryl) o-bonded porphyrins of cobalt " rhodium and iridium ° (Scheme 2). Substitution of aryl and vinyl halides by electrochemically generated iron(I) porphyrins also leads to o-bonded Fe complexes ... 

Pioneering works on functional molecules incorporating conducting polymers firstly demonstrated them as modified electrodes, on which redox molecules such as ruthenium tetraoxide [1] for photo-oxidation of water, mesotetrakis (4-sulphonatophenyl)porphyrin cobalt [2] and iron phthalocyanine [3] for redox catalysis, were incorporated chemically or electrochemically in polypyrrole conducting polymer. They suggested that functionalized conducting polymers should show the native function of a functional molecule while maintaining the native conductivity without a big decrease. 

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